Flexural behavior of ungrouted post-tensioned concrete masonry and their application in soil retaining walls

Abstract

Since ancient times, masonry has been the basis of human civilization in every aspect related to the construction of houses, as a cornerstone of the great empires of the ancient world and is used by diverse cultures all around the world. However, their poor structural performance in supporting tensile stresses compared with other materials such as steel and reinforced concrete, has marginalized the use of masonry to small buildings and nonstructural elements. It is for this reason that it is necessary to implement new techniques that improve the structural performance of conventional masonry and thus make the best use of their multiple benefits in the construction of large engineering projects. One of the most often used techniques to counteract tensile stresses effects is post-tensioning, that consists of the inclusion of a pre-compression force which considerably enhances the structural behavior of masonry. Thus, this dissertation raised the need to study the structural behavior of ungrouted post-tensioned masonry in bending to use their comparative advantages in aspects which include labor, time, and building costs, as well as their future implementation in the construction of retaining walls. For establishing the flexural behavior on ungrouted post-tensioned masonry, a series of full scale laboratory tests were conducted on simple supported beams and cantilever walls subject to out-of-plane lateral loading. The test protocol established the importance of studying the effect in the variation of the main design parameters that control the bending behavior of post-tensioned masonry, including the initial prestress, masonry strength, and tendon eccentricity, among others. The results obtained show an adequate performance of this structural system under bending loads and its great versatility for use in the construction of retaining walls. One of the observations in the study was that the loaddeflection curve exhibits an approximately bilinear behavior in all conducted tests, and additionally there was a linear relationship between the tendon stress increase and maximum deflection, a premise that allowed a new methodology to estimate ultimate flexural capacity in ungrouted post-tensioned masonry to be established. It was also observed that some proposal expressions on main worldwide design codes in posttensioned masonry predict the ultimate load capacity of ungrouted masonry adequately. These results combined with the observations obtained from wall and beam construction during this doctoral thesis have allowed innovative ideas and new research areas to be developed. These ideas are expected to be developed in the short and medium term to allow applied research in this specific area to progress dynamically in the future.