Highway IDEA Program: Active Confinement of Bridge Piers Using Shape Memory Alloys

摘要

This IDEA project focused on developing an innovative active confinement technique for the seismic retrofitting of reinforced concrete (RC) bridge columns with insufficient ductility and/or shear capacity. The new technique utilizes a novel class of smart materials known as Shape Memory Alloys (SMAs) to provide external active confinement pressure at the plastic hinge zone of vulnerable columns. Wires made of NiTiNb SMAs are prestrained to approximately 6 %- strain then wrapped around the column in the form of spiral. Once the spiral is in place, it is heated to a temperature greater than the SMAs austenite transformation temperature (approximately 320 degree F) and then left to cool. Heating the spirals can be done either directly using a torch or by simply passing an electrical current. Due to the shape memory effect of SMAs, heating the spirals will cause them to attempt to shrink to their original length, which will induce a large hoop stress in the spiral (. 65 ksi), which will in turn develop a lateral confining pressure on the perimeter of the column. Previous attempts to apply the concept of active confinement on bridge piers using steel and composite materials had all failed due to several problems related to the method of applying the confining pressure. This project provides a simple, reliable and cost-effective solution for these problems, which will facilitate and promote the application of active confinement which over performs the currently used passive confinement technique using steel jackets or fiber reinforced polymer (FRP) composites.