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RE: Seismic Joint + ETABS

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Jim,
I am still not sure if I see this clearly. As a matter of fact you may not even need to have walls on both sides of a seismic joint.
Anyway here are some general concerns:
1- The difference in vertical deflection of two slabs (one having a rigid wall at the edge, the other one nothing or a beam?) may bend the straps and interfere with the load transfer
2- The force at an angle may activate "the flexible anchorage" and bend the strap jeopardizing its capacity to transfer the load
3- With eccentricity between the center of mass and rigidity in direction perpendicular to the wall, it will be difficult to model the diaphragm such that this wall does not contribute to resisting the torsion while resisting the force in other direction (not a problem if you are doing it manually)
3- Even if this strap works fine in the first and second mode I am not sure about its behaviour in other ones.
 
Of course everything will be worse if you have a structure with plan and vertical irregularities. So generally speaking and without checking out the actual detail and connections I keep the right to think twice (or maybe more, at least as many times as the no. of major modes!<) before using such connection.
 
Reza Dashti P.Eng
Vancouver, BC


Subject: RE: Seismic Joint + ETABS
Date: Wed, 23 Aug 2006 07:56:16 -0400
From: jgetaz(--nospam--at)shockeyprecast.com
To: seaint(--nospam--at)seaint.org

From: "Reza Dashti Asl" <rezadashti(--nospam--at)hotmail.com>

To: seaint(--nospam--at)seaint.org

Subject: RE: Seismic Joint + ETABS

 

Jim,

 

So if the seismic force applies at an angle to the seismic joint, then these

straps have to transfer the component of the load parallel to the wall

(without excessive deflection or deformation) across the joint and at the

same time move freely (perpendicular to the joint) without resisting the

other component and deflect as required. Would you please elaborate? Are we

talking about concrete shearwalls and considerable shear loads?

 

Thanks,

Reza Dashti P.Eng

Vancouver, BC

 

>From: "Jim Getaz" <jgetaz(--nospam--at)shockeyprecast.com>

 

>We have also designed straps that carry horizontal load across a seismic

>joint to a shearwall on the other side, rather than having back-to-back

>shearwalls.

 

            Reza,

                        I work in SDC B, and sometimes A, which I assume is much less than Vancouver.

                        Rather than build concrete shear walls on each side of a seismic joint, we have built one on one side. We reach across that joint with straps (threaded rod or bar) that are nearly parallel to the joint, so they are rarely as short as 2’, but usually at least 3’-4’ across a 2”-3” joint. They have flexible anchorages on their ends. So we assume they carry axial load across the joint (mostly parallel), but rotation at the ends occurs before any appreciable restraint perpendicular to the joint does.

                        Is this a valid scheme? We have not had any earthquakes of a design magnitude in the years that we have been doing this. Since we usually leave those for you all on the west coast, we may never know. :-)

            Jim Getaz

            Winchester, Virginia



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