University of California-San Diego staff have completed the latest phase of tests seeking data to improve design professionals’ understanding of how precast
University of California-San Diego staff have completed the latest phase of tests seeking data to improve design professionals’ understanding of how precast concrete structures respond to seismic forces. Over a 90-day period, researchers subjected a half-scale, three-story structure resembling a parking garage to various levels of seismic forces, including simulation of a Maximum Considered Earthquake level likely to occur once every 2,500 years in regions of high seismic activity. The testing applied ground motions at increasing levels of earthquake intensity, reaching jolts as powerful as magnitude 8.
Measuring 17- _ 58-ft. Û the biggest footprint of any specimen tested on a shake table in the U.S. Û the approximately 28-ft.-tall, 1 million-lb. precast structure featured one level each of three types of flooring components: pretopped double-tees, topped double-tees, and hollow-core concrete slabs. It was erected on the world’s largest outdoor shake table, 25- _ 40-ft., with 2,240-ton load capacity. Approximately 600 channels of instrumentation located throughout the test structure provided readings.
The shake-table testing was conducted at the NEES/Englekirk Structural Engineering Research Center in San Diego, under the direction of Dr. Jose Restrepo from the University of California, San Diego. A primary objective of the research was determining the behavior of precast diaphragms, i.e., seismic response of floor systems Û an area of urgent focus since the 1994 Northridge earthquake that rocked Los Angeles. Along with significant Precast/Prestressed Concrete Institute support, program funding was provided by grants from The Charles Pankow Foundation, whose namesake was responsible for engineering advances favoring precast methods for multi-story construction in high seismic zones; National Science Foundation; and, Network for Earthquake Engineering Simulation.
The tests proceeded from a program PCI sponsored in conjunction with other organizations to explore innovative precast structural systems that participants contend can save lives and property during a major seismic event. The latest tests occurred in the final year of a five-year, $2 million-plus research program PCI cosponsored with an eye toward improving standards for the design and construction of diaphragms comprising precast, prestressed concrete components.
These tests followed a series of field studies and design applications conducted on building connections for precast concrete components during the 1990s. That 10-year initiative was called the Precast Seismic Structural Systems (PRESSS) research program. A large-scale, five-story precast building test comprised four frame systems and one shear-wall system to determine their capability for creating new seismic designs. The hybrid structural frame system proved so successful that several precast/prestressed concrete buildings have been constructed using that concept.
Current research is being carried out by a consortium of three universities. It is led by Dr. Robert B. Fleischman, associate professor in the Department of Civil Engineering & Engineering Mechanics at the University of Arizona in Tucson. Researchers there have performed comprehensive analytical research on the program, while full-scale tests of reinforcing details and precast concrete connections have been conducted at Lehigh University in Bethlehem, Pa., under the direction of Dr. Clay Naito.
In addition, several individual PCI precast concrete producers, as well as material suppliers and professional members, have contributed to the effort. Experimental data will be analyzed by the researchers and reviewed by an advisory committee headed by 2005 PCI Chairman Tom D’Arcy, principal and founding president of The Consulting Engineers Group in San Antonio, Texas, and PCI’s Research & Development Committee, chaired by Professor Douglas Sutton of the Purdue University School of Civil Engineering, West Lafayette, Ind.
Once testing results are evaluated, the group will work toward providing data and supplementary information to allow the design approaches to be adopted in code documents. That process involves peer review of various technical publications and a broad participation of knowledgeable professionals in development of code provisions.