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CONTENTS | |

Volume 5, Number 5, September 1997 |

- Complementarity and nonlinear structural analysis of skeletal structures TinLoi F

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Abstract; Full Text (1174K) | pages 491-505. |
DOI: 10.12989/sem.1997.5.5.491 |

Abstract

This paper deals with the formulation and solution of a wide class of-structures, in the presence of both geometric and material nonlinearities, as a particular mathematical programming problem. We first present key ideas for the nonholonomic (path dependent) rate formulation for a suitably discretized structural model before we develop its computationally advantageous stepwise holonomic (path independent) counterpart. A feature of the final mathematical programming problem, known as a nonlinear complementarity problem, is that the governing relations exhibit symmetry as a result of the introduction of so-called nonlinear. \'\'residuals\'\'. One advantage of this form is that it facilitates application of a particular iterative algorithm, in essence a predictor-corrector method, for the solution process. As an illustrative example, we specifically consider the simplest case of plane trusses and detail in particular the general methodology for establishing the static-kinematic relations in a dual format. Extension to other skeletal structures is conceptually transparent. Some numerical examples are presented to illustrate applicability of the procedure.

Key Words

elastoplastic analysis, large displacement, mathematical programming, nonlinear complementarity problem, structural plasticity

Address

TinLoi F, UNIV NEW S WALES,SCH CIVIL ENGN,SYDNEY,NSW 2052,AUSTRALIA

- Ultimate behavior of RC hyperbolic paraboloid saddle shell Min CS

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Abstract; Full Text (1453K) | pages 507-521. |
DOI: 10.12989/sem.1997.5.5.507 |

Abstract

The ultimate behavior of a reinforced concrete hyperbolic paraboloid saddle shell under uniformly distributed vertical load is investigated using an inelastic, large displacement finite-element program originally developed at North Carolina State University. Unlike with the author\'s previous study which shows that the saddle shell possesses a tremendous capacity to redistribute the stresses, introducing tension stiffening in the model the cracks developed are no longer through cracks and formed as primarily bending cracks. Even though with small tension stiffening effect, the behavior of the shell is changed markedly from the one without tension stiffening effect. The load-deflection curves are straight and the slope of the curves is quite steep and remains unchanged with varying the tension stiffening parameters. The failure of the shell took place quite suddenly in a cantilever mode initiated by a formation of yield lines in a direction parallel to the support-to-support diagonal. The higher the tension stiffening parameters the higher is the ultimate load. The present study shows that the ultimate behavior of the shell primarily depends on the concrete tensile characteristics, such as tensile strength (before cracking) and the effective tension stiffening (after cracking). As the concrete characteristics would vary over the life of the shell, a degree of uncertainty is involved in deciding a specified ultimate strength of the saddle shell studied. By the present study, however, the overload factors based on ACI 318-95 are larger than unity for all the cases studied except that the tension stiffening parameter is weak by 3 with and without the large displacement effect, which shows that the Lin-Scordelis saddle shell studied here is at least safe.

Key Words

reinforced concrete shells, hyperbolic paraboloid saddle shell, nonlinear finite element

Address

Min CS, CHEJU NATL UNIV,CHEJU 690756,SOUTH KOREA

- Bracing of structures to prescribed buckling loads Barbato J, Lawther R

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Abstract; Full Text (715K) | pages 523-528. |
DOI: 10.12989/sem.1997.5.5.523 |

Abstract

Stiffness and flexibility equations are combined in the buckling analysis of a braced structure - stiffness for the original structure and flexibility for the bracing. Choosing a flexibility formulation for the bracing gives a very compact computational problem. It also gives theoretical insights into the behaviour of the braced structure.

Key Words

buckling, eigenvalues & eigenvecters, bracing, stiffness, flexibility

Address

Barbato J, UNIV NEW S WALES,SCH CIVIL ENGN,SYDNEY,NSW 2052,AUSTRALIA

- Exact solutions of variable-arc-length elasticas under moment gradient Chucheepsakul S, Thepphitak G, Wang CM

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Abstract; Full Text (870K) | pages 529-539. |
DOI: 10.12989/sem.1997.5.5.529 |

Abstract

This paper deals with the bending problem of a variable-are-length elastica under moment gradient. The variable are-length arises from the fact that one end of the elastica is hinged while the other end portion is allowed to slide on a frictionless support that is fu;ed at a given horizontal distance from the hinged end. Based on the elastica theory, exact closed-form solution in the form of elliptic integrals are derived. The bending results show that there exists a maximum or a critical moment for given moment gradient parameters; whereby if the applied moment is less than this critical value, two equilibrium configurations are possible. One of them is stable while the other is unstable because a small disturbance will lead to beam motion.

Key Words

elliptic-integrals, large deflections, variable-arc-length bars, beams, elasticas

Address

Chucheepsakul S, KING MONGKUTS INST TECHNOL THONBURI,DEPT CIVIL ENGN,BANGKOK 10140,THAILAND

49 ENGN CONSULTANTS LTD,BANGKOK 10110,THAILAND

NATL UNIV SINGAPORE,DEPT CIVIL ENGN,SINGAPORE 0511,SINGAPORE

- Nonlinear behavior of R/C cooling tower shells Hara T, Kato S, Ohya M

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Abstract; Full Text (937K) | pages 541-552. |
DOI: 10.12989/sem.1997.5.5.541 |

Abstract

In this paper the ultimate strength of the R/C cooling towers, which have initial imperfection and pre-cracked elements, is analyzed. The initial geometric imperfections arise from the unavoidable inaccuracies under the construction and the pre-cracks are assumed to be produced by the temperature stress gradients or cyclic loading under wind pressure and/or earthquake load. Both effects are strongly influenced on the strength of the R/C cooling tower shell structures. The reinforcing ratio is also the important factor to evaluate the ultimate strength of the R/C cooling tower shells. However we could not analyze these structures experimentally because of their large, analyses are the powerful schemes to evaluate the safety and reliability of these structures. The analyzed model is Port Gibson cooling tower shell. In the numerical analysis the geometric and material nonlinearities are taken into account.

Key Words

R/C shell, finite element analysis, ultimate strength, geometric imperfection, cooling tower

Address

Hara T, TOKUYAMA COLL TECHNOL,DEPT CIVIL ENGN & ARCHITECTURE,KUME TAKAJO 3538,TOKUYAMA,YAMAGUCHI 745,JAPAN

TOYOHASHI UNIV TECHNOL,DEPT ARCHITECTURE & CIVIL ENGN,TOYOHASHI,AICHI 441,JAPAN

MATSUE NATL COLL TECHNOL,DEPT CIVIL ENGN,MATSUE,SHIMANE 690,JAPAN

- Transverse and longitudinal partial interaction in composite bolted side-plated reinforced-concrete beams Oehlers DJ, Nguyen NT, Ahmed M, Bradford MA

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Abstract; Full Text (995K) | pages 553-563. |
DOI: 10.12989/sem.1997.5.5.553 |

Abstract

A procedure is being developed for bolting plates to the sides of existing reinforced concrete beams to strengthen and stiffen them. Unlike standard composite steel and concrete beams in which there is longitudinal-partial-interaction at the steel/concrete interface (that is slip along the length of the beam), composite bolted side-plated reinforced-concrete beams are unique in that they also exhibit transverse-partial-interaction, that is slip transverse to the length of the beam. In this work, the fundamental mathematical models for transverse-partial-interaction and its interaction with longitudinal-partial-interaction are developed. The fundamental models are then further developed to determine the number of connectors required to resist the transverse forces and to limit the degree of transverse-partial-interaction in bolted side-plated reinforced concrete beams.

Key Words

plated beam, partial-interaction, reinforced-concrete beam

Address

Oehlers DJ, UNIV ADELAIDE,DEPT CIVIL & ENVIRONM ENGN,ADELAIDE,SA 5005,AUSTRALIA

UNIV NEW S WALES,DEPT STRUCT ENGN,SYDNEY,NSW 2052,AUSTRALIA

- Optimal reinforcement design of structures under the buckling load using the homogenization design method Min SJ, Kikuchi N

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Abstract; Full Text (1270K) | pages 565-576. |
DOI: 10.12989/sem.1997.5.5.565 |

Abstract

The material-based homogenization design method generates arbitrary topologies of initial structural design as well as reinforcement structural design by controlling the amount of material available. However, if a small volume constraint is specified in the design of Lightweight structures, thin and slender structures are usually obtained. For these structures stability becomes one of the most important requirements. Thus, to prevent overall buckling (that is, to increase stability), the objective of the design is to maximize the buckling load of a structure. In this paper, the buckling analysis is restricted to the linear buckling behavior of a structure. The global stability requirement is defined as a stiffness constraint, and determined by solving the eigenvalue problem. The optimality conditions to update the design variables are derived based on the sequential convex approximation method and the dual method. Illustrated examples are presented to validate the feasibility of this method in the design of structures.

Key Words

structural optimization, topology design, homogenization design method, buckling problem, reinforcement structure

Address

Min SJ, UNIV MICHIGAN,DEPT MECH ENGN & APPL MECH,ANN ARBOR,MI 48109

- Bypass, homotopy path and local iteration to compute the stability point Fujii F, Okazawa S

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Abstract; Full Text (833K) | pages 577-586. |
DOI: 10.12989/sem.1997.5.5.577 |

Abstract

In nonlinear finite element stability analysis of structures, the foremost necessary procedure is the computation to precisely locate a singular equilibrium point, at which the instability occurs. The present study describes global and local procedures for the computation of stability points including bifurcation points and limit points. The starting point, at which the procedure will be initiated, may be close to or arbitrarily far away from the target point. It may also be an equilibrium point or nonequilibrium point. Apart from the usual equilibrium path, bypass and homotopy path are proposed as the global path to the stability point. A local iterative method is necessary, when it is inspected that the computed path point is sufficiently close to the stability point.

Key Words

stability, buckling, bifurcation, path-tracing, pinpointing, path-switching, nonlinear solution methods, local iteration

Address

Fujii F, GIFU UNIV,GIFU 50111,JAPAN

NAGOYA UNIV,NAGOYA,AICHI 46401,JAPAN

- Structural dynamics: Convergence properties in the presence of damage and applications to masonry structures Nappi A, Facchin G, Marcuzzi C

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Abstract; Full Text (1077K) | pages 587-598. |
DOI: 10.12989/sem.1997.5.5.587 |

Abstract

A numerical model for masonry is proposed by following an internal variable approach originally developed in the field of elastic-plastic analysis. The general features of the theoretical framework are discussed by focussing on finite element models applicable to incremental elastic-plastic problems. An extremum property is derived and its implications in terms of convergence for convenient algorithms are briefly discussed, by including the case of softening materials and damage effects. Next, a numerical model is presented, which is suitable for masonry, can be developed according to the same internal variable formulation and enjoys similar properties. Some numerical results are presented and compared with the response of a masonry shear wall subjected to pseudodynamic tests.

Key Words

backward difference, damage mechanics, extremum properties, internal variables, masonry, plasticity, softening, nonlinear structural dynamics

Address

Nappi A, UNIV TRIESTE,DEPT CIVIL ENGN,PIAZZALE EUROPA 1,I-34127 TRIESTE,ITALY

- Concrete stiffness matrices for membrane elements Hsu TTC

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Abstract; Full Text (988K) | pages 599-608. |
DOI: 10.12989/sem.1997.5.5.599 |

Abstract

The concrete stiffness matrices of membrane elements used in the finite element analysis of wall-type structures are reviewed and discussed. The behavior of cracked reinforced concrete membrane elements is first described by summarizing the constitutive laws of concrete and steel established for the two softened truss models (the rotating-angle softened-truss model and the fixed-angle softened-truss model). These constitutive laws are then related to the concrete stiffness matrices of the two existing cracking models (the rotating-crack model and the fixed-crack model). In view of the weakness in the existing models, a general model of the matrix is proposed. This general matrix includes two Poisson ratios which are not clearly understood at present. It is proposed that all five material properties in the general matrix should be established by new biaxial tests of panels using proportional loading and strain-control procedures.

Key Words

concrete, constitutive laws, cracking, material matrix, membrane element, Poisson ratio, reinforced concrete, shear, stiffness, stress-strain relationship

Address

Hsu TTC, UNIV HOUSTON,DEPT CIVIL & ENVIRONM ENGN,HOUSTON,TX 77204

- Multiple cutout optimization in composite plates using evolutionary structural optimization Falzon BG, Steven GP, Xie MY

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Abstract; Full Text (1309K) | pages 609-624. |
DOI: 10.12989/sem.1997.5.5.609 |

Abstract

The optimization of cutouts in composite plates was investigated by implementing a procedure known as Evolutionary Structural Optimization. Perforations were introduced into a finite element mesh of the plate from which one or more cutouts of a predetermined size were evolved. In the examples presented, plates were rejected from around each evolving cutout based on a predefined rejection criterion. The Limiting ply within each plate element around the cutout was determined based on the Tsai-Hill failure criterion. Finite element plates with values below the product of the average Tsai-Hill number and a rejection criterion were subsequently removed. This process was iterated until a steady state was reached and the rejection criterion was then incremented by an evolutionary rate and the above steps repeated until the desired cutout area was achieved. Various plates with differing lay-up and loading parameters were investigated to demonstrate the generality and robustness of this optimization procedure.

Key Words

composite plates, optimization, evolutionary structural optimization, cutouts, failure criterion, biaxial, shear

Address

Falzon BG, UNIV LONDON IMPERIAL COLL SCI TECHNOL & MED,DEPT AERONAUT,PRINCE CONSORT RD,LONDON SW7 2BY,ENGLAND

UNIV SYDNEY,DEPT AERONAUT ENGN,SYDNEY,NSW 2006,AUSTRALIA

VICTORIA UNIV TECHNOL,DEPT CIVIL & BLDG ENGN,MELBOURNE,VIC 8001,AUSTRALIA

- Finite element analysis of RC beam-column joints with high-strength materials Noguchi H, Kashiwazaki T

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Abstract; Full Text (779K) | pages 625-634. |
DOI: 10.12989/sem.1997.5.5.625 |

Abstract

Reinforced concrete (RC) interior beam-column joints with high-strength materials: concrete compressive strength of 100 MPa and the yield strength of longitudinal bars of 685 MPa, were analyzed using three-dimensional (3-D) nonlinear finite element method (FEM). Specimen OKJ3 of joint shear failure type was a plane interior joint, and Specimen 12 of beam flexural failure type was a 3-D interior joint with transverse beams. Though the analytical initial stiffness was higher than experimental one, the analytical results gave a good agreement with the test results on the maximum story shear forces, the failure mode.

Key Words

reinforced concrete, beam-column joints, high-strength materials, shear strength, three-dimensional analysis, finite element method

Address

Noguchi H, CHIBA UNIV,DEPT ARCHITECTURE,INAGE KU,1-33 YAYOI CHO,CHIBA 263,JAPAN

- Parallel computation for transcendental structural eigenproblems Kennedy D, Williams FW

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Abstract; Full Text (952K) | pages 635-644. |
DOI: 10.12989/sem.1997.5.5.635 |

Abstract

The paper reviews the implementation and evaluation of exact methods for the computation of transcendental structural eigenvalues, i.e., critical buckling loads and natural frequencies of undamped vibration, on multiple instruction, multiple data parallel computers with distributed memory. Coarse, medium and fine grain parallel methods are described with illustrative examples. The methods are compared and combined into hybrid methods whose performance can be predicted from that of the component methods individually. An indication is given of how performance indicators can be presented in a generic form rather than being specific to one particular parallel computer. Current extensions to permit parallel optimum design of structures are outlined.

Key Words

parallel computers, structural analysis, buckling, vibration, optimum design

Address

Kennedy D, UNIV WALES COLL CARDIFF,CARDIFF SCH ENGN,STRUCT DIV,POB 686,CARDIFF CF2 3TB,S GLAM,WALES

- Layered finite element method in cracking and failure analysis of RC beams and beam-column-slab connections Guan H, Loo YC

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Abstract; Full Text (1292K) | pages 645-662. |
DOI: 10.12989/sem.1997.5.5.645 |

Abstract

A nonlinear semi-three-dimensional layered finite element procedure is developed for cracking and failure analysis of reinforced concrete beams and the spandrel beam-column-slab connections of flat plates. The layered element approach takes the elasto-plastic failure behaviour and geometric nonlinearity into consideration. A strain-hardening plasticity concrete model and a smeared steel model are incorporated into the layered element formulation. Further, shear failure, transverse reinforcement, spandrel beams and columns are successfully modelled. The proposed method incorporating the nonlinear constitutive models for concrete and steel is implemented in a finite element program. Test specimens including a series of reinforced concrete beams and beam-column-slab connections of flat plates are analysed. Results confirm the effectiveness and accuracy of the layered procedure in predicting both flexural and shear cracking up to failure.

Key Words

layered finite element, crack, failure analysis, reinforced concrete, beam, beam-column-slab connection, flate plate

Address

Guan H, UNIV SYDNEY,FAC ENGN,FINIET ELEMENT ANAL RES CTR,SYDNEY,NSW 2006,AUSTRALIA

GRIFFITH UNIV,SCH ENGN,NATHAN,QLD 4217,AUSTRALIA

- Improved numerical approach for the bond-slip behavior under cyclic loads Kwak HG

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Abstract; Full Text (1282K) | pages 663-667. |
DOI: 10.12989/sem.1997.5.5.663 |

Abstract

Bond-slip behavior between reinforcement and concrete under push-pull cyclic loadings is numerically investigated based on a reinforcement model proposed in this paper. The equivalent reinforcing steel model considering the bond-slip effect without taking double nodes is derived through the equilibrium at each node of steel and the compatibility condition between steel and concrete. Besides a specific transformation algorithm is composed to transfer the forces and displacements from the nodes of the steel element to the nodes of the concrete element. This model first results in an effective use in the case of complex steel arrangements where the steel elements cross the sides of the concrete elements and second turns the impossibility into a possibility in consideration of the bond-slip effect in three dimensional finite element analysis. Finally, the correlation studies between numerical and experimental results under the continuously repeated large deformation stages demonstrate the validity of developed reinforcing steel model and adopted algorithms.

Key Words

cyclic loading, bond-slip, double node, nonlinear analysis, embedded steel

Address

Kwak HG, KOREA ADV INST SCI & TECHNOL,DEPT CIVIL ENGN,TAEJON 305701,SOUTH KOREA