In Enercalc Masonry Wall design, what is "Parapet Height"?

[pob11646]

I posted this in the General Engineering program section but have had no luck there. Hope I can get some responses here.

In the Masonry Wall design portion of Enercalc v5.8, what does "parapet height" refer to? The definition provided in Enercalc Help is, "This portion of the wall extends above the Clear Span Height and will apply a concentrated moment due to wind or seismic loads to the top of the wall. Vertical load due to the parapet weight is also included."

What is the parapet wall? Is it part of the masonry wall, and must it be constructed of masonry?

If I just have a stud wall above my masonry wall, is that considered a "parapet wall"? I am thinking that it does not, but I hope someone can verify that.

Thanks for all your responses.

 

[structuresguy]

The parapet is the portion of the wall that cantilevers above the roof deck. Whether you make it out of block or wood studs, you should add it to the program.

 

[Lion06]

structuresguy is right. It doesn't matter what you make it out of, it will apply a load to the top of your masonry wall so you have to account for it.

 

[pob11646]

Thank you so much Thank you so much for the prompt response, structureguy and StructuralEIT. You guys are awesome, and your feedback really helps me to evaluate my situation and feel more confident in the direction I am moving.

The thing is, I have a 20 foot space I need to wall up; 8 feet of this is an 8" masonry wall. The rest of the space is taken up by 12 foot of light gauge steel studs wall with a liner panel. The stud wall is like a "wind post" type of wall, i.e. taking only lateral loads and no vertical loads at all. Weight of the stud wall on the masonry wall is 70 PLF. Per Code, my lateral loads are 5 PSF. I am using #5 at 48 inches to reinforce my masonry wall.

Now, when I run Enercalc, and include the 12 foot stud wall as a parapet wall, my masonry wall is overstressed. My allowable for Bending + Axial comp. Stress is about 0.34 of the maximum, thus N.G. My allowable for Steel Bending stree is about 0.48 of the maximum, again N.G. My allowable for Axial only compressive stress is 9 times the maximum, so that is OK.

I find that the height of the Parapet wall has a lot to do with my masonry wall failing in bending + axial comp. stress and steel bending stress. If my parapet wall is say, 7 feet, then I am OK.

Does anyone know what is happening, and how I may resolve my issue. Thank you so much.

 

[Lion06]

It is assuming that your parapet is cantilevered. If that isn't true, then you are punishing yourself too much. It also assumes the parapet is the same size and material as the wall, thus you have more axial load.
There are many problems and limitations with Enercalc which is why we have moved away from it.
If you have an analysis software (e.g. Risa or Ram Advanse) I would just model your situation and run an analysis to get the loads out and design by hand. That is what I typically do.

 

[jike]

Is the 8 foot of masonry just cantilevered off the floor and the studs are sitting on top of it? Are the studs braced just at the roof level?

It might make more sense to brace the studs at the roof and just above where it meets the CMU (above the ceiling of course, if you have one).

Hopefully, I understand what you are describing.

 

[SteveGregory]

It is not clear to me how your 20' wall is constructed and at what elevation the roof connection is made.

Are the studs 20' long and attached to the floor or foundation wall at the main floor level and attached to the roof framing at the +12' level? In this case, the masonry is only a facade and the studs resist the wind and seismic loads.

Or does the bottom of the stud wall attach to the top of an 8' tall masonry wall and to the roof framing at the +12' level? If so, the masonry wall must be cantilevered from the footing and be capable of resisting a uniform lateral load from the top of the masonry wall down to the footing and a concentrated lateral line load at the top of the masonry wall from the stud wall. The stud wall has a pinned or hinge connection to the masonry wall. It is very unlikely that you could develop a moment connection at the top of the masonry wall and the bottom of the stud wall.

 

[strainman]

Your wall should be dowelled in at the base and considered a cantilevered wall for design purposes. The cantilever will create a K of 2, so the design height will be twice the actual height. This may be what is controling your design in enercalc.

 

[pob11646]

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Total height of wall is 20, of which the bottom 8 feet is masonry. The masonry is a cantilevered wall, and anchored at base with steel rods.

The upper 12 feet is a light gauge steel stud wall. The bottom of the stud wall is anchored to the top of the masonry wall with a runner track, i.e. it is introducing an axial load (basically self weight), and even a moment to the top of the masonry wall.

The top of the light gauge stud wall is attached to the roof with a deflection track, i.e. it is not taking any vertical loads from the roof. It is merely taking nominal lateral load (5 PSF). Basically, the wall stud is simply supported by the top of the masonry wall and the deflection track.

Weight of the stud wall on the masonry wall is 70 PLF. Per Code, my lateral loads are 5 PSF. I am using #5 at 48 inches to reinforce my masonry wall.

The weight of the stud wall is definitely not the same as the masonry wall.

As previously said, when I run Enercalc, and include the 12 foot stud wall as a parapet wall, my masonry wall is overstressed.

My allowable for Bending + Axial comp. Stress is about 0.34 of the maximum, thus N.G. My allowable for Steel Bending Stree is about 0.48 of the maximum, again N.G.

My allowable for Axial only compressive stress is 9 times the maximum, so that is OK.

My original question was, should the stud wall be considered a "parapet wall"?

Is Enercalc able to work this problem?

 

[jike]

Unless I am missing something, you don't have a parapet, do you? This is simply an interior wall with 8' of masonry and 12 feet of stud with a deflection track at top. When you mentioned parapet, I thought the wall continued above the roof.

I would suggest that you brace at or near the 8 foot height and not cantilever the CMU wall. There is essentially a "pin" at this location, so it needs to be braced. Have you checked the wall for seismic?

Understanding the mechanics and the details of the problem first is much more important and then later you can try to manipulate software to do as you want. Give it a try by hand first and see what you get!

 

[SteveGregory]

I don't think that Enercalc is set up to handle this one. Hand calcs should be done. 5 psf wind sounds a little light. I think 10 psf is a minimum. I would design this wall using components and cladding loads.

Based on your last post, the top of the stud wall is anchored in a deflection track. I assume this means that the top of the studs do not extend above the roof. Therefore, there is no parapet.

 

[JStructsteel]

cant you do a masonry cantilevered wall with a lateral and gravity load at the top, and not worry about the studs as a parapet.

Then, you just need to worry about the connection of the studs to the masonry.

 

[pob11646]

Thanks for all your responses. I am sorry if I did not make myself clearer earlier that I am designing an interior masonry wall, with an interior light gauge stud wall sitting on top of the masonry.

The 5 psf interior load is from IBC 2006 Section 1607.13. However, I can increase my lateral load to 10, or even 15 PSF without affecting my design.

I did not think the stud wall qualified as "parapet height", but wanted to be sure. Nothing extends beyond the roof.

I can input the axial and lateral load from the stud wall to the top of my masonry wall, but there is also a moment from the lateral load acting on the stud wall. This moment would act on top of my masonry wall.

How do I input this into Enercalc? I do not believe there is a place for me to input the moment, although there is a space for load eccentricity.

Would I be able to use Enercalc? Thanks again for all your feedback. Please keep them coming.

 

[jike]

"there is also a moment from the lateral load acting on the stud wall. This moment would act on top of my masonry wall".

?????

Please explain, how you plan to make this connection to transfer moment.

 

[SteveGregory]

You can't develop a moment from a pinned connection.

i.e. Stud wall to masonry wall

 

[jike]

You can't develop a moment from a pinned connection.

Exactly my point!

 

[StructuralEngGuy]

I think you're better off doing this by hand. Basically, you have an 8' cantilever CMU wall design. The stud wall is simply supported between the top of CMU and roof. So add the reaction from the end of the stud wall to the top of your CMU wall as a lateral load. I'm understanding that this is an interior wall and that's why you're using 5 psf as your lateral load. I'm not sure where the project is located, but make sure you check seismic forces as well. If you absolutely must use a program, I would recommend you use the cantilevered retaining wall design in Enercalc and make your retained height zero. You can apply a uniform load on the wall (5psf) and a lateral load at the top due to your stud wall reaction.

 

[pob11646]

Oops! Sorry, my bad.

 

[BAretired]

You do not have a parapet. A parapet is a vertical cantilever above the roof. What you have is a 12' high stud wall resting on a cantilevered masonry wall 8' high.

If 'p' is the lateral pressure, the horizontal reaction from the stud wall is 6p top and bottom. This causes a bending moment of 6*8p at the bottom of the masonry wall. You also have 8p acting directly on the masonry wall which creates a moment of 8*4p at the base.

Your total moment at the base of the wall is (48 + 32)p = 80p. Assuming p to be 10 psf, the moment at bottom of wall is 800'#/'.

If you prefer, you could use columns spaced along the wall, each 20' high and a horizontal beam at the top of the masonry wall spanning horizontally between columns. You would then design the beam for a lateral load of 10p. The spacing of columns would be governed by the permissible span of the beam. Each column would be designed for a point load of 10*p*sp at an eight foot height, where sp is the spacing of columns.

The weight of stud wall on the masonry is so minor as to be negligible.



Best regards,

BA