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Footing Flexural Reinforcement - Effective Steel Area Calculation

Adam Oberholtzer
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Hello,

I am working on designing an isolated footing pile cap. I have a successful flexural reinforcement design in a file created using an older version of RC-PIER where the Effective Steel Area is reported as equal to the Provided Steel Area. When I run the same file with no changes in the current version of LEAP Bridge Concrete, the Effective Steel Area is greatly reduced and the program reports that the provided reinforcement is insufficient. Due to the magnitude of the reduction this does not appear to be a development length issue. I am hoping someone can clarify how the Effective Steel Area is calculated as I am having difficulty finding an answer in the manual.

Geometry & Reinforcement Information:

Original RC-PIER Run Flexural Reinforcement Design:

LEAP Bridge Concrete Flexural Reinforcement Design (original RC-PIER input file run in LEAP Bridge Concrete):

As you can see, the Effective Steel Area in the Z-direction has been greatly reduced. What is the program doing to calculate the Effective Steel Area?

Thank you,

Adam Oberholtzer

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  • 0 Offline
    The Area is reduced linearly.

    For example :
    At the end of development length(ld), rebar is fully developed and so 100% Ast-provided is available.
    At a location X' from the end of rebar, which is < development length, Aeff will be ( X * Rebar area / ld).

    The Development length is designed based on AASHTO article 5.11.2 and the AsT/b eff is calculated as follows.

    Example: At any location, if development length is 4' and location is 1'

    The Ast/b eff=Ast_provided* (1’ or 2’) /4.

    Ast_eff = Ast prov *( min (L/ld , 1) )

    Ast-eff : Effective top steel area, after considering development length

    If As-t eff is < than As-t req you will get a flag

    Area Provided may be larger than required but at the same time the effective may be less than required within development length.

    By providing additional rebar or increasing the length of the footing in that particular direction or trying to hook the bar will help in getting rid of the red flags.

    I hope it helps.
  • 0 Offline in reply to Vinay mysore
    Vinay,

    Thank you for your response. Using the equations you provided I get the following for the reinforcement in the Z-Direction:

    Development of #8 Bar per AASHTO 5.11.2.1.1 & 5.11.2.1.2:
    = 25.26" (Basic Development) x 1.4 (Top Bar) = 35.36" / 12 = 2.95'

    Available Development Length:
    = (Half of Footing "Hf(Z)" Dimension) - (Distance to Critical Section) - (End Clear Cover)
    = (9' / 2) - 1.55' - 0.25' = 2.70'

    Effective Area:
    = (Steel Area Provided) x (Available Development) / (Required Development Length)
    = 12.64 x (2.70') / (2.95') = 11.57 sq in effective (~9% reduction in steel area)

    The program is calculating a ~45% reduction in steel area from provided to effective (see my previous post). This is a significant difference from what I have calculated. Is there another factor that the program applies to calculate Effective Steel Area or is there something else that I am missing?

    Thank you,

    Adam Oberholtzer
  • 0 Offline in reply to Adam Oberholtzer
    Please email me you file and let me know which version you are working on.
    My email ID is--- vinay.mysore@Bentley.com
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