The Structure to Protect

July 16th, 2012 - Filed under: Cover Story

A 15-ton crane will help set up tests in the new Large Scale Structures Laboratory.

By Mary Wymer and Adam Jones

In the classic fairytale of the Three Little Pigs, the third pig – the one who used bricks to build his house – was surely an engineer. After seeing the handiwork of the Big Bad Wolf, he succeeded in constructing a house that withstood the disaster after careful study of the practices of his brothers who, in critical miscalculations, used straw and sticks to build their houses.

Of course, natural disasters aren’t fairy tales, and neither is the science of girding structures to hold up under the big, bad stress of an earthquake, hurricane, tornado or strong winds. But engineers, like the third pig, learn from past failures, and in the wake of a catastrophic natural disaster, they review whether human and economic losses can be reduced. Through structural-engineering research and experimentation, building codes and retrofitting techniques are improving, better protecting inhabitants and property. Within The University of Alabama’s South Engineering Research Center, College of Engineering professors are leading just such international research efforts.  Much of their work will be conducted within the new Large Scale Structures Laboratory.

A team of UA civil engineering faculty, students and fellow researchers throughout the country will lead numerous research projects within this lab.

The lab features an innovative hybrid testing system working in sync with the new 17-feet-by-17-feet uni-axial seismic simulator, or shake table. It will test up to two-story buildings with a full capacity of approximately 50,000 pounds.

With a set of twin actuators having 55,000-pound force capabilities, the hybrid system will simulate a multi-story building through the computer, and then the actuators will physically place the load demand on the two-story structure while it’s positioned on the table. This is the only kind of seismic hybrid system in the Southeast and one of only several in the country.

“This lab is going to have a huge impact,” said Dr. Ken Fridley, professor and department head of civil, construction and environmental engineering. “Few labs with this capacity are right on a campus.”

Installed on a 32-inch concrete slab, which exceeds one million pounds in order to prevent other vibrations during data collection, the shake table will move in one direction to replicate many of the world’s largest recorded earthquakes.

The hybrid testing system is unique in providing real-time theoretical modeling coupled with physical seismic lab simulation as it is operating, and the feedback adjusts the simulation immediately. With the largest shake table in the Southeast, Fridley and others are excited to debut this distinctive system that will dramatically improve earthquake-simulation research for buildings and structural engineering as a whole.

UA is part of an interdisciplinary team of researchers from five universities on the “NEESsoft project,” titled Seismic Risk Reduction for Soft-Story Wood-Frame Buildings. It is a $1.4 million project funded by the National Science Foundation and investigates older multi-story buildings susceptible to collapse at the first story during earthquakes.

“Soft story” buildings are commonly three or four stories, designed with first floor parking. The need for this research was identified in the San Francisco Community Action Plan for Seismic Safety project, which categorized possible action plans for reducing earthquake risks in existing buildings. According to the San Francisco-based study, 43 to 80 percent of the multi-story wood-frame buildings are unsafe after a magnitude 7.2 earthquake and a quarter of these buildings are expected to collapse.

The study, which involves three major types of experiments, will provide a fundamental understanding of the way wood-frame buildings collapse. Following the experiments, conducted at UA,   the University of California, San Diego and the State University of New York at Buffalo, the team will recommend seismic retrofit techniques.

The College’s research is not just focused on earthquakes. A research team, consisting of academic researchers from multiple universities and professional engineers, received a National Science Foundation RAPID Response Grant for Exploratory Research to investigate and gather data about the damage to, and performance of, wood-frame structures in the affected areas due to strong winds. The team primarily looked at residential and multi-family apartments, but it also reviewed some steel and masonry buildings.

UA civil, construction and environmental engineering professors, from left, are Dr. Michael Triche, Dr. Jialai Wang, Dr. Ken Fridley, Dr. Andrew Graettinger and Dr. Jim Richardson.

Through this multi-university and industry collaboration, College faculty and students can provide valuable research to help design safer homes. It is very difficult to investigate the load characteristics of buildings within a tornado path. Developing a dual objective-based design method to better mitigate the effect of tornadoes should reduce damage and save lives.

Besides the impressive shake table, the laboratory includes a 10-feet-by-10 feet-by-10-foot soil pit to test structures on the ground, a 15-ton crane, a large suite of hydraulic actuators for testing force and reconfigurable reaction blocks that tie into the million-pound strong floor for the actuators to react against.

In fact, the floor is an engineering feat in its own right. Birdwell & Associates of Lakeland, Fla., was one of the few contractors willing to take on the task of pouring and smoothing a level slab three-feet thick and elevated. With virtually no room for error, Birdwell’s crews used precision equipment and a hand-held laser to finish a floor flatter than most ground-level slabs. Birdwell won a 2011 Golden Trowel Award from FACE Companies for the flattest and most level shored elevated slab.

That flat surface means research testing doesn’t have to compensate for the floor, Fridley said. “The floor is part of the test so with the floor it is easier to set up tests at the precision we want,” he said. “We’re not starting out with a problem.”

The lab is designed for multiple experiments to operate at the same time while new situations are being set up. Set up of seismic simulations requires weeks and even months, whereas each simulation lasts only 30 to 60 seconds.

As a result of the structural engineering laboratory development, The University of Alabama is poised to pioneer new methods of structural seismic testing, revolutionizing design codes. One such effort is a paradigm known as performance-based seismic design, which enables an engineering design team to explicitly consider performance during the design process. For light-frame wood buildings, this is spearheaded at UA, and the new laboratory will provide the experimental support to further this national effort.

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