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Hinge zone tie spacing in reinforced concrete tilt-up frame panels

University of British Columbia

Tilt-up concrete buildings have concrete walls, supported on a concrete floor slab, and a light weight roof system. The exterior concrete walls, which are typically 190 mm thick with two layers of reinforcement, are cast on the floor slab and then lifted into position. Recently two storey panels with large window openings at both ground and first floor levels have become popular. The result is that the wall panels, which form lateral load resisting system, have become more like frames than walls. Given that the panels are typically only 190 mm thick, the members have very high depth to width ratios. The performance under cyclic earthquake loading of reinforced concrete frame members with these depth to width ratios is not well understood. Furthermore, since the code was written with more traditional cross sections in mind, the tie spacing rules it provides are not necessarily applicable to tilt-up frame panels. The frame panels are designed so that all inelastic deformations during an earthquake will result from flexural hinging in the frame members. The research reported in this thesis investigated the effect of hinge zone tie spacing on the displacement ductility of reinforced concrete tilt-up frame panels. The results of tests done on six full scale quarter frame panels with three different tie spacings are presented. The test specimens contained typical longitudinal reinforcement and were dimensionally representative of typical tilt-up frame panels. It was found that hinge zone tie spacing can determine the mode of failure and have a significant effect on panel ductility. The hinge zone tie spacings tested were 100 mm, 200 mm and 300 mm. The mode of failure for the 200 mm and 300 mm specimens was buckling of the longitudinal steel reinforcement in compression after the cover concrete had spalled. The 100 mm tie spacing was sufficiently close to prevent buckling of the longitudinal reinforcement after loss of the cover concrete. The 100 mm specimens failed via either local out of plane buckling of the entire hinge zone reinforcement cage, or by pullout of the longitudinal beam steel resulting from loss of bond within the hinge zone. It was found that the ultimate load attained and maintained during the ductile range was influenced by the tie spacing. The 100 mm and 200 mm tie spacing specimens attained and maintained a maximum bending moment similar to the ultimate flexural strength calculated assuming a maximum compressive strain in the concrete of 0.0035. The 300 mm tie spacing specimens only attained and maintained a bending moment approximately equal to that at first yielding of the longitudinal steel. Since the ductilities for the different tie spacings were calculated using different strength assumptions they are not directly comparable, nevertheless the full frame displacement ductilities achieved for the 100 mm, 200 mm and 300 mm tie spacings were 5.7, 3.9 and 4.7 respectively.

Thesis/Dissertation

application/pdf

2009-07-07

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http://hdl.handle.net/2429/10391

Civil Engineering

University of British Columbia

UBCV

DSpace