Ductility Estimation of Concrete Beams Longitudinally Reinforced with Hybrid FRP-Steel Bars

An experimental study was carried out to evaluate the ductility of reinforced concrete beams longitudinally reinforced with hybrid FRP-Steel bars. The specimens were fourteen reinforced concrete beams with and without hybrid reinforcement. The test variables were bars position, the ratio of longitudinal reinforcement, and the type of FRP bars. The beams were loaded up to failure using a four-point bending test. The performance of the tested beams was observed using the load-deflection curve obtained from the test. Numerical analysis using the fiber element model was used to examine the growth of neutral axis depth due to the effect of test variables. The neutral axis curves were then used to further estimate the neutral axis angle and neutral axis displacement index. The test results show that the position of the reinforcement greatly influences the flexural behavior of the beam with hybrid reinforcement. It was observed from the test that the flexural capacity of beams with hybrid reinforcement is 4% to 50% higher than that of the beams with conventional steel bars depending on bars position and the ratio of longitudinal reinforcement. The ductility decreases as the hybrid reinforcement ratio (Af/As) increases. This study also showed that a numerical model developed can predict the flexural behavior of beams with hybrid reinforcement with reasonable accuracy.

Flexural behaviour of geopolymer concrete beams reinforced with BFRP and GFRP polymer composites

The paper presents the experimental investigations on the flexural behaviour of geopolymer concrete beams reinforced with Basalt Fibre Reinforced Polymer (BFRP)/Glass Fibre Reinforced Polymer (GFRP) rebars and the effect of inclusion of the new adhesively bonded BFRP/GFRP stirrups. M30 grade geopolymer and conventional concrete beams with the dimension of 100 × 160 × 1700 mm were cast to investigae the flexural behaviour of BFRP/GFRP and steel bars. This study also examined the mode of failure, deflection behaviour, curvature moment capacity, crack width, pattern, propagation, strains and average crack width of the BFRP/GFRP bars with stirrups in the geopolymer concretes using a four-point static bending test. The results were compared to that of conventional steel-reinforced concrete, and it was found that the Basalt and Glass reinforced polymer beams demonstrated premature failure and sudden shear failure. Further, the FRP bars exhibited higher mid-span deflection, crack width and crack propagation than steel bars. Crack spacing of the FRP bars decreased with an increase in the number of cracks. The correlation between the load and the deflection behaviour of the beams was determined using statistical analysis of multi variables regression.

Bond to Bar Reinforcement of PET-Modified Concrete Containing Natural or Recycled Coarse Aggregates

The use of post-consumer plastics in concrete production is an ideal alternative to dispose of such wastes while reducing the environmental impacts in terms of pollution and consumption of natural resources and energy. This paper investigates different approaches (i.e., reducing water-to-cement ratio and incorporating steel fibers or polymeric latexes) that compensate for the detrimental effect of waste plastics on the drop in concrete mechanical properties including the bond to embedded steel bars. The polyethylene terephthalate (PET) wastes used in this study were derived from plastic bottles that were shredded into small pieces and added during concrete batching at 1.5% to 4.5%, by total volume. Test results showed that the concrete properties are degraded with PET additions, given their lightweight nature and poor characteristic strength compared to aggregate particles. The threshold PET volumetric rates are 4.5% and 3% for concrete made using natural or recycled aggregates, respectively. The reduction of w/c from 0.55 to 0.46 proved efficient to refine the matrix porosity and reinstate the concrete performance. The incorporation of 0.8% steel fibers (by volume) or 15% polymers (by mixing water) were appropriate to enhance the bridging phenomena and reduce the propagation of cracks during the pullout loading of steel bars.

Deformation analysis of axially loaded weak PVC-fiber reinforced polymer confined concrete column-strong reinforced concrete beam joints reinforced with core steel tube

This paper presents an experimental study on 11 weak PVC-FRP Confined Concrete (PFCC) Column-strong Reinforced Concrete beam joints reinforced with Core Steel Tube (CST) subjected to axial load. The influences of the joint height, joint stirrup ratio, Carbon Fiber Reinforced Polymer (CFRP) strips spacing, steel ratio and CST length on the failure mode, ultimate strength, and strain behavior of specimens are analyzed and discussed. Test results indicate that the failure mode of specimens is distinguished by the cracking of PVC tube, fracture of CFRP strips, yielding of stirrups, and longitudinal steel bars in the PFCC columns. Both the longitudinal steel bars and CST yield at the joint area, while there is no obvious damage on the joint. The ultimate stress of specimens decreases with the increment of CFRP strips spacing, while the other studied variables have little impact on the ultimate stress. As the CFRP strips spacing increases, the ultimate strain of specimens decreases, and the strain development accelerates. Considering the effect of joint dimension, a modified prediction model for the stress–strain relationship of axially loaded weak PFCC column-strong RC beam joints reinforced with CST is proposed and verified with good accuracy.

Punching shear behaviour of geopolymer concrete two-way slabs reinforced by FRP bars under monotonic and cyclic loadings

This study examines the punching shear and deflection performance of 16 Geopolymer concrete (GC) two-way slabs subjected to monotonic and cyclic loading by considering the reinforcement material, percentage of reinforcement, type of concrete and the concrete grade. The tested specimens indicated that the crack patterns at the failure and failure modes were almost similar regardless of the type of reinforcement or their ratio. Moreover, the slabs reinforced by fibre-reinforced polymer (FRP) bars exhibited a lower punching capacity than those strengthened by steel bars, even for similar reinforcement ratios. In addition, the results showed that upon increasing the concrete strength and reinforcement ratio, a higher punching shear capacity and lower deflections were obtained under cyclic and monotonic loading. In addition, the punching shear performance of GC slabs was found to be better than that of ordinary concrete (OC), even though both were reinforced by the basalt FRP (BFRP) bar. However, the ultimate load capacity of the slabs was reduced as a result of cyclic loading according to the capacity of the same specimen, resulting from static loading. However, the reduction is very low for slabs reinforced with FRP slabs. Further, the slabs reinforced by FRP had a better fatigue performance compared with slabs reinforced by steel bars with respect to cyclic loading. The results of the tests were also used to evaluate the accuracy of the available punching shear capacity equations.