Thesis Abstract

<p><b></b>        <b>ABSTRACT&nbsp;</b><br></p><p>A cooperative research project studying effect of floor diaphragm flexibility on seismic responses of building structure has been carried out at Lehigh University and the State University of New York at Buffalo (SUNY /Buffalo). An one-story one-sixth scale reinforced concrete structure consisting of shear walls, frames and floor diaphragms has been developed to be the test structure for this study. In the design of the test structure, the behavior of an one-story prototype reinforced concrete structure was studied first. The Internal forces of the prototype structure were then scaled down to the model dimension. Finally, based on the scaled internal forces, the model test structure was designed in accordance with ACI Code (318-83) and its Appendix A. In order to meet the similitude requirements for dynamic response, an ultimate strength modelling method with artificial mass simulation was adopted in the design. The modelling of the model materials was undertaken with the purpose of making a test structure possessing large ductility under seismic .loads. <br></p><p> The static and dynamic characteristics of the model assemblage and its three components, shear wall, frame and slab, are studied elastically and inelastically by computer program analysis. The diaphragm action of the slab on the distribution of lateral loads among the shear walls and frames is examined In detail ad different levels of earthquake ground motion inputs. The complete assemblage structure will be tested on the shaking table at SUNY/Buffalo. Prior to the test, three individual components (shear wall, frame and slab) will be tested cyclically at Lehigh university, the results of . which will be used to develop predictions of the dynamic response. In addition, an identical assemblage model will be tested cyclically at Lehigh University. The test setups and instrumentation for the component and assemblage tests have been designed to perform a series of proposed tests . <br></p>

Thesis Overview

<p> <b>INTRODUCTION</b></p><p>Floor slabs are used in multi-story buildings to serve many important structural functions. They not only transmit the gravity loads to the vertical structural systems, such as frames and shear walls, but also act integrally with the vertical systems in resisting lateral as well as gravity loads. The primary action of the slabs for these two functions is out-of-plane bending, a problem which has been studied extensively. The analytical tools necessary to predict out-of-plane slab behavior are readily available. Distribution of lateral loads to parallel vertical structural systems is another important function of the floor slabs. When a building is subjected to a severe earthquake, the inertial forces generated In the floor slabs must be transferred to the vertical structural systems through the diaphragm action of the slabs. The performance of the diaphragm action of the floor slab is controlled primarily by its in-plane stiffness. In many structures, a reasonable estimate of the inertial force distribution can be achieved by assuming that the slabs act as rigid diaphragms. However, for structures in which the stiffness of the vertical system and the stiffness of the slab system do not differ greatly, diaphragm deformation of the floors must be explicitly considered in analysis . <br></p><p> There is currently Insufficient knowledge to determine whether the rigiddiaphragm assumption will lead to adequate design for a given structure, whether the diaphragm flexibility requires special consideration, and how to define the rigidity of a horizontal diaphragm relative to the stiffness of the vertical lateral load resisting systems. Although the need for such information has been recognized by structural engineers, only a small amount of analytical and experimental research has been conducted, especially on reinforced concrete diaphragms. <br></p><p> In recent years, research has been carried out to study the in-plane characteristics of reinforced concrete floor diaphragms (8, 9, 13), and approximate analytical models have been proposed for investigating the effect of diaphragm flexibility on seismic building responses (6, 7, 14). The distribution of seismic forces to the vertical structural elements has been found to be very complex, especially after the floor diaphragms have experienced significant cracking and yielding. All available methods of analysis for structures with flexible diaphragms use very simple models to represent the behavior of the various structural elements. Furthermore, the results of those analyses have not been sufficiently verified by tests performed on three-dimensional structures. <br></p><p> An analytical and experimental research program is being conducted on a cooperative basis between Lehigh University and SUNY /Buffalo. The primary objective of the program is to understand the effect of the diaphragm flexibility on the redistribution of lateral forces to the vertical structural system after the floor slab system has experienced inelastic deformation. This is to be achieved by conducting a series of tests on a one story 3D reinforced concrete structure under lateral loads up to collapse load level. The test results will be used to correlate with analytical predictions and to develop specific procedures for the analysis of inelastic building systems including the effect of in-plane slab flexibility. The study presented here is part of the joint research program and includes the following tasks:&nbsp;</p><p>• Design of a one-sixth scale model test structure for both dynamic (shaking table) and quasi-static tests.&nbsp;</p><p>• Predication of the lateral load behavior of various components and the total assemblage of the model structure .&nbsp;</p><p>• Modelling concrete and reinforcement of the model structure.&nbsp;</p><p>• Planning of quasi-static tests of the model components and the model structure. The test results of the three components and the model assemblage structure and the corelation with theoretical predictions will be presented in separate reports.&nbsp;</p>