Seismic Performance of Flexible Concrete Structures

Concrete structures consisting of shallow slab and wall-like column elements are common in areas of low and moderate seismicity, and are the predominant structural system in the Eastern Meditteranean region. The structural members in the lateral force-resisting system are flexible but have limited ductility and low shear capacity. Recent earthquakes in Greece and Turkey have demonstrated the inadequacies of these systems. Since they constitute such a large portion of the building inventory throughout that region, the need for evaluation and retrofitting of existing structures is obvious.

Nonlinear dynamic time history and analyses provide information on the magnitude and distribution of internal forces and deformations in yielding structures but are very sensitive to assumptions and initial conditions. The objective of this study is to evaluate the influence of different earthquake ground motions, geometry of the structure, and material characteristics on the response of flexible concrete structures. The results are intended to provide guidance on use of nonlinear analyses for seismic design and evaluation.

A prototype basic reinforced concrete frame structure typical of practice in Lebanon was analyzed using scaled ground acceleration records from earthquakes that have occurred in the region. Variations in the basic structure include different mass distributions, variation of the column dimensions, orientation and layout of the wall-type columns, and inclusion of infill walls. The columns are of special interest because they are quite stiff in one direction and flexible in the other. Also, the performance of the prototype structure subjected to various representative ground motion records was studied. Retrofit schemes were investigated. Nonlinear static and nonlinear dynamic analyses were performed.