In suspension bridges the main cables, with many thousands of steel wires compacted together, are crucial for the overall safety; they transfer the entire load--more than several thousand tons-- including the weight of the bridge deck and of any traffic that might be on it, the wind induced forces, etc. to the towers and to the anchorage blocks. If the cable fails, the entire bridge is lost. Full inspection of cables during service is not feasible; assessing the strength of a main cable is accomplished through partial inspections and numerical models.
The goal of this research is to provide bridge engineers with experimental and numerical tools to assess the remaining strength of suspension bridge cables. The experimental part of the study will use deeply-penetrating, non-destructive, neutron beams to measure position-specific stress/strain data from model bridge cable strands under realistic boundary conditions. These data will, then, be used to develop numerical and theoretical models for predicting the load carrying capacity, safety factors and reliability, as well as service life, of parallel-wire suspension bridge cables, both under design and currently in service.
In neutron diffraction the lattice parameter of the steel is utilized as an internal strain gage. The change in this parameter as a function of applied load yields the elastic strain. In the experimental phase focussed neutron beams will be used to measure the strain partitioning within individual wires of model cables while they are loaded past failure. Thermal neutrons can easily penetrate 45 mm of steel and, thus, measurement of the local strains within the inner wires is possible. The experiments will be carried out for various bundle configurations with selected lubricant/corrosion preventative treatments. The data obtained from the experiments will then be utilized in an extended 3-D finite element model being developed on the supercomputing facilities available at Columbia University. Once finished, this model is expected to yield accurate predictions on the load carrying capabilities of parallel wires and can be extendable to the assessment of the ultimate strength of the overall main cable in a suspension bridge.
