EESD seminar

Title: "Unbonded post-tensioned shear walls as low-damage structural system".

Abstract: The research project discussed in this seminar proposes to address a grand challenge in structural engineering, which is the development of structural systems for use in resisting extreme hazards with minimum or no damage. Addressing this challenge will result in the design of the built infrastructure and in specific buildings that meet performance metrics towards achieving immediate occupancy and minimum economic losses after an extreme event, such as earthquakes. In past decades, research on un-bonded post-tensioned (UBPT) shear walls as lateral load resisting systems has certainly proven effective in achieving this goal, yet the following technical issues persist: concrete crushing at the wall toes, yielding of tendons, wall walking, and energy dissipation from ductile connectors that must be replaced and can lead to permanent deformations after an extreme hazard. This research proposes a transformative structural wall system for buildings that while performing damage free when resisting lateral loads surpasses many of the limiting issues still prevalent in UBPT systems. While similar to UBPT, in the system currently under investigation, the shear wall footing interface consists of a curved surface. This profile allows the wall to slide along the bottom-curved surface without separation from the foundation, and lateral deformations are accommodated through a pendulum-type motion. According to this system, lateral resistance is achieved by a combined friction mechanism along the curved surface and the vertical UBPT cables. The post-tensioning cables also assist in restoring the system to its initial configuration. The result is a technology related to the design of damage-free structural systems, and a new way of thinking about leveraging system geometry and deformations for enhanced resilient and sustainable design of buildings. This research will promote new design concepts that harness deformations for optimal performance rather than performance objectives set to target material limit states. In this seminar, preliminary outcomes of the research are discussed that set towards a new design philosophy envisioned to be unrestricted by traditional material failure limit states.

Bio: Dr. Pedro Silva is an Associate Professor in the Department of Civil and Environmental Engineering at the George Washington University. His main research interests are the development of innovative procedures for the design of civil structures to resist man made as well as natural hazards. Dr. Silva has over 20 years of experience in the design and experimentation of large-scale projects targeted an investigating new/retrofit design concepts for bridge and building structures. Dr. Silva is a voting member of the ACI Committees 440, where he developed specification language for the ACI 440-2 Chapter on Seismic Strengthening. Currently, this is the first code of practice worldwide for the design of Seismic Strengthening of Concrete Buildings Using FRP Composites. Currently Dr. Silva research group completed the development of numerical tools for practitioners and researchers to use in the assessment/design of reinforced concrete (RC) slender bridge columns using new state of the art seismic design practice. Products of this research include new models for plastic hinge length relations and numerical procedures used in defining stability indexes that: (1) stipulate threshold limits for neglecting P-D effects, and (2) define a collapse-prevention criterion.