Index to Earthquake Reports

Municipal Reports

THE SAN FRANCISCO EARTHQUAKE
AND FIRE OF APRIL 1906

Report on the Condition of the City Hall
by Newton J. Tharp, City Architect

General History and Construction
It was exceedingly unfortunate for the City of San Francisco that its most ambitious public building should have been planned and the construction begun at a period just prior to the introduction of the modern steel skeleton, masonry armored type that solves at once all of those principles necessary to a first-class building of any character, namely, rigidity in all directions, fireproof qualities and lightness of construction.
The various styles of construction resulted from yearly appropriations for more than 20 years by the Board of Supervisors. In 1884 only $2,200 was paid out

Although our modern steel frame type of building was evolved in Chicago during the year 1884 and it use spread rapidly through the East, its acceptance was slow upon our coast, with the result that the entire building was completed (excepting the dome) without any of the principles of the steel frame construction having been used.

All of the exterior and interior partition an carrying walls are of brick resting on footings of stone, well laid and of deep courses. The floor are of iron girders and beams, with bent corrugated iron and brick or concrete arches between, the girders in most cases having been fireproofed with suspended metal lath and plaster ceilings, quite in keeping with recent construction.

The simple engineering features of the main building were well conceived and executed with the exception of certain details of constructions. All of the brick walls, both exterior and interior, were built without bond irons, relying upon inertia and the adhesion of the mortar for rigidity which, in itself, is a fatal error in a region afflicted by earthquakes.  And the great number of larges chases for pipes, heating and ventilating ducts, etc., do nor add to the strength of the walls. Where the spans in certain portions of the floors were too great for the size of the I beams rolled in those days, simple plate and box girders were employed. These are all badly proportioned and seem to have been designed by rule of thumb, as no proper disposition of the material is made to take car of the points of greatest bending moment and shear.

The four great box girders in the roofs of the large rooms at the ends of the wings facing on McAllister street are badly designed and as absurd a solution of a simple problem of construction as might be found anywhere and no doubt their great weight, raising the center of gravity of those portions of the building, did much toward the general wrecking by the earthquake.

Dispelling The Rumors
Contrary to popular belief, the bricks and mortar used throughout the entire structure are of the finest and the workmanship of the best. So far, the most rigid inspection of the standing and fallen walls, and of the walls of portions under removal have failed to disclose any large voids or enclosed boxes, barrels or wheel-barrows that have been told in many an old tale  as evidence of lax supervision and contractor's deceits. 

3. Damage to the City Hall