Choosing correct steel beam for a span

In summary: Might have to look into other options.Very true. I was hoping to get a value and find a beam close to it. Might have to look into other options.
  • #1
roldy
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2
TL;DR Summary
Determining correct steel beam size for a span while considering self loading with distributed loading
I have a weight of 30,000 lbs distributed across a span of 100' and supported at the ends. If I have 3 beams to support this load, each beam would then need to hold 10,000 lbs, and with a F.S of 1.6 each beam would need to hold 16,000 lbs. If I assume my max deflection at 1", then I can find the moment of inertia about the x-axis and then look up a steel beam that at a minimum has this value. I then would solve for the max stress to check if it exceeds 36,000 psi. The self weight of the beam would additionally add to the distributed weight of 16,000 lbs which would then change the moment of inertia etc. How can I include self weight of the beam in the distributed loading if I don't initially know what beam I am looking for? I'm not concerned about number calculations. I just need a process check about how to include self weight of the beam.

I solve for I from this:
##\delta _{max}=\frac{5wL^{4}}{384EI}##

I check for stress limit from this:
##\sigma_{max}=\frac{M_{y}}{I}##
 
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  • #2
You can solve this problem iteratively. Pick a beam that you think might work, find out its weight per length to be used in your calculations and then crunch. If the result is safe, you can stop. If not, pick another beam, rinse, and repeat.
 
  • #3
roldy said:
Summary:: Determining correct steel beam size for a span while considering self loading with distributed loading

I have a weight of 30,000 lbs distributed across a span of 100' and supported at the ends. If I have 3 beams to support this load, each beam would then need to hold 10,000 lbs, and with a F.S of 1.6 each beam would need to hold 16,000 lbs.
What is the application? You don't live in Florida near the beach, do you?
 
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  • #4
berkeman said:
What is the application? You don't live in Florida near the beach, do

Dr.D said:
You can solve this problem iteratively. Pick a beam that you think might work, find out its weight per length to be used in your calculations and then crunch. If the result is safe, you can stop. If not, pick another beam, rinse, and repeat.
As I was creating my spreadsheet for calculations I was contemplating about using Excel's optimization tool to possibly solve for this.
 
  • #5
berkeman said:
What is the application? You don't live in Florida near the beach, do you?
The application is basically a water bypass bridge. The bridge would hold 24" diameter polymer based pipes up over an area needed to be kept clear. Unfortunately I don't live near in Florida or close to a beach. I get where you're coming from with that question in regards to ground conditions.
 
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  • #6
roldy said:
The application is basically a water bypass bridge. The bridge would hold 24" diameter polymer based pipes up over an area needed to be kept clear.
Is this for a public works project? Or is it something you are building on your own property? What kind of permits do you need to build something like this? Are there any inspections/approvals/insurance required?
 
  • #7
berkeman said:
Is this for a public works project? Or is it something you are building on your own property? What kind of permits do you need to build something like this? Are there any inspections/approvals/insurance required?

This is a conceptual problem. Not a project of any kind.
 
  • #8
This problem probably does not satisfy the necessary conditions for optimization by Excel. For one thing, steel beams are available only in discrete sized, not continuously variable.
 
  • #9
Dr.D said:
This problem probably does not satisfy the necessary conditions for optimization by Excel. For one thing, steel beams are available only in discrete sized, not continuously variable.
Very true. I was hoping to get a value and find a beam close to it.
 

1. What factors should be considered when choosing a steel beam for a span?

When choosing a steel beam for a span, the following factors should be considered:

  • The weight and load of the structure it will support
  • The span length and distance between support points
  • The type and size of the building materials being used
  • The environmental conditions, such as wind and seismic activity, in the area
  • The desired aesthetic and design of the structure

2. How do I determine the appropriate size and shape of the steel beam for a span?

The size and shape of the steel beam for a span can be determined using structural engineering calculations and software. These calculations take into account the factors mentioned above, as well as the specific properties and strength of the steel being used. It is important to consult with a structural engineer to ensure the correct size and shape of the beam is chosen.

3. What are the different types of steel beams available for spans?

There are several types of steel beams that can be used for spans, including:

  • I-beams: these are the most commonly used and are shaped like the letter "I"
  • H-beams: these have a wider flange than I-beams and are shaped like the letter "H"
  • C-beams: also known as channel beams, these have a C-shaped cross-section
  • Box beams: these have a square or rectangular cross-section
  • T-beams: these have a T-shaped cross-section and are often used for longer spans

4. Can I use a steel beam for a span in place of other building materials?

Steel beams are often used as a substitute for other building materials, such as wood or concrete, due to their strength and durability. However, it is important to consult with a structural engineer to ensure the steel beam is suitable for the specific span and load requirements of the structure.

5. How do I ensure the steel beam is installed correctly for a span?

Proper installation of a steel beam for a span is crucial for the safety and stability of the structure. It is recommended to hire a professional contractor with experience in steel beam installation. The beam should be installed according to the manufacturer's instructions and any local building codes or regulations. It is also important to regularly inspect and maintain the beam to ensure it remains in good condition.

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