Multi-hazard performance of bridge timber piles retrofitted with fiber reinforced polymer composites
Bridges with various timber structural components make up a large portion of the transportation infrastructure in the US. Bridges supported on timber pile substructure, simply referred to as timber pile bridges, are particularly common. Many timber pile bridges still in service today were constructed in the 1950’s and 60’s using simplified design approaches largely based on convention and empirical data. Since only gravity loads were considered in their original design, many timber pile bridges are deficient by modern standards. Further exacerbating this problem is their age and the susceptibility to degradation. Despite these issues, timber bridges in general are overlooked in terms of operational importance and afforded minimal maintenance effort. Furthermore, whereas countless research studies have focused on every aspect of conventional reinforced concrete or steel bridges, research activity on timber bridges has been almost non-existent. Given ever increasing demands on bridges and interest in sustainable, resilient structures, the time is now to close the gap. The first part of this research is devoted to the experimental testing of timber piles with a special focus on the short- and long-term performance of piles retrofitted with fiber reinforced polymer (FRP) composites. The impact of timber deterioration and the effectiveness of different FRP application strategies are examined to make retrofit design recommendations, and a unique accelerated aging procedure is used to study their durability. In the second part of the research, numerical approaches are used to develop methods for estimating the capacity of deteriorated timber pile bridge substructure. This includes a comprehensive load rating method for abutment timber piles in which the in-situ pile condition is a key input parameter as well as performance prediction models for bridges subject to earthquake-tsunami hazards. Under earthquake-tsunami loading considerations, a sequential analysis framework is used to perform nonlinear dynamic time history analyses and tsunami impact simulations using the particle finite element method (PFEM). Failure criteria for a typical bridge are introduced in the form of earthquake-tsunami hazard interaction diagrams then a probabilistic approach is used to quantify the effect of damage accumulation and introduce the concept of a demand amplification factor. The findings from this research clearly demonstrate the need to more carefully consider the safety of existing timber bridges, and show that proper maintenance and retrofitting can significantly improve their strength and durability. Most importantly, this research contributes simple and robust tools for assessing the vulnerability of timber pile bridges under both typical service conditions and multi-hazard scenarios.
Multi-Hazard, Earthquake-Tsunami, PFEM, Timber Piles, FRP
University of Illinois - Urbana-Champaign
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University of Illinois at Urbana-Champaign