industrial building using staad.pro

This question brings up many excellent points about modeling and setting design parameters in STAAD.Pro.  Refer to the image below: 

Assume that this structure has metal wall panels that will transmit wind loads to the steel framing, but will be considered ineffective in resisting lateral loads through shear wall action.  One approach to modeling this condition would be to create Wind Definitions and Wind Load Cases, and allow STAAD.Pro to automatically generate wind loads, which will we applied to the nodes of the model.  Another approach would be to create a mesh of plates that span between the girts, assign the IGNORE STIFFNESS specification to those plates, and apply plate pressure loads to the plates to represent the wind pressures.  The IGNORE STIFFNESS specification will instruct the program to consider the plates ONLY for the purpose of distributing the wind pressures to the supporting framing, but to ignore the plates when the stiffness matrix is formed, so the plates will not provide any resistance when the model is analyzed.

Regardless of the method used to apply the wind loads, there will always be the issue of verifying/assigning the appropriate bracing parameters when it comes to design.  For example, in the model illustrated above, we might want to indicate that:

• the buckling length of the columns about their weak axis should be set to the distance between the purlins,
• the buckling length of the columns about their strong axis should be set to something approaching the full height of the column,
• the unbraced length (for bending) of the column flange that is in contact with the metal siding should be set to some value that corresponds to the spacing of the connections between the siding and the column, and
• the unbraced length (for bending) of the column flange that is toward the inside of the building should be set to some value that corresponds to the spacing of the girts (if engineering judgment dictates that the girts are effective at bracing the inside flange).

All of these design decisions are indicated by the assignment of design parameters like Ky, Ly, Kz, Lz, UNT, UNB, etc.

Regards,

Chris

This question brings up many excellent points about modeling and setting design parameters in STAAD.Pro.  Refer to the image below: 

Assume that this structure has metal wall panels that will transmit wind loads to the steel framing, but will be considered ineffective in resisting lateral loads through shear wall action.  One approach to modeling this condition would be to create Wind Definitions and Wind Load Cases, and allow STAAD.Pro to automatically generate wind loads, which will we applied to the nodes of the model.  Another approach would be to create a mesh of plates that span between the girts, assign the IGNORE STIFFNESS specification to those plates, and apply plate pressure loads to the plates to represent the wind pressures.  The IGNORE STIFFNESS specification will instruct the program to consider the plates ONLY for the purpose of distributing the wind pressures to the supporting framing, but to ignore the plates when the stiffness matrix is formed, so the plates will not provide any resistance when the model is analyzed.

Regardless of the method used to apply the wind loads, there will always be the issue of verifying/assigning the appropriate bracing parameters when it comes to design.  For example, in the model illustrated above, we might want to indicate that:

• the buckling length of the columns about their weak axis should be set to the distance between the purlins,
• the buckling length of the columns about their strong axis should be set to something approaching the full height of the column,
• the unbraced length (for bending) of the column flange that is in contact with the metal siding should be set to some value that corresponds to the spacing of the connections between the siding and the column, and
• the unbraced length (for bending) of the column flange that is toward the inside of the building should be set to some value that corresponds to the spacing of the girts (if engineering judgment dictates that the girts are effective at bracing the inside flange).

All of these design decisions are indicated by the assignment of design parameters like Ky, Ly, Kz, Lz, UNT, UNB, etc.

Regards,

Chris