Precast concrete floor support and diaphragm action

Technical Abstract

Experimental research, engineering analysis and theoretical developments comprise a study in which various interactions between ductile moment resisting frames and precast prestressed hollow core flooring have been examined.

The most critical interaction tested involves support behaviour, and the ability of reinforcing details to provide control against loss of support and possible catastrophic flooring collapse under dilation effects. Plastic hinge dilation, also know as elongation or growth, is an inherent property of ductile concrete members when subjected to cyclic plastic deformations. Hence, the performance of floor support details is enveloped by the general design philosophy of seismic resisting structures. In the experimental phase, emphasis was placed on testing support construction joints from contemporary building practice, for direct comparison with special support tie details of known capabilities. The contemporary details were found to exhibit seriously flawed behaviour under monotonic and cyclic loading regimes.

Corroborative experiments were undertaken to establish direct shear capacities between typical composite bond surfaces. In particular, these tests addressed the discrepancy that has emerged between direct shear and shear flow strengths. Also, the continuity response of conventional and proposed support detail types was examined.

A composite model was analyzed to demonstrate the likely influence of prestressing steel on beam bending strength within a ductile frame environment. Likewise, the probable effects of prestressing steel on beam plastic hinge development were examined, but on a more theoretical basis.

Other elements of theory have been presented. These mainly concern the general topic of elastic-plastic response in reinforced concrete elements. The particular focus of this work has been to demonstrate a rational basis to stiffness transition and plastic buckling analysis. The important role of stiffness degradation in dynamic analysis has also been examined.