Scour is a major cause for bridge failure. To understand the characteristics of bridge failures under scour conditions and provide useful information for scour countermeasure, this study reviewed and analyzed totally 36 historical cases of bridge failure due to scour, including their hydraulic, geotechnical, and structural conditions and failure modes. Based on the collected data, most of scour depths (i.e. up to 41%) ranged from 0.5 to 5 m; but, the maximum scour depth could be up to 15 m. Local scour was accounted for 64% bridge failures, followed by channel migration (14%), and contraction scour (5%). Possible bridge failure modes due to scour included vertical failure, lateral failure, torsional failure, and bridge deck failure. Approximately 70% of bridge failures were lateral and vertical. The findings from this study can be updated when more cases of bridge failure under scour conditions are collected and/or become available.

This paper presents a field implementation of the structural health monitoring (SHM) of fatigue cracks for steel bridge structures. Steel bridges experience fatigue cracks under repetitive traffic loading, which pose great threats to their structural integrity and can lead to catastrophic failures. Currently, accurate and reliable fatigue crack monitoring for the safety assessment of bridges is still a difficult task. On the other hand, wireless smart sensors have achieved great success in global SHM by enabling long-term modal identifications of civil structures. However, long-term field monitoring of localized damage such as fatigue cracks has been limited due to the lack of effective sensors and the associated algorithms specifically designed for fatigue crack monitoring. To fill this gap, this paper proposes a wireless large-area strain sensor (WLASS) to measure large-area strain fatigue cracks and develops an effective algorithm to process the measured large-area strain data into actionable information. The proposed WLASS consists of a soft elastomeric capacitor (SEC) used to measure large-area structural surface strain, a capacitive sensor board to convert the signal from SEC to a measurable change in voltage, and a commercial wireless smart sensor platform for triggered-based wireless data acquisition, remote data retrieval, and cloud storage. Meanwhile, the developed algorithm for fatigue crack monitoring processes the data obtained from the WLASS under traffic loading through three automated steps, including (1) traffic event detection, (2) time-frequency analysis using a generalized Morse wavelet (GM-CWT) and peak identification, and (3) a modified crack growth index (CGI) that tracks potential fatigue crack growth. The developed WLASS and the algorithm present a complete system for long-term fatigue crack monitoring in the field. The effectiveness of the proposed time-frequency analysis algorithm based on GM-CWT to reliably extract the impulsive traffic events is validated using a numerical investigation. Subsequently, the developed WLASS and algorithm are validated through a field deployment on a steel highway bridge in Kansas City, KS, USA.

Distortion-induced fatigue cracking is a primary maintenance and structural safety concern in steel bridges built prior to the 1980s in the United States. Manual, hands-on inspections are currently the primary method departments of transportation and other bridge owners use to identify and quantify fatigue cracks. To improve the efficacy of fatigue crack inspections, previous research has proposed and examined numerous fatigue crack detection approaches, including both user-implemented technology and structural health monitoring methods. However, these approaches typically require human presence and active participation at the location of interest or prolonged mechanical contact and continuous monitoring of the structure. This limits the effectiveness and flexibility of these approaches for inspecting a large number of fatigue-susceptible regions found on steel bridges. Recently, vision-based sensing technologies have been explored for applications related to damage detection and health assessment in civil infrastructure, as they offer the benefits of being low cost, noncontact, and deployable without human presence at the specific region of interest. This paper presents a digital image correlation-based methodology developed from in-plane compact fracture specimens for the detection and quantification of fatigue cracks. The effectiveness of the proposed methodology is further evaluated through experimental tests of a fatigue crack on a large-scale steel girder-to-cross-frame connection, similar to the out-of-plane fatigue cracks commonly found on steel highway bridges. Results indicate that the digital image correlation methodology can adequately characterize fatigue cracks, both in-plane and out-of-plane, in terms of crack length. This quantification from a noncontact inspection technology has the potential to lead to future automation of steel highway bridge fatigue inspections.

Carbon-fiber reinforced polymer (CFRP)-overlay elements were developed with the purpose of enhancing the fatigue performance of welded connections in steel bridge girders. Fatigue tests of seven specimens, including four CFRP-strengthened specimens and three control specimens, were performed to quantify the effect of the CFRP overlays on the fatigue crack initiation lives of the welded connections. Results showed that bonding of CFRP overlays significantly reduced the stress demand on welded connections tested at high stress ranges, leading to a large increase in fatigue crack initiation life. The level of effectiveness of the CFRP-overlay elements in extending the fatigue crack initiation lives of the tested connections was found to be affected primarily by bond strength under cyclic loading; bond strength was found to be dependent on the composition and thickness of the resin layer used to bond the CFRP to the steel. With the AASHTO fatigue design curves as a frame of reference, it was found tha...

The effects of skew angle, cross-frame spacing, cross-frame layout, cross-frame stiffness, and load placement on the potential for distortion-induced fatigue damage in steel bridges was investigated by performing a suite of more than 1,000 analysis jobs of high-resolution three-dimensional finite-element models. Susceptibility to fatigue damage was quantified in terms of computed stress demand in the web gap region of the girders. Bridge configurations with three different cross-frame layouts were evaluated, including configurations with cross-frames placed parallel to skew angle (skewed-parallel) and perpendicular to the girder line, both staggered (skewed-staggered) and unstaggered (skewed-unstaggered). Skew angles of configurations evaluated ranged between 0 and 50°, and cross-frame spacing ranged from 2.29 to 9.14 m (7.50 to 30.0 ft). Influence and envelope surfaces were constructed to show the relationship between load placement, location of the maximum web gap stress, and the magnitude of th...