Differential temperature effect-steel stresses

[kww2008]

The example in Hambly (Chapter 11) shows calculations to obtain the stress distribution across a concrete section from differential temperature effect. There is no memtion whether the presence of steel reinforcement is to be included or whether the effect of steel reinforcement has to be included in such an analysis. I am interested in estimating the steel stresses resulting from differential temperature effects.

Please advise.

 

[kww2008]

Does anyone know why steel reinforcement is not included when calculating the primary moment from differential temperature effects ?

 

[IDS]

The differential temperature calculations in Hambly are based on the UK Bridge Design Code, which I believe used experimental data from actual bridges, probably coming from research in the 1960's, if I recall correctly. As such they would apply to structures with "typical" reinforcement content. I'm not aware of research looking at the effect of different levels of reinforcement content, variation in depth of cover, etc.

The thermal analysis assumes that the coefficient of thermal expansion is the same for steel and concrete. That's only approximately true of course, but shrinkage strains in the concrete are usually very much greater than differential temperature strains, for concrete and steel at the same temperature. The analysis described in Hambly finds a resultant bending moment due to the differential strains across the section, which is applied to the composite section, so the resulting stresses in the reinforcement come out of that analysis.

Doug Jenkins
Interactive Design Services

http://newtonexcelbach.wordpress.com/