Lateral-load Behaviour of an RC Wall Building Including Floor Diaphragm Interaction

Abstract

Reinforced Concrete (RC) has been one of most popular materials to be used in modern buildings. RC frames and RC walls are the most commonly used lateral-load resisting system. The RC frames and the RC walls are often combined called Dual System. One of the most common dual systems is the RC core wall with RC moment resisting perimeter frame structure. A series of severe earthquakes occurred in the Canterbury region during 2010 and 2011. Most modern RC buildings showed good seismic performance, as expected, but there were a few signs that the structural interactions such as wall-to-floor interaction may have altered the behaviour of the lateral-load resisting system. It was probably caused by current design method in treating the floor element. The current New Zealand standard, NZS 1170.5, does not require floor diaphragm modelling for buildings with regular configuration. Therefore, it is common to analyse buildings having regular configuration without floor elements. The former IRD Christchurch building that was damaged during Canterbury Earthquakes 2010/2011 and it was a RC core wall with RC perimeter frame structure. This structure was chosen as the reference building where non-linear pushover analyses were carried out. Two dimensional analyses of the RC frame sections showed weak beam/strong column inelastic mechanism as expected in modern buildings. However, two-dimensional analyses on coupled wall sections showed that the degree of coupling beams was small and that the RC walls acted almost like cantilevered shear walls. The three-dimensional pushover analyses were carried with various floor types differing in thickness, giving consideration to out-of-plane stiffness. The floor without out-of-plane stiffness models showed similar behaviours to the two-dimensional analyses. However, the floor with out-of-plane stiffness models showed altered behaviours. The frame sections had strong beam/weak column inelastic mechanism and the degree of coupling beams became high. Therefore the RC walls were coupled by coupling beams. The research presented shows that the interaction of floor-frames and walls needs to be considered during the seismic design, regardless of structural configuration and height recommended by the current New Zealand standard, NZS 1170.5:2004.