The Constructor

Good Construction Practices and Techniques to Prevent Structural Damage

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Good construction practices and techniques should be followed to prevent occurrence of structural damages that may occur during occupancy and with age of the structure. A structure has to go through different stages in construction process. Each and every stage of construction is important to make sure that the structure being constructed will not experience damage under any general circumstances. Development of cracks in structure is the first sign of damage. Structural damage does not only reduces strength of the structure but it may also make it unfit for use to the extent that the structure collapses It is very important for the civil engineers to ensure good construction practices are followed at every stage of construction to prevent structural damage and failure of the structure.

Good Construction Practices and Techniques to Prevent Structural Damage

Following are the good construction practices and techniques that shall be followed for good quality and durable construction of structure:

1. Masonry work:

2. Concrete work:

- Aggregate and mixing water should be shaded from direct sun. - Part of mixing water may be replaced by pounded ice. - As far as possible concreting should be done in early hours of the day.

3. RCC frame work:

4. Plastering:

5. Concrete and terrazzo floor:

5. RCC Lintels:

Bearing for RCC lintels should be on the liberal side when spans are large so as to avoid concentration of stress at the jambs.

6. RCC roof slab:

Fig.1: Constructional detail of bearing of RCC roof slab over a masonry wall

On the inside, wall plaster and ceiling plaster should be made discontinuous by a groove of about 10 mm. For introducing the slip joint, the bearing portion of supporting wall is rendered smooth with plaster (preferably with neat cement finish), which is then allowed to set and partly dry. Thereafter either it is given thick coat of whitewash, or 2 to 3 layers of tarred paper is placed over the plaster surface, before casting of slab.

7. Provision of glazed, terrazzo or marble tile on vertical surface:

Before fixing of these tiles on vertical surface background component should be allowed to undergo movement due to elastic deformation, shrinkage & creep otherwise tiles are likely to crack and dislodged.

8. RCC work in exposed condition:

For RCC work in exposed condition i.e. sunshades, balconies, canopies, open verandah etc., to prevent shrinkage cum contraction cracks, adequate quantity of temperature reinforcement shall be provided. In such condition quantity shall be increase by 50 to 100 % of the minimum amount prescribed.

9. Finish on wall:

Finishing items i.e. distemper and painting etc. should be carried out after the plaster has dried and has under gone drying shrinkage.

10. Pace of construction:

The construction schedule and the pace of construction should be regulated to ensure :

11. Provision of reinforcement for thermal stresses:

To control the cracks in concrete due to shrinkage as well as temperature effect, adequate temperature reinforcement shall be provided. This temperature reinforcement is more effective if smaller diameter bars and the deformed steel is used than plain reinforcement.

12. Extension of existing building:

(a) Horizontal extension: Since foundation of an existing building undergoes some settlement as load comes on the foundation, it is necessary to ensure that new construction is not bonded with the old construction and the two parts are separated by a slip or expansion joint right from bottom to top. Otherwise, when the newly constructed portion undergoes settlement, an unsightly crack may occur at the junction. Care should also be taken that in the vicinity of the old building, no excavation below the foundation level of that building is carried out. When plastering the new work, a deep groove should be formed separating the new work from the old. When it is intended to make horizontal extension to a framed structure later on than the twin column with combined footing shall be provided at the time of original construction itself as under:

b) Vertical extension: When making vertical extension to an existing building (that is adding one or more additional floors) work should be proceeded at a uniform level all round so as to avoid differential load on the foundation. In spite of this precaution, however, sometimes cracks appear in the lower floors (old portion) at the junction of RCC columns carrying heavy loads and lightly loaded brick masonry walls due to increase in elastic deformation and creep in RCC columns. Such cracks cannot be avoided. Renewal of finishing coats on old walls of old portion should be deferred for 2 or 3 months after the imposition of additional load due to new construction so that most of the likely cracking should take place before finish coat is applied thus concealing the cracks.

13. Rich cement treatment on external walls:

When it is proposed to give some treatment on external walls of some rich cement based material i.e. artificial stone finish, terrazzo etc., the finish should be laid in small panels with deep grooves in both directions.

14. Movement joints:

To mitigate/relieve the magnitude of stresses due to thermal movement and shrinkage movement joints i.e. Expansion joint, Control joint and Slip joint shall be provided in the structure.

15. Filling in plinth:

Filling in plinth should be done with good soil free from organic matter, brickbats and debris etc. It should be laid in 25 cm thick layers, well watered and compacted to avoid possibility of subsequent subsidence and cracking of floors.
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