To discover how the forces are affected by changing the length of the tie in the truss

To discover how the forces are affected by changing the length of the tie in the truss.

Apparatus

Roof truss Apparatus

Procedure

It is recommended that three shape of the roof truss as follow should be tested

Rafter length

a)    Pitch 45 deg  Tie 580 mm

b)    Pitch 37 deg  Tie 660 mm

c)    Pitch 30 deg  Tie 710 mm

The procedure is similar for all three

Measure along the baseboard from the fix pin and make pencil mark alongside the track plate at the required Tie length. Hook the tension spring balance onto the chain and use the thumbnut to set the Tie to length. Ensure the load hanger is suspends from the apex of the truss and adjust the length of each rafter to 410 mm. readjust the die length as requires. Treat this as the no load case and record the three balance readings in table 1.

Scale

The following results were obtained by an average student

Line of action	Direction	Load (N)
OP	0.00	5.7
OQ	138.50	7.5
OR	2700	5

By calculation using Pythagoras theorem

     OQ = 7.58 N

Apex Load (N)	Strut AB		Strut AC		Strut BC
	Balance (N)	Force (N)	Balance (N)	Force (N)	Balance (N)	Force (N)
0