Journal of Bridge Engineering

The subject matter of the present paper falls within the context of the analysis of the response to wind of long-span bridges. Although the paper stands alone, it should properly be seen as focusing on a single important aspect of such an analysis. For the last few decades, the theory of the response of flexible bridges to wind has grown in sophistication. The problems of buffeting and flutter have been brought together into a unified analytic form. This accomplishment centers on the fact that not only are the static forces and moment on a section of the deck girder experimentally measured on geometrically accurate wind tunnel sectional models, but motional coefficients—flutter derivatives—have also been so obtained for the last quarter-century or more. These experimental values have, for the most part, assured reasonable accuracy in the analytic assessment of flutter and buffeting. In the buffeting case, however, the static coefficients rather than dynamic ones were commonly employed in the force description. This practice usually resulted in erroneous estimates of buffeting response that required correction by invoking empirical frequency-dependent correction factors called aerodynamic admittances. The present paper shows how important central characteristics of such admittances can be seen to be inherent in the measured flutter derivatives.

Long span bridges are one of the most challenging kinds of structures in civil engineering. Wind loading and wind effects are highly important aspects when designing this typology. The interaction between wind and structure, studied by using aeroelasticity theory, allows us to understand several classes of structural instabilities that may appear. Also, wind tunnel data, obtained by conducting careful testing of reduced models of bridges, produce useful information about prototypes' characteristics. A fundamental aspect of bridge design under aeroelastic constraints is identification of aerodynamic forces; several models for this purpose are presented in this paper. First, a model based on a two-degrees-of-freedom plane plate moving in an incompressible fluid is reviewed; this approach, although useful in airfoil engineering, is not valid any longer in civil engineering, as bridge decks are bluff bodies. Second, a linearized theory, also based on a two-degrees-of-freedom model is analyzed; in this case, obtaining aerodynamic forces requires identification of a set of coefficients, called flutter derivatives, that can be found by carrying out testing of reduced models of a segment of bridge deck. Finally, an extension of that approach, leading to a linearized theory of a three-degrees-of-freedom model is presented.

The Toutle River Bridge is a steel tied-arch bridge, one that vibrates extensively and has sustained significant fatigue cracking. An experimental study into the cause of this behavior is described. Computer analyses of the bridge behavior are used to estimate the expected response and to establish appropriate locations for instrumentation. The instruments were installed and field tests were performed. Controlled tests were performed with trucks of known axle weight and spacing. Some controlled tests were performed with trucks traveling at known speed and in a specific driving lane with no other traffic on the bridge. Controlled tests were used to calibrate the instrumentation and establish the basic bridge behavior. The results showed that composite action had been lost in the heavily loaded stringers, and little amplification of dynamic response was noted. The measured periods of vibration generally compared well with computer predictions. Uncontrolled truck traffic was then measured for approximately one month. This data was used to establish load spectra and to estimate the fatigue life of critical components. Fatigue, which is caused by calculated stress ranges, should not be important on this bridge for another 20 to 30 years. Existing fatigue damage is driven by distortional fatigue caused by the large bridge deformations. Several options for dealing with the problem are presented.

Continuous concrete box girder bridges composed of precast reinforced and prestressed concrete beams with a U cross section and a cast-in-place top slab are frequently used for medium spans due to their competitiveness. The service behavior of such bridges is very much influenced by their segmental construction, due to time-dependent materials behavior that makes it difficult to accurately predict the stresses, strains, and deflections at long term. A 1:2 scale model of a two-span continuous bridge was tested in order to study its behavior during the construction process and under permanent loads. Time-dependent concrete properties, as well as support reactions, deflections, and strains in concrete and steel, were measured for 500 days. Important time-dependent redistributions of stresses and internal forces throughout the bridge were also measured. The test results were compared with analytical predictions obtained by means of a numerical model developed for the nonlinear and time-dependent analysis of segmentally erected, reinforced and prestressed concrete structures. Generally good agreement was obtained, showing the adequacy of the model to reproduce the structural effects of complex interactive time-dependent phenomena.

It is well known that the U.S. bridge inventory stands in need of repair. For a rational allocation of U.S. investment resources to bridge maintenance, life cycle cost and probabilistic methods must be used. This requires a quantitative estimate of the remaining strength over the intended lifespan for a given bridge. Although nondestructive evaluation methods are becoming established for bridge inspection purposes, specific recommendations for the application of these methods for individual bridges do not exist. This study focuses on reported damage and damage modeling for concrete bridges, with particular attention to Colorado bridges. A survey on degradation mechanisms is briefly presented. Bridge damage is reviewed for a variety of concrete bridges based on information in the literature and from field studies performed by the Colorado Department of Transportation. A catalog of damages and examples that illustrate the variety and severity of damage in these bridges are presented. For the bridges considered in the survey, the most common source of damage is water leaking through deck joints. A method for predicting strength loss is applied to a typical bridge in Colorado. It is shown that corrosion initiation occurs more quickly and normalized strength loss is much greater for shear than for flexure. It is also shown that many reinforced concrete bridges under corrosion attack may be more vulnerable to shear than to bending failure. The results can be used to identify critical elements for inspection and repair, and to assist in the development of rational maintenance planning strategies for concrete bridges.

Diagnostic truck-load tests and microstructural analysis were applied for structural deterioration assessment of a steel truss bridge and its rehabilitation design. The feasibility and potential benefits of using advanced field experimental techniques within a structural-identification framework have been demonstrated. Experimental information, coupled with visual inspection, engineering experience, and intuition, increased the level of confidence in the results of the condition-assessment process, permitting a more rational and cost-effective rehabilitation design. Based on the condition assessment, a two-step rehabilitation is recommended for the bridge: Restoration for a safe service life of 5–7 years, and a subsequent effort for preservation beyond.

All states in the United States issue special permits for nondivisible and/or divisible truck overloads exceeding the weight limit of the highway jurisdiction. This causes stress levels higher than those induced by normal truck traffic. The rationality of such overstress levels has not been documented. This paper addresses several aspects of this issue. It presents (1) a method to develop live load models including overload trucks; (2) associated reliability models for assessing structural safety of highway bridges; and (3) proposed permit-load factors for overload checking in the load and resistance factor format. It shows that the proposed overload checking procedure leads to relatively uniform reliability of bridge structures. A sensitivity analysis is also presented here to assure that possible variations of the input data used to prescribe the proposed load factors will not adversely affect bridge safety. The proposed procedure is intended to be used by engineers responsible for checking overload permits. It may be included in evaluation specifications for highway bridges.

Inelastic design of steel girder bridges can result in beneficial material and fabrication cost savings and reduce the susceptibility of steel girder bridges to fatigue. The ability to redistribute large negative region moments, coupled with section capacities exceeding the yield moment, results in an efficient structure used to its limit-state capacity. Proposed LRFD inelastic design provisions are presented that allow compact or noncompact pier sections resulting in consistent bridge design across the steel girder bridge inventory. This paper illustrates the simplified inelastic design provisions, presents an example design of a two-span composite bridge comprising noncompact sections at the pier, and summarizes the experimental verification of the example design. The proposed inelastic design procedures are simple to apply, removing the cumbersome continuity and iterative requirements of past inelastic design practice.

This paper presents the result of a study on the use of viscoelastic dampers at expansion joints of highway bridges for preventing superstructure decks from falling off the seats and/or from colliding with each other in the event of a severe earthquake. The Kelvin and Maxell models, consisting of an elastic spring and a linear viscous damper combined in parallel and in series, respectively, are considered for analysis. A 2D finite-element analysis using bilinear hysteretic models for bridge substructures joints was performed on example bridges constructed with one or two expansion joints. It was demonstrated that the damper is effective in suppressing the relative displacements at the expansion joints without introducing a significant increase in ductility demands for the substructures. The result also showed that the spring component of the Kelvin and Maxwell models has little effect on the performance of the damper component. This study clearly indicated that the use of linear viscous dampers offers a practical solution to the seismic problem that often arises from bridges with expansion joints.

Incremental launching is a competitive construction method for medium-span (40–65 m) prestressed concrete bridges. It does not constrain the length and width of the superstructure, and bridges longer than 1 km and wider than 20 m have been successfully launched. This method is hardly constrained by the bridge layout, as varying plan curvatures can be solved by shifting launch supports and varying vertical curvatures by shimming the bottom edges of the superstructure. The launch of a prestressed concrete bridge involves enormous forces and requires the guide and control of big volumes. The devices used for this purpose are described along with their design criteria and optimum fields of utilization, and several suggestions derived from many years of launching practice are given.

Dowel and stiffener beam deck-to-deck connections transfer shear and moment between hardwood glued-laminated (glulam) transverse deck panels in longitudinal timber bridges. The connections resist relative deflections between the deck panels and aid in the prevention of reflexive cracking of the bituminous wearing surface at panel joints. Cyclic loading can reduce the stiffness of some types of deck-to-deck connections resulting in shortened service life. The performance of dowel and stiffener beam deck-to-deck connections for hardwood glulam transverse panel bridge decks was evaluated during cyclic laoding. Five tests were conducted with steel dowel connected deck panels, and five tests were conducted with glulam stiffener beam connected deck panels. Each connection was subjected to 1,000,000 load cycles. Degradation of connector stiffness with increasing number of load cycles was determined. Stiffener beam connections had better cyclic load response than the steel dowel connections. Steel dowel connections experienced approximately 20% degradation of stiffness after 1,000,000 load cycles. Most stiffener beam connections experienced little to no stiffness degradation after 1,000,000 load cycles; the smaller stiffener beam experienced 14% degradation after 1,000,000 load cycles. All connections remained within the limits of deflection criteria established in the 1994 AASHTO LRFD Bridge Design Specifications.