I-beams size when smaller termination

  • Thread starter TexanJohn
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In summary, the conversation discusses the varying sizes of I-beams used in highway construction and the reasons behind this. It is explained that this is done in order to establish a constant stress across the span and save money by using less material where the demands on the beam are lower. There is also the option to have beams custom fabricated, but this may have higher costs. Ultimately, the decision to use varying sizes or a standard size is based on the loading demands and cost effectiveness.
  • #1
TexanJohn
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Novice question: I noticed on all the highway construction around me that the I-beams get 'smaller' where they mount to base/beginning of an overpass or even an intermediate supporting structure. For instance, the vast majority of the I-beam appears to be 8' tall, but at the termination points it might only be 4' tall.

Why not just make the same size all the way?
 
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  • #2
I can't say for sure, but the times I have seen varying cross sectional beams was an effort to establish a constant stress across the span. In the situation of overpasses etc...the loading schemes they have to take into account must be pretty complex.
 
  • #3
It has to do with the moments/forces varying along the length of the beam and saving money. (More depth is required where certain demands on the beam are greater.)

Lots of beams are made to be constant along the entire length, they are just standard sizes an engineer can pick to meet the loading demands (none 8ft deep though). The size is chosen by the highest loading demand on the beam, and the entire beam is the same section all the way through and cut to a desired length. But those beams are not an example of maximizing the efficient use of material.

There is also the option to vary a beam's depth (among other things) and have it custom fabricated. This can sometimes be cheaper because there is less material, but this strategy may also be offset by the higher fabrication costs of creating a "customized" beam. For a beam the size you describe, you would have to have it custom built anyway so why not save on material by varying the section, and have a bridge that does not look overwhelming to people driving under?

HTH
 

What is the purpose of an I-beam?

An I-beam, also known as an H-beam, is a structural component used in construction to support heavy loads. They are commonly used in buildings, bridges, and other structures to distribute weight evenly and reduce stress on the overall structure.

How is I-beam size determined?

I-beam size is determined based on the required strength and load-bearing capacity of a structure. Factors such as the type of material used, the length of the beam, and the distance between supports all play a role in determining the appropriate size.

What is the standard size for I-beams?

The standard size for I-beams varies depending on the type and purpose of the structure. In the United States, the most commonly used I-beam sizes range from 3 inches to 24 inches in height, with varying widths and thicknesses.

What happens when an I-beam is terminated at a smaller size?

When an I-beam is terminated at a smaller size, it can affect the overall strength and load-bearing capacity of the structure. This may result in an uneven distribution of weight and potential structural failure if not properly accounted for in the design and construction process.

How do I determine the appropriate I-beam size for my project?

If you are unsure of the appropriate I-beam size for your project, it is important to consult with a structural engineer or other qualified professional. They can assess the specific needs and requirements of your project and recommend the best I-beam size to ensure a safe and sturdy structure.

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