Braces
When more than one shore takes a bearing upon the sole-piece the FIG. 2 (3-in. to foot). feet of the several members are stiffened and braced either by having rough boarding nailed right across them or by being bound together with a number of rounds of hoop-iron. For further strength also braces of I-in. boards, 6 to 9 in. wide, are taken across from the wall-plate to the topmost shore and spiked to each intervening member, binding the whole together. These braces should be fixed a little below the junctions of the heads of the shores with the wall-plate. The wall-plate has already been referred to. It is tasually a deal 9 in. wide by 3 in. thick, secured tightly against the face of the wall with wrought-iron wall hooks, forming a good abutment for the shores and serving to spread the support FIG. I.
ra g a r 9'.9" afforded by them. Holes are cut through this plate to receive the needles (or joggles as they are sometimes termed to distinguish them from the needles used in dead shoring, which are large horizontal FIG. 3. - (r in. to foot.) members usually of balk timber), which are pieces of wood about 1 ft. long and 4 in. square in section, cut with a shoulder to butt against the wall-plate. A portion of a brick or stone is removed from the wall and the end of the needle is passed through the rectangular hole in the wall-plate and fitted into the recess in the wall.
FIG. 4. - (A in. to foot.) The head of the needle projects about 41 in. beyond the face of the wall-plate and forms an abutment for the head of the shore. The head of the shore is notched to fit the underside of the needle to prevent any movement sideways. If this is not done the shore is liable to be acted upon by the wind and be blown down. A small 1005 block of wood, cut somewhat after the fashion of a wedge and termed a cleat, is fixed above the needle to keep the latter quite firm. Cleats are used also in other positions to keep timbers in position. Wedges are used to obtain a tight bearing for the rider shores and are used at their base. As little force as possible must be employed in driving them as vibration is liable to injure the already weakened wall.
Horizontal shores, or flying shores as they are more often termed by the workman, may be employed for spans up to about 35 ft. They are used to support the party walls of the houses adjoining the pre mises being rebuilt. The are erected during the pulling down operations and removed as the new building is raised and there is no further need for them. A system of flying shores consists of one or more horizontal timbers, sometimes known as dog shores, cut in tightly between the wallplates fixed with hooks to the faces of the walls of the adjoining buildings (fig. 3). These horizontal members are supported at each end by cleats and needles fixed in the Fl 75 wall-plate as described for raking shoring. The shores are supported in their length by inclined braces springing from needles fixed near the lower ends of the wall-plates and serving to strut the shore at a point about a third of its length from the wall. Corresponding braces are carried from the upper surface of the shore and abut against needles at the upper ends of the plates. Straining pieces are secured to the upper and lower faces of the shore to serve as abutments for the ends of the braces. The best angle for these braces is one of 45 °, but a smaller inclination than this is frequently adopted. Wedges are inserted, usually at the end of the flyer so as to tighten this up between the wall-plates, and sometimes between the braces and the straining piece, and carefully driven to tighten up the whole and cause each timber to find a close bearing. If the adjoining premises are of considerable height and especially if it is proposed to undertake extensive excavations, the systems of flying shores may need to be somewhat complicated, each consisting of several horizontal members spaced frqm 10 to 13 ft. apart and well strutted one to another and to the wall-plate (fig. 4). In the application of this form of shoring, as in raking shores, the same rules apply as regards placing the shores on the face of the wall in a proper position to obtain a solid abutment on a floor or roof on the other side. The members should be securely dogged and spiked together to form a homogeneous framework capable of resisting the attacks of a strong wind, which in an exposed position will sometimes destroy a poorly constructed framework.
Horizontal shores should be adopted wherever possible in preference to raking shores. Besides being more economical, they are more convenient and more effectual than rakers springing from the ground, especially if the height of the building is considerable and the span at the most not much over 30 ft. Apart from the economy effected, they present a direct resistance to the thrust and are well out of the way of any building operations that may be carried on below them, so that there is no risk of their being accidentally disturbed, whereas the feet of raking shores are generally in the way of the workmen, and if not disturbed by accidental blows from materials or carts will very likely be loosened and rendered useless by the digging and pumping which is going on around them.
Needle shoring is the next method of temporary support to come under consideration. It is known also as vertical shoring and dead shoring, and is the means usually adopted to support temporarily I' ?-,. or I nude, FIG. 5. - (, in. to foot.) FIG. 6. - (in. to foot.) the upper portion of the walls of a building when it is found necessary great consequence. Such to reconstruct the foundations or to make large openings in the ordinary buildings, but in From a photograph by W. T. Green.
FIG. 7. - Shoring of the Presbytery, Exterior, Winchester Cat lower parts of the wall, as, for example, when putting a shop front in an existing building. This form of shoring consists of horizontal members of balk timber termed needles (very different from the needles used in raking and flying shoring), which are passed through holes in the wall to be supported, at a sufficient height to allow of the insertion of any arch or lintels that may be necessary above the opening it is proposed to cut (figs. 5 and 6). The needles are supported at each end by an upright timber or dead shore, one on each side of the wall to each needle. These should not be allowed to rest upon any floor or vault but be carried down to a solid foundation and set upon and securely dogged to a timber sleeper running parallel to the wall. If it is not practicable to take the inner dead shore through intervening floors down to the solid ground in one piece, and it is necessary for its base to be set upon the floor or upon sleepers placed on the floor, the strutting must be continued in a direct line below it until a firm foundation is obtained. Between the needle and the head of the dead shores folding wedges are inserted to force the horizontal supporting balk firmly up to the underside of the masonry. Connexions between the dead shores and the needles and sleepers are made with wrought iron dogs. The spacing of the systems of dead shoring depends to a large extent upon the material with which the wall is constructed; for brickwork they should be placed at intervals not greater than 6 ft. With this form of shoring especially it is often found necessary to adopt other methods auxiliary to the main shoring. These take the form of raking or flying shores from the face of the building. All the openings in the wall above should be well strutted between their reveals to prevent any alteration of shape taking place. Inside the building vertical shores or strutting must be carried up independently in a direct line between the floors with head and sole plates at floor level and ceiling. This strutting must start from a firm foundation at the bottom of the building and be tightly wedged up so as to relieve the wall of any weight from the floors and roof. To obviate settlement as much as possible, work done in underpinning should be built slowly with Portland cement mortar mixed in strong proportions. 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 withdrawn made good. The remainder of the props can then be " struck," leaving the raking or flying shores until the last. If possible this work should be spread over several days, an interval of a day or two being left between the removal of each portion of timbering to allow the work gradually to set on its new bearings.
Shoring should be the subject of careful calculations to ascertain the most suitable sizes of timbers and to determine the most appropriate points of support. This is not always done, however, and much work of this character is carried out by rule of thumb methods. The usual result is that the timber used is of a much greater size than is really necessary, although as the material is not much injured and is available on removal for re-use this fact is not of methods perhaps work very well for special cases they may very well lead to shoring being constructed in too fragile a manner, with serious results. Some rules which experience has shown to work satisfactorily for ordinary work are given below, together with the approximate scantlings of the timber required.
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 and the raking struts from 6 in. by 4 in.
shoring on a large scale may frequently hedral Restoration.
from 6 in. to 9 in. square, to 9 in. by 6 in. Interesting examples of - ?
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From a photograph by W. T. Green.
FIG. 8. - Shoring of the Presbytery, Interior, Winchester Cathedral Restoration.
be seen applied to large buildings in the course of repair or restoration. The rebuilding of the foundations of the retro-choir and lady chapel of Winchester cathedral which was carried out in the autumn of 1906 necessitated the erection of a very elaborate and complicated arrangement of shoring to uphold the masonry while the work of underpinning the walls was being carried on. The foundations of the eastern portion of the cathedral were found to be dangerously insecure, being in fact laid upon a bed of soft marl only 10 ft. below the surface of the ground, in spite of the fact that at a depth of 16 ft. a hard solid stratum of gravel, at least 6 ft. thick, is arrived at. The medieval builders without doubt entertained suspicions as to the sustaining power of their proposed foundation, and so to ensure stability, as they thought, strengthened it by placing below the masonry horizontal layers of beech trees, filling up the interstices with hard chalk and flints. These contrivances were not sufficient to prevent the gradual sinking, through succeeding centuries, of the heavy mass of masonry. This not only affected the footings of the building, but caused fissures of an alarming nature in the vaulting and walls. Under the direction of Mr T. G. Jackson a carefully designed arrangement of shoring was applied, consisting of raking shores, flying shores and needling, for the purpose of the underpinning, with specially designed timbering to support the arches and vaulting while they were undergoing repair. The foundations were found to be much undermined by water, which filled the excavations made for the underpinning in such quantities that it was necessary to employ a diver to deposit cement concrete in bagfuls upon the gravel bed to which the new foundations are taken down. The illustration (fig. 7) will readily explain the external shoring above described, while fig. 8 shows the interior shoring of the presbytery.
or 