Rajai Z. Al-Rousan

Influence of synthetic fibers on the shear behavior of lightweight concrete beams

Incorporating discontinuous structural synthetic fibers in general enhances the performance of concrete and increases its durability by minimizing its potential to cracking and providing crack arresting mechanism. Synthetic fibers are non-corrosive, alkali resistant, simple to apply, and added in small quantities due to their low density; thus, a substantial number of uniformly distributed fibers are added. In this research, an experimental program was undertaken to investigate the shear behavior of lightweight concrete beams containing discontinuous structural synthetic fibers. The studied parameters include fiber content and shear reinforcement. The tests were conducted under four-point loading in a simply supported span of 0.85 m. The beams were divided into three groups based on shear reinforcement. Group 1 was designed without shear reinforcement, Group 2 with closed vertical stirrups placed at d/4 spacing (where d is the effective depth), and Group 3 with closed vertical stirrups placed at d/2 spacing. Each group contains four identical specimens except in terms of the fiber content: 0, 3, 5, and 7 kg/m3 equivalent to fiber volume fractions of 0%, 0.33%, 0.55%, and 0.77%, respectively. The experimental results showed that the discontinuous structural synthetic fibers improve the ultimate shear strength, ductility, stiffness, and toughness of lightweight concrete beams significantly. Therefore, design codes are encouraged to consider their contribution to shear strength and revise the maximum stirrups spacing when discontinuous structural synthetic fibers are used. The results also showed that addition of discontinuous structural synthetic fibers reduces the crack width of lightweight reinforced concrete beams. The effectiveness of the discontinuous structural synthetic fibers decreases as the stirrups spacing decreases.

The effect of beam depth on the shear behavior of reinforced concrete beams externally strengthened with carbon fiber-reinforced polymer composites

The primary objective of this article is to study the effect of beam depth on the performance of shear-deficient beams externally strengthened with carbon fiber–reinforced polymer composites. The investigated parameters include overall behavior up to failure, the onset of the cracking, crack development, and ductility. The experimental results showed that externally bonded carbon fiber–reinforced polymer increased the shear capacity of the strengthened reinforced concrete beams significantly depending on the variables investigated. The use of carbon fiber–reinforced polymer composites is an effective technique to enhance the shear capacity of reinforced concrete beams. For the beams tested, as the depth of the reinforced concrete beams was increased from 225 to 450 mm which is equivalent to a/d ratio of 2.7–1.2, respectively, there was corresponding 15%–19% increase in contribution of the carbon fiber–reinforced polymer strips in terms of ultimate load. The impact of the beam depth is more pronounced on the ultimate load than the corresponding deflection of the control and strengthened beams. The results indicated that the beam depth has an influence on the angle at which primary cracking angle varied from 33, 44, 50, and 54 for beam of a/d of 2.7, 1.9, 1.5, and 1.2, respectively. If the shear crack crossed carbon fiber–reinforced polymer strips above its development length, the carbon fiber–reinforced polymer strips could not be expected to reach its ultimate strength and was thus only partially effective as observed in beams with different depths.

Modeling of Bond Stresses of Overlay-Bridge Deck System

This study investigated direct and indirect factors influencing the bond strength between the concrete overlay and the bridge deck by using finite element analysis (FEA) and experimental validation. In addition, it presents reliable guidelines for the required bond strength that is needed for concrete to avoid potential delamination under various possible induced stresses. The purpose of the FEA is to predict and correlate the live load– and shrinkage-induced stresses at the interface between the concrete overlay and the bridge deck and to correlate these induced stresses with the direct tensile bond strength of the overlay. Fifteen full-scale prototype bridge systems without and with various thicknesses of overlays were studied. In addition, 42 overlay–bridge deck slab segments were created considering the relative thickness ratio of the overlay to the bridge deck slab (toverlay/tslab) and the relative elastic modulus (Eoverlay/Eslab). Also, 210 overlay–bridge deck slab segments were created considering toverlay/tslab, Eoverlay/Eslab, and slab concrete compressive strength (f ‘ c ). The effectiveness and accuracy of the FEA guideline models were compared with Fowlers guidelines. The FEA results reveal that the live load– and shrinkage-induced shear stresses are about 1.5 to 2.5 times the induced normal stresses, in good agreement with most of the published research. Overlay thicknesses of 38 and 63 mm (1.5 and 2.5 in.) were recommended as the minimum and maximum allowable thicknesses that will prevent the overlay from debonding when the deck is subjected to AASHTO HS-20 truck loading plus impact as well as shrinkage loading.

Failure Analysis of Polypropylene Fiber Reinforced Concrete Two-Way Slabs Subjected to Static and Impact Load Induced by Free Falling Mass

The impact resistance of concrete is considered as poor due to a relatively energy dissipating characteristics and tensile strength. Therefore, this paper investigates the feasibility of using polypropylene fibers PF to enhance punching shear capacity of reinforced concrete RC two‐way slabs subjected to drop‐weight impacts. The evaluated parameters included two slab thickness 70 mm and 90 mm , five different PF per‐ centages 0%, 0.3%, 0.6%, 0.9%, and 1.2% , and two impact load height 1.2 m and 2.4 m . The tested slabs divided into three groups: not subjected to impact load, subjected to im‐ pact load at a height of 1.2 m, and subjected to impact load at a height of 2.4 m, resulting in a total of 25 slabs. The behavior of each two‐way RC slab was evaluated in terms of the crack patterns, ultimate punching shear capacity. The present ex‐ perimental data can be used for further assessment of the performance of PF reinforced concretes two‐way slabs as well as providing a well‐documented dataset related to the impact‐resistant applications which is presently limited within the literature. The results showed that adding the PF at a dosage of 0.3 to 1.2% by volume of concrete and increas‐ ing the slab thickness from 70 mm to 90 mm leads to consid‐ erable enhancement in the overall structural behavior of the slabs and their resistance to impact loading. Interestingly, the degradation in the ultimate punching capacity of the slabs subjected to impact load at a height of 1.2 and 2.4 m is 30.5% and 34.6%, respectively. Finally, an empirical model was pro‐ posed for predicting the punching shear capacity of RC two‐ way slabs based on reliable experimental results available in literature

Nonlinear finite element analysis of thermoplastic railroad bridge

Due to the environmental and financial benefits of thermoplastic materials as mentioned in literature and being a viable green solution, a nonlinear finite element analysis was conducted to study the behavior of thermoplastic materials of the No. 3 Fort Eustis railroad bridge using ABAQUS in terms of deflection, stress, and vertical forces at critical locations. Six models were simulated. These models were evaluated under GE 80-Ton switcher at 8 km/h (kph) speed and GP 16-120 Ton locomotives at speeds of 8, 24, 40, 56, and 80 kph. The models were validated against experimental results available in the literature. The models studied the effect of train speed on the deflection profile, flexural stress profile, vertical force profile, and stress profile along the bridge as well as the stress profile along the section. Based on the simulated models, it is clearly shown that the thermoplastic material has lower deflection and stress than wood; higher speeds resulted in lower stress and deflection. Based on this study, thermoplastic material can be considered as a good alternative because of its performance in terms of stress, vertical force, and corresponding deflection.

Effect of CFRP Schemes on the Flexural Behavior of RC Beams Modeled by Using a Nonlinear Finite-element Analysis

The main objective of this study was to assess the effect of the number and schemes of carbon-fiber-reinforced polymer (CFRP) sheets on the capacity of bending moment, the ultimate displacement, the ultimate tensile strain of CFRP, the yielding moment, concrete compression strain, and the energy absorption of RC beams and to provide useful relationships that can be effectively utilized to determine the required number of CFRP sheets for a necessary increase in the flexural strength of the beams without a major loss in their ductility. To accomplish this, various RC beams, identical in their geometric and reinforcement details and having different number and configurations of CFRP sheets, are modeled and analyzed using the ANSYS software and a nonlinear finite-element analysis.

Optimization of the economic practicability of fiber-reinforced polymer (FRP) cable-stayed bridge decks

This paper aims to find the optimum cable spacing and the optimum FRP deck stiffness in terms of vertical deformation. To achieve the objective of this study eighteen models are developed using ABAQUS; three different deck stiffness and six different cable spacing. Firstly, a non linear static finite-element analysis is performed on the models; then pre-tensioning forces are applied to cables, after that the shape modes for each model are presented. Secondly, a nonlinear dynamic analysis is performed on the models, the results obtained from the finite-element analysis are used in the optimization. The results show that for certain cable spacing the deflection decreased, and the cable stress increased as the deck stiffness increased. Furthermore, for certain deck stiffness, the cable stresses and the maximum deck deflection increased as the spacing between cables increased. Secondary, a relationship is performed to find the optimum cable spacing for each deck stiffness and optimum deck stiffness for each cable spacing. Finally, new twelve models are developed in order to study the effect of deck types (FRP, Concrete and steel) on the static and dynamic behavior. The results show that the using FRP deck instead of the concrete deck will lead to vertical deformation and cable stress less than the allowable proposed values by the design code because of the light weight of the FRP materials.