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CONTENTS
Volume 5, Number 4, July 1997
 

Abstract
Fiber reinforced plastic (FRP) rods provide certain benefits over steel as concrete reinforcement, such as corrosion resistance, magnetic and electrical insulation, light weight, and high strength. FRP composites can be combined with a steel core to form hybrid reinforcing rods that take advantage of properties of both materials. The objective of this study was to characterize the bond behavior of hybrid FRP rods made with braided epoxy-impregnated aramid or poly-vinyl alcohol FRP skins. Eleven rod types were tested using mio concrete strengths. Specific topics examined were bond strength, slip, and type of failure in concentric pull-out tests from concrete cubes. From analysis of identical pullout tests on both hybrid and steel rods, information on relative bond strength and behavior were obtained. It is concluded that strength is similar but slip in hybrid rods is much higher. Hybrid rods failed either by pull-out or splitting the concrete block (with or without yielding of the steel core). Experimental data showed consistency with similar test results presented in the literature.

Key Words
bond, braiding, concrete, fiber reinforced plastic (FRP), hybrid reinforcement, pull-out, slip, testing

Address
Nanni A, PENN STATE UNIV,DEPT ARCHITECTURAL ENGN,UNIVERSITY PK,PA 16802
BSW,TULSA,OK 74103

Abstract
Fiber reinforced plastic (FRP) rods are used as reinforcement (prestressed or not) to concrete. FRP composites can also be combined with steel to form hybrid reinforcing rods that take advantage of the properties of both materials. In order to effectively utilize these rods, their bond behavior with concrete must be understood. The objective of this study is to characterize and model the bond behavior of hybrid FRP rods made with epoxy-impregnated aramid or poly-vinyl alcohol FRP skins directly braided onto a steel core. The model closely examines the split failure of the concrete by quantifying the relationship between slip of the rods resulting transverse stress field in concrete. The model is used to derive coefficients of friction for these rods and, from these, their development length requirements. More testing is needed to confirm this model, but in the interim, it may serve as a design aide, allowing intelligent decisions regarding concrete cover and development length. As such, this model has helped to explain and predict some experimental data from concentric pull-out tests of hybrid FRP rods.

Key Words
bond, concrete, concrete cover, development length, fiber reinforced plastic (FRP), friction, hybrid reinforcement, modeling, pull-out test

Address
Nanni A, PENN STATE UNIV,DEPT ARCHITECTURAL ENGN,UNIVERSITY PK,PA 16802

Abstract
The classical theory of thin-walled members is unable to reflect the shear lag phenomenon since it is based on the assumption of no shearing strains in the middle surface of the walls. In this paper, an energy equation for the lateral buckling of thin-walled members has been derived which includes the effects of torsion, warping and especially, the shearing strains which reflect the shear lag phenomenon. A numerical analysis for the lateral buckling of thin-walled members with openings by using Galerkin\'s method of weighted residuals has been presented. The proposed numerical values and the predictions by experiment for the lateral buckling loads are to agree closely in the paper. The results from these comparisons show that the proposed method hen is capable of predicting the lateral buckling of thin-walled members with openings. The fast convergence of the results indicates the numerical stability of the method. By the study, a very complex practical eigenvalue problem is transformed into a very simple one of solving only a linear equation with one variable.

Key Words
lateral buckling, thin-walled member, shear lag

Address
Wang QF, NATL HUAQIAO UNIV,DEPT CIVIL ENGN,QUANZHOU 362011,FUJIAN,PEOPLES R CHINA

Abstract
High order finite element have a greater convergence rate than low order finite elements, and in general produce more accurate results. These elements have the disadvantage of being more computationally expensive and often require a longer time to solve the finite element analysis. High order elements have been used in this paper to obtain a new eigenvalue solution with out re-solving the new model. The optimisation of the eigenvalue via the differentiation of the Rayleigh quotient has shown that the additional nodes associated with the higher order elements can be condensed out and solved using the original finite element solution. The higher order elements can then be used to calculate an improved eigenvalue for the finite element analysis.

Key Words
finite element, errors, eigenvalue improvement

Address
Stephen DB, UNIV SYDNEY,FAC ENGN,FINITE ELEMENT ANAL RES CTR,BLDG J07,SYDNEY,NSW 2006,AUSTRALIA

Abstract
This paper presents an investigation into the seismic response characteristics of a proposed ligh-weight pedestrian cable-stayed bridge made entirely from Glass Fiber Reinforced Plastics(GFRP). The study employs three dimensional finite element models to study and compare the dynamic characteristics and the seismic response of the GFRP bridge to a conventional Steel-Concrete (SC) cable-stayed bridge alternative. The two bridges were subjected to three synthetic earthquakes that differ in the frequency content characteristics. The performance of the GFRP bridge was compared to that of the SC bridge by normalizing the live load and the seismic internal forces with respect to the dead load internal forces. The normalized seismically induced internal forces were compared to the normalized live load internal forces for each design alternative. The study shows that the design alternatives have different dynamic characteristics. The light GFRP alternative has more flexible deck motion in the lateral direction than the heavier SC alternative. While the SC alternative has more vertical deck modes than the GFRP alternative, it has less lateral deck modes than the GFRP alternative in the studied frequency range. The GFRP towers are more flexible in the lateral direction than the SC towers. The GFRP bridge tower attracted less normalized base shear force than the SC bridge towers. However, earthquakes, with peak acceleration of only 0.1 g, and with a variety of frequency content could induce high enough seismic internal forces at the tower bases of the GFRP cable-stayed bridge to govern the structural design of such bridge. Careful seismic analysis, design, and detailing of the tower connections are required to achieve satisfactory seismic performance of GFRP long span bridges.

Key Words
bridges, long span bridges, cable-stayed, cable-structures, advanced composite materials, FRP, analysis, seismic, response

Address
Hodhod OA, CAIRO UNIV,DEPT STRUCT ENGN,GIZA,EGYPT
UNITED ARAB EMIRATES UNIV,DEPT CIVIL ENGN,AL AIN,U ARAB EMIRATES

Abstract
Stability equations that evaluate the elastic critical axial load of stepped columns under extreme and intermediate concentrated axial loads in any type of construction with sidesway totally inhibited, partially inhibited and uninhibited are derived in a classical manner. These equations can be utilized in the stability analysis of framed structures (totally braced partially braced and unbraced) with stepped columns with rigid semirigid and simple connetions. The proposed column classification and the corresponding stability equations overcome the limitations of current methods which are based on a classification of braced and unbraced columns. The proposed stability equations include the effects of: 1) semirigid connections; 2) step variation in the column cross section at the point of application of the intermediate axial load; and 3) lateral and rotational restraints at the intermediate connection and at the column ends. The proposed method consists in determining the eigenvalue of a 2X2 matrix for a braced column at the two ends and of a 3X3 matrix for a partially braced or unbraced column. The stability analysis can be carried out directly with the help of a pocket calculator. The proposed method is general and can be extended to multi-stepped columns. Various examples are inclued to demonstrate the effectiveness of the proposed method and to verify that the calculated results are exact. Definite minimum bracing criteria for single stepped columns is also presented.

Key Words
buckling, bracing, building codes, columns, construction type, computer application, frames, loads, stability

Address
AristizabalOchoa JD, NATL UNIV,SCH MINES,AA 75267,MEDELLIN,COLOMBIA

Abstract
The objective of this work is to predict the failure loads, associated maximum transverse displacements, locations and the modes of failure, including the onset of delamination, of thin, nat, square symmetric laminates under the action of uni-axial compression. Two progressive failure analyses, one using Hashin criterion and the other using Tensor polynomial criteria, are used in conjunction with the finite element method. First order shear deformation theory and geometric nonlinearity in the von Karman sense have been employed. Five different types of lay-up sequence are considered for laminates with all edges simply supported. In addition, two boundary conditions, one with all edges fixed and other with mixed boundary conditions for (+45/-45/0/90)(2s) quasi-isotropic laminate have also been considered to study the effect of boundary restraints on the failure loads and the corresponding modes of failure. A comparison of linear and nonlinear results is also made for (+/- 45/0/90)(2s) quasi-isotropic laminate. It is observed that the maximum difference between the failure loads predicted by various criteria depend strongly on the laminate lay-ups and the flexural boundary restraints. Laminates with clamped edges are found to be more susceptible to failure due to the transverse shear and delamination, while those with the simply supported edges undergo total collapse at a load slightly higher than the fiber failure load.

Key Words
progressive failure, laminated plate, failure criteria, uni-axial compression

Address
Singh SB, INDIAN INST TECHNOL,DEPT CIVIL ENGN,KANPUR 208016,UTTAR PRADESH,INDIA
INDIAN INST TECHNOL,DEPT AEROSP ENGN,KANPUR 208016,UTTAR PRADESH,INDIA
MNREC,DEPT APPL MECH,ALLAHABAD,UTTAR PRADESH,INDIA

Abstract
Experimental work undertaken to investigate the behaviour of laminated elastomeric bridge bearings under compression and a combination of compression and shear or rotation has been reported on elsewhere. However, it is difficult to determine the state of stress within the bearings in terms of the applied forces or the interaction between the steel shims and the rubber layers in the bearings. In order to supply some of the missing information about the stress-strain state within the bearings, an analytical study using the finite element method was carried out. The available experimental results were used to validate the model after which the analyses were used to provide further information about the state of stress within the bearing.

Key Words
bridge, bearings, elastomeric rubber bearings, finite element analysis, compression, shear strain, rotation

Address
Mori A, JAPAN ENGN CONSULTANTS,EARTHQUAKE DISASTER MITIGAT DEPT,TOKYO,JAPAN
UNIV CANTERBURY,DEPT CIVIL ENGN,CHRISTCHURCH,NEW ZEALAND

Abstract
In this paper, the classical Irons\' patch tests which have been generally accepted for the convergence proof of a finite element are performed for Mindlin plate bending elements with a special emphasis on the nonconforming elements. The elements considered are 4-node and 8-node quadrilateral isoparametric elements which have been dominantly used for the analyses of plate bending problems. It was recognized from the patch tests that some nonconforming Mindlin plate elements pass all the cases of patch tests even though nonconforming elements do not preserve conformity. Then, the clues for the Mindlin plate element to pass the Irons\' patch tests are investigated. Also, the convergent characteristics of some nonconforming Mindlin plate elements that do not pass the Irons\' patch tests are examined by weak patch tests. The convergence tests are performed on the benchmark numerical problems for both nonconforming elements which pass the patch tests and which do not. Some conclusions on the relationship between the patch test and convergence of nonconforming Mindlin plate elements are drawn.

Key Words
nonconforming Mindlin plate element, Irons\' patch tests, weak patch test, convergence requirement

Address
Park YM, RES INST IND SCI & TECHNOL,STEEL STRUCT TECHNOL DIV,SEOUL 135777,SOUTH KOREA
KOREA ADV INST SCI & TECHNOL,DEPT CIVIL ENGN,TAEJON 305701,SOUTH KOREA


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