Experimental study on double composite action in the negative flexural region of two-span continuous composite box girder

In the negative flexural region of continuous composite girder, cracking of concrete slab results in a reduction in the sectional stiffness and may affect the durability of reinforcement. Double composite action defined as attaching additional concrete to steel bottom flange to improve local buckling strength can be a way to increase the sectional stiffness. It has many advantages for construction while disadvantages also exist. In this case, two continuous composite girders, both of which had two 9 m long spans with 300 mm extension at each edge support and were 0.55 m high, were designed to study the mechanical properties in concrete crack, formation of sectional plastic hinge, load-carrying capacity, etc. One was a conventional composite girder named CCG and the other one was designed with double composite action in the negative flexural region named DCG. Moreover, evaluations of concrete crack width, based on different design codes, and cracking moment were compared with test results and agreed with each other. It indicated double composite action made concrete crack development slower in service load stage. The evaluation of sectional bending–carrying capacity of CCG in the negative flexural region based on the mechanical model with full plastic section of Euro Code 4 and an analogous method was found to evaluate that of DCG. The evaluation results coincided with test results proved the summation which can be drawn from test results.

Research highlights► We executed an experiment on double composite action in continuous composite girder. ► Double composite action was good to negative bending-induced concrete cracks. ► Double composite action also can be a way to increase sectional stiffness. ► Evaluation method of double composite sectional bending–carrying capacity was found.