The worldwide engineering community has identified failures of unreinforced masonry (URM) walls as one of the major causes of material damage and loss of human life during seismic events. The development of effective and affordable retrofitting techniques for masonry members is an urgent need. Fiber Reinforced Polymer (FRP) composites may provide attractive solutions for the strengthening of URM walls subjected to in-plane and out-of-plane loads resulting from high winds or earthquakes. Reinforced concrete (RC) or steel frames with infill URM walls are a common construction practice. Interaction of infill walls with the structural frame has often been neglected to simplify the design. Ignoring the contribution of the infill wall does not necessarily indicate a conservative design. Infill walls can greatly stiffen a flexible frame and significantly affect the horizontal load distribution to different structural members of the building. Strengthening of existing walls must account for this behavior.
The proposed project will focus on the study of the shear behavior of infill masonry walls strengthened with FRP bars and laminates. The former is a novel technique denominated FRP structural repointing. FRP structural repointing consists of inserting FRP bars into the masonry bed joints. The FRP bars can be embedded either in an epoxy-based paste or a cementitious paste. Preliminary tests on masonry specimens strengthened by this technique have shown promising results. In addition to increasing in-plane wall capacity, structural repointing is less intrusive than FRP laminates because the masonry aesthetics are preserved. Two series of walls will be tested. The first series, Series A, will assess the shear behavior of URM walls strengthened with FRP composites to determine the most efficient strengthening schemes in terms of structural performance. The walls belonging to Series A will be constructed with concrete masonry units (CMU). The specimens will be tested under in-plane cyclic loading. The test setup configuration will ensure the occurrence of shear failure. The most efficient strengthening schemes tested in Series A will be selected for the strengthening of the infill walls in Series B. This series will investigate the shear behavior of infill walls and their interaction with the surrounding structural RC frame. The infill walls will be surrounded by a RC frame and tested under in-plane cyclic loading. After failure due to in-plane loading, the specimen will be moved to a shake table where it will be subjected to out-of-plane acceleration to observe the out-of-plane stability of the wall. Analytical and numerical models will be developed to verify and understand the experimental findings using both complex and simple idealizations. The analytical results will be used to implement design protocols for the shear strengthening of URM infill walls to be used by practitioners.
This project will represent a milestone in the development of affordable and effective retrofitting techniques for existing infill walls. Within the constraints of funding and time, it will integrate the three phases of experimentation, analysis, and design to provide scientists and professionals with a clear snapshot of the advantages and characteristics of a highly promising new technology.
