Verification of fuse connector performance for hybrid masonry seismic structural systems

Abstract

In steel construction, there are various seismic structural systems that have been successfully utilized in the past including eccentric and concentric braced frames and moment frame systems. When these systems are used, the building envelope between structural members is filled with architectural components such as masonry infill walls, which are only expected to carry out of plane loads, such as wind, on each individual wall panel. Hybrid masonry is a relatively new type of structural system which incorporates the masonry infill walls within steel frames into the structural system to resist lateral loads imposed on the structure. This research represents the third phase of testing at the University of Hawaii at Manoa (UHM) and is part of an ongoing project funded by the National Science Foundation (NSF) and Network for Earthquake Engineering Simulation Research (NEESR) to investigate the applicability of hybrid masonry as an adequate structural system. In phases I and II of hybrid masonry connector plate development research at UHM, a wide variety of connector designs were explored to determine the positive and negative aspects to different fuse and link connector plate designs and connection methods. Fuse connector tests demonstrated the viability of tapered fuses to dissipate large amounts of energy during cyclic loading. These tests also showed that various practical connector orientations and methods can be applied for hybrid masonry connectors, particularly the straight bolted side plate connection. In addition, during phase I of testing, a series of bolt push out tests were performed to determine the shear strength of post-installed through-bolts in masonry. Observations from the first two phases of testing were used as a guide for selecting 4-inch and 6-inch tapered fuse designs for testing on partially grouted and fully grouted masonry wall specimens. Multiple pairs of both tapered fuse connectors were slip-critically bolted to side plates, which were welded to a steel beam above the masonry wall specimens. These tests were performed to verify that the behavior of multiple pairs of connector plates in series is similar to the behavior of the individual pairs of connector plates. In addition, the tests were performed to observe the interaction between the steel connector plates and masonry wall specimens. Based on numerous observations and results in this phase of testing, the design of Type I hybrid masonry connections was improved. The fuse connector tests showed that the strength and behavior of multiple pairs of fuse connectors can be approximated by designing a single connector plate and multiplying the single plate's capacity by the number of connector plates used. These fuse connectors displayed the capability of dissipating large amounts of seismic energy before failure. Based on the results of these connector subassembly tests, recommended design procedures for connector plates were modified. Both masonry walls failed by means of shear friction at the location of the joint between the masonry and concrete slab. The results from UHM's testing will guide the development of full-scale two-story hybrid masonry test frames which will be tested at the University of Illinois Urbana-Champaign.