Interactive Column Design

Interactive Column Design

In the Column Reinforcement Design column sections and reinforcement arrangement can be examined and changed interactively.

Since columns and walls are the primary members of a structure, especially the critically loaded ones should be designed interactively where the user can view the results of each loading applied on the column clearly and update the arrangement of the reinforcement.

Using the Column Design Editor

The Column Design Editor can be loaded by clicking the “Interactive Design” button or double clicking a column line in the summary table.

Data fields in the Column Reinforcement Design display the geometry, loads and the reinforcement of the current selected column.

Fields in the “Column Reinforcement Design” are as follows:

Section Dimensions

Section dimensions include the dimensions of the column along “2” (horizontal axis) and “3” (vertical axis) directions (“b2” and “b3”).

Distances between the centre of the column to the intersection of the axes selected as the reference point for the column insertion (“e2” and “e3”), the column clear lengths (“L2” and “L3”), and the concrete cover.

In polyline columns, the “b2” and “b3” values show the maximum extents of the column section along the 2 and 3 directions. These fields cannot be updated in polyline columns.

If circular columns are modeled, the “Inner and Outer Diameters” will be displayed. If the circular column has a hollow cross-section, then the value in the “b3” field will show the inner diameter.

If you modify these fields, you have to click the “Update” button to apply the changes.

Load Combinations Table

Member force results from each load combination during the analysis procedure are listed in a table.

Fields in this table are:


Load combination number used in the building analysis. There are separate spaces reserved for column/wall top and bottom ends.


Axial Load Result of the related load combination


Bending moment rotate about Dir-3 axis of the column.


Bending moment rotate about Dir-2 axis of the column.


Shear Force along Dir-1 axis of the column.


Shear Force along Dir-2 axis of the column.

Load Combination

Name of the load combination

Column Result

Load Combinations

Load combination (or combinations) to be used in section design must be specified before going on with interactive section design. If you select “Select/Unselect All” option, all combinations in the table will be selected/unselected.

In this case, column section design will be performed for each selected combination and steel bars will be selected for the most critical one.
If steel reinforcement required are the same for all load combinations, the first load combination will be highlighted.

After unselecting all combinations by clicking “Select/Unselect All” option, you can select one or more combinations on the table. To select a specific combination from the table, just click on the leftmost header cell on the row of that combination. Watch the mouse pointer changing its shape when you hover on the leftmost cell. You can select multiple combinations by pressing CTRL on the keyboard and clicking on the leftmost cell. By this way, you can make the program use only these combinations during section design of the column.

One or more combinations can be stored as user-defined and its values can be modified. Steel bars can be selected for the critical one of these user-defined combinations. For this purpose, select the combinations you want to store as user-defined by the help of CTRL button on the keyboard.

Click on “Select Marked Combinations as User Defined” option. Table will now accommodate only the selected combinations. Others will temporarily go out of the view. 
You must notice that “User Defined Loads” checkbox is also automatically checked after this operation. If you uncheck “User Defined Loads” checkbox, all the combinations will be restored back on the table.

In order to modify the values of user-defined combinations, just click on the corresponding cell on the table. Values near the top edge of the cell are reserved for top end of column and the values near the bottom edge of the cell for bottom ends of the column.

For a quick modification in a cell:
  1. Users are required to input the top value first in this field.
  2. Then, insert "Comma" and a space after inputting the first value prior to input second value.
For example, you to enter 50kN as top value or 50kN as bottom value. (refer to the image below)

Arranging Steel Bars

Steel bars in the column section can be arranged by modifying the fields in the “Steel Bars” page.

In polyline columns, after making some modifications to the arrangement of the steel bars, you can use the “Reset Bars” option to turn back to the original arrangement.  

Rectangular and Circular Columns

While arranging the steel bars in rectangular or circular columns, bars to be placed as “Corner Bars”, “x-Intermediate Bars” and “y-Intermediate Bars” can be controlled separately. This option allows the user to select different bar sizes for these areas.

The “x-Intermediate Bars” are the ones that are placed through the global x-axis edge of the column. And the “y-Intermediate Bars” are the ones that are placed through the global y-axis edge of the column. The steel bars placed in the corners are considered separately. 

For example, if in the “Steel Bars” page the corner bars are shown as “1”, the “x-Intermediate Bars” are “3”, and the “y-Intermediate Bars” are “1”, then there will be 4x1 bars on the corners, 2x3 through the edges in the x-direction, and 2x1 through the edges in the y-direction. As a result, there will be 12 steel bars in the column section.  

Rectangular Column Reinforcement

In circular columns, only the “Corner Bars” field has a value. This value will show the total number of bars to be placed in the circular section.

When you modify any field in the “Steel Bars” table, such as the “Quantity” or the “Area Ratio”, the sketch on the screen will be updated accordingly.

Polyline Columns

In polyline columns, each steel bar need to be defined separately. Therefore each bar has a number to be specified.

When you position a bar in the sketch, the number of the bar will be selected in the “Steel Bars” table. Unlike rectangular or circular columns, in polyline columns bars are specified by their x and y coordinates.

Refer this article Define Merged Wall/Irregular column Reinforcement in Polyline Column Editor for steps to insert rebar for the polyline columns.

Bars Area Ratios

The “Area Ratio” values allow the user to select different bar sizes in the same section.

For example, if you specify the area ratios of the corner bars as1.00” and "0.8" for 1-intermediate and 2-intermediate bars, then the intermediate bars will be selected as R16 when the corner bars are R20.

Steel bar tab

When the design procedure is completed, steel area required will be displayed in the bottom of the Steel Bars table.

Steel Bar Sizes

According to the steel area required, bar sizes are selected by the program automatically. But all the fields in the Steel Bars Table are editable. Therefore, the user can modify the selected bar sizes by considering the steel area required.

The “Steel Area Supplied” will be updated according to changes made in the Steel Bars Table.

If you select the “Rebar Diameter” option under the “Settings” page, diameters of the bars will be written on the sketch. 

Steel Area Supplied

When the design procedure is completed, the steel area supplied will be displayed at the bottom of the Steel Bars table.

You can view the links selected for the current column in the “Links” page. When the “Links” page is selected, the edge numbers of the column will be shown in the sketch which will help you to follow the links described.

Link spacing for the supports and the span are calculated separately. If you want to use the same spacing both for the span and the supports, uncheck the “Create Support Regions for Links” option under “Column Design Settings/Steel Bars/Links“.

If you want to delete the support regions only in the current column, you can simply copy the size and spacing of the links calculated for the span to the supports in the “Shear Design” page. 

Rectangular and Circular Columns

ProtaStructure selects a “Single Link” for rectangular and circular columns as a default. But you can select any other type of link, such as “Cross Link” or “Double Links”, from the “Links Pattern” window in the “Links” page.

Polyline Columns

ProtaStructure selects some links for polyline columns considering their geometry in Polyline Column Editor. But if you want to delete these links in "Polyline Column Editor", you can select the link using the mouse > right click > Delete link (To delete the selected link) or Delete whole links (To delete all links).

Shear Design tab

Shear forces on the section and the links provided accordingly are displayed in the “Shear Design” page. The Shear Force calculated in the building analysis can be viewed in this page and these values cannot be edited.

Size and spacing of the links selected are displayed on the right side of the page. Links for the span and for the supports are given separately. Size and spacing of links can be edited on this page after checking "Edited" option.

If you press the “Calculate” button after setting a new dimension size, new spacing and link diameter will be calculated accordingly.   

The number of link legs provided in each direction are given in the “No. of Link Legs” fields. If a standard link type is selected then these numbers will be determined by the program automatically. But if you want to describe a special link, you can write the number of link legs into these fields.

Slenderness tab

A column may be considered braced in a given plane if lateral stability to the structure as a whole is provided by walls or bracing designed to resist all lateral forces in that plane. For the slenderness check of the columns, the braced condition in each direction should be determined either by the user or automatically by the program.

If you check the User Defined Bracing for Columns and Wallsoption in the Lateral Drift and Bracing option tab, then you can specify the bracing condition for the X and Y directions manually.                                                                  

Otherwise ProtaStructure checks the bracing for each direction automatically based on the drift of the storey levels. But in both situations, you can change the bracing condition for a single column in the “Slenderness” tab of the “Column Reinforcement Design” tab.
The “Effective Length Factors” and “Slenderness” are determined separately for braced and unbraced columns and additional moments will be calculated accordingly.

Settings tab

The labels to be displayed in the sketch can be controlled by the options given under the “Steel Labels” title.

Steel Labels

By default, there is no label shown on the sketch. If you select the “Rebar Diameter” option on the Settings page and turn back to the Steel Bars page, the diameters of the steel bars will be displayed in the sketch. Similarly, the sequence numbers of the steel bars in polyline columns can be viewed by selecting the “No Seq. Text” option. 

Column Reinforcement Design

To perform the reinforcement calculation, click the “Interactive Design” button in the Column Design form. Column design will be performed for the selected load combinations according to the parameters defined in this form.

All selected load combinations will be used for the design, and the one that requires the biggest steel area will be determined automatically. If you select only one load combination, the column design will be performed for that combination only.

In each load combination there are two moments and one axial load value. If the moment calculated according to the minimum eccentricity specifications of the codes is greater than the moment that comes from the load combination, then the moment calculated according to the codes will be used in that direction. 

Column Design Parameters

If the steel area required is less than the minimum steel area determined according to the “Min. Reinforcement %” given in the Column Design form, then the minimum steel area will be used automatically. Minimum reinforcement percentage can be determined for columns and walls separately in the “Settings and Parameters” menu.

You can break the iterations by clicking the “Close” button.

Column Analysis

After the determination of the column reinforcement, Column Interaction Diagrams can be prepared. Using the interaction diagrams, a better understanding of the behaviour of the column can be achieved. Column interaction diagrams can be drawn using the “Column Analysis” button.

Column Interaction Diagram

“Axial Load – Moment” and “Moment1 – Moment2” interactions can be plotted on an interaction diagram.

A slice cut, taken at any level of an “Axial Load-Moment” diagram will yield the “Moment1-Moment2” diagram, which represents the biaxial bending envelope at that level of axial load.

Biaxial Bending Envelope can be plotted for the combination specified in “Loading” list. Axial load level of the selected combination will be indicated by a black line on “N-M” diagram.

If both “M22-M33” and “N-M” diagrams are selected to be displayed on the same page by “Both” option, then, the slice taken at the combination axial load level will be plotted just under the “N-M” diagram. Besides these, you can query the moment capacity for any level of axial load by entering an axial load value into the “N:” field and pressing “>>” button.

If the column dimensions or steel pattern in directions 1 and 2 are different, then, the interaction diagrams for “Dir-1” and “Dir-2” will also be different.

Data points of the interaction curve can be transferred to a text file by clicking “Report” button. Enter the number of data points and intermediate angles of calculation in the “Print Form”.

In order to send the Interaction Diagrams to the printer, click on “Print” button.

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