• Structural Engineering and Mechanics
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• 제28권6호
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• pp.727-747
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• 2008

In the framework of the SPEAR (Seismic PErformance Assessment and Rehabilitation) research Project, an under-designed three storey RC frame structure, designed to sustain only gravity loads, was subjected, in three different configurations 'as-built', Fiber Reinforced Polymer (FRP) retrofitted and rehabilitated by reinforced concrete (RC) jacketing, to a series of bi-directional pseudodynamic (PsD) tests under different values of peak ground acceleration (PGA) (from a minimum of 0.20g to a maximum of 0.30g). The seismic deficiencies exhibited by the 'as-built' structure after the test at PGA level of 0.20g were confirmed by a post - test assessment of the structural seismic capacity performed by a nonlinear static pushover analysis implemented on the structure lumped plasticity model. To improve the seismic performance of the 'as-built' structure', two rehabilitation interventions by using either FRP laminates or RC jacketing were designed. Assumptions for the analytical modeling, design criteria and calculation procedures along with local and global intervention measures and their installation details are herein presented and discussed. Nonlinear static pushover analyses for the assessment of the theoretical seismic capacity of the structure in each retrofitted configuration were performed and compared with the experimental outcomes.

• Structural Engineering and Mechanics
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• 제85권4호
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• pp.511-529
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• 2023

This paper aims to better understand the bonding behavior in Reinforced Concrete beams strengthened with an Ultra-High Performance Fiber Reinforced Concrete (RCUHPFRC) layer on the compression side using experimental tests and numerical analyses. The UHPFRC mix design was obtained through an optimization procedure, and the characterization of the materials included compression and slant shear tests. Flexural tests were carried out in RC beams and RC-UHPFRC beams. The tests demonstrated a debonding of the UHPFRC layer. In addition, 3D finite element analyses were carried out in the Abaqus CAE program, in which the interface is modeled considering a zero-thickness cohesive-contact approach. The cohesive parameters are investigated, aiming to calibrate the numerical models, and a sensitivity analysis is performed to check the reliability of the assumed cohesive parameters and the mesh size. Finally, the experimental and numerical values are compared, showing a good approximation for both the RC beams and the RC strengthened beams.

• Structural Engineering and Mechanics
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• 제61권5호
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• pp.625-635
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• 2017

Sets of nonlinear formulations together with an energy-based damage index (DI) are proposed to model the behavior and quantify the damage of the confined and unconfined concretes under monotonic and cyclic loading. The proposed formulations and DI can be employed in numerical simulations to determine the stresses and the damages to the fibers or the layers within the sections of reinforced concrete (RC) components. To verify the proposed formulations, an adaptive finite element computer program was generated to simulate the RC structures subjected to monotonic and cyclic loading. By comparing the simulated and the experimental test results, on both the full-scale structural members and concrete cylindrical samples, the proposed uniaxial behavior modeling formulations for confined and unconfined concretes under monotonic and cyclic loading, based on an iterative process, were accordingly adjusted, and then validated. The proposed formulations have strong mathematical structures and can readily be adapted to achieve a higher degree of precision by improving the relevant coefficients based on more precise tests. To apply the proposed DI, the stress-strain data of concrete elements is required. It can easily be calculated by using the proposed nonlinear constitutive laws for confined and unconfined concretes in this paper.

• Structural Engineering and Mechanics
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• 제18권2호
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• pp.211-229
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• 2004

The main purpose of this paper is the numerical analysis of the non-linear seismic response of a RC building mock-up. The mock-up is subjected to different synthetic horizontal seismic excitations. The numerical approach is based on a 3D-model involving multilayered shell elements. These elements are composed of several single-layer membranes with various eccentricities. Bending effects are included through these eccentricities. Basic equations are first written for a single membrane element with its own eccentricity and then generalised to the multilayered shell element by superposition. The multilayered shell is considered as a classical shell element : all information about non-linear constitutive relations are investigated at the local scale of each layer, whereas balance and kinematics are checked afterwards at global scale. The non-linear dynamic response of the building is computed with Newmark algorithm. The numerical dynamic results (blind simulations) are considered in the linear and non linear cases and compared with experimental results from shaking table tests. Multilayered shell elements are found to be a promising tool for predictive computations of RC structures behaviour under 3D seismic loadings. This study was part of the CAMUS International Benchmark.

• Computers and Concrete
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• 제22권6호
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• pp.515-525
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• 2018

This paper presents a numerical study on the performance of reinforced concrete (RC) bridge structures subjected to heavy goods vehicle (HGV) collision. The objectives of this study are to investigate the dynamic response and failure modes of different types of bridges under impact loading as well as to give an insight into the simplified methods for modeling bridge structures. For this purpose, detailed finite-element models of HGV and bridges are established and verified against the full-scale collision experiment and a recent traffic accident. An intensive parametric study with the consideration of vehicle weight, vehicle velocity, structural type, simplified methods for modeling bridges is conducted; then the failure mode, impact force, deformation and internal force distribution of the validated bridge models are discussed. It is observed that the structural type has a significant effect on the force-transferring mechanism, failure mode and dynamic response of bridge structures, thus it should be considered in the anti-impact design of bridge structures. The impact force of HGV is mainly determined by the impact weight, impact velocity and contact interface, rather than the simplification of the superstructure. Furthermore, to reduce the modeling and computing cost, it is suggested to utilize the simplified bridge model considering the inertial effect of the superstructure to evaluate the structural impact behavior within a reasonable precision range.

• International Journal of Concrete Structures and Materials
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• 제9권1호
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• pp.89-118
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• 2015

The geometric nonlinearity of off-diagonal bracing system (ODBS) could be a complementary system to covering and extending the nonlinearity of reinforced concrete material. Finite element modeling is performed for flexural frame, x-braced frame and the ODBS braced frame system at the initial phase. Then the different models are investigated along various analyses. According to the experimental results of flexural and x-braced frame, the verification is done. Analytical assessments are performed in according to three dimensional finite element modeling. Nonlinear static analysis is considered to obtain performance level and seismic behaviour, and then the response modification factors calculated from each model's pushover curve. In the next phase, the evaluation of cracks observed in the finite element models, especially for RC members of all three systems is performed. The finite element assessment is performed on engendered cracks in ODBS braced frame for various time steps. The nonlinear dynamic time history analysis accomplished in different stories models for three records of Elcentro, Naghan and Tabas earthquake accelerograms. Dynamic analysis is performed after scaling accelerogram on each type of flexural frame, x-braced frame and ODBS braced frame one by one. The base-point on RC frame is considered to investigate proportional displacement under each record. Hysteresis curves are assessed along continuing this study. The equivalent viscous damping for ODBS system is estimated in according to references. Results in each section show the ODBS system has an acceptable seismic behaviour and their conclusions have been converged when the ODBS system is utilized in reinforced concrete frame.

• 콘크리트학회논문집
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• 제14권4호
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• pp.615-622
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• 2002

철근콘크리트 무량판 구조의 내력 및 변위를 합리적으로 예측하기 위해서는 슬래브의 휨 강성을 고려한 해석모델이 필요하다. FEMA 273과 ACI 318-99에서는 횡 하중에 대한 슬래브의 해석모델들을 제시하고 있으나 실제적인 적용 방법론은 언급하고 있지 않다. 본 연구에서는 무량판 슬래브의 모델링 방법론을 정립하고 이를 내진설계에 어떻게 적용할 것인가에 대하여 연구하였다. 연구결과는 다음과 같다. 1) 무량판 구조의 3차원 해석시 슬래브의 휨 강성을 적절히 고려하기 위해서는 본 연구진이 제시하는 유효보폭 모델을 적용하는 것이 바람직하다. 2) 예제 무량판 건물 해석에서 슬래브의 균열효과를 고려한 유효보폭을 이용할 경우 해석결과는 횡변위에 대하여 상한값을 나타낸 반면 유효보폭 계수만을 고려한 모델은 접합부 불균형 모멘트에 대하여 상한값의 결과를 나타냈다.

• 전자공학회논문지C
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• 제36C권5호
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• pp.13-26
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• 1999

본 논문은 다양한 회로 연결선 모형 중에서 연결선 변수 및 동작 환경에 다라 최적 모형을 쉽게 선택할 수 있는 기준을 제시하고자 한다. 이를 위하여 먼저 연결선의 총 저항, 인덕턴스, 커패시턴스 값 및 신호의 동작주파수를 기반으로 정량적 모형화 오차 분석에 근거하여 인덕턴스의 영향을 고려하여 모형화해야 하는 RLC-class 모형 영역과 그럴 필요가 없는 RC-class모형 영역으로 분할하는 방법을 제시한다. 칩 내부 연결선의 대부분을 차지하는 RC-class 회로 모형은 모형 차수 축소 기법을 통하여 효율적으로 해석될 수 있다. RLC-class 회로 모형은 주어진 허용 모형화 오차 및 전기 변수에 따라 ILC(Iterative Ladder Circuit) 거시 모형, MC(Method of Characteristics)거시 모형 및 상태 기반 컨벌루션(comvolution) 방법 중에서 최적인 모형을 선정하게 된다. 본 논문은 SPICE류의 범용 회로 시뮬레이션 앨고리즘을 가정할 때, 세부 모형들의 시뮬레이션 비용을 감안하고서 최적 모형을 찾는 영역 구성도를 제시한다. 본 논문에서 제시하는 거시모형화 방법은 회로의 수동성을 유지하며, 따라서 무조건적 안정도를 보장할 수 있다.

• Structural Engineering and Mechanics
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• 제18권5호
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• pp.645-669
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• 2004

In seismic analysis of moment-resisting frames, beam-column connections are often modeled with rigid joint zones. However, it has been demonstrated that, in ductile reinforced concrete (RC) moment-resisting frames designed based on current codes (to say nothing of older non-ductile frames), the joint zones are in fact not rigid, but rather undergo significant shear deformations that contribute greatly to global drift. Therefore, the "rigid joint" assumption may result in misinterpretation of the global performance characteristics of frames and could consequently lead to miscalculation of strength and ductility demands on constituent frame members. The primary objective of this paper is to propose a rational method for estimating the hysteretic joint shear behavior of RC connections and for incorporating this behavior into frame analysis. The authors tested four RC edge beam-column-slab connection subassemblies subjected to earthquake-type lateral loading; hysteretic joint shear behavior is investigated based on these tests and other laboratory tests reported in the literature. An analytical scheme employing the modified compression field theory (MCFT) is developed to approximate joint shear stress vs. joint shear strain response. A connection model capable of explicitly considering hysteretic joint shear behavior is then formulated for nonlinear structural analysis. In the model, a joint is represented by rigid elements located along the joint edges and nonlinear rotational springs embedded in one of the four hinges linking adjacent rigid elements. The connection model is able to well represent the experimental hysteretic joint shear behavior and overall load-displacement response of connection subassemblies.

• 한국전자파학회논문지
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• 제12권5호
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• pp.772-772
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• 2001

본 논문에서는 영상법 기반의 3차원 광선추적법에 패치산란모델을 이용하여 실내 구조물을 고려할 수 있는 실내 전파모델링 방법을 제시하였다. 실내 구조물을 모델링하기 위한 패치산란모델은 패치형태의 직사각형 평면에 대한 RCS를 이용하여 입사에 대한 산란현상을 정의한 것으로써, 책상이나 테이블 같은 평면적인 실내구조물에 대한 산란현상을 각각의 구조물에 대한 영상 안테나를 발생시키는 복잡한 과정 없이 간단하게 해석하기 위한 것이다. RCS는 간단히 입사 전력에 대한 산란 전력의 비로 정의되며 본 논문에서는 다양한 수신 각도에서 바라보는 bistatic RCS를 물리광학(Physical Optics)을 이용하여 수식적으로 유도하여 패치산란모델에 이용하였다. 또한 실내의 다중경로 성분에 대해 계산하지 않는 패치산란모델을 실내에 적용하기 위하여 복잡한 수식보다는 단순한 보정값인 실내보정값을 정의하였는데, 본 논문에서는 이 값을 다양한 패치 환경의 측정에 의한 경험적 상수로 처리함으로써 RCS의 고려만으로는 실내에 적용할 수 없는 점을 극복하였다.