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According to IS 456, what is the partial safety factor for loads in case of limit state collapse when dead and live loads are taken into account?

According to IS 456, what is the partial safety factor for loads in case of limit state collapse when dead and live loads are taken into account? Correct Answer 1.50

Concept:

Factor of Safety = Yield Stress/ Working Stress

Yield stress is defined as the stress at which first fiber failure occurs.

Working stress is defined as the stress which is safe to work on or it is the yield stress with factor of safety that the structure will not go to yield at this stress for a particular surrounding condition.

Values of factor of safety (partial) for load combination:

Load combination

Ultimate limit state

Serviceability limit state

1) Dead load & live load

1.5(DL + LL)

DL + LL

2) Dead seismic/wind load

 a) Dead load contributes to stability

 b) Dead load assists overturning

0.9 DL + 1.5 (EQ/WL)

 

1.5 (DL + EQ/WL)

 

DL + EQ/WL

DL + EQ/WL

3) Dead, live load and Seismic/wind load

1.2 (DL + LL + EQ/WL)

DI + 0.LL + 0.8EQ/WL

 

Where, DL = Dead load, LL = Live load WL = Wind load EQ = Earthquake load

Important Points

In WSM, the combined factor of safety is considered for incorporating effects of material quality and type of load.

In LSM, separate factors of safety called as partial safety factors are considered for material quality and type of load. 

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