What is the maximum truck axle weight based on 5 axles?

The statutory Interstate weight limit is 80,000 lbs. without requiring a permit. You can have up to 20,000 lbs. on a single axle, provided the axle and tires are rated for it. 34,000 is the default for a set of tandems, although some states have higher weights grandfathered in... for example, in Colorado, you can have 36k on a set of tandems, but are still bound by the 80k gross weight.