Evolution of Suspension Bridges Cameron Konop Fabric.a.tion Studio September 8, 2010

Simple Suspension Bridge Analysis A simple suspension bridge is an early bridge type and is still formed from native materials, chiefly grass rope, in some areas of South America. These rope bridges must of course be periodically renewed owing to the limited lifetime of the materials, and rope components are made and contributed by families as contributions to a community endeavor. A more permanent variation, suitable for pedestrian and sometimes equestrian use, may be made from simple wire rope. In such bridges, the roadbed of the bridge will follow the downward and upward arc of the load bearing cables, with additional light ropes at a higher level used to form handholds. Owing to practical limitation in the grade and the response to dynamic loads of the bridge deck this type is quite restricted in its load carrying capacity relative to its span. To walk a lighter bridge of this type at a reasonable pace requires a particular gliding step, as the more normal walking step will induce traveling waves that can cause the traveler to pitch (uncomfortably) up and down or side-to-side. Such a bridge may be stabilized by additional cables that do not bear the primary structural or live loads and so may be relatively light. These also add stability in wind.

Native Inca Bridge

Capilano Bridge Vancouver, British Columbia

Suspension Bridge Analysis A suspension bridge is a bridge that consists of two multiple column pillars (or pylons), one on either end of the central span, with two or more cables slung between them. The bridge deck is suspended from vertical cables or rods attached to the main cables. The main cables continue beyond the pillars to deck–level supports, and further continue to connections with anchors in the ground. The bridge will usually have two smaller spans, running between either pair of pillars and the land, which may be supported by suspender cables or not, — in the latter case there will be very little arc in the outboard main cables. This design was developed in the early 19th century.

Cooper River Bridge Charleston, South Carolina

Golden Gate Bridge San Francisco, California

Wrought Iron Chains Before the development of effective methods of steelmaking and the availability of large quantities of steel, wrought iron was the most common form of malleable iron. A modest amount of wrought iron was used as a raw material for manufacturing of steel, which was mainly to produce swords, cutlery and other blades. Demand for wrought iron reached its peak in the 1860s with the adaptation of ironclad warships and railways, but then declined as mild steel became more available.

Turnbuckle Connection A turnbuckle is a device for adjusting the tension in ropes, cables, and tie rods. It normally consists of two threaded eyelets, one screwed into each end of a small metal loop, one with a left-hand thread and the other with a right-hand thread. The tension can be adjusted by rotating the loop, which causes both eyelets to be screwed in (or out). Turnbuckles are most commonly used in applications which require a great deal of tension; they can range in mass from about ten grams for a small cable to tens of kilograms for structural elements in buildings and suspension bridges.

Steel Wire (Bridge Cables) High strength wire (typically 4 or 6 gauge galvanized steel wire), is pulled in a loop by pulleys on the traveler, with one end affixed at an anchorage. When the traveler reaches the opposite anchorage the loop is placed over an open anchor eyebar. Along the catwalk, workers also pull the cable wires to their desired tension. This continues until a bundle, called a "cable strand" is completed, and temporarily bundled using stainless steel wire. This process is repeated until the final cable strand is completed. Workers then remove the individual wraps on the cable strands (during the spinning process, the shape of the main cable closely resembles a hexagon), and then the entire cable is then compressed by a traveling hydraulic press into a closely packed cylinder and tightly wrapped with additional wire to form the final circular cross section. The wire used in suspension bridge construction is a galvanized steel wire that has been coated with corrosion inhibitors.

Alamillo Bridge Seville, Spain