I am trying to perform an analysis on an existing two-way concrete slab supported on each side by deep concrete grade beams using STAAD.
Background Info:
As part of a rehab project, a large section of the two-way slab needs to be cut-out and replaced; but the floor needs to remain operational during repairs. As such, steel beams will be placed directly underneath the bottom of the slab around the cut-out and connected to the deep concrete grade beams. In order to make the repairs easier and cheaper, the slab will sit directly on-top of the steel beams without any attachments between the two to resist negative (upward) bending of the slab.
STAAD Model Info:I have modeled the concrete grade beams and the steel beams as well as 1'x1' plate elements (XZ Plane) representing the 12" thick slab. I used the offset command to set the top of the steel beams equal to the top of the concrete beams. Each beam has a node every 1' which sits directly underneath a corresponding plate/slab node. All of the slab/plate element nodes are 6" above the beam nodes in the Global Y direction to represent the center of slab elevation.
Is it possible to connect the concrete slab plate nodes to the steel beam nodes using the Master-Slave Command in the FY direction?
I am concerned about using this command because the slab is only bearing on the steel. I do not want the STAAD analysis to assume a composite connection with studs that would cause the steel beam to bend upwards with the slab in regions of negative moment. I only want the master-slave command to function in the (-)FY direction. Possible?
Would the appropriate master-slave command be RIGID to connect the existing slab which is doweled into the existing grade beams?
Dear Sye,
I am having the similar question regarding the use of compression only dummy members.
Background info
I am modelling tunnel rings, in which some tunnels are broken, and the hoop force should be transferred to the steel lintels, then to to the steel curve beams as well as the picture frame, then to the adjacent complete ring. The steel curve beams located at the intrados of the tunnel, will bear against the adjacent tunnel lining, but no physical connections between them. Thus, if the adjacent tunnel lining wants to deflect outwards, the steel curve beams will not provide any restraint to it.
Staad model info
The structure is model as per actual width of the tunnel,1.6 meter (loading, beam width, spring stiffnes, etc.) The tunnel rings are supported by compression only springs. To allow load transfer from the broken ring to the lintel of internal steel frame (half moon frame), I have created 2 dummy beams to allow load transfer. The dummy members are with high stiffness, zero density and with a cross sectional radius of 0.005m.
The curve beams are connected to the complete ring through dummy beam members too. The following is what I have tried and issue I am facing:
Model dummy beam elements - compression only
When I model the dummy elements connecting between the complete ring and the curve steel beam using compression only high stiffness member, the model has instability issue and go out of whack. In the results, a few compression only members are detached from the tunnel ring and I suspect this has something to do with the spring supports applied to the tunnel lining as well.
Model dummy beam elements - end moment released (partial 0.99)
I have also tried to consider the dummy elements with end moment released. There will be no instability issue, negligible bending moment and shear force in the dummy elements, which is fine but some dummy elements has tension in it, which means, the internal steel frame is restraining the complete ring from deflecting or vice versa, the tunnel ring is dragging the internal steel frame out, causing some bending moments on the steel frame. This is not true as they do not have any connections to provide this tension capacity (only pure bearing and contact).
In my mind, I still think that using compression only members would be the right choice, but the instability issue could not be solved.
Below are some figures of the results of using compression only dummy members:
Below are some figures of the results of using end moment released dummy members:
Appreciate if you can give some advice sir. I would be happy to attach my model if it is helpful for further checks or verification.