Shoring

All openings in the wall above should be well strutted between their reveals to prevent any alteration of shape taking place. Inside the building, for support of the floors, vertical shores or strutting must be carried up independently from a firm foundation, in a direct line between the floors with head and sole plates at floor and ceiling to relieve the wall of weight from the floors and roof. To obviate settlement as much as possible, work done in underpinning should be built slowly with rich Portland cement mortar. Before the shoring is removed, at least a week should elapse to allow the work to set hard and firm. Then the needles should be carefully loosened and removed and the holes from which they were with drawn made good. The remainder of the props can then be "struck," leaving the raking or flying shores until the last.

Rules and Sizes for Raking Shores.

Walls 15 ft. to 3o ft. high should have 2 shores to each system; if more than 3o ft. in height an additional shore is required for each increase of io ft. Shoring is rarely seen more than 5 shores high. The angle of the main shores is usually about 6o° (but may be governed by local regulations concerning the use of the roadway), and none of the timbers should exceed an angle of 75° to the horizontal. Some of the lower shores will slope at angles between 4o° and 6o°. The systems should not be placed at a greater distance apart than 15 ft. and they should always be applied at the piers between window openings. The approximate section of a shore for any height of building may be determined by dividing the height of the building (at point of application) in feet, by five; then the result equals the side of the square section in inches.

For Horizontal or Flying Shores.

For spans not exceeding 15 ft. the principal strut may be 6 in. by 4 in., with raking struts 4 in. by 4 in.; for spans exceeding 15 ft. but not exceeding 35 ft. the size of the principal strut should be from 6 in. to 9 in. square, and the raking struts from 6 in. by 4 in. to 9 in. by 6 in.

The restoration of some important and ancient buildings in England by the British Office of Works has provided the oppor tunity for the design and application of new methods of shoring where great loads have had to be supported upon arcade arches while the original piers or columns were removed and restored.

The system adopted was to build very large brick piers under each arched opening and to construct brick rampant arches spring ing from each side of the pier and terminating against the soffits of the original arches thus providing pairs of side supports to each spandrel portion. As the arcade supported a high and thick wall, this latter was also shored by raking shores—with which was combined scaffolding for use in restoring the wall faces. The columns were provided with a steel core of special section, round which the original column facing was rebuilt.

The whole system was applied at Tintern abbey and at Furness abbey and met its purpose admirably. It is an excellent example of structural engineering applied to restoration work.

The principal works of reference on this subject are: C. H. Stock, Shoring and Underpinning (3rd ed., 1902) ; G. H. Blagrove, Shoring and its Application (1887) ; G. Ellis, Modern Practical Carpentry (1915).