Pratt Truss Roof 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.

Pratt truss roof design.

Pratt truss this is one of the most popular steel roof truss types and it is quite economical. Often seen in bridges it features several vertical chords that are connected by a diagonal chord. Permanent dead loads self weight of long span aluminium roofing sheet 0 55mm gauge thickness 0 019 kn m 2 weight of ceiling adopt 10mm insulation fibre board 0 077 kn m 2 weight of services 0 1 kn m 2 weight of purlin assume ch 150 x 75 x 18 kg m 18 x 3m 1 2 x 3 15. What makes it so good and gives it an advantage over the howe truss is how it spreads out the forces when under load.

Here is how it looks. This chord runs from the top of one chord down to the bottom of the other chord. 6b roof truss. 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.

This type of truss is used where gravity loads are predominant see below left. 6 6a design of gantry girder. Design of industrial roof truss 1. Selection of gantry girder design of cross section check for moment capacity buckling resistance bi axial bending deflection at working load and fatigue strength.

The pratt steel roof truss design is one of the most common designs. 2 0 load analysis span of roof truss 7 2m spacing of the truss 3 0m nodal spacing of the trusses 1 2m. The consumption of steel is less in lsm with respect to wsm. Sres sanjivani college of engineering kopargaon.

I have used it often for my model bridges including balsa basswood and popsicle sticks. 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. Sppu pune page 1 unit no.

In a conventional pratt truss diagonal members are in tension for gravity loads. Structural design i steel structures prof. In this fashion they form a pattern of interconnected ns. An alternative pratt truss is shown below right where the diagonal members are in tension for uplift loads.