This grant provides funding to design and execute a proof of concept for a practical and affordable system to repair or retrofit highly substandard confined masonry walls. This construction style is predominant in low-rise residential structures in developing areas around the world that are prone to seismic activity, and where poor design and construction practices are common. The proposed system consists of aluminum strips inserted into grooves and embedded in mortar along the bed joints, thereby providing horizontal reinforcement to enhance resilience. It enlists accessible, relatively inexpensive and durable materials as a strategy for rehabilitation, and to facilitate technology acceptance. The proof of concept will be based on laboratory tests of confined masonry wall specimens under in-plane loads, simulating no action, repair (after damage), and retrofit (prior to loading) scenarios. Design and construction of the specimens will reflect input gained from a visit in Haiti by the two PIs (an architect and a structural engineer). Resilience in terms of strength, deformability and damage mechanisms will be investigated analytically by studying the contribution of masonry, embedded reinforcement, reinforced concrete confinement, and interactions thereof.
Current design and construction practices often fail to acknowledge the economic and technological limitations found in developing areas. Through this research, information and experimental evidence will be gained to advance the knowledge and understanding of substandard practices specific to confined masonry, baseline performance of poorly designed and constructed confined masonry walls, and the potential of a rapid and affordable repair and retrofit technology whose deployment on a large scale is realistic. The proposed proof of concept is pursuant to the vision of shifting from the culture of aiding to that of enabling local practitioners to independently rehabilitate their constructed facilities, thereby also putting them in the condition to train future generations of practitioners.
Overview Confined masonry (CM), consisting of unreinforced masonry walls built first and then confined with cast-in-place reinforced concrete (RC) tie-columns and tie-beams, is the predominant construction style for low-rise residential structures in Haiti as well as in most developing areas around the world that are prone to seismic activity. No systematic knowledge and technology base has been developed on the repair and retrofit of highly substandard CM structures that combine poor materials, design and construction, as often encountered in developing areas. Still, in a context where the loss of life from earthquakes can be ten times higher than in developed areas, as witnessed after the January 12, 2010 earthquake in Haiti, the margin of improvement is important. The objective of this research project was to design and deliver a proof of concept for a practical and affordable repair and retrofit system for substandard CM. The system consists of aluminum strips inserted into grooves and embedded in mortar along the bed joints, thereby providing horizontal reinforcement to enhance resilience. The proposed technology enlists accessible, inexpensive and durable materials. The simple and yet unconventional installation operations associated with the proposed solution may prompt more care by unskilled and untrained workers. Current design and construction practices often fail to acknowledge the economic and technological limitations found in developing countries. Through the proposed project, information and experimental evidence will be gained that will advance the knowledge and understanding of substandard practices specific to CM construction and materials, baseline performance of substandard CM walls, and the potential of a rapid and affordable repair and retrofit technology whose deployment in developing areas on a large scale is realistic. The proposed proof of concept is pursuant to the vision of shifting from the culture of "aiding" to that of "enabling" local practitioners to independently rehabilitate their constructed facilities, thereby also putting them in the condition to train future generations of practitioners. Summary of conclusions 1) A conventional latex-modified cement mortar and a simple cement mortar were selected for the proposed retrofit/repair technique. Bond tests results showed that a simple cement mortar performs just as well for the case of the proposed anchorage detail. 2) Full-scale test results showed that the use of substandard materials and beam-to-column reinforcement detailing result in the shear failure of the wall immediately upon damage development in the joint, with little energy dissipation. In fact, the weak joint prevented the formation of an effective strut-and-tie confining mechanism, thereby reducing strength and deformability. Joint strengthening is thus necessary as a complement to any repair/retrofit. 3) The proposed repair/retrofit technology applied on a full-scale specimen with reasonable joint detailing and substandard materials resulted in the development of the confining mechanism, with an increase in average maximum strength and lateral displacement of 40% and 180%, respectively. 4) Together with contributing to strength and deformability, the proposed technology resulted in more stable post-hazard conditions. In fact, the aluminum reinforcing strips contribute to maintaining the masonry walls intact and reduce the risk of post-hazard collapses and falling of debris, which are often the culprits for a number of deaths and injuries. 5) Specific mechanics-based algorithms were identified that estimate the lateral strength, including the contribution of the horizontal reinforcement when used, with a minimum 10% accuracy. 6) The contribution to strength of the toothed masonry/RC column interface was not relevant in the cases examined, contrary to popular (and common-sense) belief. This interesting outcome will be further investigated leveraging the evidence from two additional full-scale specimens to be tested. Summary of open issues 1) The experimental results point to the key influence of substandard and standard joint reinforcement detailing. This issue will be further investigated leveraging the evidence from two additional full-scale specimens to be tested. In particular, one additional specimen with substandard detailing and substandard materials will be retrofitted, and will have its joints strengthened by means of easily installed U-shaped strips (again, made of aluminum); it is expected that the structural response will be similar to that of the retrofitted Type II wall tested. 2) The contribution to strength of the toothed masonry/RC column interface was not relevant in the cases examined, contrary to popular (and common-sense) belief. The basic reason is that the stress fields that develop in the structural system are not associated with sufficiently large interface stresses to produce the disengagement of the masonry when toothed edges are not used. This interesting outcome will be further investigated leveraging the evidence from two additional full-scale specimens to be tested.
