Columns

Background

The Concrete Column overview outlines the key properties, reinforcement, loads, and capacities calculated in the summary. You can learn how each of the properties are calculated within your calculation by opening your project in detailed view, or by selecting the arrow on the side of the widget to view the equations, references and descriptions in debug mode.

Project default values can also be used to link code standards, defined default loads, properties, or design criteria so that defined values are automatically pulled to your beam design. You can also check out a video for the calculator overview here

Key Properties

The column geometry and concrete strength can be defined under the key properties. You can specify the total height, or length of the column here. The buckling length factor for both the x and y axis can also be specified. A buckling length factor of 1 is generally conservative for non-sway frames and nonconservative for sway frames.

Reinforcement

The longitudinal reinforcement can be defined by specifying the bar size and reinforcement strength. By default, the calculator considers one bar at each corner. To add more reinforcement along the edges, you can specify them under the “Additional Reinforcement Bars (per side). For example, if we wanted 4 bars along each of the faces, you would input 2, since one bar is already counted at the corners. The concrete cover also needs to be defined, this should be a minimum of 1.5 in, as per ACI 318-19. The minimum size and spacing for ties are also calculated.

Loads

ClearCalcs has a variety of loading conditions that can be entered. To start, we can specify a default load eccentricity for bending about the X-axis, or we can manually change this value per load in the table. The Axial & Moments Loads about X-axis table takes into account the unfactored load conditions. These can be defined as dead, live, snow, or wind loads for example, and can be applied as a vertical load or a moment load. The location these are applied at is measured from the bottom of the column. There is also an option to use the reduced companion live load (refer to IBC Clause 1605).

The ratio of end moments can also be defined in these properties. This is a way of comparing bending moments at each end of the column, where a column with single curvature (i.e. a beam) indicates a negative ratio, and a column with double curvature (i.e. a shell) has a positive ratio, since the moments at each end are rotating in the same direction. This ratio should always be between -1 and 1. This ratio in particular impacts the calculation of slenderness effects and moment magnification.

Y-Axis Moment Loads

This input works the same way as the table for loads in the X-axis, however should consider that these will be applied in the perpendicular direction. Any axial loads defined here will be added together with the axial loads entered in the equivalent table for X-axis loads.

Results

In our summary, we can see axial and moment loads are computed, with the interaction checks and biaxial bending checks also being carried out. All capacities are factored in the summary, based on the strength reduction factor. Our graphed load combinations are shown as well.

The pure axial load capacity considers the squash load and other factors. This is for non prestressed members, taking into account the concrete strength and area, added to the steel yield strength and area.

The axial interaction capacity looks at combined axial and bending, taking the sum of forces from concrete and the reinforcement. ClearCalcs checks for this in both the X and Y directions. Next, we have moment capacity checks in both directions, where the nominal column capacity is multiplied by the eccentricity distance.

The bi-axial bending is checked as per the Bresler method, which only applies when the design axial load is under 10% of the squash load.

A passing design will be indicated with a utilization below 100%. If your design is failing, you can hover over the error to see where exactly the error is occurring. To increase capacity, typical solutions include using larger column dimensions, higher concrete strength, or more reinforcement.