Evaluation of Texas Superheavy-Load Criteria for Bridges

The number of permits for superheavy loads crossing Texas bridges has steadily increased over the years, and compared with several other states, the criteria that establish superheavy-load status are generous. The result is that many Texas bridges experience high-stress loads that cause accelerated deterioration. In this study, bridge load and rating factors and the validity of the criteria for establishing superheavy-load status are evaluated. The primary objective of this study was to evaluate Texas superheavy-load criteria for bridges. To accomplish this, field tests for the response behavior of a bridge subjected to overweight vehicles and a parametric study using finite element analysis were utilized to extract bridge criteria triggers. The field-verified solid model and related parametric study show that the Texas superheavy-load criteria are valid for the study bridge type. Load ratings computed using the distribution factors determined in this study show that the evaluated bridge has much reserve capacity, even for short 1,023 kN (230 kip) and longer 1,383 kN (311 kip) superheavy loads. The parametric study using finite element modeling shows that the criteria adequately protect this bridge type. Because the criteria are based on prior permitting by Texas Department of Transportation (TxDOT), a graphical version of the criteria might serve TxDOT and carriers better than do the gross vehicle weight limits alone. Long term collection of load frequency and load level data from a relevant bridge would help TxDOT determine the effects stress level variations have on the life of Texas bridges.