Seismic Performance Evaluation of Existing RC Buildings Without Seismic Details. Comparison of Nonlinear Static Methods and IDA

Constantinos C Repapis

doi:10.2174/1874836801610010158

Abstract

The inelastic response of existing reinforced concrete (RC) buildings without seismic details is investigated, presenting the results from more than 1000 nonlinear analyses. The seismic performance is investigated for two buildings, a typical building form of the 60s and a typical form of the 80s. Both structures are designed according to the old Greek codes. These building forms are typical for that period for many Southern European countries. Buildings of the 60s do not have seismic details, while buildings of the 80s have elementary seismic details. The influence of masonry infill walls is also investigated for the building of the 60s. Static pushover and incremental dynamic analyses (IDA) for a set of 15 strong motion records are carried out for the three buildings, two bare and one infilled. The IDA predictions are compared with the results of pushover analysis and the seismic demand according to Capacity Spectrum Method (CSM) and N2 Method. The results from IDA show large dispersion on the response, available ductility capacity, behaviour factor and failure displacement, depending on the strong motion record. CSM and N2 predictions are enveloped by the nonlinear dynamic predictions, but have significant differences from the mean values. The better behaviour of the building of the 80s compared to buildings of the 60s is validated with both pushover and nonlinear dynamic analyses. Finally, both types of analysis show that fully infilled frames exhibit an improved behaviour compared to bare frames.

Highlights

Existing reinforced concrete (RC) buildings designed according to the old Greek codes represent typical construction practice of many Southern Europe countries
The capacity curve, base shear vs. roof displacement is shown in Fig. (5) for the typical building of the 60s with and without infill walls, and for the typical building of the 80s, for uniform and triangular lateral load patterns, together with an equal area bilinear approximation for the estimation of the available ductility and behaviour factor
The design base shear Vd and the ultimate limit state (ULS) reference base shear Vu for all frames are shown, in order to quantify the overstrength of the structure

Summary

Introduction

Existing reinforced concrete (RC) buildings designed according to the old Greek codes represent typical construction practice of many Southern Europe countries. The seismic performance of these buildings needs to be investigated They were designed for low seismic coefficient using simple models without ductility detailing and capacity design provisions for buildings before 1984 or simple capacity design provisions for buildings after 1984 and before the application of the new codes. Their performance is significantly influenced by the existence of masonry infill walls and their distribution. It is obvious through their studies that infill walls can act beneficially or unfavourably, depending on their distribution, and, if used properly, can provide a practical alternative for retrofitting existing structures to resist seismic loads

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