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A probability-based reliability assessment methodology for single flexible piles and pile groups under stochastic lateral loads is developed. The methodology was based on state-of-the-art techniques for the analysis of single piles and pile groups as well as reliability assessment methods. Critical strength and serviceability modes of failure for flexible piles in sandy soil under lateral loads were defined. The reliability of a pile-group system was assessed by accounting for system redundancy with the occurrence of partial failures of the system components. Reliability indices and failure probabilities were used as relative measures for the performance of piles. A case study was presented to illustrate the proposed methodology.

The feasibility of using welded wire fabric in concrete bridge slabs was investigated by testing 15 slabs up to their ultimate capacity. The experimental and analytical studies showed that simply supported slabs reinforced with welded wire fabric are less ductile than slabs reinforced with conventional reinforcing steel. However, slabs with partial or fixed supports have a comparable load-deflection behavior when reinforced with either type of reinforcement. The load-deflection curves were predicted by using the finite element method and an analytical method which uses the strain compatibility concepts. The experimental measurements showed that the analytical results were accurate up to the point when the concrete begins to crush. It was concluded that the reinforcement ratio, transverse wire orientation, and boundary conditions are the major factors that affect the behavior of concrete slabs reinforced with welded wire fabric.

The splicing strength of welded wire fabric (WWF) in concrete bridge decks was investigated by testing three one‐way slabs reinforced with spliced WWF, and one slab reinforced with WWF without a splice. The slabs were tested up to their ultimate capacity. The experiments showed that the specimens with transverse wires in the splice zone had an early separation of the spliced steel, thereby resulting in concrete cover failure. A new splice detail without transverse wires in the splice zone resulted in a gradual (more ductile) failure mode and a strain distribution similar to the slab without a splice. It was also determined that the orientation of transverse wires, distribution of longitudinal wires, and weld shear strength are the major factors affecting the splice strength of concrete bridge slabs reinforced with welded wire fabric.

The bond strength of welded wire fabric (WWF) in concrete bridge decks was investigated by testing 22 pullout specimens for bond strength up to their ultimate capacity. The pullout study showed that after the bond between longitudinal wires and concrete failed, the specimens resisted additional loads due to the anchorage effects of transverse wires and shear strength of welds. This increase in bond strength ranged from 16 to 771%, depending upon the type and arrangement of longitudinal and transverse wires. The transverse wires and shear strength of the weld, therefore, make large contributions to the bond strength of the welded wire fabric in concrete bridge decks.

The purpose of the present paper is to provide experimental data and analytical results for the fatigue strength of welded wire fabric (WWF), so that engineers can confidently use WWF as structural reinforcement. The material for the tested specimens was provided by manufacturers in the United States, Germany, and Canada. The specimens included steel from rods (steel before the cold‐drawing process), plain wires, deformed wires, epoxy‐coated deformed wires, tempered and nontempered WWF, and nontempered wires without welds. The experiments conducted show that the WWF made in the United States can be considered a ductile steel based on the relevant ASTM specifications. In addition, the fatigue life of the epoxy‐coated WWF made in the United States exceeds those for reinforcement bars as tested by the Portland Cement Association. The results indicate that WWF meets the fatigue requirements of structural reinforcement for bridge decks.

The purpose of the present paper is to provide experimental data and analytical results for the tensile strength and ductility of welded wire fabric (WWF) so that engineers can confidently use WWF as structural reinforcement. The material for the tested specimens was provided by manufacturers in the United States, Germany, and Canada. The specimens included steel from rods (steel before the cold‐drawing process), plain wires, deformed wires, epoxy‐coated deformed wires, tempered and nontempered WWF, and nontempered wires without welds. The experiments conducted show that the WWF made in the United States can be considered a ductile steel based on the relevant ASTM specifications. In addition, the fatigue life of the epoxy‐coated WWF made in the United States exceeds those for reinforcement bars as tested by the Portland Cement Association. The results indicate that WWF is suitable as a structural reinforcement since it possesses sufficient ductility to meet ASTM specifications.

Limited experimental results were reported in the literature on the behavior of prestressed composite girders subjected to negative bending moment. This paper examines experimentally the behavior o...

A method for the structural analysis of prestressed composite steel-concrete girders was studied in this paper. The deflections, forces in the prestressing tendons, and strains in the steel beam and concrete slab of composite girders were computed throughout the entire loading range up to failure. Equations are provided for the calculation of the yield and ultimate load capacities of the girders. The developed analytical models were based on the incremental deformation method. The results of the analytical study were compared with test results of several girders. Reasonably good correlations between analytical and experimental results were obtained. Also, the results showed that a substantial increase in the yield and an increase in the ultimate load capacities can be achieved by adding prestressing tendons to the composite girders and prestressing them. It was determined that the most effective construction sequence for prestressed composite girders in negative moment regions is to posttension the composite girders with tendons in the concrete slabs.

According to the 1986 U.S. Federal Highway Administration statistics, there are 575,607 bridges on the highway systems. About half of these bridges are structurally deficient and/or functionally obsolete. To strengthen the structurally deficient bridges without replacing the girders, external prestressing techniques can be used. In this paper, the behavior of prestressed, composite steel-concrete beams under positive bending moment is examined, and the benefits of different types of prestressing are compared. Three specimens were tested to study various aspects of prestressed composite girders, including tendon type and profile. Two methods of analysis are discussed, i.e., the transformed area method and the strain compatibility method. The test results show that prestressing a composite girder increases the range of elastic behavior, reduces deflections, increases ultimate strength, and adds to the redundancy by providing multiple stress paths. Based on the experimental results, a comparison was made between three tendon types and profiles. It was concluded that strands are more effective than bars for the tendon type, and a straight tendon profile is more effective than a draped profile with regard to stiffness.

This study develops a general method for the reliability and redundancy analysis of posttensioned plane trusses composed of tension members, compression members, and several layouts of tendon members. A number of numerical examples are presented in which various types of tendon layouts are analyzed and efficiency compared. Illustrative tendon layouts, which can be used to posttension simple and continuous trusses are illustrated.

More than 80% of the steel truss bridges inventoried in the United States are structurally deficient and/or functionally obsolete. Posttensioning these bridges using different posttensioned tendon layouts can be a cost‐effective method to strengthen them to meet current and future loading and traffic requirements. A method for the structural stiffness analysis of posttensioned trusses is suggested. The stiffness matrices of straight, one‐drape, and two‐drape tendon layouts are developed. The tendon layout need not coincide with the truss members. However, it can be externally or internally attached to the truss. A closed‐form solution for the relationship between the cross‐sectional area, posttensioning force of the tendon, and the desired final member stress after posttensioning is derived for a statically determinate truss. Posttensioning enlarges the elastic range, increases the fatigue resistance, increases redundancy, and reduces deflection and member stresses. Thus, the remaining life of a truss bri...

An assessment of the strength of an existing structural component or system is commonly made by determining the strength at selected sample points in the space of the structure. Samples may be obtained as cores or nondestructive test measurements. The number of sample points and their layout affect both the cost and the accuracy of testing. The objective of this paper is to demonstrate the use of semivariogram analysis and kriging estimation in evaluating the strength of structural components. These methods provide the basis for establishing guidelines for developing a sampling program that balances the cost of data collection and accuracy requirements. Examples on the strength evaluation of columns and slabs are presented. The calculation of the relative error variances of both point and mean value estimates for the strength of columns and slabs is demonstrated. Guidelines for establishing testing programs are presented.

Prestressed steel has only recently been considered in the design of structures, despite along, successful history of prestressed concrete structures. Prestressing the steel in a composite steelcon...

This paper analyzes the behavior of steel beams prestressed with highstrength steel tendon and compositely connected to a concrete deck. In particular, the deflection and the strains in the steel b...

Commonly-used structural reliability models are reviewed, and the advantages and limitations of each method are discussed with the help of a practical example. A pressure vessel is designed against wind loading. This example is selected because the limit state equation is nonlinear and the wind speed has an extremely skewed distribution. Although the First-Order Second-Moment may be sufficient in many problems, the risk involved may still be unknown, even in a relative sense, unless the limit state equation is linear and all the variables are normal. In that sense, the Advanced Second-Moment method has several advantages. It yields probabilities of failure similar to the variance reduction techniques, at least for the pressure vessel example considered here. If simulation techniques are used to study a problem, some kind of variance reduction technique should be used for economic reasons. For the complicated example considered here, the Conditional Expectation plus Antithetic Variates variance reduction technique is modified to make the simulation more efficient.

The concept of prestressing steel structures has only recently been widely considered, despite a long and successful history of prestressing concrete members. Several analytical studies of prestres...