144 THE SAN FRANCISCO EARTHQUAKE AND FIRE. 
of the building — to speak roughly, somewhere near the middle sto- 
ries. It also seemed to have the effect of producing a horizontal 
shearing stress in the frame, particularly above and near the base- 
ment. The frames in these high buildings seemed to be the most 
severely wrenched, and the exterior walls, stairways, linings, etc., 
most injuriously cracked in these middle stories. For example, the 
magnificent eighteen-story Call Building seemed to be well braced 
against bending moment and shear, but the eyebars from the tenth 
to the sixteenth floor and the transverse wind bracing are reported 
to be somewhat buckled, the maximum occurring on the thirteenth 
floor. The braces were warped on all four sides of the building, 
and there was also probably some slight distortion of the steel frame 
from the tenth to the thirteenth floors. The exterior veneer of stone 
remained practically intact up to the tenth floor, above which, up 
to the sixteenth, there was an increasing amount of damage, some 
of the stone being considerably out of place. (See also p. 146.) The 
same thing practically can be said of the new Chronicle Building, 
the damage to the stonework of which can be noted by a close inspec- 
tion of PI. XXX, B. The earthquake proved the absolute neces- 
sity of bracing steel- frame buildings with diagonal braces, so far as 
the requirements of use will allow. The Mutual Savings Bank and 
the Shreve and Atlas high steel-frame buildings have such bracing 
and remained entirely plumb after the earthquake. The St. Francis 
Hotel and the Call Building were somewhat similarly braced and 
were also left in reasonably good condition. 
Some architectural authorities assert that wind bracing put in 
liberally for an allowance of 30 pounds pressure per square foot will 
amply care for earthquake vibrations of an intensity equal to those of 
April 18, 1906. Undoubtedly many of the high steel buildings in 
San Francisco were designed without reference to earthquakes, but 
they have nobly withstood their effects, and steel frames have proved 
themselves entirely adapted to earthquake countries. A careful in- 
spection of the high steel frames in San Francisco shows that they 
suffered comparatively little injury, and that this injury was con- 
fined to the shearing of rivets and connections, particularly in the 
lower stories and on the ground floors, and to some buckling of 
braces. 
After the earthquake, bolts and rivets in the Union Trust Building 
were found to be loose, and some were sheared off. This damage was 
due apparently to faulty construction, careless workmanship, and the 
insertion of field bolts, in some places, instead of rivets. It was 
shown that the rivets, connection joints, etc., in these steel-frame 
structures are of vital importance, and that in order to resist earth- 
quake vibrations they should be made as strong and effective as pos- 
sible, particularly at the basement and first floor. 
