Scott Walbridge

Quality assurance for high-frequency mechanical impact (HFMI) treatment of welds using handheld 3D laser scanning technology

The idea of using 3D point clouds obtained with the aid of a handheld 3D laser scanner for the quality assurance of high-frequency mechanical impact (HFMI) treatment is proposed and demonstrated in this paper. The effectiveness of impact treatments for extending the fatigue lives of welded structures has been demonstrated in numerous studies. Guidelines for the proper execution of impact treatments have been developed. A lack of suitable quality assurance (QA) procedures for accepting or rejecting the treatment after completion has been previously identified. In contrast with the existing QA procedures, which are based mainly on controlling inputs and visual inspection, a technology-based, quantitative methodology is developed in this paper. Five welded specimens were subjected to impact treatment at various levels to simulate under-, proper, and over-treatment. A handheld 3D laser scanner was then used to facilitate a point cloud-based method to determine the geometric parameters of the treated weld toe groove, which were then measured manually. The results show that the proposed methodology is successful in identifying the different treatment levels. This approach has a number of advantages over the existing QA methods, including the following: providing quantitative measures, ease of use, and archive-ability.

A methodology for the prediction of structure level costs based on element condition states

The determination of work programmes for bridges that maximise benefit to all stakeholders requires consideration of not only the condition of the elements of which a bridge is comprised, but also the performance of the structure as a whole. This is required because although some costs can be related to the condition of the elements, others, such as the costs of travelling over the bridge, cannot. One possible methodology to do this involves linking relevant costs to structure performance states (SPS) that are determined from the element condition states (CSs). However, even a bridge with a moderate number of elements and element CSs results in a large number of possible SPSs and an unwieldy amount of required work to estimate the costs associated with each. This work can be drastically reduced, however, by exploiting the almost linear system behaviour of the bridge that can occur between many combinations of element CSs. This article presents a methodology for relating SPSs to element CSs for the purpose of determining structure level costs. This methodology is demonstrated in several examples, wherein the effects of exploiting the linearity of the system behaviour to reduce the computational effort are also explored.

Fatigue Testing and Analysis of Aluminum Welds under In-Service Highway Bridge Loading Conditions

For the fatigue design of aluminum structures, most applicable international codes specify fatigue-resistance (S-N) curves with slopes that vary, depending on the detail category. This complicates the selection of appropriate damage equivalence factors for use in high- way bridge applications. The existing codes also differ in their treatment of high cycle fatigue, with single-slope S-N curves specified in some cases and multislope curves specified in others. In this paper, a recent investigation conducted to examine the fatigue behavior of aluminum welds under in-service highway bridge loading conditions is summarized. Specifically, calculations performed to establish damage equiv- alence factors for aluminum for use with the AASHTO and Canadian Standards Association (CSA) CAN/CSA-S6 codes are first reviewed. Following this, small-scale fatigue tests of aluminum welds under simulated highway bridge loading conditions are described. A fracture mechanics model is thenvalidated by comparison with the test results and used to perform simulations encompassing a wider range of loading conditions. On the basis of this work, the adequacy of the current design provisions is discussed and possibilities for further extending the employed methodology are identified. DOI: 10.1061/(ASCE)BE.1943-5592.0000223.

Total Cost-Benefit Analysis of Alternative Corrosion Management Strategies for a Steel Roadway Bridge

This paper describes a methodology for evaluating alternative corrosion management strategies for a steel roadway bridge based on a total cost-benefit analysis. In this analysis, the impacts of girder type and preservation intervention selection on the bridge owner, users, and public are considered. The methodology is demonstrated for a steel girder bridge in Wallis, Switzerland. Painted carbon steel and unpainted weathering steel girders are investigated. The investigated preservation interventions are the following: protection by painting, protection by metalizing, and replacement. Deterioration of the girders by corrosion is modeled probabilistically. Following the methodology demonstration, sensitivity studies are performed, wherein the corrosion environment, traffic volume, and detour length during interventions are varied. The effects of these variations on the various benefit types are then discussed and the conditions under which the various corrosion management strategies may be optimal are identified.

Fatigue Retrofitting of Welded Steel Cover Plates using Pre-Stressed Carbon Fibre Reinforced Polymer Strips

Abstract Past research on the use of carbon fibre reinforced polymer (CFRP) strips for the fatigue retrofitting of steel structures has shown that these materials have considerable potential for this application. Several investigations have found that this approach can be significantly improved by first pre-stressing the strips. To further explore this possibility, a study was recently undertaken with the objectives of: (a) fatigue testing steel beams with welded cover plates strengthened using pre-stressed CFRP strips and (b) employing analytical models to predict the resulting fatigue life increase. This paper summarises the main findings of this study. Specifically, it is shown that a significant fatigue life increase can be achieved with the application of pre-stressed CFRP strips to welded details, such as cover plates. This increase will be modest, however, if the introduced stress is less than the residual stress already present as a result of the welding process. The test results are predicted by a fracture mechanics model, wherein the stresses in the weld are determined by finite element analysis.

The performance of austenitic and duplex stainless steels in cracked concrete exposed to concentrated chloride brine

In order to meet the service life requirements of highway structures, which are most commonly limited by corrosion of the carbon steel reinforcing bars, many jurisdictions are turning to stainless steel as an alternative reinforcing material. To address this application, several stainless steel producers have developed less costly grades than the “traditional” UNS S30453, UNS S31653 and UNS S32205 alloys. The goal of this project has been to determine if these alloys can resist the highly concentrated anti-icing salt brines used in Ontario, Canada, when embedded in “realistic” concrete, complete with load-induced cracks. The results indicate that the duplex grades of stainless steel perform slightly better than do the austenitic grades. All the six grades showed some signs of corrosion at the intersection of the cracks with the bars, while none of them exhibited any indication of corrosion in sound (non-cracked) concrete.

Performance of Pedestrian-Load Models through Experimental Studies on Lightweight Aluminum Bridges

Aluminum structures provide a high strength-to-weight ratio, are corrosion resistant, and are esthetically pleasing. Hence, their use in bridge construction has recently begun to increase, especially for pedestrian bridges. Because of their relative light weight as compared with other structures, they often exhibit fundamental vertical frequencies outside the range of normal pedestrian walking frequencies. Despite this, they tend to be lively structures, easily excited by pedestrians, resulting in large-amplitude accelerations. An experimental program was undertaken by the authors to study the vibration characteristics and performance of three full-scale aluminum pedestrian bridges, two in the laboratory and one in the field. Although the lowest fundamental frequencies for all three bridges fall outside the normal range of pedestrian walking frequencies, there is the possibility of higher harmonics of walking loads near resonance or in resonance with the fundamental vertical mode. The aluminum bridges studied were instrumented and subjected to a range of pedestrian-load tests to understand the performance of existing periodic models in predicting the dynamic response. The performance of these models (assuming pedestrian forces to be a summation of harmonics) has thus far only been assessed for cases in which the fundamental frequency is resonant with the first harmonic of walking, often considered the most severe case for design. This is the first time, to the knowledge of the authors, that these models have been studied for the case of bridges that are nonresonant with the fundamental mode. This article notes important observations regarding the performance of these models in predicting the serviceability of bridges made out of lightweight materials, such as aluminum, for cases in which the higher harmonics of pedestrian walking are either nonresonant or near resonance with the fundamental vertical flexure mode.

Fatigue Testing and Structural Health Monitoring of Retrofitted Web Stiffeners on Steel Highway Bridges

Numerous steel highway bridges, still in use today, were built during the construction boom between the late 1950s and the late 1970s. Fatigue cracking can be considered a main source of deterioration for these bridges. The largest category of observed fatigue cracks is caused by out-of-plane distortion. The most susceptible locations are those at which transverse structural components (such as diaphragms or cross frames) are framed into longitudinal girders through web stiffeners that are not attached to the flanges. In the current study, a web stiffener detail is fatigue tested under different cyclic loading conditions. As-welded specimens are tested, along with specimens retrofitted by grinding and rewelding, needle peening, or the adhesive bonding of fiber-reinforced polymer attachments. Direct strain and deflection measurements are compared with finite element analysis predictions, and local (hot-spot) stresses are compared with hot-spot stress design curves. A time series–based method for damage detection is also explored for the prediction of fatigue crack depth with strain data. The method is validated through the use of small- and large-scale specimen strain data. It is found that damage measures based on strains in the vicinity of the critical hot spot are closely correlated with the true crack depth.

Evaluation of Design Guidelines for the Serviceability Assessment of Aluminum Pedestrian Bridges

AbstractServiceability issues related to lightweight pedestrian bridges have attracted a great deal of attention in the literature since the London Millennium Bridge incident, which involved large amplitude motions during its inauguration. Various design recommendations have since been proposed to quantify the steady-state resonant response and to mitigate excessive levels of vibration in slender pedestrian bridges. In the current study, design provisions currently used in North America and Europe are evaluated. Two full-scale aluminum pedestrian bridges were tested in the laboratory, and their performance in terms of meeting serviceability limits under pedestrian walking loads was assessed in accordance with a number of guidelines and standards. The experiments involved walking tests under different pedestrian densities. The results show significant differences in the predicted responses, which are mainly attributable to differences in the DLFs adopted in the guidelines, lack of guidance on the appropria...

Inhibiting Distortion-Induced Fatigue Damage in Steel Girders by Using FRP Angles

AbstractThe idea of retrofitting web stiffener ends in steel bridge girders susceptible to distortion-induced fatigue using adhesively bonded fiber-reinforced polymer (FRP) angles is introduced in this study. The proposed retrofit method is relatively cheap and easy to use and does not require deck removal or any other severe modification to the steel girder. Fatigue tests were conducted on specimens designed to model the conditions in the region between a web stiffener and a flange in a steel girder bridge. Fatigue life increases on the order of several hundred percent were achieved by implementing the proposed retrofit. The effect of the retrofit on the hot-spot stress in the critical weld detail can be seen in the experimental strain data and in a subsequent finite-element (FE) analysis of the tested specimen geometry. Further research is recommended to assess the performance of the retrofit on full-scale girders and to develop guidelines for fatigue verification and design of the FRP angle and adhesiv...