• Title/Summary/Keyword: residual flexural strength

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Hysteretic characteristics of medium- to low-rise RC structures controlled by both shear and flexure evaluated by FEA and pseudo-dynamic testing

  • Ju-Seong Jung;Bok-Gi Lee;Kang-Seok Lee
    • Computers and Concrete
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    • v.33 no.2
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    • pp.217-240
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    • 2024
  • The purpose of this study is to propose new hysteretic characteristics of medium- to low-rise RC structures controlled by both shear and flexure. Through previous study, the dual lateral force-resisting system composed of shear and flexural failure members has a new failure mechanism that cooperates to enhance the flexural capacity of the flexural failure member even after the failure of the shear member, and the existing theoretical equation significantly underestimates the ultimate strength. In this study, the residual lateral strength mechanism of the dual lateral force-resisting system was analyzed, and, as a result, an equation for estimating the residual flexural strength of each shear-failure member was proposed. The residual flexural strength of each shear-failure member was verified in comparison with the structural testing results obtained in previous study, and the proposed residual flexural strength equation for shear-failure members was tested for reliability using FEA, and its applicable range was also determined. In addition, restoring-force characteristics for evaluating the seismic performance of the dual lateral force-resisting system (nonlinear dynamic analysis), reflecting the proposed residual flexural strength equation, were proposed. Finally, the validity of the restoring-force characteristics of RC buildings equipped with the dual lateral force-resisting system proposed in the present study was verified by performing pseudo-dynamic testing and nonlinear dynamic analysis based on the proposed restoring-force characteristics. Based on this comparative analysis, the applicability of the proposed restoring-force characteristics was verified.

Design of Ground Floor Slab According to the Method for Evaluating the Tensile Performance of Steel Fiber Reinforced Concrete (강섬유 보강 콘크리트 인장성능 평가방법에 따른 지반 바닥슬래브의 설계)

  • Lee, Jong-Han;Cho, Baik-Soon;Cho, Chang-Oh
    • Journal of the Korea Concrete Institute
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    • v.28 no.1
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    • pp.95-104
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    • 2016
  • Flexural strength of concrete ground slab reinforced with steel fiber is evaluated using the equivalent flexural strength ratio of steel fiber reinforced concrete based on the yield line theory. Recently, the European standard specifies that the tensile performance of the steel fiber reinforced concrete be evaluated directly from the residual flexural strength after the cracking of concrete. Thus, in the study, an experiment was carried out to evaluate the conventional equivalent flexural strength ratio and the residual flexural strength of the steel fiber reinforced concrete. Then the design flexural strength was investigated according to the location of a point load, based on the ratio of the radius of contact area of the load to the radius of relative stiffness. Design flexural capacity obtained from ACI 360R-10 was smaller than that from TR 34 (2003 & 2013). In addition, TR 34 (2013), which evaluates the design flexural capacity based on the residual flexural strength, showed slightly smaller value than TR 34 (2003).

Analytical model for flexural and shear strength of normal and high-strength concrete beams

  • Campione, Giuseppe
    • Structural Engineering and Mechanics
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    • v.78 no.2
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    • pp.199-207
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    • 2021
  • In the present paper, an analytical model is proposed to determine the flexural and shear strength of normal and high-strength reinforced concrete beams with longitudinal bars, in the presence of transverse stirrups. The model is based on evaluation of the resistance contribution due to beam and arch actions including interaction with stirrups. For the resistance contribution of the main bars in tension the residual bond adherence of steel bars, including the effect of stirrups and the crack spacing of R.C. beams, is considered. The compressive strength of the compressed arch is also verified by taking into account the biaxial state of stresses. The model was verified on the basis of experimental data available in the literature and it is able to include the following variables in the resistance provision: - geometrical percentage of steel bars; - depth-to-shear span ratio; - resistance of materials; - crack spacing; - tensile stress in main bars; - residual bond resistance including the presence of stirrups;- size effects. Finally, some of the more recent analytical expressions able to predict shear and flexural resistance of concrete beams are mentioned and a comparison is made with experimental data.

The residual mechanical properties evaluation according to temperature of the amorphous metallic fiber reinforced high strength concrete (비정질강섬유 보강 고강도 콘크리트의 온도별 잔존 역학적 특성 평가)

  • Suh, Dong-Kyun;Kim, Gyu-Yong;Lee, Sang-Kyu;Hwang, Eui-Chul;Eu, Ha-Min;Nam, Jeong-Soo
    • Proceedings of the Korean Institute of Building Construction Conference
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    • 2020.11a
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    • pp.98-99
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    • 2020
  • This study is aim to assess mechanical properties which is highly related to structural safe and durability of 100MPa high strength concrete mixed with amorphous metallic fiber. All specimens were heated with low velocity heating rate(1℃/min.), residual compressive strength and residual flexural strength was evaluated. The specimens were cooled down to room temperature after heating. As a result, in the case of 100MPa high-strength concrete, the residual compressive strength enhancing effect of amorphous metallic fiber has showed with the mix proportion of fiber. In addition, residual flexural strength showed more regular pattern before 300℃ then residual compressive strength, but simillar decreasing behavior was shown after 300℃ like residual compressive strength. Further study about fiber pull-out behavior and fiber mechanical, chemical property change due to temperature is needed.

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Strength degeneracy of LWAC and flexural behavior of LWAC members after fire

  • Tang, Chao-Wei
    • Computers and Concrete
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    • v.20 no.2
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    • pp.177-184
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    • 2017
  • The characteristics of lightweight aggregate (LWA) with a low specific gravity and high water absorption will significantly change the properties of lightweight aggregate concrete (LWAC). This study aimed at exploring the effect of presoaking degree of LWA on the strength degeneracy of LWAC and flexural behavior of LWAC members exposed to elevated temperatures. The residual mechanical properties of the LWAC subjected to elevated temperatures were first conducted. Then, the residual load tests of LWAC members (beams and slabs) after exposure to elevated temperatures were carried out. The test results showed that with increasing temperature, the decreasing trend of elastic modulus for LWAC was considerably more serious than the compressive strength. Besides, the presoaking degree of LWA had a significant influence on the residual compressive strength and elastic modulus for LWAC after exposure to $800^{\circ}C$. Moreover, owing to different types of heating, the residual load bearing capacity of the slab specimens were significantly different from those of the beam specimens.

Mechanical behaviors of concrete combined with steel and synthetic macro-fibers

  • Deng, Zongcai;Li, Jianhui
    • Computers and Concrete
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    • v.4 no.3
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    • pp.207-220
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    • 2007
  • In this paper, hybrid fibers including high elastic modulus steel fiber and low elastic modulus synthetic macro-fiber (HPP) as two elements were used as reinforcement materials in concrete. The flexural toughness, flexural impact and fracture performance of the composites were investigated systematically. Flexural impact strength was analyzed with statistic analyses method; based on ASTM and JSCE method, an improved flexural toughness evaluating method suitable for concrete with synthetic macro-fiber was proposed herein. The experimental results showed that when the total fiber volume fractions ($V_f^a$) were kept as a constant ($V_f^a=1.5%$), compared with single type of steel or HPP fibers, hybrid fibers can significantly improve the toughness, flexural impact life and fracture properties of concrete. Relative residual strength RSI', impact ductile index ${\lambda}$ and fracture energy $G_F$ of concrete combined with hybrid fibers were respectively 66-80%, 5-12 and 121-137 N/m, which indicated that the synergistic effects (or combined effects) between steel fiber and synthetic macro-fiber were good.

Residual properties of high-strength fiber reinforced concrete after exposure to high temperatures

  • Tang, Chao-Wei
    • Computers and Concrete
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    • v.24 no.1
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    • pp.63-71
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    • 2019
  • Thermal energy from high temperatures can cause concrete damage, including mechanical and chemical degradation. In view of this, the residual mechanical properties of high-strength fiber reinforced concrete with a design strength of 75 MPa exposed to $400-800^{\circ}C$ were investigated in this study. The test results show that the average residual compressive strength of high-strength fiber reinforced concrete after being exposed to $400-800^{\circ}C$ was 88%, 69%, and 23% of roomtemperature strength, respectively. In addition, the benefit of steel fibers on the residual compressive strength of concrete was limited, but polypropylene fibers can help to maintain the residual compressive strength and flexural strength of concrete after exposure to $400-600^{\circ}C$. Further, the load-deflection curve of specimen containing steel fibers exposed to $400-800^{\circ}C$ had a better fracture toughness.

Numerical Study on Flexural Strength of Reinforced Concrete members Exposed to Fire (가열조건에 따른 철근콘크리트 부재의 휨 강도에 관한 해석적 연구)

  • 이상호;허은진
    • Journal of the Korea Concrete Institute
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    • v.13 no.3
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    • pp.195-205
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    • 2001
  • This Paper describes a numerical method to evaluate the flexural strength of reinforced concrete members exposed to fire. An analytical method is developed for the moment-curvature relationship for the cross section which is subjected to high temperature. The method performs heat-transfer analysis for the cross sections and subsequently performs numerical analysis using the stress-strain relationships of concrete and reinforcing steel in various heat conditions. The results of the numerical studies are ; 1) the residual flexural strength exposing at high temperature is affected by the heating time, the depth of concrete cover and reinforcement ratio, 2) the residual flexural strength after exposed at high temperature is recovered of its original strength at minimum ratio of reinforcement, while members having half of maximum ratio and maximum ratio of reinforcement do not recover its original strength, 3) furthermore, the concrete may reach its maximum capacity before reinforcement yields in reinforced concrete members having maximum ratio of reinforcement.

An Experimental Study on the Behavior of RC Beams Externally Bonded with FRPs Under Sustained Loads (지속하중을 받은 FRP 외부부착 보강 철근콘크리트 보의 거동 특성에 관한 실험적 연구)

  • Shim, Jae-Joong;Oh, Kwang-Jin;Kim, Yeon-Tae;Park, Sun-Kyu
    • Journal of the Korea institute for structural maintenance and inspection
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    • v.14 no.1
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    • pp.125-132
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    • 2010
  • In the recent construction industry, an external strengthening method using fiber reinforced polymers has been widely used. Since reinforced concrete structures strengthened with fiber reinforced polymers are always under sustained loads, influence of creep and shrinkage on the structures is inevitable. Due to the creep and shrinkage, behaviors of the structures, such as deflection, deformation, recovery capability, strength and so on are also under the influence of creep and shrinkage. Thus, in order to estimate efficacy, creep recovery and residual strength of FRP strengthened RC beams, long-term flexural experiments and static flexural experiments were carried out. As the result of the experiments, FRP strengthened RC beams were very effective in terms of deflection control. Furthermore, the strengthened beams had higher immediate deformation recovery than immediate deformation. Through the static flexural experiments, it was shown that the CFRP strengthened beam had high residual strength. It seems that the sustained loads did not affect bond and residual strength of the beams.

Analysis on Flexural Behavior of Spiral Steel Pipe Considering Residual Stress Developed by Pipe Manufacturing (조관에 의한 잔류 응력을 고려한 스파이럴 강관의 휨 거동 분석)

  • Kim, Kyuwon;Kim, Jeongsoo;Kang, Dongyoon;Kim, Moon Kyum
    • Journal of the Korean Institute of Gas
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    • v.23 no.4
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    • pp.65-73
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    • 2019
  • A spiral steel pipe has been more used widely as a structural member as well as transport pipeline because the pipe can be manufactured continuously, consequently more economical than the conventional UOE pipe. As improved pipe manufacture technology makes spiral pipes to have high strength and to have larger diameters, the spiral pipes have been recently used as long distance transport pipeline with a large diameter and strain-based design is thus required to keep structural integrity and cost effectiveness of the spiral pipe. However, design codes of spiral pipe have not been completely established yet, and structural behaviors of a spiral pipe are not clearly understood for strain-based design. In this paper, the effects of residual stresses due to the spiral pipe manufacture process are investigated on the flexural behavior of the spiral pipe. Finite element analyses were conducted to estimate residual stresses due to the manufacturing process for the pipes which have different forming angle, thickness, and strength, respectively. After that, the results were used as initial conditions for flexural analysis of the pipe to numerically investigate its flexural behaviors.