• Title, Summary, Keyword: ductility

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Experimental evaluation of splicing of longitudinal bars with forging welding in flexural reinforced concrete beams

  • Sharbatdar, Mohammad K.;Jafari, Omid Mohammadi;Karimi, Mohammad S.
    • Advances in concrete construction
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    • v.6 no.5
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    • pp.509-525
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    • 2018
  • In this paper the application of forging process as benefit technique in Reinforced Concrete (RC) beam bars and comparison to lap splices was experimentally investigated with four concrete beam specimens with same dimensions and reinforcement details. The reference specimen was with no splices and the other three beams were with different splices (100% forging in the middle, 50% forging, and 100% lap splices in the middle). Beams were tested with the four points load system. Experimental test results indicated that using forging process as new bar splicing method can have high effects on increasing ductility and energy dissipation of concrete structures. It also proved that this method increased the flexural rigidity, energy absorption, and ductility of the RC beams. And also this research results showed that the flexural capacity and ductility of the beam with 50% forging were respectively increased up to 10% and 75% comparing to that of reference specimen, but the energy absorption of this beams was decreased up to 27%. The ductility of beam with 50% forging was increased up to 25% comparing the ductility of beam with 100% forging.

New approach for Ductility analysis of partially prestressed concrete girders

  • Radnic, Jure;Markic, Radoslav;Grgic, Nikola;Cubela, Dragan
    • Structural Engineering and Mechanics
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    • v.70 no.3
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    • pp.257-267
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    • 2019
  • Expressions for the calculation of ductility index for concrete girders with different ratios of prestressed and classical reinforcement were proposed using load-displacement, load-strain and load-curvature relation. The results of previous experimental static tests of several large-scale concrete girders with different ratio of prestressed and classical reinforcement are briefly presented. Using the proposed expressions, various ductility index of tested girders were calculated and discussed. It was concluded that the ductility of girders decreases approximately linearly by increasing the degree of prestressing. The study presents an expression for the calculation of the average ductility index of classical and prestressed reinforced concrete girders, which are similar to the analysed experimental test girders.

Ductility demand of partially self-centering structures under seismic loading: SDOF systems

  • Hu, Xiaobin;Zhang, Yunfeng
    • Earthquakes and Structures
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    • v.4 no.4
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    • pp.365-381
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    • 2013
  • In this paper, a numerical simulation study was conducted on the seismic behavior and ductility demand of single-degree-of-freedom (SDOF) systems with partially self-centering hysteresis. Unlike fully self-centering systems, partially self-centering systems display noticeable residual displacement after unloading is completed. Such partially self-centering behavior has been observed in a number of recently researched self-centering structural systems with energy dissipation devices. It is thus of interest to examine the seismic performance such as ductility demand of partially self-centering systems. In this study, a modified flag-shaped hysteresis model with residual displacement is proposed to represent the hysteretic behavior of partially self-centering structural systems. A parametric study considering the effect of variations in post-yield stiffness ratio, energy dissipation coefficient, and residual displacement ratio on the displacement ductility demand of partially self-centering systems was conducted using a suite of 192 scaled ground motions. The results of this parametric study reveal that increasing the post-yield stiffness, energy dissipation coefficient or residual displacement ratio of the partially self-centering systems generally leads to reduced ductility demand, especially for systems with lower yield strength.

Structural response analysis in time and frequency domain considering both ductility and strain rate effects under uniform and multiple-support earthquake excitations

  • Liu, Guohuan;Lian, Jijian;Liang, Chao;Zhao, Mi
    • Earthquakes and Structures
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    • v.10 no.5
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    • pp.989-1012
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    • 2016
  • The structural dynamic behavior and yield strength considering both ductility and strain rate effects are analyzed in this article. For the single-degree-of-freedom (SDOF) system, the relationship between the relative velocity and the strain rate response is deduced and the strain rate spectrum is presented. The ductility factor can be incorporated into the strain rate spectrum conveniently based on the constant-ductility velocity response spectrum. With the application of strain rate spectrum, it is convenient to consider the ductility and strain rate effects in engineering practice. The modal combination method, i.e., square root of the sum of the squares (SRSS) method, is employed to calculate the maximum strain rate of the elastoplastic multiple-degree-of-freedom (MDOF) system under uniform excitation. Considering the spatially varying ground motions, a new response spectrum method is developed by incorporating the ductility factor and strain rate into the conventional response spectrum method. In order to further analyze the effects of strain rate and ductility on structural dynamic behavior and yield strength, the cantilever beam (one-dimensional) and the triangular element (two-dimensional) are taken as numerical examples to calculate their seismic responses in time domain. Numerical results show that the permanent displacements with and without considering the strain rate effect are significantly different from each other. It is not only necessary in theory but also significant in engineering practice to take the ductility and strain rate effects into consideration.

A Study on Hot Ductility Behavior of Ni-based Superalloys (니켈기 초내열합금의 고온연성거동에 관한 연구)

  • Lee, Choung-Rae;Um, Sang-Ho;Kim, Sung-Wook;Choi, Cheol;Lee, Chang-Hee
    • Journal of Welding and Joining
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    • v.22 no.2
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    • pp.59-68
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    • 2004
  • Plasma transferred arc welding (PTAW) has been taken into consideration for repairing Ni-based superalloy components used gas turbine blades. Various cracks has been generally reported to be found in the base metal heat affected zone(HAZ) along grain boundary. Thus, hot cracking susceptibility of Ni-based superalloys was evaluated according to heat treatments. Hot ductility test was conducted on specimens with solution treated at 112$0^{\circ}C$ for 2 hours and aging treated at 845$^{\circ}C$ for 24hours after solution treatment. The results of the hot ductility test appeared that solution treated specimens were the highest ductility recovery rate among three conditions. The loss of ductility at high temperature in Ni-based superalloy was mainly controlled by the degree of pain boundary wetting due to constitutional liquation of MC carbide precipitates. Meanwhile, the highest ductility recovery rate in solution-treated alloys seems to be lack of M23C6, which can be dissolved during heating and then result in the local enrichment of Cr in the vicinity of the grain boundary.

Evaluation of Site-dependent Ductility Factors for Elastic Perfectly Plastic SDOF Systems (토질조건에 따른 탄소성 단자유도 구조물의 연성계수 평가)

  • Kang, Cheol-Kyu;Choi, Byong-Jeong
    • Journal of the Earthquake Engineering Society of Korea
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    • v.8 no.4
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    • pp.11-20
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    • 2004
  • This paper suggests the site-dependent ductility factor which is a key component of response modification factor(R). To compute the ductility factor, a group of 1,860 ground motions recorded from 47 earthquake was considered. Based on the local site conditions at the recording station, ground motions were classified into four groups according to average shear wave velocity. This site classification was consistent with site categories of the UBC(1997), NEHRP(1997) and IBC 2000(1997). Based on the results of regression analysis, a simplified equations were proposed to compute site-dependent ductility factors. The proposed equations were relatively simple and provide a good estimation of mean ductility factors. Based on the proposed equation, ductility factors considering the site conditions can be evaluated in accordance with the present building codes.

Maximum axial load level and minimum confinement for limited ductility design of high-strength concrete columns

  • Lam, J.Y.K.;Ho, J.C.M.;Kwan, A.K.H.
    • Computers and Concrete
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    • v.6 no.5
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    • pp.357-376
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    • 2009
  • In the design of concrete columns, it is important to provide some nominal flexural ductility even for structures not subjected to earthquake attack. Currently, the nominal flexural ductility is provided by imposing empirical deemed-to-satisfy rules, which limit the minimum size and maximum spacing of the confining reinforcement. However, these existing empirical rules have the major shortcoming that the actual level of flexural ductility provided is not consistent, being generally lower at higher concrete strength or higher axial load level. Hence, for high-strength concrete columns subjected to high axial loads, these existing rules are unsafe. Herein, the combined effects of concrete strength, axial load level, confining pressure and longitudinal steel ratio on the flexural ductility are evaluated using nonlinear moment-curvature analysis. Based on the numerical results, a new design method that provides a consistent level of nominal flexural ductility by imposing an upper limit to the axial load level or a lower limit to the confining pressure is developed. Lastly, two formulas and one design chart for direct evaluation of the maximum axial load level and minimum confining pressure are produced.

An Analytical Evaluation of the Ductility of Reinforced High-Strength Concrete Columns (고강도 철근 콘크리트 기둥 부재의 연성해석)

  • 박훈규;장일영
    • Proceedings of the Korea Concrete Institute Conference
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    • pp.463-466
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    • 1999
  • Ductility is an important consideration in the design of reinforced high-strength concrete. Therefore, this research investigate the ductile behavior of rectangular high-strength concrete columns like as bridge piers with confinement steel. The effect on the ductility of axial load, lateral reinforcement ratio, longitudinal reinforcement ratio, shear ratio, and compressive strength of concrete were investigated analytically using layered section analysis. As the results, it was proposed the proper relationship between ductility and variables and formulated into equations.

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Ductility Improveent Methods for Cncrete Beams Prestressed with FRP (Fiber Reinforced Plastic) Tendons (FRP 긴장재를 이용한 프리스트레스트 콘크리트보의 연성개선방법)

  • 정상모
    • Proceedings of the Korea Concrete Institute Conference
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    • pp.643-648
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    • 1998
  • Despite many advantages of FRP materials, such as corrosion resistance, their linear elastic behavior up to rupture is likely to result in a lack of ductility. This paper discusses ductility improvement methods for prestressed concrete beams using FRP tendons. The methods were evaluated thorough extensive analytical and experimental investigations. The methods include optimization of sectional ductility through proper reinforcement, concrete confinement, concrete reinforcement with fibers, and prestressing with unbonded tendons.

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Effect of Microstructural Factors on Ductility of Drawn Pearlitic Steels (신선가공한 고탄소 강선의 연성에 영향을 주는 미세조직 인자)

  • Nam W. J
    • Transactions of Materials Processing
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    • v.13 no.8
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    • pp.710-715
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    • 2004
  • The effect of microstructural features on ductility of cold drawn pearlitic steels containing 0.52 ~ 0.92 wt%C was investigated. During wire drawing, reduction of area (Rh) increased initially with the progressive realignment of randomly oriented cementite, showed a maximum peak due to the completion of the alignment of most cementite, and decreased with thinning or fragmentation of the aligned cementite. Among factors on ductility, cementite thickness was found to be the most dominant microstructural feature for Rh of drawn pearlitic wires, regardless of transformation temperature and carbon content in steels.