DYNAMIC BEHAVIOR OF THE COMPOSITE ARMY BRIDGE (CAB): FIELD TESTING

摘要

Light-weight short-span mobile bridging is needed for both military and civil emergency applications. The U.S. Army and DARPA have developed a short-span advanced composite 14-meter bridge for crossing MLC-100 (100-ton) tracked and wheeled vehicles across 12-meter gaps. The Composite Army Bridge (CAB) is a technology demonstrator that is primarily fabricated using carbon/epoxy along with the Vacuum Assisted Resin Transfer Molding (VaRTM) manufacturing method to produce a bridge 20-30% lighter than an equivalent metallic (aluminum) bridge. It is observed that heavy vehicles moving quickly on these lightweight bridges can lead to large dynamic responses (bouncing) and load factors, not observed on mobile metallic bridging. Potential damage to the carbon fibers, epoxy resin, bonded joints, and bolted joints are of concern. A field test was performed to assess the long term dynamic performance of the bridge subjected to three different vehicle types: (a) a tracked M1-A1 (MLC-70) tank, (b) a wheeled 100-ton Heavy Equipment Transporter (HET), and (c) a tracked M88 towing an M1-A1 tank. Over 2000 crossings were performed at different speeds and bank conditions. Dynamic load factors of 1.5 were measured for many crossing speeds. Load factors approaching 1.66 were observed during low-speed panic braking stops due to the increased loading on the forward axles and reduced loading on the rear axles. A 1.32 dynamic factor for low-speed panic braking is calculated. A maximum mid-span tension rail strain of 2017 m in/in was observed during low speed panic braking, which is 1.9 times smaller than the mid-span tension strain (3822 m in/in) observed during laboratory treadway failure testing. Thus the observed safety factor is greater than the 1.8 required safety factor by the TDTC. Post-test comparison to pre-test static measurements revealed no damage to the bridge structure or wear surface. Thus, advanced composites (carbon/epoxy) have been proven as a high-performance alternative to conventional metallic materials for mobile bridging.