Material and Section Effective Stiffness Factors 

1. “Elasticity Modulus”, "Axial Area", "Bending Stiffness", “Shear Area” and “Torsional Constant” of member groups can be scaled by using the coefficients.
   
2. Values less than “1” will reduce the related parameter whereas values greater than “1” will increase its value.
   
3. Values in grey cannot be modified, there are auto-calculated. 

Storey Degrees of Freedom

There is a list for defining the degrees of freedom for each storey. Storey degrees of freedom options in ProtaStructure are:

1. X/Y and Torsion Permitted: Translations in X and Y directions and floor torsion about Z-axis are permitted.
   
2. X/Y Permitted, Torsion Prevented: Translations in X and Y directions are permitted. But torsion about Z-axis is prevented.
   
3. Only X Permitted: Only translation in X direction is permitted. Translation in Y direction and rotation about Z-axis are prevented.
   
4. Only Y Permitted: Only translation in Y direction is permitted. Translation in X direction and rotation about Z-axis are prevented.
   

The last two degrees of freedom options are useful for the analysis of a 2d-frame system defined along the unrestrained direction.

You can select the  “Only X permitted” or the ”Only Y permitted” options to define the degrees of freedom of a single frame system

Storey Degrees of Freedom

Rigid Zones (for concrete members)

Rigid zones formed at the “Column-beam” intersections are taken into consideration automatically by the program in the analysis model. Rigid zones are important in determining the effective lengths of concrete members. Hence, for steel structures, always set no rigid zone (none). 

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 Analysis Model has the following rigid zone options:

1. “Maximum” 
   
2. "Reduce by 50%"
3. “Reduce by 25%” 
   
4. “None” 
   

For a detail analytical comparison on the rigid zones options, refer to Rigid Zone Interpretations

Beam Section

Using the radio buttons located in this section, flanges of the beam can be taken into account in the building model.

Soil-Structure Interaction

This feature enables foundations to be integrated into building analysis model for more accurate assessment of building behaviour.  For example, effects of how the settlement of foundation will influence the forces in the superstructure members can be investigated.

This feature can be accessed by selecting Merged Foundation Model under Soil-Structure Interaction.

The following are the steps to use Merged Foundation Model :

1. Model the superstructure and the foundation in ST00
   
2. Run Building Analysis
   
3. Go to ST00 (Foundation Level)
   
4. Run FE Raft Foundation Analysis
   
5. Re-run Building Analysis
   
6. Examine the behavior of the structures in Analytical Model and Result Display.

Soil spring stiffness/Soil Subgrade Coefficient can be adjusted locally in the properties of each raft foundation panel or globally in the FE Raft Foundation Analysis Parameters.

ShearWall Model

Slab Model

Parameters related to slab model consideration such as rigid diaphragm and meshing can be changed in Slab Model tab.

Storey Diaphragm Model

Under the excitation of lateral loads, it must be specified whether the slabs in each storey level will behave infinitely rigid in their plane (i.e. rigid diaphragm action) or not. This behaviour is generally modelled as “Rigid Diaphragm”.

By assuming rigid diaphragm action in a storey level, degrees of freedom are reduced to translation X and Y directions and a torsion about Z axis normal to the plane of X and Y. There will be no axial deformation in the beams residing in rigid diaphragm.

If “Slabs To Define Rigid Diaphragm” option is selected, rigid diaphragms will be created by examining the continuity and neighbourhood of slabs both in horizontal and vertical directions. If two or more slab groups do not touch each other directly or by means of other intermediate slabs, each of these groups will form a separate rigid diaphragm. There may be nodes that do not touch any of the slabs. These nodes, then, are defined as free nodes and they do not belong to any of the diaphragms.

“Single Diaphragm per Floor Level” option forces the whole storey level to behave like a rigid diaphragm even if there is no slabs defined.

If “No Rigid Diaphragm Floor Levels” option is selected, rigid diaphragm action is not utilised in the analysis. All nodes in the storey levels will be accepted as free nodes. If there are big openings in the floor (approximately greater than 1/3 of total floor area), it will be difficult to expect a rigid diaphragm action. Then this option should be used in the analysis.

By default All Storeys are checked to assume the slabs to define rigid diaphragm. If All Storeys is unchecked, then you have the choice to pick which storeys to consider diaphragm. Storeys which are unchecked will assume No Rigid Diaphragm.

Include Slabs in Model - Finite Elements Mesh

Checking Include Slabs in Building Model enables meshed slabs to be considered together with the building analysis, i.e. the stiffness of the slab can be considered acting together with the frame elements (beams, columns and walls). This is a useful feature if you are modelling transfer plates where walls and columns may sit directly on a slab or you wish to look more closely at the interaction of the slab together with the frame. The meshing will also allow slopes and drops (or more unusual geometry) to be considered.

This option can be found in a the tab “Slab Model” in the Building Analysis tab :

The following is the explanation of the Slab Model Tab :

1. Storey Diaphragm Model options work as previous section. If No Rigid Diaphragm is chosen, then semi-rigid diaphragm will be considered based on the In-plane (Membrane) Stiffness value entered under Slab Stiffness Coefficients.
   
2. If Include Slabs in Building Model is checked,  one can specify which storeys to include by clicking on Storeys to be Meshed button.
   
3. The mesh uniformity can be controlled by specifying different Min. And Max. Shell Size.
   
4. “Yield Line” or “FE Load Decomposition” can be completely ignored by unchecked Use Decomposed Slab Loads
   
1. In this case, only self weight, beam wall loads and additional correction loads are applied on beams.
   
2. Slab self weight, live load and additional dead loads are applied on shells as “Shell Pressure”
   
3. Patch Load, Line Load and Point Loads are auto-calculated and applied on the mesh.
   
4.  Include Column Sections in FE Model allows rigid perimeter of the column to be considered. The slab  will be meshed to the perimeter of the column rather than the centreline. 
   
1. This option is specifically for flat slab system only. If the model has beam slab layout, please uncheck this option.
   
2. This option introduces meshing complexity. If there are meshing errors, kindly uncheck this option & re-run analysis. 
   

Use Decomposed Slab Loads and Ribbed Slab Loads in Meshed Storeys should be unchecked in analyzing the model which consist of flat slab system, transfer slab system and irregular slab system. 

For

1. Slab Stiffness Coefficients > In-plane (Membrane) for slab shells can be changed :
   
1. This option can simulate semi-rigid floor diaphragms. To activate it, “No Rigid Diaphragm Floor Levels” should be selected.
   
2. If “Storey Diaphragm Model” is considered (i.e. set to either “Slabs to Define Rigid Diaphragm” or “Single Diaphragm per Floor Level”), the membrane stiffnesses will be ignored since the shells will be infinitely rigid in-plane.
   
3. If a value of “0” is entered for membrane stiffness, “No Rigid Diaphragm” option should not be selected. Otherwise, there will be instability in the analysis.
   
2. Slab Stiffness Coefficients > Bending Stiffness (out of plane) for slab shells can be changed :
   
1. Minimum value for Bending Stiffness multiplier is “0.01”. In this case, the bending contribution is practically ignored.
   
2. This stiffness is applied only applied to uncracked load cases, not cracked load cases. 
   
3. If cracked load cases are used, then please modify the stiffness in Material and Section Effective Stiffness Factors. 
   
4. For more explanation on stiffness modifiers refer this article: Effective Stiffness Modifiers 
   

When you decrease the slab in plane and bending stiffness, the deflection of slab will be larger as the slab is more flexible or less stiff.

BENDING STIFFNESS: If you set the bending stiffness to i.e. 0.01, the supporting beam design moment will be also larger as the restraint from the slab is smaller. In this case, the beam design moment shall be very close to the floor without meshing (with the slab load decomposed using the “Load decomposition by FE” method).

IN-PLANE STIFFNESS: If you set the in-plane membrane stiffness lower, the lateral stiffness of the slab will also be lower, i.e. the slab is more flexible in horizontal direction. In this case, you will expect higher lateral deflection.

1. Ribbed and Waffle slabs can be included. Only beams are considered; the plates are included as UDL. 

The result of the analysis can be viewed in the Analysis tab> Analytical Model . You can use various icons in to view displacement, member or shell forces graphically.