Journal of Bridge Engineering

This paper proposes a direct displacement-based design (DDBD) methodology for seismic design of rocking shallow foundations for ordinary bridges under earthquake loads. A multilinear model is developed to represent the backbone curve of the nonlinear moment-rotation behavior. In addition, a new empirical relationship is proposed that correlates the initial rotational stiffness to the moment capacity of a rocking foundation; this correlation is proposed as an alternative to calculation of stiffness based upon elasticity theory. In the proposed design procedure, a bridge system consisting of a deck mass, a rocking foundation, and a damped elastic column is integrated into a single element from which the equivalent linear damping and period can be determined. The DDBD methodology uses the equivalent system damping and period along with a design displacement response spectrum to determine the seismic displacement demand. The approach is checked by comparing displacements predicted by this method to those computed using nonlinear time-history analyses. The methodology also includes provisions to determine footing dimensions to obtain acceptable performance in terms of foundation settlement and lateral sliding. The DDBD methodology is further illustrated with a design example.

In recent years, a number of studies have been conducted to analyze wind-induced vibrations of a bridge using computational fluid dynamics (CFD). Previous studies have been limited to analyzing two-dimensional sections only, and three-dimensional (3D) analyses of entire bridges have not yet been performed. In this study, a CFD program with fluid-structure interaction is developed to perform buffeting analysis of a 3D cable-stayed bridge. The FEM formulated by the Galerkin least-squares method and arbitrary Lagrangian-Eulerian method are used to perform fluid-structure interaction CFD. The spectral representation method is used to generate the time series turbulence, which is applied to the inlet boundary condition. A supercomputer is used to reduce the large computing time. The analysis model of an existing cable-stayed bridge, which contains an ambient atmospheric region, has been used to calculate the dynamic responses of bridges and the detailed flow of wind. The results of the 3D CFD analysis of the bridge are compared with the results of conventional frequency domain buffeting analysis. The results are essentially in good agreement with those of the conventional analysis. The numerical method developed in this study will be an efficient alternative to wind tunnel tests for verifying wind flow, wind loading, and structural vibrations.

Conservative models and code practices are usually employed for fatigue-damage predictions of existing structures. Direct in-service behavior measurements are able to provide more accurate estimations of remaining-fatigue-life predictions. However, these estimations are often accurate only for measured locations and measured load conditions. Behavior models are necessary for exploiting information given by measurements and predicting the fatigue damage at all critical locations and for other load cases. Model-prediction accuracy can be improved using system identification techniques where the properties of structures are inferred using behavior measurements. Building upon recent developments in system identification where both model and measurement uncertainties are considered, this paper presents a new data-interpretation framework for reducing uncertainties related to prediction of fatigue life. An initial experimental investigation confirms that, compared with traditional engineering approaches, the methodology provides a safe and more realistic estimation of the fatigue reserve capacity. A second application on a full-scale bridge also confirms that using load-test data reduces the uncertainty related to remaining-fatigue-life predictions.

Temperature effects have always been considered to be one of the critical issues that affect the performance of traditional concrete and steel bridges. Currently, glass fiber-reinforced polymer (GFRP) composite panels, with the advantages of high strength, light weight, good corrosion resistance, long-term durability, etc., have been applied to slab replacements in bridge engineering. The thermal behaviors of these GFRP bridges, however, have not been fully understood. More specifically, the current temperature design specifications in the AASHTO LRFD may no longer be valid for GFRP bridges. Therefore, this paper presents the thermal field distribution behaviors through studying an as-built bridge with GFRP sandwich panels. First, a transient-state numerical modeling method is proposed. This method is capable of predicting the temperature field of a GFRP bridge based on local environmental conditions. Then, a parametric study is conducted to analyze the thermal responses of bridges with different structure combinations (i.e., GFRP panels, concrete slabs, concrete beams, and steel girders). The mechanical and physical properties of GFRP panels are predicted using the micro-macro mechanics theory and validated by a field measurement and an experimental study. Based on the results from the present study, the temperature distribution patterns for GFRP panel bridges are proposed, referring to the available AASHTO LRFD sign code. The thermal strains and stresses caused by temperature gradients along the depth of bridge superstructures are examined.

Railway bridge decks are frequently constructed using a concrete slab supported by transverse beams, which in turn are connected to the main longitudinal supporting elements: arches, trusses, and so on. This is a structural design whose dynamic behavior often experiences excessive accelerations. Despite the frequent occurrence of this dynamic behavior, no studies have been completed that examine this dynamic response and the variables that cause it. This study proposes that reduced longitudinal stiffness is the cause of excessive vertical accelerations often exhibited by these decks. The study further proposes that increased stiffness in this direction, achieved by incorporating longitudinal beams connected to the underside of the slab, for example, greatly improves this structural design’s dynamic behavior.

The fracture critical (FC) classification was developed and implemented for bridges in which the failure of a single member could lead to failure or collapse of the structure. The FC classification can increase the fabrication cost of the bridge, but far more expensive are the required arms-length biennial in-service inspections. To reduce costs for state highway agencies, it would be beneficial to reconsider the FC designation or, at least, the frequency of the arms-length in-service inspections for bridges, where appropriate. This research evaluated (1) the redundancy of a full-scale 45.72-m (150-ft) truss bridge structure by conducting controlled fracture tests in the field and (2) the use of numerical analysis techniques for quantifying the postfracture behavior and redundancy of the full-scale truss bridge. The experimental results indicate that the truss bridge structure had significant member-level and system-level redundancies, which prevented failure or collapse of the structure caused by failure of the FC member. The numerical models can predict the postbehavior and redundancy of the full-scale truss bridge reasonably well, but with some limitations. The experimental and numerical approaches presented in this paper are recommended for conducting additional investigations, expanding the knowledge database, and eventually for reconsidering the FC classification or the frequency of arms-length inspections.

In this study, a numerical model is developed for the analysis of the free vibration of an open-type periodic structure, namely, a periodic viaduct supported by pile foundations. The viaduct is supposed to be composed of infinite spans, with each span consisting of a pile foundation, a pier, two longitudinal beams (left and right beams), and three linking springs. The boundary-element method (BEM) is used to solve the pile-soil interaction problem first. Based on the developed BEM model for the pile-soil system, the compliances of the pile foundation are obtained. By using the compliances of the pile foundation, the joint conditions at the beam-beam-pier (BBP) junction and the transfer matrix method, the eigenvalue equation for the periodic viaduct is established. Numerical results for the energy bands of the viaduct show that there are three kinds of characteristic waves propagating in the periodic viaduct. The first and second kinds of waves are highly decaying. The third characteristic wave can propagate in pseudopassbands with a small attenuation. Also, it is found that, unlike a closed periodic structure, because of the energy transmission from the viaduct to the half-space soil, all energy bands for the open viaduct considered in this study are complex bands with nonzero imaginary wave numbers.