S.L. LISSEL, J. GILLILAND2, and N.G. SHRIVE
Department of Civil Engineering, University of Calgary, Canada
Stantec Consulting Ltd., Calgary, Canada
Two masonry diaphragm retaining walls were designed for construction on the University of Calgary campus. Each wall has been post-tensioned with carbon fibre reinforced polymer (CFRP) tendons. One wall is 7.5m long, 2.6m high with a 7.5m radius curve in plan, convex to the retained soil. The second wall is straight, is 3.0m long and 2.2m high. The CFRP tendons used have a manufacturer’s nominal strength of 102kN. As these are the first masonry diaphragm walls post-tensioned with CFRP tendons outside a laboratory, one objective in the design was to provide a wide margin of safety, and thus the effective, or sustained prestressing force should not exceed 60% of tendon capacity. Losses of 20% were assumed from creep of the masonry. CFRP does not relax at the proposed design load and the anchors are pre-set on the tendons, avoiding losses due to anchor set. The tendons are unbonded so guidance chairs were placed during construction to meet the requirements of theclauses expected in the next edition of the Canadian Masonry Design Code. The webs of the walls were designed to interlock with the flanges, rather than be tied using traditional connectors across a continuous vertical mortar joint. This imposed restrictions on the
spacing of the webs, and a centre-to-centre spacing of 500mm was selected, with one tendon per cavity. The shear strength of the interlocked (bonded) connection between web and flange has been shown to be much greater than in the tied case. Research has also 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 also used in the design. Lateral tension in the flanges was considered in the case of the curved wall. The design of the walls the foundation and capping beams will be summarised, together with a description of the construction sequence and monitoring programme.