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Coconut shell concrete beams containing coconut shell ash are a feasible alternative to traditional reinforced concrete beams in structural applications. Coconut shells in reinforced concrete beams are essential in earthquake-prone areas because of their ductility properties, which contribute to enhancing earthquake resistance. This research investigates the flexure, ductility, shear, and cracking behavior of reinforced concrete beams made from the incorporation of a minimum quantity of untreated coconut shell particles (CSP) at 5% substitution of coarse aggregate (CA) modified with coconut shell ash (CSA) at 10% substitution of Ordinary Portland cement (OPC). Two beams were evaluated for flexural, strain, ductility, and cracking behavior. In contrast, the other two were evaluated for flexural, shear, strain, ductility, and cracking behavior by repositioning the loading point to the distance of 200 mm close to the support. In comparison to control beams evaluated for flexural, shear, strain, ductility, and cracking behavior, the ductility ratio of concrete beams with 10% CSA and 5% CSP improved by 8.8%. The ductile improvement was observed with a 17.3% decrease in flexural load. The shear capacity of reinforced concrete beams with 10% CSA and 5% CSP improved compared to the reference literature in the study. Finally, it was discovered that combining 10% CSA and 5% CSP in reinforced concrete beams can improve ductility without significantly reducing ultimate failure load.

The behavior of concrete-filled uPVC tubular columns under axial compression loads were studied experimentally by testing columns prepared from five different concrete strength classes. Accordingly, the unconfined, concrete-filled uPVC tube with and without wire-mesh reinforced mortar cover and reinforced concrete columns were evaluated. The main variables considered in this study are concrete strength$$ ({f_{co}})$$, uPVC thickness to diameter ratio (2t/D) and aspect ratio (h/D). The effect of uPVC confinement on strength, ductility, energy absorption, and post-peak behavior was explored. Also, a model was developed to predict the peak strength. Results show that the uPVC confinement increased the strength, ductility, and energy absorption in between 1.28–2.35, 1.84–15.3, and 11–243 times the unconfined, respectively. The confinement performed well on increasing the strength, ductility, and energy absorption for lower concrete strength and higher 2t/D ratios. The post-peak behavior of the stress-strain curve was affected by 2t/D and h/D ratios; an abrupt drop in the stress-strain curve was observed in specimens with lower 2t/D and higher h/D ratio. For a given value of concrete strength $$({f_{co}})$$, tensile strength$$ \left({{f_y}} \right)$$, thickness (t), diameter (D), and height (h), the stress-strain model predicted the peak strength of axially loaded concrete-filled uPVC tube column with a mean absolute error of 2.7%.

There is always a need for more durable, ductile, and robust materials for buildings, bridges, and other infrastructure due to the drawbacks of existing construction materials. Some of the drawbacks are the corrosion of steel, the brittle failure of concrete, and the performance instabilities that are caused when exposed to different environments. Thus, an innovative system is required to improve the performance and retain the integrity of structures in a harsh environment. To alleviate the situation, Un-plasticized polyvinyl chloride (uPVC) tubes are used as a confining material and their performance was experimentally evaluated by testing uPVC confined equivalent cylinders. Accordingly, unconfined and uPVC confined equivalent concrete cylinders for five different concrete classes, four types of uPVC tube sizes, and the aspect ratios of two (h/D = 2) were prepared and tested under axial compression loads. The result shows that the uPVC confinement increased the strength, ductility factor, and energy absorption in between 1.28–2.35, 1.84–15.3, and 11–243 times the unconfined levels, respectively. The confinement performed well for lower concrete classes and higher thickness to diameter ratios (2t/D). The post-peak behavior of the stress-strain curve was affected by the 2t/D ratio and the absolute value of the slope decreased as the 2t/D ratio increased. Additionally, the uPVC tube has shown several advantages, such as acting as a permanent formwork, protecting the concrete from chemical attacks, preventing the segregation of concrete, preventing peeling, and taking off concrete cover, decreasing the cross-section, and resulting in lighter sections. The uPVC confinement provided a remarkable improvement on the strength, ductility, energy absorption, and post-peak behavior of concrete. Therefore, uPVC tubes can be used as confining material for bridge piers, piles, electric poles, and highway signboards, where the fire risk is very small, though additional research is required on fire resistance mechanisms, such as wire-mesh reinforced mortar cover.