Tag: Shoring

Dead or Vertical Shores

Dead Shores or Vertical Shores

Dead Shores or Vertical Shores, In this system of shoring, the vertical members known as ‘dead shores’ are used to support temporarily the walls, roofs, floors, etc., by providing horizontal members known as needles, to meet one or more of the following objectives:

(i) To rebuild the lower part of a defective load bearing wall; or

(ii) To rebuild (or replace) or deepen the existing foundations, which have either become unsafe or require strengthening for carrying heavier loads; or

Dead Shores

Fig. Dead Shores

(iii) To provide large openings in the existing walls such as doors, windows, shop fronts or garages at a lower level.

In the above figure, the arrangement is shown to meet first two objectives. In this system, wooden need less consisting of thick sections are used to transfer the overhead loads to the properly braced vertical shores. These vertical or dead shores, in turn, transfer those loads to the ground on firm foundations below. The other details regarding introducing of rolled steel joists for supporting, strutting of floors by props, use of wedges, sole pieces, are self-explanatory).

In the below figure, the arrangement is shown to meet the third objective, i.e., providing a large opening in an existing wall. To meet this objective following procedure is adopted.

Dead shores

(i) Before providing shores to a building, all door and window openings are properly strutted to resist any possible deformation, and then inside floors of the building are also strutted by props or vertical posts. At the top and bottom of these vertical struts or posts, timber heads and sole pieces are provided to distribute the load more effectively, wedges are also used at the bottom or foot of prop for tightening purpose.

(ii) Holes are than cut in the wall by crow bar at points above the required opening, at a distance of I to 2.5 m depending upon the weight of structure above.

(iii) Through these holes, timber or steel horizontal beams, called needles, are inserted and projected at right angles on each side of the wall. The projected ends of needle beams are supported on heavy transfer the loads to the ground and hence are made to rest on a sole plate, firmly bedded on the ground.

(iv) The shores are removed only after the new construction work has attained sufficient strength and this period of removal usually is not less than 7 days.
(v) The sequence of removal of shoring system should be needles first and then strutting from openings and floor strutting inside the building.

NOTE: Sometimes, raking shores are provided to support the wall from above the proposed opening to safeguard against shocks and vibrations during wall cutting. If raking shores are used, they should be removed after the whole dead-shore system is removed.

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Flying or Horizontal Shores

Flying or Horizontal Shores

Flying or Horizontal Shores, in this type horizontal supports are provided for supporting temporarily the parallel walls of the two adjacent buildings, which may tend to collapse or damage when one of the intermediate buildings has to be pulled down and rebuilt see in the below figure.

Flying Shore

Such conditions occasionally arise when one of the intermediate buildings from a series of buildings standing side by side is either required to be reconstructed or has collapsed due to some reason.

A single flying shore consists of wall plates, struts, straining pieces, horizontal shore (or, horizontal strut), needles, cleats and wedges, as shown in the above image. Like inclined shores, in this system also, the wall plates are secured against the walls by means of needles and cleats. The horizontal shores is held in position by wedges, needles and cleats to the wall plate as shown at section (x). The inclined struts are supported by the needles at their one end and straining sill at the other end. Straining sill, in turn, is spiked to the horizontal shore.

The details of a simple raking shore (with three rakers, known as treble raking shore) are shown which can be employed up to 3-storey heights.

Flying Shores

(i) During reconstruction of the intermediate building, the flying shores temporarily take up the position of the dismantled building.

(ii) The centre-lines of flying shores and struts; and flying shore and walls, should meet at the floor levels. If the floor levels of two buildings are different or their strengths are different, then shore positions should be provided as shown in the below image.

Flying shores

(iii) The maximum distance of about 10 metre between the parallel walls can be supported by single flying shore. For a distance more than 10 m, a double flying shore, having a trussed form work as shown in Fig. 24.29, is employed.

(iv) The flying shores are kept in position so long as the adjacent buildings are made stable by constructing the building to a sufficient height.

(v) Unlike the inclined shoring in this type, only one set of shoring is employed to strengthen the two adjacent walls.

(vi) A larger factor of safety should be adopted in design analysis of flying shores because of uncertainty of actual loads. For shores to be more effective, the struts should be inclined at 45°, if possible.

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Raking Shores

Raking Shores

Raking shores is a system of giving temporary support to an unsafe wall. The construction of raking shores, also known as inclined shore, varies with the conditions of site. In all cases wall-plate 23 cm. X 5 cm. to 23 cm. x 76 cm. it size is fixed against the unsafe wall with hooks. The wall-plate is further secured to the wall by means of needles. The needles which are 10 cm. x 76 cm. in section penetrate inside the wall for a distance of about 10 cm In turn, the needles are strengthened by providing wooden cleats. The top end of the inclined rakers rest against the needles. At their base the rakers are supported by a sole piece bedded in an inclined position in the ground. The rakers are secured to the sole piece by cleats and dogs. In soft ground the area of the sole piece is increased so as to distribute the pressure over large area. In places where more rakers are provided, they are bound together by means of hoop iron or braces 25 cm. thick and 15 cm. wide. The inclination of the outer raker to the ground should vary between 60 to 75°. The sets of shores should be usually placed at 3 to 46 m. centre to centre along the wall length.

Raking shores

Fig. Raking Shores

 

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Shoring and Types of Shoring

Shoring and Types of Shoring

‘Shoring’ is the means of providing temporary support to attain stability of the structure under the following circumstances.

(i) To unsafe structures, the stability of which has been endangered due to the unequal settlement of the foundation, or due to the removal of adjacent buildings, or due to the defective or bad workmanship, or due to any other reason.

(ii) To structures which might become unstable, when certain alterations are required to be done in the structure itself (such as re-modelling of walls, etc.) or, during the alterations of adjacent buildings such as underpinning of (the adjacent building) foundations, dismantling of adjacent building, etc.

The following points in connection with the installation of shores should be noted.

(i) Temporary support by means of shores to unsafe structures may be given externally or intern ally and in certain cases they may be provided from both sides of the wall to produce additional stability. But, before the installation of shores, the necessary permission from the local authority should be obtained.

(ii) Shoring is used to maintain equilibriums the over-turning forces must be resisted by the supporting shores. To achieve this, it is essential that the lines of action of the overturning forces in floors and roofs, the forces in walls and the reaction of the shores must meet at a single point.

(iii) Shoring may be made of timber but for resisting heavy loads, it may be built of steel tubes, suitably braced steel sections or a combination of timber and steel tubes. Whatever material is used, shoring should be strong enough to resist the acting forces, consistent with economy.

(iv) This temporary shoring should be provided to unsafe structures till such times as they have been made stable.

Types of Shoring:

Shoring are classified into the following three classes either on the basis of their supporting characteristics or their position in the space:

1. Raking or Inclined Shores

2. Flying or Horizontal Shores

3. Dead or vertical shores.