What is the difference between General Column Design and the other concrete column design modules? Which module should I be using?
PROKON has three concrete column design modules: Rectangular, Circular, and General Column Design. The latter is versatile for various shapes but may not be the optimal choice for every situation.
The Code Approach to Column Design
Design codes simplify axial force and bi-axial bending interaction for concrete columns. For a slender column, increase design bending moment with slenderness moment. Account for biaxial bending using an interaction formula. Determine required reinforcement, ensuring it falls within specified limits. This approach suits regular shapes (rectangular, circular) and allows for the creation of design charts for quick reinforcement value reference.
PROKON’s Approach to Column Design
Designing Columns of General Shape
The General Column Design module adapts to code limitations by assessing column slenderness, determining the weakest axis, and incorporating additional slenderness moments. It analyzes specified reinforcement for compliance with stress-strain compatibility and code limits, offering versatility for various column shapes.
The program iteratively analyzes the column section, aligning the neutral axis perpendicular to the design moment for equilibrium with axial force and bending. It can also consider non-perpendicular orientations for a more conservative design. Analyses are conducted at top, middle, and bottom locations for each load case, using the rectangular stress block method for compressive concrete and neglecting tension. Reinforcement bars work in tension or compression based on their position within the cross-section.
Interpreting the Design Results
The General Column Design module calculates a safety factor for design loads, graphically represented on a column design curve. A safety factor around 1.0 indicates an optimal design, while values below 1.0 require increasing bar size or quantity. Conversely, reducing reinforcement may be considered for safety factors significantly above 1.0.
Estimate required reinforcement by dividing entered reinforcement by the safety factor (SF):
As,req = As / SF
Note: Accuracy may vary if the safety factor significantly deviates from unity.
Comparing Design Results
The General Column Design module may yield different results compared to Rectangular and Circular Column Design, particularly for slender columns. Key factors include the module's calculation of additional moments for the weakest axis only, as opposed to adding moments to one or both main axes in the code method. Additionally, the module employs a rational approach for stress distribution, differing from some codes that use a simplified procedure with an inflated effective design moment.
Recommended Use of The Column Design Modules
For simple rectangular and circular columns, it's advisable to use the dedicated Rectangular and Circular Column Design modules instead of the General Column Design module. These dedicated modules align with code procedures, provide clear design steps in Calcsheets for easy auditing, and streamline the reinforcement process. The General Column Design module, while versatile for any column shape, requires entering reinforcement during input and may involve multiple design attempts, making it more time-intensive. For standard columns, the specialized modules offer productivity and easy auditing, reserving the General Column Design for unique situations or irregular shapes.