Impact response and endurance of unreinforced masonry walls strengthened with cement-based composites

Abstract

Unreinforced Masonry (URM) walls are construction elements that have been found to resist in-plane forces, which proved beneficial for wind and earthquake resistant design. The out-of-plane resistance of URM walls, however, is very minimal, if any. Strengthening the walls in the out-of-plane direction is an ongoing research topic. This study aims at conducting laboratory experiments on the impact resistance of strengthened and unstrengthened URM walls. Impact tests are carried out to measure the failure resistance of structural members to suddenly applied load. The developed strengthening techniques consist of the application of fiber reinforcement cement-based composites using shotcrete technology. Two types of fibers are considered, polypropylene macro-fibers for FRC (Fiber Reinforced Concrete) and polyethylene micro-fibers for the ECC (Engineered Cementitious Composites). The FRC mixes were prepared with two dosage rates of polypropylene fibers (4.6 and 6 kg/m3) while the ECC, one dosage of polyethylene fibers (16 kg/m3) was used. A total of 12 URM walls were constructed with precast reinforced concrete frame and then infilled with hollow concrete blocks. The walls were strengthened and then tested under drop weight with a mass of 52 kg from a height of 3.8 m resulting in a kinetic energy of about 2000 J. Multiple drops were performed on each wall until failure. Test results revealed that the walls strengthened with the ECC Shotcrete (ECCS) endured ten drops, the largest number, without visible failure. The FRC Shotcrete (FRS) with 6 kg/m3 fibers ranked as the second-best strengthening technique; the FRS-6 walls endured more than six drops without major failure. In addition, the performance of each wall is evaluated in terms of endurance, impact force, energy absorption, flexural stiffness, and impact duration.