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Wednesday, November 25, 2015

CIVIL SEMINAR TOPICS - Civil Emgimeerimg

CIVIL SEMINAR TOPICS
List of topics which you can selects for your presentation of last year.

·        Corrosion Of Reinforcement In HVFA Concrete
Corrosion of reinforcements has been one of the major challenges that the civil engineers have been facing. Corrosion leads to the formation of rust which results in the spilling of concrete which in turn leads to the exposure of rebar to the aggressive environment. This will accelerate the ill effects and ultimately leads to the breakdown of the structure. Corrosion mainly occurs in areas of aggressive environment such as coastal regions. It is very important that corrosion of reinforcement must be prevented in order to have a durable structure. Even though there are many methods to prevent corrosion, most of them are uneconomical and requires great skill. Some of the recent studies in various parts of the world have revealed that high volume fly ash (HVFA) concrete can protect the steel reinforcement more efficiently, so that it can resist corrosion, and thus the structure as a whole. HVFA concrete is a type of concrete in which a part of the cement is replaced by fly ash, which is an industrial waste. Thus the implementation of h v f a concrete can minimize corrosion in an effective way. Moreover it can lead to much durable structure without considerable increase in cost.
·        Silica Fume Concrete
Silica fume is also referred to as micro silica or condensed silica fume but the term silica fume has been generally accepted. It is a by-product of manufacture of silica and ferrosilicon alloys from high purity quartz and coal in a submerged arc electric furnace. It is reported that the addition of ultra fine particle in HPC improves the strength of concrete. The optimum silica fume proportions in between 20% and 25% by weight of concrete. In itself silica fume does not have any binding properties, but it reacts with calcium hydroxide on hydration of cement and produces the gel i.e. calcium silicate hydrate which has good binding properties. Silica fume has been used in manufacture of high strength concrete.

·        Self Compacting Concrete
Self Compacting Concrete (SCC) is defined as a category of High Performance Concrete that has excellent deformability in the fresh state and high resistance to segregation, and can be placed and compacted under its self weight without applying vibration. SCC was first developed in Japan in mid 1980. Since then, it has found applications in reinforced concrete sections containing congested reinforcements. Poor quality of vibration of concrete, in congested locations, has often been a shortcoming of traditional concrete. In such situations, SCC, which flows under its self weight and does not require any external vibration, has revolutionized the concrete placement.

Construction material subjected to repetitive or cyclic loading have to be qualified for their fatigue behaviour. Generally their behaviour is considered satisfactory if they withstand two million cycle of repetitive loading without distress or failure at that required mean stress level and range stress.
The recent research in reinforcing Portland cement based material with randomly distributed fibres was spurred by pioneering research or fibre reinforced concrete (FRC) conducted in the United state in the 1960s.The addition of fibre in the concrete matrix improves the monotonic flexural strength, flexural fatigue strength, impact strength, shock resistance, ductility, and flexural toughness in concrete, besides delaying and arresting crack proportion. Fatigue is often described by a parameter ‘Fatigue life’ which essentially represents the number of cycles the material can withstand under a given pattern of repetitive loading, before falling.
This paper presents the details of the experimental investigations carried out at the structural engineering research centre (S E R C) to study the behaviour of reinforced concrete beam cast at different types of steel fibre in the concrete matrix and subjected to Fatigue loading.

·        Stress Ribbon Bridges
Passive solar heating and cooling represents an important strategy for displacing traditional energy sources in buildings. Passive solar techniques make use of the steady supply of solar energy by means of building designs that carefully balance their energy requirements with the building's site and window orientation. The term passive indicates that no additional mechanical equipment is used, other than the normal building elements. In this approach, the building itself or some element of it takes advantage of natural energy characteristics in materials and air created by exposure to the sun. Passive systems are simple, have few moving parts, and require minimal maintenance and require no mechanical systems. All solar gains are brought in through windows. All passive techniques use building elements such as walls, windows, floors and roofs, in addition to exterior building elements and landscaping, to control heat generated by solar radiation. Solar heating designs collect and store thermal energy from direct sunlight. Passive cooling minimizes the effects of solar radiation through shading or generating airflows with convection ventilation. The benefits of using passive solar techniques include simplicity, price and the design elegance of fulfilling one's needs with materials at hand.
As a design approach, passive solar design can take many forms. It can be integrated to greater or lesser degrees in a building. Key considerations regarding passive design are determined by the characteristics of the building site. The most effective designs are based on specific understanding of a building site's wind patterns, terrain, vegetation, solar exposure and other factors often requiring professional architectural services. However, a basic understanding of these issues can have a significant effect on the energy performance of a building.

Transportation contributes to all round development of a country and hence plays a vital rate towards its progress. India, being predominantly rural in nature, road links is found to have distinct advantages over other modes of transportation. The impact of highway location on the environment is a major concern of the highway engineer and the public. If the highways are not properly located and designed it will subject to erosion and may contribute sediments to streams. The control of soil and water is basic to the protection of the road structure and therefore highway design, construction and maintenance procedure must be continually evaluated to minimize erosion and sedimentation problems.
Erosion can be controlled to considerable degree by geometric design and with proper provision for drainage and fitting landscape development. Although some standardization of methods for minimizing soil erosion is also possible. Also erosion process is a natural phenomenon accelerated by man’s activity, technical competency is evaluating the severity of erosion problem and the planning and design of preventive and corrective measures is essential in obtaining economical and environmental satisfactory methods for erosion control.

Different types of Non-Destructive tests (NDT) are there to detect voids and cracks in concrete such as Ultrasonic Pulse Echo, Ultrasonic Pulse Velocity, Ground Penetrating Radar, Impact Echo Method, X-ray Scanning Method, Rebound Hammer Method, Infrared Thermography Method.
In which Infrared Thermography method is discussed in this paper
as concrete is used in newer areas and evidence is coming to light of premature deterioration in concrete structures there is a need to develop new methods for quality control at the time of concrete construction and for the evaluation of existing structures. Concrete specimens were designed and conditioned to represent some of the anomalies that may be found during construction and also in hardened concrete. From the study it emerges that Infrared Thermography is an effective tool for concrete placement and identifying location of voids and cracks in fresh and hardened concrete. It could be effectively used to narrow down areas that needed closer attention during an in-service inspection of concrete structures.

·        Trenchless Technology
Trenchless technology is a relatively new term that describes the installation of conduits beneath roadways without open-cutting. The term has been used on a global basis since the mid-1980s. However, some of the methods referred to as trenchless methods are not new. For example, auger boring and slurry boring have been used since the 1940s, and pipe jacking has been used since the early 1900s. These methods are referred to as road boring techniques or horizontal earth boring techniques. Nevertheless, many new trenchless techniques have been introduced and much advancement has taken place with the more traditional techniques. Although most of these methods require excavation for shafts, shaft locations usually can be selected to avoid or minimize traffic disruption. It is anticipated that the use of trenchless technology will continue to increase because of its inherent advantages of minimizing disruption to society and reducing environmental impact. Another driving force behind this increase is the benefit of avoiding or minimizing the handling, volume, treatment and/or disposal of contaminated soil. In many situations, these techniques have become cost-effective alternatives to traditional open-cutting methods.

·        Plastic As Soil Stabilizer

Use of plastic products such as polythene bags, bottles, containers and packing strips etc. is increasing day by day. As a result amount of waste plastic also increased. This will leads to various environmental problems. Many of the wastes produced today will remain in the environment for many years leading to various environmental concerns. Therefore it is necessary to utilize the wastes effectively with technical development in each field. Many by-products are being produced using the plastic wastes. This paper presents the details of studies, conducted by various researchers on the possible use of waste plastic for soil stabilization. The results of the studies indicate that by adding plastic strips in soil; shear strength, tensile strength and California bearing ratio (CBR) value of the soil increases.

Monday, August 24, 2015

Pile Foundation - I

PILE FOUNDATION
Introduction

A pile is basically a long cylinder of a strong material such as concrete that is pushed into the ground to act as a steady support for structures built on top of it.
Pile foundations are used in the following situations:
  1. 1   When there is a layer of weak soil at the surface. This layer cannot support the weight of the building, so the loads of the building have to bypass this layer and be transferred to the layer of stronger soil or rock that is below the weak layer.
  2.      When a building has very heavy, concentrated loads, such as in a high rise structure, bridge, or water tank.

Pile foundation is required when the soil bearing capacity is not sufficient for the structure to withstand. Pile foundations are capable of taking higher loads than spread footings.This is due to the soil condition or the order of bottom layers, type of loads on foundations, conditions at site and operational conditions.
Many factors prevent the selection of surface foundation as a suitable foundation such as the nature of soil and intensity of loads, we use the piles when the soil have low bearing capacity or in building in water like bridges and dams
A pile foundation consists of two components: Pile cap and single or group of piles. Piles transfers the loads from structures to the hard strata, rocks or soil with high bearing capacity. These are long and slender members whose length can be more than 15 m.
Piles can be made from concrete, wood or steel depending on the requirements. These piles are then driven, drilled or jacked into the ground and connected to pile caps. Pile foundation are classified based on material of pile construction, type of soil, and load transmitting characteristic of piles.
The use of pile foundations as load carrying and load transferring systems has been for many years. Timber piles were used in early days, driven in to the ground by hand or holes were dug and filled with sand and stones. The use of steel pile started since 19th century and concrete piles since 20th century.
With the change in technology and industrial revolution, many advance systems have been developed for pile driving from the invention of steam and diesel pile driving machines.
The use of pile foundations is increasing day by day due to non-availability of land for construction. Heavy multistory building are being constructed, and load from these structures can not be directly transferred to ground due to low bearing capacity issue and stability issues of building during lateral load application. So, demand for use of pile foundations are increasing day by day. Due to this demand for piles, there have been many improvements in piles and pile driving technology and systems. Today there are many advanced techniques of pile installation.

Function of Pile Foundation:

As other types of foundations, the purpose of pile foundations is:
– To transmit the buildings loads to the foundations and the ground soil layers whether these loads vertical or inclined
– To install loose cohesion less soil through displacement and vibration.
– To control the settlements; which can be accompanied by surface foundations.
– To increase the factor of safety for heavy loads buildings
The selection of type of pile foundation is based on site investigation report. Site investigation report suggests the need of pile foundation, type of pile foundation to be used, depth of pile foundation to be provided. The cost analysis of various options for use of pile foundation should be carried out before selection of pile foundation types.
Unless the ground condition is rocks, for heavy construction and multistory buildings, the bearing capacity of soil at shallow depth may not be satisfactory for the loads on the foundation. In such cases, pile foundation has to be provided. The number of piles in a pile groups required is calculate from the pile capacity of single pile and the loads on the foundation. Piles are a convenient method of foundation for works over water, such as jetties or bridge piers.

There are two types of pile foundations, each of which works in its own way.

End Bearing Piles

In end bearing piles, the bottom end of the pile rests on a layer of especially strong soil or rock. The load of the building is transferred through the pile onto the strong layer. In a sense, this pile acts like a column. The key principle is that the bottom end rests on the surface which is the intersection of a weak and strong layer. The load therefore bypasses the weak layer and is safely transferred to the strong layer.
Friction Piles


Friction piles work on a different principle. The pile transfers the load of the building to the soil across the full height of the pile, by friction. In other words, the entire surface of the pile, which is cylindrical in shape, works to transfer the forces to the soil.

To visualize how this works, imagine you are pushing a solid metal rod of say 4 mm diameter into a tub of frozen ice cream. Once you have pushed it in, it is strong enough to support some load. The greater the embedment depth in the ice cream, the more load it can support. This is very similar to how a friction pile works. In a friction pile, the amount of load a pile can support is directly proportionate to its length.

What are piles made of?

Piles can be made of wood, concrete, or steel


In traditional construction, wooden piles were used to support buildings in areas with weak soil. Wood piles are still used to make jetties. For this one needs trees with exceptionally straight trunks. The pile length is limited to the length of a single tree, about 20 m, since one cannot join together two tree trunks. The entire city of Venice in Italy is famous for being built on wooden piles over the sea water.



Cross sections of various pile foundations
Concrete piles are precast, that is, made at ground level, and then driven into the ground by hammering - more on that later. Steel H-piles can also be driven into the ground. These can take very heavy loads, and save time during construction, as the pile casting process is eliminated. No protective coating is given to the steel, as during driving, this would be scraped away by the soil. In areas with corrosive soil, concrete piles should be used.
How piles are used
As pile foundations carry a lot of load, they must be designed very carefully. A good engineer will study the soil the piles are placed in to ensure that the soil is not overloaded beyond its bearing capacity.

Every pile has a zone of influence on the soil around it. Care must be taken to space the piles far enough apart so that loads are distributed evenly over the entire bulb of soil that carries them, and not concentrated into a few areas.
Engineers will usually group a few piles together, and top them with a pile cap. A pile cap is a very thick cap of concrete that extends over a small group of piles, and serves as a base on which a column can be constructed. The load of this column is then distributed to all the piles in the group.


How piles are constructed

Engineers will usually group a few piles together, and top them with a pile cap. A pile cap is a very thick cap of concrete that extends over a small group of piles, and serves as a base on which a column can be constructed. The load of this column is then distributed to all the piles in the group.
Piles are first cast at ground level and then hammered or driven into the ground using a pile driver. This is a machine that holds the pile perfectly vertical, and then hammers it into the ground blow by blow. Each blow is is struck by lifting a heavy weight and dropping it on the top of the pile - the pile is temporarily covered with a steel cap to prevent it from disintegrating. The pile driver thus performs two functions - first, it acts as a crane, and lifts the pile from a horizontal position on the ground and rotates it into the correct vertical position, and second, it hammers the pile down into the ground.

Piles should be hammered into the ground till refusal, at which point they cannot be driven any further into the soil.
Special Piles
Pile driving is very noisy and causes massive vibrations through the soil. For this reason, it is sometimes difficult to use them in sensitive locations. For example, if an operational hospital or science lab is to be extended, driving piles would cause unwanted disturbance. Their use is also restricted in residential areas in many countries. The vibrations could also cause structural damage to older buildings that are close by. In such situations it is possible to use micro piling or helical piling, neither of which relies on hammering.

Micro piles or mini piles are small piles that are constructed in the following way:
Step 1: a hole a little larger than the pile diameter and the full length of the pile is dug into the ground using an apparatus like a soil boring machine.
Step 2: a precast concrete pile is lowered or pushed into the hole.
Step 3: a concrete grout is poured into the gap between the pile and the earth.

Helical piles are steel tubes that have helical (spiral) blades attached to them. These can be drilled into the ground, meaning that the pile acts as a giant drill bit, and is rotated and pushed into the ground from above, much like a screw drills into wood. Once the steel pile is driven into the ground, a pile cap is poured on top of the pile to prepare it for the construction above.

Saturday, August 22, 2015

Pile foundation - Static Analysis

HOW TO CALCULATE PILE LOAD CAPACITY? (STATIC ANALYSIS)



The ultimate bearing capacity of a pile is the maximum load which it can carry without failure or excessive settlement of the ground.
The bearing capacity of a pile depends primarily on 3 factors as given below,
  1. Type of soil through which pile is embedded
  2. Method of pile installation
  3. Pile dimension (cross section & length of pile)
While calculating pile load capacity for cast in situ concrete piles, using static analysis, we need to use soil shear strength parameter and dimension of pile.
pile load capacity- static analysis

LOAD CARRYING CAPACITY OF PILE USING STATIC ANALYSIS

The pile transfers the load into the soil in two ways. Firstly, through the tip-in compression, termed as “end-bearing” or “point-bearing”; secondly, by shear along the surface termed as “skin friction”.

LOAD CARRYING CAPACITY OF CAST IN-SITU PILES IN COHESIVE SOIL

The ultimate load carrying capacity (Qu) of pile in cohesive soils is given by the formula given below, where the first term represents the end bearing resistance (Qb) and the second term gives the skin friction resistance (Qs).
pile in cohesive formula



Where,
Qu = Ultimate load capacity, kN
Ap = Cross-sectional area of pile tip, in m2
Nc = Bearing capacity factor, may be taken as 9
αi = Adhesion factor for the ith layer depending on the consistency of soil. It depends upon the undrained shear strength of soil and may be obtained from the figure given below.
Variation of alpha with cohesion
Variation of alpha with cohesion
ci = Average cohesion for the ith layer, in kN/m2
Asi = Surface area of pile shaft in the ith layer, in m2
A minimum factor of safety of 2.5 is used to arrive at the safe pile load capacity (Qsafe) from ultimate load capacity (Qu).
Qsafe = Qu/2.5

LOAD CARRYING CAPACITY OF CAST IN-SITU PILES IN COHESION LESS SOIL

The ultimate load carrying capacity of pile, “Qu”, consists of two parts. One part is due to friction, called skin friction or shaft friction or side shear denoted as “Qs” and the other is due to end bearing at the base or tip of the pile toe, “Qb”.
The equation given below is used to calculate the ultimate load carrying capacity of pile.
pile load capacity formula-1
Where,
Ap = cross-sectional area of pile base, m2
D = diameter of pile shaft, m
γ = effective unit weight of the soil at pile tip, kN/m3
Nγ= bearing capacity factor
Nq = bearing capacity factor
Φ = Angle of internal friction at pile tip
PD = Effective overburden pressure at pile tip, in kN/m2
K = Coefficient of earth pressure applicable for the ith layer
PDi = Effective overburden pressure for the ith layer, in kN/m2
δi = Angle of wall friction between pile and soil for the ith layer
Asi = Surface area of pile shaft in the ith layer, in m2
The first term is the expression for the end bearing capacity of pile (Qb) and the second term is the expression for the skin friction capacity of pile (Qs).
A minimum factor of safety of 2.5 is used to arrive at the safe pile capacity (Qsafe) from ultimate load capacity (Qu).
Qsafe = Q/ 2.5

IMPORTANT NOTES TO REMEMBER

  • The value of bearing capacity factor Nq is obtained from the figure given below.
bearing factor value
bearing factor value
  • The value of bearing capacity factor Nγ is computed using the equation given below.
formula N gamma
  • For driven piles in loose to dense sand with φ varying between 300to 400 , ki values in the range of 1 to 1.5 may be used.
  • δ, the angle of wall friction may be taken equal to the friction angle of the soil around the pile stem.
  • The maximum effective overburden at the pile base should correspond to the critical depth, which may be taken as 15 times the diameter of the pile shaft for φ ≤ 300and increasing to 20 times for φ ≥ 400
  • For piles passing through cohesive strata and terminating in a granular stratum, a penetration of at least twice the diameter of the pile shaft should be given into the granular stratum.

Pile foundation - Classification

HOW TO CLASSIFY PILES BASED ON CONSTRUCTION MATERIALS?

A pile is a slender, structural member installed in the ground to transfer the structural loads to soils at some significant depth below the base of the structure. Structural loads include axial loads, lateral loads, and moments. Another term commonly used in practice for pile foundations is deep foundations. Structures that cannot be supported economically on shallow foundations are normally supported by pile foundations.

On the basis of materials used for the construction of pile foundation, it can be classified in to following 5 types.

  1. Concrete piles
  2. Steel piles
  3. Timber piles
  4. Plastic piles
  5. Composite piles

1. CONCRETE PILES

There are several types of concrete piles that are commonly used. These include cast-in-place concrete piles, precast concrete piles, drilled shafts, and barrette piles. Cast-in-place concrete piles are formed by driving a cylindrical steel shell into the ground to the desired depth and then filling the cavity of the shell with fluid concrete. They are called displacement piles. The steel shell is for construction convenience and does not contribute to the load transfer capacity of the pile. Its purpose is to open a hole in the ground and keep it open to facilitate the construction of the concrete pile. Plain concrete is used when the structural load is only compressive. If moments and lateral loads are to be transferred, then a steel reinforcement cage is used in the upper part of the pile.
Precast concrete piles usually have square or circular or octagonal cross sections and are fabricated in a construction yard or a factory from reinforced or prestressed concrete. They are preferred when the pile length is known in advance. The disadvantages of precast piles are problems in transporting long piles, cutting, and lengthening. A very popular type of precast concrete pile is the Raymond cylindrical prestressed pile. This pile comes in sections, and lengths up to 70 m can be obtained by stacking the sections.
Typical design loads are greater than 2 MN.
Micropiles (also called minipiles, pin piles, needle piles, or root piles) are small-diameter (50 mm to 340 mm) pipe piles (pushed or driven) or grouted (jet or post or pressure) piles.
They are particularly useful for
  • Sites with low headroom,
  • Congested areas,
  • Sites with restricted access, and
  • Foundation repair or strengthening.

2. STEEL PILES

Steel piles come in various shapes and sizes and include cylindrical, tapered, and H-piles. Steel H-piles are rolled steel sections. They are non-displacement piles. Steel pipe piles are seamless pipes that can be welded to yield lengths up to 70 m. They are usually driven with open ends into the soil. A conical tip is used where the piles have to penetrate boulders and rocks. To increase the load capacity of steel pipe piles, the soil plug is excavated and replaced by concrete. These piles are called concrete-filled steel piles. The soil plug may adhere to the pile surface and moves down with it during driving. This is called plugging.

3. TIMBER PILES

Timber piles have been used since ancient times. The lengths of timber piles depend on the types of trees used to harvest the piles, but common lengths are about 12 m. Longer lengths can be obtained by splicing several piles. Timber piles are susceptible to termites, marine organisms, and rot within zones exposed to seasonal changes. Timber piles are displacement piles.

4. PLASTIC PILES

Plastic piles comprise a variety of composite materials that include polymer composites, PVC, and recycled materials. These piles are used in special applications such as in marine environments and within soil zones exposed to seasonal changes.

5. COMPOSITES

Concrete, steel, and timber can be combined to form a composite pile. For example, the portion of a timber pile above groundwater level that is likely to suffer from decay due to termites or rot may be replaced by concrete. Similarly, the portion of a steel pile within a corrosive environment can be covered with concrete or other protective materials.