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In a next phase the forces caused by wind must be considered. Wind will cause pressure on the upwind side of a roof (and truss) and suction on the downwind side. This will translate to asymmetrical loads but the Cremona method is the same. Wind force may introduce larger forces in the individual truss members than the static vertical loads.
In other words, the summation of the work done on the system by the set of external forces is equal to the work stored as strain energy in the elements that make up the system. The virtual internal work in the right-hand-side of the above equation may be found by summing the virtual work done on the individual elements.
Each element is then analyzed individually to develop member stiffness equations. The forces and displacements are related through the element stiffness matrix which depends on the geometry and properties of the element. A truss element can only transmit forces in compression or tension.
English: Detail of a steel truss, like it is build nowadays, it uses welds and bolds due to the fact it is at site joint, where two parts get connected at site (see Plan of the tuss). It is a part of a Plan (File:Det JoKa008-Model.pdf), which shows three details of a truss (File:Fachwerkplan.pdf)
Most trusses use gusset plates to connect intersecting elements. Gusset plates are relatively flexible and unable to transfer bending moments. The connection is usually arranged so that the lines of force in the members are coincident at the joint thus allowing the truss members to act in pure tension or compression.
In the context to structural analysis, a structure refers to a body or system of connected parts used to support a load. Important examples related to Civil Engineering include buildings, bridges, and towers; and in other branches of engineering, ship and aircraft frames, tanks, pressure vessels, mechanical systems, and electrical supporting structures are important.
The first such bridge was built in steel at Avelgem, Belgium in 1902, following development of the truss form and a method to calculate its strength in 1896 by Arthur Vierendeel. There are many more examples in Belgium, including some built in concrete, mostly designed by Vierendeel's many students from his long career as professor in civil ...
For example, consider a spring that has Q and q as, respectively, its force and deformation: The spring stiffness relation is Q = k q where k is the spring stiffness. Its flexibility relation is q = f Q, where f is the spring flexibility. Hence, f = 1/k. A typical member flexibility relation has the following general form: