The steel roof truss is one of structural engineering’s most important and iconic elements. Made of individual members with equal counteracting tensile and compressive forces, its purpose is designed to behave as a single object which carries/supports a load over a span. The arch, uses compression and directs applied forces along its members into the ground. The arch in a truss system is a wonder of engineering and allows for greater spans to be bridged. The demise of an arched truss system is the forces of tension; the longer the span the shallower the arched truss becomes, allowing the forces of tension to take over and causing the arch to struggle with supporting the applied loads. In order to prevent this, the arched truss system takes advantage of one of structural engineering’s most simple shapes, the triangle. A truss system design is comprised of 3 members, a top chord, a bottom chord and interior members called webbing or webs. These interior members combine to form a simple system of triangles creating equilibrium of forces within the truss system. This is possible because the triangle in itself is inherently a stable and rigid structure. Triangles are comprised of 3 elements, 2 side lateral elements and a single bottom horizontal element. When pinned/connected at the nodes of the triangles 3 elements, the triangle is capable of supporting a considerable amount of vertical load, and this is because the two side lateral elements go into compression, while the single bottom horizontal element goes into tension. The two forces counteract one another, essentially creating equilibrium at the point where load is applied. Forces are exerted on each member directed along the member into two joints/pins at the end of each member, referred to as nodes. These forces exerted by each member on the pins are equal and opposite.
The arched or curved truss can be traced back to French engineer Gustave Eiffel and his bridge design in Porto, Portugal over the Douro River. At the time of construction in 1877, the Ponte Dona Maria Bridge was the largest single arch truss span in the world. Today the longest single continuous arch truss span in the world resides in Dallas, TX at The Dallas Cowboys’ AT&T Stadium designed by architect Bryan Trubey. Bryan borrowed the engineering in the curved steel roof truss design directly from Gustave Eiffel’s Ponte Dona Maria Bridge. The two massive arched steel trusses that span the entire length of AT&T stadium at 1,400ft, allow the stadium’s 104,000,000 cubic feet of interior space to be column free while supporting a domed roof equivalent to the weight of 99 Boeing 777s. While a majority of earlier arched trusses are segmented, meaning they do not use curved or rolled steel in their construction design, a vast majority of today’s curved roof trusses do use curved or rolled steel as their top and bottom chords. In today’s world where architects are ever pushing the complexity of their designs and reinforcing the use of architecturally exposed structural steel (AESS), the aesthetic appeal of using curved members is becoming more and more prevalent in truss roof construction.
Contact Chicago Metal Rolled Products for a quote on your curved steel truss design.