• Journal of the Korea Concrete Institute
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• v.20 no.3
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• pp.299-305
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• 2008

The main goal of this study was to examine the shear behavior of reinforced concrete beams strengthened with CFRP strups. Seven rectangular beams were tested. The test variables were the configuration types, spacing length of CFRP strips and the amount of reinforced stirrups bars. From this experimental study, the shear capacity of beams strengthened with CFRP increased significantly compared to the beam without CFRP strip. Maximum increase of ultimate shear strength was found about 100% more than that of the beam without a CFRP strip and the CFRP strips attached in the shear region can resist the occurrence of the initial shear cracks and the propagation of major shear cracks. In this test, most of the shear strengthened beams failed suddenly due to the debonding of CFRP strips. A calculation of the shear strength of reinforced beams strengthened with CFRP strips based on the effective stresses was conducted and the comparisons were made with the test results.

• Magazine of the Korea Concrete Institute
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• v.8 no.3
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• pp.177-185
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• 1996

Four types of experiments were performed to check the similitude of member behavior between prototype and 1 /10 scale models : (1) Test of slender columns with P-$\Delta$ effect, (2) Test of short columns with and without confinement steel, (3) Test of simple beams without stirrups, and (4) 'T-beam test. Based on the results of experiments, the conclusions were made as follows : (1) The P-$\Delta$ effect of slender columns can be almost exactly represented by 1/10 scale model. (2) The effect of confinement on short columns by the hoop steel can be also roughly simulated by 1/10 scale model. (3) The failure modes of simple beams without stirrups are brittle shear failures in prototype whereas those of 1/10 scale models are the ductile yielding of tension steel followed by large diagonal tension cracking and compressive concrete failure. (4) The behaviors of prototype and 1/10 scale model in T-beams appear very similar.

• Structural Engineering and Mechanics
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• v.24 no.1
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• pp.1-18
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• 2006

Strengthening of existing old structures has traditionally been accomplished by using conventional materials and techniques, viz., externally bonded steel plates, steel or concrete jackets, etc. Alternatively, fibre reinforced polymer composite (FRPC) products started being used to overcome problems associated with conventional materials in the mid 1950s because of their favourable engineering properties. Effectiveness of FRPC materials has been demonstrated through extensive experimental research throughout the world in the last two decades. However there is a need to use refined analytical tools to simulate response of strengthened system. In this paper, an attempt has been made to develop a numerical model of strengthened reinforced concrete (RC) beams with FRPC laminates. Material models for RC beams strengthened with FRPC laminates are described and verified through a nonlinear finite element (FE) commercial code, with the help of available experimental data. Three dimensional (3D) FE analysis has been performed by assuming perfect bonding between concrete and FRPC laminate. A parametric study has also been performed to examine effects of various parameters like fibre type, stirrup's spacing, etc. on the strengthening system. Through numerical simulation, it has been shown that it is possible to predict accurately the flexural response of RC beams strengthened with FRPC laminates by selecting an appropriate material constitutive model. Comparisons are made between the available experimental results in literature and FE analysis results obtained by the present investigators using load-deflection and load-strain plots as well as ultimate load of the strengthened beams. Furthermore, evaluation of crack patterns from FE analysis and experimental failure modes are discussed at the end.

• Journal of Korean Society of Steel Construction
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• v.12 no.5 s.48
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• pp.595-604
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• 2000

Web openings of large beams provide space for wiring, piping, and duct work to provide for proper drainage, pipes and duct must be slightly sloped with the attendant result that all web openings can not be centered on the centroidal axes of the beams. Test specimens are made for opening-depth to beam-depth ratio of 0.5 and for eccentricities of the opening center line of 10% from middepth of the beam because of the proximity of the opening edge to the flange. In this paper, available test results and theories relating to the strength of composite beams having eccentric rectangular openings are surveyed and experiments were carried out to examine the structural behaviors. In all the tests in this paper good agreement is demonstrated with maximum loads measured in tests, and observed failure modes Furthermore, compared with analytical values and experimental values of interaction diagram between moment and shear capacity were safed as it is scattered with outer part of the analytical values.

• Journal of the Korea Concrete Institute
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• v.25 no.2
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• pp.137-144
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• 2013

The use of fiber-reinforced polymer (FRP) reinforcing bars in concrete structures has been increased as an alternative of steel reinforcement which has shown greater vulnerability to corrosion problem. However, the long-term performance of concrete members with FRP reinforcement is still questioned in comparison to the used of steel reinforcement. This study presents the results of an experimental study on the long-term behaviors of GFRP (glass fiber reinforced polymer) bar reinforced concrete beams after exposed to accelerated aging in an environmental chamber with temperature of $46^{\circ}C$ ($115^{\circ}F$) and 80% of relative humidity up to 300 days. The objectives of this research was to compare strength degradation and change of ductility between GFRP reinforced concrete beams and steel reinforcement beams after accelerated aging. Two types (wrapped and sand-coated surface) of GFRP bars and steel were reinforced. in concrete beams. Test results show that the failure modes of GFRP bar reinforced concrete beams are very similar with traditional RC beams, and the change of load-carrying capacity of steel reinforcing concrete beam is greater than that of GFRP bar reinforcing concrete beam under the accelerated aging. Test result also shows that the use of GFRP reinforcing in concrete could be introduced more brittle failure than that of steel reinforcing for practical application. The deformability factor up to compression failures indicates no significant variation before and after exposure of accelerated aging.

• Journal of the Korea Concrete Institute
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• v.21 no.6
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• pp.719-727
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• 2009

The requirements of the maximum shear reinforcement in the EC2-02 and CSA-04, which are developed based on the truss model, are quite different to those in the ACI-08 code and AIJ-99 code, which are empirical equations. The ACI 318-08, CSA-04, and EC2-02 codes provide an expression for the maximum amount of shear reinforcement ratio as a function of the concrete compressive strength, but Japanese code does not take the influence of the concrete compressive strength into account. For high strength concrete, the maximum amount of shear reinforcement calculated by the EC2-02 and CSA-04 is much greater than that calculated by the ACI 318-08. Ten RC beams having various shear reinforcement ratios were tested and their corresponding shear stress-shear strain curves and failure modes were compared to the predicted ones obtained by the current design codes.

• Steel and Composite Structures
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• v.46 no.2
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• pp.175-193
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• 2023

Stainless steel-concrete composite beam has become an attractive structural form for offshore bridges and iconic high-rise buildings, owing to the superior corrosion resistance and excellent ductility of stainless steel material. In a composite beam, stainless steel shear connectors play an important role by establishing the interconnection between stainless steel beam and concrete slab. To enable the best use of high strength stainless steel shear connectors in composite beams, high strength concrete is recommended. To date, the application of stainless steel shear connectors in composite beams is still very limited due to the lack of research and proper design recommendations. In this paper, a total of seven pushout specimens were tested to investigate the load-slip behaviour of stainless steel shear connectors. A thorough discussion has been made on the differences between stainless steel bolted connectors and welded studs, in terms of the failure modes, load-slip behaviour and ultimate shear resistance. In parallel with the experimental programme, a finite element model was developed in ABAQUS to simulate the behaviour of stainless steel shear connectors, with which the effects of shear connector strength, concrete strength and embedded connector height to diameter ratio (h/d) were evaluated. The obtained experimental and numerical results were analysed and compared with existing codes of practice, including AS/NZS 2327, EN 1994-1-1 and ANSI/AISC 360-16. The comparison results indicated that the current codes need to be improved for the design of high strength stainless steel shear connectors. On this basis, modified design approaches were proposed to predict the shear capacity of stainless steel bolted connectors and welded studs in the composite beams.

• Steel and Composite Structures
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• v.42 no.4
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• pp.447-458
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• 2022

Cold-formed steel (CFS) sections are thin-walled, therefore, more susceptible to different types of geometric imperfections. Global type of geometric imperfections has a significant impact on the load-carrying capacity of flexural members. This paper reports an experimental study that discusses the influence of global imperfections on the flexural response of CFS built-up I-beams composed of two lipped channels, with simply supported ends, under four-point loading. Global imperfections of magnitude over eight times the maximum permissible ones were induced in the specimens, leading to their distress. Using various simple stiffening schemes, the capacity and stiffness of the distressed specimens were improvised. The performance comparisons were made based on the maximum loads resisted, flexural stiffnesses offered, and failure modes experienced by the specimens. As experimental data on such distressed specimens are currently lacking in the literature, the test results of the present study will provide the necessary data needed by future researchers to numerically extend this study further, which will help in the development of necessary design guidelines for the same. The stiffening schemes significantly improved the structural efficiency of distressed specimens in terms of strength and stiffness, by over 60%. As a result, an effective and time-saving solution to such realistic structural engineering problems is given.

• Structural Engineering and Mechanics
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• v.82 no.2
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• pp.173-189
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• 2022

This study presents an experimental and numerically study about the effects of fiber reinforcement ratio on the behavior of concrete-filled steel tubes (CFST) under dynamic impact loading. In literature have examined the behavior of GFRP and FRP wrapped strengthened CFST elements impact loads. However, since the direction of potential impact force isn't too exact, there is always the probability of not being matched the impact force of the area where the reinforced. Therefore, instead of the fiber textile wrapping method which strengthens only a particular area of CFST element, we used fiber-added concrete-filled elements which allow strengthening the whole element. Thus, the effect of fiber-addition in concrete on the behavior of CFST elements under impact loads was examined. To do so, six simply supported CFST beams were constructed with none fiber, 2% fiber and 10% fiber reinforcement ratio on the concrete part of the CFST beam. CFST beams were examined under two different impact loads (75 kg and 225 kg). The impactors hit the beam from a 2000 mm free fall during the experimental study. Numerical models of the specimens were created using ABAQUS finite element software and validated with experimental data. The obtained results such as; mid-span displacement, acceleration, failure modes and energies from experimental and numerical studies were compared and discussed. Furthermore, the Von Misses stress distribution of the CFST beams with different ratio of fiber reinforcements were investigated numerically. To sum up, there is an optimum amount limit of the fiber reinforcement on CFST beams. Up to this limit, the fiber reinforcement increases the structural performances of the beam, beyond that limit the fiber reinforcement decreases the performances of the CFST beam under transverse impact loadings.

• Steel and Composite Structures
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• v.35 no.2
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• pp.261-278
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• 2020

In steel-concrete composite beams, to improve the cracking resistance of the concrete slab in the hogging moment region, a new type of connector in the interface, named uplift-restricted and slip-permitted screw-type (URSP-S) connector has been proposed. This paper focuses on the behavior of steel-concrete composite beams with URSP-S connectors. A total of three beam specimens including a simply supported beam with URSP-S connectors and two continuous composite beams with different connectors arrangements were designed and tested. More specifically, one continuous composite beam was equipped with URSP-S connectors in negative moment region and traditional shear studs in other regions. For comparison, the other one was designed with only traditional shear studs. The failure modes, crack evolution process, ultimate capacities, strain responses at different locations as well as the interface slip of the three tested specimens were measured and evaluated in-depth. Based on the experimental study, the research findings indicate that the larger slip deformation is allowed while using URSP-S connectors. Meanwhile, the tensile stress reduces and the cracking resistance of the concrete slab improves accordingly. In addition, the overall stiffness and strength of the composite beam become slightly lower than those of the composite beam using traditional shear studs. Moreover, the arrangement suggestion of URSP-S connectors in the composite beam is discussed in this paper for its practical design and application.