Steel Buildings in Europe

Part 5: Detailed Design of Trusses 5 - 5 Table 1.1 Main types of trusses Pratt truss: In a Pratt truss, diagonal members are in tension for gravity loads. This type of truss is used where gravity loads are predominant In a truss as shown, diagonal members are in tension for uplift loads. This type of truss is used where uplift loads are predominant, such as open buildings. Long spans: range from 20 to 100 m Warren truss: In this type of truss, diagonal members are alternatively in tension and in compression This type of truss is also used for the horizontal truss of gantry/crane girders (see Figure 1.5) There are two different types of X truss :  if the diagonal members are designed to resist compression, the X truss is the superposition of two Warren trusses.  if the resistance of the diagonal members in compression is ignored, the behaviour is the same as a Pratt truss. This shape of truss is more commonly used for wind girders, where the diagonal members are very long. It is possible to add secondary members in order to :  create intermediate loading points  limit the buckling length of members in compression (without influencing the global structural behaviour). All these types of trusses can be used either in portal truss structures (see figure 1.2) or in simple truss structures (see figure 1.3). For any of the forms shown above, it is possible to provide either a single or a double slope to the upper chord of a roof supporting truss This example shows a duo-pitch truss Single slope upper chord for these triangular trusses, part of a “saw tooth roof” North oriented windows Simply supported, smaller spans Range from 10 to 15 m Fink truss: This type of truss is more commonly used for the roof of houses.