• 한국농공학회지
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• 제44권3호
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• pp.73-84
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• 2002

Nominal shear strength of concrete beam is the combined strength of concrete shear strength and steel shear strength in current design code. But Torsional moment strength of concrete is neglected in calculation of the nominal torsional moment strength of reinforced concrete beam in current revised code. Tensile stress of concrete strut between cracks is still in effect due to tension stiffening effect. But the tensile stresses of concrete after cracking are neglected in bending and torsion in design. The torsional behavior is similar to the shear behavior in mechanics. Therefore the torsional moment strength of concrete should be concluded to the nominal torsional moment strength of reinforced concrete beam. To verify the validity of the proposed model, the nominal torsional moment strengths according to CEB, two ACI codes(89, 99) and proposed model are compared to experimental torsional strengths of 55 test specimens found in literature. The nominal torsional moment strengths by the proposed model show the best results.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2003년도 가을 학술발표회 논문집
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• pp.223-228
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• 2003

Results of 61 framed reinforced concrete shear walls with openings were reviewed to evaluate the current design provisions for nominal shear strength. Provisions for ACI 318-02 and AIJ Code pertaining to shear design of shear walls evaluated the applicability of shear walls with openings subjected to lateral and vertical loads. Evaluation of test results indicates that the nominal unit shear strength($\Psi$=1.0) calculated using the provisions of ACI and AIJ does not represent the observed shear strength well. Based on the limited database considered in this study, A reasonable lower bound to the shear strength of high-strength concrete shear walls is found to be $1.09\sqrt{f_{cu}}$ kgf/$\textrm{cm}^2$.

• 콘크리트학회논문집
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• 제14권1호
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• pp.24-32
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• 2002

전단문제에서는 일부 설계기준(AASHTO 1994)에 이미 수정압축장이론이 도입되었다. 그리고 현행 콘크리트 설계기준에는 콘크리트의 전단강도가 철근의 전단강도와 합하여 공칭전단강도를 계산하고 있다. 그러나 최근에 개정된 콘크리트설계기준에는 콘크리트의 비틀림강도가 공칭비틀림강도 계산에서 누락되었다. 콘크리트의 인장응력은 비록 크기가 작으나 균열후에 균열사이의 콘크리트에 존재한다. 그러나 휨과 비틀림문제에서는 균열 후 콘크리트의 인장강성은 생략되고 있다. 역학적으로 콘크리트보의 비틀림거동은 전단거동과 매우 유사하다. 그러므로 균열 후 콘크리트의 비틀림강도를 철근콘크리트 보의 공칭비틀림강도의 계산에 포함시켜야 한다. 본 논문에서는 콘크리트의 평균주인장응력이 이루는 콘크리트의 비틀림강도를 횡방향 비틀림철근의 비틀림강도와 함께 공칭비틀림강도를 구성함을 밝혔으며, 이의 타당성을 검증하기 위해 개정 전후의 ACI 의 설계기준에 의한 공칭비틀림강도와 함께 실험값과 비교하였다. 그 결과 본 논문이 제안한 모델에 의한 공칭비틀림강도가 가장 좋은 결과를 보였다.

• Structural Engineering and Mechanics
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• 제16권3호
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• pp.275-294
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• 2003

In this study, 24 high-strength concrete dapped-end beams were tested to study the effects of the amount of main dapped-end reinforcement, the nominal shear span-to-depth ratio, and the concrete strength on the shear strength of dapped-end beams. Test results indicate that the shear strength of dapped ends increases with the increase in the amount of main dapped-end reinforcement and the concrete strength. The shear strength of dapped-end beam increases with the decrease of nominal shear span-to-depth ratio. A simplified method for determining the shear strength of reinforced concrete dapped ends is also proposed in this paper. The shear strengths predicted by the proposed method and the approach of PCI Design Handbook are compared with test results. The comparison shows that the proposed method can more accurately predict the shear strength of reinforced concrete dapped-end beams than the approach of PCI Design Handbook.

• Structural Engineering and Mechanics
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• 제21권3호
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• pp.333-350
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• 2005

This paper presents results of an experimental study to evaluate a new retrofit technique for strengthening shear deficient short concrete beams and columns. In this technique a mortar jacket reinforced with expanded steel meshes is used for retrofitting. Twelve short reinforced concrete specimens, including eight retrofitted ones, were tested. Six specimens were tested under a constant compressive axial force of 15% of column axial load capacity based on original concrete gross section, $A_g$, and the concrete compressive strength, ${f_c}^{\prime}$. Main variables were the spacing of ties in original specimens and the volume fraction of expanded metal in jackets. Original specimens failed before reaching their nominal calculated flexural strength, $M_n$, and had very poor ductility. Strengthened specimens reached their nominal flexural strength and had a ductility capacity factor of up to 8 for the beams and up to 5.5 for the columns. Based on the test results, it can be concluded that expanded steel meshes can be used effectively to strengthen shear deficient concrete members.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2003년도 봄 학술발표회 논문집
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• pp.925-930
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• 2003

Provisions for ACI 318-02 and NZS 3101 pertaining to shear design of shear walls evaluated the applicability of high-strength, concrete shear walls subjected to lateral loads. Results of 73 tests of reinforced concrete shear walls were reviewed. Evaluation of test results conducted in Korea, England, America, Japan, and Australia for low-aspect ratio walls indicates that the nominal unit shear strength($\phi$=1.0) calculated using the provisions of ACI and NZS does not represent the observed shear strength well. Based on the limited database considered in this study, a reasonable lower bound to the shear strength of high-strength concrete shear walls is found to be $\sqrt[0.4]{f_{cu}}$ MPa. Similar to that of normal strength concrete walls, the rate of increase of the measured shear strength with $$\rho$_n/ㆍf_y$ is less than 1.0. Therefore, the rate of increase of shear strength attributable to the web reinforcement in shear walls appears to be overestimated by the modified truss analogy.

• 한국건설순환자원학회논문집
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• 제3권1호
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• pp.58-63
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• 2015

현재까지 알칼리 활성화제를 사용한 무시멘트 콘크리트의 연구는 슬럼프, 강도 및 내구성 등 기본적인 재료성질에 대해서 주로 수행되어져 왔다. 그러나 알칼리 활성화제를 사용한 무시멘트 콘크리트의 구조부재에의 적용을 위해서는 탄성계수, 응력-변형률 관계 및 구조 부재 거동 등에 대한 연구가 필수적이다. 본 논문에서는 50MPa급 알칼리 활성 슬래그 콘크리트를 사용한 철근콘크리트 보시험체 6개를 제작한 후, 전단실험을 수행하였다. 실험과 해석에 의해 얻은 공칭전단강도는 전단철근이 배치되어 있는 시험체에서는 최대 18% 정도의 차이를 보이나, 전단철근이 없는 시험체에서는 최대 31% 정도의 차이를 보였으며 또한 알칼리 활성 슬래그 콘크리트의 설계전단강도에 비하여 전단강도 실험값이 22~57% 정도 크게 나타나 전단설계식이 상당히 안전측임을 알 수 있다.

• Steel and Composite Structures
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• 제31권2호
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• pp.159-172
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• 2019

Strengthening of civil infrastructure with advanced composites have recently become one of the most popular methods. The use of Fiber Reinforced Polymer (FRP) strips plates and fabric for strengthening of reinforced concrete structures has well established design guidelines and standards. Research on the application of FRP composites to steel structures compared to concrete structures is limited, especially for shear strengthening applications. Whereas, there is a need for cost-effective system that could be used to strengthen steel high-way bridge girders to cope with losses due to corrosion in addition to continuous demands for increasing traffic loads. In this study, a parametric finite element study is performed to investigate the effect of applying thick CFRP strips diagonally on webs of plate girders on the shear strength of end-web panels. The study focuses on illustrating the effect of several geometric parameters on nominal shear strength. Hence, a formula is developed to determine the enhancement of shear strength gained upon the application of CFRP strips.

• Steel and Composite Structures
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• 제32권3호
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• pp.411-422
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• 2019

Six shear-critical square tubed steel reinforced concrete (TSRC) columns using the high-strength concrete ($f_{cu,150}=86.6MPa$) were tested under constant axial and lateral cyclic loads. The height-to-depth ratio of the short column specimens was specified as 2.6, and the axial load ratio and the number of shear studs on the steel shape were considered as two main parameters. The shear failure mode of short square TSRC columns was observed from the test. The steel tube with diagonal stiffener plates provided effective confinement to the concrete core, while welding shear studs on the steel section appeared not significantly enhancing the seismic behavior of short square TRSC columns. Specimens with higher axial load ratio showed higher lateral stiffness and shear strength but worse ductility. A modified ACI design method is proposed to calculate the nominal shear strength, which agrees well with the test database containing ten short square TSRC columns with shear failure mode from this study and other related literature.

• Steel and Composite Structures
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• 제16권6호
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• pp.611-637
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• 2014

A single plate shear connection, or shear tab, is a very popular shear connection due to its merit in ease of construction and material economy. However, problems in understanding the connection behavior, both in terms of strength and ductility, have been well-documented. Suggestions or design model for single plate connections in AISC Design Manual have been altered several times, with the latest edition settling down to giving designers pre-calculated design strength tables if the connection details agree with given configurations. Results from many full-scale tests and finite element models in the past suggest that shear strength of a bolt group in single plate shear connections might be affected by yield strength of plate material; therefore, this research was aimed to investigate and clarify effects of plate yield strength and thickness on shear strength of the bolt group in the connections, including the validity of using a plate thickness/bolt diameter ratio ($t_p/d_b$) in design, by using finite element models. More than 20 models have been created by using ABAQUS program with 19.0- and 22.2-mm A325N bolts and A36 and Gr.50 plates with various thicknesses. Results demonstrated that increase of plate thickness or plate yield strength, with the $t_p/d_b$ ratio remained intact, could significantly reduce shear strength of the bolt group in the connection as much as 15 percent. Results also confirmed that the $t_p/d_b$ ratio is a valid indicator to be used for guaranteeing strength sufficiency. Because the actual ratio recommended by AISC Design Manual is $t_p/d_b$ + 1.6 (mm) for connections with a number of bolts less than six and plate yield strength in construction is normally higher than the nominal value used in design, it is proposed that shear strength of a bolt group in single plate connections with a number of bolts equal or greater than seven be reduced by 15 percent and the $t_p/d_b$ ratio be limited to 0.500.