• Steel and Composite Structures
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• v.13 no.4
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• pp.367-382
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• 2012

This paper is dedicated to the buckling behaviors of strengthened perforated plates under edge shear loading, which is a typical load pattern of steel plates in civil engineering, especially in plate and box girders. The square plates considered each has a centric circular hole and is simply supported on four edges in the out-of-plane direction. Three types of strengthening stiffeners named ringed stiffener (RS), flat stiffener (FSA and FSB) and strip stiffener (SSA, SSB and SSC) are mainly discussed. The finite element method (FEM) has been employed to analyse the elastic and elasto-plastic buckling behavior of unstrengthened and strengthened perforated plates. Results show that most of the strengthened perforated plates behave higher buckling strengths than the unstrengthened ones, while the enhancements in elastic buckling stress and elasto-plastic ultimate strength are closely related to stiffener types as well as plate geometric parameters including plate slenderness ratio and hole diameter to plate width ratio. The critical slenderness ratios of shear loaded strengthened perforated plates, which determine the practical buckling pattern (i.e., elastic or elasto-plastic buckling) of the plates, are also studied. Based on the contrastive analyses of strengthening efficiency considering the influence of stiffener consumption, the most efficient cutout-strengthening methods for shear loaded perforated square plates with different slenderness ratios and circular hole diameter to plate width ratios are preliminarily identified.

• Computers and Concrete
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• v.20 no.6
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• pp.719-729
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• 2017

A considerable research is available on the seismic response of Reinforced Concrete (RC) shear wall-frame buildings, but the studies on the reliability of such buildings, with the consideration of human error, are limited. In the present study, a detailed procedure for reliability assessment of RC shear wall-frame building subjected to earthquake loading against serviceability limit state is presented. Monte Carlo simulation was used for the reliability assessment. The procedure was implemented on a 10-story RC building to demonstrate that the shear walls improve the reliability substantially. The annual and life-time failure probabilities of the studied building were estimated by employing the information of the annual probability of earthquake occurrence and the design life of the building. A simple risk-based cost assessment procedure that relates both the structural life-time failure probability and the target reliability with the total cost of the building was then presented. The structural failure probability (i.e., the probability of exceeding the allowable drift) considering human errors was also studied. It was observed that human error in the estimation of total load and/or concrete strength changes the reliability sharply.

• Steel and Composite Structures
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• v.19 no.2
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• pp.417-439
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• 2015

Many methods are developed for strengthening of reinforced concrete structural members against the effects of shear. One of the commonly used methods in recent years is turned out to be bonding of fiber reinforced polymers (FRP). Impact loading is one of the important external effects on the reinforced concrete structural members during service period among the others. The determination of magnitude, the excitation time, deformations and stress due to impact loadings are complicated and rarely known. In recent year impact behavior of reinforced concrete members have been researched with experimental studies by using drop-weight method and numerical simulations are done by using finite element method. However the studies on the strengthening of structural members against impact loading are very seldom in the literature. For this reason, in this study impact behavior of shear deficient reinforced concrete beams that are strengthened with carbon fiber reinforced polymers (CFRP) strips are investigated experimentally. Compressive strength of concrete, CFRP strips spacing and impact velocities are taken as the variables in this experimental study. The acceleration due to impact loading is measured from the specimens, while velocities and displacements are calculated from these measured accelerations. RC beams are modeled with ANSYS software. Experimental result and simulations result are compared. Experimental result showed that impact behaviors of shear deficient RC beams are positively affected from the strengthening with CFRP strip. The decrease in the spacing of CFRP strips reduced the acceleration, velocity and displacement values measured from the test specimens.

• Journal of the Architectural Institute of Korea Structure & Construction
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• v.34 no.11
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• pp.19-26
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• 2018

This paper presents the shear strengthening effect of externally post-tensioning (EPT) method using high-strength steel rod in pre-cracked reinforced concrete (RC) beams. Three- and four-point bending tests were performed on a total of 8 specimens by adjusting the strengthening depths in the deviator position of EPT. The effective strengthening depths were 435, 535, and 610 mm. The pre-loading up to about 2/3 of ultimate load capacity measured in unstrengthened RC beam were applied in the beam to be post-tensioned. The EPT method was then applied to the pre-damaged RC beams and re-loading was added until the end of the test. EPT restored deflections of 3 mm or more, which account for about 40% of deflection when the pre-loading was applied. The shear strengthening increases more than 3 times and 36~107% in terms of the stiffness and load-carrying capacity compared to unstrengthening RC beams. The increased load-carrying capacities of the post-tensioned beam with strengthening depths of 435 and 535 mm are almost the same as 36~61%, and those of 610 mm are 84~107%, which shows the greatest shear strengthening effect.

• Geomechanics and Engineering
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• v.32 no.4
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• pp.411-426
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• 2023

Soft clay is widely distributed in the southeast coastal areas of China. Many large underground structures, such as subway stations and underground pipe corridors, are shallow buried in the soft clay foundation, so the dynamic characteristics of the soft clay must be considered to the seismic design of underground structures. In this paper, the dynamic characteristics of saturated soft clay in Shanghai under the bidirectional excitation for earthquake loading are studied by dynamic triaxial tests, comparing the backbone curve and hysteretic curve of the saturated soft clay under different confining pressures with those under different vibration frequencies. Considering the coupling effects of the confining pressure and the vibration frequency, a fitting model of the maximum dynamic shear modulus was proposed by the multiple linear regression method. The M-D model was used to fit the variations of the dynamic shear modulus ratio with the shear strain. Based on the Chen model and the Park model, the effects of the consolidation confining pressure and the vibration frequency on the damping ratio were studied. The results can provide a reference to the earthquake prevention and disaster reduction in soft clay area.

• Journal of the Korean Society for Nondestructive Testing
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• v.32 no.2
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• pp.122-130
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• 2012

Adhesive bend and shear tests of micro-sized bonded component have been performed to clarify the relationship between effects of heat-treatment on the adhesive strength and the bonded specimen shape using Weibull analysis. Multiple micro-sized SU-8 columns with four different diameters were fabricated on a Si substrate under the same fabrication condition. Heat-treatment can improve both of the adhesive bend and shear strength. The improvement rate of the adhesive shear strength is much larger than that of the adhesive bend strength, because the residual stress, which must change by heat-treatment, should effect more strongly on the shear loading. In case of bend type test, the adhesive bend strength in the smaller diameters (50 and $75\;{\mu}m$) widely vary, because the critical size of the natural defect (micro-crack) should vary more widely in the smaller diameters. In contrast, in case of shear type test, the adhesive shear strengths in each diameter of the columns little vary. This suggests that the size of the natural defects may not strongly influence on the adhesive shear strength. All the result suggests that both of the adhesive bend and shear strengths should be complicatedly affected by heat-treatment and the bonded columnar diameter.

• Steel and Composite Structures
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• v.35 no.2
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• pp.237-247
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• 2020

Shear connectors are essential elements in the design of steel-concrete composite systems. These connectors are utilized to prevent the occurrence of potential slips at the interface of steel and concrete. The two types of shear connectors which have been recently employed in construction projects are C- and L-shaped connectors. In the current study, the behavior of C and L-shaped angle shear connectors is investigated experimentally. For this purpose, eight push-out tests were composed and subjected to monotonic loading. The load-slip curves and failure modes have been determined. Also, the shear strength of the connectors has been compared with previously developed relationships. Two failure modes of shear connectors were observed: 1) concrete crushing-splitting and 2) shear connector fracture. It was found that the L-shaped connectors have less shear strength compared to C-shaped connectors, and decreasing the angle leg size increases the shear strength of the C-shaped connectors, but decreases the relative ductility and strength of L-shaped connectors.

• Computers and Concrete
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• v.8 no.2
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• pp.193-206
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• 2011

The use of Carbon Fiber Reinforced Polymers (CFRP) to strengthen reinforced concrete beams under bending and shear has gained rapid growth in recent years. The performance of shear strengthened beams with externally bonded CFRP laminate or fabric strips is raising many concerns when the beam is loaded under cyclic loading. Such concerns warrant experimental, analytical and numerical investigation of such beams under cyclic loading. To date, limited investigations have been carried out to address this concern. This paper presents a numerical investigation by developing a nonlinear finite element (FE) model to study the response of a cantilever reinforced concrete T-beam strengthened in shear with side bonded CFRP fabric strips and subjected to cyclic loading. A detailed 3D nonlinear finite element model that takes into account the orthotropic nature of the polymer's fibers is developed. In order to simulate the bond between the CFRP sheets and concrete, a layer having the material properties of the adhesive epoxy resin is introduced in the model as an interface between the CFRP sheets and concrete surface. Appropriate numerical modeling strategies were used and the response envelope and the load-displacement hysteresis loops of the FE model were compared with the experimental response at all stages of the cyclic loading. It is observed that the responses of the FE beam model are in good agreement with those of the experimental test. A parametric study was conducted using the validated FE model to investigate the effect of spacing between CFRP sheets, number of CFRP layers, and fiber orientation on the overall performance of the T-beam. It is concluded that successful FE modeling provides a practical and economical tool to investigate the behavior of such strengthened beams when subjected to cyclic loading.

• Geomechanics and Engineering
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• v.36 no.4
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• pp.317-328
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• 2024

Adopting a rational engineering methodology for building structures on sandy-clay soil layers has become increasingly important since it is crucial when structures erected on them often face seismic and cyclic wave loads. Such loads can cause a reduction in the stiffness, strength, and stability of the structure, particularly under un-drained conditions. Hence, this study aims to investigate how the dynamic properties of sand-clay mixtures are affected by loading frequency and clay content. Cyclic triaxial tests were performed on a total of 36 samples, comprising pure sand with a relative density of 60% and sand with varying percentages of clay. The tests were conducted under confining pressures of 50 and 100 kPa, and the samples' dynamic behavior was analyzed at loading frequencies of 0.1, 1, and 4 Hz. The findings indicate that an increase in confining pressure leads to greater inter-particle interaction and a reduced void ratio, which results in an increase in the soil's shear modulus. An increase in the shear strength and confinement of the samples led to a decrease in energy dissipation and damping ratio. Changes in loading frequency showed that as the frequency increased, the damping ratio decreased, and the strength of the samples increased. Increasing the loading frequency not only reflects changes in frequency but also reduces the relative permeability and enhances the resistance of samples. An analysis of the dynamic properties of sand and sand-clay mixtures indicates that the introduction of clay to a sand sample reduces the shear modulus and permeability properties.

• Journal of Korean Society of Steel Construction
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• v.27 no.1
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• pp.87-97
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• 2015

In this study, an experimental study was performed to evaluate the concrete breakout strength of cast-in-place(CIP) anchors in cracked concrete under static shear loading. The CIP anchors involved in this study were 30mm in diameter with an edge distance of 150mm and an embedment length of 240mm. The experiment was carried out for two specimens in uncracked concrete and three specimens in cracked concrete orthogonal and parallel to the direction of shear loading, respectively. Compared to the uncracked concrete specimen, cracked specimen orthogonal to the direction of shear loading showed no reduction in the concrete breakout strength and that parallel to the load direction about 91% strength which corresponds to 84% of uncracked concrete strength defined in ACI 318-11. Therefore, the experimental results showed smaller decrease in the shear resistance of CIP anchors in cracked concrete than that specified in ACI code which account for 71% strength of uncracked concrete in cracked concrete.