Flexural Behaviour of Stay-In-Place PVC Encased Reinforced Concrete Walls with Various Panel Types
Scott, Benjamin Donald
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The use of stay-in-place (SIP) formwork has become an increasingly popular tool for concrete structures, providing advantages in construction scheduling and labour reduction. Stay-in-place formwork made of strong materials such as fibre reinforced polymer (FRP) and steel have proven to supplement and even replace reinforcement in concrete elements. The use of polyvinyl chloride (PVC) SIP formwork has also been explored. Current research suggests that PVC provides an enhancement to reinforced concrete strength and ductility. The research herein outlines tests on reinforced concrete walls with a compressive strength 25MPa, utilizing two types of PVC panels; flat or hollow, in order to further understand the polymer’s contribution to flexural resistance. The PVC forming system consisted of panels on the tension and compression faces with evenly spaced connectors securing the faces of the wall. Variables studied included concrete core thickness (152 mm, 178 mm, and 203 mm), reinforcing ratio (3-10M bars or 3-15M bars), and panel type (hollow or flat). The walls were tested in four point bending. The concrete control walls failed due to steel yielding followed by concrete crushing. The failure of the flat panel encased walls was dependent on the reinforcing ratio. Wall reinforced with 10M bars and encased with flat panels failed due to steel yielding followed by concrete crushing, PVC buckling, and PVC rupture while walls with 15M bars did not experience PVC rupture. Finally the failure for walls encased in hollow panels was due to steel yielding, followed by concrete crushing and PVC buckling. The hollow panel encased specimens also experienced slip of the panels on the tensile face. The PVC encasement enhanced the yield load, ultimate load, ductility, and toughness of the concrete walls. For flat panel encased walls, the average improvement at yield and ultimate loads were 21% and 27% respectively. Hollow panel encased walls recorded average yield and ultimate load improvements of 8% and 27% respectively. Flat panel encased walls improved ductility by an average of 71% and toughness by 122%. Hollow panel encased walls improved ductility by an average of 29% and toughness by 70%. Concrete cores were taken from the tested PVC encased specimens and compressive strength was found to be the same as the control walls. An analytical model was developed to estimate the yield and ultimate load of PVC encased concrete walls. Calculated yield loads were in good agreement with the experimental data, with an average error of 8% for the control walls and 6% for the PVC encased walls. In addition, calculated ultimate (peak) loads showed good correlation with the experimental data. The average error for the control, flat panel and hollow panel encased walls were 3%, 3% and 8% respectively. Calculated and experimental PVC tensile strain values were in good correlation at ultimate load conditions. The average error for the calculated PVC tensile strain was 21%. With the proposed model providing results in good agreement with the test data, other PVC encased wall cross-sections were explored. An “optimized” panel layout was proposed that utilized flat panels on the compression side of the wall and hollow panels on the tension side. This configuration of panels resulted in the greatest estimated improvement at both yield and ultimate load levels.