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摘要

Question: John, bow important is lateral and longitudinal bracing on a timber trestle?rnAnswer: Both the lateral and longitudinal bracing are very important for the overall stability on long timber pile bridges and/or tall timber bents. These bracing components resist horizontal loads while limiting deflection and side sway through the trestle. Without these bracing components, the resistance to horizontal forces would depend primarily on the bending capacity of the timber piles and the pile batter. Typically, the need for bracing depends on the length of bridge and the height of bents with consideration given to the soil conditions and the depth of embedment of the piles which leads to obvious additional consideration for framed bents.rnThe lateral loads resisted by timber bents include centrifugal force, wind forces, locomotive nosing, and hydraulic (from channel flow) which can increase with possible drift build-up. Longitudinally, the larger of the braking or traction force must be resisted. The criteria for calculating the magnitude of these forces can be found in Chapter 7, Section 2 of the AREMA Manual for Railway Engineering. The order of magnitude from these forces and deflections from can become significant and must be accounted for in the designrnand maintenance of the timber trestle. One of the concepts of these bracing components is to help the trestle to react as a unit. Any evaluation that involves the capacity of an existing timber bridge must include a stability analysis using these combined forces.