Tuesday, September 14, 2010

Removal of Shuttering from Structural Elements

Many times, I have been asked what is the ideal time for maintaining formwork after casting of a structural element such as column, wall, beam and slab.

Below is only a general guideline for removal of formwork and not to be followed without the approval of your structural consultant.

a) Removal of formwork from walls, columns and vertical surfaces - 24 hours

b) Removal of formwork from slabs while keeping the props - 4 days

c) Removal of formwork from beams while keeping the props - 7 days

d) Removal of props under slabs
1) Slab span upto 4.5m - 7days
2) Slab span above 4.5m - 14 days

e)Removal of props under beams
1) For beams upto 4.5 m - 14 days
2) For beams above 4.5m - 21 days

Please remember after removal of formwork, proper curing of concrete is really important.

Power Sector Outook

Currently the installed capacity of India is 160,000 MW of which nearly 80 percent is with PSU's and govt bodies and 20 percent is with private sector.

In 2009, India was able to add about 10,000 MW to its capacity.
The good news is that the ministries are taking a very active role in fast tracking projects and its likely that another 10,000 MW would be added by end of 2010. More then 40 private projects have been cleared and would be under construction soon. Typically it takes 3-5 years for a thermal power plant to be operational once the construction starts.

Major players in Power Sector:
NTPC is the largest player with installed capacity of 32,000MW
Tata Power and Reliance Infra are the major private players.
NHPC is the largest player in hydropower space.

For the first time Ultra Mega Power Projects (UMPP) ie power plants with 4000MW capacity have been sanctioned and four of the UMPP's are expected to be commissioned by 2015.

The future of power sector looks very positive.

Friday, September 10, 2010

Top EPC Contractors in India

1. Larsen and Toubro
2. Punj Lloyd
3. Jaypee Associates
4. Lanco Infratech
5. Nagarjuna Constructions
7. Simplex Infrastructure
8. GMR
9. Gammon India
10. HCC
11. Tata Projects
12. Shapoorji Pallonji
13. GVK
14 Shobha Developers
15. IRB
16. Tata Projects
17. Siemens

Quality checks to be kept in mind while casting of concrete

The following points must be kept in mind before casting of any structural member

1. Rebar details must be correctly followed as per drawings.

2. Rings/stirrups provide strength to columns and beams and prevent the concrete from spreading out and cracking. Hence rings should not be missed out as it could cause structural failure . Its a good idea to get rings pre-fabricated from contractor who specializes in this kind of a job

3.Ring spacing along the column or beam rebar must be correctly followed.

4.Cover blocks must be placed all around the rebar to prevent the rebar from touching the shuttering

5. Ensure that the shuttering alignment is correct and shuttering is vertical.

6. Make sure to take atleast 2 samples of concrete before casting for 7 day and 28 day testing. Fill the moulds with concrete and cure them before sending them to the quality lab.

7. Do an onsite slump test of concrete by using a slump cone

8. Make sure that the inner sides of shuttering material are smooth and smeared with shuttering oil

Tuesday, September 7, 2010

Concrete vibration is important

Vibrating concrete is a must so that concrete can achieve its design properties

Vibrating concrete makes it more fluid and hence it flows into the corners of the formwork

Air-gaps in concrete are significantly reduced and results in a more consistent density of concrete both at top and bottom

However over-vibrating the concrete will result in seggregation of aggregates.

One must be careful that vibrator does not disturb the rebar arrangements especially in areas where rebars are very dense.

For optimum compaction the frequency of the vibrator should be between 10,000 to 12,000 vibrations per minute.

What is BIM and 3D, 4D and 5D ?

Building Information Modeling is the process of converting the 2D drawings into a 3D model on the computer. The structural, architectural and mep drawings are used as inputs to create an very accurate 3D model.

Archicad and Revit are the most popular softwares used for BIM modeling.

This model can be used for:

1. For spatial visualization of the building

2. For doing constructiblity analysis
eg if the slab level shown in architecural drawings and structural drawings are different or if a pipe if going through a lift shaft, then BIM would be able to identify that.

3. For generating sections from anywhere in the building. Time is saved as the BIM software does this automatically.

4. Preparing Bill of Quantities from the BIM model is fast. Take-off sheets can also be prepared. This is infact called the 4D or the cost.

5. The items in the Bill of Quantities can be exported to a scheduling software such as Primavera, MS Project or Vico Control to sequence the construction activities. The tasks have location data and quantity data already built into them, so scheduling is faster and more accurate. This is called 5D.

6. Future add-ons to BIM sofware would include structural analysis, energy analysis for calculating tonnage of air-conditioning required, preparing BBS for pre-fabrication, etc.

I have used BIM softwares on a few project and feel that a big change is underway in the construction industry.

Sunday, September 5, 2010

Types of Paints

Paints can be mainly classified as

1. Distempers
Dry Distempers are dry powder like paints and are mixed with water.
Also referred to as white-wash.
Oil Bound Distempers comes in liquid form and will last for 3 to 4 years
at the most. Its much cheaper than a emulsion.

2. Emulsions
Emulsions come as Matt, Semi-Glossy and Glossy and are also referred
to as plastic paints. Some paint companies refer to the finish as
Regular, Eggshell/Satin and Silk. Emulsions come pre-mixed with water from the paint company

3. Oil or Enamel Paints
Are very thick paints to be used on metals or woods. They cannot be
be mixed with water. They have a very strong paint like smell and have
Volatile Organic Compounds.

Boiler Milestones for Thermal Power Plants

1. Completion of boiler foundation
2. Steel structure for boiler support
3. Boiler drum lifting
4. Hydro-test for leakages
5. Boiler light-up
6. Acid Cleaning
7. Steam blowing
8. Safety valve floating
9. Synchronization with oil
10. Synchronization with coal

Saturday, September 4, 2010

Important Balance of Plant Packages for Thermal Power Plants

1. Coal Handling System
Coal is the fuel used to heat up the water in the boiler to produce steam. The coal delivered to the site is stored in bunkers and delivered to the pulverizer by conveyor belts. The pulverized coal is further transferred to the ball mill where its is converted into a powder form. This entire system is called the coal handling system of the power plant.

2. Ash Handling System
Burnt coal produces bottom ash and fly ash. The bottom ash is falls through the grate of the furnace into a silo where it is mixed with water to produce ash slurry. This slurry is then pumped out of the boiler furnace into an ash pond. The fly ash moves along with the flue gases and is trapped by an electrostatic precipitator. The trapped ash is then pnuematically sent to the ash storage area.

3. Cross Country Pipeline
Water for the power plant generally comes from a river, sea, lake reservoir or an STP plant of a city. The distance of water source to the power plant may be quite large and hence a cross-country pipe line is required along with a pumping station.

4. Water Treatment Plant
Water required by the power plant needs to be free of any suspened particles as well as dissolved salts. Hence the water is generally passed through a pre-treatment plant, RO plant and a De-mineralisation plant before being used in the boiler, turbine, etc.

5. Cooling Tower
Cooling water is required to convert the exhausted steam from the turbine back into water to create back pressure and improve thermal efficieny of the plant.Hence cooling tower is required to cool the heated water passing through the condensor.

6. Switchyard
The electrical network where the power is transferred along different routes.

7. Railway Siding
Coal needs to transferred from the coal mine to the power plant by means of a train. The train enters the power plants and dumps the coal into a underground bunker. Power plant owner needs to erect the railway tracks for the train to reach the power plant.

8. Transmission Line
The power needs to be evacuated by means of high voltage transmission line to the purchaser of power such as State Electricity Board.

Friday, September 3, 2010

Plant and Machinary Required at Construction Site for Civil Works

1. Diesel Generator for electricity of site office, area lighting, water pump,machinary, etc
2. Water Pump for drawing water from the boring well
3. Excavator
4. Rebar Cutting Machine
5. Rebar Bending Machine
6. Dewatering Pump
7. Hydra Crane of 12 T
8. Tractor with Trolley for moving shuttering material
9. Vibration Plate Compactor for back-filling of soil
10. Total Station for determining levels and aligning columns with each other
11. Tower Crane for height work
12. Batching Plant for making concrete
13. Concrete Pump
14. Field Junction Boxes and lots of cables for lighting

Management Structure of Construction Site

The typical management structure of a project at site would be:

1. Project Manger
2. Civil Engineer
3. Mechanical Engineer
4. Electrical Engineer
5. Plumbing Engineer
6. Store Manager
7. Quality Manager
8. Safety Manger
9. Time-office Manager
10. Admin and Accounts