2.3.2.5 Fatigue For fatigue loads, 2.3.2.6
,
f
should be taken as 1.0 for adverse conditions.
Vehicular impact Where vertical elements are to be designed for vehicular impact
2.3.3
at
f
ULS should be 1.25.
Loads for Serviceability Limit States (SLS)
2.3.3.1 General For most cases, if the simplified rules for design and detailing of reinforcement outlined in sections 7, 8 and 9 respectively are followed then no further checks on SLS are required. Where further checks are necessary then given in the following clauses should be followed. f 2.3.3.2
Dead load Generally, it is sufficient to take the characteristic value of dead load i.e. should be taken as 1.0. f
2.3.3.3
Imposed load Generally, it is sufficient to take the characteristic value of imposed load i.e.
should
f
be taken as
1.0. When calculating deflections, it is necessary to assess how much of the imposed load is transitory and how much is permanent. The proportion of imposed load that should be considered as permanent will depend upon the type of use of the structure. It is suggested that for normal domestic or office occupancy, 25% of the imposed load should be considered as permanent and for structures used for storage, at least 75% of the imposed load should be considered as permanent when the upper limit of deflection is being assessed. 2.3.3.4
Differential settlement of foundations Where the effects of differential settlements are considered, should be taken as 1.0 for adverse f conditions.
2.3.3.5
Creep, shrinkage, and temperature effects Where the effects of creep, shrinkage and temperature effects are considered, should be taken as f 1.0 for adverse conditions.
2.4
MATERIALS
2.4.1
General Materials should conform to acceptable standards and comply with the requirements given in this Code of Practice.
2.4.2
Characteristic strength of materials Material strengths and properties are defined in section 3.
2.4.3
Partial safety factors for material strength, m
2.4.3.1 General For the analysis of sections, the design strength for a given material and limit state is derived from the characteristic strength divided by m, where m is the appropriate partial safety factor given in clauses 2.4.3.2 and 2.4.3.3. m takes account of differences between actual and laboratory values, local weaknesses and inaccuracies in assessment of the resistance of sections. account of the importance of the limit state being considered. 2.4.3.2
It also takes
Values of m for ultimate limit state (ULS) (a)
Material design strengths In the assessment of the strength of a structure or any of its parts or cross-sections, appropriate m values should be taken from table 2.2. 11
Values of m
Material/design consideration Reinforcement (prestressing steel included)
1.15
Concrete in flexure or axial load
1.50
Concrete shear strength without shear reinforcement
1.25
Bond strength
1.40
Others (e.g. bearing stress)
1.50
Table 2.2 - Values of m for the ultimate limit state (b)
Effects of exceptional loads or localised damage In the consideration of these effects m may be taken as 1.3 for concrete in flexure and 1.0 for steel.
2.4.3.3
Values of m for serviceability limit states (SLS) (a)
General Values of m for serviceability limit states may be taken as 1.0 except where stated otherwise in particular clauses.
(b)
Prestressed concrete criteria for tensile stress criteria In assessing the cracking strength for a class 2 member, m should be taken as 1.3 for concrete in tension due to flexure. Allowable design stresses are given in clause 12.3.4.
2.5
ANALYSIS AND VERIFICATION
2.5.1
General When using the limit state method, it shall be verified that for all relevant design situations no relevant limit state is exceeded by the actions resulting from the loadings as calculated using the appropriate f specified in clause 2.3 and with material strengths as modified by m specified in clause 2.4. The analysis that is carried out to justify a design can be divided into two stages:
analysis of the structure; and
analysis of sections.
Guidelines for the analysis of structures are given in section 5. Rules for analysis of sections for ULS and SLS are given in sections 6 and 7 respectively. 2.5.2
Limitations The use of the rules given in this code of practice is limited to ultimate and serviceability limit state verifications of structures and structural members subject to static loading, or where the dynamic effects, such as those produced by wind loads, are assessed using equivalent quasi-static loads. For non-linear and dynamic analysis etc further specialist guidance should be sought.
2.6
NEW AND ALTERNATIVE METHODS
2.6.1
General The requirements of this code of practice are not to be construed as prohibiting the use of new and alternative methods.
2.6.2
Acceptance requirements. New and alternative methods must be adequately demonstrated to comply with the basic requirements of clause 2.1.
12
