Behavior of monostrand anchors in unbonded post tension flat slab system

Generally, the monostrand anchor, which is made of cast iron and used in the global market, has a rectangular shape. It is commonly used when low concrete stresses are induced and minimum slab thickness is needed. Multiple monostrand anchors can be used adjacent to each other at one or more horizontal levels in slabs to replace a multistrand anchor system, which combines two or more strands in the same anchor. Monostrand anchor has a proper stress distribution, while the multistrand has greater overlap zone stresses in post tension slabs. An experimental study was conducted on round monostrand anchors to investigate anchorage and anchor bearing zones. Concrete blocks were prepared, and tested at different ages. The goal is to evaluate the contribution of the concrete's strength improvement against bursting pressure caused by jacking forces at the edge zone of a flat slab. The blocks were stressed using jacking machine. Strands with two diameter sizes (12.7 mm and 15.7 mm) were used. A rigid steel framework was developed as an abutment that can withstand all jack's response forces on the tested concrete blocks. On the other hand, this framework serves as a fixation for the cables' dead ends. The concrete blocks were attached to this framework. After that, they were stressed up to failure. Hairpin reinforcement were used to strengthen the blocks, and resist the applied stresses. Multiple round monostrands were also placed adjacent to each other to produce stress concentration in the concrete blocks. Numerical models were also constructed using finite element to simulate the experimental tests and validate the obtained results. The results were also compared to ACI provision.