Response Measurements of DMS Cabinets and Supporting Truss Structures under Environmental and Transient Wind Loads Robert W. Bolton, Assoc. Prof., Department of Industrial and Civil Engineering, University of Southern Denmark, Campusvej 55, DK-5230, Odense M, Denmark, Brent Phares, Assoc. Director and Terry J. Wipf, Director, Bridge Engineering Center and Pitt-Des Moines Professor of Civil Engineering, Iowa State University, 2711 S. Loop Drive, Suite 4700, Ames, Iowa 50010-8664 ABSTRACT A detailed understanding of the wind forces on large highway signs is crucial for the safe and economical design of the supporting truss structures. Large dynamic message signs (DMS) are increasingly employed to manage highway traffic flow and to provide accurate, timely information to highway users. Recent field inspection data indicates that truss structures supporting DMS signs may be subject to more complex and extreme wind loads that are not accounted for in current code driven design procedures and are exhibiting increased maintenance and fatigue problems, even in relatively new sign installations. Interim results of a multi-institution 24 month analytical and field monitoring study to better understand the response and critical design characteristics of these new sign structures are present in this paper. Problem statement The current design practice for truss structures supporting normal signs and variable or dynamic message signs (VMS) is governed by the AASHTO Standard Specifications for Structural Supports for Highway Signs, Luminaires and Traffic Signals, Fifth Edition released in 2009[1]. These specifications include updated provisions addressing extreme wind loads and new fatigue design provisions. However these provisions utilize a static strength design approach that may not accurately account for the long term effects of low level cyclic stresses resulting from vortex/shedding and buffeting under steady wind conditions, unsteady or gusting wind conditions, and truck induced gusting seen by a specific VMS sup- (a) (b) Fig 1Typical DMS sign installations, (a) 4-chord arched truss design, (b) 4-chord square truss design T. Proulx (ed.), Linking Models and Experiments, Volume 2, Conference Proceedings of the Society for Experimental Mechanics Series 5, 411 DOI 10.1007/978-1-4419-9305-2_31, © The Society for Experimental Mechanics, Inc. 2011
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