The study consists of full-scale vibration tests on pedestrian MakeABridge specimens in the laboratory. The civil engineering graduate student team of Master’s student Ann Sychterz and doctoral candidate Pampa Dey, have worked nearly two years on this research at the University of Waterloo’s Structures Laboratory in the Department of Civil and Environmental Engineering in Waterloo, Ontario. Results from the study will serve international pedestrian bridge designers, as well as assisting the MAADI Group engineering team to refine their Make-A-Bridge product design.
Tests will be used to validate finite-element models of aluminum pedestrian bridges and biomechanical models for simulating vibrations caused by pedestrian loading. Resulting data will assess the vibration performance and stress behavior of aluminum pedestrian bridges. The varied length bridges are subjected to pedestrian crowd loading in order to develop effective vibration dampening guidelines and refine aluminum pedestrian bridge design. Both 40-ft (12 m) and 70-ft (21 m) bridge spans were instrumented with triple-axis load cells at the bridge’s four supports, vibration gauges at key locations to measure vibration strains, and 12 accelerometers to measure bridge acceleration responses.
“MAADI Group provided us with an in-kind MakeABridge all-aluminum structure for our vibration study. Because we are using a weld-free, interlocking modular bridge system, we can easily adjust the bridge’s length to see how vibration effects change under loads as the span changes,” says Professor Walbridge, “Laboratory tests included strain measurements from students walking across the bridge up to 30 at a time. The footbridge span, deck weight, boundary conditions, and loading characteristics were varied to generate data under dynamic loading conditions,” explains Walbridge.
Professor Narasimhan, a veteran researcher of how vibration behavior affects structures notes, “While the advantages of using aluminum in pedestrian bridge applications is clear, this study will address the issue of vibration serviceability caused by their relative light-weight.”
Professor Walbridge is a member of the Technical Committee for the Canadian Highway Bridge Design Code, Chapter 17, Aluminum Structures. He conducts research in the area of fatigue assessment and strengthening of metal structures. Professor Narasimhan conducts extensive analytical and experimental research on vibration behavior of structures retrofitted with passive and active damping systems, to understand the behavior of linear and non-linear structures and control devices, and process measurement data from vibrating structures to assess their condition. This study is co-sponsored by the Aluminium Association of Canada (AAC) and the Natural Sciences and Engineering Research Council of Canada (NSERC) who helped fund the research and testing.
MAADI Group President and CEO Alex de la Chevrotière said, “This vibration study enables civil engineers to design footbridges that best withstand crowd loading and the strains caused by heavy pedestrian use. The Make-Bridge system allows rapid construction and deconstruction of bridge sections to test and assess various length spans and geometries using a single bridge structure. We’re very pleased to be the University of Waterloo’s go-to source for the study’s lab test structure.”
As stated in AASHTO Guide Specifications for Design of Pedestrian Bridges: “The potential for significant response due to dynamic action of walking or running has been recognized by several analyses of problem bridges and is provided for in other design codes…Research into this phenomenon has resulted in the conclusion that, in addition to stiffness, damping and mass are key considerations in the dynamic response of a pedestrian bridge to ensure acceptable design.”