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Re: Precast Double Tees Diaphragm

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You might investigate the possibility of using a fiber overlay at the 
joints.  This is a fairly high-tech solution that has been used 
successfully by others.

Although the "style" of connection would be the same as the existing 
connections if you bolted additional steel plates to the joints, this 
may work.  If the capacity of the connections allows them to remain 
essentially elastic, the connection ductility problem is solved.

When you are done (employing either of the above) the diaphragm 
thickness still won't satisfy the 1997 UBC, but I suspect that 
several other features of your existing building don't satisfy the 
current UBC.  A working solution for the rehabilitation design (even 
if it doesn't satisfy the new building provisions in the UBC) may be 
the best solution for your client.


> Date:          Mon, 13 Dec 1999 20:53:08 -0700
> From:          Jake Watson <jwatson(--nospam--at)>
> Subject:       Re: Precast Double Tees Diaphragm
> One last question, do you have any recommendations on an economical
> upgrade.  The diaphragm shears are to high to add a metal roof (upwards
> of 4klf) and the walls won't support a topping slab.  We have talked
> about adding plates along the flange joints.  Simply place (2) or (3)
> bolts vertically through the top flange of each double tee and a common
> plate, then place each of these at say 4ft on center.  Unfortunately, in
> my mind this is the same style of connection and gets me nowhere.  A
> second thought, the PCI book I referred to earlier has a design
> methodology for doing a diaphragm without a topping slab.  I just can't
> find a reference in the UBC to let me use it.

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Michael Valley                                   E-mail: mtv(--nospam--at)
Skilling Ward Magnusson Barkshire Inc.                  Tel:(206)292-1200
1301 Fifth Ave, #3200,  Seattle  WA 98101-2699          Fax:        -1201