Journal of Bridge Engineering

Taizhou Changjiang Highway Bridge is the longest three-pylon two-span suspension bridge in the world. To investigate the seismic performance of different connecting configurations between the deck and pylons, which are referred to as seismic structural systems, a $1/40\text{-scale}$ model of Taizhou Changjiang Highway Bridge incorporating different seismic structural systems was tested on the shake tables at Tongji University, Shanghai, China. In this paper, the design, construction, instrumentation, and loading protocol of the test model are introduced first. The fundamental frequencies of the eight bridge models are identified and are compared with numerical results. The damping ratios corresponding to the fundamental frequencies are obtained by the half-power bandwidth method. The test results show that the seismic responses of the three-pylon two-span suspension bridge under seismic loads are highly dependent on the connecting configurations between the deck and pylons. The relative displacement responses between the deck and the pylons in the longitudinal direction can be decreased effectively by viscous dampers or elastic cables. In addition, the influences of variations in those viscous dampers and elastic cables on the response of the model are investigated. Numerical results and test results are compared, and good agreement is achieved.

Excessive deflections unexpected at the midspan have commonly appeared in long-span prestressed concrete box girder bridges, mainly because of the high degree of uncertainty in concrete creep and shrinkage, prestress loss, and variations in the environment. Arrangement of backup prestressing tendons that will be tensioned based on deflection development during the service years is an effective solution to this problem. First, an uncertainty analysis of the long-term deformation at the midspan of a bridge was performed using the Latin hypercube sampling method, with the consideration of model uncertainty of creep and shrinkage and random properties of influencing factors; consequently, the 95% confidence interval of the deformation at the midspan was determined. Then, a quantitative design of backup tendons was performed on the basis of the difference between the lower limit and mean value of the 95% confidence interval of deformation. Lastly, the efficiencies of different arrangement schemes of backup tendons were compared, and results show that arrangement of combined external tendons along the girder is the most effective measure for control of long-term deflection.

Five representative girder cross sections with various slot widths are utilized to analyze the effects of center slots on their aerodynamic performance, based on wind-tunnel tests and theoretical analyses. It is shown that the favorable aerodynamic effects of the center slot on bridge decks depend on the aerodynamic shape of the box girders and on the slot widths rather than unconditionally improving the aeroelastic stability. Further investigation of a streamlined box girder with various slot widths results in a modified Selberg formula to calculate the critical flutter wind speed for design purposes, wherein the Lorentz peak-value function is utilized. The flutter mechanism is illustrated utilizing a two-dimensional three-degrees-of-freedom (2D-3DOF) analysis scheme. The results indicate that the center slot changes the participation level of the heaving motion at the flutter onset, which is highly correlated with the critical flutter wind speed. In addition, particle image velocimetry (PIV) and proper orthogonal decomposition (POD) techniques are employed to assist in revealing the aerodynamic stabilization mechanism of the center slotting of box girders.

Ultrahigh performance concrete (UHPC) presents many superior properties, such as advanced strength, durability, and long-term stability. The use of existing cross section geometries for materials with advanced properties results in inefficient designs and less cost-effective solutions. This study focused on developing a series of finite-element optimized sections of pi-girders to effectively utilize the superior mechanical properties of UHPC over span lengths of up to 41 m (135 ft). The research was performed using a finite-element model that has been calibrated and verified against experimental results. The optimization was progressively conducted at local, element, and structural levels. At the local level, the focus of the investigation was to find the optimal deck thickness and prevent transverse bending failure of the deck. At the element level, sectional parameters, including girder height, bulb size, web thickness, and strand layouts, were investigated to find the minimal sectional size that accommodates standard loads for a span length of 23 m (75 ft) or above. At the structural level, deflection under a live load was checked such that the bridge system using the proposed sections can meet the deflection requirements specified in guidelines. Four cross sections based on the second generation pi-girder were proposed, and a design chart was provided to facilitate preliminary design for bridge engineers.

In Texas, a number of RC bridges have developed early cracking. Most of this deterioration has been identified or suspected to be from alkali-silica reaction (ASR), and in some cases from delayed ettringite formation (DEF). An area of concern for the Texas DOT is the performance of columns, and specifically their lap-splice regions, which have varying levels of cracking primarily from ASR but also possibly from DEF. Therefore, a research program was carried out (1) to evaluate the experimental behavior of a typical column using large-scale specimens under varying levels of premature concrete deterioration and (2) to develop an analytical model that can evaluate the behavior of the column based on calibration with the experimental behavior. This paper provides a brief overview of ASR and DEF; documents the design, construction, curing conditions, and instrumentation of 16 large-scale specimens; and presents the findings on the specimen dimensional changes and cracking that occurred during the deterioration (exposure) phase.

This paper describes the structural performance and analytical methodology for large-scale column specimens with a lap splice and concentric axial loading affected by varying levels of alkali-silica reaction (ASR) under displacement-controlled monotonic loading. The lap-splice length in the specimens is typical of the Texas DOT practice for the bar size used and is conservative by code standards. The specimens with varying degrees of ASR showed no evidence of bond deterioration within the splice; had similar initial stiffness and behavior up to the first cracking; had a 25–35% increase in postcracking stiffness up to yielding; had a 5–15% increase in yield strength; and showed no overall detrimental effects on the structural response when compared with control specimens without ASR deterioration. This improved behavior can be explained by the resulting volumetric expansion of the concrete because of the ASR that engaged the longitudinal and transverse reinforcement—this is believed to have resulted in increased axial loading and better confinement of the core concrete. Analytically, a proposed step-by-step postcracking stiffness model for axially loaded members provided the best fit with the force-displacement experimental data. In addition, for specimens exhibiting ASR, increasing the axial load on the column provided a better match with the measured experimental response.

With the existence of aging highway bridges within the U.S. transportation network, federal and local agencies typically encounter a wide assortment of maintenance issues ranging from cracking, spalls, delaminations, and corrosion to high load hits and fire damage. This paper presents an approach for capturing the full system-based behavior and stages of failure in the composite bridge superstructures as they approach ultimate capacity. This step is instrumental to understanding how redundant bridges behave in the presence of coupled and uncoupled damage and deteriorations. The investigation included a comprehensive nonlinear finite-element analysis of two representative intact composite steel girder bridges that were tested to failure and provided sufficient details for model validation. Results demonstrate the high degree of additional reserve capacity, inherent to redundant superstructures, over the theoretical nominal design capacity. A rational approach was established to describe the actual system-based ultimate capacity, which was not explicitly considered in the current design methodology. In addition, a limited sensitivity study was performed on one of the selected representative bridges to investigate the sensitivity of the characterized failure stages to variations in the geometrical parameters and material properties of the bridge system.

Numerous long-span cable-supported bridges have been built throughout the world in recent years. These bridges begin to deteriorate once built and continuously accumulate damage during their long service life. The growing popularity of comprehensive structural health monitoring systems (SHMSs) in recently built long-span bridges has started a new trend of integrating SHMS and damage detection technology for real-time condition assessment of these bridges. This paper explores a novel damage detection technique based on stress influence lines (SILs) of bridge components and validates the efficacy of the technique through a case study of the Tsing Ma suspension bridge. A mathematical regularization method is first introduced to identify SILs based on the in situ measurement of train information and train-induced stress responses in local bridge components. Good agreement between the identified and baseline SILs demonstrates the effectiveness of the proposed identification method. Damage indexes based on SILs are subsequently proposed and applied to hypothetical damage scenarios in which one or two critical bridge components are subjected to severe damage. The comparison suggests that the first-order difference of SIL change is an accurate indicator of the damage location. Results of this study indicate that the proposed SIL-based method offers a promising real-time technique for damage localization in long-span cable-supported bridges equipped with comprehensive SHMSs.

This article presents the findings of an investigation that used finite-element analysis to determine the influence of a concrete footing’s dimensions on its temperature development and cracking at early age. A three-dimensional finite-element model was used to predict temperatures in the footing and to assess cracking potential of the concrete. A parametric study consisting of 63 finite-element analyses was conducted on three different footing shapes: (1) a cubic shape, (2) a length:width:depth ratio of 4:4:1, and (3) a length:width:depth ratio of 4:2:1. Volume-to-surface area ratios ($v/a$) ranged from 0.33 to 4.0 m. The results showed that cracking potential does not depend on a footing’s dimensions when its $v/a$ is 1.3 m or greater. Rectangular footings that have the same $v/a$ but different shapes (dimensional proportions) developed a similar maximum temperature, a similar maximum temperature differential, and a similar minimum crack index under the same insulation condition. Smaller footings allowed slightly higher maximum temperature differential before thermal cracking occurred.