September 18, 1998

Engineer's Full-Scale Test Breaks in Constructed Facilities Lab at NC State

Dr. John Hanson (right) and graduate students David Hawkins (center) and Jeffery Morrison (left) are the first NC State researchers to use the Constructed Facilities Laboratory for testing large-scale structures. The CFL is unique in the United States, housing some of the largest testing equipment available at any university.

Breaking large concrete structures is usually the job of earthquakes and demolition specialists, but at North Carolina State University, it is the job of Dr. John Hanson. His project--testing pocketed spandrel beams--is the first of its kind in the College of Engineering's new Constructed Facilities Laboratory (CFL). Designed and built for large-scale testing, the lab is unique in the United States, housing some of the largest testing equipment available at any university.

Hanson, distinguished professor of civil engineering and construction, is the first researcher to put the new Constructed Facilities Laboratory to the test using full-scale elements of concrete structures. Located on the university's Centennial Campus, the CFL is part of the Engineering Graduate Research Center (EGRC). The facilities make testing designs of large structures possible without using scale models--a major advantage in construction engineering research. Hanson's project will use hydraulic rams reacting against the CFL's strong floor to test precast concrete spandrels, a type of member used to build parking decks.

"While the designs are very safe," says Hanson, "we need to determine the ultimate strength and the mode of failure."

Sponsored by the Precast Prestressed Concrete Institute (PCI) as a Daniel P. Jenny Research Fellowship, the project calls for testing two types of spandrel beams, each measuring 36 feet long and 7 feet tall. One type has a uniform cross section designed to sit on a corbel projecting from a column. The other type has a dapped end, a section cut out of the end of the beam, allowing the corbel to fit into the beam. The concrete spandrels are cast with pockets that are designed to hold double tee beams, the beams that support the decks. Metromont Prestress Company of Greenville, SC, supplied the beams for Hanson's tests.

Over time, the industry has refined the design to keep the face of the pockets as thin as possible and to reduce the depth below the pocket. Both of these design modifications can affect performance, says Hanson.

The two spandrel beams were specially cast to facilitate the testing. They were cast with sensors embedded in critical locations and with small holes through the pocket face to allow Hanson and his graduate students, Jeffrey Morrison and David Hawkins, to apply a load, simulating the reaction of a double tee beam on the bottom of the pocket. During testing, the sensors are connected by wires to computers that record the effects of loading and evaluate the performance data. The team will apply increasing loads to the bottoms of the pockets, eventually causing the beams to fail.

"We are testing to see where and how the beams will fail," says Hanson. "But we will also address other issues, such as the location of 'hanger' reinforcement within the spandrel and how the deep daps for the columns affect performance."

Once the testing is completed, Hanson and his team will make recommendations to the PCI. The information provided by the research project will help the PCI improve on current designs and help set standards for design, production and use of parking deck spandrels.

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