Development of prestressed clay brick masonry walls

Prestressed masonry walls offer various advantages over the current system of veneer construction which has been shown to have several problems. The cracking of masonry walls at service loads, and corrosion of wall ties due to water penetration can be effectively eliminated by the simple technique of post-tensioning. Prestress significantly compensates for the low tensile strength of masonry which is critical at service loads. A new concept of using prestressed masonry for veneer construction has been developed, and a simple yet practical technique of post-tensioning utilizing high strength threaded bars was successfully used in this research. This study included materials selection, analysis, design, and experimental testing of prestressed masonry wall panels. A total of fourteen panels of 3 x 6 ft were tested in the laboratory in two stages using newly developed two-cored brick units. The post-tensioned panels were tested for flexure to evaluate their capacity to resist out-of-plane loads. Stage I testing included six panels with three grouted and three ungrouted specimens. Results showed that the grouted specimens withstood approximately twice the capacity of the ungrouted specimens. In the Stage II testing, the prestressing force and the end bearing conditions of the panels were varied to investigate their effects. Also, the post-tensioning was applied at two different ages to investigate how early the prestress could be applied. Prestress loss study was conducted on eight 3 ft x 4 ft panels, where the stress in the prestressing steel and strain in masonry were continuously monitored for 187 days after construction. These panels were exposed to different weather conditions. This research study showed that the proposed post-tensioned veneer system is feasible. It can eliminate many of the problems associated with the conventional system of veneer construction, and the wall panels have an average factor of safety of 4.0 for cracking under service level wind loads. The results of the prestress loss study showed that moisture expansion of brick masonry significantly reduces the prestress losses in the reinforcing bars