CARQUINEZ STRAIT BRIDGE, in California, about 25m. N. of San Francisco, begun April 1923 completed May 1927, is one of the largest cantilever bridges in the world. The Carquinez bridge is notable also for its deep-water pier founda tions, built in 90f t. of water, 13 2 f t. below water-level.
It is noted also for the consideration which was given in de signing the structure to provide special protective details against possible earthquake forces.
anchor arms of Soof t., two cantilever spans of 1,1 oof t. and a central tower span of 1 Sof t. At the south ern end the bridge has a steel viaduct approach 1,13 2f t. long, mak ing the total length of the bridge 4,482ft. between abutments. The trusses are spaced 42ft. centre to centre, providing space for a roadway 30f t. wide between curbs and two sidewalks 4f t. wide. The floor is a reinforced-concrete slab and was designed for a loading of three lines of 2o-ton trucks, or two lines of 2o-ton trucks with a track for electric trains. Silicon steel (80,000 95,0oolb. ultimate strength, 45,000lb. minimum yield-point) was adopted for the main material of the towers and for compression members and built tension members in the trusses of the sus pended spans, cantilever arms and anchor arms. For the principal tension members in the main trusses (and for some tension mem bers in the viaduct trusses) heat-treated carbon steel eyebars were adopted, specified to have a minimum elastic limit of 5o,000 and a minimum ultimate resistance of 80,000lb. per square inch. Pro vision for longitudinal expansion of the main structure is made at the shore end of each anchor arm and at the shore end of each sus pended span. Each suspended span is fixed to the tower canti lever arm, the entire I 1-in. expansion of the I , I oof t. span being provided for at the shore end of the suspended span. Stops are provided at the ends of the main structure to limit the longi tudinal movement to the necessary temperature expansion. For greater security against longitudinal forces (including possible earthquake effects), six hydraulic buffers are provided at the expansion joints between the suspended spans and the shore canti lever arms, also between the main structure and the viaduct, in order to check longitudinal vibrations or any other sudden longi tudinal movement. Their valves close and arrest the motion of the main piston whenever force is applied with a velocity exceed ing o•4in. per second. The horizontal earthquake force assumed in the investigation of the structure and in the proportioning of the buffer details corresponds to an assumed maximum accelera tion of I Sin. per second per second. (D. B. S.)
