84. In large cities it is customary to utilize the space under the sidewalk for storage or other purposes. This necessitates a wall at the curb line to sustain the street and also the weight of the sidewalk.

Vault Walls 10046

Fig. 45.

Where practicable, the space should be divided by partition walls about every 10 feet, and when this is done the outer wall may be advantageously built of hard brick in the form of arches, as shown in Fig. 46.

The thickness of the arch should be at least 16 inches for a depth of 9 feet, and the "rise" of the arch one-sixth of the span.

If partitions are not practicable, each sidewalk beam may be supported by a heavy I-beam column, with either flat or segmental arches between, as shown in Fig. 47.

This latter method is more economical of space than any other, and where steel is cheap is about as economical in cost.