Joint strength depends on several factors: clearance between parts, base metal composition, service temperature and joint quality (low voids, good penetration).  Joint design will also affect strength.

The bulk tensile strength of silver braze alloys is 40,000-70,000 psi.  When brazing copper-based alloys, failure will occur in the copper or brass.  For copper this is usually the annealed strength of the copper alloy.  When brazing steel or other ferrous metals, joint strength over 70,000 psi can be achieved under the right conditions.

Keep in mind that braze joints are primarily lap type joints, so strength is a combination of tensile and shear.  Joint strength is directly influenced by the above mentioned factors.  The only way to accurately determine tensile or other values is to test the brazed assembly.