BEHAVIOR OF INDIVIDUAL STRUCTURES. 85 
work by any means. I found a few places where joints were not 
well filled, but not a greater number of such places than one would 
expect to find even in fairly good work. On the exterior the build- 
ing was finished with stucco, which was tinted to imitate the grayish - 
green sandstone so much used for building purposes in San Francisco. 
The city hall Avas of an irregular plan, as it was built on a trian- 
gular lot. The building contained in the western part an interior 
court, in which a nonfireproof structure had been erected prior to the 
earthquake and fire to accommodate the fire-alarm headquarters. 
On the southeast front of the building a little to the east of the 
center was a rotunda with a tower and dome above it. This tower 
was built of brickwork up to the base of the upper of two peristyles 
of free pillars around the outside of the tower. This peristyle was 
composed of steel columns covered with hollow tiles, so as to form a 
pillar of circular section with an entasis. The walls of the tower 
from the base of this peristyle up also seem to have been of hollow 
tiles. At the base of the dome was a floor composed of terra-cotta 
flat arches. It was reported that the masonry of the building had 
been reenforced to a great extent with embedded steel bars for the 
purpose of increasing its resistance to earthquake. I did not notice 
any such bars myself, but it was very difficult to get such access to 
the debris as would have permitted the verification of this point. 
In a general way it may be said that the southwest half of the 
building was practically destroyed by the earthquake. The heavy 
masonry was thrown down, so that the entire southwest half of the 
tower was left entirely exposed, the dome standing on the steel work 
alone. The remaining half of the building showed considerable 
damage from the earthquake, but the principal damage here was due 
to the fire. PL XXXI gives a fair idea of the earthquake damage 
in the southwest half of the building. 
It will be observed that some of the projecting pilasters on the 
exterior of the wall were badly cracked. A singular action of the 
earthquake, as exhibited here and in other places, was the tendency 
to shear off projecting pilasters even though they were built of the 
same material as the wall and well bonded to it. In my judgment 
this action was due to the fact that the earthquake caused the wall 
to rock slightly sidewise. When it rocked toward the side from 
which the pilasters projected, the entire weight would be for an 
instant concentrated on the base of the pilaster in such a way as to 
tend to shear it loose from the wall, which actually happened in 
many cases, the wall presenting no other evidence of damage what- 
soever. Instances of this damage are pointed out in the discussion 
of other buildings. 
Examination of PI. XXXT, especially with a reading glass, will 
shoAV that many of the diagonal braces in the steel work of the tower 
7171— Bull. 324—07 7 
