What Is Shoring?
Shoring is the construction of temporary lateral support for an unsafe structure. It provides further safety to the unsafe structure. Different types of shoring, such as raking shoring, flying shoring, dead shoring are used under the following situations:
- Bulging out of walls due to poor workmanship.
- Dimolishing an adjacent structure.
- Unequal settlement of foundations causing cracks in walls.
- When additions and alterations are to be done in safe structure.
All the shoring members should be strong enough so that they can withstand the expected loads. Shoring is made of steel tube, or timber, or using both. The duration of shoring depends upon the condition of the unstable structure.
It can be for a week or even up to a year. Shoring is removed when the unstable structure is made safe by providing necessary repairs and modifications.
Types Of Shoring
Depending upon the nature of supports there are mainly three types of shoring.
- Raking Shores,
- Flying Shores,
- Dead shores.
1. Raking Shores
In this type of shoring, inclined members called rakers are used to provide temporary support to an unsafe wall. Raking shores are also known as inclined shores. It consists of the following components:
- Wall plate
- Sole plate
In this arrangement, the wall plate of 23 cm x 5 cm or 23 cm x 7.5 cm in section is placed vertically against the wall and secured by needles of 10 cm x 7.5 cm in section.
These needles penetrate into the wall at a depth of 15 cm. The needles are further strengthened using cleats which are directly nailed to the wall plates.
The top ends of rakers rest on the needles, and the bottom ends rest on sole plate. The rakers are secured to the sole plate by iron dogs and grouped together by hoop irons.
All the rakers are further stiffened by bracings. Thus the wall plate uniformly distributes the pressure to the wall.
Important points to be kept in mind while using raking shores:
1. The inclination angle of top rakers should not exceed 75 with the horizontal. The angle usually varies from 45 to 75.
2. For high-rise buildings, the length of top raker can be reduced by using a rider raker.
3. All the rakers should be braced properly at intervals.
4. Wedging of members should be avoided.
5. The center line of a raker and wall should meet at floor level.
6. If a wall with longer length requires support, shoring with a spacing of 3 to 5 m can be provided.
7. Cleats should be fixed on the sole plate to prevent outward slippage.
2. Flying Shores
Flying shores are used to provide horizontal support to the parallel walls of two adjacent buildings that may collapse without support. These types of shores do not rest on the ground. Flying shores are also known as horizontal shores.
It consists of the following components.
- Horizontal or flying shores
- Wall plate
- Straining pieces
- Folding wedges
If the distance between two walls is not much ( up to 9m) single flying shore with one bully can be provided. If the distance is more double or flying shore can be constructed.
In flying shores, wall plates are placed horizontally to the wall and secured by needles. Cleats are also nailed into the wall plates to provide additional support to the needles.
The horizontal shore is placed between the wall plates and supported by needles and cleats. Inclined struts are also provided which are supported by needles and straining pieces.
Important points to be kept in mind while using flying shores
1. The center lines of flying shores and struts should meet at the floor level of two buildings. In case of different floor levels, flying shores should be provided either mid-level of two floors of equal strength or at the level of the weaker floor.
2. The inclination angle of struts should be 45 and it should not exceed 60.
3. Single shore is preferable only up to a distance of 9m between two walls. For more than that double flying shore should be provided.
4. The spacings between flying shores should be 3 to 4.5 m.
5. Large factor of safety should be considered during design.
3. Dead Shore
This type of shoring is used to support dead loads of a structure. It consists of vertical bullies or posts called dead shores and horizontal members called needles. Dead shoring is provided for the following purposes:
- To strengthen or deepen weak foundation without demolishing the whole structure.
- To rebuild the lower part of structure.
- To replace old or deteriorated walls by new walls.
- To create large openings in existing safe wall.
In this arrangement, holes for needle beams are made in the wall at such height to allow sufficient space for insertion beams to carry the load of the structure.
Then needle beams are inserted in the holes and supported by vertical props on the side of the wall. Folding wedges, sole plates, dogs, and braces are used to tighten the props.
Important points to be kept in mind while using dead shores
1. Before installation needle beams and vertical posts all the floors and openings near and above dead shore should be suitably supported and strutted.
2. The section of needles and dead shores should be adequate so that they can transfer the estimated load properly.
3. The spacing of needles should be 1 to 2 m.
4. The needles should be braced properly.
5. The length of the outer dead shore should be greater than the inner dead shore if opening has to be made in the external wall.
6. If the external wall is very weak, raking shores may also be provided along with dead shores.
7. Shores can be removed only when the new construction has gained desired strength. The correct sequence of removing shoring members is needles > Strutting > Floor strutting inside > Raking shore (if any). An interval of 2 days between the removal of these members should be considered.