Sprinkler piping shall be substantially supported from the building structure which must be able to support?

The requirement that sprinkler piping must be able to support a water-filled pipe plus an additional weight is based on safety and structural considerations. Sprinkler systems carry water under pressure, and the weight of the piping itself, coupled with the maximum possible weight of the water it could contain, must be taken into account to ensure that the building's structural elements can safely handle the load.

When considering a water-filled pipe, it is essential to account not just for the weight of the water within the pipe itself but also to include a safety margin. The additional weight (250 lbs in this case) is intended to accommodate variations in installation conditions, potential unforeseen circumstances, and to ensure that the support is adequately designed to prevent failure. This ensures the integrity and operational reliability of the fire suppression system over its lifespan.

Thus, the correct choice reflects an understanding of the necessary load-bearing requirements for sprinkler systems, incorporating both the weight of the water-filled pipe and a sufficient safety allowance.