Masonry Wall Design 2

[slickdeals]

Folks,
ACI 530 1.13.5.2.2 says that masonry walls that are not designed to resist vertical or lateral loads other than those induced by their own mass shall be isolated from the structure so that vertical and lateral forces are not imparted to these elements.

My question is thus:
If I have a masonry wall that I intend to isolate from the structure so that its mass does not contribute to the lateral mass, then I provide an isolation joint to separate it from the structure. This joint will be able to accomodate the movement of the structure under seismic loads.

However, if I have wind loads also to be resisted by this wall (as part of a facade), how does one detail a connection? This connection would have to transfer the lateral forces to the diaphragm or the floor framing unless it is designed as a cantilever element.

Any suggestions is appreciated.

Thanks

 

[nuche1973]

What is your diaphragm?

 

[Teguci]

I've seen a couple of options:

Provide a long rod tieing the masonry wall back to the structure with a slotted angle and nut.

Use a slotted insert. Dayton Richmond has some that get used in precast systems. Allowable lateral movement is minimal. Vertical movement will need to be accounted for in another way (flexibility of the tie).

 

[slickdeals]

If I allow lateral movement, then the wall will have to carry all wind loads by itself, as a cantilevered element, right?

I have a concrete diaphragm.

 

[Galambos]

i think the intent of this section is to prevent the masonry wall acting as a shearwall taking lateral loads in the plane of the wall. with the wall disconnected from the diaphragm, it doesnt act as a shearwall and does not contribute to the stiffness of the structure.
the wind load is acting perpendicular. it would be appropriate to provide a steel angle on either side of the top of the wall, with a gap between the top of the wall and underside of deck for downward movement.

 

[lrhg]

If the exterior masonry wall is laterally braced to the floor diaphragm, then the mass of the masonry contributes to the seismic mass. While I agree that you can detail the exterior masonry to act as cladding and to not contribute to the lateral stiffness of the building, I would include the mass of the masonry in the seismic mass perpendicular to the length of the wall.

Is this wall supported on a footing or grade beam? If so, I would included the mass of at least half the height. If it is on an elevated floor, I would include the mass from the full height of the wall. I don't think there's a way to detail to exclude the mass of the wall if it is on an elevated floor.

 

[tngolfer]

I agree with lrhg 100%.

 

[slickdeals]

lrhg, i agree with you.

 

[civilperson]

Wind loads are the very horizontal loads that are described as lateral loads in the original post. Can not have isolation and transfer horizontal wind loads to foundations also.

 

[msquared48]

I agree with Irhg too.

Moreover, as the wall is resisting wind load, then it is resisting more than it's own mass laterally. Hence, the need for an isolation joint for the masonry wall is a mute point here and ACI 530 falls by the wayside. Keep it simple and tie it to the structure.

Mike McCann
MMC Engineering

 

[Galambos]

i think we're missing the point here. the intent is to keep the wall from acting as a shear wall during a seismic event, not to keep it from resisting seismic and wind forces acting perpendicular to the wall.

i disagree with your statement, Mike.

the point is not mute [sic].