Ultimate behavior and ultimate load capacity of steel cable-stayed bridges

Choi, D.H.,Yoo, H.,Shin, J.I.,Park, S.I.,Nogami, K. Techno-Press 2007 Structural Engineering and Mechanics, An Int'l Jou Vol.27 No.4

The main purpose of this paper is to investigate the ultimate behavior of steel cable-stayed bridges with design variables and compare the validity and applicability of computational methods for evaluating ultimate load capacity of cable-stayed bridges. The methods considered in this paper are elastic buckling analysis, inelastic buckling analysis and nonlinear elasto-plastic analysis. Elastic buckling analysis uses a numerical eigenvalue calculation without considering geometric nonlinearities of cable-stayed bridges and the inelastic material behavior of main components. Inelastic buckling analysis uses an iterative eigenvalue calculation to consider inelastic material behavior, but cannot consider geometric nonlinearities of cable-stayed bridges. The tangent modulus concept with the column strength curve prescribed in AASHTO LRFD is used to consider inelastic buckling behavior. Detailed procedures of inelastic buckling analysis are presented and corresponding computer codes were developed. In contrast, nonlinear elasto-plastic analysis uses an incremental-iterative method and can consider both geometric nonlinearities and inelastic material behavior of a cable-stayed bridge. Proprietary software ABAQUS are used and user-subroutines are newly written to update equivalent modulus of cables to consider geometric nonlinearity due to cable sags at each increment step. Ultimate load capacities with the three analyses are evaluated for numerical models of cable-stayed bridges that have center spans of 600 m, 900 m and 1200 m with different girder depths and live load cases. The results show that inelastic buckling analysis is an effective approximation method, as a simple and fast alternative, to obtain ultimate load capacity of long span cable-stayed bridges, whereas elastic buckling analysis greatly overestimates the overall stability of cable-stayed bridges.

A new constitutive model for simulation of softening, plateau, and densification phenomena for trabecular bone under compression

Lee, Chi-Seung,Lee, Jae-Myung,Youn, BuHyun,Kim, Hyung-Sik,Shin, Jong Ki,Goh, Tae Sik,Lee, Jung Sub Elsevier 2017 Journal of the mechanical behavior of biomedical m Vol.65 No.-

<P><B>Abstract</B></P> <P>A new type of constitutive model and its computational implementation procedure for the simulation of a trabecular bone are proposed in the present study. A yield surface-independent Frank–Brockman elasto-viscoplastic model is introduced to express the nonlinear material behavior such as softening beyond yield point, plateau, and densification under compressive loads. In particular, the hardening- and softening-dominant material functions are introduced and adopted in the plastic multiplier to describe each nonlinear material behavior separately. In addition, the elasto-viscoplastic model is transformed into an implicit type discrete model, and is programmed as a user-defined material subroutine in commercial finite element analysis code. In particular, the consistent tangent modulus method is proposed to improve the computational convergence and to save computational time during finite element analysis. Through the developed material library, the nonlinear stress–strain relationship is analyzed qualitatively and quantitatively, and the simulation results are compared with the results of compression test on the trabecular bone to validate the proposed constitutive model, computational method, and material library.</P>

Design and ultimate behavior of RC plates and shells: two case studies

Min, Chang-Shik Techno-Press 2002 Structural Engineering and Mechanics, An Int'l Jou Vol.14 No.2

Two cases of design are performed for the hyperbolic paraboloid saddle shell (Lin-Scordelis saddle shell) and the hyperbolic cooling tower (Grand Gulf cooling tower) to check the design strength against a consistent design load, therefore to verify the adequacy of the design algorithm. An iterative numerical computational algorithm is developed for combined membrane and flexural forces, which is based on equilibrium consideration for the limit state of reinforcement and cracked concrete. The design algorithm is implemented in a finite element analysis computer program developed by Mahmoud and Gupta. The amount of reinforcement is then determined at the center of each element by an elastic finite element analysis with the design ultimate load. Based on ultimate nonlinear analyses performed with designed saddle shell, the analytically calculated ultimate load exceeded the design ultimate load from 7% to 34% for analyses with various magnitude of tension stiffening. For the cooling tower problem the calculated ultimate load exceeded the design ultimate load from 26% to 63% with similar types of analyses. Since the effective tension stiffening would vary over the life of the shells due to environmental factors, a degree of uncertainty seems inevitable in calculating the actual failure load by means of numerical analysis. Even though the ultimate loads are strongly dependent on the tensile properties of concrete, the calculated ultimate loads are higher than the design ultimate loads for both design cases. For the cases designed, the design algorithm gives a lower bound on the design ultimate load with respect to the lower bound theorem. This shows the adequacy of the design algorithm developed, at least for the shells studied. The presented design algorithm for the combined membrane and flexural forces can be evolved as a general design method for reinforced concrete plates and shells through further studies involving the performance of multiple designs and the analyses of differing shell configurations.

이선형 단자유도 감쇠시스템의 비탄성변위비

한상환,배문수,조종 한국지진공학회 2007 한국지진공학회논문집 Vol.11 No.6

NEHRP 지반조건 B,C,D에서 이선형 단자유도 감쇠시스템의 지반조건, 후탄성기울기, 감쇠비, 항복강도 감소계수, 고유 주기 등의 변화가 비탄성변위비에 미치는 영향을 조사하였다. 기존의 제안식은 변위일정 법칙을 따라 일정주기 이상에서 비탄성 변위비를 과대평가하게 된다. 또한 기존식은 5%이상의 감쇠비에 대하여만 제안되었다. 본 연구는 후탄성기울기, 감쇠비 20% 이하의 이선형 시스템의 비탄성 변위비의 평균과 편차를 제안하였고 범용적으로 사용할 수 있음을 보였다. 제안식을 사용하여 비탄성 변위비의 확률적 분포를 계산하여 구조물의 성능기반설계에 이용할 수 있다. This study investigates the effect of site class, post-yield stiffness ratio, damping ratio, yield-strength reduction factor, and natural period on inelastic displacement ratio of bilinear SDF systems located at the sites classified as NEHRP site class B,C,D. The previous studies developed inelastic displacement ratio using equal displacement rule in the intermediate and long period range. But, this approximation overestimates the inelastic displacement ratio. Furthermore, inelastic displacement ratio has not been developed for the systems having a damping ratio less than 5%. This study conducts nonlinear regression analysis for proposing equations for calculating median and deviation of the inelastic displacement ratio of the bilinear SDOF system having damping ratios ranging from 0 to 20%. Using median and deviation of the inelastic displacement ratio, probabilistic inelastic displacement ratio is estimated, which can be used for performance-based seismic evaluation.

Advanced analysis for planar steel frames with semi-rigid connections using plastic-zone methodAdvanced analysis for planar steel frames with semi-rigid connections using plastic-zone method

Phu-Cuong Nguyen,김승억 국제구조공학회 2016 Steel and Composite Structures, An International J Vol.21 No.5

This paper presents a displacement-based finite element procedure for second-order distributed plasticity analysis of planar steel frames with semi-rigid beam-to-column connections under static loadings. A partially strain-hardening elastic-plastic beam-column element, which directly takes into account geometric nonlinearity, gradual yielding of material, and flexibility of semi-rigid connections, is proposed. The second-order effects and distributed plasticity are considered by dividing the member into several sub-elements and meshing the cross-section into several fibers. A new nonlinear solution procedure based on the combination of the Newton-Raphson equilibrium iterative algorithm and the constant work method for adjusting the incremental load factor is proposed for solving nonlinear equilibrium equations. The nonlinear inelastic behavior predicted by the proposed program compares well with previous studies. Coupling effects of three primary sources of nonlinearity, geometric imperfections, and residual stress are investigated and discussed in this paper.

Inelastic vector finite element analysis of RC shells

Min, Chang-Shik,Gupta, Ajaya Kumar Techno-Press 1996 Structural Engineering and Mechanics, An Int'l Jou Vol.4 No.2

Vector algorithms and the relative importance of the four basic modules (computation of element stiffness matrices, assembly of the global stiffness matrix, solution of the system of linear simultaneous equations, and calculation of stresses and strains) of a finite element computer program for inelastic analysis of reinforced concrete shells are presented. Performance of the vector program is compared with a scalar program. For a cooling tower problem, the speedup factor from the scalar to the vector program is 34 for the element stiffness matrices calculation, 25.3 for the assembly of global stiffness matrix, 27.5 for the equation solver, and 37.8 for stresses, strains and nodal forces computations on a Gray Y-MP. The overall speedup factor is 30.9. When the equation solver alone is vectorized, which is computationally the most intensive part of a finite element program, a speedup factor of only 1.9 is achieved. When the rest of the program is also vectorized, a large additional speedup factor of 15.9 is attained. Therefore, it is very important that all the modules in a nonlinear program are vectorized to gain the full potential of the supercomputers. The vector finite element computer program for inelastic analysis of RC shells with layered elements developed in the present study enabled us to perform mesh convergence studies. The vector program can be used for studying the ultimate behavior of RC shells and used as a design tool.

Inelastic analysis for the post-collapse behavior of concrete encased steel composite columns under axial compression

V.S. Ky,S. Tangaramvong,T.Thepchatri 국제구조공학회 2015 Steel and Composite Structures, An International J Vol.19 No.5

This paper proposes a simple inelastic analysis approach to efficiently map out the complete nonlinear post-collapse (strain-softening) response and the maximum load capacity of axially loaded concrete encased steel composite columns (stub and slender). The scheme simultaneously incorporates the influences of difficult instabilizing phenomena such as concrete confinement, initial geometric imperfection, geometric nonlinearity, buckling of reinforcement bars and local buckling of structural steel, on the overall behavior of the composite columns. The proposed numerical method adopts fiber element discretization and an iterative Muller's algorithm with an additional adaptive technique that robustly yields solution convergence. The accuracy of the proposed analysis scheme is validated through comparisons with various available experimental benchmarks. Finally, a parametric study of various key parameters on the overall behaviors of the composite columns is conducted.

SI기법을 이용한 변단면 PSC 거더의 층상화 단면해석

김병화(Kim Byeong Hwa),박대효(Park Taehyo),전혜관(Jeon Hye-Kwan) 대한토목학회 2010 대한토목학회논문집 A Vol.30 No.6A

본 연구는 곡선배치 텐던을 갖는 변단면 PSC의 전단을 고려한 층상화 단면해석기술을 소개한다. 곡선배치 텐던의 전단평형을 고려하기 위해서, 각 층상화 단면에서 전단응력을 직접 산출 할 수 있는 새로운 방법과 각 층상화 단면의 변형률 산정시 기존의 반복법보다 수렴 속도가 효율적인 시스템인식기법을 적용하였다. 제안기법은 변단면 PSC보의 정재하실험 결과와 비교분석 되었으며, 추정된 구조응답과 실험결과가 잘 일치하고 있다. 또한, 동일 조건에서 변단면 PSC보와 균등단면 PSC보의 거동특성이 비교분석되었다. 분석결과을 살펴보면, 휨강성은 변단면과 균등단면이 동일하지만, 전단강성은 변단면이 균등단면 보다 크다. 더욱이, 변단면의 자중이 균등단면보다 크지만 변단면의 최대처짐이 균등단면 보다 작다. This study introduces a layered sectional analysis for a PSC girder with a vaiable cross section and curved tendons. To consider the shear equilibrium at a concrete layer with curved tendons, the shear stress distribution has been computed at each section. In addition, to improve the convergence to the solution, a system identification technique is newly adopted in the solution process for strain computation. To examine the feasibility of the proposed approach, a static load test has been conducted for a full scale PSC girder with variable cross section. The prediction shows a good agreement with experiment. It is seen that a uniform cross section has the same moment capacity with a variable cross section while the variable cross section has more shear capacity than the uniform cross section. It is also noted that the maximum displacement of a variable cross section is a little smaller than a uniform cross section.

3차원 강사장교의 초기형상을 고려한 비선형 비탄성 해석기법 연구

마상수 ( Ma Sang-soo ),안진희 ( Ahn Jin-hee ),신창건 ( Shin Chang-gun ),윤영조 ( Youn Young-jo ),김경진 ( Kim Kyeong-jin ) 한국구조물진단유지관리공학회 2022 한국구조물진단유지관리공학회 학술발표대회 논문집 Vol.26 No.2

본 연구에서는 강사장교의 초기형상을 고려한 비선형 비탄성 해석기법을 제시하였다. 구조시스템과 부재의 강도와 안정성을 직접 고려함으로서, 해석 후 개별부재의 강도 검토가 필요 없는 해석기법이다. 본 해석은 재료적 비선형과 기하학적 비선형을 고려하였다. 보-기둥 부재의 재료적 비선형성을 고려하기 위하여 CRC 접선계수와 포물선 함수를 사용하였고 기하학적 비선형은 케이블 새그, 보-기둥의 대변위 효과가 반영되었다.

능력스펙트럼을 이용한 최대 비탄성 변위 응답의 정확성 평가

박민규,민경원,김홍진 대한건축학회 2004 대한건축학회 학술발표대회 논문집 - 계획계/구조계 Vol.24 No.1(구조계)

In the capacity spectrum method (CSM) using a linear response spectrum, the peak response of an inelastic system under a given earthquake load is estimated transforming the system into the equivalent elastic one. The CSM for estimating the peak inelastic response is evaluated in this paper. The equivalent period and damping ratio are calculated using the A TC-40, Gulkan, Kowalsky, and Iwan methods, and the performance points are obtained according the procedure B of ATC-40. Analysis results indicate that the ATC-40 method generally underestimates the peak response resulting in the unsafe design, while the Gulkan and Kowalsky methods overestimate the responses. The Iwan method produces the values between those by the A TC-40 method and the Gulkan and Kowalsky methods, and estimates the responses relatively closer to the exact ones.