List of publications
Publication: The effect of prior out-of-plane damage on the in-plane behavior of unreinforced masonry infilled frames (1993)
The Fourth DOE Natural Phenomena Hazards Mitigation Conference
Preparation and upload by:
Filip Anic, Faculty of Civil Engineering and Architecture Osijek, Josip Juraj Strossmayer University of Osijek
Publication abstract (click to enlarge):
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In order to address the effect of prior out-of-plane damage on the in-plane behavior of unreinforced masonry infllls, two full-scale (24 feet tall by 28 feet long) structural clay tile infills and one frame-only (no infilling) were constructed and tested. The infilled frame, consisting of two wide flange columns surrounded by masonry pilasters and an eccentric wide flange purlin, was identical
In order to address the effect of prior out-of-plane damage on the in-plane behavior of unreinforced masonry infllls, two full-scale (24 feet tall by 28 feet long) structural clay tile infills and one frame-only (no infilling) were constructed and tested. The infilled frame, consisting of two wide flange columns surrounded by masonry pilasters and an eccentric wide flange purlin, was identical to many of the infiils located at the Oak Ridge Y-12 Plant*. The masonry infill was approximately 12.5 inches thick and was composed of individual four- and eight-inch hollow clay tile (HCT) units. One of the infill panels was tested out-of-plane by four quasi-static actuators - two on each column. The test structure was deflected out-of-plane equally at all four actuator locations in order to simulate the computed deflection path of the top and bottom chords of a roof truss framing into the columns at these locations. Prior to the infill testing, a bare frame was loaded similarly in order to determine the behavior and stiffness contribution of the frame only. Following the out-of-plane test of the infilled panel, the structure was loaded in-plane to failure in order to ascertain residual strength. A second, identical infilled frame was then constructed and tested in-plane to failure. In this way, in-plane behavior with and without prior out-of-plane damage could be established and compared. For both out-of-plane and in-plane testing, reversed-cyclic quasi-static loading was used in order to obtain full tension/compression hystereses.
Infillied frames subjected to seismic forces must typically resist earthquake components both in-plane and out-of-plane. Often. when buildings are composed of infilled walls in one direction and moment resisting frames in the orthogonal direction, out-of-plane damage to the URM results from seismic drift (as opposed to inertial forces of the infill material). Tests have shown that small amounts of out-of-plane drift may produce full crack patterns that completely penetrate the thickness of the infill material. Hence, the URM in most infilled frames has likely experienced some degree of post-elastic behavior (i.e.. mortar joint cracking, degradation of the frame to infill connectivity, etc.) over the structure's full displacement history. Therefore, the effect of prior damage on the in-plane behavior and capacity of infilled frames is important to understand.
AIM AND SCOPE
Toward this end, Martin Marietta Energy Systems, Inc. and Iowa State University have tested wo. full-scale frames ladled with hollow clay tile (HCT) and one, full-scale steel frame without infilling. Reversed-cyclic, sequentially-displaced, quasi-static loads were cpplied to the bare frame out-of-plane in order to determine a baseline stiffness and rotational spring constants for the column to floor connections. The first infilled frame was subjected to significant out-aftlane, quasi-static deflection followed by in-plane quasi-static loading to failure. The second infilled frame was tested to failure by applying in-plane, quasi-static loads without prior damage.
DESIGN AND CONSTRUCTION OF THE TEST SPECIMENS:
The type of construction used in this testing is unique in that an attempt was made to replicate as closely as possible the in situ conditions of many of the walls at the Department of Energy's Y-12 plant (circa 1940). The two wall specimens were full-scale (24 feet tall by 28 feet long) hollow clay tile Wills constructed with cores running horizontally. The wall panels were double writ and built with a mortar mix conforming to ASTM C 270 Type N mortar. The walls were composed of four- and eight-inch HCT with a 0.75-inch collar joint so that the full wall thiclmess was approximately 12.5 inches. The HCT were laid with running bond; however, the construction was somewhat atypical in that the four- and eight-inch block alternated positions from course to course (i.e., there was no full-height collar joint), thereby creating composite wall behavior. Bed joints were I/2-in. thick, full and continuous, and head joints were 3/8-in. thick with mortar applied to the face shells only. No reinforcement was used in the masonry.
The companson of in-plane data for the two infilled panels indicates that prior damage reduces initial in-plane stiffness. Also walls with prior damage respond to loads in a much less brittle fashion than those with no prior damage. This is in direct contrast to virgin structures that store considerable potential energy under the first few cycles of applied displacement and release it in a sudden fashion through brittle diagonal stair-step-cracking. The primary conclusion from the complete test sequence is that prior damage to infill structures has little effect on the overall in-plane performance or the final damage state as long as confinement by the frame is maintained. This fact is very important to the analysis of most older structures, which have, typically, been subjected to some cracking. The response that would logically come from conclusions drawn from this research is a reassessment of the current design standards for infilled masonry construction.
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