BEHAVIOR OF STRUCTURAL MEMBERS AND MATERIALS. 71 
been prevented with an adequate number of bolts I do not know, but 
in an important vault it would seem worth while to have the outer 
door at least filled in the same manner as the door of a fireproof safe. 
If it were built in this way it would probably not warp — at least 
not enough to let the fire in. 
To judge from the safes which I saw opened, very nearly three- 
fourths of the safes in the San Francisco fire failed to protect their 
contents (PL LII, B), and as a result the loss of valuable papers 
and records must have been very extensive. 
BEHAVIOR OF STRUCTURAL MEMBERS AND MATERIALS. 
The commercial fireproof buildings in San Francisco, in my judg- 
ment, suffered considerably more damage than corresponding build- 
ings in the Baltimore conflagration. In the San Francisco fire, for 
the first time, the collapse of protected steel frames, due to the 
destruction of the fireproof covering at a comparatively early stage 
in the fire, was a matter of common occurrence. Practically all of 
the floor construction in fireproof buildings in San Francisco consisted 
either of hollow terra-cotta flat arches or of reenforced-concrete slabs, 
carried on steel floor beams. In a few buildings steel columns and 
girders were used, with reenforced-concrete beams and slabs covering 
the space between the girders. Steel girders were more generally 
protected with metal lathing and plaster, or with solid concrete fill- 
ing, than with anything else, but terra-cotta covering was also used 
to a considerable extent. The lower flanges of beams were in some 
buildings unprotected; in others they were covered with metal lath- 
ing and plaster; and in still others (a rather general practice), there 
was a ceiling composed of light furring angles and metal lathing, 
fastened below the floor construction and plastered. Most of the steel 
beams and girders in the floor construction had no other protection 
for their lower flanges than this furred ceiling, even where the webs 
were protected by a solid concrete filling. 
Columns were generally protected in one of three different ways, 
as follows: 
I." With hollow tiles adapted to either a circular or square section, 
the webs being about five-eighths of an inch thick, and the total 
thickness of the tile, including webs and hollow space within, being 
about 2J or 3 inches. The tiles Avere from 12 to 18 inches in length 
and about 12 or 15 inches wide. 
2. With metal lathing and plaster surrounding the column, so as 
to leave an air space of about 1 or 1J inches. 
3. With a solid covering of concrete from 2 to 4 inches thick. 
In addition to this protection the columns in the walls were gener- 
ally covered with 4 inches of brickwork, and in one building there was 
a double covering of metal lathing around isolated columns, the 
