Basic civil engineering part 14

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What are the causes of building collapse?

Answer 1
The Passage of time is one reason. Buildings also collapse due to weak foundations. Earthquakes, hurricanes and other natural disasters can also damage the structure of the buildings and cause it to collapse. Bombings or demolition of buildings is also other reasons.

Answer 2
Foundation weakness and nature of soil.

What are the applications of modulus of elasticity?

Answer #1
As the term implies, "Modulus of Elasticity” relates to the elasticity or "flexibility" of a material. The value of modulus of elasticity is very much significant relating to deflection of certain materials used in the construction industry. Take for example the general E value of mild carbon steel is about 200 GPA comPAred to about 70 GPA for aluminum. This simply translate that aluminum is 3 times flexible than steel.

Answer #2
It indicates that how a material will behave under the application of load. An elactic material has more tensile strength and it can be stretched to a greater extent like steel. So basically good to resist tension at the time of bending. To BUY Our Basic Civil Engineering DVD - PLEASE CALL US AT 70 92 89 89 88

What is the difference between absorption & adsorption and sorption?

Absorption generally refers to two phenomena, which are largely unrelated. In one case, it refers to when atoms, molecules, or ions enter some bulk phase - gas, liquid or solid material. For instance, a sponge absorbs water when it is dry.

Absorption also refers to the process by which the energy of a photon is taken up by another entity, for example, by an atom whose valence electrons make transition between two electronic energy levels. The photon is destroyed in the process. The absorbed energy may be re-emitted as radiant energy or transformed into heat energy. The absorption of light during wave proPAgation is often called attenuation. The tools of spectroscopy in chemistry are based on the absorption of photons by atoms and molecules.

Adsorption is similar, but refers to a surface rather than a volume: adsorption is a process that occurs when a gas or liquid solute accumulates on the surface of a solid or, more rarely, a liquid (adsorbent), forming a molecular or atomic film (the adsorb-ate). It is different from absorption, in which a substance diffuses into a liquid or solid to form a solution.To BUY Our Basic Civil Engineering DVD - PLEASE CALL US AT 70 92 89 89 88
How do you measure concrete?

Cubic feet, Cubic yards, Cubic Meter

 

What is the meaning of soil reinforcement?

Soil reinforcement is the act of improving soil strength to enable it support or carry more load.

Two common examples are:

a) Mixing a soil amendment such as lime into weak clayey soil and re-comPActing to improve soil-bearing capacity (often done under the road base in highway construction)

b) Installing plastic or composite webbing layers (called geo-grid material) alternating with compacted soil to produce a stronger sloped soil structure (often done on steep roadway embankments to improve strength and stability)

Types of admixtures used in concrete as per IS 9103

IS 9103 define the admixture as a material other than water, aggregates, and hydraulic cement and additives like pozzolana or slag and fibre reinforcement used as an  ingredient of concrete or mortar and added to the batch immediately before or during its mixing to modify one or more of the properties of concrete in the plastic or hardened state.

The different types of admixture covered in IS 9103 are as per following

Accelerating Admixtures:

These admixtures when added to concrete, mortar or grout increases the rate of hydration of hydraulic cement, shortens the time of set, accelerates the hardening or development of strength of concrete/ mortar. These admixtures function by interaction with C3S (Tri-calcium
silicate) component of the cement thus increasing the reaction between cement and water.

Retarding Admixtures:

This type of chemical admixtures decreases the initial rate of reaction between cement and water and thereby retards the setting of concrete. It functions by coating the surface of C3S (Tri calcium silicate) components, thus, delaying this reaction with the water. Reaction products are slow to form as such the setting and hardening of concrete are delayed reducing early compressive strengths. Since the rate of stiffening of concrete can be too fast in our tropical climatic conditions, sufficient time for the concrete is required for transportation and placement before setting. In such conditions retarding admixtures can be very useful. Retardation in setting time up to 8-10 hours is possible by suitable use of retarders. The delay in hardening caused by the retarders can be exploited to obtain an architectural finish of exposed aggregate: the retarder is applied to the interior surface of the formwork so that the hardening of the adjacent cement is delayed. This cement can be brushed off after the formwork has been struck so that an exposed aggregate surface is obtained.

Plasticizer (Water Reducer) Admixtures:

A material, which either increases workability of freshly mixed concrete without increasing water cement ratio or maintains workability with a reduced amount of water, is termed as water reducing admixture. As their name implies, the function of water reducing admixture is to reduce the water content of the mix, usually by 5 to 10%, sometimes (in concrete of very high workability) upto 15%. Thus, the purpose of using a water reducing admixture in a concrete mix is to allow a reduction in the water cement ratio while retaining the desired workability or, alternatively, to improve its workability at a given water cement ratio. The actual reduction in water depends on dose of admixtures, cement content, type of aggregate used, ratio of cement, fine and coarse aggregate etc. Therefore, the trial mixes containing an actual material to be used on the job are essential to achieve optimum properties.

Superplasticizer Admixtures:

At a given water /cement ratio and water content in the mix, the dispersing action of superplasticizer increases the workability of concrete, typically by raising the slump from 75mm to 200 mm, the mix remaining cohesive. The resulting concrete can be placed with little or no  compaction and is not subject to excessive bleeding or segregation.

Air Entraining Admixture:

This is an admixture for concrete or mortar which causes air to be incorporated in the form of minute bubbles in the concrete or mortar during mixing, usually to increase workability and resistance to freezing and thawing. Air entrained also breaks the continuity of capillaries.

The dosages required are between 0.005 to 0.05% by mass of concrete and it is advisable to mix it with batching water for uniform dispersion. As per department of Atomic Energy Practice, the air content is controlled between 3 to 6%. Method of measuring air content is given in IS 1190.

SLUMP TEST to determine WORKABILITY of concrete

Basic Civil Engineering Part 13

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

The major steps involved in the process of concreting are as follows:
1. Batching
2. Mixing
3. Transporting and placing of concrete
4. Compacting.

> Batching: The process of measurement of the different materials for the making of concrete is known as batching. batching is usually done in two ways: volume batching and weight batching. In case of volume batching the measurement is done in the form of volume whereas in the case of weight batching it is done by the weight.
> Mixing: In order to create good concrete the mixing of the materials should be first done in dry condition and after it wet condition. The two general methods of mixing are: hand mixing and machine mixing.
> Transportation and placing of concrete: Once the concrete mixture is created it must be transported to its final location. The concrete is placed on form works and should always be dropped on its final location as closely as possible.
> Compaction of concrete: When concrete is placed it can have air bubbles entrapped in it which can lead to the reduction of the strength by 30%. In order to reduce the air bubbles the process of compaction is performed. Compaction is generally performed in two ways: by hand or by the use of vibrators.

What are the different type of slump test indications?

Slump tests are performed to empirically measure the workability of fresh concrete. It is used to measure the consistency of the concrete. In general there are three different types of slumps that occur in slump tests. They are as follows:
> True Slump
> Shear Slump
> Collapse Slump

True Slump: This type of slump is characterized by the general drop of the concrete mass evenly without visible signs of deterioration or disintegration.
Shear Slump: It indicates that the concrete mix is deficient in cohesion. This type of slump leads to segregation and bleeding. Henceforth in the long run effecting the durability of the concrete.
Collapse Slump: This type of slump is indicates that the mix of concrete is simply too wet. The mix is considered to be harsh and lean.

Describe briefly the various methods of concrete curing.

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 methods that are involved in saving the shrinkage of the concrete includes:
(a) Spraying of water: on walls, and columns can be cured by sprinkling water.
(b) Wet covering of surface: can be cured by using the surface with wet gunny bags or straw
(c) Ponding: the horizontal surfaces including the slab and floors can be cured by stagnating the water.
(d) Steam curing: of pre-fabricated concrete units steam can be cured by passing it over the units that are under closed chambers. It allows faster curing process and results in faster recovery.
(e) Application of curing compounds: compounds having calcium chloride can be applied on curing surface. This keeps the surface wet for a very long time.

Why are pull-out tests performed for soil nails?

Pull out tests are performed for primarily the following reasons:
> In order to detect and the verification of the bond strength among the soil and the grout adopted during the design of soil nails. This is considered to be as the primary objective of performing pull out tests for soil nails.
> For the detection of any slippage or occurrence of creeps.
> To detect the elastic and deformations (plastic) of any of the test nails employed. Observations are made during the loading and unloading cycles of the soil nails repetitively.
> To achieve the perfect balance the test nails should always be loaded so that the ultimate soil/grout mixture with an upper limit of 80%.

What reinforcements are used in the process of prestressing?

The major types of reinforcements used in prestressing are:
> Spalling Reinforcement: The spalling stresses leads to stress behind the loaded area of the anchor blocks. This results in the breaking off of the surface concrete. The most likely causes of such types of stresses are Poisson`s effects strain interoperability or by the stress trajectory shapes.
> Equilibrium reinforcements: This type of reinforcements are required where several anchorages exist where the prestressing loads are applied in a sequential manner.
> Bursting Reinforcements: These kinds of stresses occur in cases where the stress trajectories are concave towards the line of action of load. In order to reduce such stresses reinforcements in the form of bursting is required.

Why should pumping be not used in case of concreting works?

During the pumping operation the pump exerted pressure must overcome any friction between the pumping pipes and the concrete, also the weight of the concrete and the pressure head when the concrete is placed above the pumps. Since only water is pump able, all the pressure generated is by the water that is present in the concrete. The major problem due to pumping are segregation effects and bleeding. In order to rectify and reduce these effects, generally the proportion of the cement is increased in order to increase the cohesion , which leads to the reduction of segregation and bleeding. Also if a proper selection of the aggregate grading can vastly improve the concrete pump ability.

THANKS CAREERRIDE

Concrete Blocks and Sizes 

Basic Civil Engineering Q & A - Part 12

Regarding plane-table survey, which of the following statements does not hold ?

All the plotting work including contouring can be done in the field

It is quite suitable for small scale surveys

Less number of control points are required

It can be done in all seasons

Answer — It can be done in all seasons

The plotting of inaccessible points in a plane-table survey can be done by the method of

Interpolation

Radiation

Intersection

Traversing

Answer –Intersection

Total float in a planning network is

Late start time – Early start time

Early start time – Late start time

Late start time – Late finish time

Late finish time – Early finish time

Answer –Late start time – Early start time

An ideal horizontal transition curve is a

Parabola

Circle

Clothoid spiral

Hyperbola

Answer –Clothoid spiral

The transitional property of a lemniscate curve is disrupted when its deflection angle is around

30°

45°

60°

90°

Answer — 60° 

If the radius of a simple curve is R, then the length of the chord for calculating the offsets by the “method of chords produced” should not

exceed

R/5

R/10

R/20

R/25

Answer — R/20

The ratio between the adopted centrifugal ratios for roads and railways is

3 :1

4: 1

2 : 1

5 :1

Answer — 2 : 1

The needle of a magnetic compass is generally supported on a

Bush hearing

Ball bearing

Needle bearing

Jewel bearing

Answer — Jewel bearing

TYPES OF FOUNDATION


LOADING
It is a very important step in the total design process to determine the design loads for the structure. Typical loads for a building are dead load, live load, wind load and earthquake load. Special consideration is sometimes given to impact and fatigue that may occur in vehicles, cranes or machinery.

Dead load consists of the weight of the structure itself plus the weight of permanently installed equipment. It includes the weight of the structural members, floors, ceilings,duct works, exterior walls, permanent partitions and unusual items such as water in swimming pools.

Live load includes the loads specified by the loading standards for various uses and occupancies of the building. These specified loads cover the occupants, furniture, movable equipment, fixtures, books etc, and are the minimum gravity live loads for which the building can be designed within the jurisdiction of that standard.

Wind load can be treated as a static load and is computed with the aid of reference velocity pressures, gust factors, exposure factors and shape factors. Tall, slender buildings must be designed using a dynamic approach to the action of wind gusts or with the aid of experimental methods such as wind tunnel tests.

Conventional earthquake (seismic) design procedures replace the dynamic earthquake loads with equivalent static loads. The earthquake loads which are stipulated are recognized to be much less than the maximum loads possible from a very severe earthquake.
Do you Know ??

The free fall of concrete as per IS 456 : 2000 should be limited to maximum of 1.5 m

Basic civil Engineering Q & A Part 11

The surface joining the static levels in several non-pumping wells penetrating a continuous confined aquifer represents
Water-table surface
Capillary fringe
Piezometric surface of the aquifer
Physical top surface of the aquifer
Answer –Piezometric surface of the aquifer

Critical shear stress of cohesive sediment
Decreases with the void ratio for a given plasticity index
Increases with the plasticity index for a given void ratio
Increases with shear strength for a given clay content
All of the above
Answer –All of the above

EDTA titration method of hardness determination of water sample uses an indicator which combines with hardness-causing divalent cations and forms a coloured complex.The name of the indicator and the colour of the formed complex respectively are
Ferroin and dark blue
Ferroin and wine red
Eriochrome Black T and dark blue
Eriochrome Black T and wine red
Answer — Eriochrome Black T and wine red

The porosity of a soil sample having its void ratio equal to unity would be
33.33%
60.0%
66.66%
75.0%
Answer –60.0%

The porosity of a certain soil sample was found to be 80% and its specific gravity was 2.7 the critical hydraulic gradient will be estimated as
0.34
0.92
1.0
1.5
Answer –0.34

For the determination of shear strength parameters, a and b, of soil in the laboratory,the test to be conducted will be
Triaxial compression test
Sieve analysis
Compaction test
Relative density test
Answer –Triaxial compression test

The field density and field moisture content of a soil can be determined by 1.Core cutter method
2.Sand replacement method
3.Proctor compaction test
4.Modified proctor compaction test
1, 2,3 and 4
1 and 2 only
2 and 3 only
2 and 4 only
Answer — 1 and 2 only

If the whole circle bearing is 315°20′, its quadrantal bearing would be
S 36° 30′ W
N44°40’W
N 57° 24′ W
S 60° 40′ W
Answer –N44°40’W

If the observed fore-bearing of a line xy is 16° 26′, the back bearing of this line is
103° 26′
118° 36′
196° 26′
206° 26′
Answer — 196° 26′

The sub-tense tacheometry method is adopted when the ground is
Flat
Inclined
Undulating
A water-body
Answer — A water-body

In an instrument, the bubble tube with divisions of 1mm and a radius of 0.9m has the sensitivity of
1/2
1/70
1/90
1/900
Answer — 1/900

A contour may be defined as an imaginary line passing through
Points on the longitudinal section
Points of equal elevation
Point of equal local ground slope
Points of transverse section surveys
Answer — Points of equal elevation

A closed contour line with two or more higher contours inside it will represent a
Depression
Hill
Cave
Well
Answer — Hill

Concrete Recycling

The CSI hopes that raising awareness of concrete recycling will promote discussion among all relevant stakeholders and lead to an increase in recycling of concrete. Cement producers can indirectly support this through the work of subsidiaries in the concrete, aggregates and construction industry.

In its report “Recycling Concrete” the CSI argues that the recycling of concrete can reduce natural resource exploitation and waste going to landfill. The report asks for an ultimate goal of “zero landfill” of concrete.

The recovery of concrete falls between standard definitions of reuse and recycling: concrete is broken down into aggregates (granular material), generally to be used in road works, but also as aggregates in new concrete. Recovering concrete has two main advantages: it reduces the use of new virgin aggregate and the associated environmental costs of exploitation and transportation, and it reduces landfill of valuable materials.

While in some countries near full recovery of concrete is achieved, in most parts of the world the potential to recover concrete is overlooked and it ends up as unnecessary waste in landfill. This is generally the result of low public concern, as the waste poses relatively low hazard risks compared to other materials.

The CSI recommends that governments and key stakeholders publicize data on construction and demolition waste and develop reliable and consistent statistics; that they develop economic incentives and legislation to allow infrastructure that promotes concrete recycling (particularly green building schemes); and that they set targets for the use of recycled concrete in both road construction and building industries.

Full Report : http://www.wbcsdcement.org/index.php/key-issues/sustainability-with-concrete/concrete-recycling

Properties of Concrete

Concrete’s properties make it the building material of choice for most purposes. The most important features are:

• Strength and Durability

• Versatility
• Low maintenance
• Affordability
• Fire-resistance
• Thermal mass
• Locally produced and used
• Albedo effect
• Low life-cycle CO₂ emissions
  
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Characteristics of Concrete
1	Strength and Durability	Used in the majority of buildings, bridges, tunnels and dams for its strength Gains strength over time Not weakened by moisture, mould or pests Concrete structures can withstand natural disasters such as earthquakes and hurricanes Roman buildings over 1,500 years old such as the Coliseum are living examples of the strength and durability of concrete
2	Versatility	Concrete is used in buildings, bridges, dams, tunnels, sewerage systems pavements, runways and even roads
3	Low maintenance	Concrete, being inert, compact and non-porous, does not attract mould or lose its key properties over time
4	Affordability	Compared to other comparable building materials, concrete is less costly to produce and remains extremely affordable
5	Fire-resistance	Being naturally fire-resistant concrete forms a highly effective barrier to fire spread LIKE US NOW   Acivcrete   - Share it with your friends.
6	Thermal mass	Concrete walls and floors slow the passage of heat moving through, reducing temperature swings This reduces energy needs from heating or air-conditioning, offering year-round energy savings over the life-time of the building
7	Locally produced and used	The weight of the material limits concrete sales to within 300km of a plant site Very little cement and concrete is traded and transported internationally This saves significantly on transport emissions of CO2 that would otherwise occur
8	Albedo effect	The high "albedo" (reflective qualities) of concrete used in pavements and building walls means more light is reflected and less heat is absorbed, resulting in cooler temperatures This reduces the "urban heat island" effect prevalent in cities today, and hence reduces energy use for e.g. air-conditioning
9	Low life-cycle CO2emissions	80% of a buildings CO2 emissions are generated not by the production of the materials used in its construction, but in the electric utilities of the building over its life-cycle (e.g. lighting, heating, air-conditioning LIKE US NOW   Acivcrete   - Share it with your friends.

Basic Civil Q&A Part 10

Here are the next set of Basic Civil Engineering Questions and Answers - 10 .

All these questions and answers are taken from various online sources, to share informations .

If there is any uncertainty/Correction, You can let us know the same .

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The maximum number of unknown forces that can be determined in a concurrent coplanar force system under equilibrium is
2
3
6
1
Answer –2

A uniformly distributed load of length 8 m crosses a simply supported girder of span 20 m. The maximum bending moment at the left quarter-span point occurs when the distance between the point of CG of the total load and mid-span is
2 m
3 m
4 m
0 m
Answer — 2m

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A suspension bridge with a two-hinged stiffening girder is statically
determinate
indeterminate to 1 degree
indeterminate to 2 degree
indeterminate to 3 degree
Answer –determinate


The moment required to rotate the near end of a prismatic beam through unit angle without translation, when the far end is fixed, is
EI/L
2EI/L
3EI/L
4EI/L
Answer –4EI/L

The Muller-Breslau principle in structural analysis is used for
drawing influence line diagram for any force function
superimposition of load effects
writing virtual work equation
None of the above
Answer — drawing influence line diagram for any force function
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The effective throat thickness of a fillet weld depends upon
angle between fusion faces
length of weld
permissible shear stress
type of weld
Answer — angle between fusion faces

When the load line coincides with the centroid of the rivet group, the rivets are subjected to
shear only
tension only
bending only
shear as well as tension
Answer — shear only

A column member of length I which cannot sway has a rigid foundation at its bottom. Its top is held with heavy beams. The effective length of the column is
1.51
1.01
0.81
0.651
Answer — 0.651

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An ISMB 500 is used as a beam in a multistorey construction. From the viewpoint of structural design,it can be considered to be laterally restrained when
the tension flange is laterally restrained
the compression flange is laterally restrained
the web is adequately stiffened
the conditions in both (a) and (c) are met
Answer — the compression flange is laterally restrained

A steel column pinned at both ends has a buckling load of 200 M. If the column is restrained against lateral movement at its mid-height,its buckling load will be
200 kN
283 kN
400 kN
800 kN
Answer –800 kN

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Deflection limitations over beams are imposed because excessive deflection may cause
undesirable twisting and distortion of end connections
problems in drainage system
psychological effect on users
All of the above
Answer –All of the above

For a hydraulically efficient rectangular channel of bed width 4.0 m, the depth of flow is
4 m
0.5 m
1m
2 m
Answer — 2 m

The design flood commonly adopted in India for barrages and minor dams is
Probable maximum flood
A flood of 50-100 years return period
Peak flood
Standard project flood or a 100-year flood, whichever is higher
Answer –Standard project flood or a 100-year flood, whichever is higher
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The Muskingum method of flood routing is a
Form of hydraulic routing of a flood
Form of reservoir routing
Complete numerical solution of St. Venant equations
Hydrological channel routing method
Answer –Hydrological channel routing method

What would be the volume of water stored in a saturated column with a porosity of 0.35 with a cross-sectional area of 1 m square and depth of 3 m ?
2.0 m cube
0.105 m cube
1.05 m cube
3.0 m cube

Answer –1.05 m cube

IS 456-2000 recognises several types of cement for RCC construction.

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