The wall may also be treated in like manner if of even thickness. If of varying thickness, the centre of gravity of each portion of even thickness should be found.
The resultant will be found by the method already given for finding the centre of gravity of a number of bodies.
The base of the erection in this case should include the base of the wall.
The effect of ordinary loads upon the stability of a scaffold of this type is practically nil. No weight that the scaffold was capable of carrying in itself could bring the resultant centre of gravity of the scaffold and wall outside of the base; so that unless the scaffold failed from rupture of its members or connections, it may be considered safe from collapse due to instability.
To find the Centre of Gravity of a Gantry.—This can be found by the method given for independent pole scaffolds.
To find the Centre of Gravity of a Scotch Derrick.—Owing to the unevenly distributed weights about these scaffolds, they cannot be taken as regular bodies. It will therefore be necessary to take each part of the erection separately, and after finding the centre of gravity of each, to find the resultant centre of gravity of the mass by the method already given.
To find the Centre of Gravity of each Part.—Each leg can be treated as an evenly disposed rigid body.
The mass of brickwork that is placed at the foot of the legs may be treated similarly.
The platform may be considered as a surface. If triangular, the centre of gravity is found by the following method:—
Bisect the base and join the point of bisection to the opposite angle. The centre of gravity is at a point one-third of the length of the line measured from the side divided ([fig. 131]).