Connection and structural level analysis of precast hybrid frame systems

Abstract

<p>Experimental studies have shown that precast hybrid frames with dry jointed connections can provide adequate performance in high seismic zones. This framing concept, which has been accepted by the International Conference of Building Officials (ICBO), utilizes unbonded post-tensioning and mild steel reinforcement debonded over a short distance to establish a moment resisting connection between precast beams and columns. As a result, the hybrid frame systems have the ability to sustain minimal residual displacements while dissipating more energy when subjected to seismic lateral forces. However, this connection concept introduces strain incompatibility between concrete and steel making the analysis and design methods very complex. Consequently, the available analysis and design methods are based on many simplified assumptions. In this analytical investigation, an improved set of expressions using the monolithic beam analogy was established for connection level analysis, which accurately account for the material behavior, strain penetration effects, strain hardening in the tension reinforcement, and compression force contribution of the mild steel reinforcement. The accuracy of the improved expressions was demonstrated at the section and system levels using experimental data. The improved analysis procedure was then used to examine the response of a five-story precast hybrid building model under different earthquake loading. From the response of the building, it has been shown that the hybrid building will perform satisfactorily under earthquakes of different intensities. An investigation on a suitable response modification reduction (R) factor for design hybrid building is also presented.</p>