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How the Bridge Spans the Golden Gate
l. Deck Trusses
Look at the trusses that extend along the length of the Bridge. The weight of the roadway and sidewalk structure, and of the cars, pedestrians, and bicyclists, is supported by the deck trusses. The diagonal struts outline the basic structural unit of a truss, the triangle, which is inherently strong and stiff. However, the deck trusses are not strong enough to span all the way across the Golden Gate. They are held up every 50 feet (15 meters) by vertical steel suspender ropes.
2. Suspender Ropes
See the 500 vertical lines (steel suspender ropes) across the Bridge? They are the next step in the "load path", which is the term that describes how the weight of the Bridge, including the weight of traffic, is transferred ultimately to the ground. The deck trusses hand off their load to the ropes, which pull that weight up to the curving main cables. The weight of the deck is suspended from the main cables by these suspender ropes, hence their name.
3. Main Cables
When you look at the tops of the two towers of the Bridge, you see where the two cables are supported. All the weight of the roadway and sidewalk deck structure, the traffic, the steel suspender ropes, and the self-weight of the curving main cables, is placed on the tops of the two towers by the cables.
4. Towers
What holds up the two main cables? When you wear a backpack, the straps pull the weight up to your shoulders, and then that load must travel a path down your body all the way through your legs to the ground. The poles that hold up a tent, or a tightrope walker at the circus, or a clothesline, must also carry the weight to the ground. In the Bridge, the towers carry all the gravity loads of the entire suspension structure, from one end to the other, down to the ground.
5. Foundations
The foundations are the final step in the load path. The forces carried down through the steel towers are resisted by the strength of the concrete foundations, which extend into bedrock. The pulling or tension forces in the cables are resisted by the massive concrete anchorages at both ends of the Bridge, and those anchorages are also embedded in bedrock. The loads of the Bridge flow through the foundations and reach the earth, completing the load path. |