Fragility Modeling and Cost Benefit Analysis of An Sma Enhanced Bridge Expansion Joint

Abstract eng:
This work demonstrates through fragility modeling and cost benefit analysis, how a shape memory alloy (SMA) enhanced modular bridge expansion joint (MBEJ) offers long-term benefits to a bridge system. An SMA enhanced MBEJ aims to reduce joint system failure during an earthquake that would otherwise lead to damage and limiting of bridge functionality post event. Two levels of large capacity MBEJs exist: seismic and service joints. During an earthquake, service joints are often assumed to fail, requiring costly road closures and joint system replacement. For regions where a service joint is typically required, but where earthquake risks exist, this SMA enhanced MBEJ can be an alternative. One advantage of Nickel Titanium SMAs is that they exhibit 8-10% recoverable strain elongation which, when the material is formed to a compact size and shape, offers the MBEJ improved performance without significantly altering its mechanical configuration. This enhanced MBEJ uses an SMA spring placed in-series with existing MBEJ components to increase displacement capacity without modifying the service level performance. Though such joints are often neglected in bridge analysis, in order to gauge the benefit and impact of the SMA enhancement over a baseline system, an expansion joint model is placed in a representative bridge model, characteristic of one that incorporates large capacity MBEJs. This bridge model, when subjected to a suite of ground motions, captures the MBEJs response, which is used to generate unique component fragility curves that describe their failure probability if a ground motion intensity is realized. Looked at over 25, 50 and 75 year time intervals in specific regions of the United States, a cost benefit analysis shows that investment in the SMA enhanced MBEJ system can be worthwhile.

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