Design of carbon fibre reinforced polymer post-tensioned masonry diaphragm retaining walls

Two masonry diaphragm retaining walls were constructed on the University of Calgary campus and post-tensioned with carbon fibre reinforced polymer (CFRP) tendons. As these are the first masonry diaphragm walls post-tensioned with CFRP tendons outside of a laboratory, one objective in the design was to provide a wide margin of safety, especially concerning the effective, or sustained, prestressing force and losses. The tendons are unbonded, so guidance chairs were placed during construction to meet the requirements of the clauses expected in the next edition of the Canadian masonry design code. Research has shown that the strength of masonry to resist shear in the webs is enhanced by the normal stress induced by post-tensioning, so this was used in the design. The webs of the walls interlock with the flanges, imposing restrictions on the spacing of the webs. A centre-to-centre spacing of 500 mm was selected, with one tendon per cavity. The design of the walls and capping beams is detailed, and the construction sequence and monitoring program are described briefly.