3. Design of Pad Foundations According to EC2

3. Design of RC Pad Foundations to Eurocodes CTR11101/CTR11501 Foundation to Design to Eurocode 7

3. DESIGN OF REINFORCED CONCRETE PAD FOUNDATIONS TO ENROCODES Dr. Ben Zhang SEBE, Edinburgh Napier University

3. Design of RC Pad Foundations to Eurocodes Foundations  Those structural elements, primarily designed to distribute the pressure more evenly onto the soil ground.

CTR11101/CTR11501

Dr. Ben Zhang

FOUNDATION DESIGN TO EUROCODE 7

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3. Design of RC Pad Foundations to Eurocodes Influencing Factors on Foundation Type  The magnitude and type of applied loading (dead loads, imposed loads, wind loads, etc.)  The pressure the ground can safely support (permissible bearing pressure)  The acceptable levels of settlement  The location and proximity of adjacent structures (structural interactions)

CTR11101/CTR11501

Dr. Ben Zhang


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3. Design of RC Pad Foundations to Eurocodes Requirements for Foundation Design (EC2)  Where ground-structure interaction has significant influence on the effects of actions in the structure, the properties of the soil and the effects of the interaction should be considered to EN 1997-1.  When significant differential settlements are likely, their influence on the effects of actions in the structure should be checked.  Concrete foundation size should be determined to EN 1997-1.  Where relevant, the design should include the effects of phenomena such as subsidence, heave, freezing, thawing, erosion, etc. CTR11101/CTR11501

Dr. Ben Zhang


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3. Design of RC Pad Foundations to Eurocodes Special Requirements for Foundation Design  Where ground-structure interaction has significant influence, the properties of the soil and the effects of the interaction should be considered to EN 1997-1.  For the design of spread foundations, simplified models for soilstructure interaction may be used. For simple pad footings and pile caps, however, such effects may be ignored.  For the strength design of individual piles, the actions should be determined including the interaction between the piles, the pile cap and the supporting soil.  Where the piles are located in several rows, the action on each pile should be evaluated by considering the interaction between the piles.  This interaction may be ignored when the clear distance between the piles is greater than two times the pile diameter. CTR11101/CTR11501

Dr. Ben Zhang


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3. Design of RC Pad Foundations to Eurocodes Eurocode 7 Geotechnical Design  Two parts: BS EN 1997-1 : 2004 General rules BS EN 1997-2 : 2007 Ground investigation and testing

 BS EN 1997-1 gives design guidance and actions for geotechnical design of buildings and civil engineering works.  BS EN 1997-1 is intended for clients, designers, contractors and public authorities and is intended to be used with EN 1990 and EN 1991 to EN 1999.  BS EN 1997-1 contains a total of 12 sections and 1 normative and 8 informative annexes. CTR11101/CTR11501

Dr. Ben Zhang


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3. Design of RC Pad Foundations to Eurocodes Assumptions and Conditions (1.3 of EC7-1)  Data required are well collected, recorded and interpreted;  Structures are designed by qualified and experienced personnel;  Adequate continuity and communication exist between the personnel in data collection, design and construction;  Adequate supervision and quality control are provided;  Execution is carried out according to the relevant standards and specifications by skilful personnel;  Construction materials and products are used as specified in this standard or in the relevant material or product specifications;  The structure will be adequately maintained to ensure its safety and serviceability for the designed service life;  The structure will be used for the purpose defined. CTR11101/CTR11501

Dr. Ben Zhang


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3. Design of RC Pad Foundations to Eurocodes Relevant BS Codes for Geotechnical Design  BS 1377 Part 1 - Part 8 : 1990 Methods of test for soils for civil engineering purposes  BS 5930 : 1999 Code of practice for site investigations  BS 6031 : 1981 Code of practice for earthworks  BS 8002 : 1994 Code of practice for earth retaining structures  BS 8004 : 1986 Code of practice for foundations  BS 8008 : 1996 + A1 : 2008 Safety precautions and procedures for the construction and descent of machinebored shafts for piling and other purposes  BS 8081 : 1989 Code of practice for ground anchorages CTR11101/CTR11501

Dr. Ben Zhang


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3. Design of RC Pad Foundations to Eurocodes Ultimate Limit States for Geotechnical Design  EQU: loss of equilibrium of the structure or the ground, considered as a rigid body, in which the strengths of structural materials and the ground are insignificant in providing resistance;  STR: internal failure or excessive deformation of the structure or structural elements, including footings, piles or basement walls, in which the strength of structural materials is significant in providing resistance;  GEO: failure or excessive deformation of the ground, in which the strength of soil or rock is significant in providing resistance;  UPL: loss of equilibrium of the structure or the ground due to uplift by water pressure (buoyancy) or other vertical actions;  HYD: hydraulic heave, internal erosion and piping in the ground caused by hydraulic gradients. CTR11101/CTR11501

Dr. Ben Zhang


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3. Design of RC Pad Foundations to Eurocodes Serviceability Limit States for Geo-Design  Serviceability limit states (SLS) needs to be verified for design of individual foundations.  Limit state GEO often governs the dimensions of structural elements, e.g. foundations and retaining structures, and sometimes the resistance of structural elements.

CTR11101/CTR11501

Dr. Ben Zhang


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3. Design of RC Pad Foundations to Eurocodes Geotechnical Categories of Structures Category 1 2

3

Description Small and relatively simple structures Conventional types of structure and foundation with no difficult soil or loading conditions

Risk of failure Negligible

All other structures or parts of structures

Exceptional

Non-exceptional

Examples in EC7-1 N/A

Responsibility Structural engineers Structural engineers or geotechnical engineers

Spread foundations Raft foundations Pile foundations Retaining walls Excavations …… Geotechnical Very large or unusual structures engineers Structures with unusual or exceptionally difficult ground or loading conditions Structures in highly seismic areas Structures in areas of probable site instability or persistent ground movements

CTR11101/CTR11501

Dr. Ben Zhang


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3. Design of RC Pad Foundations to Eurocodes Characteristic Values  Actions  Characteristic and representative values of actions should be derived in accordance with EN 1990 and various parts of EN 1991.

CTR11101/CTR11501

Dr. Ben Zhang


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3. Design of RC Pad Foundations to Eurocodes Characteristic Values  Geo-Parameters  Effective stress c' and tan' 

- Geological and other background information -

Variability of measured properties and other info Extent of the field and laboratory investigation Type and number of samples Extent of the zone of ground Ability of the geotechnical structure to transfer loads from weak to strong zones in the ground

CTR11101/CTR11501

Dr. Ben Zhang


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3. Design of RC Pad Foundations to Eurocodes Characteristic Values  Geo-Data    

Ground levels Ground water levels Free water levels Dimensions of geotechnical structures or elements

CTR11101/CTR11501

Dr. Ben Zhang


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3. Design of RC Pad Foundations to Eurocodes Design Values  Actions Fd = F Frep

(Eq.(2.1a) of EN 1997-1 & Eq.(6.1a) of EN 1990)

with Frep =  Fk where Fk is the characteristic value of the action Frep is the relevant representative value of the action F is a partial factor  is either 1,00 or 0, 1 or 2 CTR11101/CTR11501

Dr. Ben Zhang


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3. Design of RC Pad Foundations to Eurocodes Design Values  Geo-Parameters Xd = Xk / M

(Eq.(6.3) of EN 1990)

where Xk is the characteristic value of the geotechnical parameter M is a partial factor for the geotechnical parameter

CTR11101/CTR11501

Dr. Ben Zhang


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3. Design of RC Pad Foundations to Eurocodes Design Values  Geometrical Data ad = anom + Da

(Eq.(2.3) of EN 1997-1 & Eq.(6.5) of EN 1990)

where anom is the nominal value of geometrical data Da is the deviation in geotechnical data

CTR11101/CTR11501

Dr. Ben Zhang


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3. Design of RC Pad Foundations to Eurocodes Design Values  Material or Product  Concrete

fcd = acc fck / C

(Eq.(3.15) of EN 1992-1)

fctd = act fctk,0,05 / C

(Eq.(3.16) of EN 1992-1)

 Reinforcement

fyd = fyk / S

(Figure 3.8 of EN 1992-1)

CTR11101/CTR11501

Dr. Ben Zhang


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3. Design of RC Pad Foundations to Eurocodes Verification of Static Equilibrium (EQU) Edst;d ≤ Estb;d + Td

(Eq.(2.4) of EN 1997-1)

where Edst;d = E{F Frep; Xk / M; ad}dst (Eq.(2.4a) of EC7-1) Estb;d = E{F Frep; Xk /M; ad}stb (Eq.(2.4b) of EC7-1) Td is the design total shearing resistance around a block of ground where a group of tension piles is placed  Use Tables A.NA.1 and A.NA.2 of UK NA to EN 1997-1! CTR11101/CTR11501

Dr. Ben Zhang


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3. Design of RC Pad Foundations to Eurocodes Verification of Static Equilibrium (EQU)  Effect of actions for EQU

Ed    G,j Gk,j " "  P P " "  Q,1 Qk,1 " "   Q,i  0,i Qk,i j 1

i 1

(Eq.(6.10) of EN 1990)

CTR11101/CTR11501

Dr. Ben Zhang


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3. Design of RC Pad Foundations to Eurocodes Verification of Static Equilibrium (EQU)  Table A.NA.1 of UK NA to EN 1997-1 Partial factors on actions (F) Partial factors on actions (F) Permanent

Action

a

Destabilising;

b

b

a

b

Unfavourable

Favourable

Unfavourable

Favourable

G;dst

G;stb

Q;dst

Q;stb

1,1 1,35

0,9 1,1

1,5

0

Symbol Recommended Alternative a

Variable

Stabilising.

CTR11101/CTR11501

Dr. Ben Zhang


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3. Design of RC Pad Foundations to Eurocodes Verification of Static Equilibrium (EQU)  Table A.NA.2 of UK NA to EN 1997-1 Partial factors for geotechnical parameters (M) Partial factors for geotechnical parameters (M)

Geotechnical parameter

Angle of shearing resistance (applied to tan')

Effective cohesion

Undrained shear strength

Unconfined strength

Weight density

Symbol Value

'

c'

cu

qu



1,1 (1,25)

1,1 (1,25)

1,2 (1,4)

1,2 (1,4)

(1,0)

Note: The values of partial factors for soil parameters in the brackets are quotes from Table A.2 of EN 1997-1.

CTR11101/CTR11501

Dr. Ben Zhang


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3. Design of RC Pad Foundations to Eurocodes Verification of resistance for structural and ground limit states (STR and GEO) Ed ≤ Rd

(Eq.(2.5) of EN 1997-1)

where Ed = E{F Frep; Xk/M; ad} (Eq.(2.4a) of EC7-1) Ed = E E{Frep; Xk/M; ad} (Eq.(2.4b) of EC7-1) E is the partial factor for the effect of actions  Use Tables A.NA.3 and A.NA.4 of UK NA to EN 1997-1! CTR11101/CTR11501

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3. Design of RC Pad Foundations to Eurocodes Verification of resistance for structural and ground limit states (STR and GEO)  Effect of actions for STR and GEO

   G,j Gk,j " "  P P " "  Q,1  0,1 Qk,1 " "   Q,i  0,i Qk,i  j 1 i 1 Ed      j  G,j Gk,j " "  P P " "  Q,1 Qk,1 " "   Q,i  0,i Qk,i i 1  j 1 (Eqs.(6.10a) and (6.10b) of EN 1990)

CTR11101/CTR11501

Dr. Ben Zhang


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3. Design of RC Pad Foundations to Eurocodes Verification of resistance for structural and ground limit states (STR and GEO)  Table A.NA.3 of UK NA to EN 1997-1 (Tables NA.A1.2(B) and NA.A1.2(C) of UK NA to EN 1990) Partial factors on actions (F) or on the effects of action (E) Action Symbol Set A1 Set A2

Permanent Unfavourable Favourable

Variable Unfavourable Favourable

G

Q

1,35 1,0

1,0 1,0

1,5 1,3

0 0

CTR11101/CTR11501

Dr. Ben Zhang


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3. Design of RC Pad Foundations to Eurocodes Verification of resistance for structural and ground limit states (STR and GEO)  Table A.NA.4 of UK NA to EN 1997-1

Partial factors for geotechnical parameters (M) Geotechnical parameter

Angle of shearing resistance (applied to tan')

Effective cohesion

Undrained shear strength

Unconfined strength

Weight density

Symbol Set M1 Set M2

'

c'

cu

qu



1,0 (1,0) 1,25 (1,25)

1,0 (1,0) 1,25 (1,25)

1,0 (1,0) 1,4 (1,4)

1,0 (1,0) 1,4 (1,4)

(1,0) (1,0)

Note: The values of partial factors for soil parameters in the brackets are quotes from Table A.4 of EN 1997-1. CTR11101/CTR11501

Dr. Ben Zhang


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3. Design of RC Pad Foundations to Eurocodes Verification of resistance for structural and ground limit states (STR and GEO)  Design resistance Rd (ground properties Xd)

Rd = R{F Frep; Xk/M; ad}

(Eq.(2.7a) of EC7-1)

Rd = R{F Frep; Xk; ad}/R

(Eq.(2.7b) of EC7-1)

Rd = R{F Frep; Xk/M; ad}/R (Eq.(2.7c) of EC7-1) where R is the partial factor for a resistance  Use Tables A.NA.5 to A.NA.8 and A.NA.12 to A.NA.14 of UK NA to EN 1997-1! CTR11101/CTR11501

Dr. Ben Zhang


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3. Design of RC Pad Foundations to Eurocodes Verification of resistance for STR and GEO  Tables A.NA.5, A.NA.13 & A.NA.14 of UK NA to EN 1997-1 Partial resistance factors (R) Resistance Symbol

Bearing

Sliding

Earth

R;v

R;h

R;e

Set R1 Set R2 Set R3

For spread foundations 1,0 (1,0) 1,0 (1,0) (1,4) (1,1) (1,0) (1,0) For retaining structures 1,0 (1,0) 1,0 (1,0) (1,4) (1,1) (1,0) (1,0)

1,0 (1,0) (1,4) (1,0)


For slopes and overall stability / / / / / /

1,0 (1,0) (1,1) (1,0)


/ / /

CTR11101/CTR11501

Dr. Ben Zhang


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3. Design of RC Pad Foundations to Eurocodes Verification of Uplift (UPL) Vdst,d ≤ Gstb;d + Rd

(Eq.(2.8) of EN 1997-1)

with Vdst,d = Gdst;d + Qdst;d where Gdst;d is the design destabilising permanent actions; Qdst;d is the design destabilising variable actions.  Use Tables A.NA.15 and A.NA.16 of UK NA to EN 1997-1! CTR11101/CTR11501

Dr. Ben Zhang


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3. Design of RC Pad Foundations to Eurocodes Verification of Seepage of Ground Water (HYD)

udst;d ≤ sstb;d Sdst;d ≤ G'stb;d

(Eq.(2.9a) of EN 1997-1) (Eq.(2.9b) of EN 1997-1)

where udst;d is the design value of the destabilising total pore water pressure at the bottom of the column sstb;d is the design stabilising total vertical stress Sdst;d is the design value of the seepage force in the column Qdst;d is the design value of the submerged weight of the column

 Use Table A.NA.17 of UK NA to EN 1997-1! CTR11101/CTR11501

Dr. Ben Zhang


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3. Design of RC Pad Foundations to Eurocodes Verification of Serviceability Limit States Ed ≤ Cd

(Eq.(2.10) of EN 1997-1 or Eq.(6.13) of EN 1990)

CTR11101/CTR11501

Dr. Ben Zhang


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3. Design of RC Pad Foundations to Eurocodes Verification of Serviceability Limit States  Characteristic combination (Prescriptive method for spread)

 Gk,j " " P " " Qk,1 " "  0,i Qk,i j 1

(Eq.(6.14b) of EN 1990)

i1

Normally used for irreversible SLS.

 Frequent combination (Direct method for foundation size)

 Gk, j " " P " " Ad " "1,1 Qk,1 " "  2,i Qk,i j 1

i 1

(Eq.(6.15b) of EN 1990)

Normally used for reversible SLS.

 Quasi-permanent combination (Direct method for settlement)

 Gk, j " " P " "  2,i Qk,i j 1

i1

(Eq.(6.16b) of EN 1990)

Normally used for long-term effects and appearance of the structure. CTR11101/CTR11501

Dr. Ben Zhang


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3. Design of RC Pad Foundations to Eurocodes Approaches for Geotechnical Design  Design Approach 1 (Adopted in the UK!) (not applicable for axially loaded piles and anchors)

Combination 1: Combination 2:

A1 “+” M1 “+” R1 A2 “+” M2 “+” R1

where “+” denotes “to be combined with”; A denotes actions; M denotes ground strength; R denotes ground resistance. CTR11101/CTR11501

Dr. Ben Zhang


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3. Design of RC Pad Foundations to Eurocodes Approaches for Geotechnical Design  Design Approach 1 (Adopted in the UK!) (applicable for axially loaded piles and anchors)

Combination 1: Combination 2:

A1 “+” M1 “+” R1 A2 “+” (M1 or M2) “+” R4

where “+” denotes “to be combined with”; A denotes actions; M denotes ground strength; R denotes ground resistance. CTR11101/CTR11501

Dr. Ben Zhang


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3. Design of RC Pad Foundations to Eurocodes Approaches for Geotechnical Design  Design Approach 2 (Adopted in France!)

Combination:

A1 “+” M1 “+” R2

where “+” denotes “to be combined with” A denotes actions M denotes ground strength R denotes ground resistance

CTR11101/CTR11501

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3. Design of RC Pad Foundations to Eurocodes Approaches for Geotechnical Design  Design Approach 3 (Adopted in Germany!)

Combination:

(A1a or A2b) “+” M2 “+” R3

where a b

“+” A M R

F on structural actions F on geotechnical actions denotes “to be combined with” denotes actions denotes ground strength denotes ground resistance CTR11101/CTR11501

Dr. Ben Zhang


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3. Design of RC Pad Foundations to Eurocodes Geotechnical Design Report (from Ground Investigation Report)      

a description of the site and surroundings a description of the ground conditions a description of the proposed construction, including actions characteristic and design values of soil and rock properties statements on the codes and standards applied statements on the suitability of the site for the proposed construction and the level of acceptable risks  geotechnical design calculations and drawings, e.g. limit states, combinations, etc.  foundation design recommendations  a note of items to be checked during construction or requiring maintenance or monitoring CTR11101/CTR11501

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3. Design of RC Pad Foundations to Eurocodes Geotechnical Design Report       

the purpose of observations or measurements the parts of the structure to be monitored and observed the frequency of readings the methods of evaluation the range of expected results the period of post-construction monitoring time the parties responsible for making measurements and observations, for interpreting the results obtained and for maintaining the instruments CTR11101/CTR11501

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3. Design of RC Pad Foundations to Eurocodes Spread Foundations  Pad foundations

Square Squarepad pad foundation foundation

Rectangular Rectangularpad pad foundation foundation

CTR11101/CTR11501

Dr. Ben Zhang


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3. Design of RC Pad Foundations to Eurocodes Rectangular combined foundation

Spread Foundations  Combined foundations

Trapezoidal combined foundation

Combined rectangular foundation

Reversed T-section foundation CTR11101/CTR11501

Dr. Ben Zhang


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3. Design of RC Pad Foundations to Eurocodes Spread Foundations  Strip foundations

Strip foundation

Strip foundation

CTR11101/CTR11501

Dr. Ben Zhang


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3. Design of RC Pad Foundations to Eurocodes Limit States for Spread Foundations  Ultimate Limit States (ULS) ̶ loss of overall stability ̶ bearing resistance failure, punching failure, squeezing ̶ failure by sliding ̶ combined failure in the ground and in the structure ̶ structural failure due to foundation movement  Serviceability Limit States (SLS) ̶ excessive settlements ̶ excessive heave due to swelling, frost and other causes ̶ unacceptable vibrations CTR11101/CTR11501

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3. Design of RC Pad Foundations to Eurocodes Methods for Spread Foundation Design  Direct method: Separate analyses are carried out for each limit state. For ULS, the model should be close to the failure mechanism. For SLS, a settlement calculation should be used.  Indirect method: Experience and field or laboratory are used to determine SLS loads.  Prescriptive method: A presumed bearing resistance is used where calculation models are not available or not necessary. These involve conventional and generally conservative rules in the design, and attention is paid to specification and control of materials, workmanship, protection and maintenance procedures. (UK!) CTR11101/CTR11501

Dr. Ben Zhang


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3. Design of RC Pad Foundations to Eurocodes Presumed Allowable Bearing Values  For Category 1 and Category 2 structures (BS 8004) Category Noncohesive soils

Types of soil Dense gravel, or dense sand and gravel Medium dense gravel, or medium dense sand and gravel Loose gravel, or loose sand and gravel Compact sand Medium dense sand Loose sand

Cohesive soils

Very stiff boulder clays and hard clays Stiff clays Firm clays Soft clays and silts Very soft clays and silts

Presumed allowable bearing values (kN/m2) > 600 < 200 to 600 < 200 > 300 100 to 300 < 100 300 to 600 150 to 300 75 to 150 < 75 Not applicable

Remarks Foundation width not less than 1 m. Groundwater level assumed to be below the base of the foundation. Susceptible to long-term consolidation settlement.

Note: These values are for preliminary design purposes only.

CTR11101/CTR11501

Dr. Ben Zhang


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3. Design of RC Pad Foundations to Eurocodes Effects of Actions for Foundations  Horizontal forces due to lateral loading or friction between the underside of the base and the soil  Vertical forces from columns and/or walls and bearing pressure from the ground underneath  Moments due to loading from columns and/or walls, etc. V M H

CTR11101/CTR11501

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3. Design of RC Pad Foundations to Eurocodes Base Pressure Distribution at the ULS V M

V/B(L – 2e) e V

e = M/V CTR11101/CTR11501

Dr. Ben Zhang


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3. Design of RC Pad Foundations to Eurocodes Middle Third Rule at the SLS  If the eccentricity e of the load lies within the middle third of the base length, i.e. e ≤ L/6, then no tension will occur under the base.

CTR11101/CTR11501

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3. Design of RC Pad Foundations to Eurocodes Base Pressure Distribution at the SLS  Case 1 (uniform full compression): e = 0 Uniform compression and no tension V

B V / BL L V CTR11101/CTR11501

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3. Design of RC Pad Foundations to Eurocodes Base Pressure Distribution at the SLS  Case 2 (full compression): e ≤ L/6 Linearly distributed compression and no tension V M B

L

V  6e  1   BL  L e = M/V Pmax

V

V  6e  1 +   BL  L Pmax CTR11101/CTR11501

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3. Design of RC Pad Foundations to Eurocodes Base Pressure Distribution at the SLS  Case 3 (partial compression): e > L/6 Linearly distributed partial compression and no tension V M B 4V 3 B(L - 2e)

L e = M/V

V CTR11101/CTR11501

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3. Design of RC Pad Foundations to Eurocodes Design Procedure for Shallow Foundations 1. 2. 3. 4.

5.

6. 7. 8.

Start the design process. Obtain soil parameters from Ground Investigation Report. Decide if Direct Method is used. If not, go to Step 5. Determine the foundation size (geotechnical design) using the worst of Combinations 1 or 2 (ULS) for actions and geotechnical material properties. Combination 2 will usually govern. Go to Step 6. Use Prescriptive Method to determine the foundation size (geotechnical design) using SLS for actions and presumed bearing resistance. Check if there is an overturning moment. If not, go to Step 8. Check overturning using EQU limit state for actions and GEO Combination 2 for material properties. Design foundation (structural design) using the worst of Combinations 1 and 2 (ULS) for actions and geotechnical material properties. CTR11101/CTR11501

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3. Design of RC Pad Foundations to Eurocodes Design of Reinforced Concrete Pad Footings  sufficient reinforcement to resist bending moments  punching shear strength  direct shear strength

CTR11101/CTR11501

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3. Design of RC Pad Foundations to Eurocodes

Critical Shear Surfaces for Pad Foundations Punching shear perimeters, (load within deducted from VEd)

Direct shear faces

2d

d

h

Bends may be required d

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Punching Shear for Pad Footings at ULS

CTR11101/CTR11501

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3. Design of RC Pad Foundations to Eurocodes Critical Punching Shear Checks for Pad Foundations  At the column perimeter, or the perimeter of the loaded area

vEd < vRd,max  Punching shear reinforcement not required

vEd ≤ vRd  Punching shear reinforcement required

vEd > vRd CTR11101/CTR11501

Dr. Ben Zhang


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3. Design of RC Pad Foundations to Eurocodes Net Punching Shear Force VEd,red VEd,red = VEd - ΔVEd

Eq.(6.48) of EN 1992-1-1

where VEd is the design value of the applied shear force; ΔVEd is the design value of the net upward force within the control perimeter considered, i.e. upward pressure from soil minus self-weight of the base.

CTR11101/CTR11501

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3. Design of RC Pad Foundations to Eurocodes Design Punching Shear Stress vEd

vEd = b VEd,red / (u1 d) Eq.(6.51) of EN 1992-1-1 where d is the mean effective depth of the pad footing, which may be taken as (dy + dz)/2 dy, dz are the effective depths in the y- and z-directions of the control section u1 is the length of the control perimeter being considered

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3. Design of RC Pad Foundations to Eurocodes Typical basic control perimeters around loaded areas, u1

CTR11101/CTR11501

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3. Design of RC Pad Foundations to Eurocodes Basic control perimeters for loaded areas close to or at edge or corner, u1 u1

2d

2d

2d u1

u1

2d 2d

2d CTR11101/CTR11501

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3. Design of RC Pad Foundations to Eurocodes For concentric loading to the control perimeter

b = 1,0

(Eq.(6.49) of EC2-1-1)

CTR11101/CTR11501

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3. Design of RC Pad Foundations to Eurocodes For eccentric loading to the control perimeter

M Ed u1 β  1+ k  VEd,red W1

(Eq.(6.51) of EC2-1-1)

where k is a coefficient dependent on the ratio between the column dimensions c1 and c2, its value depending on the proportions of the unbalanced moment transmitted by uneven shear and by bending and torsion, see Slide 62 W1 corresponds to a distribution of shear as shown in the figure in Slide 62 and is a function of the basic control perimeter u1 as u W  dl is a length increment of the perimeter 1 0 e dl e is the distance of dl from the axis the moment MEd acts about 1

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3. Design of RC Pad Foundations to Eurocodes Parameters k and W1 c1/c2 k

 0,5 0,45

1,0 0,60

2,0 0,70

 3,0 0,80

 For rectangular column c12 W1  +c1 c2 + 4 c2 d  16 d 2  2 π d c1 2

(Eq.(6.41) of EC2-1-1) CTR11101/CTR11501

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3. Design of RC Pad Foundations to Eurocodes Parameter b  For internal circular columns

e β  1  0, 6 π D  4d

(Eq.(6.42) of EC2-1-1)

where D is the diameter of the circular column

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3. Design of RC Pad Foundations to Eurocodes Parameter b

u1

2d

2d

2d u1

u1

 For edge columns

u1 u1 β k epar u1* W1

2d 2d

2d

(Eq.(6.44) of EC2-1-1)

where u1 is the basic control perimeter, see the figure in Slide 59 u1* is the reduced basic control perimeter, see the figures in Slides 65 and 66 epar is the eccentricity parallel to the pad edge caused by a moment about an axis perpendicular to the pad edge k may be determined from the table in Slide 62 with c1/c2 replaced by c1/2c2 W1 is calculated for the basic control perimeter u1, see the figure in Slide 62 CTR11101/CTR11501

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3. Design of RC Pad Foundations to Eurocodes Parameters W1 and u1*  For a rectangular column

≤ 1,5d ≤ 0,5c1

c22 W1  + c1 c2 + 4 c1 d  8 d 2  π d c2 2 (Eq.(6.45) of EC2-1-1)

2d c2 u1*

c1

2d

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3. Design of RC Pad Foundations to Eurocodes ≤ 1,5d Parameter ≤ 0,5c1

b

 For corner columns

β  u1 / u1*

2d

(Eq.(6.46) of EC2-1-1) c2 u1*

c1

c2

≤ 1,5d ≤ 0,5c2

u1*

2d

2d c1

2d

≤ 1,5d ≤ 0,5c1 CTR11101/CTR11501

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3. Design of RC Pad Foundations to Eurocodes Punching Shear Resistance Without Shear Reinforcement

vRd  CRd,c k (100 l fck )1/ 3 (2d / a)  vmin (2d / a) (Eq.(6.47) of EC2-1-1) where k is a parameter considering size effect and k = min [ 1+ 200 / d ; 2,0] 1 is a tension reinforcement ratio and 1 = min 1y  1z ; 0, 02





1y, 1z are the tension reinforcement ratios relating to the bonded tension steel in y- and z-directions respectively Ac is the area of concrete according to the definition of NEd CRd,c is a parameter and CRd,c = 0,18 / C = 0,18 / 1,5 = 0,12 a is the distance from the column periphery to the control perimeter CTR11101/CTR11501

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3. Design of RC Pad Foundations to Eurocodes Punching Shear Resistance with Shear Reinforcement vRd,cs = 0,75vRd,c + 1,5(d/sr) Asw fywd,ef [1/(u1d)] sina (Eq.(6.52) of EC2-1-1) where Asw is the area of one perimeter of shear reinforcement around the column sr is the radial spacing of perimeters of shear reinforcement fywd,ef is the effective design strength of the punching shear reinforcement, according to fywd,ef = 250 + 0,25 d ≤ fywd, see the table in Slide 70 d is the mean of the effective depths in the orthogonal directions in mm a is the angle between shear reinforcement and the plane of pad footing CTR11101/CTR11501

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3. Design of RC Pad Foundations to Eurocodes Punching Shear at Periphery of the Column

vEd =

b VEd,red u0 d

 vRd,max

(Eq.(6.47) of EC2-1-1)

where u0 is the periphery for calculations u0 = length of column periphery in mm for an interior column u0 = c2 + 3d ≤ c2 + 2 c1 in mm for an edge column u0 = 3d ≤ c1 + c2 in mm for a corner column c1, c2 are the column dimensions as shown in the figure of Slide 62 b see Clauses 6.4.3 (3), (4) and (5) CTR11101/CTR11501

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3. Design of RC Pad Foundations to Eurocodes Maximum Design Punching Shear Strength vRd,max

fck  fck fck     0,5n f cd  0,5  0,6 1  a cc  0, 2a cc f ck 1    C  250   250 

(UK NA to EC2-1-1) where n is the strength reduction factor for concrete cracked in shear  

f ck  250 

28 4,23

30 4,49

n  0, 6 1  fck (MPa) vRd,max (MPa)

20 3,13

25 3,83

(Eq.(6.6) of EC2-1-1) 32 4,74

35 5,12

40 5,71

45 6,27

50 6,80

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3. Design of RC Pad Foundations to Eurocodes Design Procedure for Checking Punching Shear Capacity of Pad Foundations 1. Start the design process. 2. Determine the value of b. 3. Determine the punching design shear stress at column face, vEd,max, from Eq.(6.53)

vEd,max = b (VEd  DVEd) / (u0 d) 4. Determine the value of vRd,max from the table in Slide 70. 5. Check if vEd < vRd,max . If yes, go to Step 6. Otherwise redesign the pad footing. 6. Determine the punching design shear stress, vEd, from Eq.(6.51)

vEd = b (VEd  DVEd) / (u1 d) The control perimeter is normally located at 2d from the column surface. CTR11101/CTR11501

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3. Design of RC Pad Foundations to Eurocodes Design Procedure for Checking Punching Shear Capacity of Pad Foundations (cont.) 7. Determine concrete punching shear capacity without shear reinforcement, vRd, for a = 2d where l = (ly lz)0,5. 8. Check if vEd ≤ vRd . If yes, punching shear reinforcement is not required. Go to Step 9. Otherwise either increase main steel area, or provide punching shear reinforcement required. However, there are no recommendations for foundations.

9. Finish.

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3. Design of RC Pad Foundations to Eurocodes Design of Raft Foundation  Lightly loaded structures on soft ground  Heavy structures on normal ground  Structures on ground with uneven settlement  Mining subsidence

Raft foundation

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3. Design of RC Pad Foundations to Eurocodes Piled Foundations  Often used for transferring loads through strata with a low bearing capacity to strata with a higher capacity or to rock.  Also used for resisting high uplift forces or to transfer horizontal loads through poor soil.  Essentially long, slender members, mostly under compression. Column

Pile cap: resisting vertical and horizontal loads and moments

Piles CTR11101/CTR11501

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3. Design of RC Pad Foundations to Eurocodes Design of Piled Foundations  Both direct shear and punching shear should be checked /5

Direct shear: ≤ d from column face

/5 Punching shear: ≤ 2d from column face

 CTR11101/CTR11501

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3. Design of RC Pad Foundations to Eurocodes Design of Piled Foundations  When assessing the shear capacity in a pile cap, only the tension reinforcement placed within the compressed zone should be considered as contributing to the shear capacity.

A

45

A  Compressed zone

≥ 50 mm

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3. Design of RC Pad Foundations to Eurocodes Design of Plain Concrete Foundations  acc,pl = 0,6 and act,pl = 0,6 should be taken.  The following needs to be verified

0,85 hF  a

9 s gd f ctd

hF

Eq.(12.13) of EC2-1-1 a where hF is the foundation depth a is the projection from the column face sgd is the design ground pressure

a bF

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3. Design of RC Pad Foundations to Eurocodes Crack Control: Crack width wk  wk = 0,3 mm for all exposure classes under the quasipermanent combination, in the absence of specific durability requirements (e.g. water tightness)  wk = 0,4 mm for exposure classes X0 and XC1, in the absence of requirements for appearance  wk = 0,2 mm for prestressed members with bonded tendons under the frequent load combination.

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3. Design of RC Pad Foundations to Eurocodes Crack Control Maximum bar size s,max or spacing sr,max to wk Steel stress

ss

(MPa) 160 200 240 280 320 360 400 450

Crack width wk = 0,4 mm sr,max s,max (mm) (mm) 40 300 32 300 20 250 or 16 200 12 150 10 100 8 / 6 /

Crack width wk = 0,3 mm sr,max *s,max (mm) (mm) 32 300 25 250 16 200 or 12 150 10 100 8 50 6 / 5 /

Crack width wk = 0,2 mm sr,max *s,max (mm) (mm) 26 200 16 150 12 100 or 8 50 6 / 5 / 4 / / /

Notes: s,max is the maximum bar diameter, and sr,max is the maximum bar spacing. The values in the table are based on the following assumptions c = 25mm; fct,eff = 2,9MPa; hcr = 0,5; (h-d) = 0,1h; k1 = 0,8; k2 = 0,5; kc = 0,4; k = 1,0; kt = 0,4 and k' = 1,0.

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3. Design of RC Pad Foundations to Eurocodes Minimum area of principal steel As,min = max [0,26 fctm bt d / fyk; 0,0013 bt d ] (Eq.(9.1(N)) of EC2-1-1)

where bt is the mean width of the tension zone fctm is the mean tensile concrete strength which should be determined with respect to the relevant strength class according to Table 3.1 of EN 1992-1-1

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3. Design of RC Pad Foundations to Eurocodes Maximum area of reinforcement As,max = 0,04 Ac where Ac is the cross-sectional area of the concrete

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3. Design of RC Pad Foundations to Eurocodes Minimum Spacing of Reinforcement smin,slabs = smin,clear + s = max [(k1 s); (dg + k2); 20 mm] + s where s is the bar diameter in mm dg is the maximum aggregate size in mm k1 is a parameter which is recommended as k1 = 1,0 k2 is a parameter which is recommended as k2 = 5 mm

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3. Design of RC Pad Foundations to Eurocodes Deep elements (Section 9.7 of EN 1992-1-1)  A reinforcement ratio of 0,2% provided in each face  The distance between adjacent bars of the mesh not exceeding the lesser of twice the beam depth or 300 mm

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Thank you!

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3. Design of Pad Foundations According to EC2

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