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CONTENTS
Volume 14, Number 2, August 2002
 

Abstract
A beam-column fiber element for the large displacement, nonlinear inelastic analysis of Concrete-Filled Steel Tubes (CFT) is implemented. The method of description is Total Lagrangian formulation. An 8 degree of freedom (DOF) element with three nodes, which has 3 DOF per end node and 2 DOF on the middle node, has been chosen. The quadratic Lagrangian shape functions for axial deformation and the quartic Hermitian shape function for the transverse deformation are used. It is assumed that the perfect bond is maintained between steel shell and concrete core. The constitutive models employed for concrete and steel are based on the results of a recent study and include the confinement and biaxial effects. The model is implemented to analyze several CFT columns under constant and non-proportional fluctuating concentric axial load and cyclic lateral load. Good agreement has been found between experimental results and theoretical analysis.

Key Words
Concrete-Filled steel Tubes (CFT), composite fiber element, cyclic loads, hysteretic, material models, Lagragian shape functions, Hermitian shape functions, quartic shape functions

Address
Golafshani AA, Sharif Univ Technol, Dept Civil Engn, Tehran, Iran
Sharif Univ Technol, Dept Civil Engn, Tehran, Iran
New Jersey Inst Technol, Dept Civil & Environm Engn, Newark, NJ 07102 USA

Abstract
Numerical analysis of ultimate behaviour of thin bionics shells is treated in present paper. Interactive conditions in resonance and stability ultimate response are considered. Numerical treatment of nonlinear problems appearing is made using the updated Lagrangian formulation of motion. Each step of the iteration approaches the solution of linear problem and the feasibility of parallel processing FETM-technique with adaptive mesh refinement and substructuring for the analysis of ultimate action of thin bionics shells is established. Some numerical results are submitted in order to demonstrate the efficiency of the procedures suggested.

Key Words
adaptive mesh refinement, bionics shell, FETM-method, parallel processing, resonance, stability, substructuring, ultimate dynamics, updated Lagrangian formulation of motion, wave propagation

Address
Tesar A, Slovak Acad Sci, Inst Construct & Architecture, Dubravska Cesta 9, Bratislava 84220, Slovakia
Slovak Acad Sci, Inst Construct & Architecture, Bratislava 84220, Slovakia

Abstract
Moving force identification is a very important inverse problem in structural dynamics. Most of the identification methods are eventually converted to a linear algebraic equation set. Different ways to solve the equation set may lead to solutions with completely different levels of accuracy. Based on the measured bending moment responses of the bridge made in laboratory, this paper presented the time domain method (TDM) and frequency-time domain method (FFDM) for identifying the two moving wheel loads of a vehicle moving across a bridge. Directly calculating pseudo-inverse (PI) matrix and using the singular value decomposition (SVD) technique are adopted as means for solving the over-determined system equation in the TDM and FTDM. The effects of bridge and vehicle parameters on the TDM and FTDM are also investigated. Assessment results show that the SVD technique can effectively improve identification accuracy when using the TDM and FTDM, particularly in the case of the FTDM. This improved accuracy makes the TDM and FTDM more feasible and acceptable as methods for moving force identification.

Key Words
moving force identification, bridge-vehicle interaction, time domain method, frequency-time domain method, singular value decomposition, bending moment, response measurement

Address
Yu L, Hong Kong Polytech Univ, Dept Civil & Struct Engn, Kowloon, Hong Kong, Peoples R China
Hong Kong Polytech Univ, Dept Civil & Struct Engn, Kowloon, Hong Kong, Peoples R China

Abstract
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.

Key Words
reinforcement design in plate and shell, hyperbolic paraboloid saddle shell, hyperbolic cooling tower, nonlinear inelastic behavior, finite element analysis

Address
Min CS, Dongguk Univ, Dept Civil & Environm Engn, Chung Gu, Pil Dong 26, Seoul 100715, South Korea
Dongguk Univ, Dept Civil & Environm Engn, Chung Gu, Seoul 100715, South Korea

Abstract
A comparative assessment study for a generation of the pressure-temperature (P-T) limit curve of a reactor vessel is performed in accordance with ASME code. Using cooling or heating rate and vessel material properties, stress distribution is obtained to calculate stress intensity factors, which are compared with the material fracture toughness to determine the relations between operating pressure and temperature during reactor cool-down and heat-up. P-T limit curves are analyzed with respect to defect orientation, clad thickness, toughness curve, cooling or heating rate and neutron fluence. The resulting P-T curves are compared each other.

Key Words
pressure-temperature limit curve, fracture toughness, stress intensity factor, heat-up, cool-down, reactor vessel, ASME code

Address
Jhung MJ, Korea Inst Nucl Safety, Yusong Gu, 19 Kusong Dong, Taejon 305338, South Korea
Korea Inst Nucl Safety, Yusong Gu, Taejon 305338, South Korea
Korea Power Engn Co Inc, Yongin 449713, Kyunggi Do, South Korea

Abstract
In this paper a fracture criterion is proposed for cracked cylindrical samples of high-strength prestressing steels of different yield strength. The surface crack is assumed to be semi-elliptical, a geometry very adequate to model sharp defects produced by any subcritical mechanism of cracking: mechanical fatigue, stress-corrosion cracking, hydrogen embrittlement or corrosion fatigue. Two fracture criteria with different meanings are considered: a global (energetic) criterion based on the energy release rate G, and a local (stress) criterion based on the stress intensity factor K-1. The advantages and disadvantages of both criteria for engineering design are discussed in this paper on the basis of many experimental results of fracture tests on cracked wires of high-strength prestressing steels of different yield strength and with different degrees of strength anisotropy.

Key Words
high-strength steel, cracked cylindrical bars, stress intensity factor, energy release rate, fracture criterion

Address
Toribio J, Univ Salamanca, Dept Mat Engn, EPS, Campus Viriato,Avda Requejo 33, Zamora 49022, Spain
Univ Salamanca, Dept Mat Engn, EPS, Zamora 49022, Spain

Abstract
The main objective of the present paper is to address a formal procedure for orthotropic steel plates design. The theme of the proposed approach is to recast the design procedure into a mathematical programming model. The objective function to be optimized is the total weight of the structure. The total weight is function of its layout parameters and structural element design variables. Mean while the proposed approach takes into consideration the strength and rigidity criteria in addition to other dimensional constraints. A nonlinear programming model is developed which consists of a nonlinear objective function and a set of implicit/explicit nonlinear constraints. A transformation method is adopted for minimization strategy, where the primal model constrained problem is transformed into a sequence of unconstrained minimization models. The search strategy is based on the well-known Fletcher/Powell algorithm. The finite element technique is adopted for discretization and analysis strategies. Mindlin theory is selected to simulate the finite element model and a selective reduced integration scheme is exploited to avoid a shear lock problem.

Key Words
optimization, orthotropic, steel plates

Address
Maaly H, Zagazig Univ, Coll Engn, Dept Struct Engn, Zagazig, Egypt
Zagazig Univ, Coll Engn, Dept Struct Engn, Zagazig, Egypt
Zagazig Univ, Coll Engn, Dept Mech Engn, Zagazig, Egypt

Abstract
It is well known that torsionally unbalanced buildings are more vulnerable to earthquake hazards than are the regular structural systems. In this paper, a parametric investigation is presented, in order to observe the amplification in the internal forces, when increased eccentricities are used instead of the ones corresponding to the 5% accidental eccentricity. A series of five, ten-story framed and walled structures, with rather high torsional irregularity coefficients, are selected and a numerical test procedure is applied. Numerical results show that the maximum amplification in the internal forces at the most critical beams and columns at the flexible sides of the structures is about 10%. It is concluded that, more serious measures in the codes are needed in the case of this rather dangerous type of irregularity.

Key Words
irregular structures, torsional irregularity, earthquake resistant design, seismic code, seismic response

Address
Ozmen G, Istanbul Tech Univ, Dept Civil Engn, TR-80626 Istanbul, Turkey
Istanbul Tech Univ, Dept Civil Engn, TR-80626 Istanbul, Turkey


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