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Re: Steel Terminology

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The about-to-be-released, new, but in my opinion, not-improved, ACI 302 has a detail of what they are calling a "pin-wheel joint."  The text below is mine,  the ACI 302 document just has a detail,  no accompanying text.


Columns are typically supported on separate footings because the loads they support are much higher than what the slab is designed for.  Because of the heavier loading, they are likely to settle more than the adjacent floor slab and should thus be isolated to prevent damage to the adjacent slab.  Column footings can be isolated from the floor slab with either circular or square isolation joints. Circular isolation joints are usually made with a wax-covered cardboard form; square isolation joints are often formed with wood.  The cardboard or wood is removed after the slab concrete is cast, and replaced with joint material.  Square isolation joint should be rotated 45 deg so that the corners align with contraction and construction joints. This can result in a fairly large slab blockout, however, and some designers chose to use a "pin-wheel" joint with wide-flanged steel members.  

To create a pin-wheel joint, concrete is placed in the area between the flanges and troweled smooth. In facilities such as food processing plants, the concrete between the flanges is typically sloped up to the column, to avoid trapping dirt and debris; this is sometimes referred to as a column wash.  The column is then wrapped with compressible isolation joint material and the remainder of the slab is placed. Contraction joints are cut on alternate sides of the column. The joints in both directions are offset by the column dimensions, resulting in a layout that resembles a pin-wheel. Offsetting the joints in both directions avoids creating any re-entrant corners but can be difficult to lay out in large block construction such laser screed placements.

Gail Kelley

In a message dated 5/3/2004 4:50:16 PM Eastern Daylight Time, Mlcse(--nospam--at) writes:

I am not aware of anyone doing this for steel columns, filling the area between the steel flanges and then wrapping the column prior to placing the slab-on-grade.