• Computers and Concrete
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• v.8 no.1
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• pp.59-70
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• 2011

A theoretical model known as the modified rotating-angle softened-truss model (MRA-STM), which is a modification of Rotating-Angle Softened-Truss Model and Modified Compression Field Theory, is presented for the analysis of reinforced concrete membranes in shear. As an application, shear strength and behaviour of reinforced concrete exterior beam-column joints are analysed using the MRA-STM combining with the deep beam analogy. The joints are considered as RC panels and subjected to vertical and horizontal shear stresses from adjacent columns and beams. The strut and truss actions in a beam-column joint are represented by the effective transverse compression stresses and a softened concrete truss in the proposed model. The theoretical predictions of shear strength of reinforced concrete exterior beam-column joints from the proposed model show good agreement with the experimental results.

• Earthquakes and Structures
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• v.18 no.5
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• pp.599-607
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• 2020

This paper deals with the experimental investigation on the behavior of RCS beam-column exterior joints. Two full-scale specimens of joints between reinforced concrete columns and steel beams are tested under cyclic loading. The objective of the test is to study the effect of steel fiber reinforced concrete (SFRC) on the seismic behavior of RCS joints. The load bearing capacity, story drift capacity, ductility, energy dissipation, and stiffness degradation of specimens are evaluated. The experimental results point out that the FRC joint is increased 20% of load carrying capacity and 30% of energy dissipation capacity in comparison with the RC joint. Besides, the FRC joint shown lower damage and better ductility than RC joint.

• Computers and Concrete
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• v.6 no.5
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• pp.377-390
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• 2009

In this paper an improved one-dimensional frame element for modelling of reinforced concrete beams and columns subjected to impact is presented. The model is developed in the framework of a flexibility fibre element formulation that ignores the shear effect at material level. However, a simple shear cap is introduced at section level to take account of possible shear failure. The effect of strain rate at the fibre level is taken into account by using the dynamic increase factor (DIF) concept for steel and concrete. The capability of the formulation for estimating the element response history is demonstrated by some numerical examples and it is shown that the developed 1D element has the potential to be used for dynamic analysis of large framed structures subjected to impact of air blast and rigid objects.

• Structural Engineering and Mechanics
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• v.47 no.2
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• pp.185-207
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• 2013

In flexural strength design of normal-strength concrete (NSC) beams, it is commonly accepted that the distribution of concrete stress within the compression zone can be reasonably represented by an equivalent rectangular stress block. The stress block it governed by two parameters, which are normally denoted by ${\alpha}$ and ${\beta}$ to stipulate the width and depth of the stress block. Currently in most of the reinforced concrete (RC) design codes, ${\alpha}$ and ${\beta}$ are usually taken as 0.85 and 0.80 respectively for NSC. Nonetheless, in an experimental study conducted earlier by the authors on NSC columns, it was found that ${\alpha}$ increases significantly with strain gradient, which means that larger concrete stress can be developed in flexure. Consequently, less tension steel will be required for a given design flexural strength, which improves the ductility performance. In this study, the authors' previously proposed strain-gradient-dependent concrete stress block will be adopted to produce a series of design charts showing the maximum design limits of flexural strength and ductility of singly-and doubly-NSC beams. Through the design charts, it can be verified that the consideration of strain gradient effect can improve significantly the flexural strength and ductility design limits of NSC beams.

• Structural Engineering and Mechanics
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• v.84 no.5
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• pp.619-632
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• 2022

Reinforced concrete (RC) structures may be subjected to sudden dynamic impact loads such as explosions occurring for different reasons, the collision of masses driven by rockfall, flood, landslide, and avalanche effect structural members, the crash of vehicles to the highway and seaway structures. Many analytical, numerical, and experimental studies focused on the behavior of RC structural elements such as columns, beams, and slabs under sudden dynamic impact loads. However, there is no comprehensive study on the behavior of the RC column-beam connections under the effect of sudden dynamic impact loads. For this purpose, an experimental study was performed to investigate the behavior of RC column-beam connections under the effect of low-velocity impact loads. Sixteen RC beam-column connections with a scale of 1/3 were manufactured and tested under impact load using the drop-weight test setup. The concrete compressive strength, shear reinforcement spacing in the beam, and input impact energy applied to test specimens were taken as experimental variables. The time histories of impact load acting on test specimens, accelerations, and displacements measured from the test specimens were recorded in experiments. Besides, shear and bending crack widths were measured. The effect of experimental variables on the impact behavior of RC beam-column connections has been determined and interpreted in detail. Besides, a finite element model has been established for verification and comparison of the experimental results by using ABAQUS software. It has been demonstrated that concrete strength, shear reinforcement ratio, and impact energy significantly affect the impact behavior of RC column-beam connections.

• Journal of the Korea Institute of Building Construction
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• v.8 no.2
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• pp.113-119
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• 2008

Recently, fiber reinforced polymers(FRP) composite materials are used extensively in the rehabilitation of concrete structural members. A main application is to wrap beams and columns using the continuous fibers sheets to improve their strength and ductility. The corner chamfering affects significantly the performance of the continuous fibers sheets, and could lead to environmental problem with waste and dust. The main purpose of this paper is to verify the effect of corner conditions on the strength of the continuous fiber sheets, and to introduce new attached components which can avoid environmental problem. A total of 15 specimens were tested and carefully checked for three types of continuous fiber sheets(carbon, glass, and aramid) and three types of corner conditions(non-chamfering, chamfering, and device attaching). It is proved that the devices proposed in this research have some capabilities to use for RC member. But additional research will be needed for commercializing.

• Journal of the Korea Concrete Institute
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• v.17 no.5 s.89
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• pp.835-842
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• 2005

This paper presents an experimental investigation of bond-strengthening hooks as a new method to increase bond strength along flexural reinforcing bars in reinforced concrete (RC) beams and columns. The RC members, which consisted of 1,300 MPa-class spirals as shear reinforcement, often suffered from bond splitting failure. The proposed method attempts to increase confining stiffness around the flexural bars by placing U-shaped hooks and to prevent premature bond splitting failure. Twelve specimens with varied amounts and sizes of the hooks were prepared to verify the strengthening effectiveness under monotonic and cyclic loading conditions. The test result indicated that the hooks increased the bond strength along the flexural bars although the strengthening effectiveness was limited by effective reinforcement ratio $P_{be}$. This limit is determined by size of stress-transmitting zones of concrete around anchors of the hooks. Anchors of the hooks are recommended to be longer than twelve times the hook diameter and inserted deeper than a quarter of the member depth (D/4). Proposed design equations provide modest estimates of the shear strengths.

• Journal of Korean Society of Steel Construction
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• v.28 no.4
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• pp.231-242
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• 2016

Earthquake resistance of RC column-steel beam (RCS) joints with simplified details were studied. Simplified details are necessary for large columns to improve the productivity and constructability. To strengthen the beam-column joint, the effects of transverse beams, studs, and U-cross ties were used. Four 2/3 scale interior RCS connections were tested under cyclic lateral loading. The specimens generally exhibited good deformation capacity exceeding 4.0% story drift ratio after yielding of both beam and beam-column joint. Ultimately, the specimens failed by shear mechanism of the joint panel. The test strengths were compared with the predictions of existing design methods.

• Steel and Composite Structures
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• v.23 no.1
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• pp.95-105
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• 2017

The use of superelastic shape memory alloys (SMAs) as reinforcements in concrete structures is gradually gaining interest among researchers. Because of different mechanical properties of SMAs compared to the regular steel bars, the use of SMAs as reinforcement in the concrete may change the response of structures under seismic loads. In this study, the effect of SMAs as reinforcement in concrete structures is analytically investigated for 3-, 6- and 8-story reinforced concrete (RC) buildings. For each concrete building, three different reinforcement details are considered: (1) steel reinforcement (Steel) only, (2) SMA bar used in the plastic hinge region of the beams and steel bar in other regions (Steel-SMA), and (3), beams fully reinforced with SMA bar (SMA) and steel bar in other regions. For each case, columns are reinforced with steel bar. Incremental Dynamic Analyses (IDA) are performed using ten different ground motion records to determine the seismic performance of Steel, Steel-SMA and SMA RC buildings. Then fragility curves for each type of RC building by using IDA results for IO, LS and CP performance levels are calculated. Results obtained from the analyses indicate that 3-story frames have approximately the same spectral acceleration corresponding with failure of frames, but in the cases of 6 and 8-story frames, the spectral acceleration is higher in frames equipped with steel reinforcements. Furthermore, the probability of fragility in all frames increases by the building height for all performance levels. Finally, economic evaluation of the three systems are compared.

• Advances in concrete construction
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• v.9 no.3
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• pp.313-326
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• 2020

Glass fiber-reinforced polymer (GFRP) bars have been introduced as an effective alternative for the conventional steel reinforcement in concrete structures to mitigate the costly consequences of steel corrosion. However, despite the superior performance of these composite materials in terms of corrosion, the effect of replacing steel reinforcement with GFRP on the seismic performance of concrete structures is not fully covered yet. To address some of the key parameters in the seismic behavior of GFRP-reinforced concrete (RC) structures, two full-scale beam-column joints reinforced with GFRP bars and stirrups were constructed and tested under two phases of loading, each simulating a severe ground motion. The objective was to investigate the effect of damage due to earthquakes on the service and ultimate behavior of GFRP-RC moment-resisting frames. The main parameters under investigation were geometrical configuration (interior or exterior beam-column joint) and joint shear stress. The performance of the specimens was measured in terms of lateral load-drift response, energy dissipation, mode of failure and stress distribution. Moreover, the effect of concrete damage due to earthquake loading on the performance of beam-column joints under service loading was investigated and a modified damage index was proposed to quantify the magnitude of damage in GFRP-RC beam-column joints under dynamic loading. Test results indicated that the geometrical configuration significantly affects the level of concrete damage and energy dissipation. Moreover, the level of residual damage in GFRP-RC beam-column joints after undergoing lateral displacements was related to reinforcement ratio of the main beams.