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Durability of concrete structure is a critical issue especially in severe environment when the concrete structure is exposed to sulfate attack, such as shorelines. nanoSilica is high pozzolanic material which is used recently in concrete to improve its mechanical properties. However, the durability of concrete against sulfate attack containing nanoSilica (NS) has not been investigated completely. In this study, the effects of NS has been studied on compressive strength, sulfate attack and morphology characteristics. The results show that increasing of compressive strength in specimens with NS is significant in early ages. Resistance of concrete specimen against sulfate attack was measured in 5% sodium sulfate solution for expansion of prime specimens. After a period of 180 days the samples containing zero, 2, 4, 6 and 8% NS lost 3.51%, 2.4%, 2.23%, 1.13% and 1% of their weights compared to the initial weights, respectively. The results indicate that the concrete samples containing 8% NS show best performance in terms of resistance against sulfate attack.

This paper investigates the buckling and free vibration analysis of functionally graded carbon nanotube-reinforced composite thick rectangular nanoplates resting on a Kerr foundation under different boundary conditions. Quasi-three-dimensional hyperbolic shear deformation theory is employed to study the effects of transverse shear deformation and thickness stretching. To capture the small-size effects of nanoscale dimensions, the nonlocal strain gradient theory is used, which includes nonlocal parameters and length scale of the material. In this study, rectangular nanocomposite plates are reinforced by carbon nanotubes which are assumed to be graded through the thickness direction with four types of distributions, namely, uniformly, FG-O, FG-V, and FG-X. The governing equations and boundary conditions are extracted within Hamilton’s principle. They are discretized and numerically solved by utilizing a generalized differential quadrature method. The critical buckling loads and natural frequencies are determined by solving the eigenvalue problem. The accuracy of present results is validated with those available in the literature. Also, the effect of various factors, such as aspect ratio, length-to-thickness ratio, in-plane loading factor, length scale parameter, nonlocal parameter, volume fraction and dispersion profile of carbon nanotubes, elastic foundation coefficients, and different boundary conditions, on the buckling behavior and free vibration of nanoplates is investigated.

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This paper proposes a new beam to column connection which has slit dampers to increase ductility and moment capacity of structures. After Northridge and Kobe earthquakes, many researchers have tried to achieve more ductile connections. Ductility of connections causes to dissipate more energy before failure of connections. Also, some researchers have tried to find methods that plastic hinge occurs out of the beam to column connection zone. The proposed detail connects beam to column by two I-shape slit dampers. One experimental specimen of the proposed connection was tested under cyclic loading. Based on the experimental results, the connection has high seismic performance and rotational capacity more than 0.04 radians. Also, the slit damper connection has more moment capacity than other common connections and indicates a good hysteretic behavior. Experimental observations showed that no cracks and fractures occurred in welds and high energy absorption of the slit dampers prevented damages of other parts. Also, local buckling didn't occur on the flanges and web of the beam. The column and beam remain in elastic state. Some numerical models were made in ABAQUS software. Analysis results had good agreement with experimental results and showed high energy dissipation and ductility in the proposed connection.

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This article examines the application of simplified Mindlin’s strain gradient theory to free vibration analysis of functionally graded carbon nanotube–reinforced composite (FG-CNTRC) thick rectangular nanoplates resting on Kerr elastic foundation in thermal environment. The theory contains only one length scale parameter corresponding to strain gradient effects. Also, a quasi-3D hyperbolic theory considering transverse shear deformation and thickness stretching effects is employed to present the formulation. In this study, properties of the carbon nanotubes (CNTs) and the polymeric matrix are assumed to be temperature dependent. Distribution of CNTs across the thickness of the nanoplate is considered to be uniform (UD) or functionally graded (FG-X, FG-V, and FG-O). According to Hamilton’s principle and the generalized differential quadrature method, the governing equations and associated boundary conditions are obtained and discretized, respectively. The natural frequencies of FG-CNTRC nanoplates are determined by solving eigenvalue problem. The numerical results of the present formulation are compared with those available in the literature to explain the accuracy of the suggested theories. Then, parametric studies are presented to examine the effects of elastic foundation coefficients, size parameter, temperature change, volume fraction and dispersion profile of CNTs, aspect ratio, length-to-thickness ratio, and different boundary conditions on vibration behavior of FG-CNTRC nanoplates. The results confirmed that size parameter and changes in temperature play an important role in determining natural frequencies. In addition, the shear layer parameter of Kerr foundation has more influence with respect to the coefficients of the upper and lower layers.

FRP rods as lightweight materials with extraordinary properties of high strength to weight ratio, corrosion resistance, potentially high overall durability, tailor ability and high specific attributes are one of the most favorable materials to strengthen existing reinforced structures. The present study aimed to identify the behavior of reinforced concrete flexural beams strengthened with fiber reinforced polymer (FRP) rods through near surface mounted method (NSM). The results of the current study were based on nonlinear finite element software ABAQUS which can accurately simulate the experimental investigations on flexural behavior of reinforced concrete beams strengthened with NSM FRP rods. Validation of the proposed model was confirmed first by making a comparison with the experimental study presented in the literature. A parametric analysis was conducted on validated specimens to investigate the effect of FRP rod diameters, rod arrangements, FRP materials, as well as rods groove intervals on flexural behavior of strengthened reinforced beams. The numerical results of mid-span bending moment deflection, ultimate bending moment, failure deflection and ductility index were reported. For the sake of simplicity to be used by engineers, the results of the current study were drawn in the form of design charts and tables.