The epoxy-concrete interface is a critical phase in a bonded system, such as FRP-bonded to a concrete structure. The effectiveness of this bond is generally affected by the presence of moisture at the interface. In this paper, a nanoscale adhesion mechanism of the epoxy-cement interface under moisture variations was studied using molecular dynamics (MD) modeling. The epoxy-cement interface was first modeled by representing calcium silicate hydrate (C–S–H), and diglycidyl ether of bisphenol-A (DGEBA) resin. The surface moisture was simulated by inserting different layers of water. In addition, the macroscopic pull-off adhesion test was performed to validate the MD findings, where the latter provided an explanation for the observed macroscopic behavior. The results indicated that the interatomic and intermolecular forces across the interface at dry and relatively low moist systems are mainly due to the van der Waals (vdW) interactions. However, at relatively higher moisture content, the electrostatic interaction becomes more significant, which is responsible for the degradation process in the adhesion energy. Further, the increase in the debonding work was mainly caused by an increase in the adhesion between the C–S–H and water molecules at the interface where the latter forms hydrogen bonds with the substrate (i.e., C–S–H).
The spiral reinforcement is a very common technique used for reinforcing columns in active seismic regions due to its high ductility and high ability of energy absorption. This paper presents a nonlinear finite element analysis of high-strength concrete confined with opposing circular spiral reinforcements. The results are compared with tested scaled concrete columns made with opposing spirals under monotonic axial loads. The developed model is used to investigate the effect of spiral spacing, γ (ratio of the core diameter to the whole cross section diameter) and compressive strength on behaviour of circular spiral reinforced concrete column confined with opposing spiral reinforcements. The results of the parametric study demonstrated that for the same spacing between spirals and same strength of concrete, increasing γ will result into increasing the failure load of the column. It is also concluded that the ductility of the studied columns is not affected by changing the value of γ.
Fine aggregate and cement have been partially replaced by 10% and 56% crumb rubber and class F-fly ash, respectively, in order to manufacture rubberized concrete interlocking bricks (RCIBs). The newly developed product has been used for masonry construction without the need for mortar (mortarless), and the experimental testing under compression load was investigated by Al-Fakih et al. Therefore, in line with that, this study carried out finite element (FE) analysis for experimental result validation of masonry walls and prisms made of RCIBs. ANSYS software was utilized to implement the FE analysis, and a plasticity detailed micro-modeling approach was adopted. Parametric studies were carried out on masonry prisms to investigate the effect of the slenderness ratio and the elastic modulus of grout on the prism behavior. The results found that the adopted FE model has the ability to predict the structural response, such as compressive strength, stiffness, and failure mechanism, of the interlocking masonry prisms with about a 90% agreement with the experimental results. Based on the parametric studies, the compressive strength for a 6-course prism is approximately 68% less than a 3-course prism and 60% less than a 5-course prism, which means that the slenderness ratio plays a vital role in the behavior of the RCIB masonry prism under the vertical compression load. Moreover, the results showed that the difference between FE and experimental results of the walls was less than 16%, indicating a good match. The findings also reported that masonry walls and prisms experienced higher ductility measured by the post-failure loading under compression. The finite element model can be used for further investigation of masonry systems built with rubberized concrete interlocking bricks.
This article aims to investigate the flexural behavior of strengthened corroded reinforced concrete (RC) beams using carbon fiber‐reinforced polymer (CFRP) laminates and using a hybrid system of CFRP laminates and ultrahigh‐performance concrete (UHPC) layers. A total of 15 RC beam specimens were prepared, out of which one specimen was uncorroded–unstrengthened, and 14 specimens were corroded using accelerated corrosion set up to cause a significant reduction in the load‐carrying capacity of the RC beams. The damaged covers of the corroded RC beam specimens were first repaired and then strengthened with different strengthening strategies involving CFRP laminates alone as well as the CFRP laminates and UHPC jacketing together. The experimental results obtained by testing the strengthened RC beam specimens in flexure showed a significant enhancement in the load‐carrying capacity and stiffness of the strengthened corroded RC beams. The number of CFRP laminates, hybridization of the CFRP laminates and UHPC layer, and the thickness of the UHPC layer all significantly improved the load‐carrying capacity and stiffness of the strengthened corroded RC beams indicating the possibility of selecting an optimal strategy out of different options for strengthening the corroded beams to achieve a targeted degree of the efficacy of the strengthening. The analytical model developed in this study to estimate the flexural capacity of the strengthened RC beams was found to predict the values of the load‐bearing capacity of the RC beams strengthened using different strategies very close to their respective experimental values.
The focus of this paper is to investigate the effect of column axial load levels on the performance of shear deficient reinforced concrete beam column joints (BCJs) under monotonic and cyclic loading. The problem of interaction between shear stress in BCJ and axial load on column has been addressed in this work by initially postulating a mechanistic model and substantiated by an experimental test program. This was achieved by conducting appropriate tests on seven BCJ sub-assemblies subjected to monotonic and reversed cyclic loading, with varying levels of the column axial load. Experimental results were further validated using a finite element model in an ABAQUS environment. The effect of variation of compressive strength of concrete was considered in a subsequent parametric study, in order to obtain sufficient data, and utilized to develop a new shear strength model for BCJs which includes influences of all the important parameters required to predict the shear strength of BCJs. The results showed that column axial load affects the seismic performance of BCJs significantly. Experimental results demonstrated that at initial stages of loading, increase in axial load enhances the shear capacity of the joint and reduces its ductility. However, when the column axial load/axial strength ratio increases to about 0.6–0.7, shear strength starts to decrease rapidly, leading to pure axial failure of the joint. The magnitude of axial load/axial capacity ratio also dictates the failure mode and development of crack patterns in BCJs. Results of reverse cyclic tests on BCJs showed that high value of axial load/axial capacity ratio increases the initial stiffness of BCJ but rate of stiffness degradation is accelerated after peak strength attenuation.
Many recently developed materials have proven their capability as retrofitting materials for different applications. These materials include carbon fiber-reinforced plastic (CFRP) and ultra-high-performance concrete with steel fiber reinforcement (UHPFRC). In this work, the influence of wrapping the UHPFRC cylinders with CFRP was investigated numerically. Different parameters were considered, including the grades of UHPFRC and configurations of CFRP. A 3D finite element model (FEM) of UHPFRC cylinders wrapped with CFRP under static loading was developed using nonlinear finite element software (ABAQUS). The model was first verified using the experimental results provided in the literature. After that, parametric studies were carried out to study the impact of grades of UHPFRC and the different confining CFRP schemes (fully and partially) on the overall behavior of strengthened cylindrical UHPFRC, as well as the impact of increasing the thickness of CFRP layers on the strength and ductility ratio of the confined specimens. The results indicated that using CFRP to warp the UHPFRC specimens significantly improved their strength and ductility. As expected, the use of CFRP to partially wrap specimens did not show a significant enhancement in the strength of the confined specimens when the CFRP layers were less than 60% of the height.
Unconfined compressive strength (UCS) of rocks, determined by loading the rock specimens along their longitudinal axis without lateral restraint, is one of
No abstract is provided for this article.
In the present research work, the effectiveness and the efficiency of a retrofitting approach using a layer of ultra-high performance fiber reinforced concrete (UHPFRC) jacket for damaged substandard exterior beam-column joints (BCJs) is experimentally investigated. The main objective of this study is to rehabilitate the already damaged BCJs to meet the serviceability requirements without compromising safety. According to the proposed strengthening technique, a chipped surface, lightly brushed with a dry condition was selected for making a successful bond between normal concrete substrate surface (NCSS) and UHPFRC. Then a fresh UHPFRC jacket with a thickness of 30 mm was cast around the damaged specimens. The entire test matrix was comprised of three 1/3 scale damaged exterior BCJs with a different column axial load (CAL). These specimens were repaired with UHPFRC and retested under monotonic loading. Based on the experimental results, repaired specimens showed an excellent performance in terms of their load-displacement response, maximum strength, displacement ductility, initial stiffness, secant stiffness and energy dissipation capacity when compared with the corresponding values registered when these specimens were tested in their virgin state. This rehabilitative intervention not only restored the strength, stiffness, ductility and energy dissipation capacity of severely damaged specimens but also improved their performance.
