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Use of Steep roofs in buildings

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Steep slopes generally serve both the purposes. In areas of heavy snowfall, flat roofs would be loaded with snow which may jeopardize the roof's load bearing capacity and may lead to cracks. If cracks occur, the melted snow would also enter the building. Steep slopes slide down the fallen snow in pretty short time. The Roof pitch is decided on the basis of annual snowfall in the region. 

We know that air is a bad conductor of heat, and while constructing steep roofs, there is usually a layer of air between the timber/concrete roof and the roof tiles. Thus the house remains insulated and warm during the winters.

Another advantage of steep roofs is they are of great importance when it comes to water harvesting. Water is collected in eaves attached at the end part of the roof and stored for use in the summers for plant irrigation. 

Also, Solar panels can be installed on the roof which in turn generate electricity for the house. The steep roofs aren't used for the purposes served by flat roofs, so they can be used for purposes like this. 

The photograph above shows how a steep roof helps in all the purposes mentioned above.

Fatigue in Building materials

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Fatigue is the weakening of a building material when it is loaded and unloaded repeatedly, the load being above the particular value called the fatigue strength/fatigue limit/endurance limit. Fatigue strength is defined as the load value below which the material would not yield for any number of cycles of loading and unloading.

The fun fact is the nominal stress values which cause the fatigue are mostly much smaller than the actual strength, technically known as the Ultimate tensile strength of the particular material. Fatigue results in microscopic cracks, which grow to significant size with repetitive cycles, and when they reach the critical size, the structure fractures.

Internship at Indian Railways

Most of the zonal offices under the Indian Railways organize training and internship camps for both under-graduate and post-graduate engineering students during the summers. In cities like Jabalpur, Allahabad, etc. which are important divisions of their respective Railway zones, training camps of 15 days and/or 1 month are conducted and interested students can apply for them as per the deadlines. 

For civil engineering students, Construction department and the Maintenance department are of main interest. It is less likely to see advertisements about the application vacancies for internships in newspapers, so its better to personally visit the office of the Section engineer/Senior Section engineer (of  Construction or Maintenance department) and inquire about the commencement of the camp and other details such as location of the site, etc, about 2 months before summer vacations commence, i.e. in the month of March and early April. Also, carry your college ID card with you to the office.

Unlike the zonal offices, small towns do not have training camps every year. Sometimes students have to go through the entire internship program being the only internee at the site. The process to approach for an internship is the same as above, i.e. meeting the concerned engineer of a site. At the end of the training, internees are also given certificates by the concerned Railway office. 

Indian Railways have a huge variety of Civil engineering projects going all over the nation, including laying of new tracks, repairing of old tracks and bridges, building construction, tunnel construction, etc. If you see any such innovative project taking place in your area, don't miss the chance. Get that internship now!

Structural Cracks: Causes and their identification

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The various causes are:
• Structural cracks 

1) Due to incorrect design
2) Faulty construction 
3) Overloading

• Non Structural cracks

1) Moisture changes: Shrinkage effect,depending on the water content, cement concrete and aggregates.
2) Thermal movement: Concrete made in hot weather needs more water for same work-ability and hence results in more shrinkage.
3) Elastic deformation
4) Creep: Building items such as concrete and brick work when subjected to a sustained load not only undergo elastic strain but also develop gradual and slow time dependent deformation known as creep or plastic strain.
5) Chemical reaction: Certain chemical reaction in building materials result is appreciable change in volume of resulting products and internal stresses are set up which may result in outward thrust and formation of cracks.
6) Foundation movement and settlement of soil: Buildings on expansion clays are extremely crack prone. 
7) Vegetation: Large trees growing in the vicinity of buildings cause damage in all type of soil conditions. If the soil is a shrinkable clay, the cracking is severe.

Structural cracks due to shrinkage can be identified as: 
  1. Corrosion of the reinforcement: If the reinforcement is placed too near the surface, it has chances to corrode. The iron expands due to oxidation and conversion to Iron oxide, which in turn results in cracks. So if the reinforcement is visible from the concrete surface, there are chances of cracks present and upcoming.

  1. Vertical cracks: These cracks mostly occur when the foundation has settled or disturbed unequally along its surface.

  2. Linear cracks: These cracks gradually grow and though they appear to be linear, there are interruptions in the crack-line which implies the crack is towards spreading itself.
  3. Network of cracks: These are due to the reaction of aggregate with some alkali hydroxide present in the concrete and can be easily seen by a network of cracks roughly growing as a circle in a group. 

Greatest Civil engineers of all time

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I'll go with Indian engineers first:

  1. Sir Mokshagundam Visvesvarayachief designer of the flood protection system for the city of Hyderabad, and India's greatest Civil engineer till date. 
  2. Kanwar Sen : Came up with the ideas of Rajasthan Canal, Ganga Canal and the master plan for the development of Narmada Project. He contributed his utmost in design and building up the Central Water and power Commission.
  3. E. Sreedharan: Well known as the 'Metro Man'.  Was put in charge for implementation, planning and design of Calcutta metro, was the  chairman and managing director of Cochin Shipyard Limited and later of Konkan Railways. He was made the managing director of Delhi Metro Rail corporation (DMRC) and is currently appointed as Principal Advisor of the Kochi Metro Rail Project. 
  4. John Smeaton: Also known as the  Father of Civil Engineering. His paper, “An Experimental Enquiry Concerning the Natural Powers of Water and Wind to Turn Mills and Other Machines Depending on Circular Motion”, showed the direct correlation between pressure and velocity for objects moving in the air. He contributed greatly with his work on windmills and waterwheels. 
  5. Benjamin Wright: Declared as the father of American Civil Engineering by the American Society of Civil engineers. He was the Chief Engineer during the construction of the Erie Canal, and later designed the Delaware canal, Hudson canal, Chesapeake canal and Ohio canal. 
  6. Squire Whipple: Designed and built a weight lock scale of 300 ton capacity to measure weight of Canal boats. He also built the first long span trapezoidal railroad bridges for the New York Railroads, along with seven short-span iron bridges. 
  7. Isambard Kingdom Brunel: He was the chief engineer of the project of network of tunnels, viaducts and bridges for the Great Western Railways which linked London to Bristol.  His designs revolutionised public transport and modern engineering. 
  8. John Bradfield: He was a prominent Australian engineer who designed and oversaw the construction of the Sydney Harbour Bridge and theBradfield Railway scheme. He was also appointed Chief Engineer for the metropolitan railway construction in New South Wales. 

Things Civil Engineers know better than anybody!

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The few ones I suppose are:

1. Technically diamond is more elastic than rubber as Elastic modulus of Diamond is in the range 1000-1200 GPa whereas that of rubber is approximately 0.1 GPa. This means on application of large loading, diamond may be in the elastic limit but rubber might go beyond it.

2. While widening road pavements on Horizontal Curves, apart from providing mechanical widening based on calculations, psychological widening is also provided to provide extra space and comfort while steering at high speeds.

3. The rails on a railway track generally shift by about 7.5 to 15 cm per month (known as creep) on an average in one of the opposite directions. 

4. On curves, the level of outer rail is raised above the inner rail by a certain amount depending on the centrifugal forces’s effects, known as Cant (road/rail).

5. The runway orientation on an airport is done in the direction of prevailing winds which is decided by studying Wind rose diagrams and not in any random way.

6. For buildings with height above 30 meters, the minimum open space (left inside and around a building to meet the lighting and ventilation requirements) of 10 m required for heights of 30 m, shall be increased at a rate of 1 m for every additional height of 5 meters, to a maximum of 16 m.

7. The minimum distance for construction of any building from center line of any street shall not be less than 7.5 m. for future widening of the road.

8. There are about 18 types of contracts for undertaking a tender of construction of any building.

9. Failure of steel reinforcement before the failure of concrete is safer as steel failure occurs with signs whereas concrete failure occurs without giving any previous hints. Thus the structures are designed as under-reinforcement following the Limit state design.

10. While designing RCC Structures, the design strength of the structure is taken 1.5 times less than the Characteristic strength" (fck) of concrete while the design load is taken 1.5 times of the expected load. The value 1.5 is the factor of Safety of concrete.

11. Fish ladders are provided in weirs as it is essential to make the provision of some space in the construction of a weir for the uninterrupted migration of fishes from upstream to downstream in search of relatively warm water in the beginning of winter season.

12. Sometimes land plots are left as it is after laying the foundation. This is generally done to allow natural Consolidation of the soil. In a year or two, a significant amount of pore water in the soils dissipates and the soil settles down. After this settlement, construction is started again.

13. The sewer pipes are designed to carry the maximum hourly sewage flow quantity, which is thrice the average daily sewage flow quantity while the sewage is flown according to the minimum hourly sewage flow quantity to maintain the minimum sewage velocity. 

Watering of bricks: What's the reason behind?

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There are three reasons for submerging bricks/blocks:

1. Test for absorption: A brick is submerged in water for 24 hours. If its weight after 24 hours exceeds its dry weight by 20%, the brick is not used for construction. 

2. Test for presence of soluble salts: After 24-hour submergence, if grey/white deposits occur on the brick, soluble salts are present. If white deposits cover more than 50% of the surface, the bricks are not used for construction purpose.

3. Quench the thirst: Its said that bricks are very thirsty. So the selected bricks are submerged for sufficient time so that they absorb sufficient water and fill most of their pores with it. Or else they will absorb the water of the mortar, thus reducing its strength to a great strength.

Also, they are used to remove the dirt from the bricks.