What is Shoring?
- When a wall shows signs of bulging out due to bad workmanship.
- When we have to repair a crack on the wall due to unequal settlement of foundation.
- When an adjacent structure is to be dismantled.
- When openings are to be made or enlarged in the wall.
Types of Shoring
Shores may be of the following types:
- Raking Shores
- Flying Shores
- Dead Shores
1. Raking Shores
In this method, inclined members, called rakers are used to give lateral support to the wall as shown in Fig.1.
A raking shore consists of the following components:
- Rakers or inclined members,
- Wall plate,
- Bracing, and
- Sole plate.
The wall plate (20 to 25 cm wide and 5 to 7.5 cm thick) is placed vertically along the face of the wall and is secured by means of needles.
These needles (10 cm x 7.5 cm) penetrate the wall by about 10 to 15 cm. In order that the needles do not get sheared off due to the thrust of the raker, the needles are further strengthened by means of cleats which are nailed directly to the wall plate.
Rakers about against the needles in such a way that the centerline of the raker and the wall meet at the floor level. Thus, there will be one raker corresponding to each floor. These rakers are inter-connected by struts, to prevent their buckling.
An inclined sole plate is embedded into the ground on which the feet of rakers are connected. The feet of rakers are further stiffened near the sole plate by means of hoop iron. The wall plate distribute the pressure to the wall uniformly.
The following points are keep in mind when using Raking shores:
- Rakers should be inclined to the ground by 45° to 75°, but 45° is more effective. The Top of raker should not be inclined steeper than 75°.
- For tall buildings, the length of raker can be reduced by introducing rider raker.
- Rakers should be properly braced at intervals.
- The size of the rakers should be decided on the basis of anticipated thrust from the wall.
- The centre line of a raker and the wall are maintained at the same level of floor.
- If longer length of the wall needs support, shoring may be spaced at 3 to 4.5 m spacing, depending upon the requirements.
- The sole plate should be properly embedded into the ground, at an inclination and should be of proper sectiod. The sole plate should be sufficient widen so that it can easily support all the rakers, and a cleat provided along the outer edge.
- Wedges should not be used on sole plates since they are likely to give was under vibrations which are likely to occur.
2.Flying or Horizontal Shores
Flying shores are a support system which provides horizontal support to two parallel party walls when removal or collapse of the intermediate building takes place.
All types of shoring system of supporting the unsafe structure in which the shores do not reach the ground are the flying shores. If the walls are quite near to each other (distance up to 9 m), single flying shore (Fig.2)
It consists of well plates, needles cleats, struts, horizontal shore straining pieces and folding wedges. When the distance between the walls is more, a compound or double flying shore (Fig.3) may be provided.
In this system operations of the building in the ground are not obstructed.
The following points should be kept in mind while connecting the flying shores:
- The center lines of flying shore and struts and those of the walls should meet at floor levels of the two buildings. If the floor level are different, the horizontal shore should be placed either mid-way between the levels of the two floor of equal strength, or it should be placed at the level of weaker floor.
- The struts should preferably be inclined at 45°. In no case should this inclination exceed 60°.
- Single shores should be used only up to 9 m distance between walls. For greater distance, double shores should be provided. In that case, both the horizontal shores should be symmetrically placed with respect to the floor levels.
- The flying shores should be spaced at 3 to 4.5 m centers, along the two walls; and horizontal braces should be introduced between adjacent shores.
- In this system, various members of the shoring are determined by using large factor of safety because it is uncommon to assess the actual loads.
- When there is a structural gap between two building due to removal of old building then, flying shore are inserted and removed after construction of new structure.
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3.Dead or Vertical Shores
Dead shore is a shoring system in which a dead shore in the form of vertical member support horizontal needles which transfer the load of the wall, roofs and floors etc.
The needles transfer the load of the wall etc., to the dead shores.
This type of shoring is use for the following purposes:
- To rebuild the defective lower part of the wall.
- To rebuild or deepen the existing foundation.
- To make large opening in the existing wall at lower level for underpinning and such type of work.
First of all holes are made in the wall at calculated height. Then needles made of thick wood or steel sections are inserted into the holes and are supported on vertical posts or dead shores on both sides. This type of shoring system is keep away from the wall for easy to do repair work. Dead shores are supported and anchor on plates and folding wedges.
The following points are to be considered for vertical shore:
- The section of needle and dead shores should be perfect to transfer the load, which can estimate with a fair degree of accuracy.
- The needles are spaced at 1 to 2 meters. A minimum of three needles should be used for and opening.
- The needles should be suitably braced.
- Sometimes opening is made in an external wall, that case the length of the outer shores is longer than inner ones.
- The dead shores are stable and rest on sole plates. Folding wedges should be inserted between the two. It is preferable to use one single sole plate between dead shores in a raw.
- The floors should be suitably supported from inside.
- In case the external wall is week then dead shore is not provided, in that case raking shores are provided.
- After 7 days of completion of the work shoring is removed making sure that new work has gained sufficient strength. The new work should have proper strutting.
- The sequence of removal should be (i) needles, (ii) strutting from opening, (iii) floor strutting inside, and (iv)raking shore if any at the interval of 2 days.
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