Journal of Bridge Engineering

This paper presents a sensitivity and reliability analysis of a self-anchored suspension bridge by applying a new hybrid method proposed by the authors based on integration of the Latin hypercube sampling technique (LHS), artificial neural network (ANN), first-order reliability method (FORM), Pearson’s linear correlation coefficient (PLCC), and Monte Carlo simulation with important sampling technique (MCS-IS). The framework consists of three stages of analysis: (1) selection of training, validation, and test datasets for establishing an ANN model by the LHS technique; (2) formulation of a performance function from the well-trained ANN model; and (3) sensitivity analysis using PLCC, identification of the most probabilistic failure point based on FORM, and estimation of the failure probability using the MCS-IS technique. Upon demonstration of its efficiency through analysis of a 12-story frame structure, the method is applied to sensitivity and reliability analysis of the Jiangxinzhou Bridge, a five-span self-anchored suspension bridge, in which both structural parameters and external loads are considered as random variables. The analysis identified a number of structural parameters, as well as external loads, that have a significant influence on structural serviceability and safety.

Based on the experimental data from a $1/10$ scaled model of the Liede Bridge in Guangzhou, China, the nonlinear behavior of a self-anchored suspension bridge during the process of structural system transformation has been systematically and comprehensively studied. The variation of main cable deformation, hanger tension, and main girder stress during the transformation process is analyzed, and their relationships with the different states of structural system are studied. The characteristics and distribution patterns of the lateral torsional angle of spatial cable clamps are identified. In this paper, the principles of the two stages of construction control for self-anchored suspension bridges are introduced, and construction control targets and error elimination methods for each stage are also discussed. Based on the measured results of an in situ static load test, the response characteristics of main cable axial deformation, hanger tension, and deflection stress of the main girder are described under the most unfavorable unbalanced loading case. The effects induced by the secondary dead and live load are obtained by a linear analysis procedure according to the accumulative theory.

A stabilizing cable (SC), used for mitigating buffeting vibration in a cantilevered structure of a cable-stayed bridge during construction, is normally installed with pretension. When a situation arises where only SCs are allowed in side spans, heavy counterweights in the center span are required to satisfy the force balance. The mitigating effect of unpretensioned cables was investigated using a wind tunnel in an attempt to eliminate the need for counterweights. An elastic wind tunnel test at a scale of $1/125$ was prepared, and a series of comparative wind tunnel tests were performed. The vertical displacement at the cantilever tip of the center span and the horizontal displacement at the top of the pylon were measured, and stabilizing effects were then estimated. An unpretensioned cable produces a nonlinear motion because of a loss of tension. A quantitative evaluation of the stabilizing effect of an unpretensioned stabilizing situation indicated that the counterweight could be removed only when a moderate level of stabilization is required for a small- or medium-sized, cable-stayed bridge.

During a bridge’s life cycle, the stresses from multiple dynamic loads might be superposed and progressive fatigue damage might accumulate and induce serious fatigue damage issues. This paper presents a comprehensive framework for fatigue reliability analysis of long-span bridges under combined dynamic loads from vehicles and wind. After modeling the complicated structure details with equivalent orthotropic material, dynamic stress ranges of a long-span bridge are obtained via solving the equations of motion for the vehicle-bridge-wind dynamic system with multiple random variables considered, for instance, vehicle speed, road roughness conditions, and wind velocity and direction. After counting the number of stress cycles at different stress range levels using the rain flow counting method, fatigue damage increments are obtained using the fatigue damage accumulation rule. The probability of failure for the fatigue damage at the end of each block of stress cycles and the cumulative probability of failure can be obtained. As a result, the fatigue life and reliability for the given structure details can be obtained. Based on the results from a case study, the dynamic effects from vehicles are found to be relatively small for long-span bridges and the effects from vehicle speeds and road roughness conditions can be neglected. Nevertheless, even though the stresses from either the vehicle loads or wind loads may not be able to induce serious fatigue problems alone, the superposed dynamic stress ranges cannot be ignored for fatigue reliability assessment of long-span bridges.

Cable tension is one of the important indexes of cable integrity as well as bridge stability and can be measured by various tension measurement methods. In this study, three widely used methods (i.e., the lift-off test, electromagnetic sensor method, and vibration method) have been implemented for two multistrand cables of a cable-stayed bridge under construction. The test bridge is Hwamyung Bridge in Korea, which has a prestressed concrete box girder. The field tests are executed during the second tensioning stage just after the installation of the key segment. The tensions are estimated before and after tensioning the cable and 5 days later (i.e., after finishing the tensioning of all the cables). The tensions measured by the three methods are compared with the design tension of the tensioning stage, and all three methods show very good performance in accuracy with minimal difference. Their cost and difficulty are compared based on test experiences. Additionally, an improved vibration method is proposed by ignoring apparent negative bending stiffness identified from measurement errors and validated in this test by improving the accuracy.

Bridge expansion joint sealants are used to deter water and corrosive materials from leaking through the joint and damaging the bridge structure. However, problems with leakage from failing joint sealants have been observed. In response to this situation, a silicone foam sealant designed for small-movement bridge expansion joints was developed. The foam sealant proved to be easy to use and economical. In previously reported studies, various laboratory tests were conducted to evaluate the foam sealant’s tensile strength, compressive strength, reaction to various temperatures, stress relaxation, creep behavior, and bonding capabilities to various substrate materials, such as steel, asphalt, concrete, and polymer concrete. In the current study, further laboratory tests were conducted on the sealant. These tests included ponding and freeze-thaw resistance. The subject study included the development and use of an application procedure to install the silicone foam sealant into bridge expansion joints. After being applied to expansion joints on four bridges in the Northeast (Connecticut, New Hampshire, Rhode Island, and New York), continuous monitoring of the temperature, precipitation, and physical condition of the sealant was conducted for over 1 year. Based on these tests, it can be concluded that the silicone foam sealant is as easy to install and as durable as conventional solid sealants.

One of the main factors affecting the durability of bridge structures is the presence of expansion joints at bridge support locations. The inability of current joint systems to provide reliable, long-term, leak-proof performance generally leads to early leakage of chloride-contaminated water through these joints, thereby causing premature corrosion in the deck elements below. This problem is particularly evident in older-type multispan bridges in which the girders are simply supported at the piers and are separated by expansion joints or simple paved-over joints. To address this problem, the Ministry of Transportation of Ontario (MTO) has recently rehabilitated a number of bridge decks using a debonded link slab system to replace the deck joints at the pier locations. To get a better understanding of the performance and reliability of this new rehabilitative technique, MTO recently carried out an experimental research study of the long-term performance of the system on scale test models that were subjected to extensive cyclic loading in the laboratory. At the same time, it carried out a load test of a recently rehabilitated structure to study its structural behavior both before and after the link slab was constructed. The test structure was instrumented with sensors that measured deflections and strains in the link slab and girders. This paper describes the experimental research study and the behavioral load tests that were carried out, and discusses the results obtained. The experimental study showed that the long-term performance of the link slab was not affected by the extensive cyclic loading to which the model was subjected, whereas the load testing of the test structure showed that it satisfied the serviceability limit state requirements of the Canadian Highway Bridge Design Code, thus validating the design methodology of the system.

This paper investigates the horizontal effect of fresh concrete on precast arches. A number of different models of horizontal pressure of fresh concrete are considered in this regard. The effects of fresh concrete on a precast arch are represented as a ratio of maximum normal stress from horizontal action of fresh concrete to the normal stress induced by the self-weight of the precast concrete arch. A parameter study on a number of geometric and operational variables was carried out. The implications of this horizontal loading from fresh concrete are discussed within the context of the potential financial effects.

Recently, structural optimization has become an important tool for structural designers, because it allows a better exploitation of material, thus decreasing a structure’s self-weight and saving material costs. Moreover, structural optimization helps the designer to find innovative design solutions and structural forms that not only better exploit material but also give the structure greater aesthetic value from an architectural point of view. In this article, the seismic retrofitting of a bridge originally designed in reinforced concrete is illustrated, showing how lightening the bridge superstructure, rather than reinforcing the already completed foundations and abutments, allowed these latter features to resist greater seismic actions as required in the recent update of the Italian seismic code. Therefore, besides using the steel-concrete composite typology, the bridge superstructure was lightened through structural optimization. After having optimized the thickness of webs and flanges, it was necessary to further lighten the bridge superstructure by removing unexploited material from the bottom flange through the insertion of large cavities. For this purpose, topology optimization is shown to be a powerful tool that allowed the designer to find that the hole shape was basically elliptic, thus suggesting their regularization as ellipses. Comparisons were made between several design solutions, each characterized by a specific volume reduction of the bottom flange. Identification of the highest-performing solutions through computer-aided procedures led to a weight reduction of 40% with respect to the design solution in reinforced concrete. Retrofitting the already existing foundations and abutments to satisfy the updated provisions of the new seismic code was thus avoided by defining an innovative layout of arch bridges with holes in the bottom flange, which has never been used before.

In the current investigation, nondestructive testing (NDT) techniques were applied to evaluate the condition of existing jetty bridge structure. The structure serves as an access point for the loading and unloading of various oil products. The nondestructive strategies included crack-opening measurements using the concrete crack microscope, impact-echo test to measure the depth of the different cracks, and shear-wave testing to detect various defects inside the concrete girders and prestressed ducts. Two AASHTO girders of the jetty were chosen to carry out the various NDTs. The primary objectives of the tests are to assess the overall general condition of the structure and to provide recommendations that could be used to maintain the jetty for its current usage. The combination of the two nondestructive techniques (impact-echo and shear-wave) enabled inspectors to visualize the extension of the cracks in three dimensions and to specify the location of various regions of deterioration within the structural members with a satisfactory level of efficiency. Repair recommendations for the damaged regions were made to maintain safe and economic operation of the Jetty’s facilities.