Figure 5

Figure 5 illustrates my analysis: With no bearing assumed, all the load is transferred through the weld — the left half being in tension, the right half in compression. Because the weld size was rounded up to ⅝ in., the peak stress on the weld was 20.8 ksi — tension on the left, compression on the right.

Figure 6 illustrates the customer's concern: If both the weld and part of the base of the bitt were effective in transferring the compressional load, the neutral axis of the resisting force would shift to the right.

I determined that if the entire bitt base was in contact with the deck plate on the compression side, along with the right side of the welding being in compression, this shift would amount to 0.98 in.

Thus, the “leverage” on the tension portion of the weld would no longer be 6 in., but 6.98 in. — and that was the customer's concern.

What the customer had failed to realize is that with more load transferred in compression (due to bearing), there was less load that needed to be resisted in tension.

The maximum compressive force decreased from 20.8 ksi to 13.0 ksi, while the maximum tensile stress dropped from 20.8 ksi to 17.2 ksi.

Figure 6

My analysis was correct and conservative: Bearing, if it occurred, would increase the capacity of the connection and would actually decrease the stress on the weld.

The simple conclusion is that the designer need not worry about bearing in such cases. If bearing actually occurs, the stresses on the welds are reduced.

The designer could, of course, plan on such bearing and actually reduce the weld size.

However, before taking this step, it is imperative to assure bearing, and that only occurs when mating surfaces are properly prepared, typically by machining. The expense of machining usually will exceed the savings in welding costs.

Omer W. Blodgett, Sc.D., P.E., senior design consultant with The Lincoln Electric Co., struck his first arc on his grandfather's welder at the age of ten. He is the author of Design of Welded Structures and Design of Weldments, and an internationally recognized expert in the field of weld design. In 1999, Blodgett was named one of the “Top 125 People of the Past 125 Years” by Engineering News Record. Blodgett may be reached at (216) 383-2225.