STR-964: STUDIES ON VIBRATION SERVICEABILITY ASSESSMENT OF ALUMINUM PEDESTRIAN BRIDGES

Vibration serviceability is often the governing design factor for slender, lightweight footbridges. However, there is currently a large gap that exists between our understanding from a modeling perspective and their actual vibration behaviour. Recent experimental tests conducted at the University of Waterloo have underscored these discrepancies and have provided an unique opportunity to not only validate many of the models currently in use, but also to propose new modifications to better align with experimental test results. Specifically, issues such as how to design for lateral vibrations and crowd-induced loading and calibration of load factors, will be addressed in this presentation. Recent results obtained by the pedestrian bridge research group at the University of Waterloo through their extensive crowd-testing program on a full-scale aluminum pedestrian bridge located at the university will aim to address both of these issues. The ultimate objectives of this experimental program are to validate or extrapolate existing analytical frameworks, and to develop new, practical models that can be used in a design guideline to better account for lateral vibrations and crowd-induced loading

STR-934: FATIGUE RESPONSE OF UHPC AS A CLOSURE STRIP MATERIAL IN PREFABRICATED BRIDGE APPLICATIONS

Replacement of concrete bridge decks can be an expensive process. In order to decrease costs and time of construction, precast deck panels can be used with closure strips cast in place between the panels. In order to ensure that these connections can withstand the rigors of a bridge’s life cycle, fatigue testing was completed on a specimen consisting of two precast concrete panels reinforced with GFRP and connected using a UHPC closure strip. These panels were subjected to 2,000,000 cycles of fatigue loading at three locations and subject to static failure loading at one location following fatigue loads. It was found that under fatigue loading the panels were able to maintain structural integrity while deflection values increased linearly following the initial cracking phase. At ultimate load, the panel failed in punching shear at levels less than those specified by bridge code. This is primarily due to the failure location adjacent to the closure strip failing on three punching shear planes and one plane along the interface between the UHPC

A probabilistic assessment of the effect of post-weld treatment on the fatigue performance of tubular truss bridges

In the design of tubular truss bridges, engineers have found the fatigue performance of the joints to be a critical aspect. In looking for ways to improve this performance, the use of residual stress-based post-weld treatments has been suggested. Although these treatments have been shown to increase the average fatigue lives of welded details under constant amplitude loading conditions in a number of studies, concerns exist regarding their reliability, in particular under realistic, variable amplitude loading conditions. With this in mind, the effect of post-weld treatment on the fatigue performance of tubular truss bridges is assessed herein using a previously developed probabilistic, fracture mechanics-based model, modified to analyze entire bridge structures under realistic, variable amplitude loading conditions. This model uses a systems reliability approach to consider the influences of the various potential crack sites on the overall reliability of the bridge. By analyzing several variants of a typical tubular truss bridge, it is shown that post-weld treatment can result in a significant fatigue performance improvement for this bridge type. This improvement is quantified herein in terms of either a savings in steel weight or an increase in fatigue life. Several additional studies examine the sensitivity of the results of this assessment to variations in the treatment coverage, intensity, and uniformity. These studies show that similar results can be obtained with a partial treatment strategy to those observed when the entire bridge is treated, and that the treatment benefit depends more on the intensity than the uniformity of the treatment

STR-923: FATIGUE OF STUD SHEAR CONNECTORS IN STEEL-PRECAST COMPOSITE BRIDGES

Modular bridge systems consisting of precast concrete deck panels connected to steel girders are becoming increasingly popular due to their rapid construction and optimal material utilization. The shear connection is a critical element of the system, having significant impacts on construction time, economic and environmental cost, structural integrity, and durability. Today welded shear studs are by far the most common type of shear connection. In steel-precast composite bridges, the studs are commonly grouped together so that the precast deck panels can be affixed to the girders by providing full depth “shear pockets” filled with grout. A laboratory beam testing program is underway at the University of Waterloo to investigate the effect of cyclic loading on stud shear connectors in cast-in-place and precast bridge girders. The program consists of twelve beam specimens, uniquely tested using a variable amplitude load history simulating Canadian highway truck traffic. In addition to yielding valuable S-N (stress plotted vs. the number of cycles until fatigue failure) data, initial test results provide evidence of the benefits of redundancy in the structural system and the value of beam tests over push-out tests. Calculating connector stresses in a composite beam is made complicated by interfacial slip and neutral axis migration. The end goal of this research is to provide Canadian bridge designers and erectors with improved design and construction recommendations in order to improve the efficiency and economy of this structural system for rapid bridge replacement projects

A Review of the Fatigue Limit for Steel Bridges under Ontario Highway Traffic Loading

This is an Accepted Manuscript of an article published by Canadian Science Publishing in Canadian Journal of Civil Engineering on August 17, 2022, available at: https://doi.org/10.1139/cjce-2021-0602In many design codes for roadway bridges, it is required that a design truck be passed over influence lines for stress at various locations on the bridge to obtain nominal stress ranges for design. For the fatigue design of Canadian bridges in the infinite or very long-life domain, the nominal stress range is compared with a fatigue limit, after modification by an appropriate correction factor to account for the difference between the nominal stress range and some measure of the extreme stress range in the expected real traffic histogram, which governs infinite life design. The extent to which the influence of simultaneous truck crossings was considered in the establishment of the correction factors is believed to be limited. With this in mind, a simulation-based study, conducted to investigate the effects of simultaneous vehicle crossings on the fatigue limits for steel bridges under Ontario highway traffic loading, is presented in this paper

Simultaneous Vehicle Crossing Effects on Fatigue Damage Equivalence Factors for North American Roadway Bridges

In many design codes for roadway bridges, fatigue design involves passing a load model over an influence line for a critical location on the bridge and then determining the resulting nominal stress range. For fatigue design in the finite-life domain, this stress range is then multiplied by a damage equivalence factor to account for differences in the fatigue damage because of the load model and the expected real traffic. In general, the effects of simultaneous vehicle crossings are not considered in the calibration of the damage equivalence factor. In this paper, fatigue design procedures in the U.S., Canadian, European, and Swiss codes applicable for the design of steel or aluminum roadway bridges are first reviewed. A simulation-based study, conducted to investigate the effects of simultaneous vehicle crossings on the damage equivalence factors for North American roadway bridges, is then presented. Based on the results of this study, recommendations are made for amplifying the North American damage equivalence factors in cases where the effects of simultaneous vehicle crossings are expected to be significant

Probabilistic Fretting Fatigue Analysis of Bridge Stay Cables at Saddle Supports

This is an Accepted Manuscript of an article published by Taylor & Francis in Structural Engineering International on October 10, 2019, available at: https://doi.org/10.1080/10168664.2019.1661332Saddle systems have been used on recent projects to support the cables in cable-stayed and extradosed bridge structures. A major design consideration for these anchorage systems is the in-service fretting fatigue behaviour of the cables within the pylon saddle. In order to better understand the fatigue behaviour of these anchorage systems, a research project was undertaken, wherein fatigue tests were performed on saddle test specimens, analytical models for calculating displacements and contact forces were developed, and a multiaxial stress-based fretting fatigue model was developed for calculating fatigue life. In the current paper, it is shown how the developed models can be used to perform probabilistic analysis of fretting fatigue life for the purpose of assessing the fatigue reliability of saddle systems, using two approaches – fretting maps, in conjunction with Monte Carlo simulation (MCS) or the multiplicative dimensional reduction method (MDRM)

Influence of tool offsetting and base metal positioning on the material flow of AA5052-AA6061 dissimilar friction stir welding

This study examines dissimilar friction stir welding of AA5052-AA6061 aluminum alloys with varying tool offsets. The base metals were positioned and fixed at a slight diagonal positioning such that varying tool offset position from the centreline can also be varied along the length of the weld. After the fabrication process, microstructural and mechanical property characterization was subsequently conducted. The results show that, above a certain threshold for tool offset, incomplete consolidation (i.e. kissing bond defects) will occur. Regardless of the base material positioning, a zero tool offset shows optimum intermixing in the stir zone. EDX mapping confirms the presence of a distinct interface between both materials in the stir zone region. However, enhanced material intermixing and better elongation are observed when AA6061 alloy is positioned at the tool advancing side

Effect of quality control parameter variations on the fatigue performance of aluminum friction stir welded joints

The final publication is available at Elsevier via https://dx.doi.org/10.1016/j.ijfatigue.2018.09.004 © 2019. This manuscript version is made available under the CC-BY-NC-ND 4.0 license https://creativecommons.org/licenses/by-nc-nd/4.0/This paper describes fatigue tests performed on 6061-T651 and 5083-H321 aluminum friction stir welded joints with dimensions and loading conditions typical for structural applications. Butt and lap joint details with various defects intentionally introduced were tested under tension-only constant and variable amplitude loading conditions. In this paper, the fatigue test results are presented along with supporting metallurgical and nonlinear fracture mechanics analyses. Based on this work, it is concluded that kissing bond defects on the order of 0.3–1.0 mm can result in a significant fatigue life reduction and a shift in the failure mode to the weld root. The investigated toe-flash defect had less of an effect on fatigue performance. The lap joint did not perform as well as the butt joint detail.Aluminum Association of Canada (AAC)National Science and Engineering Research Council of Canada (NSERC

Influence of tool offsetting and base metal positioning on the material flow of AA5052-AA6061 dissimilar friction stir welding

This study examines dissimilar friction stir welding of AA5052-AA6061 aluminum alloys with varying tool offsets. The base metals were positioned and fixed at a slight diagonal positioning such that varying tool offset position from the centreline can also be varied along the length of the weld. After the fabrication process, microstructural and mechanical property characterization was subsequently conducted. The results show that, above a certain threshold for to ol offset, incomplete consolidation (i.e. kissing bond efects) will occur. Regardless of the base material positioning, a zero tool offset shows optimum intermixing in the stir zone. EDX mapping confirms the presence of a distinct interface between both materials in the stir zone region. However, enhanced material intermixing and better elongation are observed when AA6061 alloy is positioned at the tool advancing side