Intermediate Bents— Calculation of Restraint Factor [Research Summary]
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Intermediate Bents— Calculation of Restraint Factor [Research Summary]

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English
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  • Corporate Creators:
    University of Missouri--Columbia
  • Corporate Contributors:
    Missouri. Department of Transportation. Construction and Materials Division
  • Subject/TRT Terms:
  • Publication/ Report Number:
    CMR 24-004
  • Resource Type:
    Brief
  • Geographical Coverage:
    United States
  • Edition:
    Research Summary
  • Contracting Officer:
    Harper, Jennifer
  • Corporate Publisher:
    Missouri. Department of Transportation. Construction and Materials Division
  • Abstract:
    This report investigates the restraint at the top of the column of non-integral intermediate bents with closed diaphragms, a common connection configuration utilized by the MoDOT. Although closed diaphragms inherently possess some level of rotational restraint, the current design approach considers this type of connection as free, resulting in the use of design k-factors of 2.1. However, rotational restraint significantly influences the k-factor. Utilizing an integration of experimental and numerical analyses, the study determined the approximate level of restraint of these types of intermediate bents. The main source of rotational flexibility was in the diaphragm to bent cap connection. A parametric analysis showed that the dowel bar area, diaphragm width, and skew angle were all parameters that needed to be considered in the simplified equation to predict the rotational restraint developed as part of this study. A comparison of the simplified equation to predict rotational restraint showed at most a 10% difference compared to that found in the FE models. Calculations of the k-factors, using a simplified bilinear equation, showed k-factors less than the assumed 2.0 theoretical value for fixed-free columns (on average1.5), and in the case of the steel column bridge a k-factor of only 1.2. A procedure for analyzing telescoping columns was also formulated in which an effective moment of inertia can be used to treat the column as a uniform diameter. Three examples showed that the use of rotational restraint increased the buckling capacity of the concrete column by 24% to 40%. However, for steel HP columns this increase was most significant at 62%, which changed the controlling buckling mode to the weak axis direction. If buckling capacity controls the design of the column this could result in a potential cost savings of 20 to 30% of the column cost. The work culminates in a suggested design procedure to use rotational restraint in the design of intermediate bent bridge columns.
  • Format:
    PDF
  • Funding:
    TR202203
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