Blocking to counteract moment of beam.

[Zoobie777]

Hi,

I have a situation where a beam is failing due to excess moment. This beam is 18" deep (LVL) and is running parallel to 11-7/8" deep I-joists (top of beam and top of joists are flush). The beam is supporting is a single column at approx. mid-span taking a very large point load from the roof above along with a bearing wall for about half the span. Here are my questions:

1. Can I block the beam on each side to the adjacent joists at 2' intervals to counteract the moment? My software (iStruct) won't let me block it but the beam passes if I specify top bracing at 2' intervals.
2. The customer has specified joist direction, but I might be able to rotate the joists on one side of the beam. Would joists at 16" oc hung from ONE FACE of the 18" beam constitute top bracing?
3. Does sheathing count as lateral restraint? The floor is 3/4" T&G plywood, glued and screwed.
4. Is there some other method to laterally restrain the beam?

Below is a snip of the output:




Thanks,

Zoobie777

 

[JAE]

1. Can I block the beam on each side to the adjacent joists at 2' intervals to counteract the moment? My software (iStruct) won't let me block it but the beam passes if I specify top bracing at 2' intervals. You can add blocking but the load shared by the adjacent, parallel joists will only be to the extent of their relative stiffness to the main 18" beam.
2. The customer has specified joist direction, but I might be able to rotate the joists on one side of the beam. Would joists at 16" oc hung from ONE FACE of the 18" beam constitute top bracing? Joists perpendicular to a wood beam certainly brace the beam against LTB.
3. Does sheathing count as lateral restraint? The floor is 3/4" T&G plywood, glued and screwed. Yes
4. Is there some other method to laterally restrain the beam? The sheathing alone would be adequate.

 

[XR250]

Floor sheathing or blocking is usually fine to brace the beam. I use BCCalc occasionally and it always defaults to the beams being totally unbraced. Kind of annoying as they rarely are.

 

[rb1957]

I think your problem is the "very large load", #11; you need to double the bending strength of the beam. I think you need a post/column under this load. Or find some way to distribute this large point load across the whole area, onto several beams.

 

[Zoobie777]

1. Can I block the beam on each side to the adjacent joists at 2' intervals to counteract the moment? My software (iStruct) won't let me block it but the beam passes if I specify top bracing at 2' intervals. You can add blocking but the load shared by the adjacent, parallel joists will only be to the extent of their relative stiffness to the main 18" beam.
2. The customer has specified joist direction, but I might be able to rotate the joists on one side of the beam. Would joists at 16" oc hung from ONE FACE of the 18" beam constitute top bracing? Joists perpendicular to a wood beam certainly brace the beam against LTB.
3. Does sheathing count as lateral restraint? The floor is 3/4" T&G plywood, glued and screwed. Yes
4. Is there some other method to laterally restrain the beam? The sheathing alone would be adequate.

Thank you so much. I guess I don't have to worry so much since most of the time my beams are either sheathed as part of a floor or restrained by joists or trusses.

 

[Zoobie777]

Floor sheathing or blocking is usually fine to brace the beam. I use BCCalc occasionally and it always defaults to the beams being totally unbraced. Kind of annoying as they rarely are.

It is kind of annoying. This is very helpful. I don't have any issue with the concept of bracing, more like what is enough bracing. I've been reading a lot more about sheathing/diaphragms lately and now realize just how much lateral force plywood resists/transfers.

 

[ANE91]

Seems like you’re all taken care of. I’ll add that changing up the directions of joists mid-floorplan can have unintended consequences. Just make sure that, in doing so, you’re not inadvertently creating a stiffness problem.

 

[JoshPlumSE]

1. Can I block the beam on each side to the adjacent joists at 2' intervals to counteract the moment? My software (iStruct) won't let me block it but the beam passes if I specify top bracing at 2' intervals. You can add blocking but the load shared by the adjacent, parallel joists will only be to the extent of their relative stiffness to the main 18" beam.
2. The customer has specified joist direction, but I might be able to rotate the joists on one side of the beam. Would joists at 16" oc hung from ONE FACE of the 18" beam constitute top bracing? Joists perpendicular to a wood beam certainly brace the beam against LTB.
3. Does sheathing count as lateral restraint? The floor is 3/4" T&G plywood, glued and screwed. Yes
4. Is there some other method to laterally restrain the beam? The sheathing alone would be adequate.

I don't agree with JAE on item 1.... I don't think blocking with allow you to share the load very much. It will reduce the unbraced length of the compression length of the beam.

Honestly, for something like this, the easiest thing to do is to sister another beam with the LVL. I'd probably just double it up.... Conservative. Simple structurally. Obvious load path. Shouldn't be crazy expensive.

 

[JAE]

Josh here has a valid point but usually with blocking the adjacent joists do tend to deflect in unison with the main beam.

Yes there can be a bit of give in the blocking so the answer here probably depends a lot on the actual fixity and connection of the blocking to the beam. If they deflect in unison then the load will be distributed according to stiffness.

If they deflect together in general but with some slip in the blocking then probably per Josh's concern here you should simply design the main beam for 100% of the load.

 

[Respawn]

I don't agree with JAE on item 1.... I don't think blocking with allow you to share the load very much. It will reduce the unbraced length of the compression length of the beam.

Honestly, for something like this, the easiest thing to do is to sister another beam with the LVL. I'd probably just double it up.... Conservative. Simple structurally. Obvious load path. Shouldn't be crazy expensive.

I would recommend following Josh's approach. If an alternative material to LVL is selected, ensure the beam is analyzed as a composite section.