Reliability Assessment of the flexural Behavior of Reinforced Concrete Beam with embedded PVC Pipes
Beams are major structural elements in structures against flexural failure. Increasing the span of building, increases the risk of deflection leading to increase in structural member thickness. Structural elements failures, due to the presence of electrical wire installation, are minimized by conducting them through the hollow polyvinyl chloride (PVC) pipes. In the tensile zone below the neutral axis, some concrete and reinforcing steel are eliminated by the presence of PVC pipes; hence, paving way for effective materials utilization. Therefore, the aim of this study was to investigate the reliability of the flexural strength of reinforced concrete beam with embedded PVC pipes below the neutral axis by experiment and modelling using ANSYS Pro 15.0. The objectives were to: (i) determine the compressive strength of concrete cubes with and without embedded PVC pipes and their stress-strain relationship; (ii) investigate the flexural behaviour of the beams with and without PVC pipes and their relationship with compressive strength; and (iii) evaluate the reliability of the beam with and without PVC pipes using the First Order Reliability Method (FORM). Finite Element Method (FEM) was used and adopted for designing and modelling the beams (1000 x 150 x 150 mm) using a FORTRAN subroutine created and linked with the reliability software (FORM5). Experimental tests were carried out on conventional reinforced concrete beams with and without PVC pipes (diameter; 50 mm, density; 1.41g/cm3, thickness; 3 mm) below the neutral axis. Flexural strength tests were carried out using ASTM C 293 standard method. Stress, modulus of elasticity, peak and ultimate strain were measured and an improved analytical model was developed for the study of the flexural behaviour of reinforced concrete beams with and without PVC pipes using BioStat Pro and MS-Excel respectively. Finite Element Analysis and validation of experimental results of flexural strength were carried out using ANSYS Pro 15.0. The findings of the study were that: (i) average compressive strength of all the non-embedded PVC concrete increased with curing age and ranges between 2-14% higher than specimen with embedded PVC pipes; (ii) flexural modulus of rupture (MoR) for beams without embedded PVC pipes were higher than PVC beams by 2.9% with similar failure pattern; (iii) proposed models using regression analysis at 5% level of significance for all beam specimens were in close agreement (within the range of 98%) with experimental data; (iv) finite element modeling and simulation show close agreement (within the range of 96%) with experimental results for all the specimens when subjected to the same test conditions; and (v) reliability analysis using the first order reliability method (FORM) for PVC beams revealed a safety index, within the range (3.7 ≤ β ≤ 4.7) specified by ASTM C 293 with volume reduction between 6.1-9.9% compared to the non-embedded PVC beams. The study concluded that beams with embedded PVC pipes below the neutral axis are economical and reliable. Therefore, it is recommended for same application with the conventional beam since their capacities recorded by experiment are in agreement with theoretical and simulation values.