Double Wythe Brick Screen Wall 1

[mattmlm]

I have a 10 ft tall screen wall that the architect wants to be double wythe brick. He has placed 12"x12" pilasters (that I assume he wants also to be out of brick) at 9 ft on center. He doesn't want the brick wall to have a space in the middle that would allow for me to use reinforcing steel so I'm assuming that the wall will span horizontally between the pilasters. I do have a high amount of wind on the wall, so I know I will have to alter the pilasters to be concrete in order for them to hold up the wall.

My question is, how do I design the double wythe brick wall to span horizontally between the pilasters? I know I will use horizontal joint reinforcement (ladder wire mesh), but how do I size and space that?

Thank you,

MLM

 

[DaveAtkins]

With masonry, working stress design is generally used. The area of steel would be the area of one wire of the ladder type wall reinforcing, because only one wire will be in tension.

DaveAtkins

 

[Lion06]

I've often wondered about the joint reinforcement. Is there really enough bond (and strong enough bond) between the reinforcement and the thin layer of mortar to really count on this?

 

[csd72]

Check out

http://www.maconline.org/

 

[civilperson]

Yes, the ladders are developed in mortar or in grout filled cells due to the continuity of the ladder beyond the location under analysis.

 

[minorchord2000]

I know it has been done and the theory says it can be done but, as a matter of my own engineering judgement and our office engineering policies, I personally do not rely on the horizontal reinforcing to resist lateral forces such as wind or seismic. They provide the requisite minimum steel ratios required in both directions, but I do not use for main lateral force resistance.

I would the tell the architect that you need that space to adequately reinforce the wall. Why would he want a double-wythe wall in the first place? With a 1" or 1-1/2" space, you can adequately provide suitable horizontal and vertical reinforcing to resist the wind loads as they gather at the pilasters.

Just my opinion.

 

[UcfSE]

You would size the joint reinforcement and spacing just like you would size rebar size and spacing if it were spanning vertically. You just use the properties of the brick wall spanning horizontally, and correct material properties and so on.

There is room to get creative too. You can talk the architect into structural brick instead of the typical brick used for veneer. You can use very small rebar, such as #2 if it's available in your area, instead of joint reinforcing. You could reinforce the wall vertically as you would any other wall and require the masons to create a "cell" by cut a portion of the side out of each brick.

I would try to convince the architect to use structural brick or provide a void between in which you can place reinforcement. This is a guess obviously but I think you could have problems getting the wall to work horizontally if you have high winds.

 

[msquared48]

With two widths of brick and a 1" mortar space, the width of the wall is 8", the standard width of a similar CIP wall for that height and application. Use #3 rebar both directions and tell the Architect he will have to live with it. Take charge dude!

Seriously though, just communicate with him. If he is good, he will listen. If not, seek future business from an architect who will and drop this one.

Mike McCann
McCann Engineering

 

[concretemasonry]

This is really not a major structural problem. Terminology is the key.

Is the wall composed of two wythes of brick with a gap between them? If so, at best, they act as separate 3 5/8" thin walls.

Is the proposed wall the common arrangement that consists of two 3 5/8" layers of brick bonded together with a 2/8" collar joint that permits the total wall to act as one structural element (7 5/8" thick)?

With the second configuration and close spacing of the pilasters, usually extra heavy joint reinforcement instead of standard joint reinforcement may be used unless the wind or seismic conditions are very unusual and severe. Your 10' height does create a bit of a problem and you may wish to consider analyzing the wall panel as supported on three sides.

I would be more concerned about getting enough reinforecing into a 12x12 brick pilaster, which is probably the critical point since effective vertical reinforcement of the brick wall is not practical with standard brick. If locally available, you may like to look into using 16x16 concrete block with vertical bars and ties.

I recall an older document available fron Dur-O-Wal (joint reinforcement supplier) that may give you some insight if it is still available.

 

[mattmlm]

Thank you all for your help and advice.

I have had the wall lowered a foot and with the site grading I'm now at 8 ft above ground. That reduced the loading. The wall is 7-5/8 inch and acts as one. I've sized heavy gage Dur-O-Wal truss type horizontal joint reinf at 8 inches on center based on calculations assuming that the wall will span between the pilasters. Also, I've had the pilasters increased to 16x16. This allows for the pilasters to have a reinforced concrete core to resist overturning.

Thank you again for you input. I appreciate it.

MLM