Rehabilitation of Hybrid RC-I Beams with Openings Using CFRP Sheets

This research presents an experimental investigation of the rehabilitation efficiency of the damaged hybrid reinforced concrete beams with openings in the shear region. The study investigates the difference in retrofitting ability of hybrid beams compared to traditional beams and the effect of two openings compared with one opening equalized to two holes in the area. Five RC beams classified into two groups, A and B, were primarily tested to full-failure under two-point loads. The first group (A) contained beams with normal weight concrete. The second group (hybrid) included beams with lightweight concrete for web and bottom flange, whereas the top flange was made from normal concrete. Two types of openings were considered in this study, rectangular, with dimensions of 100×200 mm, and two square openings with a side dimension of 100 mm. A full wrapping configuration system for the shear region (failure zone) was adopted in this research. Based on the test results, the repaired beams managed to recover their load carrying capacity, stiffness, and structural performance in different degrees. The normal concrete beam regains its total capacity for all types of openings, while the hybrid beams gain 84% of their strength. The strength of hybrid concrete members compared with normal concrete is 81 and 88% for beams of one opening and two openings, respectively. Doi: 10.28991/CEJ-2022-08-01-012 Full Text: PDF

Flexural Behavior of Reactive Powder Concrete with Hybrid Section T- Beams

Reactive powder concrete (RPC) is unique of the present and greatest significant improvements in constructions field, it has usual excessive kindness happening current duration in the world owing toward its higher concrete properties, great ductility, durability, shrinkage, great opposition to corrosion and abrasion. In this experimental investigation is carried out on the way to revision the RPC flexural activity with Hybrid Segment T- Beams and the mechanical characteristics of this building material. In order to analyze the belongings of steel fiber volumetric ratio, silica fume ratio, tensile steel ratio, hybrid section on RPC T-beam flexural efficiency, the experimental program included testing five beams. The study was focused on determining the load-deflection behavior, letdown mode, strain supply across the depth of the beams and crack pattern at failure. The results of the volumetric ratio of steel fibers and the silica fume ratio were also considered in studying the mechanical properties of RPC mixes. Moreover, a study of hybrid beams showed that use of RPC web and normal concrete in flange efficiently improves the performance of T-beams compared to normal concrete T-beams with a percentage rise of 12 percent and hybrid beams have also shown that the use of RPC flange and normal concrete in web efficiently improves the display of T-beams associated to regular concrete T-beams with percentages increase of 28%.

Influence of graphene fillers on vibration characteristics of tapered hybrid GFRP composite beams under elevated temperature condition: Numerical and experimental study

In this study, numerically and experimentally the dynamic characteristics of graphene-reinforced glass fiber–reinforced polymer hybrid uniform and thickness tapered laminated composite beams were investigated. First, the graphene-epoxy nanocomposite solution without and with 0.25, 0.50, and 0.75 wt.% of graphene reinforcement is prepared by the heat shearing technique and then used for the fabrication of glass fiber–reinforced polymer hybrid uniform and thickness tapered composite beams using the hand lay-up method. The elastic properties of the hybrid beams were evaluated using the impulse excitation of vibration technique (ASTM E1876-15) under elevated temperature. Further, the numerical and experimental modal analysis of the hybrid beams with uniform and tapered configurations were conducted with variation in wt.% of graphene particles under fixed-fixed and fixed–free end supports. The results reveal that the natural frequencies of the glass fiber–reinforced polymer hybrid uniform and tapered configurations with 0.25 wt.% of graphene are greater than those of the glass fiber–reinforced polymer beams without graphene reinforcement and observed lesser for 0.5 and 0.75 wt.% of graphene under fixed-fixed and fixed-free end supports, respectively, due to unavoidable agglomeration effects. Furthermore, the parametric study was performed with the influence of weight fraction of graphene and temperature on the transverse response of the tapered composite beam. Hence, it can be concluded that the use of graphene filler in the glass fiber–reinforced polymer composites in the tapered composite beams improves the bending natural frequencies significantly when the weight fraction of the graphene is used lesser as agglomeration is unavoidable in practical condition. Therefore, the comprehensive numerical and experimental work presented in this study will be useful to the designers while using graphene fillers to improve the bending characteristics of the tapered composite beams.

Load-Deflection Behavior of Over- and Under-Reinforced Concrete Beams with Hybrid FRP-Steel Reinforcements

The present study pertains to the load-deflection behavior and cracking moments of concrete beams with hybrid FRP-steel reinforcement. Under and over-reinforced hybrid beams were tested for failure along with reference beams with only steel or FRP reinforcement. The first-cracking moments of the beams were estimated analytically by using different uncracked moments of the inertia and modulus of rupture definitions. The uncracked moment of inertia definitions include the gross and uncracked transformed moments. The adopted modulus definitions are comprised of the experimental values from tests on prisms and the analytical values from the equations in different concrete codes. Furthermore, analytical methods were developed for estimating the deflections of concrete beams with hybrid FRP-steel or only FRP reinforcement. Two different types of elastic moduli, namely the secant modulus corresponding to the extreme compression fiber strain and the ACI 318M-19 modulus, were used in deflection calculations. Closer estimates were obtained by using the secant modulus, particularly in hybrid-reinforced beams. In the post-yielding region of the steel tension reinforcement, the deflection estimates were established to lay in closer proximity to the experimental curve when obtained by adding up the deflection increments instead of directly calculating the total deflections from the elastic curve equation. Accurate estimation of the cracking moment was found to be vital for the close prediction of deflections.

The Impact and Modelling of Concentrated Butt-Joints on Vertically Laminated Bamboo-Timber Hybrid Bio-Flitch Beams

This paper presents the experimental and analytical studies to investigate the impact of concentrated laminated bamboo butt-joints on the flexural properties of vertically laminated bamboo-timber hybrid beams (VLHBs, or flitch beam). The experimental results reveal that the concentrated butt-joints significantly reduce the flexural strength of the VLHB. They also suggest that the failure mechanism of the VLHBs with or without concentrated butt-joints are completely different. In addition, laminated bamboo lumber with concentrated butt-joints was found to be unsuitable for structural applications. The analytical estimations show close agreement with the experimental results. However, due to the layout of the sample VLHB, the experimental study cannot confirm the impact of the butt-joints on the modulus of elasticity in bending.

Behavior of Hybrid CFRP Laminated Thin-Walled Beams: Experimental, Numerical, and Analytical Evaluations

The aim of this paper is to assess the structural behavior of hybrid thin-walled beams which were fabricated using laminated carbon fiber reinforced polymer (CFRP). Seven hybrid (CFRP) I-beams were fabricated, instrumented, then have been tested under monotonic four-point loading in order to evaluate their behavior up to failure. In constructing the I-beam specimens which were evaluated in this study, plywood core was implemented on both the web and flanges. Several important parameters were conducted in this study considering changing both of the ply orientations and stacking sequences of laminated fibers, also changing the shear span-to-depth ratio (a/d) of the specimens. The experimental results showed that stacking sequence is the most significant parameter that influences both flexural strength and stiffness of the hybrid beams. Also, the experimental results promoted the effectiveness of the core material for enhancing the flexure (bending) stiffness of beams. Then, these results were compared with a previous simulated study which used the finite element modeling to model the beams. Also, in order to evaluate the efficiency of the CRFP beams, the results were compared to similar steel beams having the same dimensions of the CFRP beams. As compared to steel beams, the load carrying capacity of the laminated beams is being high compared with steel beams when taking into consideration their specific strength ratio.