• Structural Engineering and Mechanics
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• 제67권4호
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• pp.347-358
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• 2018

The main aim of this research was to investigate the shear strength of non-prismatic steel fiber reinforced concrete beams under monotonic loading considering different parameters. Experimental program included tests on fifteen non-prismatic reinforced concrete beams divided into three groups. For the first and the second groups, different parameters were taken into consideration which are: steel fibers content, shear span to minimum depth ratio ($a/d_{min}$) and tapering angle (${\alpha}$). The third group was designed mainly to optimize the geometry of the non-prismatic concrete beams with the same concrete volume while the steel fiber ratio and the shear span were left constant in this group. The presence of steel fibers in concrete led to an increase in the load-carrying capacity in a range of 10.25%-103%. Also, the energy absorption capacity was increased due to the addition of steel fibers in a range of 18.17%-993.18% and the failure mode was changed from brittle to ductile. Tapering angle had a clear effect on the shear strength of test specimens. The increase in tapering angle from ($7^{\circ}$) to ($12^{\circ}$) caused an increase in the ultimate shear capacity for the test specimens. The maximum increase in ultimate load was 45.49%. The addition of steel fibers had a significant impact on the post-cracking behavior of the test specimens. Empirical equation for shear strength prediction at cracking limit state was proposed. The predicted cracking shear strength was in good agreement with the experimental findings.

• Computers and Concrete
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• 제34권1호
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• pp.1-14
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• 2024

The design of disturbed regions in reinforced concrete structures usually applies the well known Strut and Tie Method (STM). As an alternative, the Stringer-Panel Method (SPM), an intermediate model between STM and the Finite Element Method (FEM), consists in dividing a structure into two distinct elements: the stringers (which carry axial forces) and panels (which carry shear forces). SPM has already showed good applicability in manual calculations and computer implementations, and its most known application was SPanCAD, an AutoCAD plugin for linear and nonlinear analysis by SPM. Unfortunately, SPanCAD was discontinued by the developers, and it's not compatible with the most recent versions of AutoCAD. So, this paper aims to present a computer program that was developed as an upgrade to the latter: the Stringer Panel Modelling Tool (SPMTool), which is intended to be an auxiliary design tool and it presents improvements, in comparison to SPanCAD. It is possible to execute linear and nonlinear analysis by three distinct formulations: Modified Compression Field Theory (MCFT), Disturbed Stress Field Model (DSFM) and Softened Membrane Model (SMM). The nonlinear results were compared to experimental data of reinforced concrete elements that were not designed by SPM; these elements were also analyzed in SPanCAD. On overall, SPMTool made more realistic predictions to the behavior of the analyzed structures than SPanCAD. Except for DSFM predictions for corbels (1.24), in overall average, the ultimate load predictions were conservative (0.85 to 0.98), which is a good aspect for a design tool. On the other hand, the cracking load predictions presented overestimations (1.06 to 1.47) and higher variations (25.59% to 34.25%) and the post-cracking behavior could not be accurately predicted; for this use case, a more robust finite element software is recommended.

• Computers and Concrete
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• 제28권6호
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• pp.549-557
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• 2021

Nowadays, strengthening of buildings is an inclusive and effective field in civil engineering that is not only applicable to the buildings but also it can be developed for the bridges. Rehabilitation and strengthening of structures are highly recommended for the existing structures due to the alter in codes and provisions as well as buildings' use change. Extensive surveys have been conducted in this field in the world that propose wide variety of methods for strengthening of structures. In recent years, more specific researches have been carried out that present novel materials for rehabilitation beside proposing methods and performing techniques. In the current study, a novel technique for developing the bending capacity of reinforced concrete beams to enhance their performance as well as rehabilitating and reforming the performance of reinforced concrete beams with nonstandard lap splices, has been proposed. In this method, a post-tensioned concrete layer is added to the side face of the concrete beams built in 1:1 scale. Results reveals that addition of the post-tensioned layer enhances the beams' performance and covers their weaknesses. In this method, 18 reinforced concrete beams were prepared for the bending test which were subjected to the four-point pushover test after they were reinforced. The testing process ended when the samples reached complete failure status. Results show that the performance and flexural capacity of reinforced beams without lap splice is improved 22.7% compared to the samples without the post-tensioned layer, while it is enhanced up to at least 80% compared to the reinforced beams with nonstandard lap splice. Furthermore, the location of plastic hinges formation was transformed from the beam's mid-span to the 1/3 of span's end and the beam's cracking pattern was significantly improved.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2010년도 춘계 학술대회 제22권1호
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• pp.75-76
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• 2010

고성능 철근으로 휨 보강된 이방향 슬래브를 제작하고 펀칭 전단실험을 실시하였다. 휨철근의 항복강도, 휨 철근비 및 기둥 인접부 휨철근의 집중배근을 변수로 하여 실험하였고, 펀칭 전단강도, 균열후 강성, 변형률 분포, 균열제어 효과 등을 비교, 분석하였다.

• 한국구조물진단유지관리공학회 논문집
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• 제1권2호
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• pp.151-156
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• 1997

An experimental study was performed on the pull-out behavior of 90-deg standard hooks from exterior beam-column connections. The effects of the number of hooked bars of joint area were investigated. Under the pull-out action of hooked bars, the damage and cracking of joint area tends to be more extensive as the number of hooks pulling out from a joint increases. The pull-out strength and post-peak ductility of hooked bar are adversely influenced by the increase in number of hooks pulling out from an exterior joint. Current hooked bar anchorage design guidelines may be improved by considering the effect of the number of hooked bars on anchorage conditions at exterior joints.

• Structural Engineering and Mechanics
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• 제41권4호
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• pp.441-458
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• 2012

The shear strength is an important factor in the design of prestressed concrete beams. Therefore, researchers have utilized various methods to determine the shear strength of these elements for the design purposes. To evaluate some of the proposed theoretical methods, numerous models of post-tensioned beams with or without vertical prestressing are selected and analyzed using the finite element method and assuming nonlinear behavior for the materials. In this regard the validity of modeling is evaluated based on some tests results. In the second part of the study two beam specimens are built and tested and their load-deformation curve and cracking pattern are studied. The analytical results consist of compressive strut slope and mid span load deflection are compared with some experimental results, and the results of some codes' formulas. Finally comparing the results of nonlinear analysis with the experimental values, a new formula is proposed for determining strut slopes in prestressed concrete beams.

• Advances in concrete construction
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• 제14권5호
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• pp.299-307
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• 2022

Cement-based matrixes have low tensile strength and negligible ductility. Adding fibres to these matrixes will improve their mechanical properties and make these composites suitable for structural applications. Post-cracking tensile strength of steel fibers-reinforced cementitious composite materials is directly related to the number of transverse fibers passing through the crack width and the pulling-out behavior of each of the fibers. Therefore, the exact recognition of the pullout behavior of single fibers is necessary to understand the uniaxial tensile and bending behavior of steel fiber-reinforced concrete. In this paper, an experimental study has been carried out on the pullout behavior of 3D (steel fibers with totally two hooks at both ends), 4D (steel fibers with a total of four hooks at both ends), and 5D (steel fibers with totally six hooks at both ends) in which the fibers have been located either perpendicular to the crack width or in an inclined manner. The pullout behavior of the mentioned steel fibers at an inclination angle of 0, 15, 30, 45, and 60 degrees and with embedded lengths of 10, 15, 20, 25, and 30 millimetres is studied in order to explore the simultaneous effect of the inclination angle of the fibers relative to the alongside loading and the embedded length of fibers on the pullout response in each case, including the maximal pullout force, the slip of the maximum point of pullout force, pullout energy, fiber rupture, and concrete matrix spalling. The results showed that the maximum pullout energy in 3D, 4D, and 5D steel fibers with different embedded lengths occurs at 0 to 30° inclination angles. In 5D fibers, maximum pullout energy occurs at a 30° angle with a 25 mm embedded length.

• 콘크리트학회논문집
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• 제29권1호
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• pp.53-64
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• 2017

강섬유 보강 초고성능 콘크리트(UHPFRC)는 높은 압축강도 뿐 아니라 강섬유 보강에 의한 뛰어난 응력분산효과로 인해 높은 인장강도를 가지며, 미세균열의 확장을 통해 균열 후에도 경화거동을 하여 구조부재가 안정적으로 외력에 저항하도록 한다. 본 연구에서는 UHPFRC 재료 인장강도를 정의함에 있어 노치가 있는 휨실험과 직접인장실험을 비교하여 실험법 및 결과 분석의 장단점을 알아보았다. I-형 보의 전단부재실험은 복부의 면내전단거동을 알아보기 위하여 전단 경간비, 유효높이, 재료인장강도를 변수로 계획하였다. 실험결과를 통해 전단보강근이 없는 UHPFRC I형 보의 균열발생 이후 전단거동의 응력 재분배효과를 정량적으로 판단하고, 균열 후 거동을 기존 전단 강도식이 잘 반영하고 있는지 검토하였다. 전단철근 보강이 없는 UHPFRC 전단부재의 경우 파괴모드는 사인장 파괴로 동일하였고, 이러한 파괴모드를 가지는 부재는 전단 경간비와 유효높이에 크게 영향을 받게 되어 부재 설계 시 이러한 변수에 대한 고려가 필요한 것으로 나타났다.

• 콘크리트학회논문집
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• 제23권2호
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• pp.235-244
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• 2011

세그멘탈 교량의 파괴는 부적절한 접합에 의해 파괴를 일으키게 되는데 이는 세그멘탈 접합부를 가로지르는 횡방향 텐던의 부식을 야기하게 된다. 이 연구에서는 현장 타설 접합 및 에폭시 접합 조건에 따른 초고성능 프리캐스트 콘크리트 접합부에서의 전단키 거동을 전단 및 극한거동 측면에서 평가하였다. 또한, PC 세그멘탈 교량 접합부의 전단 거동을 파악하기 위하여 전단키 접합부의 전단 거동과 전단강도 특성을 실험적으로 연구하였다. 이 연구를 통하여 접합부 형상에 따른 하중-변위 관계, 균열 거동, 파괴 모드, 전단 강도 등을 구명하고, 접합부의 역학적 거동에 영향을 미치는 여러 인자들에 대해 분석한다. 또한 이로부터 최적의 접합부 형상을 도출하고, 이에 따른 최적의 접합 방식을 검토함으로서 접합부 설계의 지침과 해석의 근거를 제시하도록 한다.

• Geomechanics and Engineering
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• 제17권4호
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• pp.333-342
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• 2019

Geological dynamic hazards during coal mining can be caused by the failure of a composite system consisting of roof rock and coal layers, subject to different loading rates due to different advancing velocities in the working face. In this paper, the uniaxial compression test simulations on the composite rock-coal layers were performed using $PFC^{2D}$ software and especially the effects of loading rate on the stress-strain behavior, strength characteristics and crack nucleation, propagation and coalescence in a composite layer were analyzed. In addition, considering the composite layer, the mechanisms for the advanced bore decompression in coal to prevent the geological dynamic hazards at a rapid advancing velocity of working face were explored. The uniaxial compressive strength and peak strain are found to increase with the increase of loading rate. After post-peak point, the stress-strain curve shows a steep stepped drop at a low loading rate, while the stress-strain curve exhibits a slowly progressive decrease at a high loading rate. The cracking mainly occurs within coal, and no apparent cracking is observed for rock. While at a high loading rate, the rock near the bedding plane is damaged by rapid crack propagation in coal. The cracking pattern is not a single shear zone, but exhibits as two simultaneously propagating shear zones in a "X" shape. Following this, the coal breaks into many pieces and the fragment size and number increase with loading rate. Whereas a low loading rate promotes the development of tensile crack, the failure pattern shows a V-shaped hybrid shear and tensile failure. The shear failure becomes dominant with an increasing loading rate. Meanwhile, with the increase of loading rate, the width of the main shear failure zone increases. Moreover, the advanced bore decompression changes the physical property and energy accumulation conditions of the composite layer, which increases the strain energy dissipation, and the occurrence possibility of geological dynamic hazards is reduced at a rapid advancing velocity of working face.