Seismic Retrofit of Horizontal Lateral Force Resisting Systems in Buildings

This project aims to advance understanding of the vulnerabilities in the horizontal lateral force resisting system of concrete buildings subject to seismic loads and create new approaches for fiber reinforced polymer retrofit through patterns of targeted strengthening and enhanced ductility. The horizontal lateral force resisting system, consisting of the diaphragm, chords, and collectors, often requires retrofit during renovations, when penetrations are cut in the slab, or in older buildings when deficiencies in the in-plane load path, strength, or ductility are discovered.

Externally bonded fiber reinforced polymers are increasingly being used to improve diaphragm performance because they are easier to install and do not increase the building weight as compared with conventional concrete and steel strengthening. However, because of their relatively large size and other factors, little research has been conducted to understand how externally bonded composites can be best used to retrofit deficient horizontal lateral force resisting systems.

The new retrofit approaches to be developed in this research are important for their potential to increase infrastructure resilience to natural hazards such as earthquakes, as well as improving infrastructure sustainability through adaptive reuse rather than demolition and reconstruction. This project will provide training for graduate and undergraduate students and will curate a social media microblog to excite and inspire individuals underrepresented in science and engineering.

This award will contribute to the National Science Foundation (NSF) role in the National Earthquake Hazards Reduction Program (NEHRP). Data from the project will be archived and made publicly available in the NSF-supported Natural Hazards Engineering Research Infrastructure (NHERI) Data Depot (http://www.designsafe-ci.org).

The project objectives are to (1) elucidate efficient patterns of triangulated targeted strengthening that are not constrained to orthogonal building axes, (2) enhance cyclic behavior of axial elements in the floor through new concrete confinement techniques, and (3) establish force transfer between the horizontal and vertical systems that may not occur along orthogonal lines. The new fundamental knowledge will unlock opportunities related to nonorthogonal elements, more efficient force flow patterns, and optimization that will be used to advance new design and analysis approaches for diaphragms.

The research plan consists of integrated computational and experimental tasks that include: (1) using topology optimization and strut and tie concepts on a set of archetype buildings to develop targeted strengthening approaches, (2) a large-scale experimental study to investigate behavior of existing and retrofitted floors, (3) validation of computational models that can capture the behavior of complex concrete floor systems with and without composite retrofitting, (4) evaluating retrofit approaches using computational models, and (5) synthesizing generalizable design strategies that can be applied to practical diaphragms. The research impact will be broadened through wide dissemination of the research results to the academic community, practicing engineers, and appropriate building code committees.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.