Brick Lintel Design - Torsional effects
Brick Lintel Design - Torsional effects
(OP)
In sizing brick lintels, I have only been considering bending in the vertical leg (the "x-axis"). I started thinking and asked myself this question: At what point do I start considering torsional effects (or bending about the "z-axis") due to the eccentric loading of the brick? Is this a legitimate concern or am I just crazy? In school we learned about lateral torsional bending, but I haven't considered it in this application. Thanks in advance for any help.






RE: Brick Lintel Design - Torsional effects
Just some random thoughts:
It's interesting that the 3rd Ed. LRFD Single Angle Spec. doesn't mention torsion. It does mention angles with and without lateral-torsional restraint and gives some equations in 5.2.2, 5.2.3, and 5.3.
I guess one could calculate the pure torsion shear stress and add it to the shear stress from flexure. There also seems to be warping, but I've never seen equations for how to calc the associated normal stress. It could be approximated using mechanics, though. Imagine the section trying to twist--the legs would be bending out of their planes.
Now the tough one: twisting angle. I guess one could calculate the pure torsion part using dphi/dz=T/GJ and then calc the warping part using the physical analogy of the legs bending out of their planes.
Here's a weird one that I've been wondering about. The 13th Ed. Manual lists Cw properties for angles. Anybody here know how to calc that?!
RE: Brick Lintel Design - Torsional effects
RE: Brick Lintel Design - Torsional effects
Hokie66:
Could you please explain what you mean here?
RE: Brick Lintel Design - Torsional effects
Some comments about arching action and brick restraint. Often there are control joints at one or both ends of the lintel which eliminates or reduces arching action. Charles W. Allen, M. ASCE indicated in an article, published in Civil Engineering-ASCE March 1981, that cracking often occurs in the lintel area reducing the masonry's ability to brace the lintel.
His article provideds a lintel table and some design equations for sizing lintels. I have used his table many times. However when I did, my lintels were alway larger then what others were commonly using.
RE: Brick Lintel Design - Torsional effects
Dik
RE: Brick Lintel Design - Torsional effects
javascript:openindex(450,450,'h
RE: Brick Lintel Design - Torsional effects
RE: Brick Lintel Design - Torsional effects
This is the EXACT argument I made (and was castigated for by many LOLOL) for CMU walls restraining torsion of a steel beam lintel below. Gotta watch those BCs in both cases. One big difference between this and the CMU is that the CMU has a good connection to the steel beam, LOL.
RE: Brick Lintel Design - Torsional effects
When the angle starts to rotate under the 'torsion', the brickwork will tend to stay vertical. The result is that the center of load moves closer to the inside face of the brick.
RE: Brick Lintel Design - Torsional effects
RE: Brick Lintel Design - Torsional effects
depends on the length of the lintel, I wouldnt rely on the lateral restraint from the brick for anything over about 10'.
RE: Brick Lintel Design - Torsional effects
RE: Brick Lintel Design - Torsional effects
DaveAtkins
RE: Brick Lintel Design - Torsional effects
I agree, longer spans need another solution. I normally would not go beyond 8 ft with a loose angle lintel.
DaveAtkins,
How do you restrain the angle at the ends?
As a matter of interest, in Australia we tend to use lintels with ribs which are supposed to help the lintel and brick to work compositely. Just Google "galintel"
RE: Brick Lintel Design - Torsional effects
The lintel bears on the brick at each jamb. At the end of the lintel, the reaction will consist of a vertical force, which is located at the heel of the angle, and a torque. If you divide this torque by the vertical force, and use this eccentricity to relocate the vertical force, you will find that the resultant force is located at the center of the brick at the jamb.
DaveAtkins
RE: Brick Lintel Design - Torsional effects
I thought the ribs in the galintel were for rendering I didnt think it was for composite.
Dave Atkins,
By this theory the same applies to when you have a backing member, the reaction still ends up at the center of the brick (which is what I was trying to get at in the last post). The one thing this ignores is strain compatability. At mid span the angle will rotate and the load will be closer to the shear center. Reaction at the center of the wall is conservative for the lintel but not necessarily for the brcks at the ends.
Pedantics I know, but worth a thought.
RE: Brick Lintel Design - Torsional effects
Torsion is going to occur.
So what's stopping it from rolling over?
First: I believe the mortar bed is such, the leg of the upright angle is pretty much against the face of the brick. Masons I have seen want to make sure the brick sticks so they place a pretty good mortar bed under and behind the brick. Whether that is typical, I don't know. I'm just basing it on what I've seen.
Second: The brick ties are typically spaced vertically @ 18" o.c., and horizontally @ 32" o.c., thus providing some lateral restraint.
Third: We assume a point load at the center of the brick. It would actually be a bearing pressure. As the angle begins to rotate, the bearing pressure goes from uniform pressure, to triangular pressure, thus moving the ecentricity closer to the centroid of the angle, until it balances with the restraining forces.
That's my thoughts anyway.
However, what do you do at the supports? I haven't researched this so it might be straight forward. We always assume pinned, however, it's more partially fixed, and creates a prying action at the end. Numerous times I've seen cracks develop at this location, coinciding with vertical displacement of the brick.
RE: Brick Lintel Design - Torsional effects
JW
RE: Brick Lintel Design - Torsional effects
The literature definitely says that the ribs are for composite action. They are on both the horizontal and vertical face at the mortar-brick interface, and although parallel to the wall, would give some benefit, I think.
RE: Brick Lintel Design - Torsional effects
In your last paragraph, you mention prying action and vertical displacement of the brick. When I have seen this, it is usually due to corrosion of the end of the lintel. It occurs frequently in coastal areas. Some people still don't hot dip lintels.