Effects of Increasing Truck Weight Limits on Highway Bridges in Thailand

Any increasing of truck weight limits would affect an existing bridge safety. Besides, the increasing weight would shorten the time of repair and replacement of many bridges. Thai truck weights specified by Department of Highways were raised according to several government gazettes. This paper aimed to study the safety factors of the bridges due to the increasing of Thai truck weights compared with those from the design live loads of selected bridges. As indicated in the bridge standard drawings from Department of Highways, the reinforced concrete bridges with the span length ranging from 5 to 30 meters were studied. It was found that the average of maximum bridge responses from Thai truck weights were approximately 25% to 18% greater than those from the design live loads for moment and shear, respectively. Without bridge strengthening, the safety factors of the bridges were reduced due to the increase in truck weights especially for 5 to 8 meters span lengths. The results of this study would be used as a reference data for bridge strengthening in Thailand in order to maintain the bridge safety level consistent with the standard specifications.