FOOTING AND ITS TYPES

Building Construction Ideas - Topic 6

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What is Footing ?
Footings are structural elements, which transfer loads to the soil from columns, walls or lateral loads from earth retaining structures. In order to transfer these loads properly to the soil, footings must be design to
• Prevent excessive settlement
• Minimise differential settlement, and
• Provide adequate safety against overturning and sliding.

Broadly, footing can be classified in following types as shown in the chart below:

CONVEYING METHODS OF CONCRETE

Building Construction Ideas 

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How to supply and transport concrete ?

The structural concrete shall be supplied to each part of the structure being concreted without unnecessary unloading and reloading. Distributing it on the structure is performed by using light conveyor feeders, vibrating feeders, chutes, skips, pumps, compressed air and vibrating troughs. The method of handling and conveying and the composition of the concrete shall be so adjusted among the various operations as to obviate segregation and shall be subject to the approval by the Engineer.

Buckets

The capacity of the buckets shall conform to the size of the concrete batch, or a multiple thereof, in order that there will be no splitting of batches in loading buckets. It shall be capable of prompt discharge of low-slump, lean-mix concrete. The dumping mechanism shall permit discharge of a relatively small portion of concrete in one place. Buckets shall be filled and discharged without noticeable separation of coarse aggregate.

Trucks

Trucks are convenient for conveying concrete from batching plant to structures in exceptional cases only. No free water shall be on the surface of the concrete as delivered, nor shall segregation of coarse aggregate occur.

Chutes

Use of chutes is to be avoided as far as reasonably possible but the operations if any must be controlled in a way that segregation and objectionable loss of slump will be avoided. Concrete which has been transported in non-agitating equipment and whose consistency has suffered from transport vibrations shall not be reworked by adding water prior to placing and shall thus not be used unless explicitly approved by the Engineer.

Belt Conveyors

Slump loss, in use of belt conveyor, is largely preventable by protecting the belt from the sun and wind. Segregation, which occurs chiefly at transfer points and at the end of the conveyor, shall be avoided by use of a suitable hopper and drop chutes.When belt conveyor carries concrete, scrapers and devices for holding the concrete together at the throw-off point shall be provided.

Pumping

For conveying concrete by pumping, it shall not be permitted to use light alloy pipes. Pipelines for pumping concrete shall be laid in such a way that no interruption can occur in the flow of concrete in the pipe. Pump lines shall be as short as possible.

The concrete pumping plant shall be provided with a water pressure valve, connecting pipe with needle valve cleaning rods, outlets for drainage of water, and a high-pressure (30-35 kg/cm2) centrifugal pump for flushing out the concrete pipelines. Pipes for pumping concrete shall have a

minimum inner diameter of 15 cm. Pipe joints for concrete pumping shall permit a deviation in pipeline axis by at least 3 degrees. They shall be of the quick-connection type to permit easy disconnection and emptying if concrete gets stuck in the conveying pipeline and cannot be moved.

At the end of the pumping operation the conveying pipeline shall be immediately emptied and cleaned (blowing out).

Truck Mixers

Truck mixers consist of equipment mounted on trucks and capable of mixing concrete in conveying between the batching plant and the point of placing. There is often considerable slump loss in truck-mixed concrete, especially in warm weather. Such loss shall be kept to a minimum by stopping the initial mixing at 30 revolutions and/or to reduce the rotary speed to avoiding over mixing.

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PCC BELOW FOOTING

Building Construction Ideas - Topic 5

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After completing Boulder Soling of required depth in footing, PCC Should be done over it.

PCC stand for Plain Cement Concrete. It is called plain because there is no reinforcement involved in it. The height of the PCC in foundation ranges from 10-15 cm and it is done of exact size (L*B) of footing. 

Fig 1: PCC in foundation ( Rebar as column centre) 

Here are the process of doing PCC in foundation:

Preparation of Surface

1) Check the line and level of the boulder soling in all the footings ( check level by the help of auto level) . If there is +- 2 cm in level difference, you can proceed for PCC.

2) Give a required level in all the foundation with the help of auto level or give it in one foundation and transfer the level in other foundation with the help of level pipe.

3) Prepare the formwork of required size and place it on the boulder soling. Formwork is not mandatory for the PCC but it is advised for good finish. Boulder soling of extra 5cm on all faces is advised for perfect placement of formwork.

4) Once the line and level is fixed, the surface should be cleaned by water. The mud attached with stones should be washed completely for the placement of concrete. 

Concreting

1) Generally, the ratio of concrete used for PCC is 1:3:6 ( M10).

2) 1 bag of cement is used for preparing 1 batch concrete and aggregate shall be measured by volume in a gauge box of correct and approved size based on the weight of the material or by other approved accurate means i.e. 3 box of sand and 6 box of aggregate.

Fig 2: Wheelbarrow

3) Water Cement Ratio for M10 concrete is taken approximately 0.70 i.e. 34-36 Ltr of water is required for 1 batch of concrete.

4) The cement and aggregates shall be thoroughly mixed together until the mix is uniform in the specified proportions by volume in a batch type mechanical mixer. 

5) Concrete shall be transported with the help of wheelbarrow (gada).

BOULDER SOLING IN FOUNDATION

Building Construction Ideas - Topic 4

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Once the Earthwork Excavation work is completed for footing, next immediate permanent work to be done is Boulder (stone) Soling.

Fig 4.1: Boulder Soling for Isolated Footing

But before this the bed on which boulder soling is to be laid shall be cleared of all loose materials, levelled,watered and compacted and got approved by the Engineer before laying boulder soling. All soft places in the sub-grade(soil) should be excavated and filled with compaction. 

Over the prepared surface, the stone should be set as closely as possible and well packed and firmly set. The rubble stone should be of best variety of black trap/granite/basalt or other approved variety of stone. The stone should be hard, durable, free from defects and weathering and of required size. The size of the rubble stone shall not be less than the soling thickness. The stones should be of full height and should be laid so as to have their bases of the largest area resting on the sub-grade. Soling should be laid in one layer of specified thickness of soling with a tolerance of 25 mm. After packing the stones properly in position, the gaps between them should be carefully filled with quarry spoils or stone chips of larger size possible to obtain a hard, compact surface. Spreading of loose spoils or stone chips should not be done. After soling, the finished surface should be in required line & level and the surface should look neat finish.

Fig 4.2: Boulder Soling for Combined Footing

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EARTHWORK EXCAVATION

Building Construction Ideas - Topic 3
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After proper setting out is done as per previous article (setting out) we start the earthwork excavation work.

Earthwork excavation shall include removal of all materials, of whatever nature and whether wet or dry, necessary for the construction of foundation and substructure exactly in accordance with the lines, levels, grades and curves as shown on the drawing or as directed. It shall be taken to the exact width of the lowest step of the foundation and its sides shall be left plumb where the nature of the soil admits it. If necessary, depending on the nature of the soil, it could be cut in slope up to 1 in 6 (1 horizontal to 6 vertical).  Any caving in of earth should be cleared and re-excavated.

Excavated material should be handled to allow suitable material to be recovered and placed in the embankment. Suitable materials shall be deposited within the designated areas of the work as shown in the plans or as directed by the Engineer. If at the time of excavation, it is not possible to place any suitable material in its proper section of the permanent construction, it shall be stockpiled in approved areas for later use. The excavation shall not be carried out below the level of the existing adjacent foundations.If it is necessary for some reason to excavate below the adjacent foundations, these foundations shall be underpinned and shored.

LAYOUT (SETTING OUT) OF BUILDING

Building Construction Ideas- Topic 2

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After clearing the site as mentioned in previous article (site clearance) centre lines should be fixed and install substantial reference marks, benchmarks etc. and maintain them as long as required true to line, curve, slopes and level. Engineers should give proper alignment, elevation and dimension of each and all parts of the work.

Basic Process of Layout

Step 1: Find a centre point of a corner or centre of column by the given references in the drawing with the help of two tape measurement. It is always good to measure on the ground and if it's not possible, measure at minimum possible height and with the help of plumb bub, transfer the point on the ground for accuracy. Insert the peg/rebar at that point.

Step 2: Measure one of the adjacent side from that point and fix it. Measure the distance from reference point to the second point. If its not correct, shift the point so that the distance from first point and reference point match according to drawing. Fix the point permanently. ( One of the side of building is fixed) 

NEPAL ROAD STANDARD 2070 PDF

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SITE CLEARANCE FOR BUILDING CONSTRUCTION

Building Construction Ideas- Topic 1

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What is Site Clearance ?

    Once the design, contract process and mobilisation are completed, the site where building is to be constructed should be cleared. Site clearance might include the clearance of rubbish, top soil, all trees, stumps, bushes, roots, down timber, rotten wood, rubbish, debris, humus, swamp material and any other vegetation or unacceptable material.

Clearance of Bushes and Grasses

All material removed by clearing and grubbing operation which is useful to the Employer shall be stockpiled in accordance with the requirements of the Employer. Unwanted material shall be removed from the Site and dumped on places after prior permission has been obtained.