The construction of New York City’s bridges required massive amounts of steel, stone, and human labor. Work on the Brooklyn Bridge began in 1869 under the direction of John Roebling. Engineers used huge wooden boxes called caissons to sink the foundations into the bed of the East River. These boxes were filled with compressed air to keep the water out while workers dug into the silt. Many laborers suffered from decompression sickness because they rose to the surface too quickly. The bridge towers reached 276 feet above the water and were built from limestone, granite, and cement. Once the towers were finished, workers spun four massive cables across the river. They used over 14,000 miles of steel wire to create the strength needed to hold the roadway.
North of the Brooklyn Bridge, the Manhattan Bridge opened in 1909. This project used a specific engineering method called deflection theory to make the structure lighter and stronger. Leon Moisseiff designed the bridge to carry both vehicle traffic and subway lines. Construction crews erected steel towers instead of the stone ones used on older bridges. This allowed the bridge to be completed faster. Workers installed stiffening trusses along the sides of the road to prevent the bridge from swaying in high winds. The bridge was the first suspension bridge to use a Warren truss design for its roadway.
The George Washington Bridge spans the Hudson River and connects Manhattan to New Jersey. Work started in 1927 under the guidance of Othmar Ammann. The construction team used a unique method of wire spinning to create the cables. They used a traveling wheel that moved back and forth across the river, carrying wires that were eventually bundled into four main cables. Each cable measures 36 inches in diameter. The original plan called for the steel towers to be covered in decorative granite. The city ran out of money during the Great Depression, so the raw steel towers remained exposed.
In the early 1960s, crews began building the Verrazzano-Narrows Bridge between Brooklyn and Staten Island. This bridge was so long that engineers adjusted for the curvature of the earth. The tops of the two 693-foot towers are one and five-eighths inches farther apart than their bases. Workers used 143,000 miles of wire to support the massive double-deck roadway. They lifted pre-assembled steel sections into place using giant cranes. The bridge opened in 1964 as the longest suspension bridge in the world.
