BEHAVIOR OF STRUCTURAL MEMBERS AND MATERIALS. 75 
In steel-frame buildings put up in the ordinary way, without any 
special bracing, most of the earthquake effect was localized in piers 
between windows, as if a horizontal force had been applied to the 
floor above, tending to slide it with reference to the floor below. As 
this effect occurred in both directions, the piers referred to were gen- 
erally marked with X-shaped cracks, and in addition the masonry 
was apt to be very much shattered. There seemed to be no general 
rule as to the place where this shattering effect occurred. In some 
buildings the piers in the one or two stories near the middle of the 
height of the building seemed to have suffered the most ; in others, the 
piers nearer to the roof. One tall building, which extended far above 
its neighbors, was seriously damaged in practically every story above 
the neighboring buildings. 
It was apparent that in some buildings the shock was so severe that 
probably no structure, however well built, could have withstood it 
absolutely without damage. It was equally apparent, however, that 
such great exhibitions of energy were confined to small areas, and 
that it would be possible to put up buildings in San Francisco which 
would come through a similar earthquake with very little damage 
except to individual buildings here and there. 
Hollow-tile work seemed to be badly shattered by the earthquake 
in a great many places. Well-executed stone masonry, as a rule, 
stood better than brickwork. Brickwork built with good hard bricks, 
laid in Portland-cement mortar, stood better than that built with 
inferior bricks or inferior mortar. 
Of all the structures which were manifestly exposed to severe shock 
the concrete buildings at Palo Alto stood best. It would seem 
to be a general rule that increased tensile strength, even in a brittle 
material, greatly increased the resistance to earthquake shock. The 
height above the ground at which the damage was greatest appeared 
to be largely a function of the distribution of mass in the structure 
itself, combined with the distribution of the bracing. If the base of a 
tall steel-frame building were subjected to a vibration tending to tilt 
it, manifestly some time would be required to set the upper part of the 
building in motion. As the vibration evidently occurred in both 
directions, there would be a reversal of motion before the upper part 
of the building had responded to the first impulse. Under these cir- 
cumstances there would be established somewhere a center of oscilla- 
tion, where very severe stresses, due to the acceleration of the superin- 
cumbent mass, would be largely concentrated. 
It might have been supposed that most of the destructive effect of 
such action would be manifested at the joints in a steel-frame build- 
ing; but around the joints are concentrated the ends of the floor 
beams and girders, together with the floor construction, and at the 
level of these joints is the only portion of the walls which is per- 
