This is a question about how concrete panels in a tiltup building resist out-of-plane loads. Do they span horizontally between pilasters or span vertically between the diaphragm and the floor slab.
A colleague and I are looking an existing tiltup with 6" thick panels, elevated floor slab at 3' above grade and pilasters at 24" o.c. There is an arched wood diaphragm, 220' x 116'. The diaphragm is supported by bow string trusses, 18' above the floor slab and supported by the pilasters every 24' and spanning the 116' direction. The pilasters are braced out-of-plane by the trusses and the diaphragm.
The owner wants to cut some new roll-up door openings in some panels and fill in others with CMU or shotcreet.
And, oh yeah, the building is in seismic design category D.
The arched diaphragm slopes about 1:3 and doesn't have sub-diaphragms (it's an old building).
One question will determine how to reinforce the panels at the new openings.
Plan A is to assume that the panels span vertically and that the diaphragm is stiff enough support the panels out-of-plane, even in between the pilasters. Therefore, it is only necessary to reinforce with a HSS section over the new opening and attach it to the panel at the edge of the opening, not all the way over to the pilasters. Or to run two HSS sections vertically at the sides of the new openings spanning from bottom to just under the diaphragm in between the pilasters.
Plan B is to assume that the panels span horizontally between pilasters and reinforce with an HSS above the new openings spanning the full distance between pilasters and thru-bolted to the walls just above the openings. Although the panels attach to the diaphragm in between the pilasters, the assumption is that there is nothing in the diaphragm in between the pilasters (probably plywood or 1x sheathing) which would offer any significant out-of-plane resistance to the panels because the trusses only occur at the pilasters.
Another subject of discussion is whether to recreate the stiffness in the original concrete panels with the HSS reinforcement or just to recreate the strength required by the out-of-plane forces.
Thursday, December 22, 2011
How to Reinforce Openings in Tiltup Panels
at 9:43 AM