Pratt Roof Truss Design

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Pratt roof truss design.

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. The pratt truss was patented in 1844 by two boston railway engineers caleb pratt and his son thomas willis pratt. 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.

While this article focuses on configurations we also have a very cool set of illustrations showcasing the different parts anatomy of roof trusses. The pratt truss design remained popular as bridge designers switched from wood to iron and from iron to steel. 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. Pratt truss this is one of the most popular steel roof truss types and it is quite economical.

Here is how it looks. American standard steel c channels dimensions and static parameters of. The pratt truss structure we will be working with a design called the pratt truss originally designed by thomas and caleb pratt in 1844. This chord runs from the top of one chord down to the bottom of the other 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. 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. This type of truss is used where gravity loads are predominant see below left. In a conventional pratt truss diagonal members are in tension for gravity loads.

Often seen in bridges it features several vertical chords that are connected by a diagonal chord. Statics loads force and torque beams and columns. An alternative pratt truss is shown below right where the diagonal members are in tension for uplift loads. In this fashion they form a pattern of interconnected ns.

The pratt steel roof truss design is one of the most common designs. A roof truss based on two pratt trusses and a bottom chord. Design hub pratt truss design in solidwork. This particular 6 section structure has 21 truss members and 12 joints.

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