GENERAL LESSONS OF THE EARTHQUAKE AND FIRE. 57 
The structures which suffered most from the earthquake were* — 
1. The municipal and county buildings. The greatest destruction 
was sustained by these buildings, which were generally badly de- 
signed and poorly constructed of inferior materials, while the well- 
built, substantial Government buildings suffered less. 
2. Lightly and flimsily constructed wooden buildings. Well-con- 
structed wooden buildings generally withstood the shock, but those 
that were flimsily built, resting upon posts or equally insufficient 
foundations, collapsed, even where they were fairly well designed. 
The essentials of earthquake-resisting power are vertical continuity, 
adequate diagonal bracing, and first-class foundations. 
3. Improperly built brick and stone structures. The brick walls 
which failed, either by being shaken down entirely or by shattering, 
were laid in lime mortar with few header courses, and generally had 
wooden frames with little or no bracing and no tie to the walls. 
Stone and brick masonry cracked diagonally in the form of an X. 
Hollow-tile partitions and masonry of brick or stone were similarly 
cracked, although this injury was small where Portland -cement 
mortar was used. Where the walls were laid with hard brick, with' 
plenty of headers and in Portland-cement mortar, and were properly 
tied to the floor and roof members there was little, if any, damage. 
Chimneys collapsed most generally, breaking about halfway up, and 
destroyed in part at least the structures upon which they fell. While 
the evidence was by no means conclusive, it appeared to the writer 
that brick stacks of circular section proved more substantial than 
square ones. The stack of the Valencia street power plant, which 
was of eight-pointed star section, collapsed, the part which remained 
standing showing cracks at one of two opposite reentrant angles 
almost to the base (PI. LIII, A). It is quite evident that brick 
stacks and similar tall structures built of brick or stone without 
reenforcement against flexure, or without being guyed, are unsuitable 
for use in countries liable to earthquake shock. They should be con- 
structed either of steel, guyed, or, if self-supporting, of steel or reen- 
forced concrete. (See also PI. XIII, A.) 
4. Insufficiently braced and loosely constructed steel structures. 
In structures which were deficient in diagonal bracing the effect of 
the earthquake was localized in the piers between openings and cur- 
tain walls in characteristic X cracks. In tall structures like the Call 
Building, the tower of the Union Ferry Building, and others, the 
diagonal bracing that had been installed proved insufficient, and the 
diagonals at about the middle distance between the top and base were 
strained beyond the elastic limit of the material, acquiring a perma- 
nent set, which was indicated by a slight buckling. It is assumed 
that the effect of earthquake shock on diagonal bracing is equiva- 
lent to a heavy wind pressure, variously estimated at 30 to 50 pounds 
