Bridges, Tunnels and other Transportation Structures
This presentation discusses the formulation of damage states and repair strategies for hybrid sliding-rocking (HSR) bridge columns. Damage states and repair strategies are defined by leading experts in the field, coming both from academic and professional backgrounds, based on the damage observed during testing of large-scale HSR columns. The experts formed an expert panel and the damage states and repair strategies were established using the nominal group technique (NGT).
HSR bridge columns is recently proposed system for accelerated bridge construction (ABC) in high seismic areas (Sideris 2012). ABC systems are becoming increasingly popular because of the reduced onsite construction time and higher construction quality. HSR columns include precast concrete column segments with end rocking joints, intermediate sliding joints distributed over the column height, and internal unbonded post-tensioning. Rocking joints eliminate concrete tension damage and offer self-centering, while sliding joints offer energy dissipation without damage, reducing displacement demands. Past experimental research has shown the potential of this system in seismic applications (Sideris 2012; Sideris et al. 2014). However, more work is needed to demonstrate that the seismic performance of this system is a significant improvement over conventional systems, in terms of metrics of interest to decision makers, such as economic losses.
Seismic loss assessment for the HSR bridges is hampered by a lack of information on the critical damage states and repair strategies of this system. This study develops a set of damage states for HSR columns, and identifies corresponding repair strategies. In the experiments, two half-scale HSR column specimens are subjected to quasi-static lateral cyclic loading up to three different displacement demands, corresponding to ground motions with likelihood occurrence of 5% in 50 years, 2% in 50 years, and the minimum of 1% in 50 years or deterioration in lateral strength of 50% for high seismic site. After each of the critical displacement demands is reached, the column is inspected by a panel of experts consisting of 6 practitioners and academics in the field of bridge engineering to determine the damage of the column, defining the damage states qualitatively. These damage states should align with and distinguish between repair actions. After each experimental test is finished, the panel determines the repair strategies for each of the identified damage types using NGT, a technique designed to obtain expert opinion that uses several rounds of targeted questionnaires and discussions to converge to consensus (Sillars and Hallowell 2009). Lastly, experimentally-measured strains, displacement, and forces in the post-tension strands are examined and tied to the observed damage, defining the damage states quantitatively. The result is a set of repair descriptions, which can be costed and linked to simulation results, to comprehensively examine life-cycle seismic losses.