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01-11-2012, 11:58 PM   #1
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## Distribution of load over 3 supports.

Hello!

If a beam is supported at both ends and also at the center, and it carries an evenly distributed load, does the center support take half of the load and the end supports a quarter of the load each?

Thank you!

01-12-2012, 12:07 AM   #2
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Hmmm I think that should be right. If it is evenly continuously distributed.

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 01-12-2012, 06:57 AM #3 Disabled wood vet     Join Date: Nov 2011 Location: California Posts: 1,661 Rewards Points: 1,004 Odd question. Why? Not if your beam is unbroken. If it is unbroken, the center post is- more or less-just preventing the structure from sagging. The beam itself is carrying much of the load, not the post. If it is broken in the center, the center is carrying the ends of two beams and the load above. The bigger the load gets, the lesser the percentage of the weight of the beam and joists only is, so the calculation changes. It's a calculation best left to an engineer. Sent from a Samsung Galaxy S2 Last edited by titanoman; 01-12-2012 at 07:27 PM.
 01-12-2012, 05:51 PM #4 journeyman carpenter     Join Date: Sep 2011 Location: nova scotia canada Posts: 3,192 Rewards Points: 1,000 the amount of weight each point load is carrying depends entirely on teh house.. one half of a house can have more going on structurally than the other half via bathrooms, dormers on the roof which have point loads on them..
01-12-2012, 05:54 PM   #5
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Quote:
 Originally Posted by abracaboom If a (edit: JOIST) is supported at both ends and also at the center, and it carries an evenly distributed load, does the center support take half of the load and the end supports a quarter of the load each?
Sorta.The actual engineering can get complicated.
But the principle is why the floor joists in a house will have a beam
supported by lolly columns running down the middle of the basement

Last edited by TarheelTerp; 01-12-2012 at 05:57 PM.

01-12-2012, 06:12 PM   #6
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Quote:
 Originally Posted by abracaboom Hello! If a beam is supported at both ends and also at the center, and it carries an evenly distributed load, does the center support take half of the load and the end supports a quarter of the load each? Thank you!
The simple answer to your question is yes assuming the beam is in the center of the joist span and the center of the beam span and the supported structure is of equal load.

Mark
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When its all said and done there is usually more said than done

Last edited by Jackofall1; 01-12-2012 at 06:18 PM.

 01-12-2012, 06:58 PM #7 Member   Join Date: May 2008 Location: Near Philly Posts: 2,301 Rewards Points: 1,522 I think Daniel explained how the forces acted on a beam in a post some time ago; went into some detail about where the loads were placed and how they were transferred to the beam and its support(s). Might try searching for it if interested.
 01-12-2012, 08:13 PM #8 Civil Engineer   Join Date: Mar 2009 Location: Boston Posts: 5,467 Rewards Points: 4,514 Assuming: 1. Continuous, uniform vertical load. No other loads besides vertical load. 2. The beam is in close contact with each post. The post supports act as pins. 3. The posts are uniformly spaced 4. The beam is continuous over the center post 5. The beam is level, and the top of the posts are level. 6. The beam is of constant cross section. Then the center post carries 5/8 of the total vertical load, and the end posts carry 3/16 of the total vertical load each. If the beam is NOT continuous over the center post, then the vertical load distributes 1/2 to the center post, 1/4 to each outer post. The mathematical derivation of this result is complex, and cannot be presented on an internet chat forum. For derivation, see any mechanics of materials textbook.
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01-12-2012, 08:18 PM   #9
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Quote:
 Originally Posted by Daniel Holzman Assuming: 1. Continuous, uniform vertical load. No other loads besides vertical load. 2. The beam is in close contact with each post. The post supports act as pins. 3. The posts are uniformly spaced 4. The beam is continuous over the center post 5. The beam is level, and the top of the posts are level. 6. The beam is of constant cross section. Then the center post carries 5/8 of the total vertical load, and the end posts carry 3/16 of the total vertical load each. If the beam is NOT continuous over the center post, then the vertical load distributes 1/2 to the center post, 1/4 to each outer post. The mathematical derivation of this result is complex, and cannot be presented on an internet chat forum. For derivation, see any mechanics of materials textbook.
You explained it much more eloquent than I.

Sent from a Samsung Galaxy S2

01-13-2012, 01:48 AM   #10
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