Question

Q (a)why steel formwork is preffered ? Explain with neat sketchs , the formwork for RCC beam.

(b) What is meant by Demolition ? What are the factors affecting the evaluation of Demolition methods ?

Answer 1

Ans. (A)

(1) Steel forms are stronger, more durable and have longer life as compared with timber forms.

(2) They can be put to sufficiently larger number of re-used. For estimation purposes the number of re-used can be assumed to vary from 100 to 120.

(3) Steel forms can be installed and dismantled with greater ease and speed which results in saving in labour cost for this item of work.

(4) The quality of exposed concrete surface obtained by use of steel forms is excellent and it needs no further treatment. Thus there is saving in the cost of finishing the surface by use of steel forms.

(5) there is no danger of the formwork absorbing water from the concrete and thus the chances of honeycombing are minimised.

(6) they are not liable to shrink or distort and hence it is possible to achieve better workmanyand higher degree of accuracy by the use of steel forms.

FORMWORK FOR A RCC BEAM

A) Propping and Centering

The props used for Centering may be of steel, timber posts or balloes. Pillars made up of brick masonry in mud mortar are also sometimes used as props. Double wedges are essentially provided between the sole plates and the timber props with a view to permit accurate adjustments of the shuttering prior to the concreting operation and to facilitate easy removal of the shuttering afterwards.

B) Shuttering

The Shuttering is adjusted and fixed Accord to the shape of the designed beam. It can be made up of timber planks, or plulywood or by welding steel plates to angle framing. Shuttering should be constructed in such a manner that the joints should be tight against the leakage of the cement grout.

C) Camber

An upward camber is provided to the shuttering during the construction of the formwork to allow for the deflection of the beam which is inevitable. The provision of desired camber is made during the erection particularly in case of beams having long spans.

D) Cleats

Cleats are used at regular intervals along the span of the beam to hold the Shuttering at its position.

E) Struts

Struts are used to support the ledgers which in turn support the Shuttering of the beam in its position. The ledgers are horizontal members which are fixed at regular intervals along the span of the beam.

Ans. b

Demolition is the process of destroying down or dismantling or collapsing down of large
buildings after its useful life period. The process of demolition is carried out with the help of some
equipment or other methods with legal procedure followed by the consent of the local authority. We
know that every structure is designed for a specific life period generally 100 years. The existence of
the structure after the service life period is over is very dangerous to its occupants and surrounding
buildings. The purpose of demolition is to prevent the accidental collapse of any part of the building
and to ensure safety of workers, public and neighboring properties.

METHODS OF DEMOLITION
The demolition sequence will depend on things like the type of construction, location, and
demolition methods selected. Buildings and structures should generally be demolished in reverse
order to their construction, that is, by "sequential demolition‟.

The different methods of demolition
are as below –
1. Demolition of building by Top Down- Manual Method
Manual methods are carried out top down, proceeding, in general, from the roof to ground. The
particular sequence of demolition may vary, depending on site conditions and structural elements to
be demolished.
2. Demolition of Cantilevered Structures and Balconies
Cantilevered structures, balconies and canopies may project out of the building over the
pedestrian footpath or in some cases over a portion of the traffic lane. The general sequence of dismantling cantilevered slabs and beams are described in the following:
i. The exterior wall shall be demolished first.
ii. Any structure or dead load supported by the cantilevered system shall be removed prior to
demolishing the cantilevered slabs and beams.
iii. The concrete shall be broken down gradually starting from the exterior edge of the
cantilevered floor, working inwards and toward its supporting beams.

3. Demolition of building by Top Down- By Machines
The sequence of demolition by machine is typically the same as the top down manual method,
except that most of the demolition is done by mechanical plant. The demolition begins with the
lifting of the mechanical plant on to the building top floor. When rope or tie wire is used for pulling,
the workers shall be protected or stay away from the area within reach of the rope or tie wire. The
concrete shall be broken away first before the cutting of reinforcement. Alternatively the reinforced
concrete slab may be cut by saw cutting.

4. Demolition of building by implosion
Implosion is the strategic placing of explosive material and timing of its detonation so that a structure
collapses on itself in a matter of seconds, minimizing the physical damage to its immediate
surroundings. The technique weakens or removes critical supports so that the building can no longer
withstand the force of gravity and falls under its own weight.