Shoring

Shoring

This is the process of applying temporary supports to a building to avoid the danger of it collapsing on any person.

The functions of shoring or the situations where it‟s commonly required are as follows;

1. To give support to walls which are dangerous or are likely to become unstable due to subsidence, bulging or leaning.
2. To avoid failure of sound walls caused by the removal of subjacent supports such as where a basement is being constructed near to a sound wall.
3. To give support to an adjacent building or structure during demolition works.
4. To support the upper part of the wall during formation of a large opening in the lower section of the wall.
5. To give support to a floor or roof to enable a support wall be removed and be replaced by a beam.

Structural softwood is the usual material used for shoring members it‟s strength to weight ratio compares favourably with that of structural steel.

Types of shoring (shoring systems)

There are three shoring systems; namely:

1. Dead shoring: This type of shoring is used to support dead loads, which act vertically It consists of a vertical prop or leg with a head plate, sole plate and some means of adjustment for tightening and easing the shore.

The steps taken or the operational sequence for erecting a successful dead shoring arrangement are as follows;

1. Carry out a thorough site investigation to determine;
   1. Number of shores required,
   2. ii) Bearing capacity of soil and floors,
      • Location of underground services which may have to be avoided.
2. Fix ceiling struts between suitable head and sole plates to relieve the wall of floor and roof loads. The struts should be positioned close to the walls.
3. Strut all window openings with in the vicinity of the shores to prevent movement or distortion of the opening.
4. Cut holes through the walls slightly larger in size than the needles to enable them pass through.
5. Cut holes through ceilings and floors for the shore legs.
6. Position and level sleepers on a firm base.
7. Erect, wedge and secure shoring arrangements.

Upon completion of the builders work it’s advisable to leave the shoring in place for at least seven days before easing the supports to ensure that the new work has gained sufficient strength to be self-supporting. See fig 2.6a

2. Raking shores: This shoring arrangement transfers the floor and wall loads to the ground by means of sloping struts or rakers. One rake for each floor is required and ideally should be to an angle between 40 and 70 with the horizontal.

The steps taken or the operational sequence for erecting raking shores are as follows;

1. Carrying out site investigations as described for dead shoring,
2. Mark out and cut mortises and housings in wall plates,
3. Set out and cut holes for needles in external walls,
4. Excavate to a firm subsoil and lay a grillage platform and sole plate,
5. Cut and erect rakers commencing with the bottom shore,
6. Fix cleats, distance blocks, binding and if necessary cross bracing over the backs of the shores. See fig 2.6b

3. Flying shores: These shores fulfil the same functions as raking shores but do so between any parallel surfaces. This has the advantage of providing a clear working space under the shoring. The site operations for the setting out and erection of flying shoring systems are similar to those for raking shoring. See fig 2.6c

Scaffolding

This is the process of putting up a temporary structure (scaffold) from which persons can gain access to a place of work in order to carry out building operations. This includes any working platforms, ladders and guardrails.

There are two basic forms of scaffolds and these are:

2. Putlog scaffolds: This type of scaffolding consists of a single row of uprights set away from the wall and tied to the building with cross members called putlogs. The uprights or standards are joined together with horizontal members called ledgers and the whole scaffold is erected as the building rises. It‟s mostly used for buildings of traditional brick construction. See fig 2.7a
3. Independent scaffolds: This has two rows of uprights or standards, which are tied by cross members called transoms. This type of scaffold does not rely upon the building for support and is therefore suitable for use in conjunction with framed structures. See fig 2.7b

The materials used for scaffolding include;

1. Tubular steel
2. Tubular aluminum
3. Timber.

Timber scaffold

Logs obtained from young fairly straight trees, which are cut to about 4m lengths are used. The members are lashed together with wire or rope and nails may also be used to join one piece to another.

Advantages

1. In areas where timber is plentiful it is cheap and easily obtained.
2. No fittings used.
3. No extra maintenance costs.
4. Easily cut to size.
5. Wastes and old logs can be sold as firewood. It therefore has high scrap value

Disadvantages

1. Use is restricted to low-rise buildings only.
2. As the logs are made from young trees, they are prone to insect attack, thus limiting their length of usefulness.
3. Large holes are left in the wall after use and these need to be patched.
4. Regular replacement is essential in order to avert likely failure resulting from over dried logs.

Tubular scaffold

Steel and light-alloy tubes are the commonest materials used for this type of scaffolding and metal coupling fittings are used to secure members together.

Advantages

1. Less likely to deteriorate compared to timber.
2. If correctly used its more rapidly erected.
3. More convenient for internal work owing to wider range of widths.
4. Takes up less space when stored.
5. Used for multi-storey buildings

Disadvantages

1. High cost of preservation.
2. High initial cost.
3. Many types of couplers needed.

Gantries

These are elevated platforms used when the building being maintained or under construction is adjacent to a public footpath. A gantry over a public footpath can be used to support an independent scaffold, housing units of accommodation or storage of materials. See fig 2.8a