Analytical and experimental investigation of dynamic amplification factor for the load rating of reinforced concrete box culverts
Date
2016
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Publisher
University of Delaware
Abstract
This thesis seeks to better understand the factors that influence the dynamic amplification of reinforced concrete box culverts (RCBC) resulting from moving traffic loads. Due to large discrepancies between observations made during inspections and the results of load rating many RCBC in the State of Delaware, it is believed that the dynamic amplification factor ( DAF) is overconservative. The DAF is a ratio of a structure’s dynamic response to its static response, used to amplify static loads to account for the maximum dynamic loading condition. ☐ According to American Association of State Highway and Transportation Officials (AASHTO) provisions, DAF for RCBC is specified as 1.33 when zero meters of fill is present between the culvert and pavement, and decreases linearly to 1.00 when 2.44 m of fill is present. Two approaches are taken to investigate the adequacy of this specification. First, a parametric finite element analysis is conducted to examine the influence of fill depth, soil elastic modulus, span length, slab thickness and asphalt pavement thickness on DAF. In total 324 two-dimensional, plane-strain model configurations are analyzed. Second, five culverts representative of the Delaware Department of Transportation’s inventory are instrumented and tested to investigate the behavior of in-service RCBCs. ☐ Prior to the finite element analysis and field testing program, a literature review was conducted that revealed DAF to be extremely complex in nature. Particularly, it was noted that many studies examining structural dynamics have conflicting results due to the many factors that influence these systems. ☐ The finite element analysis shows good agreement between the two-dimensional, numerical results and the theoretical solution to a single degree of freedom (SDOF) system. This subsequently suggests that the dynamic amplification is related to the ratio of the applied load’s pulse duration to the structure’s natural period. The maximum DAF calculated during the parametric study is 1.28. Based on the linear fit trend lines for each parameter, DAF has a positive relation with fill depth and pavement thickness, and a negative relation with soil elastic modulus, span length, and slab thickness. However, relative to fill depth and soil elastic modulus, span length, slab thickness and asphalt pavement thickness have little influence on DAF. The trend of increasing DAF with increasing fill depth is opposite those suggested by AASHTO specifications. ☐ During field testing, the maximum DAF recorded for any culvert at the location of maximum static strain was 1.20. Two of the five culverts tested did not record DAF values greater than 1.05 at the location of maximum static strain. Contrary to the numerical results, field test results show fill depth to have a negative relation with DAF and slab thickness to have a positive relation. These differences may be due to the disparity between the limited number of field tests conducted and the number of model configurations analyzed. Additionally, the maximum fill depth of any culvert instrumented and tested is 0.5 m while the finite element analysis examined model configurations with up to 1.83 m of fill. ☐ Depending on the statistic used, field tests do appear to corroborate trends suggested by AASHTO. However, based on the limited number of tests conducted and the contradictory results presented in the parametric finite element study it is difficult to elaborate on the extent to which that is true. The scope of field tests was limited to RCBC with less than 0.5 m of fill and with road surfaces in good condition. For culverts within the range of these and other parameters tested in the field, a maximum DAF of 1.20 is recommended.