Strengthening of Masonry with Concrete Slab Using Spring Box and Heat Stretched Post-Tensioning Bars

Abstract eng:
Non-engineered masonry houses constitute a major portion of the building stock in developing countries. Although masonry houses have major walls resisting lateral earthquake forces, the unreinforced nature and commonly weak inter-bonding and material properties of these walls make them vulnerable to earthquakes. A simple yet effective and economical strengthening technique was investigated for the seismic strengthening of masonry houses which have reinforced concrete decks. Placement of vertical post-tensioning bars between the floor and ceiling provided increase in strength multiple times the original capacity and improved behavior of masonry walls. A special spring box system was developed to maintain the major portion of the post-tensioning force in vertical tendons although almost all of the post-tensioning force is lost with the conventional systems as the walls pass their cracking capacity and move into nonlinear range. A heat stretching technique was developed to further reduce the application cost by eliminating complicated hydraulic based stretching tools or intermediate systems such as turnbuckle or bolted connections. A number of loading tests were conducted on ½ scale 6m long laboratory specimens to obtain level of improvement by comparing measured results. The findings indicate that rebar based post-tensioning is a very cost-efficient, effective, and simple way for strengthening against earthquakes for non-engineered masonry houses that have concrete slab or upper wall (spandrel) beams.

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