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I want to use 4 rectangular hollow ms pipes 40*25*2 mm. 25 mm vertical use. All 4 pipes will be equally spaced between a width of 490 mm. The length of pipes is 1390 mm, with these 4 pipes resting on similar rectangular pipes at both ends. They will be bolted with 2 nut bolts at both end each.Total load will be 300 kgs resting on a length of 1310 mm.4 vertical square hollow ms pipes are provided. 40*2 mm. Height from floor is 135 mm Will this structure hold weight and not sag at any point.

Hemant
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  • 40mm x 25mm rectangular hollow steel with a 2mm wall thickness. that sounds like it will be fairly rigid over a 1.4m length , why not go to the steel shop and jump on some and see how much it flexes. – Jasen Sep 28 '19 at 08:43

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It will sag. This is known as "deflection", and is known for various materials and cross-sections, including your steel pipes.

https://www.engineering.com/calculators/beams.htm

Scroll down to "Hollow rectangular beams" and enter your numbers. Unfortunately, this calculator is in inches, but it's easy enough to convert.

Your 300kg mass would cause a deflection of 17.25" or 438mm, but that is based on a single 300kg mass placed on a single tube. In reality, your load will be spread out more, right? If it is evenly spread over all 4 of your pipes, then one pipe has to carry 300kg/4 = 75kg, which would result in 1/4 of that deflection, or about 4.3" or 110mm.

These are just estimates, as the specific material and how you load your shelf will make a difference.

To improve on (reduce) the deflection, you have the following basic options:

  1. Reduce the total load.
  2. Add more tubes. This would distribute the load more. Divide your total load by the number of pipes for an "ideal" estimate assuming perfect distribution, as I did above.
  3. Stronger material (thicker tubes).
  4. Shorter span. If you can move your end supports in towards the center, or add a center support, your effective span length is reduced.
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