Editor’s Note

The November 2010 issue of the ASCE Journal of Bridge Engineering features 14 technical papers, one technical note, and one closure. The issue begins with four papers on the dynamic behavior of bridges during seismic and wind loads. The paper titled “Performance Test of Energy Dissipation Bearing and Its Application in Seismic Control of a Long-Span Bridge” by Guan et al. describes a performance test of an energy-dissipation bearing (EDB) consisting of a conventional steel bridge bearing in connection with well-designed mild steel dampers. Experimental results show the bearings to be very stable and have high dissipation characteristics. Through their application on the long-span bridge over the Nanjing Jia River, the authors show that EDBs achieve a very high effectiveness in seismic control in both the longitudinal and transverse directions. Compared with other damping devices, these bearings provide a simple but valid seismic control solution with low maintenance requirements, especially in the transverse direction. In “Theoretical Studies of the XY-FP Seismic Isolation Bearing for Bridges,” Marin-Artieda and Whittaker present research on the XY-friction pendulum (XY-FP) bearing, which is a modified friction pendulum bearing consisting of two perpendicular steel rails with opposing concave surfaces and a connector. The connector resists tensile forces, allows independent sliding in the two orthogonal directions, and enables small relative rotation of the rails about a vertical axis. Two of the key features of the XY-FP bearing for the seismic isolation of bridges are (1) resistance to tensile axial loads and (2) opportunity to provide a different period of isolation in each principal direction of the isolated structure. The authors have demonstrated the effectiveness of XY-FP bearings through numerical analyses of an XY-FP isolated bridge with different isolation periods in the principal directions subjected to near-field ground motions. The authors also show that an analysis considering upper and lower bounds on estimates of coefficients of friction generally provides conservative estimates of displacements and shear forces for isolation systems with nonuniform isolator properties. In the paper “Investigation of Turbulence Effects on Torsional Divergence of Long-Span Bridges by Using Dynamic Finite-Element Method,” Zhang et al. investigate the effect of turbulence on bridge torsional divergence. To take into account the effects of turbulence on torsional divergence, the authors propose a dynamic time domain finite-element (FE) procedure for predicting bridge aerostatic stability. Through numerical simulations, they show that the torsional divergence pattern in turbulent flow differs considerably from that in smooth flow. Whereas torsional instability in smooth flow manifests as an abrupt mounting up of the twist deformation of the main girder with an increase in the wind velocity, in turbulent flow it manifests as an unstable stochastic vibration with large peak values. Wind velocity for divergence in turbulent flow is found to be lower than that in smooth flow and is without any threshold. On the other hand, torsional divergence in smooth flow is characterized by a clear threshold. Using the time domain FE analysis procedure, the authors also investigate the influence of turbulence intensity and gusts spatial correlation on torsional divergence. The paper “Dynamic Analysis of a Composite Cable-Stayed Bridge: Escaleritas Viaduct” by Pantaleón et al. presents some of the most important results of the experimental and numerical analyses of the Escaleritas Viaduct in Spain. Before the inauguration of this composite cable-stayed bridge in 2006, the bridge authority required a dynamic load test to identify natural vibration modes, dynamic magnification factor, and maximum vertical acceleration for the bridge. The authors show a good correlation between test and analysis data. The viaduct has been demonstrated to comply with the requirements for dynamic structural behavior defined in the standards.

The next two papers in this issue focus on various aspects of bridge inspection, management, and deterioration modeling. In “Influence of Surface Condition on the Inspection of Steel Bridge Elements Using the Time-of-Flight Diffraction Method,” Gordon and Pincheira evaluate the influence of the surface condition of steel elements (i.e., painted or rusted) on the ability of the time of flight diffraction (TOFD) method to accurately detect and size flaws. They performed a number of tests on plates with saw cuts or implanted fatigue cracks with different surface conditions. Their data show that rusted surfaces reduce the amplitude of the ultrasonic signals. However, the TOFD method can still detect and accurately size flaws. A painted surface also causes a reduction in signal amplitude and the appearance of additional wave signals that could be interpreted as false indications. Based on the results of this study, the authors present recommendations for field inspection of rusted or painted surfaces using the TOFD method. The paper titled “Reliability-Based Modeling of Bridge Deterioration Hazards” by Sobanjo et al. presents the results from a study on the deterioration patterns of highway bridges using estimated sojourn times of bridge components in various deterioration states. Uncertainties in the estimated times are best fitted as Weibull probability distribution functions, and emphasis is placed on the age at which a bridge leaves a specified threshold condition state. Using both complete data from observations and the right-censored data from a $13\text{-year}$ condition data history for the bridges, the maximum likelihood estimates (MLE) were obtained for parameters of the fitted distributions, and reliability analyses were conducted for various categories of bridges, based on, for example, the type of roadways carried (interstate, noninterstate, and local roads) or the material type (cast-in-place concrete decks, prestressed concrete superstructures, or steel superstructures). Results show that all types of bridges deteriorate faster with age (nonexponential times), and bridge components located on interstate roadways deteriorate faster than similar bridges on noninterstate roadways.

The next eight papers are about various aspects of bridges. In “Flexural Lateral Load Distribution Characteristics of Sandwich Plate System Bridges: Parametric Investigation,” Harris et al. investigate the sandwich plate system (SPS), which is a relatively new bridge deck system consisting of steel face plates bonded to a rigid polyurethane core. The decks are thin, lightweight, and modular in design and can be tailored to numerous applications. This system provides an excellent alternative for the rapid construction and rehabilitation of bridge decks. The paper presents the results of a finite-element parametric investigation of the lateral load distribution characteristics of SPS bridges. The parametric study primarily focuses on the influence of deck thickness on distribution behavior as compared to conventional reinforced concrete decks. Results from the study demonstrate that the inherent flexibility of a thin SPS deck yields larger distribution factors (up to 20%) than a typical reinforced concrete deck, but these distribution factors can still be conservatively estimated with current AASHTO Load and Resistance Factor Design (LRFD) methods. Additional comparisons indicate that the distribution behavior of SPS bridges can also be estimated with the equations proposed by the National Cooperative Highway Research Program (NCHRP) 12–62 project. The paper titled “Selection of Durable Closure Pour Materials for Accelerated Bridge Construction” by Zhu and Ma presents results of the procedure and methods for selecting durable closure pour (CP) materials for joining full-depth precast bridge decks or decked bulb tees (DBTs) for accelerated construction of bridge decks. The accelerated construction is divided into two categories: overnight cure of CP materials and $7\text{-day}$ cure of CP materials. For both categories, candidate materials are selected based on review of published data and tests of compressive strength and flow and workability. Then, the performance criteria for selecting durable CP materials for both categories is developed based on durability tests of the selected candidate materials. These durability tests include freezing-and-thawing durability, shrinkage, bond, and permeability tests. The paper titled “Frequency Spectrum Analysis of Impact-Echo Waveforms for T-Beams” by Zein and Gassman presents numerical and experimental studies to assess the transient impact response of $11\mathrm{T}$ -beams with various dimensions and aspect ratios. Numerical modeling was performed using a three-stage finite-element modeling procedure, which included modal analysis, resonant analysis, and three-dimensional transient dynamic analysis. The response at impact locations on both the top centerline of the flange and bottom centerline of the web was investigated. Physical models of three beams were constructed in the laboratory to determine the physical response of the beams when subjected to a transient impact and to verify the numerical results. Relationships between the fundamental frequencies and the frequencies of higher cross-sectional modes of vibration were established for the various aspect ratios. Shape factors were derived from the numerical and experimental results. The practical significance of the results for a project where impact-echo testing was used to nondestructively assess the condition of a decommissioned concrete T-shaped girder is demonstrated. In “Effect of Intermediate Diaphragms on Decked Bulb-Tee Bridge System for Accelerated Construction,” authors Li and Ma investigate the use of decked precast prestressed concrete girders, or decked bulb tee (DBT) girders, one of the promising systems for accelerated bridge construction, for bridge superstructure. Using calibrated 3D FE models through field tests, a parametric study was conducted to determine the effect of intermediate diaphragms on the deflections and flexural strains of girders at the midspan as well as the live load forces in the longitudinal joint. The following diaphragm details were considered: different diaphragm types (steel and concrete), different diaphragm numbers between two adjacent girders, and different cross-sectional areas for steel diaphragms. Five bridge models with different diaphragm details were developed, and the short-span length effect on the bridge behavior was also studied. The authors found that as long as one intermediate diaphragm was provided between two adjacent girders at midspan, changing the diaphragm details did not significantly affect the girder deflection, the girder strain, or the live load forces in the longitudinal joint. The effect of diaphragms on the midspan deflection was more prominent in the short-span bridge; however, the reduction of the maximum bending moment by the diaphragms was more significant in the long-span bridge than in the short-span bridge. The paper presents specific design recommendations for the use of these systems for accelerated bridge construction. The paper titled “Bridge Deck Patching Material Evaluation” by Cervo and Schokker presents the outcome of a testing program that evaluates a number of deck patch materials and the development of a testing protocol for material evaluation. Deck patching is a common practice used when bridge decks have local deterioration but do not yet warrant full replacement. Rapid-setting patch materials provide a quick and economical way to patch deteriorated areas without significant lane closure time. While these materials set quickly and often achieve high early strength, their long-term performance in corrosive environments and under heavy traffic loads is sometimes poor. The paper titled “Parametric Study of Posttensioned Inverted-T Bridge System for Improved Durability and Increased Span-to-Depth Ratio” by Nayal et al. presents results of a study on an inverted-T (IT) bridge system that has gained increasing popularity in recent years owing to its lower weight and relatively larger span-to-depth ratio compared to the prestressed I-girder bridges. There are some limitations in replacing the existing cast-in-place (CIP) bridges with an IT system. Implementation of posttensioning, which is the focus of this paper, is a promising solution for these limitations. This leads to a higher span-to-depth ratio and reduces potential transverse cracks in the CIP deck, which can promote corrosion of the reinforcement. An analytical study was conducted to identify major parameters influencing the performance of a posttensioned IT bridge system. This was followed by a parametric study to explore the scope of these parameters and specify the design limits in terms of posttensioning stages, timing scenarios, and posttensioning forces. Concrete strength and different methods for estimating time-dependent restraining moments have been addressed in this parametric study. In “Load Configuration and Lateral Distribution of NATO Wheeled Military Trucks for Steel I-Girder Bridges,” authors Kim et al. present the lateral load distribution of various North Atlantic Treaty Organization (NATO) wheeled military trucks on a simple-span steel I-girder bridge $(\mathrm{L}=36\mathrm{m})$ . The military trucks are classified using the military load classification (MLC) system. The MLC trucks demonstrate different load configurations when compared to the standard HS20 truck in terms of wheel-line spacing, number of axles, and weight. A calibrated three-dimensional finite-element analysis was conducted to examine the MLC load effects. The applicability of the AASHTO LRFD provisions was evaluated using 72 different load models. The wheel-line spacing and weight of the MLC trucks caused different flexural behavior of and load distributions on the bridge than does the HS20. The current AASHTO LRFD approach to determine the live load distribution factors may be reasonably applicable to the MLC trucks, including approximately 20% of conservative predictions. The paper titled “Current Design and Construction Practices of Bridge Pile Foundations with Emphasis on Implementation of LRFD” by AbdelSalam et al. presents deep foundation practices established through a 2008 nationwide survey of more than 30 State departments of transportation (DOTs). This study highlights the benefits of LRFD as well as how its flexibility is being exploited in design practice. The study collected information on current foundation practice, pile analysis and design, pile drivability, pile design verification, and quality control. Since this is the first nationwide study conducted on LRFD following the Federal Highway Administration (FHWA) mandate, the status of the implementation of LRFD for bridge foundation design has also been examined. The study found that: (a) more than 50% of responding DOTs are using LRFD for pile design, while 30% are still in transition to LRFD; and (b) about 30% of the DOTs using LRFD for pile foundations are utilizing regionally calibrated resistance factors to reduce the foundation costs.

This issue has one technical note: “Steel Girder Stability during Bridge Erection: AASHTO LRFD Check on L/b Ratios” by Hastings et al. The erection of steel plate girders during the construction process of a steel bridge is a complex operation that is often left to the contractor and/or the subcontractor to plan and execute. Rules of thumb to check the lateral torsional buckling of the steel girder during erection using the maximum L/b (unbraced length/compressive flange width) ratio—below which no lateral torsional buckling would occur—have been developed through experience. Although the L/b ratio check has proved useful and convenient on site, it is necessary to provide a more rational basis for the rules of thumb and to find the maximum L/b ratios by checking the lateral torsional buckling failure of girders under erection according to the latest AASHTO LRFD code. A series of parametric studies on cantilever and simply supported girders under self-weight as well as self-weight plus wind load were conducted in order to (1) check the rules of thumb on L/b ratios; (2) determine the effects of girder flange width, flange thickness, web depth, web thickness, and yield strength on the maximum L/b ratio and girder stability during erection. From the results, the rules of thumb were modified for girders with common shapes. It has been observed that: (1) self-weight plus wind load controls the girder stability during erection in most cases and (2) flange width and web depth have the most effect on the maximum L/b ratio and girder stability during erection.

This issue of the Journal has one closure to a discussion published previously. Authors Frangopol et al. present “Closure to ‘Bridge Reliability Assessment Based on Monitoring’” [May/June 2008, Vol. 13, No. 3, pp. 258–270, DOI: 10.1061/(ASCE)1084-0702(2008)13:3(258)]. The discussion by Quan Qin and Rui He was published in Journal of Bridge Engineering, Vol. 15, No. 3, May/June 2010, on page 344.