Advantages and disadvantages of reinforced concrete

Reinforced Concrete is a structural material, is widely used in many types of structures. It is competitive with steel if economically designed and executed.
 
Advantages of reinforced concrete

• It has relatively high compressive strength
• It has better resistance to fire than steel
• It has long service life with low maintenance cost
• In some types of structures, such as dams, piers and footings, it is most economical structural material.
• It can be cast to take the shape required , making it widely used in pre-cast structural components.
• It yields rigid members with minimum apparent deflection.
• Yield strength of steel is about 15 times the compressive strength of structural concrete and well over 100 times its tensile strength
• By using steel, cross sectional dimesions of structural members can b ereduced e.g in lower floor columns.

Disadvantages of reinforced concrete

• It needs mixing, casting and curing, all of which affect the final strength of concrete.
• The cost of the forms used to cast concrete is relatively high.
• It has low compressive strength as compared to steel (the ratio is about 1:10 depending on material) which leads to large sections in columns/beams of multistory buildings Cracks develop in concrete due to shrinkage and the application of live loads

Hoover dam bridge finally completed

A soaring bridge that will let drivers bypass the Hoover Dam - and steer clear of its security checkpoints and tourists - will open after nearly eight years and £151 million worth of work.

The 1,900ft engineering wonder perched 890ft above the Colorado River is expected to slash travel time along the main route between Las Vegas, Nevada, and Phoenix, Arizona, as motorists will no longer have to make their way across the dam's winding two-lane road at a snail's pace.

DATA REQUIRED TO PREPARE AN ESTIMATE

 DATA REQUIRED TO PREPARE AN ESTIMATE
 1. Drawings i.e.plans, elevations, sections etc
.2. Specifications.
 3. Rates.


1.4.1 DRAWINGS If the drawings are not clear and without complete dimensions the preparation of estimation become very difficult. So, It is very essential before preparing an estimate.

1.4.2. SPECIFICATIONS

a) General Specifications: This gives the nature, quality, class and work and materials in general terms to be used in various parts of wok. It helps no form a general idea of building.

 b) Detailed Specifications: These gives the detailed description of the various items of work laying down the Quantities and qualities of materials, their proportions, the method of preparation workmanship and execution of work.

 1.4.3. RATES: For preparing the estimate the unit rates of each item of work are required.
1. For arriving at the unit rates of each item.
2. The rates of various materials to be used in the construction.
3. The cost of transport materials.
4. The wages of labour, skilled or unskilled of masons, carpenters, Mazdoor, etc., 

General Introduction Of Estimation

1.1 DEFINITION OF ESTIMATING AND COSTING
Estimating is the technique of calculating or Computing the various quantities and the expected Expenditure to be incurred on a  particular work or project. In case the funds avilable are less than the estimated cost the work is done in part or by reducing it or specifications are altered, the following requirement are necessary for preparing an estimate.
a ) Drawings like plan, elevation and sections of important points.
b) Detailed specifications about workmenship & properties of materials etc.
 c) Standard schedule of rates of the current year.

1.2 NEED FOR ESTIMATION AND COSTING
1. Estimate give an idea of the cost of the work and hence its feasibility can be determined i..e whether the project could be taken up with in the funds available or not.
2. Estimate gives an idea of time required for the completion of the work.
3. Estimate is required to invite the tenders and Quotations and to arange contract.
 4. Estimate is also required to control the expenditure during the execution of work.
 5. Estimate decides whether the proposed plan matches the funds available or not.

1.3 PROCEDURE OF ESTIMATING OR METHOD OF ESTIMATING. Estimating involves the following operations
1. Preparing detailed Estimate.
 2. Calculating the rate of each unit of work
3. Preparing abstract of estimate

Stairs

Stairs give access from floor to floor. The space/room housing stairs is called staircase. Stairs consists of a number of steps arranged in a single flight or more number of flights.

The requirement of good stairs are
(a) Width: 0.9 m in residential buildings and 1.5 m to 2.5 m in public buildings.
(b) Number of Steps in a Flight: Maximum number of steps in a flight should be limited to 12 to 14, while minimum is 3.
(c) Rise:
Rise provided should be uniform. It is normally 150 mm to 175 mm in residential buildings while it is kept between 120 mm to 150 mm in public buildings. However in commercial buildings more rise is provided from the consideration of economic floor area.
(d) Tread:
Horizontal projection of a step in a stair case is called tread. It is also known as going.In residential buildings tread provided is 250 mm while in public buildings it is 270 mm to 300 mm.
The following empirical formula is used to decide rise and tread:
2R + T > 550 mm but < 700 to 600 mm
where R is rise in mm and T is tread in mm.
(e) Head Room: Head room available in the stair case should not be less than 2.1 m.
(f) Hand Rails: Hand rails should be provided at a convenient height of a normal person which is from 850 mm to 900 mm.

Causes of failure in foundation

i.    Unequal settlement of subsoil: All soils, except rock and murum yield under the load of the structure. Uniform yielding and within a particular limit is harmless, but unequal yielding creates cracks in the building and ultimately results in failure of the structure.

ii.   Unequal settlement of masonry: It is caused by shrinkage and compressibility of mortar joints and the poor quality of material used in foundation.

ii.    Withdrawal of subsoil moisture: This occurs in wet soil.  As the moisture of the soil evaporates in dry weather, the soil becomes compressed and cracks thereby causing failure of the foundation.

 iv. Volumetric change in soil: Black cotton soil has the property to shrinks while dry and swells while wet. This character makes it unsuitable for building construction as during the seasonal changes its volumetric composition changes in a large extent. A foundation on such soil condition is detrimental as the change in volumetric composition greatly impacts the foundation.

v.   Lateral pressure on super structure: When the structure is subjected to lateral pressure due to wind or the lateral thrust of arches or a sloping roof or wide cantilever projections, which causes eccentricity of the loads, a tendency of tilting or overturning is developed, resulting in failure of the foundations.

vi.  Lateral escape of subsoil: When the building is situated near a deep cliff or a river, the soil below the foundation may escape laterally and cause settlement of the foundation. Similarly, if the depth of the foundation is small or the subsoil below the foundation is of a sliding nature, it may slip away under the loads and cause the failure of the foundation.

 vii. Action of atmosphere: Atmospheric action also contributes in the deterioration of the existing foundation.  Rain is the main element that should be kept away from reaching anywhere near the foundation.  A proper drainage system is prescribed. The foundation should be constructed at a sufficient depth, beyond the reach of surface water. 

Strap Footing

It consists of two isolated footings connected with a structural strap or a lever, as shown in figure below.

The strap connects the footing such that they behave as one unit. The strap simply acts as a connecting beam. A strap footing is more economical than a combined footing when the allowable soil pressure is relatively high and distance between the columns is large.