A stadium roof truss is shown in fig. Find the forces in members AB, AG and FG

 (Q. 1 ) A stadium roof truss is shown in fig. Find the forces in members AB, AG and FG.

Solution :  First of all we have to cut All the member Required I.e AB, AG and FG. By a Sectional Plane .

Step 1 : Let , AA' be a Sectional plane.

Step 2 : We have to cut the members in such a manner that at least 3 unknown member cut out.

Step 3 : Select the smaller portion for solving this problem.

Step 4 : Draw the F.B.D (Free Body Diagram ) of the Structure and Show the proper direction of forces acting if any.

Step 5 : Draw F.B.D of Each joints separately and Find the necessary Unknown Quantity , we Can Use the Law of Equilibrium  I.e

• Sumation of X-axis = 0
• Sumation of Y-axis= 0
• Sumation of Moment = 0

We can also use the Lami's Theorem when necessary.

*Note :  The Sign convention should be carely use when solving Such type of Problems.

Take +ve Sign for +ve X-axis and +ve Y-axis for Forces.

Take -ve Sign for -ve X-axis and -ve Y-axis for Forces.

Take +ve Sign for clock wise and - ve Sign for counter clockwise direction of the Rotation of the forces forthe Moment 

Thanks