resist tension. In these the limit may be raised to one hundred and twenty (120).

The corresponding limit for all struts belonging to sway-bracing shall be one hundred and forty (140).

GENERAL PRINCIPLES IN DESIGNING
ALL STRUCTURES.

In designing all structural metal-work the following principles are invariably to be observed:

1. All members must be straight between panel-points, as curved struts or ties will under no circumstances be allowed.

2. The axes of all members of trusses or girders and those of lateral systems coming together at any apex of a truss or girder must intersect at a point, whenever such an arrangement is practicable; otherwise the greatest care must be employed to ensure that all the induced stresses and bending moments caused by the eccentricity be properly provided for.

3. Truss members and portions of truss members must always be arranged in pairs symmetrically about the central plane of the truss, except in the case of single members, the axes of which lie in said central plane of truss. This applies also to the designing of open-webbed, riveted girders.

4. In proportioning main members of bridges, symmetry of section about two principal planes at right angles to each other is to be attained wherever practicable; but in designing top chords and inclined end posts this rule cannot be followed.

5. In both tension and compression members, the centre line of applied stress must invariably coincide with the axial right line passing through the centres of gravity of all cross-sections of the member taken at right angles thereto.

6. The principle of symmetry in designing must be carried even into the riveting; and groups of rivets must be made to balance about centre lines and central planes to as great an extent as is practicable.

7. In all structural metal-work, excepting only the machinery for operating movable bridges,  no torsion on any