Live load distribution factors for multi-span girder bridges with plank decking subjected to farm vehicles

The American Association of State Highway and Transportation Officials (AASHTO) specifications provide simplified formulae to determine Live Load Distribution Factors (LLDFs) for highway bridges. The formulae for the AASHTO code-specified LLDFs have been developed, considering the effect of typical highway trucks. In addition to highway bridges, there are a large number of bridges located on secondary roadways where farm vehicles having varying configurations and weights frequently travel. Unfortunately, LLDFs for the bridges loaded with farm vehicles are not well known. In this study, hence, two bridge types, including steel girder bridges with plank decking and timber girder bridges with plank decking, were selected to determine LLDFs of the bridges under the effects of farm vehicles. The procedure adopted include the AASHTO code-specified formulae, field testing, finite element modeling, and analytical simulations of all the bridges. Field testing of each bridge was conducted with four different farm vehicles and a five-axle highway truck used as a benchmark for exploring highway truck-induced LLDFs. Commercially available Finite Element Analysis (FEA) software was utilized to generate analytical models of all the bridges, and the models were calibrated with field data. To consider the effects of vastly different farm vehicles, information on 121 existing farm vehicles were collected and used as input loads in the models to compute analytical LLDFs for the bridges. The analytical LLDFs resulting from 121 farm vehicles were used to establish statistical limits representing deterministic values for LLDFs for each bridge. The field, analytical, and statistical LLDFs were compared to those obtained from the AASHTO specifications. Results showed that the AASHTO LLDFs were, in some cases, inadequate for the timber girder bridges, while those were, in most cases, adequate for the steel girder bridges

Study of the Impacts of Implements of Husbandry on Bridges Volume III: Appendices

The objectives of this study were to develop guidance for engineers on how implements of husbandry loads are resisted by traditional bridges, with a specific focus on bridges commonly found on the secondary road system; provide recommendations for accurately analyzing bridges for these loading effects; and make suggestions for the rating and posting of these bridges. To achieve the objectives, the distribution of live load and dynamic impact effects for different types of farm vehicles on three general bridge types\u2014steel-concrete, steel-timber, and timber-timber\u2014were investigated through load testing and analytical modeling. The types of vehicles studied included, but were not limited to, grain wagons/grain carts, manure tank wagons, agriculture fertilizer applicators, and tractors. Once the effects of these vehicles had been determined, a parametric study was carried out to develop live load distribution factor (LLDF) equations that account for the effect of husbandry vehicle loads. Similarly, recommendations for dynamic effects were also developed. The live load distribution factors and dynamic load allowances are covered in the first volume of the report. Finally, suggestions on the analysis, rating, and posting of bridges for husbandry implements were developed. Those suggestions are covered in the second volume of the report. This third volume of the report contains six appendices that include the 19 mini-reports for field tested and analytically modeled steel-concrete, steel-timber, and timber-timber bridges, the farm implement and bridge inventories for the project, and survey responses

Live load distribution factors for multi-span girder bridges with plank decking subjected to farm vehicles

The American Association of State Highway and Transportation Officials (AASHTO) specifications provide simplified formulae to determine Live Load Distribution Factors (LLDFs) for highway bridges. The formulae for the AASHTO code-specified LLDFs have been developed, considering the effect of typical highway trucks. In addition to highway bridges, there are a large number of bridges located on secondary roadways where farm vehicles having varying configurations and weights frequently travel. Unfortunately, LLDFs for the bridges loaded with farm vehicles are not well known. In this study, hence, two bridge types, including steel girder bridges with plank decking and timber girder bridges with plank decking, were selected to determine LLDFs of the bridges under the effects of farm vehicles. The procedure adopted include the AASHTO code-specified formulae, field testing, finite element modeling, and analytical simulations of all the bridges. Field testing of each bridge was conducted with four different farm vehicles and a five-axle highway truck used as a benchmark for exploring highway truck-induced LLDFs. Commercially available Finite Element Analysis (FEA) software was utilized to generate analytical models of all the bridges, and the models were calibrated with field data. To consider the effects of vastly different farm vehicles, information on 121 existing farm vehicles were collected and used as input loads in the models to compute analytical LLDFs for the bridges. The analytical LLDFs resulting from 121 farm vehicles were used to establish statistical limits representing deterministic values for LLDFs for each bridge. The field, analytical, and statistical LLDFs were compared to those obtained from the AASHTO specifications. Results showed that the AASHTO LLDFs were, in some cases, inadequate for the timber girder bridges, while those were, in most cases, adequate for the steel girder bridges.</p