Eurocode 6 - Introduction

How to design masonry structures using Eurocode 6

1. Introduction to Eurocode 6 Eur Ing, Prof.

Revision 2

J J Roberts BSc(Eng), PhD, CEng, FIStructE, FICE, FIMS, FCMI, MICT O Brooker BEng, CEng, MICE, MIStructE

Introduction This publication is part of a series of three guides entitled How to design masonry structures using Eurocode 6. The aim is to make the use of Eurocode 6, Design of masonry structures as easy as possible by drawing together in one place key information and commentary required for the design of typical masonry elements.

Guidance on Eurocode 6 The purpose of this series of guides is to introduce designers to the basic approach adopted in Eurocode 6. This is the first guide in the series of three and provides: ■■ A brief outline of the scope of Eurocode 6. ■■ An introduction to design, including fire resistance and movement. ■■ Assessment of actions and combination of actions using Eurocode*. ■■ How to specify mortar and masonry units. ■■ Glossary of Eurocode 6 terms.

The Concrete Centre (and, originally, The Modern Masonry Alliance) recognised that effective guidance was required to ensure that the UK design profession was able to use Eurocode 6 quickly, effectively, efficiently and with confidence. Therefore a steering group, with members from across the masonry industry (see back cover for a list of members), was established to oversee the development and publication of the original guides. This second revision addresses the publication of PD6697 in 2010 and revised National Annex to BS EN 1996-1-1 in 2013. It was overseen by a reconstituted steering group from industry (see back cover).

The second guide in the series, Vertical resistance1, explains how to design for vertical actions, whilst the third guide, Lateral resistance2, covers the design of laterally loaded masonry panels. Further information on Eurocode 6 can be found at www.eurocode6.org.

Eurocode 6 Eurocode 6 comprises the following parts: ■■ Part 1–1, General rules for reinforced and unreinforced masonry structures3. ■■ Part 1–2, Structural fire design4. ■■ Part 2, Design considerations, selection of materials and execution of masonry5. ■■ Part 3, Simplified calculation methods for unreinforced masonry structures6.

Each part also has a National Annex (NA) which provides the Nationally Determined Parameters (NDPs) to be used in the application of Eurocode 6 in the UK. The UK NDPs have been used throughout this guide. In addition PD 6697 contains useful guidance complementary to Eurocode 67. This series concentrates on Eurocode 6, Part 1–1 but includes material from Part 2 to explain the exposure and durability requirements. The scope and content of Part 1–2 and Part 3 are also briefly explained. Eurocode 6 is intended to be used with Eurocode*: Basis of structural design8, Eurocode 1: Actions on structures9 and, where appropriate, the other Eurocodes and relevant European Standards. The guide Introduction to Eurocodes10 provides more information on the Eurocode family. Eurocode 6 has been developed to enable the designer to use the following types of masonry unit: clay, calcium silicate, aggregate concrete, autoclaved aerated concrete (aircrete), manufactured stone and natural stone. European standards for these materials have been published by BSI and form part of an array of standards relating to masonry produced under the auspices of the European Committee for Standardisation (CEN), committee TC/125 (Masonry). *BS EN 1990 is entitled ‘Eurocode’, but is often referred to as Eurocode 0.


Scope of Part 1–1 of Eurocode 6 Part 1–1 describes the principles and requirements for safety, serviceability and durability of masonry structures. It is based on the limit state concept used in conjunction with a partial factor method. For the design of new structures, BS EN 1996–1–1 is intended to be used together with the other relevant Eurocodes.

Scope of Part 1–2 of Eurocode 6 This part deals with the design of masonry structures for the accidental situation of fire exposure and identifies differences from, or supplements to, normal temperature design. Only passive methods of fire protection are considered and active methods are not covered. It addresses the need to avoid premature collapse of the structure and to limit the spread of fire.

Scope of Part 2 of Eurocode 6 This part gives the basic rules for the selection and execution of masonry to enable it to comply with the design assumptions of the other parts of Eurocode 6. It includes guidance on factors affecting performance and durability, storage and use of materials, site erection and protection, and the assessment of the appearance of masonry.

Scope of Part 3 of Eurocode 6 This part provides simplified calculation methods to facilitate the design of a range of common wall types under certain conditions of use. The methods are consistent with Part 1–1 but result in more conservative designs, and other methods are available in the UK; see 'Simplified calculation methods' on page 7. The simplified methods are not applicable to design for accidental situations, which should be designed for in accordance with CI 5.2 of Part 1–1.

Basis of design Masonry structures are required to be designed in accordance with the general rules given in Eurocode, which requires that: Ed ≤ Rd where Ed = design value of the effect of actions Rd = design value of the resistance The basic requirements of Section 2 of Eurocode are deemed to be satisfied for masonry structures when the following are applied: ■■ Limit state design in conjunction with the partial factor method described in Eurocode. ■■ Actions as given in Eurocode 1. (See ‘Assessment of actions’ below.) ■■ Combination rules as given in Eurocode. ■■ The principles and application rules given in Eurocode 6. Thus using the partial factor method, the design value for a material property is obtained by dividing its characteristic value by the relevant partial factor for materials as follows: R Rd = g k

M

where Rd = design value of resistance Rk = characteristic value of the resistance gM = partial factor for a material property

Partial factors for materials

This Published Document contains non-contradictory complementary information and additional guidance for use in the UK with Part 1-1 and Part 2 of Eurocode 6.

The partial factors for use with masonry are given in Table NA.1 of the National Annex to Eurocode 6, Part 1–1 and shown here as Table 1. Two levels of attestation of conformity are recognized, Category I and Category II and this will be declared by the manufacturer of the masonry units. There are also two classes of execution control that are recognized: 1 and 2.

Supporting standards

Assessment of actions

There are European Standards that support Eurocode 6, and whilst they were developed within a common framework, it has not proved possible to standardise all the test methods used for the different materials. Words like brick and block have disappeared from the European vocabulary and they are all referred to as masonry units. Products should be specified by their performance requirements.

The Eurocodes use the term action to refer to a set of forces, deformations or accelerations acting on the structure; this includes horizontal and vertical loads. The guide How to design concrete structures using Eurocode 2: Introduction to Eurocodes9 gives guidance on determining the design value of actions and should ideally be consulted. However, a brief explanation on how to determine the partial factors for masonry design to Eurocode 6 is given below.

Scope of PD 6697

The Standards that support the use of masonry in Eurocode 6 are published by BSI. Two key factors that changed from previous UK practice are: ■■ The six masonry unit standards introduced methods for

determining the compressive strength of masonry units11. ■■ The method of determining characteristic compressive and shear strengths of masonry changed. 2

There are a number of combinations of actions that are described in Eurocode, but for masonry design (excluding retaining structures) the ultimate limit state, STR (STR represents an internal failure or excessive deformation of the structure or structural member) will normally be used. For plain masonry, Eurocode 6 indicates that,

1. Introduction to Eurocode 6

Table 1 Values of gM for ultimate limit state Material

Class of execution control gM 1a

2a

Masonry When in a state of direct or flexural compression Unreinforced masonry made with: Units of category I 2.3 b Units of category II 2.6 b Reinforced masonry made with mortar M6 or M12: Units of category I 2.0 b Units of category II 2.3 b When in a state of flexural tension Units of category I and II but in 2.3 b laterally loaded wall panels when removal of the panel would not affect 2.0 b the overall stability of the building When in a state of shear Unreinforced masonry made with: Units of category I and II 2.5 b Reinforced masonry made with mortar M6 or M12: Units of category I and II 2.0 b Steel and other components Anchorage of reinforcing steel 1.5 d Reinforcing steel and prestressing steel 1.15 d Ancillary components – wall ties 3.0 b Ancillary components – straps 1.5 e Lintels in accordance with EN 845-212 See NA to BS EN 845–2f

2.7 b 3.0 b –c –c 2.7 b 2.4 b

2.5 b –c –c –c 3.0 b 1.5 e See NA to BS EN 845–2f

Key a

Class 1 of execution control should be assumed whenever the work is carried out following the recommendations for workmanship in BS EN 1996–2, including appropriate supervision and inspection, and in addition: i the specification, supervision and control ensure that the construction is compatible with the use of the appropriate partial safety factors given in BS EN 1996–1–1; ii the mortar conforms to BS EN 998-2, if it is factory made mortar. If the mortar is site mixed, preliminary compressive strength tests, in accordance with BS EN 1015-2 and 1015-11, are carried on the mixture of sand, lime (if any) and cement that is intended to be used (the proportions given in Table NA.2 may be used initially for the tests) in order to confirm that the strength requirements of the specification can be met; the proportions may need to be changed to achieve the required strengths and the new proportions are then to be used for the work on site. Regular compressive strength testing is carried out on samples from the site mortar to check that the required strengths are being achieved. Class 2 of execution control should be assumed whenever the work is carried out following the recommendations for workmanship in BS EN 1996–2, including appropriate supervision.

b When considering the effects of misuse or accident these values may be halved. c

Class 2 of execution control is not considered appropriate for reinforced masonry and should not be used. However, masonry wall panels reinforced with bed joint reinforcement used:

provided the ultimate limit state is satisfied, no checks for the serviceability limit states are required. This assumes compliance with the limiting dimensions and ratios specified in Eurocode 6. There are three combinations that can be used for the STR limit state Expression (6.10), which is always conservative, or the most onerous of Expressions (6.10a) or (6.10b) (see Table 2). For laterally loaded masonry walls, where self-weight is usually beneficial, it will be sufficient to use Expression (6.10) only. For vertically loaded walls there will be some benefit in using Expression (6.10b), which, for members supporting one variable action (except storage loads) is the most economical of the three expressions, provided that the permanent actions are not greater than 4.5 times the variable actions. In Table 2 c0 is a factor that reduces the design value of a variable action when it acts in combination with another variable action (i.e. when it is an accompanying action). The value of c0 can be obtained from Table 3. The UK NA to Eurocode values can be applied to Expression (6.10), and this is shown in Table 4, which also shows the factors to be used when wind loads act in combination with imposed loads. Note that wind loads and imposed loads are both considered to be variable actions. Table 2 Design values of actions, ULS (Table A1.2 (B) of Eurocode) Combination Permanent actions Expression Unfavourable Favourable reference gG,j,inf Gk,j,inf gG,j,sup Gk,j,sup Exp. (6.10)

Accompanying variable action gQ,i c0,i Qk,i

Exp. (6.10a)

gG,j,sup Gk,j,sup

gG,j,inf Gk,j,inf

gQ,1 c0,1 Qk,1 gQ,i c0,i Qk,i

Exp. (6.10b)

jgG,j,sup Gk,j,sup

gG,j,inf Gk,j,inf

gQ,1 Qk,1

gQ,i c0,i Qk,i

Notes Gk = characteristic value of a permanent load Qk = characteristic value of the variable action gG,sup = partial factor for permanent action upper design value gG,inf = partial factor for permanent action lower design value gQ = partial factor for variable actions c0 = factor for combination value of a variable action j = reduction factor/distribution coefficient Where a variable action is favourable Qk should be taken as 0.

Table 3 Recommended combination values of variable actions (c0) buildings (from UK National Annex to Eurocode) Action

c0

Imposed loads in buildings (see BS EN 1991–1–1) Category A: domestic, residential areas

0.7

Category B: office areas

0.7

Category C: congregation areas

0.7

i to enhance the lateral strength of the masonry panel,

Category D: shopping areas

0.7

ii to limit or control shrinkage or expansion of the masonry,

Category E: storage areas

1.0

Category F: traffic area, vehicle weight < 30 kN

0.7

Category G: traffic area, 30 kN < vehicle weight < 160 kN

0.7

Category H: roofs a

0.7

can be considered to be unreinforced masonry for the purpose of class of execution control and the unreinforced masonry direct or flexural compression gM values are appropriate for use. d

When considering the effects of misuse or accident these values should be taken as 1.0.

e

For horizontal restraint straps, unless otherwise specified, the declared ultimate load capacity depends on there being a design compressive stress in the masonry of at least 0.4 N/mm2. When a lower stress due to design loads may be acting, for example when autoclaved aerated concrete or lightweight aggregate concrete masonry is used, the manufacturer’s advice should be sought and a partial safety factor of 3 should be used.

Snow loads on buildings (see BS EN 1991–3)

Yet to be published.

Key

f

Leading variable action gQ,1 Qk,1

For sites located at altitude H > 1000 m above sea level

0.7

For sites located at altitude H < 1000 m above sea level

0.5

Wind loads on buildings (see BS EN 1991–1–5)

0.6

a See also 1991–1–1: Cl 3.3.2

3


Imperfections Eurocode 6 also recognizes that imperfections should be taken into account in design and requires that, at the ultimate limit state, the horizontal forces to be resisted at any level should be the sum of 1 and 2 below. 1. The horizontal load due to the vertical load being applied to a structure with the following notional inclination angle v to the vertical: 1 v= radians 100 Rhtot where htot = the total height of the structure in metres. Each vertical action therefore produces a horizontal action to which the same load factor and combination factor as the vertical load apply. 2. The wind load derived from Eurocode 1, Parts 1–4 multiplied by its partial factor and distributed across the elements resisting the load in proportion to their stiffness.

Mortar The way in which mortar is specified is shown in Table 5. The primary method of designation for mortar is the strength grade. Thus an M12 mortar should have a minimum compressive strength of 12 N/mm2 at 28 days. Eurocode 6 recognises three types of masonry mortar: general purpose, thin layer and lightweight mortar, and they may all be either designed or prescribed (see Glossary). The use of mortars should be in accordance with the recommendations given in Eurocode 6, Part 2. For site made mortars, the mixing of the mortar should be in accordance with Part 2 (PD 66977 provides more detailed information). For factory made, semi-finished factory made and pre-batched masonry mortars, BS EN 998–213 applies.

Table 4 Design values of actions derived for UK design, ultimate limit state Combination Permanent actions Leading Accompanying expression variable action variable actions Unfavourable Favourable (unfavourable) (unfavourable) reference Combination of permanent actions and one variable action Exp. (6.10)

1.35 Gka

1.0 Gka

Exp. (6.10a)

1.35 Gka

1.0 Gka

Exp. (6.10b)

0.925 x 1.35 Gka 1.0 Gka

1.5 Qkb

For designed mortars, the compressive strength of the mortar provides the control of the hardened mortar quality, whereas prescribed mortars use set proportions. When samples are taken from a designed mortar in accordance with BS EN 1015–214, and tested in accordance with BS EN 1015–1115, the compressive strength of the mortar should not be less than the declared compressive strength.

Durability of materials Eurocode 6, Part 2 gives the basic rules for selection of mortar and masonry units for durability. Exposure conditions are defined in CI 2.1.2(3) of Part 2, with further guidance given in Annexes A, B and C. The UK NA to Part 2 advises that Annexes B and C should not be used because the information is not as extensive as that given in PD 6697; this advice is included in Table 6.

Structural fire design Eurocode 6, Part 1–2 provides information on the passive fire resistance of masonry walls so that the designer can ensure that the loadbearing performance is maintained for the necessary period of time and that the fire is appropriately contained. Designers will find that the tabulated data covers most situations but there is also the provision for testing and calculations. (Calculation methods are excluded by the UK NA to Part 1–2.) The tables cover loadbearing and non-loadbearing walls, single leaf, cavity and separating walls. Table 5 Acceptable assumed equivalent mixes for prescribed masonry mortars for use with Class 2 of Execution control ComPrescribed mortars (traditional proportion Mortar designpressive of materials by volume) (see Note) ation strength b b Cement : Cement : Masonry Masonry classa c d lime: sand sand with cement : cement : sand with or or without sand without air entrainair entrain- ment ment

Suitable for use in environmental condition

M12

1 : 0 to ¼: 3 1 : 3

Not suitable

Not suitable

(i)

Severe(S)

M6

1 : ½: 4 to 4½

1 : 3 to 4

1 : 2½ to 3½

1:3

(ii)

Severe(S)

M4

1 : 1: 5 to 6 1 : 5 to 6

1 : 4 to 5

1 : 3½ to 4 (iii)

Moderate(M)

M2

1 : 2: 8 to 9 1 : 7 to 8

1 : 5½ to 6½

1 : 4½

Passive(P)

– 1.5 c0-1 b Qk

1.5 Qk

Combination of permanent actions, wind load (Qk,W) and imposed load (Qk,I) Exp. (6.10) Case 1

1.35 Gka

1.0 Gka

1.5 Qk,W

1.05 c Qk,I

Exp. (6.10) Case 2

1.35 Gka

1.0 Gka

1.5 Qk,I

0.75 d Qk,W

(iv)

Key a The number following the M is the compressive strength for the class at 28 days in N/mm2 that may be assumed for the proportions given in columns 2 to 4; site compressive strength testing is not required for these traditional mixes. Checking of prescribed mortars should only be done by testing the proportions of the constituents. b Cement or combinations of cement (which include CEM I and many CEM IIs) in accordance with NA.2.3.2, except masonry cements c Masonry cement in accordance with NA.2.3.2, (inorganic filler other than lime) d Masonry cement in accordance with NA.2.3.2 (lime)

Key

Notes

a Where the variation in permanent action is not considered significant Gk,j,sup and Gk,j,inf may be taken as Gk b Where a variable action is favourable Qk should be taken as 0 c The value of c0 has been taken as 0.7, for storage loads c0 = 1.0 and a factor of 1.5 must be used d The value of c0 has been taken as 0.5

When the sand portion is given as, for example, 5 to 6, the lower figure should be used with sands containing a higher proportion of fines whilst the higher figure should be used with sands containing a lower proportion of fines.

4

For Class 2 of execution control site compressive strength testing is not required for these traditional mixes and checking of prescribed mortars should only be done by testing the proportions of the constituents.


Table 6 Durability of masonry in finished condition Masonry condition or situationa

Quality of masonry units and appropriate mortar designations Clay unitsb

Calcium silicate units

Aggregate concrete bricks

Aggregate concrete and autoclaved aerated concrete blocks

Without or with freezing:



Compressive strength class 20 or above in M4 or M2

Compressive strength 16.5 N/mm2 or above in M4

As Notes 4A, 4B, 4C or 4Dc. All in M4 or M2d

A – Work below or near external ground level A1 – Low risk of saturation

Without freezing: LD – F0 and S0 or HD: F0, F1 or F2 and S0, S1 or S2 in M12, M6 or M4 With freezing: HD – F1 or F2 and S0, S1 or S2 in M12, M6 or M4 unless a manufacturer advises against the use of HD-F1

A2 – High risk of saturation without freezinge

HD – F1 or F2, and S1 and S2 in M12 or M6


Compressive strength 16.5 N/mm2 or above in M6 or M4

A3 – High risk of saturation with freezinge

HD – F2 and S1 or S2 in M12 or M6


Compressive strength 22 N/mm2 or above in M6 or M4

As for A1 in M6

B1 – In buildings

D.P.C units, max. water absorption 4.5% in M12fg

Not suitable

Not suitable

Not suitable

B2 – In external works

D.P.C. units, max. water absorption 7 % in M12fg

Not suitable

Not suitable

Not suitable

As for A1 in M6 or M4

B – Masonry d.p.c.s

C – Unrendered external walls (other than chimneys, cappings, copings, parapets and sills)h C1 – Low risk of saturation

HD – F1 or F2 and S1 or S2 in M12, M6 or M4



Any in M4 or M2

C2 – High risk of saturation


Compressive strength class 20 or above in M4

Compressive strength 18 N/mm2 or above in M4

Any in M4


Any in M4 or M2

D – Rendered external walls (other than chimneys, cappings, copings, parapets, sills)ij Rendered external walls

HD –F1 or F2 and S1 or S2 in M12, M6 or M4


E – Internal walls and inner leaves of cavity walls above d.p.c level Internal walls and inner leaves of cavity walls

LD – F0 and S0 or HD: F0, F1 or F2 and S0, S1 or S2 in M12, M6, M4 or M2


Compressive strength 7.3 N/mm2 or above in M4 or iv

Any in M4 or M2

F – Unrendered parapets (other than cappings and copings)klm F1 – Low risk of saturation e.g. low parapets on some single storey buildings




As Notes 4A, 4B, 4C or 4Dc in M4.

R2 – High risk of saturation e.g. where a capping only is provided for the masonry




As for F1 in M6

HD – F1 or F2 and S2 in M12, M6 or M4 or HD – F1 or F2 and S1 in M12 or M6



Any in M4

H1 – Unrendered with low risk of saturation




Any in M4

H2 – Unrendered with high risk of saturation

HD –F2 and S1 or S2 in M12 or M6




H3 – Rendered

HD – F1 or F2 and S2 in M12, M6 or M4 or HD – F1 or F2 and S1 in M12 or M6



Any in M4



As Notes 4A, 4B or 4C in M6.

G – Rendered parapets (other than cappings and copings)jo Rendered parapets

H – Chimneysn

I – Cappings, copings and sillskl Cappings, copings and sills

HD – F2 and S1 or S2 in M12

J – Freestanding boundary and screen walls (other than cappings and copings) J1 – With coping

HD – F1 or F2 and S1 in M12 or M6 or HD – F1 or F2 and S2 in M12, M6 or M4



Any in M4

J2 – With capping




As Notes 5A, 5B, 5C or 5D in M6.

K – Earth-retaining walls (other than cappings and copings)p K1 – Waterproofing retaining face and coping

HD – F1 or F2 and S1 or S2 in M12 or M6




K2 – With coping or capping but no waterproofing on retaining face

HD – F2 and S1 or S2 in M12


Compressive strength 33 N/mm2 or above in M12 or M6

As for K1 but in M12 or M6q



As Notes 5A, 5B or 5C in M4.

L – Drainage and sewage, e.g. inspection chambers and manholes L1 – Surface water

Engineering bricks or F1 or F2 and S1 or S2 in M12

L2 – Foul drainage (continuous contact with masonry)


Compressive strength class 50 or above in M6r

Compressive strength 48 N/mm2 or above with cement content ≥ 350 kg/m3 in M12 or M6

Not suitable

L3 – Foul drainage (occasional contact with masonry)


Compressive strength class 20 or above in M6 or M4r

Compressive strength 48 N/mm2 or above with cement content ≥ 350 kg/m3 in M12 or M6

Not suitable

Table continues on page 6 5


Table 6 – Continued from page 5 Notes

Key

1 Table 6 is a reduced version of the information provided in PD 6697 which should be consulted when detailed guidance is required.

a Refer to PD 6697 for guidance on sulfate bearing ground.

i Rendered walls are suitable for most wind driven rain conditions.

2 For designations (i), (ii), (iii) and (iv) see Table 5.

b Consult masonry unit manufacturer for use below or near ground level.

j For rendered walls follow guidance in PD 6697.

c Consult masonry unit manufacturer.

k AAC blocks are not suitable for cappings, copings and cills.

3 4

LD - clay masonry unit with a low gross dry density for use in protected masonry. HD - clay masonry unit for unprotected masonry as well as clay masonry unit with a high gross dry density for use in protected masonry. Categories used for clay masonry for freeze/thaw are as follows: F0 Passive exposure F1 Moderate exposure F2 Severe exposure.

Categories used for clay masonry for active salt content are as follows: S0 No requirement for active salt content S1 Limited active salt content (see BS EN 771–1, Cl. 5.3.9) S2 Limited active salt content (see BS EN 771–1, Cl. 5.3.9).

5

Concrete block options: A Of net density ≥ 1500 kg/m3 B Made with dense aggregate conforming to BS EN 12620 C Having a compressive strength of 7.3 N/mm2 D Most types of autoclaved aerated block (consult manufacturer).

d

M2 mortar does not meet the minimum requirements of Approved Document A and if used refer to PD 6697 for limitations and guidance.

e

Masonry is very vulnerable between 150mm above and 150mm below finished ground level. Refer to PD 6697 and consult manufacturer as required.

f Masonry dpcs do not resist water percolating downward. g Dpcs of clay units are not normally suitable for use with other types of unit. h Protect with good roof overhang and detailing.

Reinforced and prestressed masonry Eurocode 6, Part 1–1 contains information relating to the design of reinforced masonry, but provides no application rules on the design of prestressed masonry. Annex J of Part 1-1 provides additional guidance for reinforced masonry when subjected to shear. PD 6697 extends the information provided in Part 1-1 for both reinforced and prestressed masonry as well giving guidance on the use of bed joint reinforcement to enhance resistance to lateral loads.

Masonry movement The potential for movement in completed masonry needs to be allowed for in design, and Eurocode 6, Part 2 makes recommendations for controlling differential movements; for example, the use of movement tolerant ties between the leaves of a cavity wall. Movement joints need to be provided to deal with the effects of moisture, temperature and movement caused by other agents. The position of movement joints needs to be considered with care to ensure that the structural integrity of the wall is maintained. Factors affecting the location of joints include: ■■ The type and group of masonry unit. ■■ The geometry of the structure. ■■ The degree of restraint. ■■ The effect of loading, thermal and climatic conditions. ■■ Requirements for fire, sound and thermal performance. ■■ The presence of reinforcement.

6

l Bed dpcs for cappings, copings and cills in same mortar as the masonry units. m Parapets are likely to be severely exposed coping and dpc should be provided. n For chimneys follow guidance in PD 6697. o Single leaf walls should be rendered only on one face. p Masonry in retaining walls particularly prone to frost and sulfate attack. Check with unit manufacturer. q Some types of aggregate concrete units are not suitable for capping and copings. r Some types of calcium silicate units are not suitable for foul drainage.

Movement joints that pass through the full thickness of the wall should be provided. The maximum horizontal distance, lm, between vertical movement joints for use for all walls in the UK (in the absence of other guidance from the manufacturer) is shown in Table 7.

Execution of masonry Eurocode 6, Part 2 gives guidance on the execution of masonry including: ■■ Permissible deviations. ■■ Jointing and pointing. ■■ Storage, preparation and use of materials on site. ■■ Masonry protection during execution. Further detail on the first two points is given in the following paragraphs.

Permissible deviations The permissible deviations of the constructed masonry from the position in which it is intended to be built should form part of the design specification. The permissible deviations should not normally be greater than the values shown in Table 8 for structural imperfections.

Mortar pointing Most masonry is constructed in such a way that the bedding mortar also forms the tooled surface of the finished mortar joint. If it is necessary to point the mortar joint the unhardened mortar should be raked out to a depth not less than 15 mm, but no more than 15% of the wall thickness.


Simplified calculation methods

historically, been used in the UK, unlike some European countries. In the UK guidance on the Building Regulations16–18 and BS 8103–219 provide a very effective and economic set of simple rules for low rise masonry and it is anticipated that these will continue to be the primary method of demonstrating compliance for many small buildings.

Eurocode 6, Part 3 contains simplified calculation methods for unreinforced masonry structures. These methods are based on the principles contained in Part 1 and should not be confused with simple rules developed on the basis of experience. In general, these methods are more conservative than design based on Part 1 and have not,

Table 8 Permissible deviations for structural design purposes

Table 7 Maximum horizontal distance between vertical movement joints in walls (in the absence of other guidance from the manufacturer) Type of masonry

lm (m)

Clay masonry – unreinforced

15a

Calcium silicate masonry

9b

Aggregate concrete and manufactured stone masonry

9b

Autoclaved aerated concrete masonry

9b

Natural stone masonry

20 c

Position

Maximum deviation

Verticality In any one storey

± 20 mm

In total height of building of three storeys or more

± 50 mm

Vertical alignment

± 20 mm

Straightness a In any one metre

± 10 mm

In 10 metres

± 50 mm

Thickness Of wall leaf b

± 5 mm or ± 5 % of the leaf thickness, whichever is the greater

Key

Of overall cavity wall

± 10 mm

The value for clay masonry walls containing bed joint reinforcement may be greater a than 15 m subject to expert advice. This value applies when the ratio, length to height of panel, is 3 to 1 or less. It should b be reduced for long horizontal panels of masonry which lie outside this ratio. When using this figure, movement joints should be located at not more than 8 m c from the corner.

Key Deviation from straightness is measured from a straight reference line between any a two points. Excluding leaves of single masonry unit width or length, where the dimensional b tolerances of the masonry units govern the leaf thickness.

References 1 ROBERTS, J J & Brooker, O How to design masonry structures using Eurocode 6: Vertical resistance (TCC/03/36). The Concrete Centre, 2013. 2 ROBERTS, J J & Brooker, O How to design masonry structures using Eurocode 6: Lateral resistance (TCC/03/37). The Concrete Centre, 2013. 3 BRITISH STANDARDS INSTITUTION. BS EN 1996–1–1: Eurocode 6 – Design of masonry structures. General rules for reinforced and unreinforced masonry structures. BSI, 2005. Including NA to BS EN 1996-1-1:2005+A1:2012. 4 BRITISH STANDARDS INSTITUTION. BS EN 1996–1–2: Eurocode 6 – Design of masonry structures. General rules. Structural fire design. BSI, 2005. Including NA to BS EN 1996-1-2:2005:2007. 5 BRITISH STANDARDS INSTITUTION. BS EN 1996–2: Eurocode 6 – Design of masonry structures. Design considerations, selection of materials and execution of masonry. BSI, 2006. Including NA to BS EN 1996-2:2006:2007. 6 BRITISH STANDARDS INSTITUTION. BS EN 1996–3: Eurocode 6 – Design of masonry structures. Simplified calculation methods for unreinforced masonry structures. BSI, 2006. Including NA to BS EN 1996-3:2006:2007. 7 BRITISH STANDARDS INSTITUTION. PD 6697. Recommendations for the design of masonry structures to BS EN 1996-1-1 and BS EN 1996-2. BSI, 2010. 8 BRITISH STANDARDS INSTITUTION. BS EN 1990: Eurocode – Basis of structural design. BSI, 2002. Including NA to BS EN 1990:2002+A1:2005:2004. 9 BRITISH STANDARDS INSTITUTION. BS EN 1991: Eurocode 1 – Actions on structures. BSI (10 parts). Including their NAs. 10 NARAYAN, R S & BROOKER, O. How to design concrete structures using Eurocode 2: Introduction to Eurocodes (TCC/03/16). The Concrete Centre, 2005. 11 BRITISH STANDARDS INSTITUTION. BS EN 771: Specification for masonry units. BSI, 2011 (6 Parts). 12 BRITISH STANDARDS INSTITUTION. BS EN 845–2: Specification for ancillary components for masonry – Lintels. BSI, 2013. 13 BRITISH STANDARDS INSTITUTION. BS EN 998–2: Specification for mortar for masonry: Masonry mortar. BSI, 2013. 14 BRITISH STANDARDS INSTITUTION. BS EN 1015–2: Methods of test for mortar for masonry: Bulk sampling of mortars and preparation of test mortars. BSI, 1999. 15 BRITISH STANDARDS INSTITUTION. BS EN 1015–11: Methods of test for mortar for masonry: Determination of flexural and compressive strength of hardened mortar. BSI, 1999. 16 DEPARTMENT FOR COMMUNITIES AND LOCAL GOVERNMENT, Building regulations (England and Wales) Approved Document A (2004). DCLG, revised 2006. 17 SCOTTISH BUILDING STANDARDS AGENCY. Scottish building standards technical handbooks: domestic – for compliance with 'Building Scotland regulations 2004'. SBSA, 2007. 18 THE STATIONERY OFFICE. The Building Regulations (Northern Ireland) 1994 Technical Booklet D: Structure. TSO, 2000. 19 BRITISH STANDARDS INSTITUTION. BS 8103–2: Structural design of low-rise buildings– Code of practice for masonry walls for housing. BSI, 2005. 20 BRITISH STANDARDS INSTITUTION. BS 772: Methods of test for masonry units. BSI (20 parts).

7


Glossary of Eurocode 6 terminology Term Definition Adhesion

The effect of mortar developing a tensile or shear resistance at the contact surface of masonry units.

Category I masonry unit

Units with a declared compressive strength with a probability of failure to reach it not exceeding 5%. This may be determined via the mean or characteristic value.

Category II masonry unit

Units not intended to comply with the level of confidence of Category 1 units.

Confined masonry

Masonry provided with reinforced concrete or reinforced masonry confining elements in the vertical and horizontal direction. (Not usually used in the UK.)

Designed masonry mortar

A mortar whose composition and manufacturing method is chosen in order to achieve specified properties (performance concept).

General purpose masonry mortar

Masonry mortar without special characteristics.

Griphole

A formed void in a masonry unit to enable it to be more readily grasped and lifted with one or both hands or by machine.

Groups 1, 1s, 2, 3 and 4 masonry units

Group designations for masonry units, according to the percentage, size and orientation of holes in the units when laid. Note: The group designation will normally be declared by the manufacturer. Historically only Groups 1, 1s and 2 units have been used in the UK. Group 1s is referred to in BS EN 1996–1–2.

Hole

A formed void which may or may not pass completely through a masonry unit.

Lightweight masonry mortar

Designed masonry mortar with a dry hardened density below a prescribed figure.

Normalized compressive strength of masonry units

The compressive strength of masonry units converted to the air dried compressive strength of an equivalent 100 mm wide x 100 mm high masonry unit (see BS EN 772-120).

Orthogonal ratio, m

The ratio of the flexural strength of masonry when failure is parallel to the bed joints to that when failure is perpendicular to the bed joints.

Prescribed masonry mortar

Mortar made in predetermined proportions, the properties of which are assumed from the stated proportions of the constituents (recipe concept).

Shell

The peripheral material between a hole and the face of a masonry unit.

Shell bedded wall

A wall in which the masonry units are bedded on two or more strips of mortar, two of which are at the outside edge of the bed face of the units.

Thin layer masonry mortar

Designed masonry mortar with a maximum aggregate size less than or equal to a prescribed figure.

Web

The solid material between the holes in a masonry unit.

Members of the steering group

Acknowledgements

Ali Arasteh, Brick Development Association; Owen Brooker, The Concrete Centre; Ken Fisher, International Masonry Society; Cliff Fudge, Aircrete Products Association; Charles Goodchild, The Concrete Centre; Gerry Pettit, Concrete Block Association; John Roberts, Consultant.

This publication was jointly sponsored by the following organisations:

Members of the steering group for 2nd revision

■■ Concrete Block Association - www.cba-blocks.org.uk

Cliff Fudge, Aircrete Products Association; Charles Goodchild, The Concrete Centre; Simon Hay, Brick Development Association; Andy Littler, Concrete Block Association; John Roberts, Consultant; Guy Thompson, The Concrete Centre.

■■ MPA - Mortar Industry Association - www.mortar.org.uk

For more information on Eurocode 6 and other questions relating to the design, use and performance of concrete units, visit www.eurocode6.org

Ref: TCC/03/35. ISBN 978-1-904818-56-4 First published November 2007 (in partnership with the Modern Masonry Alliance) revised January 2009 and June 2013 Price Group M © MPA The Concrete Centre™

■■ Aircrete Products Association - www.aircrete.co.uk ■■ Brick Development Association - www.brick.org.uk

■■ MPA - The Concrete Centre - www.concretecentre.com

Published by The Concrete Centre Gillingham House, 38-44 Gillingham Street, London, SW1V 1HU Tel: +44 (0)207 963 8000 | www.concretecentre.com

All advice or information from MPA The Concrete Centre (TCC) et al is intended only for use in the UK by those who will evaluate the significance and limitations of its contents and take responsibility for its use and application. No liability (including that for negligence) for any loss resulting from such advice or information is accepted by TCC or their subcontractors, suppliers or advisors. Readers should note that the publications from TCC et al are subject to revision from time to time and should therefore ensure that they are in possession of the latest version.


2. Vertical resistance Eur Ing, Prof.

Revision 2


Introduction This publication is part of a series of three guides entitled How to design masonry structures using Eurocode 6. The aim is to make the use of Eurocode 6, Design of masonry structures as easy as possible by drawing together in one place key information and commentary required for the design of typical masonry elements. The Concrete Centre (and, originally, The Modern Masonry Alliance) recognised that effective guidance was required to ensure that the UK design profession was able to use Eurocode 6 quickly, effectively, efficiently and with confidence. Therefore a steering group, with members from across the masonry industry (see back cover for a list of members), was established to oversee the development and publication of the original guides. This second revision addresses the publication of PD6697 in 2010 and revised National Annex to BS EN 1996-1-1 in 2013. It was overseen by a reconstituted steering group from industry (see back cover).

Guidance for vertical resistance This guide is the second in a series of three giving guidance on the design of masonry structures to Eurocode 61. The first guide, Introduction to Eurocode 62 gives an introduction to design and assessment of actions using Eurocode 6 and also covers the specification and execution (workmanship) of masonry. This guide explains how to design for vertical actions and determine vertical resistance. The third guide in the series3 covers the design of laterally loaded masonry panels. Throughout this guide the Nationally Determined Parameters (NDPs) from the UK National Annexes (NAs) have been used. These enable Eurocode 6 to be applied in the UK.

Design procedure This guide explains how to determine the design resistance for a vertically loaded wall. The first guide in the series, Introduction to Eurocode 6, should be referred to so that the design load can be determined. In essence, when using the Eurocodes the designer should check that the resistance is greater than or equal to the effect of the actions. A flow chart for the design of masonry walls to resist vertical actions is shown as Figure 1.

Compressive strength Eurocode 6 introduces some new concepts when dealing with the design of masonry for vertical loads. The first of these relates to the way the compressive strength of the masonry units is expressed. For design purposes the normalized compressive strength, fb, of the masonry units is used. This is the compressive strength of the units converted to the air-dried compressive strength of an equivalent 100 mm wide by 100 mm high masonry unit. The detail is contained in Part 1 of BS EN 772, Methods of test for masonry units4. The advantage to the designer is that the normalized strength is independent of the size and shape of the units used in the final construction.

Grouping of masonry units The second change relates to the way in which masonry units are classified. This is dealt with by grouping masonry into one of four groups as shown in Table 3.1 of Eurocode 6. The group designation will normally be declared by the manufacturer. The designation depends upon the volume and direction of holes in the unit and the thickness of webs and shells. Historically only Group 1 and Group 2 units have been used in the UK, so only values for these groups are given in the UK NAs.

How to design masonry masonrystructures structuresusing usingEurocode Eurocode66

The characteristic compressive strength of masonry The characteristic compressive strength of masonry (other than shell bedded masonry) is determined from the results of tests in accordance with BS EN 1052–15. The tests are carried out on small wallette specimens rather than the storey-height panels used in the past. The designer has the option of either testing the units intended to be used in a project or using the values determined from a database. Values from a large database are provided in the UK NA to Eurocode 6, Part 1–1 in the form of the constants to be used in the following equation: fk = K fba fmb

[Equation (3.1) of Eurocode 6, Part 1–1]

where fk = characteristic compressive strength of the masonry, in N/mm2 K = constant – see Table 1 and Figure 2 a, b = constants – see Table 2 fb = normalized mean compressive strength of the units, in the direction of the applied action effect, in N/mm2 fm = compressive strength of the mortar, in N/mm2

For blocks laid flat, Table 8 of the National Annex to Eurocode 6, Part 1–1 contains a specific value for K to be used in Equation (3.1) of Eurocode 6, Part 1–1. The following limitations are placed on Equation (3.1): ¢¢ The masonry is detailed and constructed in accordance with the requirements of BS EN 1996–1–1, section 8. ¢¢ fb is taken to be not greater than 110 N/mm2 when units are laid in general purpose mortar and 50 N/mm2 when laid in thin layer mortar (fb is determined in the normal direction of loading). ¢¢ fm is taken to be not greater than fb nor greater than 12 N/mm2 when units are laid in general purpose mortar or 10 N/mm2 when units are laid in lightweight mortar. ¢¢ The coefficient of variation of the strength of the masonry unit is not more than 25%. For masonry made with general purpose mortar, adjustments are made to the value of K as shown in Figure 2. In addition the following points should be noted: ¢¢ For masonry made of general purpose mortar where Group 2 and Group 3 aggregate concrete units are used with the vertical cavities filled completely with concrete, the value of fb should be obtained by considering the units to be Group 1 having a compressive strength corresponding to the compressive strength of the units or of the concrete infill, whichever is the lesser.

Figure 1 Flow chart for the design of masonry walls to resist vertical actions

Characteristic vertical actions

Masonry unit properties • Type and group • Dimensions • Strength Determine requirements for mortar strength and durability. See tables 5 & 6 of Introduction to Eurocode 6

Determine normalized compressive strength, fb.

Determine characteristic compressive strength of masonry, fk, from Equation (3.1) of Eurocode 6 and Tables 1 & 2

Determine effective height, hef, of the wall (see page 4) .

Determine effective thickness, tef, of the wall (see page 4)

Check area ≥ 0.04 m2

Check slenderness ratio hef /tef ≤ 27

Determine design value of vertical actions (per unit length), Ed, using Expression (6.10), (6.10a) or (6.10b) of Eurocode (see Introduction to Eurocode 6)

Where cross-sectional area, A < 0.1 m2, factor fk by (0.7 + 3A)

Calculate design resistance (per unit length) from least favourable of: NRd = Fm t fk / gM and NRd = Fi t fk / gM

Check Ed ≤ NRd

Determine eccentricity (see page 5)

Determine capacity reduction factors, Fm and Fi from (see page 6)

2

Obtain gM from table 1 of Introduction to Eurocode 6

Check complete

2. Vertical resistance

¢¢ For collar jointed aggregate concrete masonry made with general

purpose mortar, with or without the collar filled with mortar, the unit shape factor correction to obtain the normalized strength should use the width of the wall as the unit width and the height of the masonry units. ¢¢ Where action effects are parallel to the direction of the bed joints, the characteristic compressive strength may be determined from Equation (3.1) with fb derived from BS EN 772–1, where the direction of application of the load to the test specimens is in the same direction as the direction of the action effect in the masonry, but with the shape factor, d, as given in BS EN 772–1 taken to be no greater than 1.0. For Group 2 and 3 units, K should then be multiplied by 0.5. Table 1 Values of K to be used with equation (3.1) Masonry unit

General purpose mortar

Thin layer mortar (bed joint ≥ 0.5 mm and ≤ 3 mm)

Lightweight mortar of density (kg/m3) 800 < rd 600 ≤ rd ≤ 800 ≤ 1300

Clay Group 1

0.50

0.75

0.30

0.40

Group 2

0.40

0.70

0.25

0.30

–a

–a

–a

Group 3 and 4 – a Calcium silicate Group 1 0.50

0.80

–b

–b

Group 2

0.70

–b

–b

0.90

0.45

0.45

Group 1 c 0.50 d (units laid flat) Group 2 0.70

0.70d

0.40d

0.40d

0.76

0.45

0.45

Group 3 and 4 – a

–a

–a

–a

Autoclaved aerated concrete Group 1 0.75 0.90

0.45

0.45

Manufactured stone Group 1 0.75

–b

–b

–b

–b

0.40

Aggregate concrete Group 1 0.75

0.90

Dimensioned natural stone Group 1 0.45 –b

¢¢ When the perpendicular joints are unfilled, Equation (3.1) may be

used, with consideration of any horizontal actions that might be applied to, or be transmitted by, the masonry. (See also CI. 3.6.2(4) of BS EN 1996–1–1.)

The characteristic compressive strength of shell bedded masonry Shell bedding provides two strips of mortar rather than a full mortar bed. It serves to improve rain penetration resistance but reduces the strength of the masonry. A typical shell bedded unit is shown in Figure 3. For Group 1 and Group 4 units the procedure above may be used to obtain the characteristic compressive strength of the masonry. Figure 2 Modifications to K for units laid with general purpose mortar

Plan sections of bonded masonry Masonry thickness a) K from Table 1 Masonry thickness b) K from Table 1 Masonry thickness

Key a Group 3 and 4 units have not traditionally been used in the UK, so no values are available. b T hese masonry unit and mortar combinations have not traditionally been used in the UK, so no values are available.

c) K from Table 1 multiplied by 0.8

c If Group 1 aggregate concrete units contain formed vertical voids in the normal direction, multiply K by (100 – n) /100, where n is the percentage of voids, maximum 25%.

Masonry thickness

d W hen aggregate concrete masonry units are to be used laid flat the normalised strength of the unit should be calculated using the width and height of the unit in the upright position along with the compressive strength of the unit tested in the upright position. Note Where a mortar joint is parallel to the face of the wall K should be modified (see Figure 2)

Figure 3

Table 2

Shell bedding

Values to be used in Equation (3.1) Type of mortar General purpose mortar Lightweight mortar Thin layer mortar in bed joints of thickness 0.5 to 3 mm (using clay units of Group 1, calcium silicate units, aggregate concrete units and autoclaved aerated concrete units) Thin layer mortar in bed joints of thickness 0.5 to 3 mm (using clay units of Group 2)

d) K from Table 1 multiplied by 0.8

Values to be used a = 0.7 and b = 0.3 a = 0.7 and b = 0.3 a = 0.85 and b = 0

a = 0.7and b = 0

3


provided that: ¢¢ The width of each strip of mortar is at least 30 mm. ¢¢ The thickness of the masonry wall is equal to the width or length

of the masonry units so that there is no longitudinal mortar joint through all or part of the length of the wall. ¢¢ The ratio g/t is not less than 0.4 where g = total width of the mortar strips t = the thickness of the wall. ¢¢ K is taken as above when g/t = 1.0 or half this value when g/t = 0.4. Linear interpolation may be used for intermediate values. Groups 2 and 3 may be designed as non-shell bedded masonry provided that the normalized mean compressive strength of the units used in Equation (3.1) is obtained from tests carried out in accordance with BS EN 772–14 for shell bedded units.

Effective height The effective height of a masonry wall is obtained by applying a factor to the clear height of the wall such that: hef = rn h where hef = effective height of the wall h = clear storey height of the wall rn = reduction factor, where n = 2, 3 or 4, depending upon the edge restraint or stiffening of the wall The reduction factor to be applied depends upon the restraint offered by adjoining elements. Masonry walls may be stiffened by a number of rigid structural elements such as floors, roofs and other walls. Stiffening walls should have a length of at least 1/5 of the clear height

and have a thickness of at least 0.3 times the effective thickness of the wall to be stiffened. When the stiffening wall contains openings, the minimum length of wall should be as shown in Figure 4 and the stiffening wall should extend a distance of at least 1/5 of the storey height beyond each opening. Where a wall is restrained at the top and bottom by reinforced concrete floors or roofs spanning from both sides at the same level or by a reinforced concrete floor spanning from one side only and having a bearing of at least 2/3 of the thickness of the wall then: r2 = 0.75 unless the eccentricity of the load at the top of the wall is greater than 0.25 times the thickness of the wall, in which case r2 = 1.0. Where the wall is restrained by timber floors or roofs spanning from both sides at the same level or by a timber floor spanning from one side having a bearing of at least 2/3 the thickness of the wall but not less than 85 mm, then: r2 = 1.0. For walls restrained at the top and bottom and stiffened on one vertical edge, use rn = the value r3 from Figure 5 and where both vertical edges are stiffened, use rn = the value r4 from Figure 6. Note that Equations (5.6), (5.7) and (5.8) in Eurocode 6, Part 1–1 may be used as an alternative to the use of the graphs.

Effective thickness For a single-leaf wall, a double-leaf wall (with ties at a density of 2.5 per m2 or greater), a faced wall, a shell bedded wall and a grouted cavity wall, the effective thickness, tef, is taken as the actual thickness

Figure 4

Figure 5

Minimum length of stiffening wall with openings

Graph showing values of r3

1.0

Stiffened wall

Stiffening wall

r2 = 1.0

0.9

t

h

>h/5

h1

h2 (window) h2(door)

Reduction factor, r3

0.8 0.7

r2 = 0.75

0.6 0.5 0.4 0.3 0.2 0

1 (h1+ h2) 5

4

2

>t

1

2

3 Ratio hef /tef

4

5


of the wall (t), provided this is greater than the minimum thickness, tmin. The value of tmin for a loadbearing wall should be taken as 90 mm for a single-leaf wall and 75 mm for the leaves of a cavity wall. For a cavity wall the effective thickness is determined using the following equation: tef = 3R t13 + t23 ≥ t2

Assessment of eccentricity When a wall is subjected to actions that result in an eccentricity at right angles to the wall, Eurocode 6 requires the resistance of the wall to be checked at the top, mid-height and bottom. The eccentricity at top or bottom of the wall is: Mid

ei =

where t1 = actual thickness of the outer or unloaded leaf t2 = actual thickness of the inner or loaded leaf Note that the effective thickness of the unloaded leaf should not be taken to be greater than the thickness of the loaded leaf and that ties should be provided at a density of 2.5 per m2 or greater. When a wall is stiffened by piers the effective thickness is enhanced by using the following equation: tef = rtt where tef = effective thickness rt = coefficient obtained from Table 3 t = thickness of the wall

Nid

+ ehe + einit ≥ 0.05t

where Mid = design value of the bending moment at the top or the bottom of the wall resulting from eccentricity of the floor load at the support Nid = design value of the vertical load at the top or the bottom of the wall ehe = the eccentricity at the top or bottom of the wall resulting from the horizontal loads einit = initial eccentricity for construction imperfections, which may be taken as hef/450, with a sign that increases the absolute value of ei and em as appropriate t = thickness of the wall The mid-height eccentricity, emk, is: emk = em + ek ≥ 0.05t

Slenderness ratio The slenderness ratio of the wall is obtained by dividing the effective height by the effective thickness and should not be greater than 27 for walls subjected to mainly vertical loading. Note also that the effects of creep may be ignored in walls with a slenderness ratio up to 27.

Figure 6

1.0

ek

Mmd = design value of the greatest moment at the mid-height of the wall resulting from the moments at the top and bottom of the wall, including any load applied eccentrically to the face of the wall (see Figure 7) Nmd = design value of the vertical load at the mid-height of the wall, including any load applied eccentrically to the face of the wall ehm = the eccentricity at mid-height resulting from horizontal loads

r2 = 1.0

= 0, when the slenderness ratio ≤ 27 (ie. ignoring creep)

A sub-frame analysis may be used as a simplified method for obtaining the moments at the top and bottom of vertically loaded walls, as given in Annex C in Part 1–1 of Eurocode 6.

0.8 Reduction factor, r4

Graph showing values of the reduction factor, r4

0.9

where Mmd em = + ehm + einit Nmd

0.7 0.6

Table 3

r2 = 0.75

Stiffness coefficient, rt, for walls stiffened by piers

0.5

Ratio of pier spacing (centre to centre) to pier width

0.4 0.3 0.2 0

1

2

3 Ratio h/l

4

5

Ratio of pier thickness to actual thickness of wall to which it is bonded 1

2

3

6

1.0

1.4

2.0

10

1.0

1.2

1.4

20

1.0

1.0

1.0

Note Linear interpolation is permitted in this Table.

5


Capacity reduction factors At the top or bottom of the wall, the reduction factor for slenderness and eccentricity is given by: e Fi = 1 – 2 i t where Fi = reduction factor at the top or bottom of the wall ei = eccentricity at the top or bottom of the wall t = thickness of the wall A method for calculating a capacity reduction factor at the mid-height of the wall, Fm, is given in Annex G of Eurocode 6, Part 1–1, which simplifies the principles given in Cl. 6.1.1. This is shown graphically in Figure 8, which shows the corresponding capacity reduction factors for different values of slenderness and eccentricity for an elastic modulus 1000 fk , which is the value recommended in the UK NA. The least favourable value of Fi and Fm should be used to calculate NRd.

Vertical load resistance of solid walls and columns The design resistance of a single-leaf wall per unit length, NRd, is given by the following:

t = thickness of the wall fd = design compressive strength of the masonry ( fk /gM) For sections of small plan area, less than 0.1 m2, fd should be multiplied by (0.7 + 3A) where A = loadbearing horizontal cross-sectional area of the wall in m2 In the case of a faced wall, the wall may be designed as a single-leaf wall constructed entirely of the weaker material with a longitudinal joint between leaves. A double-leaf (collar-jointed) wall may also be designed as for a single-leaf wall provided that the leaves are tied together adequately and both leaves carry similar loads and the cavity does not exceed 25 mm, or it may be designed as a cavity wall with one leaf loaded. In the case of cavity walls, check each leaf separately using a slenderness ratio based on the effective thickness of the wall.

Concentrated loads For a Group 1 unit (not shell bedded) the vertical load resistance is: NRdc = b Ab fd where b

= 1 + 0.3

where F = capacity reduction factor allowing for the effects of slenderness and eccentricity of loading

1.5 – 1.1

Ab

hc Aef = e nhancement factor for load that should not be less than 1.0 nor taken to be greater than: a 1.25 + 1 or 1.5, whichever is the lesser 2hc

NRd = F tfd

a1

Figure 8

Capacity reduction factor, Fm at the mid-height of the wall

Figure 7 Moments from calculation of eccentricities

Eccentricity =

1.0

0.05t

0.9

N1d

h2 Nmd

Mmd (at mid-height of wall)

h h2 N2d

M2d (at top of floor)

0.10t

0.8 Capacity reduction factor, Fm

M1d (at underside of floor)

0.15t

0.7

0.20t

0.6

0.25t

0.5

0.30t

0.4

0.35t

0.3

0.40t

0.2 0.1 0.0 0

a) Section

6

b) Bending moment diagram

5

10

15 20 Ratio, hef /ltef

25

Values of Fm at the mid-height of the wall against slenderness ratio for different eccentricities, based on E =1000 fk

30


a1

= distance from the end of the wall to the nearer edge of the loaded area hc = height of the wall to the level of the load Ab = loaded area Aef = effective area of the bearing, lefm t lefm = effective length of the bearing as determined at the mid-height of the wall or pier t = thickness of the wall, taking into account the depth of recesses in joints greater than 5 mm wide Ab/Aef ≤ 0.45 The enhancement factor, b, is shown graphically in Figure 9. For walls built with Groups 2, 3 and 4 masonry units and when shell bedding is used, it is necessary to check that, locally under the bearing of a concentrated load, the design compressive stress does not exceed the design compressive strength of the masonry, fd (i.e. b is taken to be 1.0). In any case, the eccentricity of the load from the centre line of the wall should not be greater than t/4 as shown in Figure 10. In all cases where a concentrated load is applied, the requirements for vertical load design should be met at the mid-height of the wall below the bearings. Account should be taken of the effects of any other superimposed vertical loading, particularly where concentrated loads are sufficiently close together for their effective lengths to overlap. The concentrated load needs to bear on a Group 1 unit or other solid material. The length of this unit or bearing should equal the required bearing length plus a length on each side of the bearing based on a 60° spread of load to the base of the solid material. For an end bearing the extra length is required on one side only.

The concentrated load may be applied through a spreader beam of adequate strength and stiffness that has a width the same as the wall thickness, a height greater than 200 mm and a length greater than three times the bearing length of the load. In this case the design value of compressive strength beneath the concentrated load should not exceed 1.5fd.

Walls subject to shear forces The design value of shear resistance is given by: VRd = f vd tl c where VRd = the design value of shear resistance of the wall fvd = the design value of the shear strength of the masonry (the characteristic shear strength divided by the partial factor for masonry, gM) based on the average vertical stresses over the compressed part of the wall that is providing the shear resistance t = the thickness of the wall resisting the shear lc = the length of the compressed part of the wall, ignoring any part of the wall that is in tension In calculating lc assume a linear distribution of the compressive stress, take into account openings, etc. and do not include any area of the wall subjected to vertical tensile stresses.

Effect of chases Eurocode 6 recognises that chases and recesses should not impair the stability of a wall and provides appropriate guidance. Further explanation is given in the third guide in this series, Lateral resistance3.

Figure 9

Figure 10

Enhancement factor, b, concentrated load under bearings

Walls subjected to concentrated load

NEdc

NEdc

NEdc

1.6

a1 60o

Enhancement factor, b

1.5

60o

60o hc/2

h

1.4

+

2a1 = 1 hc

1.3

+

lefm

lefm

+ + lefm

a1 = 0 a) Elevation

1.2

NEdc a 1

1.1

NEdc Ab

60o hc

1.0 0

0.1

0.2

0.3

0.4 0.45 0.5

≤ t /4 t

lefm

t

Ratio, Ab / Aef b) Section

c) Plan

d) Section

7


Selected symbols Symbol Definition

Symbol Definition

A

Loadbearing horizontal cross-sectional area of the wall in m2

a1

Distance from the end of the wall to the nearer edge of the loaded area

Ab

Loaded area

Aef

Effective area of the bearing

ehe

Eccentricity of the top or bottom of the wall resulting from horizontal loads

ehm

Eccentricity at the middle of a wall, resulting from horizontal loads

Nid

Design value of the vertical load at the top or the bottom of the wall

ei

Eccentricity of the wall

Nmd

einit

Initial eccentricity

Design value of the vertical load at the mid-height of the wall, including any load applied eccentrically to the face of the wall.

em

Load eccentricity

NRd

Design resistance of a single-leaf wall per unit length

emk

Eccentricity at the mid-height of the wall

NRdc

Design vertical load resistance to a concentrated load

fb

Normalized mean compressive strength of a masonry unit

fd

Design compressive strength of the masonry in the direction being considered

t2

Effective thickness of the of the inner or loaded leaf

fm

Compressive strength of the mortar

tef

Effective thickness

fk

Characteristic compressive strength of the masonry, in N/mm2

tmin

Minimum thickness of loadbearing wall

fvk

Characteristic shear strength of masonry

VRd

Design value of shear resistance of the wall

fvd

Design value of the shear strength of the masonry

v

Notional inclination angle to the vertical

g

Total of the widths of the mortar strips

a and b

Constants to be used with Equation (3.1) of Eurocode 6, Part 1–1

h

Clear storey height of the wall

b

An enhancement factor for concentrated load

hc

Height of the wall to the level of the load

F

hef

Effective height of the wall

Capacity reduction factor allowing for the effects of slenderness and eccentricity of loading

htot

Total height of the structure

K lc

lefm

Effective length of the bearing as determined at the mid-height of the wall or pier

Mid

Design value of the bending moment at the top or the bottom of the wall resulting from eccentricity of the floor load at the support

Mmd

Design value of the greatest moment at the mid-height of the wall resulting from the moments at the top and bottom of the wall, including any load applied eccentrically to the face of the wall

t

Thickness of the wall

t1

Effective thickness of the outer or unloaded leaf

gM

Partial factor for a material property

Constant to be used with Equation (3.1) of Eurocode 6, Part 1–1

rn

Reduction factor (depending upon the edge restraint or stiffening of the wall, h/l and floor restraint)

Length of the compressed part of the wall, ignoring any part of the wall that is in tension.

rt

Stiffness coefficient

References 1

BRITISH STANDARDS INSTITUTION. BS EN 1996: Eurocode 6 – Design of masonry structures. BSI (4 parts). Including their NAs.

2

ROBERTS, JJ & Brooker, O. How to design masonry structures to Eurocode 6: Introduction to Eurocode 6. The Concrete Centre, 2013.

3

ROBERTS, JJ & Brooker, O. How to design masonry structures to Eurocode 6: Lateral resistance. The Concrete Centre. 2013.

4

BRITISH STANDARDS INSTITUTION. BS EN 772–1: Methods of test for masonry units – Determination of compressive strength. BSI, 2011.

5

BRITISH STANDARDS INSTITUTION. BS EN 1052–1: Methods of test for masonry – Determination of compressive strength. BSI, 1999.


Acknowledgements




¢¢ Concrete Block Association - www.cba-blocks.org.uk


¢¢ MPA - Mortar Industry Association - www.mortar.org.uk


Ref: TCC/03/36. ISBN 978-1-904818-57-1 First published December 2007 (in partnership with the Modern Masonry Alliance) revised January 2009 and June 2013 8 Price Group M © MPA The Concrete Centre™

¢¢ Aircrete Products Association - www.aircrete.co.uk ¢¢ Brick Development Association - www.brick.org.uk

¢¢ MPA - The Concrete Centre - www.concretecentre.com




3. Lateral resistance Eur Ing, Prof.

Revision 2


Introduction This publication is part of a series of three guides entitled How to design masonry structures using Eurocode 6. The aim is to make the use of Eurocode 6, Design of masonry structures as easy as possible by drawing together in one place key information and commentary required for the design of typical masonry elements. The Concrete Centre (and, originally, The Modern Masonry Alliance) recognised that effective guidance was required to ensure that the UK design profession was able to use Eurocode 6 quickly, effectively, efficiently and with confidence. Therefore a steering group, with members from across the masonry industry (see back cover for a list of members), was established to oversee the development and publication of the original guides. This second revision addresses the publication of PD6697 in 2010 and revised National Annex to BS EN 1996-1-1 in 2013. It was overseen by a reconstituted steering group from industry (see back cover).

Guidance for lateral resistance This guide is the third in a series of three giving guidance on the design of masonry structures to Eurocode 61. The first guide, Introduction to Eurocode 62 gives an introduction to design and assessment of actions using Eurocode 6 and also covers the specification and workmanship of masonry. The second guide in the series3 covers the design of vertically loaded masonry. This guide explains how to design for horizontal actions. Throughout this guide the Nationally Determined Parameters (NDPs) from the UK National Annexes (NAs) have been used. These enable Eurocode 6 to be applied in the UK.

Eurocode 6 methods for lateral resistance Eurocode 6 offers two approaches to the design of laterally loaded panels. The first method relies on the flexural strength of the masonry and makes use of yield line analysis to provide bending moment coefficients. The second method is an approach based on arching and the assumption of a three-pinned arch being formed within the wall. Both methods are presented in this guide. The flexural strength approach is the most widely used and does not depend upon rigid supports to resist arch thrust. In the UK, the reliance on the development of tensile strength in the masonry has meant that this design approach has usually been limited to transitory loads only. Eurocode 6 indicates that the flexural strength of masonry should not be used in the design of walls subjected to permanent lateral actions, e.g. gravity or reinforced retaining walls. The assessment of the edge conditions is a requirement for the flexural strength approach. A free edge is easily identified but some judgement on the part of the engineer is necessary in deciding between simply supported or fixed conditions. When considering the vertical support condition, attention also needs to be paid to the potential position of movement joints and the changes the provision of such joints make to the panel size and restraint conditions. Where the walls are not rectangular, for instance a trapezoidal-shaped wall to a mono-pitched structure, engineering judgement may be applied to determine the effective wall height. Wall panels with openings need to be treated with care and may typically be sub-divided into smaller panels around the opening. It is beyond the scope of this guide to deal with the topic in detail and reference should be made to suitable handbooks4,5. Alternatively, a yield line analysis from first principles may be used; the guidance in Practical yield line design6 can be applied to wall panels.


MEd2 = a 2 WEd l2 when the plane of failure is perpendicular to the bed joints where a1 = bending moment coefficient parallel to the bed joints (= μa2, see Table 2) a2 = bending moment coefficient perpendicular to the bed joints (see Table 2) WEd = design wind load per unit area (g Q Wk) l = length of panel between supports μ = orthogonal ratio (fxk1/fxk2)

If a damp proof course (dpc) is present in a wall subjected to flexure then the degree of fixity may be altered. The bending moment coefficient at a dpc may be taken as that for an edge over which full continuity exists, provided that there is sufficient vertical load on the dpc to ensure that the flexural strength capacity is not exceeded. Walls may be either horizontally and/or vertically spanning and the ultimate strength of the wall is governed by the capacity of the masonry to resist flexural tension. This capacity is enhanced by the presence of vertical load. Clearly the potential flexural strength is greater if the potential plane of failure is perpendicular rather than parallel to the bed joint.

Lateral resistance using flexural strength

Figure 1 shows a flow chart for lateral load design. The designer needs to assess the panel support conditions (or assume a free edge) and decide whether these provide simple or continuous (fully restrained) support. Care also needs to be exercised in considering the effect of dpcs, movement joints, openings in walls, etc. There are handbooks that provide further guidance on these aspects4,5.

Bending moments using coefficients For panels without openings, the bending moments per unit length (MEd) are: MEd1 = a1 WEdl2 when the plane of failure is parallel to the bed joints

The presence of a vertical load increases the flexural strength of a panel in the direction parallel to the bed joints. The design moment of resistance within the height of the wall is given by: f MRd = gxk1 + s d Z

M

where fxk1 = characteristic flexural strength of masonry bending about an

axis parallel to bed joints (see Table 1) gM = appropriate partial factor for materials s d = design vertical load per unit area (< 0.2 fk /g M) Z = section modulus of the plan shape of the wall fk = characteristic compressive strength (see Vertical resistance3).

Figure 1 Flow chart for the design of masonry walls to resist lateral actions

t

Masonry unit properties • Type and group • Dimensions • Strength

h Determine requirements for mortar strength and durability. See tables 5 & 6 of Introduction to Eurocode 6

Characteristic lateral actions

l

Obtain height, h

Determine design value of lateral actions, WEd, using Expressions (6.10), (6.10a) or (6.10b) of Eurocode. (see Introduction to Eurocode 6)

Obtain water absorption for clay masonry unit or declared compressive strength from manufacturer for other masonry types

Obtain fxk1 and fxk2 from Table 1 and calculate orthogonal ratio, m where: m = fxk1 / fxk2

Obtain thickness, t

Check slenderness ratio h/t ≤ 30 for walls supported top and bottom only

Obtain a from Table 2 and calculate, MEd1 and MEd2, where: MEd1 = a1 WEd l 2, parallel to the bed joints or MEd2 = a2 WEd l 2, perpendicular to the bed joints

Check serviceability slenderness limits using Figures 2, 3 or 4 as appropriate

Characteristic vertical actions

Obtain, gM from table 1 Introduction to Eurocode 6

Determine design value of vertical load, GEd, using Expressions (6.10), (6.10a) or (6.10b) of Eurocode. (see Introduction to Eurocode 6)

2

Obtain fxk1 from Table 1 and calculate design moment of resistance parallel to the bed joints, MRd1, where:

Check MEd1 ≤ MRd1 and MEd2 ≤ MRd2

f MRd1 = gxk1 + s d Z M

Obtain fxk2 from Table 1 and calculate design moment ˘ of resistance perpendicular to the bed joints, MRd2, where:˙ z

f

MRd2 = gxk2 Z M

˚

Check shear

3. Lateral resistance

The design procedure is iterative and may be summarised as follows: 1 Make initial assumption of support condition. 2 Make assumptions as to strength and thickness of masonry unit required; the minimum wall thickness or thickness of one leaf of a cavity wall is 100mm. 3 Check serviceability slenderness limits. For wall panels supported top and bottom only, h should be limited to 30t. For other support conditions use Figure 2 below or Figures 3 and 4 on page 6. 4 Determine orthogonal ratio, μ, and hence bending moment coefficient appropriate to panel shape (Table 2). 5 Determine the design value of the applied moment, MEd. 6 Check the design value of the moment of resistance, MRd. 7 If MEd ≤ MRd then the wall is acceptable – if not return to either step 1 or 2 and modify. 8 Check shear.

Cavity walls In a cavity wall, the design lateral load per unit area, WEd , may be apportioned (either according to capacity or stiffness) between the two leaves, provided that the wall ties are capable of transmitting the actions that result from the apportionment.

Table 1 Characteristic flexural strength of masonry, fxk1 and fxk2, in N/mm2 Values of fxk1 Plane of failure parallel to bed joints

Mortar strength class: M12

M6 & M4 M2

Limiting height and length to thickness ratios of walls restrained on all four edges

80

0.5

0.4

2.0

1.5

1.2

Between 7% 0.5 & 12%

0.4

0.35

1.5

1.1

1.0

Over 12%

0.3

0.25

1.1

0.9

0.8

0.4

Calcium silicate

brick-sizedb

0.3

Ratio h/t

50

0.9

0.6

masonry units

0.2

0.9

0.6

Aggregate concrete masonry units and manufactured stone of Groups 1 and 2 and AACc masonry units used in walls of thickness up to 100 mmd,e of declared compressive strength (N/mm2): 2.9 3.6

0.25

0.2

7.3

0.4

0.4

0.45

0.4

0.6

0.5

Aggregate concrete masonry units and manufactured stone of Groups 1 and 2 and AACc masonry units used in walls of thickness of 250 mm or greaterd,e, of declared compressive strength (N/mm2): 2.9

0.25

0.2

3.6

0.25

0.2

0.35

0.3

10.4

40

≥ 17.5

0.15

0.1

0.25

0.2

0.75

0.6

0.9f

0.7f

Key

Permissible range

a Tests to determine the water absorption of clay masonry units are to be conducted in accordance with BS EN 772–77.

20

b Units not exceeding 337.5 mm × 225 mm × 112.5 mm.

10 0

0.2 brick-sizedb

Aggregate concrete masonry units and manufactured stone of Groups 1 and 2 and AACc masonry units used in walls of any thicknessd, of declared compressive strength (N/mm2):

60

30

0.3

masonry units

7.3

70

M6 & M4 M 2

Less than 7% 0.7

Lateral resistance using arching

Figure 2

M12

Clay masonry units of Groups 1 and 2 having a water absorptiona of:

Aggregate concrete

Where a masonry wall is built between supports capable of resisting an arch thrust, then it may be assumed that a horizontal or vertical arch develops within the thickness of the wall in resisting a lateral load. The analysis can be based upon a three-pin arch, and the bearing of the arch thrust at the supports and at the central hinge should be assumed to be 0.1 times the thickness of the wall.

Values of fxk2 Plane of failure perpendicular to bed joints

c Autoclaved aerated concrete (aircrete).

10 20 30 40 50 60 70 80 90 100 110 120

Ratio l/t

e Linear interpolation may be used to obtain the values of fxk1 and fxk2 for: 1) wall thicknesses greater than 100 mm and less than 250 mm; 2) compressive strengths between 2.9 N/mm2 and 7.3 N/mm2 in a wall of given thickness.

l Key h

d The thickness should be taken as the thickness of the wall, for a single-leaf wall, or the thickness of the leaf, for a cavity wall.

Simply supported or with full continuity

f When used with flexural strength in the parallel direction, assume the orthogonal ratio μ = 0.3.

3


Table 2 Bending moment coefficient, a2, in single-leaf laterally loaded wall panels of thickness ≤ 250 mm

Wall support conditions

l

a2

h

a2

a1 = ma2

A

D

G

B

E

H

C

F

I

J

K

a1 = ma2

Key

L

Free edge Simply supported edge Fully restrained continuous edge

Notes 1 m is the orthogonal ratio (fxk1/fxk2). 2 Linear interpolation may be used. 3 Walls having an h/l ratio of less than 0.3 will tend to span vertically.

Wall support condition A µ h/l 1.00 0.90 0.80 0.70 0.60 0.50 0.40 0.35 0.30 0.25 0.20 0.15 0.10 0.05

0.30 0.031 0.032 0.034 0.035 0.038 0.040 0.043 0.045 0.048 0.050 0.054 0.060 0.069 0.082

0.50 0.045 0.047 0.049 0.051 0.053 0.056 0.061 0.064 0.067 0.071 0.075 0.080 0.087 0.097

Wall support condition C µ h/l 0.75 0.059 0.061 0.064 0.066 0.069 0.073 0.077 0.080 0.082 0.085 0.089 0.093 0.098 0.105

1.00 0.071 0.073 0.075 0.077 0.080 0.083 0.087 0.089 0.091 0.094 0.097 0.100 0.104 0.110

1.25 0.079 0.081 0.083 0.085 0.088 0.090 0.093 0.095 0.097 0.099 0.102 0.104 0.108 0.113

1.50 0.085 0.087 0.089 0.091 0.093 0.095 0.098 0.100 0.101 0.103 0.105 0.108 0.111 0.115

1.75 0.090 0.092 0.093 0.095 0.097 0.099 0.101 0.103 0.104 0.106 0.108 0.110 0.113 0.116

2.00 0.094 0.095 0.097 0.098 0.100 0.102 0.104 0.105 0.107 0.109 0.111 0.113 0.115 0.117

Wall support condition B µ h/l 1.00 0.90 0.80 0.70 0.60 0.50 0.40 0.35 0.30 0.25 0.20 0.15 0.10 0.05

4

0.30 0.024 0.025 0.027 0.028 0.030 0.031 0.034 0.035 0.037 0.039 0.043 0.047 0.052 0.060

0.50 0.035 0.036 0.037 0.039 0.042 0.044 0.047 0.049 0.051 0.053 0.056 0.059 0.063 0.069

4 Walls having an h/l ratio of more than 2.0 will tend to span horizontally. 5 Data based on tables presented in Concrete masonry designers handbook 4.

1.00 0.90 0.80 0.70 0.60 0.50 0.40 0.35 0.30 0.25 0.20 0.15 0.10 0.05

0.30 0.020 0.021 0.022 0.023 0.024 0.025 0.027 0.029 0.030 0.032 0.034 0.037 0.041 0.046

0.50 0.028 0.029 0.031 0.032 0.034 0.035 0.038 0.039 0.040 0.042 0.043 0.046 0.048 0.052

0.75 0.037 0.038 0.039 0.040 0.041 0.043 0.044 0.045 0.046 0.048 0.049 0.051 0.053 0.055

1.00 0.042 0.043 0.043 0.044 0.046 0.047 0.048 0.049 0.050 0.051 0.052 0.053 0.055 0.057

1.25 0.045 0.046 0.047 0.048 0.049 0.050 0.051 0.052 0.052 0.053 0.054 0.055 0.056 0.058

1.50 0.048 0.048 0.049 0.050 0.051 0.052 0.053 0.053 0.054 0.054 0.055 0.056 0.057 0.059

1.75 0.050 0.050 0.051 0.051 0.052 0.053 0.054 0.054 0.055 0.056 0.056 0.057 0.058 0.059

2.00 0.051 0.052 0.052 0.053 0.053 0.054 0.055 0.055 0.056 0.057 0.058 0.059 0.059 0.060

0.75 0.029 0.031 0.032 0.033 0.035 0.037 0.039 0.040 0.041 0.043 0.044 0.046 0.049 0.053

1.00 0.035 0.036 0.038 0.039 0.040 0.042 0.043 0.044 0.046 0.047 0.048 0.050 0.052 0.055

1.25 0.040 0.040 0.041 0.043 0.044 0.045 0.047 0.048 0.049 0.050 0.051 0.052 0.054 0.056

1.50 0.043 0.043 0.044 0.045 0.046 0.048 0.049 0.050 0.051 0.052 0.053 0.054 0.055 0.057

1.75 0.045 0.046 0.047 0.047 0.048 0.050 0.051 0.051 0.052 0.053 0.054 0.055 0.056 0.058

2.00 0.047 0.048 0.048 0.049 0.050 0.051 0.052 0.053 0.053 0.054 0.055 0.056 0.057 0.059

Wall support condition D µ h/l 0.75 0.046 0.047 0.049 0.051 0.053 0.055 0.057 0.059 0.061 0.062 0.065 0.067 0.070 0.074

1.00 0.053 0.055 0.056 0.058 0.059 0.061 0.063 0.065 0.066 0.068 0.069 0.071 0.074 0.077

1.25 0.059 0.060 0.061 0.062 0.064 0.066 0.067 0.068 0.070 0.071 0.072 0.074 0.076 0.079

1.50 0.062 0.063 0.065 0.066 0.067 0.069 0.070 0.071 0.072 0.073 0.074 0.076 0.078 0.080

1.75 0.065 0.066 0.067 0.068 0.069 0.071 0.072 0.073 0.074 0.075 0.076 0.077 0.079 0.081

2.00 0.068 0.068 0.069 0.070 0.071 0.072 0.074 0.074 0.075 0.077 0.078 0.079 0.080 0.082

1.00 0.90 0.80 0.70 0.60 0.50 0.40 0.35 0.30 0.25 0.20 0.15 0.10 0.05

0.30 0.013 0.014 0.015 0.016 0.017 0.018 0.020 0.022 0.023 0.025 0.027 0.030 0.034 0.041

0.50 0.021 0.022 0.023 0.025 0.026 0.028 0.031 0.032 0.034 0.035 0.038 0.040 0.043 0.048


Wall support condition I µ h/l

Wall support condition E µ h/l 1.00 0.90 0.80 0.70 0.60 0.50 0.40 0.35 0.30 0.25 0.20 0.15 0.10 0.05

0.30

0.50

0.75

1.00

1.25

1.50

1.75

2.00

0.008 0.009 0.010 0.011 0.012 0.014 0.017 0.018 0.020 0.023 0.026 0.032 0.039 0.054

0.018 0.019 0.021 0.023 0.025 0.028 0.032 0.035 0.038 0.042 0.046 0.053 0.062 0.076

0.030 0.032 0.035 0.037 0.040 0.044 0.049 0.052 0.055 0.059 0.064 0.070 0.078 0.090

0.042 0.044 0.046 0.049 0.053 0.057 0.062 0.064 0.068 0.071 0.076 0.081 0.088 0.098

0.051 0.054 0.056 0.059 0.062 0.066 0.071 0.074 0.077 0.080 0.084 0.089 0.095 0.103

0.059 0.062 0.064 0.067 0.070 0.074 0.078 0.081 0.083 0.087 0.090 0.094 0.100 0.107

0.066 0.068 0.071 0.073 0.076 0.080 0.084 0.086 0.089 0.091 0.095 0.098 0.103 0.109

0.071 0.074 0.076 0.078 0.081 0.085 0.088 0.090 0.093 0.096 0.099 0.103 0.106 0.110

0.30 0.008 0.008 0.009 0.010 0.011 0.013 0.015 0.016 0.018 0.020 0.023 0.027 0.032 0.043

0.50 0.016 0.017 0.018 0.020 0.022 0.024 0.027 0.029 0.031 0.034 0.037 0.042 0.048 0.057

0.75 0.026 0.027 0.029 0.031 0.033 0.036 0.039 0.041 0.044 0.046 0.049 0.053 0.058 0.066

1.00 0.034 0.036 0.037 0.039 0.042 0.044 0.048 0.050 0.052 0.054 0.057 0.060 0.064 0.070

1.25 0.041 0.042 0.044 0.046 0.048 0.051 0.054 0.055 0.057 0.060 0.062 0.065 0.068 0.073

1.50 0.046 0.048 0.049 0.051 0.053 0.056 0.058 0.060 0.062 0.063 0.066 0.068 0.071 0.075

1.75 0.051 0.052 0.054 0.055 0.057 0.059 0.062 0.063 0.065 0.066 0.068 0.070 0.073 0.077

2.00 0.054 0.055 0.057 0.058 0.060 0.062 0.064 0.066 0.067 0.069 0.070 0.072 0.074 0.078

0.30 0.007 0.008 0.008 0.009 0.010 0.011 0.013 0.014 0.016 0.018 0.020 0.023 0.027 0.035

0.50 0.014 0.015 0.016 0.017 0.019 0.021 0.023 0.025 0.026 0.028 0.031 0.034 0.038 0.044

0.75 0.022 0.023 0.024 0.026 0.028 0.030 0.032 0.033 0.035 0.037 0.039 0.042 0.045 0.050

1.00 0.028 0.029 0.031 0.032 0.034 0.036 0.038 0.039 0.041 0.042 0.044 0.046 0.049 0.053

1.25 0.033 0.034 0.035 0.037 0.038 0.040 0.042 0.043 0.044 0.046 0.047 0.049 0.052 0.055

1.50 0.037 0.038 0.039 0.040 0.042 0.043 0.045 0.046 0.047 0.048 0.050 0.051 0.053 0.056

1.75 0.040 0.041 0.042 0.043 0.044 0.046 0.047 0.048 0.049 0.050 0.052 0.053 0.055 0.057

2.00 0.042 0.043 0.044 0.045 0.046 0.048 0.049 0.050 0.051 0.052 0.054 0.055 0.057 0.058

0.30 0.005 0.006 0.006 0.007 0.008 0.009 0.010 0.011 0.013 0.014 0.016 0.019 0.023 0.031

0.50 0.011 0.012 0.013 0.014 0.015 0.017 0.019 0.021 0.022 0.024 0.027 0.030 0.034 0.041

0.75 0.015 0.016 0.017 0.019 0.020 0.022 0.024 0.026 0.028 0.030 0.032 0.035 0.039 0.045

1.00 0.021 0.022 0.023 0.025 0.026 0.028 0.031 0.032 0.034 0.036 0.038 0.041 0.044 0.049

1.25 0.026 0.027 0.028 0.030 0.031 0.033 0.035 0.037 0.038 0.040 0.042 0.044 0.047 0.052

1.50 0.030 0.031 0.032 0.033 0.035 0.037 0.039 0.040 0.042 0.043 0.045 0.047 0.050 0.053

1.75 0.033 0.034 0.035 0.037 0.038 0.040 0.042 0.043 0.044 0.046 0.047 0.049 0.052 0.055

2.00 0.036 0.037 0.038 0.039 0.041 0.042 0.044 0.045 0.046 0.048 0.050 0.051 0.054 0.056

1.00 0.90 0.80 0.70 0.60 0.50 0.40 0.35 0.30 0.25 0.20 0.15 0.10 0.05

0.30 0.009 0.010 0.012 0.013 0.015 0.018 0.021 0.024 0.027 0.032 0.038 0.048 0.065 0.106

0.50 0.023 0.026 0.028 0.032 0.036 0.042 0.050 0.055 0.062 0.071 0.083 0.100 0.131 0.208

0.75 0.046 0.050 0.054 0.060 0.067 0.077 0.090 0.098 0.108 0.122 0.142 0.173 0.224 0.344

1.00 0.071 0.076 0.083 0.091 0.100 0.113 0.131 0.144 0.160 0.180 0.208 0.250 0.321 0.482

1.25 0.096 0.103 0.111 0.121 0.135 0.153 0.177 0.194 0.214 0.240 0.276 0.329 0.418 0.620

1.50 0.122 0.131 0.142 0.156 0.173 0.195 0.225 0.244 0.269 0.300 0.344 0.408 0.515 0.759

1.75 0.151 0.162 0.175 0.191 0.211 0.237 0.272 0.296 0.325 0.362 0.413 0.488 0.613 0.898

2.00 0.180 0.193 0.208 0.227 0.250 0.280 0.321 0.347 0.381 0.428 0.488 0.570 0.698 0.959

1.00 0.90 0.80 0.70 0.60 0.50 0.40 0.35 0.30 0.25 0.20 0.15 0.10 0.05

0.30 0.009 0.010 0.011 0.012 0.014 0.016 0.019 0.021 0.024 0.028 0.033 0.040 0.053 0.080

0.50 0.021 0.023 0.025 0.028 0.031 0.035 0.041 0.045 0.050 0.056 0.064 0.077 0.096 0.136

0.75 0.038 0.041 0.045 0.049 0.054 0.061 0.069 0.075 0.082 0.091 0.103 0.119 0.144 0.190

1.00 0.056 0.060 0.065 0.070 0.077 0.085 0.097 0.104 0.112 0.123 0.136 0.155 0.182 0.230

1.25 0.074 0.079 0.084 0.091 0.099 0.109 0.121 0.129 0.139 0.150 0.165 0.184 0.213 0.260

1.50 0.091 0.097 0.103 0.110 0.119 0.130 0.144 0.152 0.162 0.174 0.190 0.210 0.238 0.286

1.75 0.108 0.113 0.120 0.128 0.138 0.149 0.164 0.173 0.183 0.196 0.211 0.231 0.260 0.306

2.00 0.123 0.129 0.136 0.145 0.155 0.167 0.182 0.191 0.202 0.217 0.234 0.253 0.279 0.317

0.75 0.029 0.032 0.034 0.038 0.042 0.048 0.055 0.060 0.066 0.073 0.084 0.098 0.121 0.164

1.00 0.044 0.047 0.051 0.056 0.061 0.068 0.078 0.084 0.092 0.101 0.114 0.131 0.156 0.204

1.25 0.059 0.063 0.067 0.073 0.080 0.089 0.100 0.108 0.116 0.127 0.141 0.159 0.186 0.235

1.50 0.073 0.078 0.084 0.090 0.098 0.108 0.121 0.129 0.138 0.150 0.165 0.184 0.212 0.260

1.75 0.088 0.093 0.099 0.106 0.115 0.126 0.139 0.148 0.158 0.170 0.185 0.205 0.233 0.281

2.00 0.102 0.107 0.114 0.122 0.131 0.142 0.157 0.165 0.176 0.190 0.206 0.226 0.252 0.292

Wall support condition L µ h/l

Wall support condition H µ h/l 1.00 0.90 0.80 0.70 0.60 0.50 0.40 0.35 0.30 0.25 0.20 0.15 0.10 0.05

0.50 0.009 0.010 0.010 0.011 0.013 0.014 0.016 0.017 0.019 0.021 0.023 0.026 0.031 0.038

Wall support condition K µ h/l

Wall support condition G µ h/l 1.00 0.90 0.80 0.70 0.60 0.50 0.40 0.35 0.30 0.25 0.20 0.15 0.10 0.05

0.30 0.004 0.004 0.005 0.005 0.006 0.007 0.008 0.009 0.010 0.011 0.013 0.016 0.020 0.027

Wall support condition J µ h/l

Wall support condition F µ h/l 1.00 0.90 0.80 0.70 0.60 0.50 0.40 0.35 0.30 0.25 0.20 0.15 0.10 0.05

1.00 0.90 0.80 0.70 0.60 0.50 0.40 0.35 0.30 0.25 0.20 0.15 0.10 0.05

0.75 0.018 0.019 0.020 0.022 0.024 0.025 0.028 0.029 0.031 0.033 0.035 0.038 0.042 0.047

1.00 0.024 0.025 0.027 0.028 0.030 0.032 0.034 0.036 0.037 0.039 0.041 0.043 0.047 0.051

1.25 0.029 0.030 0.032 0.033 0.035 0.036 0.039 0.040 0.041 0.043 0.045 0.047 0.050 0.053

1.50 0.033 0.034 0.035 0.037 0.038 0.040 0.042 0.043 0.044 0.046 0.047 0.049 0.052 0.055

1.75 0.036 0.037 0.038 0.040 0.041 0.043 0.045 0.046 0.047 0.048 0.049 0.051 0.053 0.056

2.00 0.039 0.040 0.041 0.042 0.043 0.045 0.047 0.047 0.049 0.051 0.052 0.053 0.054 0.056

1.00 0.90 0.80 0.70 0.60 0.50 0.40 0.35 0.30 0.25 0.20 0.15 0.10 0.05

0.30 0.006 0.007 0.008 0.009 0.010 0.012 0.014 0.016 0.018 0.021 0.025 0.031 0.041 0.064

0.50 0.015 0.017 0.018 0.021 0.023 0.027 0.032 0.035 0.039 0.044 0.052 0.061 0.078 0.114

5


The arch rise, r, is given by: r = 0.9t – da where t = thickness of the wall da = deflection of the arch under design load If the length to thickness ratio is 25 or less, da may be taken as zero. The maximum design arch thrust per unit length of wall, Nad, may be determined from: t Nad = 1.5fd 10 Figure 3 Limiting height and length to thickness ratios of walls restrained at the bottom, the top and one vertical edge

80 70

qlat,d = fd

( lt )

2

a

where t = thickness of the wall fd = design compressive strength of the masonry in the direction of the arch thrust (BS EN 1996–1–1 Cl. 3.6.1) la = length or height of wall between supports capable of resisting the arch thrust Note the following: ■■ The slenderness ratio should not exceed 20. ■■ The design value of vertical stress should not be less than 0.1 N/mm2. ■■ Any dpc must be capable of transmitting the horizontal forces.

Shear strength of masonry

60

Ratio h/t

Where the deflection is small the lateral strength, qlat,d, is given by the following:

50

The characteristic shear strength of masonry is a function of the characteristic initial shear strength of the masonry and the design compressive stress orthogonal to the shear plane being considered. The values of the initial shear strength of masonry are given in table NA.6 and shown in Table 3.

40 30

Permissible range

20 10 0

10 20 30 40 50 60 70 80 90 100 110 120

Ratio l/t

l

Key Simply supported or with full continuity

h

Figure 4 Limiting height and length to thickness ratios of walls restrained at the vertical edges and at the bottom edge, but not the top edge

80

fvk = 0.5fvko + 0.4 sd ≤ 0.045fb where fvk = characteristic shear strength of masonry fvko = characteristic initial shear strength of masonry, under zero compressive stress sd = design compressive stress perpendicular to the shear in the member at the level under consideration, using the appropriate load combination based on the average Table 3

70

Values of the initial shear strength of masonry, fvko

60

Ratio h/t

The characteristic shear strength is given by the following relationships: ■■ For fully filled mortar joints: fvk = fvko + 0.4 sd ≤ 0.065fb ■■ For unfilled perpend joints, units abutting:

Masonry units

50 40 30

Permissible range

Clay

20

10 20 30 40 50 60 70 80 90 100 110 120

Ratio l/t

l

M12

0.30

General purpose mortar

h

Calcium silicate

M2

0.10

M12

0.20

M4 & M6 0.15 M2

Key

6

Initial shear strength fvko (N /mm2)

M4 & M6 0.20

10 0

Strength class of general purpose mortar

Simply supported or with full continuity

Thin layer Lightmortar (bed weight joint ≤ 0.5 mm mortar and ≥ 3 mm)

0.30

0.15

0.40

0.15

0.30

0.15

0.10

Aggregate concrete, M12 0.20 autoclaved aerated concrete, manufactured M4 & M6 0.15 stone and dimensioned M2 0.10 natural stone


vertical stress over the compressed part of the wall that is providing shear resistance fb = normalized compressive strength of the masonry units (as described in Cl.3.1.2.1 of BS EN 1996–1–1) for the direction of application of the load on the test specimens being perpendicular to the bed face For shell bedded masonry in which two or more equal strips of general purpose mortar are used, each at least 30 mm wide, the following relationship may be used: g fvk = f + 0.4sd t vko but not greater than the value above for unfilled perpends. where g = total of the widths of the mortar strips t = the thickness of the wall The applied shear force, VEd, should be less than the shear resistance of the wall, VRd, where VRd = fvd t lc Table 4 Value of tch,v, the maximum depth of a vertical chase or recess allowed without calculation calculation Thickness of singleleaf wall or loaded leaf of a cavity wall (mm)

Chases and recesses formed after construction of masonry

Chases and recesses formed during construction of masonry

tch,v (mm)

Min. wall thickness after chase formed (mm)

Maximum width (mm)

Maximum width (mm)

75 – 89

30

75

60

300

90 – 115

30

100

70

300

116 – 175

30

125

90

300

176 – 225

30

150

140

300

226 – 300

30

175

175

300

30

200

215

300

> 300 Notes

1 T he maximum depth of the recess or chase should include the depth of any hole reached when forming the recess or chase. 2 V ertical chases which do not extend more than one third of the storey height above floor level may have a depth up to 80 mm and a width up to 120 mm, if the thickness of the wall is 225 mm or more. 3 T he horizontal distance between adjacent chases or between a chase and a recess or an opening should not be less than 225 mm. 4 T he horizontal distance between any two adjacent recesses, whether they occur on the same side or on opposite sides of the wall, or between a recess and an opening, should not be less than twice the width of the wider of the two recesses.

where fvd = design value of the shear strength ( fvk /gM) t = thickness of the wall lc = length of wall under compression

Effect of chases Eurocode 6 requires that chases and recesses should not impair the stability of all walls, whether designed for vertical or lateral actions, and provides guidance on the value of the depth of a vertical chase, tch,v , at which the reduction in performance (vertical, shear and flexural) may be neglected. Similarly, limits for horizontal and inclined chases, tch,h , are also provided, but there is an overriding requirement that such chases should be positioned above or below a floor within of the clear height of the wall. It is also a requirement for horizontal and inclined chases that the eccentricity in the region of the chase is less than t/3, where t is the thickness of the wall. The values for the maximum depth of vertical chases and recesses allowed without calculation, tch,v , are given in table NA.11 and shown in Table 4. The values for the maximum depth of a horizontal or inclined chase allowed without calculation, tch,h, are given in table NA.12 and shown in Table 5. Table 5 Value of tch,h , the maximum depth of a horizontal or inclined chase allowed without calculation Thickness of singleleaf wall or loaded leaf of a cavity wall (mm)

Unlimited chase length (mm)

Limited chase length ≤ 1250 (mm)

75 – 115

0

0

116 – 175

0

15

176 – 225

10

20

226 – 300

15

25

20

30

> 300

tch,h

Notes 1 T he maximum depth of the chase should include the depth of any hole reached when forming the chase. 2 T he horizontal distance between the end of a chase and an opening should not be less than 500 mm. 3 T he horizontal distance between adjacent chases of limited length, whether they occur on the same side or on opposite sides of the wall, should be not less than twice the length of the longest chase.

5 T he cumulative width of vertical chases and recesses should not exceed 0.13 times the length of the wall.

4 In walls of thickness greater than 175 mm, the permitted depth of the chase may be increased by 10 mm if the chase is machine cut accurately to the required depth. If machine cuts are used, chases up to 10 mm deep may be cut in both sides of walls of thickness not less than 225 mm.

6 The minimum thickness of load bearing masonry is 90 mm.

5 The width of chase should not exceed half the residual thickness of the wall.

7

3. Lateral resistance Selected symbols Symbol Definition

Symbol Definition

da

Deflection of an arch under design load

lc

Length of the compressed part of a wall

fb

Normalised mean compressive strength of a masonry unit.

MEd

Design value of moment applied

fd

Design compressive strength of masonry in the direction being considered

MRd

Design value of moment of resistance

fvd

Design shear strength of masonry

Nad

The maximum design arch thrust per unit length of wall

fk

Characteristic compressive strength of masonry

q lat,d

Design lateral strength per unit area of wall

fvk

Characteristic shear strength of masonry

r

Arch rise

fvko

Characteristic initial shear strength of masonry, under zero compressive stress

t

Thickness of the wall

tch,v

Maximum depth of vertical chases or recesses without calculation

fxk1

Characteristic flexural strength of masonry having the plane of failure parallel to the bed joints

tch,h

Maximum depth of a horizontal or inclined chase

fxk2

Characteristic flexural strength of masonry having the plane of failure perpendicular to the bed joints

WEd

Design lateral load per unit area

Z

Elastic section modulus of a unit height or length of the wall

g

Total of the widths of the mortar strips

a1, 2

Bending moment coefficients

h

Clear height of a masonry wall gM

l

Length of a wall (between other walls, between a wall and an opening, or between openings)

Partial factor for materials, including uncertainties about geometry and modelling

Length or height of wall between supports capable of resisting the arch thrust

sd

Design compressive strength

la

μ

Orthogonal ratio of the flexural strengths of masonry

References 1

BRITISH STANDARDS INSTITUTION. BS EN 1996: Eurocode 6 – Design of masonry structures. BSI (4 parts). Including their NAs.

2

ROBERTS, J J. & BROOKER, O. How to design masonry structures to Eurocode 6: Introduction to Eurocode 6. The Concrete Centre, 2013.

3

ROBERTS, J J. & BROOKER, O. How to design masonry structures to Eurocode 6: Vertical resistance. The Concrete Centre, 2013.

4

ROBERTS, J J, Tovey, A K & Fried, A. Concrete masonry designer's handbook. Taylor & Francis, 2001.

5

MCKENZIE, W M C. Design of structural masonry. Palgrave Macmillan, 2001.

6

KENNEDY, G & GOODCHILD, C. Practical yield line design. The Concrete Centre, 2004.

7

BRITISH STANDARDS INSTITUTION. BS EN 772–7: Methods of test for masonry units – Determination of water absorption of clay masonry damp proof course units by boiling in water. BSI, 1999.


Acknowledgements




¢¢ Concrete Block Association - www.cba-blocks.org.uk


¢¢ MPA - Mortar Industry Association - www.mortar.org.uk


Ref: TCC/03/37. ISBN 978-1-904818-58-8 First published December 2007 (in partnership with the Modern Masonry Alliance) revised January 2009 and June 2013 Price Group M © MPA The Concrete Centre™

¢¢ Aircrete Products Association - www.aircrete.co.uk ¢¢ Brick Development Association - www.brick.org.uk

¢¢ MPA - The Concrete Centre - www.concretecentre.com



Eurocode 6 - Introduction

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