Application of live loading in the design and rating of combined railway and highway bridges

摘要

In the early days of the founding of the United States,bridges were constructed of wood and other local materials.These bridges provided stream and river crossings for coaches,wagons,pedestrians,and livestock.These structures were not designed according to our modern definition of the word.The engineers and builders of these bridges were behavior or constructed scale models to confirm their designs.The life span of their structures varied depending on the quality of the construction,the knowledge of the builder,the skill of the craftsman building the span,and the local site conditions; many spans were swept away by ice and high water.