ProtaStructure : Rigid Zone Interpretations

Rigid Zone Interpretations

In order to consider concrete cracks that can be formed in the intersections, rigid zones may be reduced by a certain amount to calculate more realistic effects. ProtaStructure’s interpretation of rigid zones in member intersections can be summarized as follows:

No Rigid zones (0%) 

When no rigid zones option is requested, all analysis programs calculate and returns the results at nodes of member ends. Generally maximum support forces are returned.

The Effective Length of the member is considered equal to the full length.

Full Rigid zones (100%) 

When full rigid zones option is requested, all analysis programs still calculate the results at nodes of member ends but returned forces/moments are those transformed to the rigid zone ends (member faces).

The Effective Length of the member is considered as below and the member stiffness is calculated using this length:-

Leff = L – (Rzi + RZj) 

Reduced Rigid zones (by 25% & 50%) 

When full rigid zones option is requested, all analysis programs still calculate the results at nodes of member ends but returned forces/moments are those transformed to the rigid zone ends (member faces).

The Effective Length of the member is considered as below and the member stiffness is calculated using this length:-

Leff = L – (RZi + RZj)x(1 – RZRed)

Here, RzRed is Rigid Zone Reduction Factor (ProtaStructure uses 0.25 & 0.5)

It should be noted that despite the fact that a reduction factor is applied, results are still returned at member face.

Verification Example

Calculations are tested on a portal frame model having 1000x250 columns at both ends of a 250x500 mm beam. All results are checked against a general-purpose analysis program SAP2000.

As seen in the figures below, depending on the size of the rigid zones, generally the results are more economical when use of rigid zones is activated. Furthermore, reduction of rigid zones may not yield to forces and moments that falls between no rigid zone and full rigid zone cases.

ProtaStructure uses the same algorithms used by most of the well-known analysis programs and results for reduced rigid zone cases fully complies with that of SAP2000 in this example as shown in Figures below.


                                     

 

  


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