Re Entrant Corner Crack

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This paper examines cracks which occurred at the re-entrant corners at the dapped ends of bulb tee girders used on the MIA Mover APM System at Miami International Airport. Cracks were initially identified during load testing at the precast yard, although typically they did not occur until the beams were erected. The load test and crack mechanism is described herein. Post-erection cracking is compared with that observed under load test conditions and differences are discussed. FDOT criteria were applied in determining the appropriate protection strategy.

Crack widths, but also leads to a conceptually clear method of design. For the D-regions of reinforced concrete structures such as the re-entrant corners, the strut-and-tie model (Schlaich et al., 1987) is a very powerful tool for visualizing the internal flow of forces and for arranging the steel bars and concrete struts. Answer: There are a number of ways to reduce the chance that a random crack will develop off a re-entrant corner. Along foundation walls, the most reliable method is to isolate pilasters with a diamond-shaped box-out, such that the point on the diamond is aligned with the proposed sawcut (see Diagram 4).

  • Record URL:
      https://doi.org/10.1061/41193(424)14
  • Availability:
    • Find a library where document is available. Order URL: http://worldcat.org/isbn/9780784411933
  • Supplemental Notes:
    • Copyright © 2011 ASCE
  • Authors:
    • Leverenz, David G.
    • Davidson, Thomas E.
  • Conference:
    • Location: Paris , France
    • Date: 2011-5-22 to 2011-5-25
  • Publication Date: 2011

Language

  • English

Media Info

Reentrant Corners Steel

  • Media Type: Web
  • Monograph Title: Proceedings of the Thirteenth International Conference on Automated People Movers and Transit Systems, 2011

Subject/Index Terms

  • TRT Terms: Load tests; People movers; Precast concrete
  • Identifier Terms: Miami International Airport
  • Uncontrolled Terms: Bulbtee girders
  • Geographic Terms: Florida
  • Subject Areas: Maintenance and Preservation;

Filing Info

  • Accession Number: 01365047
  • Record Type: Publication
  • ISBN: 9780784411933
  • Files: TRIS, ASCE
  • Created Date: Nov 29 2011 3:00PM

Typical Creo Elements models have many inside or re-entrant corners. In the real world you could not build a part with perfect sharp inside corners. There will always be some radius resulting from the tooling used to make the part. Sometimes fillets are left off the CAD parts and are specified in the drawing notes. In the FEA world re-entrant corners are a bad thing. These represent an infinite change in stiffness inside the part, which will result in an infinite stress concentration. The MPA convergence algorithm will not converge on infinity and the SPA algorithm will ignore any elements touching a re-entrant corner during its error estimation. The resulting stress convergence plot will be a line that continues to increase without ever starting to reach an asymptote.

Reentrant Corner

If this is a problem in your Creo Simulate model you should probably ask the question “Is this a good design having the highest stress in the model at a re-entrant corner?” The answer may be ‘yes’ if the material is ductile and fatigue loading is not an issue. If this is true and you are planning to ignore this stress just add a small fillet to prevent a convergence problem or use the ‘Isolate for Exclusion’ option under Mesh Control. Otherwise you may want to rethink the design.

Reentrant Corner Check

Corner

Reentrant Structure

Theoretically re-entrant corners should always cause a problem for convergence, however, due to the coarseness of the error estimation process re-entrant corner convergence problems generally only show up in higher stress areas of the model.

Reentrant Corner Bars

Other similar stiffness discontinuity problems are shown below.