Parpet affect on wind load 4

[Mohamed Maher]

Hi all

I have on roof steel building with span 43 m , its fixed on parapet which is cover most of area of the steel element. Is this parapet can decrease the affect of wind load and which part in the ASCE code can support this please. for example can i neglect wind on all levels below the parapet i know this hard to be considered but i believe that parapet will also decrease the wind affect.
Kindly refer to the attached.

Thanks
Maher

 

[human909]

No you can't neglect wind load all levels below the parapet. You would still likely expect lower pressures across leading edge of the roof.

True the parapet could reduce the wind loads, it would create some funky turbulence too which is currently above my pay grade to calculate.

 

[Aesur]

I haven't come across a scenario like this before, but I would probably approach it as follows: The parapet is the portion that extends above the roof plane (top of truss and diaphragm sheathing). For building lateral design, I would design for the parapet loading on the parapets and the gable roof loading on the truss.

If I understand your question correctly, you want to know if adding the new gable truss above the existing roof will lower your parapet height to be from top of truss/new roof to top of parapet. I would say that yes this is the case if your new roof is entirely enclosed and sheathed. As for an example or code reference, I'm not sure this exists as this case isn't common and to my knowledge is engineering judgement.

If you are designing a new gable truss with integral parapets, I would argue that the parapet is the portion above roof sheathing and the portion below is wall loading and the truss itself would see gable wind loading.

 

[sdz]

I would expect something like this.
Take a line sloping down at 10 deg from the parapet edge until it intersects the roof. The area to the left of that will be shielded BUT that does not mean it has no load.
I would take the pressure coefficient as that on the back of the parapet which looks to be ~-0.9. (Cp for a free standing wall is 1.7) This could be higher for tall buildings.
You should however be able use reduced local pressure effects in this zone.

AS1170.2 5.4.4 Local pressure factor (Kl) for cladding
For flat or near-flat roofs (slope less than 10°) with parapets, values of Kl for areas RA1,RA2 and RC1 in the lee of the parapet
may be modified by multiplying the values from Table 5.6 by the parapet reduction factor (Kr), given in Table 5.7.​

You will need to refer to your local design codes for details.

 

[Mohamed Maher]

THANK YOU ALL..