Study of Concrete Filled UPVC Tubes as Column under Axial Loading

Statement of the problem. This article aims to examine the behavior of UPVC bounded columns reinforced with polypropylene fibers under axial compression. Results. To develop this model, a number of samples of concrete filled UPVC pipe (CFUT) with different geometric properties were tested. To obtain the specimens, different material volume levels were used to investigate the sensitivity of these columns to various parameters. 3, 4 and 5 class pipes with 160-, 200- and 225-mm diameters and 800 mm length with 0.6, 0.8 and 1.0 MPa nominal/working pressure were taken and M30 and M40 grades of concrete were to fill the tubes. The effect of each variable on the ultimate strength, ductility and confinement efficiency of the samples was investigated. All the specimens were compressed by applying load only to the concrete core to obtain the load-displacement variations and the corresponding deformation mode. All the specimens failed with the development of shear cracks and slightly bulging macrocracks. Conclusions. A finite element model was developed using the proposed stress-strain variation of confined concrete with UPVC tubes to simulate axial compression of CFUT specimens. According to the results obtained, the effect of the change in the diameter-thickness ratio failure stress of concrete limited by (D/t) is obtained and discussed with an empirical relationship. Polypropylene fibers were found to slightly increase the column strength up to a certain volume fraction, after which the strength generally expe-rienced a decrease.