EDUCACIÓ EMOCIONAL

Each column and each wall carrying vertical load should be tied continuously from the foundation to the roof level. The reinforcement provided is required only to resist a tensile force equal to the maximum design ultimate load (dead and imposed) received from any one storey.

Bearingfor Precast Units

Precast units shall have a bearing at least of 100 mmon masonry supports and of 75 mm at least on steel or concrete. Steel angle shelf bearings shall have a 100 mm horizontal leg to allow for a 50 mm bearing exclusive of fixing clearance. When deciding to what extent, if any, the bearing width may be reduced in special circumstances, factors, such as loading, span, height of wall and provision of continuity, shall be taken into capacity in the particular situation in which the joint is to function.

b) Practicability — Practicability of joint shall be determined by the amount and type of material required in construction; cost of material, fabrication and erection and the time for fabrication and erection.

c) Serviceability — Serviceability shall be determined by the joints/expected behavior to repeated or possible overloading andexposure to climatic or chemical conditions.

d) Fire rating — The fire rating for joints of precast components shall be higher or at least equal to connecting members.

e) Appearance — The appearance of precast components joint shall merge with architectural aesthetic appearance and shall not be physically prominent compared to other parts of structural components.

2.11.6 Design Requirements for Safety againstProgressive Collapse

Prefabricated buildings shall be designed with proper structural integrity to avoid situations wheredamage to small areas of a structure or failure of singleelements may lead to collapse of major parts of the structure.

The following precaution may generally provide adequate structural integrity:

a) All buildings should be capable of safely resisting the minimum horizontal load of 1.5 percent of characteristic dead load applied at each floor or roof level simultaneously.

b) All buildings shall be provided with effective horizontal ties, 1) Around the periphery;

2) Internally (in both directions); and 3) Columns and walls.

c) All buildings of five or more storeys shall be provided with vertical ties.

In proportioning the ties, it may be assumed that no other forces are acting and the reinforcement is acting at its characteristic strength.

Normal procedure may be to design the structure for the usual loads and then carry out a check for the tie forces.

2.12. Stages of Loadings

There were two stages of loadings. In the first stage, the structure is loaded with the Ultimate Superimposed Design Load. In the second stage, going beyond the Ultimate Superimposed Design Load, the structure is loaded with a point load in the center, which was increased until the structure failed. In this case, the test is stopped before catastrophic failure because of space limitations of the test setup.

2.13Stages of Prefabricated Concrete Product

2.14 Materials

Concrete: The most common grade of concrete for precast is M30 to M60. The type of concrete depending upon the structural requirements. The code specify SCC, Light weight aggregate concrete and Cellular Concrete.

Steel: Generally High tensile hot rolled ribbed bars are used for precast reinforced construction.

Diameter of steel varies from 6mm to 40mm.

2.15 Methods of Prefabrication Site prefabrication:

In this scheme, the components are manufactured at site near the site of work as possible. This system is normally adopted for a specific job order for a short period. The work is normally carried out in open space with locally a valuable labour force. The equipment machinery and moulds are of mobile nature. Therefore there is a definite economy with respect to cost of transportation. This system suffers from basic drawback of its non-suitability to any high degree of mechanization. It has no elaborate arrangements for quality control.

Plant prefabrication:

Factory prefabrication is restored in a centrally located plant for manufacture of standardized components on a long form basis. It is a capital intensive production where work is done throughout the year preferably under a covered shed to avoid the effects of seasonal variations high level of mechanization can always be introduced in this system where the work can be organized in a factory like manner with the help of constant team of workmen.

The basic disadvantage in factory prefabricated, is the extra cost in occurred in transportation of elements from plant to site of work sometimes the shape and size of prefabrication.

Semi-mechanized

The work is normally carried out in open space with locally available labour force. The equipment machinery used may be minor in nature and mouldsare of mobile or stationary in nature.

Fully-mechanized

The work carried out under shed with skilled labour. The equipment’s used are similar to one of factory production. This type of precast yards will be set up for the production of precast components of high quality, high rate of production.

2.16 Process of Manufacture

The various processes involved in the manufacture of precast elements are classified as follows:

Main Process

It involves the following steps.

1) Providing and assembling the moulds, placing reinforcement cage in position for reinforced concrete work, and

2) Fixing of inserts and tubes where necessary.

3) Depositing the concrete in to the moulds.

4) Vibrating the deposited concrete into the moulds.

5) Demoulding the forms.

6) Curing (steam curing if necessary)

7) Stacking the precast products.

Secondary (Auxillary) Process

This process is necessary for the successful completion of the process covered by the main process.

1) Mixing or manufacture of fresh concrete (done in a mixing station or by a matching plant).

2) Prefabrication of reinforcement cage (done in a steel yard of workshop)

3) Manufacture of inserts and other finishing items to be incorporated in the main precast products.

4) Finishing the precast products.

5) Testing the precast products.

2.17 Production Methods

The term production of systems is describes a series of operation directly concerned In the process of making or more apply of moulding precast units on the face of it there are very many techniques since almost every type prefabricates requires a specific series of operation in its production.

These techniques however may be grouped into three basic method of production. These are 1. Stand Method

2. Flow Method

a) The ‘Stand Method’ where the mouldsremainstationary at places, when the various processes involved is carried out in a cyclic order at the same place.

b) The ‘Flow Method’ where the precast unit under consideration is in movement according to the various processes involved in the work which are carried out in an assembly-line method.

The various accepted precasting methods are listed in below Table (given in IS: 15916-2011) with details regarding the elements that can be manufactured by these methods.

2.18 Quality Control At Factory

Ordinance (“BO”) and the approved plans.

to conditions stipulated by the BO and in the approved plans.

e precast concrete works.

“QAS”) provided by the manufacturer satisfies the purpose in that the manufacturer has made adequate provisions ensuring the production of the precast elements complies with the provisions of the BO and the approved plans.

with the QAS prepared by the manufacturer in application for consent to commence work.

’s stream) to supervise the precast concrete production works at a frequency of not less than once a week.

g book recording details of the supervisory personnel and details of the production, inspection, auditing and testing carried out for the production of the precast units.

book at the site office.

elements at least once every month. Prepare audit reports for submission.

s.

to carry out regular technical audits of the factory and the production of the precast units at a minimum frequency of once per month.

to conditions stipulated by the BO and in the approved plans.

tor (T3 TCP under the RC’s stream) to provide continuous supervision of the precast concrete production works. Provide supervisory personnel at the factory and an inspection log book recording details of the supervisory personnel and details of the production, inspection, auditing and testing carried out for the production of the precast units.

Make sure the log book is available for inspection at all time by keeping the log book at the site office.

d production of the precast units at least once every month by the Authorized Signatory of the RC. Prepare and submit the audit reports to the AP/RSE for endorsement and onward submission for record purposes.

Duties of the manufacturer

lements shall be manufactured by a factory possessing an ISO9000 quality assurance certification.

subsequently to make application for consent to commence works.

aintain the quality of the manufacturing of the precast elements.

to carry out regular technical audits of the factory and the production of the precast elements at a minimum frequency of once per month.

The QAS shall cover but not be limited to the following items:

-bars, finishes and building services provisions.

such as the frequency and standards adopted for the equipment used for the cube compressive strength test.

employed and demoulding details.

such as details of the curing procedure and associated controls.

by the independent parties employed by the manufacturer or the RC.

quality assurance scheme and in accordance with the specification and the approved plans.

Where Authorized Person (AP),

Number of moulds with estimated production rate Machinery employed

3. Production procedures (casting and transportation of the precast units within the yard).

4. Quality control procedures on materials and check points for Concrete

re-bar Couplers finishes

Building services installations

5. Quality control procedures on production and check points.

Approved plans used.

6. Calibration of testing equipment (responsible parties, frequency, and standards)

7. Testing of precast units such as dimensional check, cover meter test, pull-out test for tiled finishes, bonding test for building services installation, etc.

8. Concrete repair procedures.

9. Handling of non-compliant precast units with corrective/preventive action.

10. Inspection forms.

11. Identification system of the precast units.

12. Audit by independent parties.

2.20 Construction Methodology 1. Production Planning

Generally, the production cycle is one day for a non-complicated precast element. In planning the production of precast elements, time of construction of each floor is a key factor in estimating the number of precastingmoulds.

For example, in a project consisting of 15 precast façades per storey and a working cycle of 6 days per storey, the number of mould required is 3. A storage area in the precast yard should be sufficient to accommodate precastelements delivered to the construction site and extra precast elements in caseof emergency delivery.

Example of a working schedule for production planning is shown in below figure.

Working schedule for precast unit.

For the production of precast elements, the precast manufacturer requires about or at least 1.5 months for manufacturing the moulds and 0.5 month for production of the precast units.

Therefore, the precast shop drawing (showing geometrical size) should be consolidated at least 2 months in advance of the scheduled date of delivered to site. All the above should be allowed for in addition to the time required for approval and consent by government or client.

Embedded items including window frames, E/M pipe sleeves and openings in precast elements should be delivered to the precast yard before production.

Unlike traditional in-situ construction, this requires coordination and approval of embedded items at an early stage. For projects with a large number of precast elements, time required for the above would be much longer and has to be taken into account.

2. Moulds