John B. Kennedy

Evaluation of impact factors for composite concrete-steel cellular straight bridges

Abstract This paper presents a method for determining the dynamic impact factors for straight composite concrete deck–steel girder cellular bridges under AASHTO truck loading. The bridges are modeled as three-dimensional structures using commercially available software. The vehicle is idealized as a pair of concentrated forces, with no mass, travelling across the bridge. An extensive parametric study is conducted, in which 120 composite multi-cell bridge prototypes are analyzed. The key parameters considered in this study are: number of cells, number of lanes, span length, number and area of cross-bracing and top-chord systems, and truck(s) speed and truck(s) positioning. Based on the data generated from the parametric study, expressions for dynamic impact factors for moment, reaction, and deflection for such bridges are proposed. The results from this practical-design-oriented study would enable bridge engineers to design new composite cellular bridges more reliably and economically. Furthermore, the results can be used to evaluate the load-carrying capacity of existing composite cellular bridges since even a small increase in strength for live load can make the difference between closing a bridge and leaving it open.

Fatigue Resistance of Corrugated Steel Sheets Bolted Lap Joints under Flexture

Corrugated steel sheets are used extensively in construction. They are often bolted together in lap joints for quick and easy assemblage. These structures are built to form different shapes, such as underground curved conduits of medium and short-span bridges. Due to stress concentration around the bolt holes and reversal of loading, the bolted lap joints in such structures become susceptible to considerable reduction in the fatigue resistance of the metal. Such reduction in the fatigue resistance has not been accounted for in current codes of practice. In this technical note, the effects of bolt arrangement, steel sheet thickness and initial bolt misalignments on the fatigue resistance of bolted joints are investigated. As a result of the study, design expressions are recommended for the design of bolted lap joints under cyclic loading.

Mechanical properties of reinforced soil

Since reinforced soil samples are extensively used in practice, it is important to determine the mechanical properties of reinforced frictional soils. Laboratory triaxial tests were run using different values of confining pressure. Both reinforced and unreinforced soils were examined. Based on the results obtained in the laboratory, a simplified description is proposed for the initial modulus of elasticity, cohesion and angle of internal friction of reinforced soil. The reinforcing strips were found to have a significant influence on the mechanical properties of the soil. A practical design example on the analysis of a reinforced embankment with one, three and five layers of reinforcement is given.

Distributions of residual stresses in stiffened plates with one and two stiffeners

This study was undertaken for a better understanding of the residual stress distributions associated with welds typically found in ship hulls. Specimens that represent small sections of an actual ship hull were built and tested using the neutron diffraction method at the Canadian Neutron Beam Centre in the Chalk River Laboratories. The specimens comprised 9.5 mm thick steel plates stiffened by L127 × 76 × 9.5 steel angles. This paper presents one- and three-dimensional distributions of all three components of residual stress created from the production of the steel plate and from the welding of one and two stiffeners onto the parent steel plate. Subsequently, the longitudinal stress in the transverse direction of the stiffened plate specimens was compared with the Faulkner model. It was found that the Faulkner model is able to predict the general distributions of this stress; however, it was unable to predict the stress values correctly.

Imperfection sensitivity of stiffened cylinders subjected to external pressure

Abstract The effect of initial imperfections on the elastic-buckling behaviour of ring-stiffened cylinders under external pressure is examined using the potential energy approach. Experimental results in the open literature of four ring-stiffened cylinders tested under external pressure were used to compare and verify the theoretical analysis. Both the theoretical and experimental results indicate no apparent influence of initial imperfections on the buckling behaviour within the elastic range. This was so in spite of the presence of an appreciable amount of initial imperfections. The results from this work indicate that less stringent requirements in the manufacturing of ring-stiffened cylinders may be tolerated, leading to possible economy.

Dynamic response of thick plates and shells

Abstract A method for solving the nonlinear dynamic problem of moderately thick plates and shells is presented using an incremental finite element method. In the solution the nonlinear shear factor is derived and plastic-fracture stress-strain relationships of progressively fracturing solids are used. Furthermore, an incremental force-displacement relationship is developed using the principle of virtual work. The minimum number of degrees of freedom for an element is employed in order to reduce the computer solution time. Numerical studies are presented to demonstrate the accuracy and efficiency of the method of solution.

Comparative Structural Behaviour of Multi-Cell and Multiple-Spine Box Girder Bridges

Publisher Summary The use of curved box girder bridges in interchanges of modern highway systems has become increasingly popular for economic and esthetic considerations. Composite concrete deck-steel box girder bridges may take the form of single-cell, multi-cell, and multiple-spines. They provide considerable flexural and torsional strengths to resist the applied loads. This chapter discusses three types of curved box-girder bridges of the same material content—namely, braced multi-cell bridge, multiple-spine bridge with internal bracings, and multiple-spine bridge with internal and external bracings among boxes. The finite-element method is used to model the bridges. Shell elements are used to model the concrete deck slab, steel cells, and end diaphragms; while three-dimensional beam elements are used to model top steel flanges and cross-bracings. Comparison of the theoretical values of selected structural quantities, such as support reactions, tangential stresses, and overall load carrying capacity, are presented for the three types of bridges. A comparison of the dynamic characteristics, natural frequencies, and corresponding mode shapes of such bridges is also presented in the chapter. The chapter concludes that curved bridge of cellular cross-section is the most economic section to resist applied loads.

NEW DESIGN METHOD FOR REINFORCED SLOPED EMBANKMENTS

Abstract This paper is concerned with the stability of reinforced sloped embankments. The effects of both vertical and horizontal loads are considered. Different embankment geometries such as: spacing between reinforcements in the vertical, horizontal and transverse directions; embankment height; degree of slope and reinforcing elements length are studied. The tensile force distribution in the reinforcing elements, displacements of the slope facing elements, displacements at the foundation-embankment interface and the change in stresses within the soil mass are also investigated. A total of five models including 50 experiments are tested to failure. The results from these tests are used to investigate the improvements in the load-carrying capacity of the embankment due to the presence of reinforcement and to verify the finite element modelling used in the parametric study. An extensive parametric study is conducted to examine the behaviour of the structure. A design equation for predicting the maximum tensile force within the embankment is proposed.

Analysis of prestressed girders with openings

Abstract Web openings in beams and girders occur quite often in practice to provide a convenient passage for environmental services. As a result storey heights in buildings can be reduced resulting in major cost savings. A theoretical and experimental study is carried out to determine the influence of openings on the static and dynamic responses of prestressed concrete girders. The ABAQUS computer code, based on the finite element technique, is used to examine the effects of opening size, eccentricity and horizontal location on the shear distribution as well as on the potentially-splitting tensile stress at the opening when the girder is subjected to static load applied at mid-span and at the opening. The computer code is also applied to study the dynamic response. Simply supported and two-span continuous girders of rectangular, T- and I-sections are considered. The theoretical results are verified and substantiated by experimental results.

Progressive failure analysis of orthotropic bridges

Abstract The elastic and ultimate responses of orthotropic slab bridges have been predicted by a finite element technique using a progressive failure analysis. Orthogonally reinforced or prestressed solid, waffle or voided slab bridges with single or continuous spans can be analyzed. The deduced failure patterns of such bridges verified the patterns used in a yield-line analysis. Results from tests on seven reinforced and prestressed bridge models confirmed the analytical results.