NEHRP Clearinghouse
- Title
- Effects of Axial Force on Frequency of Prestressed Concrete Bridges.
- File
- PB93112118.pdf
- Author(s)
- Saiidi, M.; Douglas, B.; Feng, S.; Hwang, E.; Maragakis, E.
- Source
- National Science Foundation, Washington, DC., August 1992, 52 p.
- Identifying Number(s)
- CCEER-92-4
- Abstract
- The purpose of the study presented in this report was to determine if vibration frequencies of prestressed concrete member can be used to establish prestress losses. A post-tensioned concrete bridge (called the Golden Valley bridge) which had been instrumented for another study was the primary subject of the study. The bridge was a simply-supported, multi-cell box girder. Because the actual stresses in the bridge were known, it was possible to determine if the changes in the measured frequencies of the bridge would correlate with the prestress losses. The dynamic characteristics of the bridge were measured on days 105, 202, and 455 from the prestressing completion date. The bridge was excited by impact from a heavy truck or by ambient truck traffic. Several data sets were collected in each test, and the frequencies were determined from the free-vibration acceleration data using a fast Fourier transformation method. The theoretical prediction for homogenous members was that, as the prestress force decreased, the frequency would increase because a reduction in the axial compressive load should stiffen the element. The measured frequencies for the bridge showed an opposite trend. Based on the measured data for the laboratory specimen, an empirical equation was developed that accounts for the effect of axial force on the rigidity of the element.
- Keywords
- ; Prestressed concrete; Structural vibration; Fourier transformation; Mathematical models; Dynamic response; Concrete structures; Earthquake engineering; Displacement; Deflection; Girder bridges; Loads (Forces); Resonant frequencies; Dynamic structural analysis