SEMIACTIVE VIBRATION ABSORBERS (SAVA) AT THE I-35 WALNUT CREEK BRIDGE

The project was undertaken to develop and field test an automatically controlled bridge mounted vibration absorber. The system, referred to as a semiactive vibration absorber (SAVA) consists of a hydraulic cylinder coupled to structural steel elements that bolt to an existing bridge. The hydraulic cylinder (HC) is equipped with a computer-controlled valve and sensors. The sensors are used to detect the motion of the bridge girders that results from the passage of heavy multi-axle trucks. The research resulted in the establishment of a smart software code that opens and closes the valve on the HC at appropriate times during the vibration. The modulation of the valve affords an optimized combination of both stiffness and damping, which results in a significant reduction of vibration amplitude and maximum stress in the girders. Field testing of the SAVA system was conducted on the Walnut Creek Bridge at the 92.7 mile marker on I-35 between Dallas, Texas and Oklahoma City, Oklahoma. The bridge has a two-lane, 38 ft (12.6 m) wide composite deck, supported by five 134 lb/ft (199.4 kg/m) girders mounted at 8 ft 6 in. (2.6 m) centers. The continuous 400 ft (122 m) long girders were supported at 100 ft (30.5 m) intervals by three piers and abutments at either end of the bridge. The SAVA system was installed in summer 1996 on one span of the bridge, and field tested for over 12 months. The results indicate a nominal reduction of truck-induced stress and deflection of over 55%. The tests were conducted using four multi-axle trucks with weights ranging from 27 klb (12,247 kg) to 120 klb (54,432 kg), traveling at the posted speed limit. NCHRP Report 299 (1989) was used to determine the remaining safe life of the bridge. The most conservative estimate indicated that the span in which the SAVA system is mounted gained an additional 60 years of safe life and over 150 years of mean life. The estimated safe life of the bridge prior to the installation of the SAVA system was -7 years. The system operated on a 12-volt battery that is rated to last over two years. The instrumentation required includes two sensors (per actuator). The entire SAVA system was mounted from below, without having to impede traffic. The estimated cost of the system is approximately 7% to 10% of the cost to replace the bridge. The performance of the system and the integrity of the electronics is routinely checked via a remote monitoring system. The work proved conclusively that the semiactive vibration absorber system is robust to climate conditions and is inherently safe. A patent has been awarded (#5545372) for this technology.

• Corporate Authors:

  University of Oklahoma, Norman

  Center for Structural Control, 865 Asp Avenue
  Norman, OK  United States  73019

  Oklahoma Department of Transportation

  Office of Research, 200 NE 21st Street
  Oklahoma City, OK  United States  73105

  Federal Highway Administration

  1200 New Jersey Avenue, SE
  Washington, DC  United States  20590
• Authors:
  • PATTEN, W N
  • Sun, Jinlong
• Publication Date: 1997-9

Language

• English

Media Info

• Features: Figures; Photos; References; Tables;
• Pagination: 180 p.

Subject/Index Terms

• TRT Terms: Automation; Bridges; Control systems; Cost estimating; Estimates; Field tests; Highway bridges; Hydraulic equipment; Performance evaluations; Service life; Software
• Uncontrolled Terms: Vibration absorbers
• Old TRIS Terms: Bridge life; Hydraulic devices
• Subject Areas: Bridges and other structures; Design; Highways; I24: Design of Bridges and Retaining Walls;

Filing Info

• Accession Number: 00748837
• Record Type: Publication
• Report/Paper Numbers: FHWA/OK 97(08),, Final Report,, OK Univ Rept 2125
• Files: TRIS, USDOT
• Created Date: Jun 1 1998 12:00AM