Research Grant for Outstanding Researchers
Abstract: Adding Flexibility to Stiff Masonry Shear WallsReturn to previous page
By D.P. Abrams, University of Illinois at Urbana-Champaign, US
Lateral-force resistance for low-rise buildings is often provided by structural masonry shear walls which may serve a dual function as an enclosure of stair and elevator shafts, and/or satisfy architectural needs to provide a building envelope. Because of the relatively large area of masonry walls relative to the floor area, such walls are commonly much stiffer than needed to meet serviceability constraints. This can be undesirable with respect to the attraction of lateral seismic forces since the natural period of vibration of the building system will be relatively short, resulting in high seismic accelerations. Because of this, seismic demand forces can be unnecessarily large relative to lateral-force capacity of shear walls, and damage may be likely in the event of a moderate or strong earthquake motion.
A novel structural engineering design approach is described in this paper where flexibility can be added to a masonry shear wall system with the use of a series of steel connector plates that transfer seismic story shear forces to individual masonry wall panels. This innovative form of building construction is termed “hybrid masonry” since structural steel frames resist gravity and lateral forces with engineered structural masonry panels. The steel connector plates are undersized to have considerable flexibility and a relatively low flexural strength. Acting as fuses, these connectors will not only reduce the overall lateral stiffness of a building system, but also dissipate seismic energy through hysteresis. In so doing, the integrity of the structural system to withstand earthquake motions is enhanced. As well, repair costs will be minimized since masonry damage can be circumvented. Replacement of fuse connectors represents a small cost in terms of materials, labor and interruption of building function. Thus, maintenance issues associated with costly seismic repairs can be avoided.
Results of computations will be given that show how lateral flexibility and seismic demand forces can be reduced. A simple two-story, one-bay steel frame with reinforced masonry panels will be used as an example to demonstrate load sharing between the frame and panels when connector strength and stiffness is varied. This test-bed structure has the same configuration as a series of large-scale test structures that were tested at the MUST-SIM facility at the University of Illinois at Urbana-Champaign. Computational models will be calibrated with measured results from large-scale experiments, and then used to examine sensitivities of seismic design parameters to various combinations of connector plate and steel frame stiffnesses.
The paper will highlight the need for adding flexibility to otherwise stiff masonry shear wall structures by making reference to the recent earthquake in Italy (August 2016) where numerous stiff, but weak, masonry buildings were severely damaged. The need to enhance deformation capacity of such structures will be emphasized as well as the overall design objective to reduce the potential for demolition following a destructive earthquake. In general, the paper will promote new innovations in structural design where structural steel and structural masonry are paired to result in a new standard of structural integrity that exceeds the sum of the parts.
Daniel P. Abrams is Donald Biggar Willett Professor at the University of Illinois at Urbana-Champaign. He holds a B.S. (Illinois Institute of Technology 1970), a M.S. (University of Illinois at Urbana-Champaign 1974), and a Ph.D. (University of Illinois at Urbana-Champaign 1979), all in civil engineering. He has been on the faculty of the department of Civil and Environmental Engineering at the University of Illinois at Urbana Champaign since 1985.
He is a licensed professional engineer, has worked as a practicing structural engineer in Chicago and San Francisco, and continues to take part in consulting assignments with industry. Dr. Abrams teaches graduate and undergraduate courses in structural engineering. He has written over 180 papers or reports on seismic response of concrete or masonry buildings. He was responsible for writing the masonry chapter of the NEHRP Guidelines for Seismic Rehabilitation of Buildings (FEMA 273/356), and has chaired the Building Seismic Safety Council's Technical Subcommittee 5 on Masonry Structures.
He is also a past chair of the EERI Experimental Research Committee and the TMS Research Committee, and currently serves on TMS. He is a former President of The Masonry Society (TMS), recipient of the TMS Scalzi and Presidents Awards, an Honorary Member of TMS, and a Fellow of TMS, ACI and SEI.