Pratt Roof Truss Design

Often seen in bridges it features several vertical chords that are connected by a diagonal chord.

Pratt roof truss design.

The pratt truss structure we will be working with a design called the pratt truss originally designed by thomas and caleb pratt in 1844. In a conventional pratt truss diagonal members are in tension for gravity loads. The pratt truss was patented in 1844 by two boston railway engineers caleb pratt and his son thomas willis pratt. A roof truss based on two pratt trusses and a bottom chord.

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 pratt steel roof truss design is one of the most common designs. 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. 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.

An alternative pratt truss is shown below right where the diagonal members are in tension for uplift loads. 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. Here is how it looks. This chord runs from the top of one chord down to the bottom of the other chord.

In this fashion they form a pattern of interconnected ns. Pratt trusses are commonly used in long span buildings ranging from 20 to 100 m in span. Design hub pratt truss design in solidwork. This type of truss is used where gravity loads are predominant see below left.

While this article focuses on configurations we also have a very cool set of illustrations showcasing the different parts anatomy of roof trusses. Statics loads force and torque beams and columns. American standard steel c channels dimensions and static parameters of. Pratt truss this is one of the most popular steel roof truss types and it is quite economical.

Mechanics forces acceleration displacement vectors motion momentum energy of objects and more. The ones in the photo above are in a heritage building of around the 1950 s fannie bay gaol darwin nt. The pratt truss design remained popular as bridge designers switched from wood to iron and from iron to steel. This particular 6 section structure has 21 truss members and 12 joints.

Beams and columns deflection and stress moment of inertia section modulus and technical information of beams and columns.