The performance of cast in situ reinforced concrete frames incorporating precast prestressed concrete U-beam shells, subjected to seismic loading, is investigated. The precast U-beams act as permanent formwork and are not connected by steel to the cast in situ concrete of the beam or column. A review of the design provisions of the New Zealand concrete design code NZS 3101 relevant to the design of such composite structures is made and supplementary design recommendations are proposed where necessary.
Three full scale reinforced concrete beam-exterior column subassemblies with precast prestressed concrete U-beam shells were constructed and tested to determine their seismic performance characteristics. Two of the subassemblies were designed for
seismic loading with potential plastic hinge regions in the beams. One of these subassemblies had the bond between the precast and
the cast in situ concrete in the beam deliberately broken in the potential plastic hinge region, while the other was bonded. The third subassembly was not designed for seismic loading. The test results for the two subassemblies designed for seismic loading demonstrated that the seismic provisions of the New Zealand concrete design code, in conjunction with the supplementary design recommendations, resulted in adequately ductile behaviour with satisfactory energy dissipating characteristics. It was observed that the U-beam was less damaged during seismic loading when the bond between the precast and the cast in situ concrete in the potential plastic hinge region was deliberately broken. The performance of the other composite beam-column subassembly, which was not designed for seismic loading, was unsatisfactory, since the energy dissipating characteristics were poor and excessive sliding shear displacements occurred in the plastic hinge region.
Behaviour of cast in situ reinforced concrete frames incorporating precast prestressed concrete beam shells subjected to seismic loading
