Elaina Jennings

Full-scale experimental verification of soft-story-only retrofits of wood-frame buildings using hybrid testing

The FEMA P-807 Guidelines were developed for retrofitting soft-story wood-frame buildings based on existing data, and the method had not been verified through full-scale experimental testing. This article presents two different retrofit designs based directly on the FEMA P-807 Guidelines that were examined at several different seismic intensity levels. The effects of the retrofits on damage to the upper stories were investigated. The results from the hybrid testing verify that designs following the FEMA P-807 Guidelines meet specified performance levels and appear to successfully prevent collapse at significantly higher seismic intensity levels well beyond for which they were designed. Based on the test results presented in this article, it is recommended that the soft-story-only retrofit procedure can be followed when financial or other constraints limit the retrofit from bringing the soft-story building up to current code or applying performance-based procedures.

Numerical Retrofit Study of Light-Frame Wood Buildings Using Shape Memory Alloy Devices as Seismic Response Modification Devices

AbstractWoodframe buildings have historically performed well during earthquakes primarily because of their high strength/stiffness to weight ratio. Even still, these structures possess the potential for significant damage and even collapse when exposed to very large earthquakes. New design techniques and advanced technologies can provide an alternative for improved building performance. The use of dampers and other seismic response modification devices is one such method being explored in earthquake engineering. In this paper, shape memory alloy (SMA) devices are investigated for the response modification of light-frame wood buildings during strong earthquakes. A numerical model for a suite of SMA wood shearwalls is developed based on existing data. The numerical models of the shearwalls are examined using incremental dynamic analysis at the single wall level. Design charts are developed for the shearwall models for a range of seismic weights and targeted performance levels. The wall database is then used...

Distributed Knee-Braced (DKB) System as a Complete or Supplemental Retrofit of Soft-story Wood-frame Buildings

The NEES-Soft, NSF sponsored project, evaluated the performance of various retrofit schemes for “soft-story” light wood-frame buildings subjected to seismic loading as one of its objectives. The DKB (Distributed Knee-Braced) system retrofit was one of the retrofits evaluated. This system consists of an assembly of light wood-frame knee-braced frames placed so as to reinforce an existing deficient line of resistance. The individual knee-braced frames are constructed by reinforcing existing wall studs of the existing soft-story building with additional stud(s) and connecting them to the existing floor joists with a new diagonal 2x wood member. The reinforcement of the members and connections along the knee-braced frame load path are designed to exceed the capacity of the knee-brace connection to the stud assembly and floor joist, thus creating a ductile load path fuse at these connections. The DKB system was numerically evaluated using 2D non-linear dynamic analyses. The numerical results were validated using, reversed-cyclic tests of two full scale DKB configurations and a follow up shake table test of one of the configurations. The four-frame 10ft DKB system was able to develop maximum lateral load capacity of approximately 2,400 lbs (1088 kg) at 4.5% drift and at 7.5% drift was still able to support close to 1,000 lb (454 kg). The findings of this research suggest that the DKB system, for certain structural archetypes, can be an effective alternative to other more traditional “softstory” timber structure retrofits.

Overview of the NEES-soft experimental program for seismic risk reduction of soft-story woodframe buildings

The existence of thousands of soft-story woodframe buildings in California has been recognized as a disaster preparedness problem resulting in mitigation efforts throughout the state. The considerable presence of these large multi-family buildings in San Francisco prompted the city to mandate their retrofitting over the next seven years. The NEES-Soft project, whose full title is “Seismic Risk Reduction for SoftStory Woodframe Buildings,” is a five-university multi-industry three-year project which has many facets including improved nonlinear numerical modeling, outreach, retrofit methodology development, and full-scale system-level experimental validation of soft-story retrofit techniques. In 2013, two full-scale buildings were tested within NEES-Soft. A hybrid test of a three-story building consisting of a onestory numerical substructure and a two-story physical structure above at the University at Buffalo, and a shake table test of a four-story building at the University of California – San Diego. A series of retrofits, based on methodologies ranging from FEMA P-807 to performance-based seismic retrofits developed as part of the project, were tested at both sites. Collapse testing for both building specimens was also conducted at the end of each test program. This paper presents a summary of selected test results for these full-scale building tests within the NEES-Soft project.

Full-scale testing of soft-story woodframe buildings with stiffness-based retrofits

The existence of thousands of soft-story woodframe buildings in California has been recognized as a disaster preparedness problem with concerted mitigation efforts underway in many cities throughout the state. The NEES-Soft project, whose full title is “Seismic Risk Reduction for Soft-Story Woodframe Buildings,” is a five-university multi-industry three-year project which has many facets including improved nonlinear numerical modeling, outreach, design method development, and full-scale system-level experimental validation of soft-story retrofit techniques. This paper summarizes the retrofit and test results for two full-scale buildings that were tested in 2013. The first is a three-story building at the University at Buffalo NEES facility using slow pseudo-dynamic testing. The bottom story, representing a soft story with garage openings, was the numerical substructure and reproduced by computer, while the damage to the two upper stories, representing the physical substructure, was observed in the lab. Then, testing of a full-scale four-story 4,000 sq-ft soft-story building at the UCSD NEES outdoor shake table was conducted. Retrofits ranged from crosslaminated timber rocking walls with rod hold downs to steel special moment frames combined with wood structural panels. 1 George T. Abell Distinguished Professor in Infrastructure, Civil and Environmental Engineering, Colorado State University, Fort Collins, Colorado, 80523-1372. 2 Ph.D. Candidate, Civil and Environmental Engineering, Colorado State University, Fort Collins, Colorado. 3 Ph.D. Candidate, Civil and Environmental Engineering, Colorado State University, Fort Collins, Colorado. 4 Assistant Professor, Glenn Department of Civil Engineering, Clemson University, Clemson, South Carolina. 5 Ph.D. Candidate, Glenn Department of Civil Engineering, Clemson University, Clemson, South Carolina. 6 Principal, Structural Solutions Inc, Walnut Creek, California. 7 Professional Practice Professor, Civil Engineering, Cal Poly, Pomona, California. 8 International Director of Building Systems, Simpson Strong-Tie, Pleasanton, California. 9 Assistant Professor, Civil and Environmental Engineering, Western Michigan University, Kalamazoo, Michigan. 10 Associate Professor, Civil and Environmental Engineering, Rensselaer Polytechnic Institute, Troy, New York. 11 Ph.D. Candidate, Civil and Environmental Engineering, Rensselaer Polytechnic Institute, Troy, New York. 12 Research Engineer, Forest Products Laboratory, Madison, Wisconsin. van de Lindt, J.W., Bahmani, P., Jennings, E.N., Pang, W., Ziaei, E., Mochizuki, G., Gershfeld, M., Pryor, S., Shao, X., Symans, M., Tian, J., Rammer, D. Full-scale testing of a soft-story woodframe building with stiffness-based retrofits. Proceedings of the 10 National Conference in Earthquake Engineering, Earthquake Engineering Research Institute, Anchorage, AK, 2014. Full-Scale Testing of Soft-Story Woodframe Buildings with StiffnessBased Retrofits J.W. van de Lindt P. Bahmani, E.N. Jennings, W. Pang, E. Ziaei, G. Mochizuki, M. Gershfeld, S. Pryor, X. Shao, M. Symans, J. Tian, D. Rammer

Low Cost Shape Memory Alloy Devices for Seismic Response Modification of Light-Frame Wood Buildings

Light-frame wood buildings have performed well with regard to life safety during recent U.S. earthquakes with several exceptions being the Loma Prieta and Northridge earthquakes. In these earthquakes, particularly Northridge, there was substantial damage resulting from several and perhaps even a single large amplitude inter-story drift during seismic excitation. Designing buildings to be more resilient to earthquakes is the impetus for the study presented in this paper. Architectural features and the ever-increasing demand for larger (and more) windows reduces the strength and stiffness of light-frame wood structures necessitating alternative procedures to be considered. An alternative procedure is developed and presented in this paper. Superelastic shape memory alloys (SMA’s) which have been shown to perform well as energy dissipation devices thereby improving the response of civil engineering systems to earthquakes, are applied to modify the response of light-frame wood building systems with large openings. Fragility curves and design charts for a range of seismic weights and desired performance levels are developed for a portfolio of SMA walls to be treated as replacement walls for wood shear walls in design or retrofit. The design of a large custom residential building using this technology is presented and performance verification is achieved using nonlinear time history analysis.