STAIRS TYPES AND THEIR USES

Types of stairs is broadly based on the shape of the stairs. Straight stairs, Turning stairs and Continuous stairs are broad types of stairs.

A stair is a set of steps leading from one floor of a building to another, typically inside the building. The room or enclosure of the building, in which the stair is located is known as staircase. The opening or space occupied by the stair is known as a stairway.

Types of Stairs – Classification of stairs:

Stairs can be broadly classified into three types:

1. Straight stairs

2. Turning stairs

3. Continuous stairs

1. Straight stairs:

Generally for small houses, available width is very retractable. So, this type of straight stairs are used in such conditions which runs straight between two floors. This stair may consists of either one single flight or more than one flight with a landing.

2. Turning stairs:

Turning stairs are sub classified as:

a) Quarter turn stairs

b) Half turn stairs ( dog legged stairs)

c) Three – quarter turn stairs

d) Bifurcated stairs

a) Quarter turn stairs:

A quarter turn stair is the one which changes its direction either to the right or to the left but where the turn being affected either by introducing a quarter space landing or by providing winders. In these type of stairs the flight of stair turns 90 degrees art landing as it rises to connect two different levels. So it is also called as L-stair. Again these quarter turn stairs are two types.

i. Newel quarter turn stairs:

These type of stairs have clearly visible newel posts at the beginning of flight as well as at the end. At the quarter turn, there may either be quarter space landing or there may be winders.

ii. Geometrical quarter turn stairs:

In geometrical stairs, the stringer as well as the hand rail is continuous without any newel post at the landing area.

b) Half turn stairs:

In case of half turn stairs its direction reversed, or changed for 180^o. Such stairs are quite common. Again these are three types.

i. Dog-legged stairs

Because of its appearance in sectional elevation this name is given. It comes under the category of newel stairs in which newel posts are provided at the beginning and end of each flight.

ii. Open newel half turn stair

In this type of open newel half turn stairs, stair has a space or well between the outer strings. This is the only aspect in which it differs from the doglegged stair.

iii. Geometrical half turn stairs

In case of geometrical half turn stairs the stringers and the hand rails are continuous, without any intervening newel post. These stairs may contains either with half space landing or without landing.

c) Three quarter turn stairs:

The direction of stairs changed three times with its upper flight crossing the bottom one in the case of three quarter turn stairs. These stairs are may either be newel or open newel type. This type stairs are generally used when the vertical distance between two floors is more and as well as length of the stair room is limited.

d) Bifurcated stairs:

Bifurcated stairs are commonly used in public building at their entrance hall. This has a wider flight at the bottom, which bifurcates into two narrower flights, one turning to the left and other to the right, at landing.it may be either of newel type with a newel post or of geometrical type with continuous stringer and hand rails.

3. Continuous stairs:

This type of stairs neither have any landing nor any intermediate newel post. They are geometric in shape. These are may be of following types.

• Circular stairs
• Spiral stairs
• Helical stairs

Circular stairs or spiral stairs are usually made either of R.C.C or metal, and is placed at a location where there are space limitations. Sometimes these are also used as emergency stairs, and are provided at the back side of a building. These are not comfortable because of all the steps are winders and provides discomfort.

 A helical stair looks very fine but its structural design and construction is very complicated. It is made of R.C.C in which a large portion of steel is required to resist bending, shear and torsion.

PREPARATION OF DETAILED CONSTRUCTION ESTIMATE

To preparations of detailed estimate consist of working out quantities of various items of work and then determine the cost of each item. This is prepared in two stages.

i) Details of measurements and calculation of quantities:

The complete work is divided into various items of work such as earth work concreting, brick work, R.C.C. Plastering etc., The details of measurements are taken from drawings and entered in respective columns of prescribed proforma. The quantities are calculated by multiplying the values that are in numbers column to Depth column as shown below:

Details of measurements form

 

ii) Abstract of Estimated Cost:

The cost of each item of work is worked out from the quantities that already computed in the detals measurement form at workable rate. But the total cost is worked out in the prescribed form is known as abstract of estimated form. 4%of estimated Cost is allowed for Petty Supervision, contingencies and unforeseen items.

Abstract of Estimate Form

 

The detailed estimate should be accompanied with:

i) Report

ii) Specification

iii) Drawings (plans, elevation, sections)

iv) Design charts and calculations

v) Standard schedule of rates.

Factors to be considered while Preparing Detailed Estimate:

i) Quantity and transportation of materials: For bigger project, the requirement of materials is more. Such bulk volume of materials will be purchased and transported definitely at cheaper rate.

ii) Location of site: The site of work is selected, such that it should reduce damage or in transit during loading, unloading, stocking of materials.

iii) Local labour charges: The skill, suitability and wages of local laboures are considered while preparing the detailed estimate.

Data for detailed estimate:

The process of working out the cost or rate per unit of each item is called as Data. In preparation of Data, the rates of materials and labour are obtained from current standard scheduled of rates and while the quantities of materials and labour required for one unit of item are taken from Standard Data Book (S.D.B).

Fixing of Rate per Unit of an Item:

The rate per unit of an item includes the following:

1) Quantity of materials & cost: The requirement of materials is taken strictly in accordance with standard data book (S.D.B). The cost of these includes first cost, freight, insurance and transportation charges.

ii) Cost of labour: The exact number of labourers required for unit of work and the multiplied by the wages/ day to get of labour for unit item work.

iii) Cost of equipment (T&P): Some works need special type of equipment, tools and plant. In such case, an amount of 1 to 2% of estimated cost is provided.

iv) Overhead charges: To meet expenses of office rent, depreciation of equipment salaries of staff postage, lighting an amount of 4% of estimate cost is allocated.

 

PREPARATION OF APPROXIMATE CONSTRUCTION COST ESTIMATE

Preliminary or approximate construction cost estimation is required for studies of various aspects of work of project and for its administrative approval. It can decide, in case of commercial projects, whether the net income earned justifies the amount invested or not.

The approximate estimate is prepared from the practical knowledge and cost of similar works. The estimate is accompanied by a report duly explaining necessity and utility of the project and with a site or layout plan. A percentage 5 to 10% is allowed for contingencies.

Approximate Construction Cost Estimation Methods:

The following are the methods used for preparation of approximate construction cost estimates:

a) Plinth area method

b) Cubical contents method

c) Unit base method

a) Plinth area method:

The cost of construction is determined by multiplying plinth area with plinth area rate. The area is obtained by multiplying length and breadth (outer dimensions of building). In fixing the plinth area rate, careful observation and necessary enquiries are made in respect of quality and quantity aspect of materials and labour, type of foundation, height of building, roof, wood work, fixtures, number of storeys etc.

As per IS 3861-1966, the following areas include while calculating the plinth area of building:

Types of Estimates:

• Area of walls at floor level.
• Internal shafts of sanitary installations not exceeding 2.0 sqm, lifts, air-conditioning ducts etc.,
• Area of barsati at terrace level: Barsati means any covered space open on one side, constructed on one side, constructed on terraced roof which is used as shelter during rainy season.
• Porches of non-cantilever type.

Areas which are not to include

• Area of lofts.
• Unenclosed balconies.
• Architectural bands, cornices etc.,
• Domes, towers projecting above terrace level.
• Box louvers and vertical sun breakers.

b) Cubical Contents Method:

This method is generally used for multi-storeyed buildings. It is more accurate that the other two methods viz., plinth area method and unit base method. The cost of a structure is calculated approximately as the total cubical contents (Volume of buildings) multiplied by Local Cubic Rate. The volume of building is obtained by Length x breadth x depth or height. The length and breadth are measured out to out of walls excluding the plinth off set.

The cost of string course, cornice, corbelling etc., is neglected.

The cost of building = volume of buildings x rate/ unit volume.

c) Unit Base Method:

According to this method the cost of structure is determined by multiplying the total number of units with unit rate of each item. In case schools and colleges, the unit considered to be as ‘one student’ and in case of hospital, the unit is ‘one bed’. The unit rate is calculated by dividing the actual expenditure incurred or cost of similar building in the nearby locality by the number of units.