Shear flow on reinforced steel joists
Shear flow on reinforced steel joists
(OP)
I was not able to find an answer on the other (numerous) threads on shear flow, hope you guys can help.
I am in the process of designing the welding for reinforcing of existing joists. See attached sketch (sketch does not show new web members that will be connected to the new chord reinforcing angles). The reinforcing angles will be welded to the existing angles through a fillet weld at the horizontal and vertical leg.
I have designed cover plates for wide-flange beams in the past, so I am familiar with shear flow (VQ/I). However, I am a confused about its application when it comes to joist reinforcing.
The maximum NEW shear force that will need to be transferred from the existing chord to the new angles (at joist ends) is 30 kN.
-When calculating the first moment of area, should I be treating the top chord as its own section, therefore taking the neutral axis of the reinforced/combined top chord instead of the neutral axis of the whole joist?
-When calculating the first moment of area at the vertical leg fillet weld, should I only take the area of the existing angle above the fillet weld times the distance from the center of the existing horizontal leg to the neutral axis of the reinforced/combined top chord, or the entire area of the existing angle times the distance from the neutral axis of the existing angle to the neutral axis of the reinforced/combined top chord?
-The above calculations will tell me how much welding is required between the reinforcing angles to the existing top chord at the joist END. What criteria should I use to weld at panel points closer to mid-span, or to weld between panel points (if the latter is even required)?
Thanks all.
I am in the process of designing the welding for reinforcing of existing joists. See attached sketch (sketch does not show new web members that will be connected to the new chord reinforcing angles). The reinforcing angles will be welded to the existing angles through a fillet weld at the horizontal and vertical leg.
I have designed cover plates for wide-flange beams in the past, so I am familiar with shear flow (VQ/I). However, I am a confused about its application when it comes to joist reinforcing.
The maximum NEW shear force that will need to be transferred from the existing chord to the new angles (at joist ends) is 30 kN.
-When calculating the first moment of area, should I be treating the top chord as its own section, therefore taking the neutral axis of the reinforced/combined top chord instead of the neutral axis of the whole joist?
-When calculating the first moment of area at the vertical leg fillet weld, should I only take the area of the existing angle above the fillet weld times the distance from the center of the existing horizontal leg to the neutral axis of the reinforced/combined top chord, or the entire area of the existing angle times the distance from the neutral axis of the existing angle to the neutral axis of the reinforced/combined top chord?
-The above calculations will tell me how much welding is required between the reinforcing angles to the existing top chord at the joist END. What criteria should I use to weld at panel points closer to mid-span, or to weld between panel points (if the latter is even required)?
Thanks all.






RE: Shear flow on reinforced steel joists
RE: Shear flow on reinforced steel joists
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Shear flow on reinforced steel joists
Regarding your last sentence:
"What criteria should I use to weld at panel points closer to mid-span, or to weld between panel points (if the latter is even required)?"
I have found buckling in the reinforcements to occasionally govern weld spacing at the compression chord.
RE: Shear flow on reinforced steel joists
Link
Link
If you've got $30 kicking around, this is an excellent summary of the state of the art: Link
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Shear flow on reinforced steel joists
The maximum NEW shear force that will need to be transferred from the existing chord to the new angles (at joist ends) is 30 kN. provides the total weld requirement between each end reaction and the point of zero shear. The distribution follows the shear diagram for the joist. Welds can be restricted to panel point locations if buckling is not a problem but could be more closely spaced if preferred.
The weld capacity at each panel point is equal to the change in horizontal component of each web member.
BA
RE: Shear flow on reinforced steel joists
Your second link does not appear to be a valid address and/or link. Anyway it won't display. Maybe the problem is on my end. The first link displays fine as does the third link.
Jim
RE: Shear flow on reinforced steel joists
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Shear flow on reinforced steel joists
Still doesn't display. I assume it is another Jim Fisher presentation or his Joist Book.
Jim
RE: Shear flow on reinforced steel joists
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Shear flow on reinforced steel joists
Thanks,
Jim