• Steel and Composite Structures
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• v.46 no.1
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• pp.75-92
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• 2023

The novel composite cold-formed steel (CFS)/engineered cementitious composites (ECC) beams have been recently presented. The new composite section exhibited superior structural performance as a flexural member, benefiting from the lightweight thin-walled CFS sections with improved buckling and torsional properties due to the restraints provided by thinlayered ECC. This paper investigated the shear performance of the new composite CFS/ECC section. Twenty-eight simply supported beams, with a shear span-to-depth ratio of 1.0, were assembled back-to-back and tested under a 3-point loading scheme. Bare CFS, composite CFS/ECC utilising ECC with Polyethylene fibres (PE-ECC), composite CFS/MOR, and CFS/HSC utilising high-strength mortar (MOR) and high-strength concrete (HSC) as replacements for PE-ECC were compared. Different failure modes were observed in tests: shear buckling modes in bare CFS sections, contact shear buckling modes in composite CFS/MOR and CFS/HSC sections, and shear yielding or block shear rupture in composite CFS/ECC sections. As a result, composite CFS/ECC sections showed up to 96.0% improvement in shear capacities over bare CFS, 28.0% improvement over composite CFS/MOR and 13.0% over composite CFS/HSC sections, although MOR and HSC were with higher compressive strength than PE-ECC. Finally, shear strength prediction formulae are proposed for the new composite sections after considering the contributions from the CFS and ECC components.

• Journal of the Korea institute for structural maintenance and inspection
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• v.18 no.3
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• pp.108-115
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• 2014

Mechanical properties of GFRP rebars significantly decrease due to high temperature as well as alkalinity of concrete. This study focuses on the long-term reduction of inter-laminar shear strength of pre-damaged GFRP rebars by high temperature. For this investigation, bare GFRP rebar specimens were exposed to $270^{\circ}C$ for 1hour and then immerged in alkali solution for several months and tested in shear. No thermally conditioned specimens were immerged and tested for the comparisons. In results, the reduction of thermally damaged GFRP rebars was greater than that of no thermally damaged ones. Based on the accelerated experimental test data, an polynomial equation is presented for prediction of long-term residual inter-laminar shear strength of GFRP rebars previously damaged by high temperature.

• Proceedings of the Korea Concrete Institute Conference
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• 2001.11a
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• pp.879-884
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• 2001

The use of recycled-aggregate concrete is increasing faster than the development of appropriate design recommendations. In addition, recycled-aggregate and higher compressive strengths are two of the most desired characteristics to improve the use of concrete as a construction material. The paper reports limited experimental data on the shear capacity of high-strength recycled aggregate concrete beams. Ten beams were tested to determine their diagonal cracking and ultimate shear capacities. The variable in the test program were concrete strength(300, 500 and 700kgf/$cm^{2}$), and shear span/depth ratio (a/d : 2.0, 3.0 and 4.0). Test results indicate that the ACI Building code prediction of Eq.(11-3) and (11-5) for high-strength recycled aggregate concretes are unconservative for all beams (with concrete strength 300, 500 and 700kgf/$cm^{2}$, a/d ratios 2.0, 3.0 and 4.0). But Zsutty Equation for high-strength recycled aggregate concretes is conservative for all beams. The results of the experimental investigation on the cracking patterns for beams show that the angle that the critical inclined crack makes with the horizontal axis decreases with increasing a/d.

• Proceedings of the Korea Concrete Institute Conference
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• 1999.10a
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• pp.373-376
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• 1999

The techniques of dimensional analysis and statistical regression analysis is applied to existing voluminous data available from tests covering a wide range of slab properties, which then leads to an equation to predict the punching shear strength of slabs.

• Journal of the Korea Concrete Institute
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• v.14 no.6
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• pp.982-988
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• 2002

Current design equations for shear strength of reinforced concrete columns generally overestimate the shear strength contribution by the circular transverse reinforcement. This is due to the simplification of the discrete distribution of the reinforcement to the continuous one and the imprudent application of the classical truss model to the circular section, which is different in shear-resisting mechanism from the rectangular section. This study presents a rational model for the prediction of shear strength contribution by the circular transverse reinforcement considering the starting location of a diagonal crack, the number of transverse reinforcing bars crossing the main crack and the geometrical strength component of the transverse resistance. It was found that, for lower amount transverse reinforcement, the crack starting point and the number of crack crossing bars greatly influence the shear-resisting capacity. Proposed model leads to a reliable design equation which is derived using a linear regression method and is in good agreement with the lower bound of exact strength curve.

• Journal of the Korea Concrete Institute
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• v.23 no.2
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• pp.159-168
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• 2011

In the present study, an improved design method was developed for the punching shear strength of interior slabcolumn connections and column footings with and without shear reinforcement. In the evaluation of the punching shear strength, the possible failure mechanisms of the connections and column footings were considered. The considered failures modes were inclined tensile cracking of concrete, yielding of shear re-bars, and concrete crushing of compression zone/strut. The punching shear applied to the concrete critical section was assumed to be resisted mainly by the compression zone. The punching shear strength of the concrete compression zone was evaluated based on the material failure criteria of the concrete subjected to the compressive normal stress and shear stress. For verification of the proposed design method, its prediction was compared with the existing test results. The result showed that the proposed method predicted the strengths of the test specimens better than the current design methods of the KCI code for both the shear reinforced and unreinforced cases.

• Journal of the Korea Concrete Institute
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• v.17 no.5 s.89
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• pp.717-726
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• 2005

Shear test data have been extracted from previous experimental research and compiled into a database that may be the largest ever made. In this paper, the shear database (SDB) was used for evaluating shear design provisions for both reinforced concrete (RC) beams and prestressd concrete (PSC) beams. A discussion on the use of the results of this evaluation related to calibration and strength reduction factor for the shear design provisions was also provided. It was observed that the shear design provisions did not provide good predictions for RC members and gave very poor predictions especially for RC members without shear reinforcement. On the other hand, the limit on shear strength contributed by transverse reinforcement was observed to be lower than necessary. The shear design provisions gave very unconservative results for the large RC members (d>700mm) without shear reinforcement having light amount of longitudinal reinforcement $(\rho_w<1.0\%)$. However, for PSC members the shear design provisions gave a good estimation of ultimate shear strength with a reasonable margin of safety. Despite of a large difference of accuracy in prediction of shear strength for RC members and PSC members, the shear design provisions used a same shear strength reduction factor for these members. As a result, the shear design provisions did not provide a uniform factor of safety against shear failure for different types of members.

• Smart Structures and Systems
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• v.22 no.4
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• pp.413-424
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• 2018

The factors affecting the shear strength of the angle shear connectors in the steel-concrete composite beams can play an important role to estimate the efficacy of a composite beam. Therefore, the current study has aimed to verify the output of shear capacity of angle shear connector according to the input provided by Support Vector Machine (SVM) coupled with Firefly Algorithm (FFA). SVM parameters have been optimized through the use of FFA, while genetic programming (GP) and artificial neural networks (ANN) have been applied to estimate and predict the SVM-FFA models' results. Following these results, GP and ANN have been applied to develop the prediction accuracy and generalization capability of SVM-FFA. Therefore, SVM-FFA could be performed as a novel model with predictive strategy in the shear capacity estimation of angle shear connectors. According to the results, the Firefly algorithm has produced a generalized performance and be learnt faster than the conventional learning algorithms.

• Structural Engineering and Mechanics
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• v.73 no.5
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• pp.515-527
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• 2020

This paper presents a stress field approach for the shear capacity of stirrup-reinforced concrete beams that explicitly incorporates the contribution of principal tensile stresses in concrete. This formulation represents an extension of the variable strut inclination method adopted in the Eurocode 2. In this model, the stress fields in web concrete consist of principal compressive stresses inclined at an angle θ combined with principal tensile stresses oriented along a direction orthogonal to the former (the latter being typically neglected in other formulations). Three different failure mechanisms are identified, from which the strut inclination angle and the corresponding shear strength are determined through equilibrium principles and the static theorem of limit analysis, similar to the EC-2 approach. It is demonstrated that incorporating the contribution of principal tensile stresses of concrete slightly increases the ultimate inclination angle of the compression struts as well as the shear capacity of reinforced concrete beams. The proposed stress field approach improves the prediction of the shear strength in comparison with the Eurocode 2 model, in terms of both accuracy (mean) and precision (CoV), as demonstrated by a broad comparison with more than 200 published experimental results from the literature.

• Journal of the Korea Concrete Institute
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• v.15 no.6
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• pp.820-828
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• 2003

Recent research has indicated that the current ACI shear provision provides unconservative predictions for large slender beams and beams with low level of longitudinal reinforcement, and conservative results for deep beams. To modify some problems of ACI shear provision, ultimate shear strength equation considering size effect and arch action to compute shear strength in high-strength concrete beams without stirrups is presented in this research. Three basic equations, namely size reduction factor, rho factor, and arch action factor, are derived from crack band model of fracture mechanics, analysis of previous some shear equations for longitudinal reinforcement ratio, and concrete strut described as linear prism in strut-tie model deep beams. Constants of basic equations are determined using statistical analysis of previous shear testing data. To verify proposed shear equation for each variable, effective depth, longitudinal reinforcement ratio, concrete compressive strength and shear span-to-depth ratio, about 300 experimental data are used and proposed shear equation is compared with ACI 318-99 code, CEB-FIP Model code, Kim &Park's equation and Zsutty's equation. The proposed shear equation is not only simpler than other shear equations, it is but also shown to be economical predictions and reasonable safety margin. Hence proposed shear strength equation is expected to be applied to practical shear design.