Performance of Steel Fiber Reinforced and Conventionally Reinforced Post-Tensioned Flat Plates

With the increasing need for commercial and residential buildings, post-tensioned (PT) flat plates have become a preferred choice for floor systems, because of the numerous advantages over non-prestressed slabs such as better efficiency, reduced slab self-weight, as well as crack and deflection control. To improve the competitive advantage of PT flat plates through improved economy and performance, a study was undertaken. This study investigated the performance and behavior of three one-third scale models of a nine-panel two-way unbonded post-tensioned flat plate. One of the slabs had conventional reinforcement with uniform-banded tendon layout, another had conventional reinforcement with banded-banded tendon layout while the last had banded-banded tendon layout reinforced with steel fiber. The specimens were loaded to service limit state, factored load and then to failure, using a whiffle tree loading system that approximated a uniformly distributed load. Experimental results were compared to analytical results from finite element and yield line analysis. The performance of the banded-banded specimens was very similar to the uniform-banded specimens at service and factored load. The failure loads for all specimens were considerably higher than the design factored load of 197 psf. Steel fiber was able to replace conventional reinforcement and the performance of the specimens with steel fibers was satisfactory, and comparable to their corresponding conventional reinforced specimens at service and factored limit state. Analytical results from finite element analysis showed a fairly reasonable agreement with experimental results. The results from the experimental tests showed that the use of steel fiber in post-tensioned flat plates is a viable and safe technology that will lead to improved performance and economy. The experimental results seem to indicate that the requirement of conventional reinforcement may be unnecessary in the negative moment regions and also in the positive moment region if the tensile stress is not more than 3√(f'c ) in this region. ACI 318-19 code design recommendations were provided for design of banded-banded PT system and SFRC post-tensioned flat plate. Additional testing should be conducted before SFRC post-tensioned flat plates are incorporated in the ACI 318 code (ACI 318, 2019) with a maximum allowable tensile stress of 6√(f'c). Doctor of Philosophy Over the years, the use of post-tensioned flat plates as flooring system has increased and became popular in residential and commercial buildings. Post-tensioned flat plates are a type of concrete structural slabs typically used for flooring in high-rise building because of the numerous advantages over non-prestressed slabs such as better efficiency, reduced slab self-weight, as well as smaller crack and deflection. This type of slab typically consists of high strength steel strands called tendons, which are stretched to compress the concrete slab in both directions. To improve the performance of this type of slabs a research study was performed. This study investigated the performance and behavior of three one-third scale models of a nine-panel two-way post-tensioned flat plate. One of the slabs was strengthened with conventional steel bars and the tendon layout was uniform-banded tendon, another had conventional steel bar with banded-banded tendon layout while the last had banded-banded tendon layout reinforced with steel fiber. Actual load that will act on the slab when in use was applied and then this load was increased by a factor as specified in the building code, before loading the slab to the point where it cannot carry any more load. Results from the load test were compared to results obtain from analytical software package. The performance of the specimens that had banded-banded tendon layout was very similar to the specimens that had uniform-banded tendon layout, at actual operational load when in use. The failure loads for all specimens were considerably higher than the load they were designed for. The results suggest that steel fiber is a good alternative to conventional steel bars. The results from the load tests suggest that steel fiber can be used to strengthen post-tensioned flat plates which will lead to better performance and reduced cost.