Lintel Lateral Bracing

[krus1972]

The question of lintel lateral bracing has come up. Some engineers are designing steel lintels assuming the block provides lateral bracing for the lintel (either top flange lateral bracing or torsional bracing) and some engineers assume fully unbraced along the span. We even have some guys who are taking the unbraced length as half of the lintel span.

I am looking for a formal paper or write-up or documentation that disucsses this topic as I need to come up with presentation material to back up an engineering opinion. Can anyone please help.

Jeff

 

[JAE]

I don't rely on the brick to brace the lintel. There is some obvious help by the masonry of course, but you really have no way to verify whether the strength and stiffness of the brick is adequate.

Brick veneer is tied back to the metal wall, but it also has varying stiffnesses depending on the span of the opening and the way in which the stud wall (whether metal or wood) is framed.

 

[AggieYank]

I also use the full length as unbraced. There will be occasions where the brick and stud wall will be strong and stiff enough to count on as a brace, but there will be more times when it doesn't. As JAE mentioned, quantifying the strength and stiffness of a brick / backup wall combination would be impossible.

If you're coming up with a huge wide flange beam for a large lintel span, you may try using a tube, as unbraced length won't have much of an effect.

 

[SlideRuleEra]

Brick Industry Assciation, Technical Note 31B "Structrural Steel Lintels"

The allowable stress, Fb, for ASTM A 36 structural steel is 22,000 psi (150 MPa) for members laterally supported. Solid brick masonry walls under most conditions provide sufficient lateral stiffness to permit the use of the full 22,000 psi (150 MPa). This is especially true when floors or roofs frame into the wall immediately above the lintel. The design for non-laterally supported lintels should be in accordance with the AISC Specification for the Design, Fabrication and Erection of Structural Steel for Buildings.

Available at this link:

http://www.bia.org/html/frmset_thnt.htm

Here is another document - althought not specifically about structural steel lintels it has some similar concerns. In particular see Paragraph 8-6

http://www.usace.army.mil/publications/armytm/tm5-809-3/chap8.pdf

http://www.SlideRuleEra.net

 

[JAE]

Keep in mind that SlideRuleEra's quote says "solid brick masonry walls". This is not the same as brick veneer.

The brick depends on the lintel to hold it up and the lintel then depends on the brick to keep it from failing?? Sounds like the analogy of two drunks leaning against each other....who is holding up whom?

 

[krus1972]

Thanks for the info.

The document mentioned in "SlideRuleEra"'s first post outlines an "opinion" as to the lateral bracing requirments. There is no supporting calculations or research information. I am still at square one with this topic. Some engineers design steel linteals at UNBRACED, some engineers design as fully brace, and others use their own magic/theory to determine unbraced length

Since Steel linteals are not a new invention I would suspect that someone out there has some form of technical document or research paper that discusses the lateral bracing capablity on the linteal from the block while ignoring how close the linteal is to the roof or floor framing.

Any help would be well appreciated.

Jeff

 

[UcfSE]

The lintel will twist along its length, causing the wall to bend as though you applying a forced rotation. Some of the stiffness for the lintel-wall system at the lintel location will be provided by the torsional stiffness of the lintel and some by the rotational stiffness of the wall. It seems you could calculate your total stiffness for the lintel-wall system and, assuming compatible deflections, distribute some of the rotation to bending in the wall and some to twisting in the angle. If you compare the resulting twist of the lintel with the twist you would get from both unbraced and fully braced assumptions, you may figure out how far from the ideal you are and go from there.