Effect of Endogenous Deformations in Composite Bridge Beams

Early age endogenous deformations due to concrete hydration heat, shrinkage and creep can represent a real cracking risk for composite bridge beams. The phenomenon is difficult to take into account during design of composite bridges, as it takes place just after slab casting, when material properties of concrete are quickly changing with time. Recommendations on this topic in design codes and literature are generally poor and sometimes ambiguous. For instance, EN 1994-2 (CEN, 2005) states that short term elastic modulus and 20 K temperature difference between concrete slab and steel beam should be used. SETRA Guidance book Eurocodes 3 and 4 (Davaine et al., 2007) reduces the temperature difference to 10 K, but it gives no precise indication on the elastic modulus to be used. The aim of this work is to perform a set of non-linear thermo-mechanical analyses in order to evaluate the cracking sensitivity of a simply supported composite bridge and to understand if early age endogenous deformations can be modelled in elastic analysis by an equivalent temperature difference between concrete and steel with an appropriate elastic modulus for young concrete.