Torsion In Masonry Lintels
Torsion In Masonry Lintels
(OP)
When working with CMU cavity walls, people in my office often specify steel I-beam lintels centered over the CMU. Bottom plates are welded to them to support the brick facade at an eccentricity dictated by the geometry involved.
I'm concerned with the torsion that is introduced into the system with this design. I've no problem with designing the lintels for torsion if necessary; however, I don't understand how the torsion in the lintels gets transfered out to the masonry walls at the bearing points.
It has occured to me that, once rotation occurs in the I-beam, the weight of the masonry above the beam would rest on the inside of the top flange and create some counteracting torque. However, considering the typical geometries involved, this resisting torque hardly seems adequate.
So what is left then for resiting the torque? All that I can think of is the tensile capacity of the mortar and I don't think that it would be wise to count on that. Does anyone have any suggestions? Perhaps I a missing something significant in the way that I am visualizing the situation? Any help would be greatly appreciated. Thanks
Adam
I'm concerned with the torsion that is introduced into the system with this design. I've no problem with designing the lintels for torsion if necessary; however, I don't understand how the torsion in the lintels gets transfered out to the masonry walls at the bearing points.
It has occured to me that, once rotation occurs in the I-beam, the weight of the masonry above the beam would rest on the inside of the top flange and create some counteracting torque. However, considering the typical geometries involved, this resisting torque hardly seems adequate.
So what is left then for resiting the torque? All that I can think of is the tensile capacity of the mortar and I don't think that it would be wise to count on that. Does anyone have any suggestions? Perhaps I a missing something significant in the way that I am visualizing the situation? Any help would be greatly appreciated. Thanks
Adam






RE: Torsion In Masonry Lintels
This results in smaller loads on the plate and resulting smaller torsional loads on your beam but you are correct - you still have an issue with "where does the torsion go?".
In most smaller openings, I would suggest that the ends of the beams are pinched into the wall and this creates a bending moment on the wall at either side of the opening that is resisted by the wall's flexural capacity. How much of the wall participates is a question to be considered in each case....usually use 16 to 32 inches of wall.
For larger openings, we have welded reinforcing bars to the top of the wide flange, extended up into the wall, to transfer some of the torsional bending into wall flexure above the beam. In other cases, we use additional braces as the WF doesn't possess very much torsional rigidity.
RE: Torsion In Masonry Lintels
RE: Torsion In Masonry Lintels
RE: Torsion In Masonry Lintels
RE: Torsion In Masonry Lintels
RE: Torsion In Masonry Lintels
This must be coordinated with the ceiling/finishes so the "ugly" braces aren't seen.
Also...the vertical rebar welded to the top flange creates a sort of tension/compression mechanism that resists the rotation of the beam. This can be used instead of or in addition to the external braces.