This presentation/paper presents the findings of a large-scale testing program conducted at the Texas A&M University on a novel bridge substructure design incorporating polyure-thane (PU)-enhanced rocking columns. PU-enhanced columns are precast concrete rocking columns that integrate: (i) polyurethane damage-resistant segments at the column ends to ac-commodate large rotations without damage, (ii) external replaceable energy dissipating (ED) links in the form of buckling-restrained yielding elements, to provide supplemental hysteretic damping and flexural stiffness and strength, and (iii) internal unbonded post-tensioning to provide self-centering. Polyurethanes are visco-elastic/visco-plastic polymeric materials, which, compared to concrete, exhibit large deformability, low stiffness and large strength, which increases with the loading rate, further preventing damage. As a result, under strong earthquakes, damage is mainly concentrated at the (external) ED links, which can be rapidly replaced without bridge operation disruptions, eliminating any residual deformations.
The experimental program included cyclic testing at various loading rates of large-scale (~1:2.5) PU-enhanced cantilever rocking columns with various designs for the PU segment: (a) solid PU segment, (b) axi-symmetrically bi-layered segment with an exterior PU layer to withstand seismic loads and an internal reinforced concrete core to sustain long-term service loads and provide resistance against creep. The specimens are subjected to displacement-controlled lateral cyclic loading of increasing amplitude (up to a 15% drift ratio) at several drift ratio rates (up to 1/sec). Tested columns are retrofitted via ED link replacement to demonstrate their rapid reparability characteristics and re-tested to demonstrate that the origi-nal column properties have been nearly recovered. Rocking-only precast concrete columns are also tested under the same loading protocols to provide a basis for comparison. Experi-mental performance is evaluated in terms of force and ductility capacity, self-centering and energy dissipation capacity, observed damage, and residual strength, before and after retrofit.
• Considering the need for rapid replacement of the aging bridge infrastructure in in the U.S. and worldwide, as well as the poor performance of bridges in recent earthquakes, this presentation will be of national and international interest.
• The target audience will include structural, bridge and earthquake engineers from academia, practice and State Agencies as well as engineers that are interested in use of advanced materials to improve structural performance.
• The audience will be introduced to a bridge substructure design that combines the novel concepts of construction rapidity, damage avoidance and rapid post-earthquake repair, through advanced materials and response mechanisms. These concepts can be extended into various structural systems, such as buildings, and integrated in research efforts and teaching curricula.