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CONTENTS
Volume 2, Number 1, February 2002
 

Abstract
Fiber-Reinforced Plastics (FRP) have received significant attention for use in civil infrastructurerndue to their unique properties, such as the high strength-to-weight ratio and stiffness-to-weight ratio, corrosionrnand fatigue resistance, and tailorability. It is well known that FRP wraps increase the load-carrying capacity andrnthe ductility of reinforced concrete columns. A number of researchers have explored their use for seismicrncomponents. The application of concern in the present research is on the use of FRP for corrosion protection ofrnreinforced concrete columns, which is very important in cold-weather and coastal regions. More specifically,rnthis work is intended to give practicing engineers with a more practical procedure for estimating the strength ofrna deficient column rehabilitated using FRP wrapped columns than those currently available. To achieve thisrngoal, a stress-strain model for FRP wrapped concrete is proposed, which is subsequently used in therndevelopment of the moment-curvature relations for FRP wrapped reinforced concrete column sections. Arncomparison of the proposed stress-strain model to the test results shows good agreement. It has also been foundrnthat based on the moment-curvature relations, the balanced moment is no longer a critical moment in therninteraction diagram. Besides, the enhancement in the loading capacity in terms of the interaction diagram due tornthe confinement provided by FRP wraps is also confirmed in this work.

Key Words
Fiber-Reinforced Plastics (FRP); columns; concrete; strength; ductility; confinement.

Address
Hsiao-Lin Cheng, Department of Civil Engineering, Chung Cheng Institute of Technology, CCIT, Yuanshulin, Tahsi, Taoyuan, 33508, TaiwanrnElisa D. Sotelino, School of Civil Engineering, Purdue University, W. Lafayette, IN 47907, U.S.A.rnWai-Fah Chen, College of Engineering, University of Hawaii, Honolulu, HI 96822, U.S.A.

Abstract
A model of the process of local buckling in tubular steel structural elements is presented. It isrnassumed that this degrading phenomenon can be lumped at plastic hinges. The model is therefore based on thernconcept of plastic hinge combined with the methods of continuum damage mechanics. The state of this newrnkind of inelastic hinge is characterized by two internal variables: the plastic rotation and the damage. Thernmodel is valid if only one local buckling appears in the plastic hinge region; for instance, in the case of framedrnstructures subjected to monotonic loadings. Based on this damage model, a new finite element that canrndescribe the development of local buckling is proposed. The element is the assemblage of an elastic beam-columnrnand two inelastic hinges at its ends. The stiffness matrix, that depends on the level of damage, thernyielding function and the damage evolution law of the two hinges define the new finite element. In order tornverify model and finite element, several small-scale frames were tested in laboratory under monotonicrnloading. A lateral load at the top of the frame was applied in a stroke-controlled mode until local bucklingrnappears and develops in several locations of the frame and its ultimate capacity was reached. These tests werernsimulated with the new finite element and comparison between model and test is presented and discussed.

Key Words
local buckling; damage mechanics; structural failure; structural steel; inelastic behavior.

Address
Pether Inglessis, Samuel Medina

Abstract
A series of tests on simple-welded plate specimens (SWPS) and T-stub tension specimensrnsimulating some of the joint details in moment frame connections were conducted in this investigation. Therneffects of weld strength mismatch and weld metal toughness on structural behavior of these specimens werernconsidered under both static and dynamic loading conditions. Finite element analyses were performed byrntaking into account typical weld residual stress distributions and weld metal strength mismatch conditions tornfacilitate the interpretation of the test results. The major findings are as follows: (a) Sufficient specimen sizernrequirements are essential in simulating both load transfer and constraint conditions that are relevant tornmoment frame connections, (b) Weld residual stresses can significantly elevate stress triaxiality in addition tornstructural constraint effects, both of which can significantly reduce the plastic deformation capacity inrnmoment frame connections, (c) Based on the test results, dynamic loading within a loading rate of 0.02 in/in/rnsec, as used in this study, premature brittle fractures were not seen, although a significant elevation of the yieldrnstrength can be clearly observed. However, brittle fracture features can be clearly identified in T-stubrnspecimens in which severe constraint effects (stress triaxiality) are considered as the primary cause, (d) Basedrnon both the test and FEA results, T-stub specimens provide a reasonable representation of the joint conditionsrnin moment frame connections in simulating both complex load transfer mode and constraint conditions.

Key Words
moment frame connections; finite element analysis; T-stub specimens; brittle fracture; stress triaxiality; residual stresses; joint constraint; weld strength mismatch.

Address
P. Dong and T. Kilinski, Center for Welded Structures Research, Battelle Memorial Institute, Columbus, OH 43201, USA

Abstract
Perforated shear connectors currently used in composite steel and concrete structures arerndescribed and evaluated. Modifications of the perforated connector suitable for common use in civil andrnbridge engineering are proposed. The connectors were tested in laboratories of CTU Prague for shear loadrncapacity. Push tests of connectors with 32 mm openings and with 60 mm openings, both in normal andrnlightweight concrete of different strength characteristics and with different transverse reinforcement, wererncarried out. The experimental study also dealt with the connector height and parallel arrangement of twornconnectors and their influence on shear resistance. While extensive tests with static loading were carried out,rnfatigue tests under repeated loading are still in progress. After statistical evaluation of the experimental resultsrnand comparisons with other available data the authors developed reasonable shear resistance formulas for allrnproposed arrangements.

Key Words
characteristic resistance; composite steel and concrete structure; design resistance; lightweight concrete; perforated shear connector; push test; shear connector; slip; statistical evaluation.

Address
Josef Machacek and Jiri Studnicka, Czech Technical University in Prague, Thakurova 7, 166 29 Czech Republic

Abstract
Traffic decks of steel or composite motorway bridges sometimes provide the opportunity ofrnusing the composite action between an existing steel deck and a reinforced concrete plate (RC plate) in thernprocess of rehabilitation, i.e., to increase the load-carrying capacity of the deck for concentrated traffic loads.rnThe steel decks may be orthotropic decks or also unstiffened steel plates, which during the rehabilitation arernconnected with the RC plate by shear studs, such developing an improved local load distribution by the jointrnbehaviour of the two plate elements. Investigations carried out, both experimentally and numerically, werernperformed in order to quantitatively assess the combined static behaviour and to qualitatively verify thernusability of the structure for dynamic loading. The paper reports on the testing, the numerical simulation asrnwell as the comparison of the results. Conclusions drawn for practical design indicated that the staticrnbehaviour of these structures may be very efficient and can also be analysed numerically. Further, the resultsrngave evidence of a highly robust behaviour under fatigue equivalent cyclic traffic loading.

Key Words
composite structures; traffic decks; orthotropic steel plates; RC plates; rehabilitation; motorway bridges; steel bridges; composite bridges.

Address
R. Greiner, R. Ofner and H. Unterweger, Institute for Steel, Timber and Shell Structures, Graz University of Technology Lessingstrasse 25/3, A-8010 Graz, Austria


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