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RE: Concrete plank - weld plates

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The plank manufacturer is correct! This seems to go against your intuition of fastening everthing down and the more the better. In the 50's, many precast buildings (with multiple bays) had structural problems where plank were welded down at both ends. 
This is generally not too much of an issue with temperature but much more a problem with axial shortening. Any member that is pretensioned or post tensioned will undergo long term creep (axial shortening) because of the high stress in the tendons. If welded down at both ends, the stress will build up enough to damage one or more ends of the plank or its supports.
Precasters and engineers have learned (the hard way) to weld plank at only one end and allow the movement to occur at the other. The technique that is typically used (and seems to work) is to weld alternate ends of adjacent plank. The structure can still be made stable if lateral forces are able to be adequately transfered to all weld plates thru the grouted joints between planks and/or the topping.
I hope this helps!
Jim K.
 -----Original Message-----
From: hadiprawira djohan [mailto:hadiprawira(--nospam--at)]
Sent: Thursday, January 05, 2006 8:18 AM
To: seaint(--nospam--at)
Subject: Concrete plank - weld plates

Fellow Engineers,
From what i encountered in the past, If a plank is resting on top of a steel beam, the plank is ussualy tack welded to the top flange at both end of the concrete planks.
Until recently, a plank manufacturer argue that the plank is only need to be welded at one end, in order to allow expansion and contraction of the building, which may result in the disloding of the weld plates and spalling of the plank.
I disagree with his argument, considering that concrete planks are located inside the building, where temperature is constantly regulated, thus no extreme expansion and contraction can occur.
Besides, 3" weld plates at every 48" plank section is not that rigid, If one is to argue that welding plank at both sides will create a very rigid structure, which may not perfrom too well in the seismic event. 
Would anyone please tell me what i am missing here? Thank you.

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