What Is the Shear Strength of a Cut I-Beam in a Cantilevered Structure?

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Discussion Overview

The discussion revolves around the shear strength of a cut I-beam used in a cantilevered structure, specifically in the context of a two-story townhome project. Participants explore various factors affecting the beam's performance, including bearing stress on the top flange, buckling considerations, and design loads.

Discussion Character

  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant inquires about the shear strength of a cut I-beam that spans 10 feet and supports a cantilevered structure extending 6 feet.
  • Another participant emphasizes the importance of controlling buckling in both the top and lower flanges depending on the loading conditions.
  • A detailed list of calculations necessary for verifying the beam's adequacy is provided, including design loads, buckling, yielding, web crippling, bearing stress, shear in the web, deflection, and connection strength.
  • The original poster expresses a desire to focus specifically on the bearing stress of the top flange, given the beam's configuration with cut flanges and web.
  • The original poster describes the beam's setup, noting that the top flange will be welded to a beam plate embedded in concrete, with no support under the web or lower flange.

Areas of Agreement / Disagreement

Participants present multiple viewpoints and considerations regarding the structural integrity of the beam, with no consensus reached on the specific shear strength or the implications of the design choices made.

Contextual Notes

Participants acknowledge the complexity of the problem, highlighting the need for specific calculations based on various design loads and structural factors. The discussion reflects a reliance on engineering principles and codes, with limitations noted regarding the depth of assistance possible in an online forum.

vernierdesign
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Hello, I'm in the process of building a 2 story townhome project and had a question on a beam. The structural engineer is calling for a cut I-beam on top foundation which spans over the garage (10') and the load will be placed on just the top flange (see attached). The structure will cantilever 6' over this beam and I'm curious on the shear strength of the beam with this type of alteration.
 
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There is no attached ...
In a span, buckling of the top flange must be controlled.
In a cantilever, buckling of the lower flange must be controlled.
 
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If you want to cross check the engineer, you need to calculate the following:

1) The design loads on the beam. Your building code specifies design loads and safety factors, which could be snow, wind, earthquake, equipment, people, etc.
2) Buckling of whichever flange is in compression.
3) Yielding of flanges.
4) Web crippling.
5) Bearing stress at support points.
6) Shear in web.
7) Deflection, and its effect on the structure.
8) Strength of connections.

A good resource is the AISC Steel Construction Manual. Note that this manual assumes a background consisting of several engineering courses, so our ability to help you is quite limited. Especially in the context of an internet forum.
 
Thank you for your response... I know there's many variables to this question but I'm trying to just focus on the bearing stress of the top flange.

The pic that I attempted to download shows that the lower flange and web is cut back 8" on both sides of the beam so the beam would fit between the foundation over the garage entrance. Then top flange will extend 8" over to top of the foundation. The top flange will be welded to a beam plate that's embedded in the concrete on the top of the foundation. There will be no support under the web/lower flange. So, the the weight of the structure will essentially resting on the top flange. The engineer is calling out for a w10x19 beam.

Any thoughts on this would be greatly appreciated.
 
vernierdesign said:
The pic that I attempted to download
Try the "Attach files" link below the Edit window to upload a JPG or PDF file with the image.

You may also be able to drag and drop the image into the Edit window as another way to attach it to a Reply.
 

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