Techno Press


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CONTENTS
Volume 41, Number 2, January25 2012
 

Abstract
The paper presents a review of the application of the newly proposed mixed finite element model for seismic simulation of different types of composite frame structures. To evaluate the performance of the element, a comparison with displacement-based and force-based models is conducted. The study revealed that the mixed model is superior to the others in terms of both speed of convergence and numerical stability, and is therefore considered the most practical approach for modeling of composite structures. In this model, the element is derived using independent force and displacement shape functions. The nonlinear response of the frame element is based on the section discretization into fibers with uniaxial material models. The interfacial behavior is modeled using an inelastic interface element. Numerical examples to clarify the advantages of the model are presented for the following structural applications: anchored reinforcing bar problems, composite steel-concrete girders with deformable shear connectors, beam on elastic foundation elements, R/C girders strengthened with FRP sheets, R/C beam-columns with bond-slip, and prestressed concrete girders. These studies confirmed that the model represents a major advancement over existing elements in simulating the inelastic behavior of composite structures.

Key Words
composite structures; composite girders; bond; interface element; displacement formulation; force formulation; mixed finite element

Address
Ashraf Ayoub: Department of Civil and Environmental Engineering, University of Houston, Houston, TX 77204, USA

Abstract
Several issues regarding the structural idealization of steel buildings with perimeter moment resisting steel frames (MRSFs) and interior gravity frames (GFs) are studied. Results indicate that the contribution of GFs to the lateral structural resistance may be significant. The contribution increases when the stiffness of the connection of the GFs is considered and is larger for inelastic than for elastic behavior. The interstory shears generally increase when the connections stiffness is taken into account. Resultant stresses at some base columns of MRSFs also increase in some cases but to a lesser degree. For columns of the GFs, however, the increment is significant. Results also indicate that modeling the building as planes frames may result in larger interstory shears and displacements and resultant stresses than those obtained from the more realistic 3-D formulation. These differences may be much larger when semi-rigid (SR) connections are considered. The conservativism is more for resultant stresses. The differences observed in the behaviour of each structural representation are mainly due to a) the elements that contribute to strength and stiffness and b) the dynamics characteristics of each structural representation. It is concluded that, if the structural system under consideration is used, the three-dimensional model should be used in seismic analysis, the GFs should be considered as part of the lateral resistance system, and the stiffness of the connections should be included in the design of the GFs. Otherwise, the capacity of gravity frames may be overestimated while that of MRSFs may be underestimated.

Key Words
semi-rigid connections; steel buildings; perimeter moment frames; interior gravity frames; time history analysis; seismic codes

Address
Alfredo Reyes-Salazar, Manuel Ernesto Soto-Lopeza,
Eden Bojorquez-Mora and Arturo Lopez-Barraza: Facultad de Ingenieria, Universidad Autonoma de Sinaloa, Culiacan, Sinaloa, Mexico

Abstract
This paper presents a new nine-node Lagrangian quadrilateral plate bending element (MQP9) using the Integrated Force Method (IFM) for the analysis of thin and moderately thick plate bending problems. Three degrees of freedom: transverse displacement w and two rotations ox and oy are considered at each node of the element. The Mindlin-Reissner theory has been employed in the formulation which accounts the effect of shear deformation. Many standard plate bending benchmark problems have been analyzed using the new element MQP9 for various grid sizes via Integrated Force Method to estimate defections and bending moments. These results of the new element MQP9 are compared with those of similar displacement-based plate bending elements available in the literature. The results are also compared with exact solutions. It is observed that the presented new element MQP9 is free from shear locking and produced, in general, excellent results in all plate bending benchmark problems considered.

Key Words
integrated force method; mindlin-reissner plate theory stress-resultant fields; displacement fields; shear locking

Address
H.R. Dhananjaya: Department of Civil Engineering, Nitte Meenakshi Institute of Technology, Bangalore-560 064, India; Department of Civil Engineering, University of Malaya, Kuala Lumpur-50603, Malaysia
P.C. Pandey: Department of Civil Engineering, Indian Institute of Science, Bangalore-560 012, India
J. Nagabhushanam: Department of Aerospace Engineering, Indian Institute of Science, Bangalore-560 012, India
Zainah Ibrahim: Department of Civil Engineering, University of Malaya, Kuala Lumpur-50603, Malaysia

Abstract
This research work aims to develop an optimal design using Finite Element (FE) and Genetic Algorithm (GA) methods to replace the traditional concrete and timber material by a Synthetic Polyurethane fibre glass composite material in railway sleepers. The conventional timber railway sleeper technology is associated with several technical problems related to its durability and ability to resist cutting and abrading action of the bearing plate. The use of pre-stress concrete sleeper in railway industry has many disadvantages related to the concrete material behaviour to resist dynamic stress that may lead to a significant mechanical damage with feasible fissures and cracks. Scientific researchers have recently developed a new composite material such as Glass Fibre Reinforced Polyurethane (GFRP) foam to replace the conventional one. The mechanical properties of these materials are reliable enough to help solving structural problems such as durability, light weight, long life span (50-60 years), less water absorption, provide electric insulation, excellent resistance of fatigue and ability to recycle. This paper suggests appropriate sleeper design to reduce the volume of the material. The design optimization shows that the sleeper length is more sensitive to the loading type than the other parameters.

Key Words
structural optimization; composite; dynamic stress analysis; railway engineering

Address
Ziad K. Awad and Talal Yusaf: Faculty of Engineering and Surveying, University of Southern Queensland (USQ), Toowoomba, QLD4350, Australia

Abstract
Nonlinear static analysis as an essential part of performance based design is now widely used especially at design offices because of its simplicity and ability to predict seismic demands on inelastic response of buildings. Since the accuracy of nonlinear static procedures (NSP) to predict seismic demands of buildings affects directly on the entire performance based design procedure, therefore lots of research has been performed on the area of evaluation of these procedures. In this paper, one of the popular NSP, FEMA356, is evaluated and compared with modal pushover analysis. The ability of these procedures to simulate seismic demands in a set of reinforced concrete (RC) buildings is explored with two level of base acceleration through a comparison with benchmark results determined from a set of nonlinear time history analyses. According to the results of this study, the modal pushover analysis procedure estimates seismic demands of buildings like inter story drifts and hinges plastic rotations more accurate than FEMA356 procedure.

Key Words
nonlinear static analysis; nonlinear time history analysis; modal pushover analysis; FEMA356; inter story drift; plastic hinge rotation; performance based design

Address
Hamid Reza Khoshnoud and Kadir Marsono: Faculty of Civil Engineering, University of Technology of Malaysia, Skudai, Johor, Malaysia

Abstract
This paper aims to propose a computational technique for estimating the region of attraction (RoA) for autonomous nonlinear systems. To achieve this, the collocation method is applied to approximate the Lyapunov function by satisfying the modified Zubov\'s partial differential equation around asymptotically stable equilibrium points. This method is formulated for n-scalar differential equations with two classes of basis functions. In order to show the efficiency of the suggested approach, some numerical examples are solved. Moreover, the estimated regions of attraction are compared with two similar methods. In most cases, the proposed scheme can estimate the region of attraction more efficient than the other techniques.

Key Words
autonomous systems; Lyapunov function; Region of Attraction (RoA); modified Zubov\'s PDE; collocation method

Address
M. Rezaiee-Pajand and B. Moghaddasie: Department of Civil Engineering, Ferdowsi University of Mashhad, Mashhad 91175-1111, Iran

Abstract
An inverse approach is presented for calculating the flexibility coefficient of open-side cracks in the cross sectional of beams. The cracked cross section is treated as a massless rotational spring which connects two segments of the beam. Based on the Euler-Bernoulli beam theory, the differential equation governing the forced vibration of each segment of the beam is written. By using a mathematical manipulation the time dependent differential equations are transformed into the static substitutes. The crack characteristics are then introduced to the solution of the differential equations via the boundary conditions. By having the time history of transverse response of an arbitrary location along the beam, the flexibility coefficient of crack is calculated. The method is applied for some cracked beams with solid rectangular cross sections and the results obtained are compared with the available data in literature. The comparison indicates that the predictions of the proposed method are in good agreement with the reported data. The procedure is quite general so as to it can be applicable for both single-side crack and doubleside crack analogously. Hence, it is also applied for some test beams with double-side cracks.

Key Words
crack; forced vibration; flexibility coefficient; Euler-Bernoulli beam

Address
N. Fallah and M. Mousavi: Civil Engineering Department, University of Guilan, P.O. Box 3756, Rasht, Iran

Abstract
Stiffened coupled shear walls (SCSW) are under axial load resulting from their weight and this axial load affects the behavior of walls because of their excessive height. In this paper, based on the continuum approach, the optimal position of the stiffening beam on the stiffened coupled shear walls is investigated considering the effect of uniformly distributed axial loads. Moreover, the effect of the height of stiffened coupled shear walls on the optimal position of the stiffening beam has been studied with and without considering the axial force effect. A computer program has been developed in MATLAB and numerical examples have been solved to demonstrate the reliability of this method. The effects of the various flexural rigidities of the stiffening beam on the internal forces and the lateral deflection of the structure considering axial force effect have also been investigated.

Key Words
stiffened coupled shear walls; continuous medium; optimal position; stiffening beam; axial force effect; closed-form solution

Address
B. Farahmand Azar, A. Hadidi and H. Khosravi: Faculty of Civil Engineering, University of Tabriz, Tabriz, Iran


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