Flexural behavior of hybrid precast concrete beams with H-steel beams at both ends

A hybrid precast concrete beam system, which is a coupling of an H-steel beam and a reinforced concrete beam, was developed to propose a simple ductile connection practically useful for precast concrete structures. Three beam specimens were tested to failure to explore the effectiveness and limitations of the developed hybrid precast concrete beam system in transferring externally applied flexure to a supporting column. The three hybrid precast concrete beam specimens tested were as follows: specimen S was the control beam, and specimens U and P were used to evaluate the effect of in-situ concrete and the effect of prestressing force on the flexural behavior of the beam, respectively. Test results showed that the introduction of prestressing force for longitudinal tension reinforcement significantly improved the flexural capacity and ductility of the hybrid precast concrete beam. The flexural behavior of specimen U after placement of the upper concrete was very similar to that of the control specimen S, showing that no slippage was observed at the interface between the two concretes cast at different times. In addition, no crack was developed around the H-steel beam at the composite section region until the failure of the beams, and the strain values measured in the bottom flange of the H-steel beam were very close to the predictions calculated using elasticity theory. Furthermore, the flexural capacities predicted from extended versions of ACI 318-08 and the section laminae method were in good agreement with the test results.