• Computers and Concrete
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• 제7권4호
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• pp.347-364
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• 2010

Since its invention in the $19^{th}$ century, Reinforced Concrete (RC) has been widely used in the construction of a lot of different structures, as buildings, bridges, nuclear central plants, or even ships. The details of the mechanical response for this kind of structures depends directly upon the material behavior of each component: concrete and steel, as well as their interaction through the bond-slip, which makes a rigorous engineering analysis of RC structures quite complicated. Consequently, the practical calculation of RC structures is done by adopting a lot of simplifications and hypotheses validated in the elastic range. Nevertheless, as soon as any RC structural element is working in the inelastic range, it is possible to obtain the numerical prediction of its realistic behavior only through the use of non linear analysis. The aim of this work is to develop a new kind of Finite Element: the "Enhanced Solid Element (ESE)" which takes into account the complex composition of reinforced concrete, being able to handle each dissipative material behavior and their different deformations, and on the other hand, conserving a simplified shape for engineering applications. Based on the recent XFEM developments, we introduce the concept of nodal enrichment to represent kinematics of steel rebars as well as bonding. This enrichment allows to reproduce the strain incompatibility between concrete and steel that occurs because of the bond degradation and slip. This formulation was tested with a couple of simple examples and compared to the results obtained from other standard formulations.

• 한국전산구조공학회논문집
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• 제32권6호
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• pp.409-416
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• 2019

본 논문에서는 폭발하중을 받는 철근콘크리트 슬래브의 비선형 해석을 위한 개선된 수치 모델을 제안한다. 제안된 모델은 2축 응력 상태를 반영한 등가 강도에 의해 정의된 응력-변형률 관계를 사용하여 응력 상태를 직접 결정하는 변형률 속도 의존 이등방성 구성 모델을 다룬다. 또한, 균열 발생 후 콘크리트와 철근 사이의 부착 슬립이 점차 확대되어 소성힌지 영역으로 집중된다. 2축 응력 상태에서 콘크리트의 균열 방향은 주응력 방향에 따라 달라지므로 이를 고려한 부착 슬립 모델을 해석에 도입하였다. 해석 모델의 검증을 위해 수치해석과 실험결과의 상관관계 연구(correlation studies)가 수행되었다. 해석결과는 재료모델의 2축 거동과 부착 슬립의 영향을 고려하는 것이 해석결과의 정확성 향상에 중요함을 보여주며 제안된 해석 모델이 철근콘크리트 슬래브 부재의 폭발해석에 효과적으로 사용될 수 있음을 확인하였다.

• Coupled systems mechanics
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• 제10권6호
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• pp.509-520
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• 2021

Fiber-reinforced concrete (FRC) is a composite material where small fibers made from steel or polypropylene or similar material are embedded into concrete matrix. In a material model each constituent should be adequately described, especially the interface between the matrix and fibers that is determined with the 'bond-slip' law. 'Bond-slip' law describes relation between the force in a fiber and its displacement. Bond-slip relation is usually obtained from tension laboratory experiments where a fiber is pulled out from a matrix (concrete) block. However, theoretically bond-slip relation could be determined from bending experiments since in bending the fibers in FRC get pulled-out from the concrete matrix. We have performed specially designed laboratory experiments of three-point beam bending with an intention of using experimental data for determination of material parameters. In addition, we have formulated simple layered model for description of the behavior of beams in the three-point bending test. It is not possible to use this 'forward' beam model for extraction of material parameters so an inverse model has been devised. This model is a basis for formulation of an inverse model that could be used for parameter extraction from laboratory tests. The key assumption in the developed inverse solution procedure is that some values in the formulation are known and comprised in the experimental data. The procedure includes measured data and its derivative, the formulation is nonlinear and solution is obtained from an iterative procedure. The proposed method is numerically validated in the example at the end of the paper and it is demonstrated that material parameters could be successfully recovered from measured data.

• Computers and Concrete
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• 제1권2호
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• pp.151-168
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• 2004

A two-dimensional nonlinear finite element model is developed to simulate time-dependent cracking of reinforced concrete members under service loads. To predict localized cracking, the crack band model is employed to model individual crack opening. In conjunction with the crack band model, a bond-interface element is used to model the slip between concrete and reinforcing steel permitting large slip displacements between the concrete element nodes and the steel truss element nodes at crack openings. The time-dependent effects of concrete creep and shrinkage are incorporated into the smeared crack model as inelastic pre-strains in an iterative solution procedure. Two test examples are shown to verify the finite element model with good agreement between the model and the observed test results.

• Computers and Concrete
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• 제2권4호
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• pp.267-291
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• 2005

To date, many studies have been conducted for the analysis and design of reinforced concrete members with disturbed regions. However, prestressed concrete deep beams have not been the subject of many investigations. This paper presents an evaluation of the behavior and strength of three pre-tensioned concrete deep beams failed by shear and bond slip of prestressing strands using a nonlinear strut-tie model approach. In this approach, effective prestressing forces represented by equivalent external loads are gradually introduced along strand's transfer length in the nearest strut-tie model joints, the friction at the interface of main diagonal shear cracks is modeled by the aggregate interlock struts along the direction of the cracks in strut-tie model, and an algorithm considering the effect of bond slip of prestressing strands in the strut-tie model analysis and design of pre-tensioned concrete members is implemented. Through the strut-tie model analysis of pre-tensioned concrete deep beams, the nonlinear strut-tie model approach proved to present effective solutions for predicting the essential aspects of the behavior and strength of pre-tensioned concrete deep beams. The nonlinear strut-tie model approach is capable of predicting the strength and failure modes of pre-tensioned concrete deep beams including the anchorage failure of prestressing strands and, accordingly, can be employed in the practical and precise design of pre-tensioned concrete deep beams.

• Geomechanics and Engineering
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• 제14권3호
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• pp.233-240
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• 2018

Pullout tests are usually employed to determine the ultimate bearing capacity of reinforced soil, and the load-displacement curve can be obtained easily. This paper presents an analytical solution for predicting the full-range mechanical behavior of a buried planar reinforcement subjected to pullout based on a bi-linear bond-slip model. The full-range behavior consists of three consecutive stages: elastic stage, elastic-plastic stage and debonding stage. For each stage, closed-form solutions for the load-displacement relationship, the interfacial slip distribution, the interfacial shear stress distribution and the axial stress distribution along the planar reinforcement were derived. The ultimate load and the effective bond length were also obtained. Then the analytical model was calibrated and validated against three pullout experimental tests. The predicted load-displacement curves as well as the internal displacement distribution are in closed agreement with test results. Moreover, a parametric study on the effect of anchorage length, reinforcement axial stiffness, interfacial shear stiffness and interfacial shear strength is also presented, providing insights into the pullout behaviour of planar reinforcements of MSE structures.

• Smart Structures and Systems
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• 제16권1호
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• pp.67-79
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• 2015

Acoustic emission analysis is an effective technique for monitoring the evolution of damage in a structure. An experimental analysis on a set of reinforced concrete beams under flexural loading was carried out. A mixed AE analysis method which used both parameter-based and signal-based techniques was presented to characterize and identify different failure mechanisms of damage, where the signal-based analysis was performed by using the Hilbert-Huang transform. The maximum instantaneous energy of typical damage events and the corresponding frequency characteristics were established, which provided a quantitative assessment of reinforced concrete beam using AE technique. In the bending tests, a "pitch-catch" system was mounted on a steel bar to assess bonding state of the steel bar in concrete. To better understand the AE behavior of bond-slip damage between steel bar and concrete, a special bond-slip test called pullout test was also performed. The results provided the basis of quantitative AE to identify both failure mechanisms and level of damages of civil engineering structures.

• Structural Engineering and Mechanics
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• 제81권3호
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• pp.305-316
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• 2022

Externally bonded ultrahigh performance fiber-reinforced concrete (UHPFRC) is commonly used as a strengthening material for reinforced concrete (RC) structures. This study reports the results of an experimental program investigating the bonding behavior between concrete and prefabricated UHPFRC plates. The overall experimental program is consisting of five RC specimens, which are strengthened using the different lengths and widths of prefabricated UHPFRC plates. These specimens were analyzed using the pull-pull double-shear test. The performance of each strengthened specimen is presented, discussed and compared in terms of failure mode, maximum load, load-slip relationship, fracture energy and strain distribution. Specimen C-25-160-300 which bonded along the whole width of 160 mm recorded the highest maximum load (109.2 kN) among all the analysed specimens. Moreover, a 3D numerical finite element model (FEM) is proposed to simulate the bond behavior between concrete and UHPFRC plates. Moreover, this study reviews the analytical models that can predict the relationship between the maximum bond stress and slip for strengthened concrete elements. The proposed FEM is verified against the experimental program and then used to test 36 RC specimens strengthened with prefabricated UHPFRC plates with different concrete grades and UHPFRC plate widths. The obtained results together with the review of analytical models helped in the formation of a design equation for estimating the bond stress between concrete and prefabricated UHPFRC plates.

• 한국구조물진단유지관리공학회 논문집
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• 제12권2호
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• pp.131-138
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• 2008

최근 지진, 노후화 등에 따라 손상된 많은 콘크리트 구조물을 보강하기 위하여 고강도이면서 가볍고 내구성이 뛰어난 특성을 가지고 있는 FRP(Fiber-reinforced polymer) 시트가 구미에서 뿐만 아니라 우리나라에서도 널리 사용되고 있으며 관련연구도 활발히 체계적으로 이루어지고 있다. 일반적으로 FRP 시트로 보강된 RC구조물은 지진, 교통, 온도 등에 의해 자주 반복하중을 받는다. 그러나 대부분의 연구가 일축 하중하에 이루어진 경우가 대부분이며 이러한 연구결과를 토대로 FRP의 부착특성을 확인하고 있으며 다양한 부착모델을 제안하고 있다. 이러한 관점에서 본 연구에서는 아라미드섬유, 탄소섬유, 폴리아세탈 섬유와 매수를 변수로 하여 총 18개의 시험체를 제작하고 최대부착강도, 최대변위, 변형률을 측정하고 그 결과에 근거하여 부착응력, 슬립을 계산하여 반복하중하의 FRP 시트와 콘크리트의 부착특성을 미시적으로 살펴보았다.

• 콘크리트학회지
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• 제7권1호
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• pp.117-125
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• 1995

철근과 콘크리트의 부착성능에 영향을 미치는 인자들을 평가하기 위하여 부착실험을 수행하였다. 주요변수로는 콘크리트의 압축강도($f_c$'=340, 460, 650, $904kg/cm^2$), 콘크리트의 피복두께(25, 38, 51, 105, 110mm), 철근의 직경(D13, D22)으로 하였으며 구속철근의 효과와 철근간격은 고려하지 않았다. 철근이 일축인장력을 받을 때 철근의 전 부착길이에 걸쳐 응력이 일정하다는 가정하에 32개의 실험체를 제작, 실험하였다. 각 실험체별로 파괴모드를 고찰하였고, 부착응력.변위관계를 통하여 변수의 영향을 평가하였으며, 실험결과에 다른 최대부착응력을 ACI 규준의 상한선($700kg/cm^2$)을 초과하여도 부착응력 및 최대 부착응력이 증가하는 것으로 나타나 콘크리트 압축강도 상한선을 초과하는 경우 정착길이 산정시 압축강도 증가에 따른 영향을 고려하여야 하는 것으로 나타났다.