• Title/Summary/Keyword: shear strength of concrete

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Elastic stiffness of perfobond connections in composite structures

  • Qin, Xi;Yang, Guotao
    • Steel and Composite Structures
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    • v.42 no.2
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    • pp.221-241
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    • 2022
  • Perfobond rib connectors are widely used in composite structures to achieve the composite action between the steel and the concrete, and empirical expressions for their strength and secant stiffness have been obtained by numerical simulations or push-out tests. Since perfobond connections are generally in an elastic state in the service process and the structural analysis are always based on the elastic properties of the members, the secant stiffness is not applicable for the normal structural analysis. However, the tangent stiffness of perfobond connections has not been introduced in previous studies. Moreover, the perfobond connections are bearing tension and shear force simultaneously when the composite beams subjected to torque or local loads, but the current studies fail to arrive at the elastic stiffness considering the combined effects. To resolve these discrepancies, this paper investigates the initial elastic stiffness of perfobond connections under combined forces. The calculation method for the elastic stiffness of perfobond connections is analyzed, and the contributions of the perfobond rib, the perforating rebar and the concrete dowel are investigated. A finite element method was verified with a high value of correlation for the test results. Afterwards, parametric studies are carried out using the reliable finite element analysis to explore the trends of several factors. Empirical equations for predicting the initial elastic stiffness of perfobond connections are proposed by the numerical regression of the data extracted by parametric studies. The equations agree well with finite element analysis and test results, which indicates that the proposed empirical equations reflect a high accuracy for predicting the initial elastic stiffness of perfobond connections.

Experimental and numerical analysis of the punching behavior of RC isolated footings

  • Walid, Mansour;Sabry, Fayed;Ali, Basha
    • Steel and Composite Structures
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    • v.45 no.5
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    • pp.665-682
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    • 2022
  • In the current study, punching behavior of Reinforced concrete (RC) isolated footings was experimentally and numerically investigated. The experimental program consisted of four half-scale RC isolated footing specimens. The test matrix was proposed to show effect of footing area, reinforcement mesh ratio, adding internal longitudinal reinforcement bars and stirrups on the punching response of RC isolated footings. Footings area varied from 1200×1200 mm2 to 1500×1500 mm2 while the mesh reinforcement ratio was in the range from 0.36 to 0.45%. On the other hand, a 3D non-linear finite element model was constructed using ABAQUS/standard program and verified against the experimental program. The numerical results agreed well with the experimental records. The validated numerical model was used to study effect of concrete compressive strength; longitudinal reinforcement bars ratio and stirrups concentration along one or two directions on the ultimate load, deflection, stiffness and failure patterns of RC isolated footings. Results concluded that adding longitudinal reinforcement bars did not significantly affect the punching response of RC isolated footings even high steel ratios were used. On the contrary, as the stirrups ratio increased, the ultimate load of RC isolated footings increased. Footing with stirrups ratio of 1.5% had ultimate load equal to 1331 kN, 19.6% higher than the bare footing. Moreover, adding stirrups along two directions with lower ratio (0.5 and 0.7%) significantly enhanced the ultimate load of RC isolated footings compared to their counterparts with higher stirrups ratio (1.0 and 1.5%).

Seismic control of concrete rectangular tanks subjected to bi-directional excitation using base isolation, considering fluid-structure-soil interaction

  • Mohammad Hossein Aghashiri;Shamsedin Hashemi;Mohammad Reza Kianoush
    • Structural Engineering and Mechanics
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    • v.92 no.1
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    • pp.25-52
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    • 2024
  • In the current paper, the various responses of concrete rectangular liquid storage containers under seismic load, each isolated by a lead-rubber bearing subjected to bi-directional earthquake forces are investigated. A parametric study is conducted to investigate the effects of isolation period, yield strength of the isolator and the effects of soil-foundation interaction for non-isolated and base-isolated tanks located on different soil types. In most cases, the value of base shear, base moment, wall displacement and hydrodynamic pressure is reduced by the effect of the isolators whose effective frequency is within the appropriate range. The sloshing displacement is amplified due to seismic isolation of the tanks for both tall and shallow tank configurations. Also, it is found that the seismic isolation technique is more efficient for the more flexible tank. Studying various soil types indicates that, unlike the responses of non-isolated tanks which change drastically for different soil types, the responses of base-isolated structures are less affected. Finally, it is observed that the variation in structural responses is not only related to the superstructure configuration and bearings properties but also depends on the earthquake specifications.

Design of Precast Circular Piers with Prestressing Bars (강봉으로 긴장한 프리캐스트 원형교각의 설계)

  • Shim, Chang-Su;Chung, Chul-Hun;Yoon, Jae-Young;Kim, Cheol-Hwan;Lee, Yong-Jin
    • Proceedings of the Korea Concrete Institute Conference
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    • 2008.04a
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    • pp.121-124
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    • 2008
  • Fast construction of bridge substructures is a new trend of bridge design. A precast pier system with bonded prestressing bars was proposed. In this paper, quasi-static tests on precast prestressed piers were conducted to evaluate the seismic behavior of the precast piers with bonded prestressing bars. In order to strengthen the shear strength of the joints between column segments, steel tubes filled with mortar were used. Displacement ductility and energy dissipation capacity of the precast piers were evaluated. The suggested precast pier system showed better seismic performance than the required ductility. Based on the research results, an example bridge pier for light-railway lines was designed and design considerations were discussed.

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Structural Behaviour of the Wing Wall with Columns (날개벽이 있는 기둥의 구조적 거동 특성)

  • Kang, Young-Woong;Yang, Won-Jik;Kang, Dae-Eon;Yi, Waon-Ho;Song, Dong-Yup
    • Proceedings of the Korea Concrete Institute Conference
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    • 2009.05a
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    • pp.73-74
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    • 2009
  • Current buildings have complex shaped walls where the wing wall system is a popular option. When the wing wall is attached to a column, or a short span is produced due to the wing wall system, the system affects the behaviour of the column such as by increasing the strength and decreasing the ductility of the members. Calculations for internal shear force and internal bending moment of the vertical members are considered an important matter in design, but currently Korea does not have studies on the effects of the wing wall on the columns.

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Assessment of System Reliability and Capacity-Rating of Concrete Box-Girder Highway Brdiges (R.C 박스거교의 체계신뢰성 해석 및 안전도 평가)

  • 조효남;신재철
    • Magazine of the Korea Concrete Institute
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    • v.7 no.3
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    • pp.187-198
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    • 1995
  • This paper develops practical and reallstic reliabllity models and methods for the evaluation of system rehability and system rellabllity based ratlng of R.C box glrder bridge superstructures. The precise prediction of reberved carrying capacity of bridge as d system is extremely difficult especially when the brldges are highly redundant and slgnlficantly deter 1or;itcd or dainagetl. Thls papel proposes a nt2w approach for the evaluation of reseived system c,drrying capaaty of br~dges in terms ot equ~vdleiit system strength, which may b~ ddcflned as a brtdge system strength correipcmdlng tu the system rehability of the bridge. This cm be ticrAvcd from an Inverse process bami or1 the con~ept of FOSM(F1rst Order Second Moment) form of system reliabihty index. The sf rength llmt state models for K C box girder br~dges suggested In the paper dre based on the basi~ bending and shear strength And thc system reliatxllty pro,~lerri of box gritier super structure 1s formuldted as parallel serles models obtalncd f ~ o m thc FMA(Fdilure blode Rp proath) based on major failure mc>clmusrns or c~itlcal fdure ,>tatcs of each nuder .WOSM(Ad-vanced First Order Second Moment) and IST(1mportance Sampling Technique) simulation algorithm are used for the reliability analysis of the proposed models.

Seismic Performance of Post Tensioned Flat Plate Frames according to Slab Bottom Reinforcement (하부철근 유무에 따른 PT 플랫 플레이트 골조의 내진성능)

  • Park, Young-Mi;HwangBo, Jin;Ryu, Jong-Hyuk;Han, Sang-Whan
    • Proceedings of the Korea Concrete Institute Conference
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    • 2008.11a
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    • pp.233-236
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    • 2008
  • This study evaluates the seismic performance of post-tensioned(PT) flat plate frames with or without slab bottom reinforcement. For this purpose, 3 and 9 story PT flat plate frames designed only considering gravity loads. This study conducts a nonlinear static pushover analysis. This study use an analytical model which is able to represent punching shear failure and fracture mechanism. The analytical results showed that seismic performance of PT flat plate frame is strongly influenced by the existence of slab bottom reinforcement through column. By placing slab bottom reinforcement in PT flat plate frame, lateral strength and deformation capacity are significantly increased.

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Seismic Capacity Evaluation of Existing Medium-and low-rise R/C Frame Retrofitted by H-section Steel Frame with Elastic Pad Based on Pseudo-dynamic testing (유사동적실험에 의한 탄성패드 접합 H형 철골프레임공법으로 보강 된 기존 중·저층 R/C 골조의 내진성능 평가)

  • Kim, Jin-Seon;Lee, Kang-Seok
    • Journal of the Korea institute for structural maintenance and inspection
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    • v.25 no.4
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    • pp.83-91
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    • 2021
  • In this study, to improve the connection performance between the existing reinforced concrete (R/C) frame and the strengthening member, we proposed a new H-section steel frame with elastic pad (HSFEP) system for seismic rehabilitation of existing medium-to-low-rise reinforced concrete (R/C) buildings. This HSFEP strengthening system exhibits an excellent connection performance because an elastic pad is installed between the existing structure and reinforcing frame. The method shows a strength design approach implemented via retrofitting, to easily increase the ultimate lateral load capacity of R/C buildings lacking seismic data, which exhibit shear failure mechanism. Two full-size two-story R/C frame specimens were designed based on an existing R/C building in Korea lacking seismic data, and then strengthened using the HSFEP system; thus, one control specimen and one specimen strengthened with the HSFEP system were used. Pseudodynamic tests were conducted to verify the effects of seismic retrofitting, and the earthquake response behavior with use of the proposed method, in terms of the maximum response strength, response displacement, and degree of earthquake damage compared with the control R/C frame. Test results revealed that the proposed HSFEP strengthening method, internally applied to the R/C frame, effectively increased the lateral ultimate strength, resulting in reduced response displacement of R/C structures under large scale earthquake conditions.

Research on hysteretic characteristics of EBIMFCW under different axial compression ratios

  • Li, Sheng-cai;Lin, Qiang
    • Earthquakes and Structures
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    • v.22 no.5
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    • pp.461-473
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    • 2022
  • Energy-saving block and invisible multiribbed frame composite wall (EBIMFCW) is an important shear wall, which is composed of energy-saving blocks, steel bars and concrete. This paper conducted seismic performance tests on six 1/2-scale EBIMFCW specimens, analyzed their failure process under horizontal reciprocating load, and studied the effect of axial compression ratio on the wall's hysteresis curve and skeleton curve, ductility, energy dissipation capacity, stiffness degradation, bearing capacity degradation. A formula for calculating the peak bearing capacity of such walls was proposed. Results showed that the EBIMFCW had experienced a long time deformation from cracking to failure and exhibited signs of failure. The three seismic fortification lines of the energy-saving block, internal multiribbed frame, and outer multiribbed frame sequentially played important roles. With the increase in axial compression ratio, the peak bearing capacity and ductility of the wall increased, whereas the initial stiffness decreased. The change in axial compression ratio had a small effect on the energy dissipation capacity of the wall. In the early stage of loading, the influence of axial compression ratio on wall stiffness and strength degradation was unremarkable. In the later stage of loading, the stiffness and strength degradation of walls with high axial compression ratio were low. The displacement ductility coefficients of the wall under vertical pressure were more than 3.0 indicating that this wall type has good deformation ability. The limit values of elastic displacement angle under weak earthquake and elastic-plastic displacement angle under strong earthquake of the EBIMFCW were1/800 and 1/80, respectively.

Influence of Facing Stiffness on Global Stability of Soil Nailing Systems (전면벽체의 강성이 Soil Nailing 시스템의 전체안정성에 미치는 영향)

  • Kim, Hong-Taek;Kang, In-Kyu;Kwon, Young-Ho
    • Journal of the Korean GEO-environmental Society
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    • v.5 no.3
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    • pp.51-60
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    • 2004
  • In Korea there are recently many attempts to expand a temporary soil nailing system into a permanent soil nailing system since the first construction in 1993. In the soil nailing system, the rigid facing walls act on restraining the deformation of the ground. These are purposed to minimize the damage of adjacent buildings or underground structures. In Korea, to minimize the relaxation of the ground, the soil nailing system in the downtown area is often used experientially together with braced cuts, sheet pile walls, soil cement walls (SCW), or jet grouting walls. However, for the conservative design, the confining effects by the stiff facing have been ignored because the proper design approach of considering the facing stiffness has not been proposed. In this study, various laboratory model tests are carried out to examining the influence the rigidity of facings on the global safety of soil nailing system. Also, the parametric studies using the numerical technique as shear-strength reduction technique are carried out. In the parametric study, the thickness of concrete facing walls is changed to identify the effects of the facing wall stiffness.

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