Doctoral Dissertations

Date of Award

8-1994

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Civil Engineering

Major Professor

Edwin G. Burdette

Committee Members

Max L. Porter, Dale Jones

Abstract

The use of structural steel frames infilled with unreinforced masonry is a common construction technique and has been shown to provide significant strength and ductility for the resistance to lateral loads. The research described herein addresses the effect that prior damage -- resulting from seismic drift -- has on the stiffness and ultimate capacity of infilled frames. The two-fold objective was (1) to study the out-of-plane and in-plane behavior of unreinforced masonry infills with and without prior damage, and (2) to determine accurate and efficient means of modeling infilled frame behavior. The experimental phase of the research consisted of (1) out-of-plane testing of a bare frame without infilling, (2) out-of-plane followed by in-plane testing to failure of an infilled frame, and (3) in-plane testing to failure of an undamaged infill. The structures tested were laboratory replicas of an existing facility at the Department of Energy's Y-12 plant; however, results obtained from this research are representative of most infilled frames resisting lateral loads. The structural steel frames consisted of W10x33 columns and a W16x36 purlin. Column spacing was 24 feet and the purlin height was 21 ft -1 in. The infill material was approximately 13 inches thick and composed of individual four-and eight-inch structural clay tile that alternated position from course to course. The bare frame and the first infill panel were tested out-of-plane in a quasi-static fashion by applying loads at four actuator locations in order to simulate drift loads applied by the top and bottom chords of a roof truss. The maximum applied out-of-plane displacement for Wall 1 was approximately 2.6 inches. Cracking damage to the first infill was extensive with numerous complete through-cracks; however, the structure was still completely stable and laterally resistive upon discontinuing the out-of-plane loads. The first and second infilled frames were then tested in-plane to failure. The in-plane displacement required to cause considerable comer crushing was approximately 3 inches for both infills. The maximum in-plane loads were 64 kips for the first infill (predamaged) and 61 kips for the second infill (no prior damage). Crack patterns and final damage states were very similar for both infilled frames. The conclusion from this testing was that prior damage has little effect on the in-plane capacity of infills provided confinement by the steel frame is maintained. In addition to the full-scale testing, numerous correlative tests were performed including mortar cube, mortar cylinder, unit block, prism compression and bond wrench tests as well as out-of-plane modal surveys. Following the experimental phase of this research, the out-of-plane and in-plane behavior and ultimate capacity were predicted using various analytical techniques. The out-of-plane analysis consisted of a series of piece-wise linear finite element models. This analysis reproduced the maximum tensile and compressive load/deflection behavior within ten percent of the actual test results, and predicted crack patterns were very close to those that resulted from the out-of-plane testing. Four classical methods for the prediction of in-plane damage and ultimate capacity were evaluated based on the test data. The methods by Holmes, Stafford-Smith, and Liauw were found to significantly overpredict ultimate capacity. Wood's penalty factor in conjunction with Liauw's plastic collapse method reproduced the ultimate capacity within 10 percent.

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