Serviceability Stress Limits for Composite Beams

by Alan R. Kemp, Univ of the Witwatersrand, Johannesburg, South Africa,
Paolo Trinchero, Univ of the Witwatersrand, Johannesburg, South Africa,

Document Type: Proceeding Paper

Part of: Composite Construction in Steel and Concrete II


Serviceability limits are increasingly becoming the critical design requirement for composite beams. A set of three illustrative design studies indicates that this is particularly true if a serviceability limit is placed on elastic stress as specified in some recent design codes. This stress limit is applied irrespective of whether the deflection associated with this level of stress is critical or not. This research has therefore been initiated to determine how nonlinear stresses may be modelled in calculating serviceability deflections, thereby making stress checks unnecessary. An empirical proposal is described allowing for nonlinear deflection from the load at which the elastic stress limit is achieved, over a range up to about 20% above this load. This proposal is shown to compare satisfactorily with experimental measurements on four test beams as well as theoretical models of this nonlinear behaviour allowing for yielding, residual stress, shrinkage and slip strain.

Subject Headings: Composite beams | Serviceability | Stress analysis | Residual stress | Plastic design | Elastic analysis | Load factors | Failure analysis

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