Designing column bases

Transcript

Designing column bases in ILX Connection. We will design a base plate on a concrete pier, then look at embedded and braced-frame bases.

Start a base plate

Open the New connection wizard, and pick Base plate in the Column bases group. Choose the column, enter the dead and live loads, and pick how the shear reaches the concrete: friction, a shear lug, or the anchor rods. Our example is a W12 column with a moment, carried by a shear lug.

Loads

In the editor, the Loads section holds the axial load, the moment, and the shear. Here we also have a smaller moment about the weak axis, so the base is designed for biaxial bending. Leave those minor-axis values at zero for a simple, one-direction design. ILX Connection builds the load combinations for you. You can also enter required strengths, ASCE 7 components, or your own load cases.

Plate, rods and shear lug

Set the plate size, then the anchor rods: the grade, diameter, spacing, and embedment. In Shear transfer, size the shear lug and its weld. ILX Connection checks the lug, the weld, and the concrete in front of it. The elevation shows the lug, the grout, and the rods to scale.

Checks and auto-design

Our first try does not pass. The status bar shows that plate bending governs, and the failed check tells you why. Click Auto-design. It searches the plate thickness, the rod diameter, and the embedment, and lists the designs that work. Apply the best one, and the base plate is adequate.

Biaxial bending

With moments about both axes, the plan view outlines the bearing zone under the plate. A biaxial check combines the two directions, following Design Guide 1.

Concrete pier

Next, the concrete pier. In the Concrete pier section, tick Design concrete pier. ILX Connection picks the vertical bars and ties, checks the pier for axial load and bending in both directions, and keeps every bar clear of the anchor rods. The pier gets its own drawing sheet, with an elevation, a section, and a top view.

Anchor reinforcement

When the concrete breakout needs help, add anchor reinforcement. Let the pier bars and top ties do the job, or design hooked bars around the rods in the Concrete support section. ILX Connection checks where the bars sit and how far they are developed, and circles the bars it uses on the top view of the pier.

Seismic: weak or strong base

For seismic design, choose a weak base or a strong base. In a weak base, the anchor rods are the part that yields. Enter a reduced shank and a stretch length. The concrete is then designed for the full strength of the yielded rods, so watch the breakout and pullout checks. Here the breakout no longer passes, so the next step is anchor reinforcement. With a strong base, the base plate is designed for the full moment strength of the column instead.

Embedded column base

When the column is set into the footing, use the Embedded column base. In Type I, the column flanges bear sideways on the concrete to hold the moment. Type II adds an embedded base plate that also bears down on the concrete below. ILX Connection reports the required embedment depth, and you can add face bearing plates, anchor rods, or attached bars.

Braced-frame base

At the foot of a braced frame, use the Braced-frame base. Enter the brace force, the face the gusset is welded to, and the work point height. ILX Connection splits the brace force between the column and the plate, then checks the brace, the gusset, the welds, and every base plate check.

Sheet and report

Every base prints a drawing sheet with your title block, and a calculation report with the code references for each check.

To learn more, open the user manual from the help button in any section. Try it at ilxconnection.com, or write to us at support@ilxstudio.com. ILX Studio, LLC is not affiliated with AISC.