Truss Configuration

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3. ANALYTICAL INVESTIGATION
3.1 Truss Configuration
• Truss type : How truss
• Span length:6.1m
• Basic wind speeds:44 m/sec
• Centre to centre distance span: 2m
• Height of building : 5m
The dimension details of the truss are given in table 1. Roof trusses are subjected to the following types of load:
• The dead loads of roof trusses consists of weight of roof covering , weight of purlins, weight of festering and self weight of the trusses.
• live load or imposed load
IS 875-1987 (Part-2) recommends that for roofs with slope up to and including 100. Live load measured on plan should be taken as 1500 N/m2 where access to roof is provided and as 750 N/m2 where access is not provided except for the maintenance. For sloping roofs with slope greater than 100, the live load may be taken as 750 N/m2 for every degree increases in slope over 100, subjected to a minimum of 400 N/m2.The live load may be taken equal to 2/3 of the above load
• Wind load
The load due to wind is one of the most important loads to be considered in the design of roof trusses .A details wind design as per IS 875-1987 (Part-3)
The three design load cases considered for roof truss analysis and they are:
a. 1.5x( Dead load + Live load)
b. 1.5x(Dead load + Wind load)
c. 1.2x(Dead load + Live load + Wind load)
The load details are given in table 2.
TABLE 1: DIMENSION DETAILS OF TRUSS
S.No Span Length
M Central Rise
M
Slope

Angle

00 Top chord length m Bottom chord length m 1 6.1 0.554 1:11 100130 1.03 1.02
2
6.1 0.610 1:10 110190 1.04
1.02
3 6.1 0.680 1:9 120340 1.04 1.02
4 6.1 0.760 1:8 140 1.05 1.02
5 6.1 0.870 1:7 150550 1.06 1.02
6 6.1 1.020 1:6 180260 1.07 1.02
7 6.1 1.220 1:5 210480 1.09 1.02
8 6.1 1.524 1:4 260300 1.14 1.02
9 6.1 2.032 ...

... middle of paper ...

...t is found to be 18o26”. The weight of the different trusses is given in table 4.
TABLE 4: OPTIMUM DESIGN OF TRUSS
Rise
M Top chord members
Mm Bottom chord members mm Web members
Mm Weight of truss
Kg
0.554 100x50x20x4 80x50x25x4 50x40x15x2 98
0.610 80x40x25x4 80x50x25x4 50x40x15x2 92
0.680 80x40x20x3.15 80x50x25x4 50x40x15x2 85
0.760 70x30x20x3.15 80x50x20x3.15 50x40x15x2 78
0.870 70x30x20x3.15 80x40x20x3.15 50x40x15x2 65
1.020 70x40x15x2 60x30x10x3.15 50x40x10x1.25 48.5
1.220 70x40x15x3.15 60x30x20x3.15 50x40x10x1.25 52.5
1.524 70x30x15x2 60x30x20x3.15 50x40x10x2 56.78
2.032 60x30x15x2 60x30x20x3.15 50x40x15x2 63.02
3.048 60x30x15x2 60x30x20x3.15 50x40x15x2 76.40

The optimum weight of the cold formed steel truss is the minimum weight of 48.5 kg corresponding to the central rise of 1.02 m as shown in the figure 2.

Figure 2: Optimum Design Of Truss

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