PRECAST WALL AND ROOF

[deereman]

I HAVE A JOB WHERE WE ARE CUTTING OUT A 9'-0" HIGH X 16'-0" WIDE OPENING IN A PRECAST DOUBLE T-SHAPED WALL. I WILL BE USING STRUCTURAL STEEL TO SUPPORT THE WALL ABOVE THE OPENING THAT REMAINS. I PLAN TO RUN A COLUMN ON EITHER SIDE OF THE OPENING AND BOLT INTO THE DOUBLE TEE ROOF MEMBER (INTO THE 2" PORTION BETWEEN TEES) IS THERE TYPICALLY ANY PRESTRESSED REINFORCING IN THIS AREA THAT I SHOULD BE CONCERNED WITH NOT DRILLING THROUGH?

ALSO, IS THERE TYPICALLY ANY PRESTRESSED REINFORCING IN THE WALLS THAT I SHOULD BE CONCRENED WITH ONCE THE OPENING IS CUT. IS THERE TYPICALLY ANY NONPRESTRESSED REINFORICING IN THE WALL THAT I CAN COUNT ON FOR STRENGTH AFTER THE CUT.

IS THERE ANY MANUALS OR BOOKS THAT CAN HELP ME WITH THIS SINCE THE COMPANY THAT MADE THEM IS NO LONGER IN BUSINESS?

 

[azcats]

Is the roof framing bearing on this wall or parallel to it?

What is your roof height? Parapet or roof overhang?

What I typically do in a situation like this is design the beam across the opening for the gravity loads above and any lateral loads (beam spanning horizontally) if the wall height above the opening is significant. The column would be designed for the gravity loads as well as the lateral loads from the cross beam and jamb loads from the door in the opening. Your connections will be dependant on where your column hits within the tee. I like to use TS columns and beams with angle tabs and bolts epoxied into the wall. Thru-bolts may be required if you hit in a flange though. Limit deflection on the column and the beam to the requirements for the concrete. I'm especially careful on the cross beams. Probably in the L/600 range or better. The deflection requirements will likely govern both the column and beam design.

 

[daski]

I don't design precast for a living, but what i've seen from checking shop drawings is that most of the prestress is in the stems of the tees, towards the bottom. There are also prestress strands in the deck portion, spaced at 2 or 2 1/2 foot or so. The mild reinforcing in the deck portion is usually a heavy gage welded wire fabric.
You should call a local precaster and ask for their engineering department to get their opinion. They are usually glad to help.


Mark Daski