Date of Award

12-15-2014

Document Type

Open Access Dissertation

Department

Civil and Environmental Engineering

First Advisor

Fabio Matta

Abstract

Confined masonry (CM) is a construction system consisting of load-bearing masonry panels that are confined with cast-in-place reinforced concrete tie columns and beams. Due to satisfactory seismic performance, CM has become the predominant low-rise residential construction system in several areas around the world. However, in developing regions, the use of substandard materials, details and construction practices may result in inadequate performance as highlighted in the 2010 earthquakes in Haiti and Chile. In the aftermath of an earthquake, households are often reluctant to reoccupy their dwellings due to concerns about safety of structures. If feasible, preventive (pre-hazard) strengthening or structural repair (post-hazard), to complement to temporary sheltering, are realistic options to respond to the pressing need for shelter on a large scale, since reconstruction poses greater barriers of cost and time. However, there is little knowledge on whether strengthening and repair can realistically improve the seismic behavior of a CM dwelling structure, especially using context-sensitive techniques with locally available (and often relatively lowquality) materials. Addressing this knowledge gap is important to inform pre- as well as post-hazard planning and decision making for hazard mitigation and disaster recovery. The goal of this research is to contribute to filling this gap by investigating whether it is feasible to strengthen (pre-hazard) or repair (post-hazard) substandard CM walls using context-sensitive materials and practices, and make them safe, that is, offering a performance comparable to that of an undamaged counterpart built with acceptable-quality materials and seismic details. Supporting experimental evidence is based on in-plane cyclic tests on six fullscale CM wall specimens (including control, strengthened and repaired specimens) built with substandard materials (e.g., concrete with cylinder compressive strength in the range of 9 - 14 MPa) and seismic details (e.g., open stirrups with relatively large on-center spacing). The in-plane load-displacement envelopes of the strengthened and repaired specimens are compared with the theoretical envelope of a benchmark CM wall built with acceptable-quality materials (e.g., concrete with cylinder compressive strength of 26 MPa) and seismic details (e.g., closed stirrups with suitable on-center spacing). It is shown that the strengthened and repaired specimens exhibited comparable shear strength and ductility to those of “standard” walls. It is also shown that the shear strength of all walls tested can be conservatively predicted. Finally, the seismic performance of the wall specimens is assessed in accordance with the Mexico City Building Code (MCBC) Requirements for Design and Construction of Masonry Structures (NTCM 2004). This code was selected as an authoritative reference since masonry construction in Mexico is code-regulated since 1976 and the seismic provisions for masonry structures were developed from results of a comprehensive research program of over 20 years, and were updated after the 1985 Mexico City earthquake. It is shown that the strengthened and repaired specimens do satisfy all criteria to qualify as earthquake-resistant structures. It is concluded that it is feasible to strengthen or repair a substandard CM wall using context-sensitive materials and practices, such that both strength and ductility are comparable to or better than those of a CM wall built with acceptable-quality materials and details. In addition, this study offers a novel contribution for large-scale structural testing by demonstrating a three-dimensional digital image correlation method for the non-contacting full-field measurement and visualization of deformations, offering comparable accuracy to that of traditional contact-based and point-wise sensors. As presented in chapter 2, these results enabled an in-depth description of the load-resistance mechanisms and damage evolution in CM wall specimens. The measurement setup and procedure demonstrated herein can be applied to large-scale specimens to obtain radically more detailed information compared to traditional measurement methods for large-scale laboratory testing of civil engineering structures.

Rights

© 2014, Rahim Ghorbani

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