Abstract

Metal building systems are a common form of construction but the behavior of roof diaphragms in metal buildings that are subjected to earthquake ground motions is not entirely understood. In this study, the strength and ductility of rod-braced diaphragms with hillside washer connections or rod-pad connections was determined using experimental tests and computer simulation. Tensile tests of rods were used to determine the effect of the type of rod on strength and ductility. Two types of rods were tested, full-body rods with cut threads at each end of the rod and bracing rods with rolled threads. Three rod sizes (5/8 in., 3/4 in., and 1 in.) were examined. Full-body rods achieved maximum strains of 2.5% on average, while bracing rods were nearly four times as ductile and achieved maximum strains along of 9.6% on average. These strains included the threaded and unthreaded regions of the rod. Cyclic tests of diaphragm subassembly specimens were used to determine the effect of the type of rod connection on strength and ductility. Two types of connections were examined (hillside washer connections and rod-pad connections), and two rod sizes (3/4 in., and 7/8 in.) were tested under fully-reversed cyclic loading and monotonic loading. The bracing rods yielded in all tests. The tests also revealed that the 7/8 in. rod connection had a significant effect on behavior for rods due to eccentricity of the connection and purlin. Diaphragm subassembly overstrength was 1.5 for hillside washer connections, compared to 2.0 for rod-pad connections, and diaphragm subassembly ductility was 3.9 for hillside washer connections, compared to 8.6 for rod-pad connections, on average. An archetype metal building in a high-seismic location was designed using a diaphragm design force that was reduced by 2.5, and a finite element model was used to predict the effect of the rod connection on the seismic collapse safety of the building. Nonlinear static pushover analysis was used to determine the diaphragm design force reduction factor (����s), and incremental nonlinear dynamic response history analyses were used to determine the conditional probability of collapse. The simulations indicated that ����s was 2.7 for hillside washer connections, and 4.9 for rod-pad connections, which exceeded the design reduction. Both types of rod connections met the target conditional probability of collapse of 10% in ASCE 7. The findings suggest that rod-braced diaphragms in metal buildings could be designed using a reduced diaphragm design force.

Degree

MS

College and Department

Ira A. Fulton College of Engineering; Civil and Construction Engineering

Rights

https://lib.byu.edu/about/copyright/

Date Submitted

2025-04-16

Document Type

Thesis

Keywords

rod-braced diaphragms, cut threads, rolled threads, diaphragm design force reduction factor, diaphragm ductility, seismic design

Language

english

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