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Static and dynamic characteristics of composite structures

UNIVERSITY COMPUTER CENTER COLORADO STATE UNIVERSITY, FORT COLLINS, COLORADO

Abstract

The results of a theoretical and experimental investigation regarding the static and dynamic characteristics of shear walls are described. Solutions were obtained for the natural frequencies, mode shapes, and response quantities for an appropriate mathematical model, consisting of a distributed mass shear panel having a concentrated roof load mass at its top. Damping for such a structure may be represented in terms of an experimentally determined equivalent viscous damping ratio, v_eq. Using numerical analysis techniques, appropriate equations were derived and programmed, and a digital computer used to obtain the desired response quantitites resulting from either harmonic or arbitrary forcing functions. The 1940 El Centro earthquake, N-S component ground accelerations were utilized for most of the latter calculations. Using experimentally obtained static-cyclic load-deflection curves, values of v_eq were found to average 0.08-0.10 for low design-type loads, a range which was further verified by vibration generator and "snap" test dynamic testing. It was thus deemed satisfactory to recommend constant damping ratios of 0.07-0.08 for response calculations. Numerical accuracy of the computer solutions was investigated, with it being noted the acceleration values provided a good criterion for stability of solutions. Being least accurate because of the numerical procedure used, the accelerations always became unstable at a time prior to that of the displacements, thus giving a simple check as to the time span of correct solutions. Another effective procedure simply involved making two computer runs with the same input data, but different time increments, and then comparing results. If results were basically the same, the larger time increment was adequate; otherwise, another run was made with an even smaller time increment, answers compared, etc., until results essentially agreed.