Pratt Roof Truss Design

A way of making a larger truss out of pre fabricated elements of smaller trusses these roof trusses are simple in design but very effective and cheap to build.

Pratt roof truss design. This particular 6 section structure has 21 truss members and 12 joints. The design uses vertical members for compression and diagonal members to respond to tension. The pratt truss design remained popular as bridge designers switched from wood to iron and from iron to steel. Often seen in bridges it features several vertical chords that are connected by a diagonal chord.

An alternative pratt truss is shown below right where the diagonal members are in tension for uplift loads. Pratt trusses are commonly used in long span buildings ranging from 20 to 100 m in span. This particular type of truss offers some interesting features mainly thanks to the fact that the vertical members provide tension while the diagonal ones are bringing in compression. This type of truss is used where gravity loads are predominant see below left.

The pratt truss was patented in 1844 by two boston railway engineers caleb pratt and his son thomas willis pratt. American standard steel c channels dimensions and static parameters of. Just as there are many types of roofs with many roof parts there are many different types of roof trusses this extensive article explains through a series of custom truss diagrams the different truss configurations you can use for various roofs. Mechanics forces acceleration displacement vectors motion momentum energy of objects and more.

Beams and columns deflection and stress moment of inertia section modulus and technical information of beams and columns. While this article focuses on configurations we also have a very cool set of illustrations showcasing the different parts anatomy of roof trusses. Design hub pratt truss design in solidwork. From above analysis and design of pratt truss following limit state method is more reliable and economical than the working stress method for designing roof trusses for the same configuration of truss total percentage saving in weight of steel is by limit state method is 23 as compare to working stress method.

The ones in the photo above are in a heritage building of around the 1950 s fannie bay gaol darwin nt. The consumption of steel is less in lsm with respect to wsm. In this fashion they form a pattern of interconnected ns. This chord runs from the top of one chord down to the bottom of the other chord.

A roof truss based on two pratt trusses and a bottom chord. Pratt truss this is one of the most popular steel roof truss types and it is quite economical. The pratt steel roof truss design is one of the most common designs. Design hub pratt truss design in solidwork.

Here is how it looks.