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Masonry Block Moment Frame

Masonry Block Moment Frame

(OP)
Hi all.

I have a gable end wall, constructed of concrete masonry blocks, which needs to act as a portal frame/moment frame to take lateral loads from wind/earthquake.

This portal frame holds a garage door, spanning 5.4 metres. The lateral loads it is taking come from the masonry walls perpendicular to this gable end wall. The maximum moment I calculated based on the earthquake force from the perpendicular walls is 119 kNm.

The walls are 2.4 metres high as is the garage door. There is 200 mm above the garage door before the roof slopes. The height of the roof is 2.1 metres. The columns are 800 mm wide.

Now since this is residential I assume I am using elastic analysis and therefore am not designing for plastic hinges? So I therefore do not need to detail the reinforcement of the plastic hinge regions differently? If this is correct am I therefore just designing the columns and beam ends to support 119 kNm?

Any help is appreciated.
Thanks

RE: Masonry Block Moment Frame

Level of force reduction is a decision that you make and your detailing needs too be consistent with that. Residential <> elastic. I expect that you'll have a difficult time making a go of this.

The greatest trick that bond stress ever pulled was convincing the world it didn't exist.

RE: Masonry Block Moment Frame

(OP)
Thanks for your reply.

I've done some calcs and it's looking pretty difficult to get sufficient moment capacity at the ends. Though I am not
quite sure what depth of the beam I can use at the ends for the maximum moment - whether its the 200 mm or the depth at the column centreline (roughly 450 mm) or the depth at the column face?

If this isn't go to work - would you suggest a steel portal frame be a better option?

Thanks

RE: Masonry Block Moment Frame

Simpson makes lateral and moment systems. If you need a CMU appearance, you could add a veneer.

RE: Masonry Block Moment Frame

At the beam to column connections, you would need to detail your rebar to transfer opening and closing moments across the joints. You can use whatever space is physically available and come what may.

As for true portal frame options (having a beams), Jed's prefab steel moment frames are about all that you're likely to be able to fit within the space available.

Another approach that you could take is to treat the piers at either and as cantilevered shear walls, flag poled up from the foundations. You might be able to make this system work in steel, wood, or masonry.

The greatest trick that bond stress ever pulled was convincing the world it didn't exist.

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