Quick Repair of Damaged Infill Walls with Externally Bonded FRPU Composites: Shake Table Tests

The paper presents the results of research on a nearly full-scale, 1-story reinforced-concrete (RC) spatial frame structure with masonry infill walls tested on a shake table. The experiment was conducted in four phases to investigate the in-plane and out-of-plane responses of the infill walls of the specimen. The use of a digital image correlation (DIC) technique with noncommercial analysis system allowed the computation of principal strains for the infill. Two methods of infill-RC frame protection using polyurethane resin (PU) flexible joints (PUFJ) at the RC frame-infill connection and an external innovative fiber-reinforced PU (FRPU) repair system were considered in the research. The test results indicated that the in-plane and out-of-plane infill performance was enhanced under seismic excitations. The PUFJs at the interface of the frame and infill walls helped the infills to withstand dynamic excitation of high intensity with repairable damage. Furthermore, the externally applied glass FRPU repair system efficiently protected the damaged masonry infills against collapse under out-of-plane excitation while restoring a significant portion of their in-plane stiffness. The variable contributions of the RC frame and of the brick infills when protected with innovative joints are evaluated through three-dimensional finite-element models. Practical Applications: Externally bonded fiber-reinforced PU composite is prefabricated or constructed on-site repair and strengthening solution, consisting of strengthening fibers and flexible polyurethane matrix. It is capable of carrying high loads and high deformations simultaneously and allows for reducing of stress concentrations and redistributing them over large bonding area, what results in higher load capacity of the composite strengthening systems. This innovative composite solution is dedicated to structures made of brittle materials (concrete, masonry) located in seismic areas. Flexible polyurethane matrix allows working with even low-strength fibers and low-strength brittle substrates, introducing greater strength, ductility, and load-bearing capacity, making it safer in exploitation. This composite strengthening system was examined as emergency strengthening of infill walls damaged by vibrations on a shake table. Repeated seismic excitations of high intensity were unable to cause collapse of the infill walls protected by this innovative composite system, neither in in-plane nor in out-of-plane modes. The tested building specimen of natural scale, protected by the flexible composite system, survived many seismic excitations remaining in good structural shape. This paper presents results of dynamic tests, proving practical efficiency of the composite system examined in more dangerous conditions than are present during strong earthquakes.