WHAT ARE THE CAUSES OF BUILDING?

WHAT ARE THE CAUSES OF BUILDING? 

The following factors can be defined as the most common reasons causes building collapse:

1. Overload… Too many people on a balcony or deck is a common reason for collapse of such structures or when the occupancy of areas are changed without an evaluation.

2. Lack of maintenance… A lack of maintenance will lead to things like not noticing a problem before it becomes catastrophic.

3. Use of inferior materials/chemicals… Such as older (1960s - 1980s) fire retardant treated wood roof assemblies made with cheap ammonium phosphate are prone to collapse after 25 years of service.

4. Bad engineering… Structural engineers make mistakes, everyone does, but in small firms a lack of multiple people checking designs can lead to bad calculations and structural failures.

5. Under-designed… Don’t confuse this with bad engineering, under-designed means you followed the code correctly and performed good calculations but it still was inadequate for the loads.

6. Fire… Fire reduces steel yield strengths, causes concrete to undergo chemical changes that weaken it, causes masonry to spall/crack and will consume wood materials… All of which can result in collapse.

7. Bad construction… The most common reason for an attached and self-supported deck to collapse is the contractor only provided nails between the deck ledger and the structure of the house, resulting in the deck pulling away.

8. Impact damage… Such as someone driving a car into a house, which can result in partial collapses.

9. Storm damage… Winds generally dont result in a collapse as things are lifted away and not falling downwards, but floods can cause buildings/bridges to collapse.

10. Soils… Development of a sinkhole (man made or natural) can obviously cause a building/bridge to collapse.

11. Seismic… Earthquakes can make just about anything collapse if it is not designed for the magnitude of accelerations occurring.

WHAT IS THE MEANING OF SOIL REINFORCEMENT?

WHAT IS THE MEANING OF SOIL REINFORCEMENT? 

(JOB INTERVIEW QUESTION) 

Reinforcement of Soil can generally be subdivided into 2 categories: 

A-Reinforced Soils

B-In-situ Reinforcement. The latter is often termed “soil nailing”. 

Soil Reinforcement may be made with a number of materials:

1. Woven Geotextiles

2. Polymer Geogrids of Polyethylene (usually uniaxial) & polypropylene (usually biaxial)

3. Polyester and Fiberglass Geogrids (often knitted or stitched at junctions) and usually coated with a polymer such as polyethylene or PVC or with bitumen.

4. Steel Strips (the original “Reinforced EarthTM”) 

5. Welded wire mesh 

Soil nailing technique:

Soil nailing is an in-situ reinforcement technique, was originally introduced in France in the 1970s. It can be described as an in-situ reinforcing of soil using an array of nails installed as passive inclusions in a grid. The construction begins with the excavation of a shallow cut (Fig) on the face of which wire mesh is laid followed by applying shotcrete to the face. When the latter is set, soil nails are drilled through the shotcrete and grouted, followed by 9 anchoring them to the wall. The sequence is repeated until the final depth is reached. The nail being rigid, unlike the reinforcing strip in reinforced earth, can resist some bending and shear in addition to axial tension. An innovative step is the use of screw nails which are installed by rotation (like screw piles), giving rise to enhanced friction at the soil-nail interface. (This is akin to increased bond in the case of deformed reinforcement bars.)

Soil nailing cannot replace all other methods of soil retention technically or economically. Notwithstanding the same, it has the following advantages:

1. It is not dependent on heavy equipment

2. It is economical where the geometry of the wall is complex and where space restrictions exist

3. Since nails are of low strength steel, the need for corrosion protection stands reduced

4. Construction can be carried out with little disturbance to the environment in terms of noise and vibration

Soil nailing is not practical in:

- Soft, plastic clays

- Organics/Peat

- Fills (rubble, cinder, ash, etc.)

WHAT ARE THE ADVANTAGES OF PRESTRESSED CONCRETE OVER R.C.C ?

WHAT ARE THE ADVANTAGES OF PRESTRESSED CONCRETE OVER R.C.C?

(JOB INTERVIEW QUESTION)

Concrete weak in tension and strong in compression. Therefore, Reinforcement concrete system has been created to overcome the weakness of concrete with rapidly development in construction, the concrete technology has to walk parallel with this development. Therefore, the Prestressed concrete was created to overcome the limit of reinforcement concrete span.

Prestressed concrete is a concrete construction material which is placed under compression prior to it supporting any applied loads or defined as Structural concrete in which internal stresses have been introduced to reduce potential tensile stresses in the concrete resulting from loads

The prestressing of concrete has several advantages as compared to traditional reinforced concrete without prestressing. A fully prestressed concrete member is usually subjected to compression during service life. 

This rectifies several deficiencies of concrete.

Serviceability and Strength

1-Reduces occurrence of cracks .

2-Freezing & thawing durability is higher than non prestressed concrete

3-Section remains uncracked under service loads

4-Reduction of steel corrosion

5-Increase in durability.

6-Full section is utilized

7-Higher moment of inertia (higher stiffness)

Less deformations (improved serviceability).

8-Increase in shear capacity.

9-Improved performance (resilience) under dynamic and fatigue loading.

10-In areas where there are expansive clays or soils with low bearing capacity, post-tensioned slabs-on-ground and mat foundations reduce problems with cracking and differential settlement.

11-Reduces self weight of building thereby reducing the lateral load resisting system. 12-Suitable for use in pressure vessels, liquid retaining structures.

Application

1-High span-to-depth ratios

2-They do not crack under working loads, and whatever cracks may be developed under overloads will be closed as soon as the load is removed, owing to the cambering effect of pre-stress.

3-This becomes an important consideration for such structures as long cantilevers. Under live loads the def section is also smaller because of the effectiveness of the entire un-cracked concrete section.

4-Larger spans possible with prestressing (bridges, buildings with large column-free spaces)

5-Post-tensioning allows bridges to be built to very demanding geometry requirements, including complex curves, and significant grade changes.

6-Another advantage of post-tensioning is that beams and slabs can be continuous, i.e. a single beam can run continuously from one end of the building to the other.

7-Crack control helps in constructing high performance water tanks

8-More aesthetic appeal due to slender sections

9-Applications of various prestressed techniques enable quick assembly of standard units such as bridge members,building frames, bridge decks providing cost-time savings

Economy

1-Rapid construction

2-Better quality control

3-Reduced maintenance

4-Suitable for repetitive construction

5-Multiple use of formwork

6-There is also a definite savings stirrups, since shear in post-tensioned concrete is reduced in the inclination of the tendons, and the diagonal tension is further minimized bathe presence of pre-stress.

7-A lower building height can also translate to considerable savings in mechanical systems and façade costs.

8-Thinner slabs mean less concrete is required. It means a lower overall building height for the same floor-to-floor height.

9-Pre-tensioning is suitable for precast members produced in bulk.

10-The high tensile strength & precision of placement gives maximum efficiency in size & weight of structural members.

HOW TO IMPROVE BEARING CAPACITY OF SOIL? (JOB INTERVIEW QUESTION)

HOW TO IMPROVE BEARING CAPACITY OF SOIL? 

(JOB INTERVIEW QUESTION)

The following techniques can be used for improving bearing capacity of soil as per the site condition:

-Increasing depth of foundation

-Draining the soil

-Compacting the soil

-Confining the soil

-Replacing the poor soil

-Using grouting material

-Stabilizing the soil with chemicals

1. INCREASING DEPTH OF FOUNDATION

At deeper depths, the over burden pressure on soil is higher; hence the soil is more compacted at deeper depth. As a result it shows higher bearing capacity. This is applicable only for cohesionless soils such as sandy and gravelly soils. This method of improving bearing capacity of soil is not applicable if the subsoil material grows wetter as depth increase. This method has a limited use because with increase in depth, the weight and cost of foundation also increases.

2. DRAINING THE SOIL

With increase in percentage of water content in soil, the bearing capacity decreases. In case of sandy soil, the bearing capacity may reduce as much as 50% due to presence of water content. Cohesionless soils (i.e. sandy & gravelly soils) can be drained by laying the porous pipes to a gentle slope, over a bed of sand and filling the trenches above the pipes with loose boulders. These trenches subsequently should lead to the nearest well or any water body.

3. COMPACTING THE SOIL

If we compact soil using appropriate method, then there will be increase in its density and shear strength. As a result the bearing capacity of soil also increases. There are many methods of compacting soils on site. Few of them are mentioned below.:

--By spreading broken stones, gravel or sand and thereafter ramming well in the bed of trenches.

--Using an appropriate roller as per the soil type to move at a specified speed.

--Br driving concrete piles or wood piles and withdrawing piles and subsequently filling the holes with sand or concrete.

4. CONFINING THE SOIL

In this method, the soils are enclosed with the help of sheet piles. This confined soil is further compacted to get more strength. This method is applicable for shallow foundations.

5. REPLACING THE POOR SOIL

In this method the poor soil is first removed and then the gap is filled up by superior material such as sand, stone, gravel or any other hard material. In order to do this, first excavate a foundation trench of about 1.5 m deep, and then fill the hard material is stages of 30 cm. Then compact the hard material at every stage. This method is useful for foundations in black cotton soils.

6. USING GROUTING MATERIAL

This method is applicable for soils where there is presence of pores, fissures or cracks etc underneath the foundation. In this method, poor soil bearing strata is hardened by injecting the cement grout under pressure, because it scales off any cracks or pores or fissures etc. For proper distribution of the cement grout, the ground is bored and perforated pipes are introduced to force the grout.

7. STABILIZING THE SOIL WITH CHEMICALS

This method of improving bearing capacity of soil is costly and applied in exceptional cases. In this method, chemical solutions, like silicates of soda and calcium chloride is injected with pressure into the soil. These chemical along with the soil particles form a gel like structure and develop a compact mass.This is called chemical stabilization of soil and used to give additional strength to soft soils at deeper depths.

WHAT ARE THE VARIOUS METHODS OF CONCRETE CURING ( JOB INTERVIEW )?

What are the various methods of concrete curing?

(Job interview)

This is also one of the most important question asked in Civil Engineering Job Interview.

For this Question. Provide the definition of Concrete curing and point out the major steps and explain each of them in short. Please Check the explaination below.

Curing is the process of maintaining the moisture and temperature conditions for freshly deployed concrete. This is done for small duration of time to allow the hardening of concrete.

The various methods involved in the concrete curing process are as follows:

•Water curing

a) Sprinkling Method :- Shading concrete work than sprinkling of water on concreted surface. Used for ( Walls , Beams & Columns ). In General, walls, and columns can be cured by sprinkling water.

b) Ponding Method :- the horizontal surfaces including the slab and floors can be cured by stagnating the water.

c) Applying the chemical membrane on concreted surface.

d) Wet covering of surface: It can be cured by using the surface with wet gunny bags or straw

e) Curing Compounds: Easy to apply and inexpensive. Sprayer needed; inadequate coverage allows drying out; film can be broken or tracked off before curing is completed; unless pig- mented, can allow concrete to get too hot.

•Application of heat

a) Steam curing at ordinary pressure

b) Steam curing at high pressure

c) Curing by Infra-red radiation

d) Electrical curing.

What are Daily Activities of Civil Site Engineering at Construction Site?

What are Daily Activities of Civil Site Engineering at Construction Site?

The daily activities of civil site engineers at the construction site are as following:

1. A shift at site starts with the safety talk, where a site engineer alerts the workmen regarding the importance of safety in construction and insists on avoiding unsafe acts.

2. Engage manpower (Supervisors, labours, helpers etc) at different locations such that the productivity of work increases.

3. Then, Safety permits are issued to the concerned workmen for any hot work, work at height etc.. after inspecting the checklist along with safety officer at site.

4. Any lapses on the part of Safety needs to be addressed on an immediate basis.

5. Calculate the quantities (concrete, shutter and other materials) required to cast the structural members as per the site plan and execute the same by the end of the day.

6. Make a note of material availability and inform the same to the store in-charge (in advance) if there is any material shortage.

7. Prepare Bar Bending Schedule (BBS) for the required structural members.

8. Study & understand the drawings and make necessary changes in the soft copy (AutoCAD) as suggested by the manager and get the approval changes by the client.

8. Prepare monthly consumption (material, fuel, manpower etc) report and daily progress reports which will be helpful in finding the monthly turnover.

9. At the end of the day, the activities carried out in the shift needs to be reported in the daily progress report.

There are many other roles but these are 

the main roles of a fresh site engineer.

Design of Steel Structures

This book introduces the design concept of Eurocode 3 for steel structures in building construction, and their practical application. Following a discussion of the basis of design, including the limit state approach, the material standards and their use are detailed. The fundamentals of structural analysis and modeling are presented, followed by the design criteria and approaches for various types of structural members. The following chapters expand on the principles and applications of elastic and plastic design, each exemplified by the step-by-step design calculation of a braced steel-framed building and an industrial building, respectively. Besides providing the necessary theoretical concepts for a good understanding, this manual intends to be a supporting tool for the use of practicing engineers. In order of this purpose, throughout the book, numerous worked examples are provided, concerning the analysis of steel structures and the design of elements under several types of actions. These examples will provide for a smooth transition from earlier national codes to the Eurocode.

Password : th3civilengineer

Steel Design (5th Edition)

Steel Design (5th Edition) by William T Segui

STEEL DESIGN covers the fundamentals of structural steel design with an emphasis on the design of members and their connections, rather than the integrated design of buildings. The book is designed so that instructors can easily teach LRFD, ASD, or both, time-permitting. The application of fundamental principles is encouraged for design procedures as well as for practical design, but a theoretical approach is also provided to enhance student development. While the book is intended for junior-and senior-level engineering students, some of the later chapters can be used in graduate courses and practicing engineers will find this text to be an essential reference tool for reviewing current practices

Pre-Engineered Buildings (PEB)

Pre-engineered buildings are buildings that are built in factories and are made of steel that are shipped to site and bolted together. PEB (Pre-engineered Building) revolution the construction market using built up sections in place of conventional hot rolled sections. A large column free area is the utmost requirement for any type of industry which is provided by PEB.

Typical Pre-engineered Building

PEB concept involves the steel building systems which are pre designed and prefabricated. As the name itself indicates, there is involvement of pre engineering of structural elements. The basis of PEB is to provide the section at the specified location only according to the need at that spot. The sections may differ along the length according to the bending moment diagram. The use of optimal least section leads to the effective saving of steel and also reduction in the cost.

Various systems of PEB – Pre-Engineered Buildings:

Primary system:

This system involves tapered or parallel columns or tapered beams which are called rafters. Base of column is either fixed or pinned based on the load requirements.

Secondary system:

It consists of purlins, grits which are the side claddings and eave struts stiffened by sag rods. This system also includes the flange stiffeners which joins the untied flanges of the PEB primary system to the secondary system.

Wind bracing system:

Rod bracing and the portal system are the two types of wind bracing systems. Each one is chosen accordingly depending on design and functional requirement.

Accessories:

This part includes the Turbo ventilator, ridge vents, Flashings, gutters, down pipes, ladders etc.

Advantages of PEB – Pre-Engineered Buildings:

• Construction time: PEB reduces the total construction cost by the least 40% which leads to faster occupancy and early revenue.
• Lower cost: Saving is accomplished in design, manufacturing and erection cost.
• Large clear span: In PEB the buildings can be given up to 90m clear spans which is the important advantage of PEB with column free space.
• Flexibility of expansion: PEB can be easily expanded in length by adding additional bays.
• Quality control: PEB’s are manufactured under controlled conditions depending on the site and hence the quality is assured.
• Low maintenance: PEB’s have high quality paint systems for cladding which gives long durability and low maintenance costs.

Pre-engineered Building Under Construction

Applications of Pre-Engineered Buildings – PEB:

Some of the many applications of PEB are:

• Factories, Warehouses, Workshops, Offices
• Gas stations
• Showrooms
• Aircraft hangers
• Metro stations
• Vehicle parking sheds
• Schools, Indoor stadium roofs
• Bridges, Railway platform shelters
• Outdoor stadium canopies

PEB are more advantageous than the conventional structures in economy, speed of construction and simple erection. As these structures have a wide scope, they must be preferred and utilized.

PEB Assembly

Video below shows step by step assembly of a Pre engineered structure.

what is chemical composition of cement?

what is chemical composition of cement?

""Question 74""

""brief description""

The raw materials used for the manufacture of cement consist mainly of lime, silica, alumina and iron oxide. These oxides interact with one another in the kiln at high temperature to form more complex compounds. The relative proportions of these oxide compositions are responsible for influencing the various properties of cement; in addition to rate of cooling and fineness of grinding.

Approximate Oxide Composition Limits of Ordinary Portland Cement

Oxide Per cent content

CaO 60–67

SiO2 17–25

Al2O3 3.0–8.0

Fe2O3 0.5–6.0

MgO 0.1–4.0

Alkalies ( K2O, Na2O) 0.4–1.3

SO3 1.3–3.0

The identification of the major compounds of cement is largely based on Bogue’s equations and hence it is called “Bogue’s Compounds”. The four compounds usually regarded as major compounds are listed in below.

Major compounds of cement

Name of Compound Formula

Tricalcium silicate 3 CaO.SiO2

Dicalcium silicate 2 CaO.SiO2

Tricalcium aluminate 3 CaO.Al2O3 

Tetracalcium 4CaO.Al2O3.Fe2O3

aluminoferrite

It is to be noted that for simplicity’s sake abbreviated notations are used. C stands for CaO, S stands for SiO2, A for Al2O3, F for Fe2O3 and H for H2O. 

The equations suggested by Bogue for calculating the percentages of major compounds are given below.

C3S = 4.07 (CaO) – 7.60 (SiO2) – 6.72 (Al2O3) – 1.43 (Fe2O3) – 2.85 (SO3)

C2S = 2.87 (SiO2) – 0.754 (3CaO.SiO2)

C3A = 2.65 (Al2O3) – 1.69 (Fe2O3)

C4AF= 3.04 (Fe2O3)

Two International Finance Center, Hong Kong

Two International Finance Center, 

Hong Kong

Height : 415 meters

Cost to build : US$2.5

billion

Completion date: August

2008

Fast facts : In "Lara

Croft Tomb Raider: The

Cradle of Life," Lara

Croft leaped off the

building. In "The Dark

Knight," Batman leaped from 2IFC to IFC. Two

International Financial Center is the definitive

point of Hong Kong’s awe-inspiring skyline and a

symbol of its wealth.

Located in the center of Hong Kong’s financial

district, this shimmering 415-meter obelisk fits every

criterion of a financial powerhouse.

It houses some of the world’s largest financial

institutes, it is situated on 8 Finance Street and

has 88 floors -- the number eight is an auspicious

digit in Hong Kong.

The building is topped with a crown that some liken

to a beard trimmer.

75 CIVIL ENGINEERING INTERVIEW QUESTIONS

75 CIVIL ENGINEERING 

INTERVIEW QUESTIONS:

1. What is bending moment (BM) & Shear force (SF) – Explain.

2. What are the steps involved in the concreting process, explain?

3. Describe briefly the various methods of concrete curing.

4. What is the minimum curing period?

5. What Do You Understand by M25 Concrete?

6. What is Water-Cement Ratio and How it is related to the strength of concrete?

7. What is a bearing capacity of soil?

8. How to increase the bearing capacity of soil?

9. What are the different types of foundation?

10. Explain moment of inertia and its importance.

11. How do we determine the specific gravity of a cement?

12. Density Of 1 cum cement?

13. What are the causes of building collapse?

14. What is bar bending schedule (BBS) & how to prepare it?

15. Why is concrete cube test carried out?

16. Why is concrete slump test carried out?

17. What is bleeding, segregation, honeycombing of concrete?

18. What is pre-stressed concrete? Which reinforcement is used in prestressed concrete?

19. What is the ratio of steel and concrete to use in slabs, beams, columns?

20. Difference between pre-tensioning and post-tensioning?

21. What are the weights of 16mm, 12mm, 20mm, 25mm, 8mm Dia. Bars.

22. What is the minimum Propping Period of Beams and Slabs of various Spans?

23. What are the advantages of Prestressed Concrete over R.C.C?

24. Quantity of materials required for different works.

25. Which is stronger solid steel rod or hollow steel pipe?

26. Initial & final setting time of concrete?

27. Why we provide steel in concrete?

28. Is brick strength more or concrete block?

29. How many bricks are there in 100cft?

30. 28 days compressive strength of concrete in PSI?

31. How to calculate the unit weight of steel bars?

32. What is Plinth Level and Sill Level?

33. What is Brest Wall?

34. What is Brick crushing strength(PSI)?

35. How many are the types of joints?

36. How can cracks in concrete be avoided?

37. Types Of DPC and its Thickness used?

38. 28 Days Strength of Concrete (1:2:4)?

39. How many types of slabs are there & how to design it?

40. How much is the cover for slab?

41. Maximum % of Steel in columns and beams?

42. What is fineness modulus?

43. What is Packing Factor?

44. Difference between one way slab & two way slab?

45. Difference between QA & QC?

46. What do you mean by Fe415?

47. What are the functions of a column in a building?

48. How many feet are in 4 square yards?

49. What is the average density of soil?

50. What is the ratio of Grades M5, M7.5, M10, M15, M20, M25, M30, M35, M40?

51. Why foundation is provided?

52. The concrete slump recommended for beams and slabs; is-

53. What is the meaning of soil reinforcement?

54. What is the different type of slump test indications?

55. What is buckling or crippling load?

56. Define slenderness ratio. What is its effect on the design of compression member?

57. Shear force and BM diagrams for different types of loadings on beams.

58. Difference between mild steel and HYSD bars?

59. What do you understand by 80/100 bitumen?

60. What is differential settlement?

61. What do 53 stands for in 53-grade cement?

62. How do you construct a 25 storey building with no columns?

63. Types of loads on structure?

64. Difference between pre-tensioning and post-tensioning?

65. What is the L/D ratio of a cantilever beam?

66. What is camber?

67. What is batching? Difference between volume and weight batching?

68. How is a theodolite leveled?

69. What is a benchmark? Name the different types.

70. Types of admixtures?

71. What are the CAD softwares you have used?

72. Interpret a strss vs strain curve.

73. Define modulus of elasticity.

74. What are the chemical compositions of cement?

75. What is creep & shrinkage of concrete?

Skin Friction of Soil

Skin Friction of Soil

Skin friction of soil is considered in pile designs. Mainly, there are two types of skin frictions. Negative and positive skin friction are considered in pile designs.