Effect of the Temperature on the Modal Properties of a Steel Railroad Bridge

The article is devoted to a study of the impact of various environmental conditions on modal parameters, such as natural frequencies and damping ratios. The modal analysis has been performed using the Stochastic Subspace Identification (SSI) method of measuring data every month on the same steel bridge structures located on an important railroad route from Prague (the Czech Republic) to Košice (Slovakia). The structure is approximately 60 m long, and the bearing structure is formed by two arch trusses. The bridge was exposed to ambient vibrations as well as to vibrations caused by a train passage. Accelerations and temperatures (the temperature of the air and the structure) were logged during the measurements. Natural frequencies were obtained from these acceleration data using the SSI method and processed into graphs of the dependencies between the natural frequencies and temperatures. Some statistical procedures were also applied.

Joint- or Crack-Opening Resistance Evaluation of Waterproofing Material and System for Structural Sustainability in Railroad Bridge Deck

A joint- or crack-opening resistance evaluation method for the selection of optimal waterproofing material for a railroad bridge deck is proposed. The joint opening range (mm) for the evaluation, and a typical load case of a high-speed double-track railroad bridge structure deck, is analyzed through the finite element method (FEM) and the results of analysis are used to calculate the minimum opening range. The evaluation method is then demonstrated with 4 commonly used waterproofing types of cementitious membrane system: a polyurethane coating system, self-adhesive asphalt sheet system and synthetic polymerized rubber gel composite asphalt sheet system. Five specimens of each type are subjected to continuous joint opening under 4 different joint width range conditions (1.5, 3.0, 4.5, and 6.0 mm), and the joint-opening resistance performance is compared. The proposal for the evaluation criteria and the specimen test results demonstrate how the evaluation method is pertinent for future selection of waterproofing membranes for the sustainability of high-speed railroad bridge deck structures.

Probabilistic fatigue assessment of monitored railroad bridge components using long-term response data in a reliability framework

Fatigue is a primary concern for railroad bridge owners because railroad bridges typically have high live load to dead load ratios and high stress cycle frequencies. However, existing inspection and post-inspection analysis methods are unable to accurately consider the full influence of bridge behavior on the fatigue life of bridge components. Reliability-based fatigue analysis methods have emerged to account for uncertainties in analysis parameters such as environmental and mechanical properties. While existing literature proposes probabilistic fatigue assessment of bridge components, this body of work relies on train parameter estimates, finite element model simulations, or controlled loading tests to augment monitoring data. This article presents a probabilistic fatigue assessment of monitored railroad bridge components using only continuous, long-term response data in a purely data-driven reliability framework that is compatible with existing inspection methods. As an illustrative example, this work quantifies the safety profile of a fracture-critical assembly comprising of six parallel eyebars on the Harahan Bridge (Memphis, TN). The monitored eyebars are susceptible to accelerated fatigue damage because changes in the boundary conditions cause some eyebars to carry a greater proportion of the total assembly load than assumed during design and analysis; existing manual inspection practices aim to maintain an equal loading distribution across the eyebars. Consequently, the limit state function derived in this article accounts for the coupled behavior between fatigue and relative tautness of the parallel eyebars. The reliability index values for both the element (i.e. individual eyebars) and system (i.e. full eyebar assembly) reliability problems are assessed and indicate that under the conservative assumption that progressive failure is brittle, first failure within the parallel eyebar system is generally equivalent to system failure. The proposed method also serves as an intervention strategy that can quantify the influence of eyebar realignment on the future evolution of the reliability index.

Economies of Scale (1848–51)

Between 1847 and 1852, John built four separate aqueducts for the Delaware and Hudson Canal; moved his home, family, and wire rope factory from western Pennsylvania to Trenton, New Jersey; secured the contract to build a huge railroad bridge over the Kentucky River; and continued to mount substantial campaigns to win contracts to span the Ohio at Wheeling and the Niagara Gorge. The four D&H spans were mini masterpieces of engineering and planning. Each structure was very different; each required new solutions to site-specific problems. One of the spans, the Delaware Aqueduct, exists to this day, the oldest suspension bridge in the United States and one of the oldest “modern” suspension bridges in the world. On the larger projects, John again lost out to his old rival Ellet on both the Wheeling and the Niagara spans.