3. Method of solution in spColumn
Two options are provided in spColumn for where the engineer can design a new column by selecting the shape and reinforcement (Run Option: Design), or investigate an existing section with known bar arrangement (Run Option: Investigation)
In the Design run option, the reinforcement ratio cannot be less than 1.0% if Structural column type is selected in design criteria and 0.5% if Architectural column type is selected. For Architectural type, the capacity of the designed column is reduced as described above. Additionally, User Defined column type is provided in the design criteria, which allows designs with reinforcement ratios not less than 0.1%. No reduction in capacity is applied for User Defined column type. The following figures shows the dialog windows for column design criteria.
Figure 1 - Selection of Column Type (Structural) in design mode (Design Criteria)
Figure 2 - Selection of Column Type (Architectural) in design mode (Design Criteria)
Figure 3 - Selection of Column Type (User-defined) in design mode (Design Criteria)
3.2. Column Investigation Option
In the investigation run option the program will calculate the capacity for any provided area of reinforcement. However, if the reinforcement area falls below the code-specified minimum of 0.01 times the gross area, Ag, then spColumn will issue a user note requesting a decision to determine the column treatment as Architectural or user-defined as shown below.
Figure 4 - spColumn user note when reinforcement ratio is less than 1% in investigation mode
By default Architectural option is selected for which the capacity of the section is reduced. For the ACI codes, the reduction results from multiplying the maximum concrete stress, fc’, by the ratio of reinforcement area to 0.01Ag. This produces the same effect as reducing the effective concrete area to achieve ratio of reinforcement 1.0%. For the CSA standards, the factored axial and flexural resistances are multiplied by ratio 0.5 (1+ ρt / 0.01).
For user-defined option, the section is treated “as is” without any reductions in capacity. This option is provided for informational purposes only, since the capacity of compression members with reinforcement area less than 0.01Ag has to be reduced and areas below 0.005Ag are not allowed by all codes supported by spColumn.
A 24 in. square column is used to illustrate spColumn interaction diagrams superimposed for both column design criteria showing the impact of capacity reduction for the Architectural (oversized) column type. The structural column interaction (with ratio under 1%) is shown by spColumn for information only since it is not sanctioned by code provisions for column section. However, the diagram may be informative for non-column structural members where lower reinforcement ratios are permissible such as walls where the permissible vertical reinforcement ratio can be as low as 0.12% (ACI 318-19 Table 11.6.1) or in oversized beams and diaphragm slabs where reinforcement ratio can be as low as 0.18% (ACI 318-19 24.4.3.2).
Figure 5 - Superimposed Architectural and User-Defined Factored Column Interaction Diagrams