Self-Centering Connections for Traffic Sign Structures: Phase II Large-Scale Subassembly Tests

Self-centering traffic sing supporting structures have the potential for the following features: (a) energy dissipation is provided by cost-effective external devices, not by member permanent deformations; (b) elastic stiffness and strength are similar to conventional traffic sign structures; (c) gap opening at connections enables relative rotations without damage to members; (d) forces in pretensioned bolts close connection gap opening and bring the structure back to its plumb position (i.e., self-centering behavior). The features described above are due to the self-centering behavior of pre-tensioned bolted connections. As one example of applications to traffic sign structures, the traffic pole base plate-support connection is pre-compressed by tensioned bolts. The connection conceptual behavior is presented by the overturning moment-relative rotation (M-r) response. When connection overturning moment reaches the imminent gap opening overturning moment (MIGO), the softening behavior at point A occurs, and a gap opens at the base plate-support interface which initiates a connection relative rotation. Note that this rotation is not a result of member permanent deformations (i.e. damage). Excessive relative rotation might yield the tensioned bolts; however, the bolts can be re-tensioned to the targeted force without replacement. Self-Centering traffic structural systems use similar components (ex. bolts, base plate, etc.) as used in existing structural systems. The differences are: (1) the initial tension force in the bolts is controlled; and (2) cost-effective ED devices are added. Calibrated torque wrenches can be used on site to control the bolt initial tension force during construction. ED devices could be sealed friction dampers that made of sandwiched corrosion-free metal plates to meet the cost-effective consideration. If MIGO is selected to be smaller than the overturning moment at member yielding capacity (My), the connection can open a gap and rotate without damage to the structure. Direct tension indicator (DTI) washers and Belleville washers can be used to provide warnings for bolts re-tightening maintenance when experiencing bolt yielding. The washers can be selected so when reaching bolt tensile yielding capacity, they are squeezed, and the bright-colored gel in DTIs or a flattened shape in Belleville can be the indicator for retightening maintenance requirement. If re-tightening is needed, the washers should be replaced for future indicator. Gap opening does not occur under frequently occurring loads (ex. small wind or truck pumper/bed tapping loads), but only occurs when overloads (ex. extreme wind or truck hitting loads). Therefore, self-centering traffic sign structures act like conventional structures under frequently occurring loads; under overloads, they do not damage nor collapse.

    Language

    • English

    Project

    • Status: Active
    • Funding: $137891.00
    • Contract Numbers:

      930-912

    • Sponsor Organizations:

      Alabama Department of Transportation

      1409 Coliseum Boulevard
      Montgomery, AL  United States  36130-3050
    • Start Date: 20150501
    • Expected Completion Date: 0
    • Actual Completion Date: 20160501
    • Source Data: RiP Project 40010

    Subject/Index Terms

    Filing Info

    • Accession Number: 01569290
    • Record Type: Research project
    • Source Agency: Alabama Department of Transportation
    • Contract Numbers: 930-912
    • Files: RiP, STATEDOT
    • Created Date: Jul 9 2015 1:00AM