Doubler plate is also called as "doublers". Generally, in moment connection doubler plates are the plates which are welded to column web. And continuity plates are welded to column flanges adjacent to beam flanges.
In steel moment resisting frames, the region of the column located within the beam-column joint is known as the panel zone. When a steel moment resisting frame is subjected to lateral load, due to wind or seismic loads, the panel zone is subject to high shear.In this article, you will learn about the application of doubler plates, and various considerations in their design.
Doubler plates
In moment connection, when the flanges of a beam is connected to a column they form a force couple which causes the column to twist. If the column web is too thin to handle that unbalanced load then it will fail through tearing or buckling. In order to prevent this failure on connections use of web doubler plates are necessary. These plates are applied directly to the web, and welded all around.
When using these plates they are considered to increase the column web thickness, which in turn increases the panel zone shear capacity significantly. Doubler plates can be a costly feature in steel moment resisting frames because of the substantial amount of welding involved. Therefore, designer often a design featuring a column with a thicker web is ultimately cheaper.
Continuity plates
In steel moment connection, columns are subjected to unbalance moment that is transmitted into the joint through a couple of concentrated forces at the centroid of the beam’s flanges. If the flexural capacity of the column flange is less than produced moment by these tensile or compressive forces, use of continuity plates in the panel zone is necessary.
Doubler plates welding
- (a) CJP groove weld detail.
- (b) Fillet welded detail with plate bevel equal to plate thickness.
- (c) Fillet welded detail with plate bevel less than plate thickness.