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Redline Conquest Aluminum Frame Failed at Bottom Bracket

1999 frame, failed in 2012. No obvious signs of accident or abuse

Failures at the bottom bracket are not especially rare, as pedaling loads tend to bend side-to-side at the joint between seat tube and bottom bracket. It is likely that was why this failure started.

There are several typical approaches to reduce failure rates, including:

a large-diameter seat tube, or larger-diameter down tube so the down tube carries more of the load;
ovalizing the seat tube so it is wider, and thus has better leverage;
a joint that includes anchoring the seat and down tubes all the way around (sometimes all three tubes are placed and then welded, which means there is a "hidden" edge that is not welded);
joining techniques that heat the metal less, and thus damage it less;
gussets or lug material along the sides of the seat tube; and/or
using a tube that is butted so it is thicker at the joint but thinner above the joint, to distribute stresses more evenly.

See FAIL-157.html for some photos of some of these approaches.