Calculating Hold Downs at the end of shearwalls
Calculating Hold Downs at the end of shearwalls
(OP)
Can anyone clarify whether I am on the right track? When you calculate shear due to wind, this is the method I used to calculate the demand V. Wind pressure according to MWFRS with all appropriate factors X width of the face of the building X total height of the wall+any roof. Then I used the same method of the lower stories until I reached the foundation. The Hold down force at the end of the shearwall is a cumulative of the forces for the upper walls? For a two storey building on the Texas coast with about 40 psf wind pressure, I am getting hold down forces of the order of 30,000 lbs, for a 27' mean roof height x 30 x 30 building. Is that in the ball park? What sort of reduction factors I can use? Can I use 1/2 height of the building in V.h/Co.Li = T = C? This may be pretty basic stuff, but it is always good to check one's basics.






RE: Calculating Hold Downs at the end of shearwalls
RE: Calculating Hold Downs at the end of shearwalls
RE: Calculating Hold Downs at the end of shearwalls
Regarding the methodology - yes the holddown forces are cumulative, as are the OTM resisting dead load forces. However, remember that for the lower story holddowns, the OTM forces from the shearwall system in the floor above must be added to the overturning force generated by the second story shear forces to obtain the proper holddown force. Otherwise, the holddown will to be too small. This is not good...
Mike McCann
MMC Engineering
RE: Calculating Hold Downs at the end of shearwalls
http://www.mcvicker.com/vwall/page000.htm
RE: Calculating Hold Downs at the end of shearwalls
old CA SE
RE: Calculating Hold Downs at the end of shearwalls
You can get some of the holdown forces to cancel out if the upper and lower walls are offset with just one end overlapping. In the simple case of one shearwall each level, you get at the foundation: one upper shearwall holdown force, one holdown force equal to the difference between the upper and lower wall holdown forces, and one lower shearwall holdown force.
Instead of using an enormous chunk of concrete to resist the holdown forces, I've used two approaches:
1. Recognize that holdown forces come in opposing pairs, determine the moment, design the footing as a grade beam to resist the moment, and check the entire line of footing for overturning. Reinforcing will be substantial.
2. Install helical piers at the holdown points.