Paranoid About Uplift on light weight Flat Roof
Paranoid About Uplift on light weight Flat Roof
(OP)
Hi,
I have a flat roof on a steel frame building. The structural flat roof is light weight and will be constructed as per the attached sketch. In terms of wind load I have nothing but suction forces on the roof.
Originally I had no strapping of the bottom flange a midspan. My colleague thinks strapping of the bottom flange (compression flange in the uplift scenario) is not required as the joists are effectively stopping the UB from going side ways in this loading condition.
I have a suspended ceiling scenario on the soffit of the steel frame/timber joists.
I'm just wondering if the attached detail gives me full lateral restraint in the uplift scenario (thus giving me the full buckling capacity of the UB) or should I provide some sort of strapping of the bottom flange as shown in red on the attached sketch......or is this overkill.
Any thoughts welcome.
John.
I have a flat roof on a steel frame building. The structural flat roof is light weight and will be constructed as per the attached sketch. In terms of wind load I have nothing but suction forces on the roof.
Originally I had no strapping of the bottom flange a midspan. My colleague thinks strapping of the bottom flange (compression flange in the uplift scenario) is not required as the joists are effectively stopping the UB from going side ways in this loading condition.
I have a suspended ceiling scenario on the soffit of the steel frame/timber joists.
I'm just wondering if the attached detail gives me full lateral restraint in the uplift scenario (thus giving me the full buckling capacity of the UB) or should I provide some sort of strapping of the bottom flange as shown in red on the attached sketch......or is this overkill.
Any thoughts welcome.
John.






RE: Paranoid About Uplift on light weight Flat Roof
RE: Paranoid About Uplift on light weight Flat Roof
DaveAtkins
RE: Paranoid About Uplift on light weight Flat Roof
John.
RE: Paranoid About Uplift on light weight Flat Roof
On one of my roof rafters the beam is loaded 6m on one side and only 3.9m on the other side. The dead load is only 0.9kN/m2. I assume I don't have to worry about the beam twisting due to this uneven loading as if it tries to twist the floor joists will hold it in position? Do you agree?
The rafter is a 254x146x43UB
Your thoughts are welcome.
John.
RE: Paranoid About Uplift on light weight Flat Roof
Mike McCann, PE, SE (WA)
RE: Paranoid About Uplift on light weight Flat Roof
RE: Paranoid About Uplift on light weight Flat Roof
John.
RE: Paranoid About Uplift on light weight Flat Roof
RE: Paranoid About Uplift on light weight Flat Roof
BA
RE: Paranoid About Uplift on light weight Flat Roof
DaveAtkins
RE: Paranoid About Uplift on light weight Flat Roof
John.
RE: Paranoid About Uplift on light weight Flat Roof
BA
RE: Paranoid About Uplift on light weight Flat Roof
Good thinking about providing gap for joist shrinkage.
John.