Masonry Wall Opening

[JStructsteel]

I have a question on strengthing a masonry wall. I need to change two single doors (9'-0 span) to a single door by removing the pilaster between. I was going to span a channel as a header beam, and bolt into the precast headers over each door. The thing I am worried about is the torsion in the channel, and also if there will be torsion in the CMU that is left. There is about 4' of wall that the channel has to carry. Am I over anylizing this?

 

[msquared48]

Sounds like you are worried about torsion because you are intending to place the channel vertically in the opening?

Normally when channels are used to accomplish this, they are placed flat with the flanges up, i.e., no torsion.

Normally for retrofit construction, I use steel tubes. These take vertical as well as horizontal loads well, plus, are inherently good to resist any induced torsion.

Mike McCann
McCann Engineering

 

[Zambo]

I believe you want to use the channel with flanges up. This means that the channel will effectively be the lintel (header beam) and the door height clearance shall be reduced by the thickness of the channel's web.

If this is correct then the channel is acting on its weak axis, depending on the section size I would expect some bending.

I expect it will work and that if a crack appears above then it will be filled. The other option is to remove the lintels for the single door openings and replace with one new longer concrete lintel.

 

[JStructsteel]

the channel will go on the inside of the wall, spanning from the pilasters on the outside of the two existing doors. (strong axis vertical) then, the middle pilaster will be cut out, and then a new wider door installed. The masonry is still above, and the channel is taking the load and transfering to the outside pilasters. I feel that there is some torsion to worry about, but I cant decide if the wall takes it out and transfers it to the two outside pilasters, without the channel taking any.
Hope this clarifies

 

[fepc]

If there is only 4 feet of wall above the openings one solution is to shore the roof or floor above and remove the wall above the openings. Then install a new lintel and wall above. Remove the shoring after the new lintel and masonry has cured.

A second solution is to use needle beams to support the wall above the openings, remove the existing lintels and wall in between the openings, install the new lintel, then remove the needle beams after the wall and lintels have cured and repair the wall where the needle beams went thru.

A third solution is to use channels on each side of the wall with thru bolts at 8 , 12, or 16 inches o.c. connecting the channels and supporting the wall above. At the end of the channels you will need to transfer the load back to the wall with thru bolts. The exterior channel will have to be covered if it is aesthetically objectionable.

 

[msquared48]

Another solution is to install a continuous flat metal plate to the bottom of the lintel (Can be full pen welded on site to get around shoring) and install enough afterset (epoxy) bolts vertically into the bond beam to generate the required horizontal shear to develop the bond beam. This solution depends on the grouted depth of the bond beam and the need for shear steel. The plate just substitutes for the required steel of the bond beam. Would probably not be able to do this if more shear steel was required and/or full depth grouting did not give enough shear capacity.

Mike McCann
McCann Engineering

 

[DaveAtkins]

You may want to consider two angles, toe to toe, one on each face of the wall. I have heard that they can be installed without shoring--while the first angle is being installed, the pilaster is still partially intact and can temporarily support the pcc lintels. As the second angle is being installed, the first angle can temporarily support the pcc lintels.

Bottom line (everyone here seems to agree) is that a steel lintel should not be installed on just one side of the wall.

And remember--try to develop a solution that is easy for the contractor to implement, but at the end of the day means and methods are his responsibility.

DaveAtkins

 

[JStructsteel]

Thanks. I was temped to check the masonry wall that is left above as a deep beam and see what my stresses are. I know that I have a couple lintels that have steel, I just need to tie them together, and use that as my steel. I think that the angle idea will be next, as long as the client doesnt mind a angle on the outside.

 

[MarcbSE]

I modify and add masonry openings all the time. The easiest option for you would be steel on both sides using either channels or angles as mentioned above. Either of these options can be installed with no shoring required since they can be installed prior to removal of the central pier.

For channels: Install one on each face of the wall and through bolt. If desired a flat plate can be installed at the head after removal of the pier to clean up the appearance by welding to the channels.

For angles: Install one on each face and then weld a flat plate across the bottom from angle to angle after removal of the pier to brace the angles and prevent any possible shifting.

If the client will not accept steel on the outside of the wall, then you should shore the wall, roof, etc. and remove the old lintels and install a new masonry or steel tube lintel.

I would not recommend a single steel lintel on the inside face only.