yieldA36
Structural
- Jul 25, 2011
- 4
Can anyone say that how i can choose a connection in design? Is there any specific way so that i can select a joint (shear or moment) in steel frame design?
Thanks in advance
Thanks in advance
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Shear or Moment connections ??? 2
- Thread starter yieldA36
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If it is stable without the moment connection then use a pinned connection. i.e. when you have cross bracing or shear walls to provide the lateral stability then you can use pinned connections.
You tend to only use moment connections when framing action is required for stability or when you need the continuity to keep the deflection down.
Steelworks with complex fixed xonnections can cost more than double that for simple pinned construction.
These are really fundamental concepts that you should be discussing with your mentor.
You tend to only use moment connections when framing action is required for stability or when you need the continuity to keep the deflection down.
Steelworks with complex fixed xonnections can cost more than double that for simple pinned construction.
These are really fundamental concepts that you should be discussing with your mentor.
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Principally, it depends on the type of your structure. The choice of the type of structure becomes prior to choice of the connections. Then, if your conenctions are supposed to be close to rigid, you let them carry moments, therofore you design them as moment connections. If the connections are permitted for rotation, then you let them only shear forces, therefore you design them as shear conenctions. I suggest you to read some books on rigid frames, braced frames, truss structures.
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yieldA36
Structural
- Jul 25, 2011
- 4
@csd72.....thank you for your reply...But i think i could not clear my question...Before start an analysis i need to define the connection properties...That means at first i have to release the moment at joint or not...As a designer how could i know that or decide...Is there any rules or specifications....e.g. when i need to control drift of RCC building then i provide shear wall at different location....But for steel frame where i will provide moment connection? Where as primary beam, secondary beam,column,bracing etc. are connected..You know for shear connection it will required to design 1.5 times capacity of beam or girder....So how it becomes economic??
yieldA36...I'll briefly get on my soapbox about analytical compatibility...
The structure doesn't care how you modeled it in your design. Ultimately the way the connections are detailed and constructed will create the response of the structure.
Almost all connections develop some rotational resistance. Our selection of "pinned" or "fixed" in our analyses becomes an approximation.
A rigid structure is more likely to perform as analyzed than a non-rigid structure. Pinned conditions are conservative in many respects, but can be misleading. Conversely, it is sometimes difficult to achieve true fixity due to deformation at the connection.
The others have given the basics of frame type selection....
Connectegr....what's your take?
The structure doesn't care how you modeled it in your design. Ultimately the way the connections are detailed and constructed will create the response of the structure.
Almost all connections develop some rotational resistance. Our selection of "pinned" or "fixed" in our analyses becomes an approximation.
A rigid structure is more likely to perform as analyzed than a non-rigid structure. Pinned conditions are conservative in many respects, but can be misleading. Conversely, it is sometimes difficult to achieve true fixity due to deformation at the connection.
The others have given the basics of frame type selection....
Connectegr....what's your take?
- Thread starter
- #6
yieldA36
Structural
- Jul 25, 2011
- 4
Dear Ron thank you for your reply...I think this discussion obviously enrich my design philosophy ...You told " ...Pinned conditions are conservative in many respects.." and ".....The others have given the basics of frame type selection....."
So my question is what are the respects and what are the basics which should i consider...
...You told " ...Pinned conditions are conservative in many respects.." and ".....The others have given the basics of frame type selection....."So my question is what are the respects and what are the basics which should i consider...
As csd72 noted, you sometimes require moment connections to reduce deflection. A pinned connection creates a condition whereby only the member at hand is able to resist deflection. In a moment connection, the connected members also help to resist deflection.
Further, if you need lateral stability of a frame, you must either provide moment connections, knee braces, or a shear wall concept to resist lateral loads (as others noted above). It is sometimes a trade-off between the additional effort of a moment connection and the additional members required when pinned connections are used.
Further, if you need lateral stability of a frame, you must either provide moment connections, knee braces, or a shear wall concept to resist lateral loads (as others noted above). It is sometimes a trade-off between the additional effort of a moment connection and the additional members required when pinned connections are used.
A steel "shear" connection is typically modelled as a pin connection. It is not a pin connection for the following reasons:
1. When the beam rotates relative to the column, there is still a modest amount of moment placed on the column due to the stiffness and eccentricity of the shear connection.
2. A shear connection allows a limited amount of rotation. However, if that rotation amount is exceeded additional moment will be tyransferred to the column.
3. For fatigue design, a shear connection will not act as a perfect pin and fail under fewer cycles than a perfect pin (you can see this employed on older crane designs and bridge girders).
1. When the beam rotates relative to the column, there is still a modest amount of moment placed on the column due to the stiffness and eccentricity of the shear connection.
2. A shear connection allows a limited amount of rotation. However, if that rotation amount is exceeded additional moment will be tyransferred to the column.
3. For fatigue design, a shear connection will not act as a perfect pin and fail under fewer cycles than a perfect pin (you can see this employed on older crane designs and bridge girders).
msquared48
Structural
In general, the use of moment connections will give you smaller member sizes and less deflection whether it is vertical or lateral.
But remember though the famous saying that "All generalizations are not worth a da$% including this one." So take it with a grain of salt.
Mike McCann
MMC Engineering
But remember though the famous saying that "All generalizations are not worth a da$% including this one." So take it with a grain of salt.
Mike McCann
MMC Engineering
Assuming pinned connections is conserative in some respects but it is also ethical. I watched a webcast once where the presenter had built a structure and measured the deflections to be 85% of those calculated. I'm not saying you should reduce your calculated deflections by 15% but some rotational capacity at the joint is there.
Try to avoid Moment Connections in earthquake zones. Bolted connections, being more flexible tend to survive earthquakes. Shear connections, being rigid, tend to rupture during the event. I have heard of at least one building in the L.A. area that had to be torn down because the cost to repair all the ruptured moment connections would have cost too much.
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