There are approximately 600,000 bridges in the United States, including bridges on the National Highway System and bridges maintained and operated by various State and local entities. These bridges are essential to our Nation's mobility. The Structures Laboratory is a unique facility at Federal Highway Administration’s (FHWA’s) Turner-Fairbank Highway Research Center that specializes in developing and testing bridge designs, materials, and construction processes that promise safer and more efficient structures in the Nation's highway system.
The purpose of the Structures Laboratory is to support FHWA's strategic focus on improving mobility through analytical and experimental studies to determine the behavior of bridge systems under typical and extreme loading conditions. These experimental studies may also include tests of bridge systems developed to enhance bridge durability and constructability over time. Data from these studies help upgrade national bridge design specifications and improve the safety, reliability, and cost effectiveness of bridge construction in the United States.
The Structures Laboratory also provides bridge failure forensic investigation services to State departments of transportation, FHWA divisions, National Transportation Safety Board (NTSB), and other organizations. Through this forensic service, the laboratory determines the causes of bridge structural failures and develops practices and procedures to help avoid similar failures from occurring in the future.
The Structures Laboratory has the capability to perform a broad range of tests to characterize the performance of bridge structures and structural systems. This capability resides in five individual facilities: the main Structures Laboratory, the annex structures laboratory facility, the outdoor testing facilities, the computer modeling and simulation facility, and the metallic material testing facility.
The main Structures Laboratory (figure 1) is a state-of-the-art facility for indoor testing of full-scale bridge structures and large components under static and dynamic loads. This laboratory, built in 1984, consists of a strong floor with a universal loading frame that can be customized to erect and test full-scale bridges. This strong floor measures 181 by 51 feet (55.2 by 15.5 meters) and includes a grid of 573 tie-down holes. Static loads are applied using a large inventory of hydraulic rams. Dynamic loads are applied using a network of closed-loop servo-hydraulic test stations. Two 20-ton (178-kilonewton) overhead cranes service the entire floor area and can operate separately or together to unload trucks, erect structures, and set up experiments.
Figure 1. Overhead view of the main Structures Laboratory showing: (1) Full-scale box girder experiment with blue frame (left), (2) Concrete reaction wall (center) used to perform gusset plate experiments, and (3) Two blue frames (back right) to perform fatigue of steel composite girders.
The annex structures laboratory facility—the original Structures Laboratory—was built in the 1960s and still provides additional testing capability. The annex structures laboratory facility has a strong floor area measuring 12 by 40 feet (3.7 by 12 meters) and has one 15-ton (89-kilonewtons) overhead crane.
The Structures Laboratory's outdoor testing facilities, consisting of permanent geosynthetic reinforced soil abutments and an outdoor strong floor, were constructed during the late 1990s to provide additional capacity for testing large-scale components subjected to environmental loading. The permanent test abutments cover a single 70-foot-long (21.35-meters-long) span with a width of 13 feet (3.95 meters), and the outdoor strong floor measures 25 by 30 feet (7.6 by 9.2 meters).
The material testing laboratory maintains the capability to evaluate a wide variety of material properties of steel and concrete, including strength, elastic modulus, dynamic fracture toughness, static fracture toughness, and fatigue crack growth. Digitally controlled servo-hydraulic load frames are used for fracture and small specimen material strength testing. The laboratory also maintains the capability to perform microscopic examination of fracture surfaces and the microstructure of metallic materials and welds. These capabilities are utilized to support the research activities in the Structures Laboratory and to assist in forensic evaluation of failures in the fields.
The computer modeling and simulation laboratory allows researchers to build and analyze detailed models capable of simulating experimental test results with very high accuracy.
The Structures Laboratory provides the following services:
- Fundamental research into the strength, fatigue resistance, serviceability, and safety of bridge structures and components.
- Applied research to assess the suitability of various structural components and systems for different services.
- Field evaluation of in-service structures.
- Forensic evaluation of structural failures.
- Systems integration at superstructure and substructure interfaces.
The Structures Laboratory and facilities contain the following equipment.
- Numerous static and dynamic load actuators of 10,000 to 2 million pound force (44- to 8,896-kilonewton-) capacity.
- State-of-the-art data acquisition with the capability to perform very large structural experiments with thousands of channels.
- Numerous instruments to measure load, displacement, rotation, and strain in structures.
- Servohydraulic Load Frames:
- One MTS (Material Testing System) 312.31 Load Frame with an axial load capacity of 110 kips in compression and 110 kips in tension.
- One MTS 312.21 Load Frame with an axial load capacity of 22 kips in compression and 22 kips in tension.
- One Instron 8803 Load Frame (figure 2) with an axial load capacity of 113 kips in compression and 113 kips in tension.
- One MTS 315.04 Load Frame with an axial load capacity of 1,000 kips in compression and 509 kips in tension.
- One MTS 311.41 Load Frame (figure 3 ) with an axial load capacity of 550 kips in compression and 550 kips in tension.
- Two Structural Frames (figure 4), each frame with axial load capacity of 1,000 kips for static test and 550 kips for dynamic tests.
- One MTS 311.31 Load Frame (figure 5) with an axial load capacity of 200 kips and 200 kips in tension.
- A Charpy V-notch tester and two hardness testers.
- Microscopes and metallurgical testing equipment.
- MTS Advantage video extensometer.
- Three-dimensional laser measurement system with a volumetric accuracy up to 0.002 inches (0.049 millimeters) with a diameter range up to 361 feet (100 meters).
- Cementitious composite mixing, casting, and curing equipment.
- Software licenses to perform advanced, nonlinear finite element modeling of structural behavior.
Figure 2. Image of 11 0-kip servohydraulic test frame in the Material Testing Laboratory performing a tensile test on a steel plate by grasping and holding the ends of the steel plate using hydraulic grips.
Figure 3. Image of 550-kip servohydraulic test frame in the Material Testing Laboratory performing a tensile test on a steel plate in a controlled temperature chamber. The image also shows the steel plate grasped and held by the hydraulic grips in the frame.
Figure 4. Image of a full-scale fatigue experiment (front left) showing: 1) large-scale steel girder with full depth precast concrete deck panel grouted into place on top of the girder, 2) blue pedestal supporting the end of the steel girder; and 3) two blue load frames, each supporting an actuator.
Figure 5. Picture of 110-kip servohydraulic test frame in the Material Testing Laboratory performing tensile test on steel strand by grasping and holding the ends of the steel plate using hydraulic grips
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