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Monday, April 30, 2012

How to install pile to foundation




The installation process and method of installations are equally important factors as of the design process of pile foundations. In this section we will discuss the two main types of pile installation methods; installation by pile hammer and boring by mechanical auger. 

In order to avoid damages to the piles, during design, installation Methods and installation equipment should be carefully selected. If installation is to be carried out using pile-hammer, then the following factors.

should be taken in to consideration: 
  • the size and the weight of the pile 
  • the driving resistance which has to be overcome to achieve the design penetration 
  • the available space and head room on the site 
  • the availability of cranes and 
  • the noise restrictions which may be in force in the locality. 

Pile driving methods (displacement piles)
Methods of pile driving can be categorised as follows:
  1. Dropping weight
  2. Explosion
  3. Vibration
  4. Jacking (restricted to micro-pilling)
  5. Jetting 


Drop hammers 
A hammer with approximately the weight of the pile is raised a suitable height in a guide and released to strike the pile head. This is a simple form of hammer used in conjunction with light frames and test piling, where it may be uneconomical to bring a steam boiler or compressor on to a site to drive very limited number of piles.
 
There are two main types of drop hammers:  
  1. Single-acting steam or compressed-air hammers; comprise a massive weight in the form of a cylinder. Steam or compressed air admitted to the cylinder raises it up the fixed piston rod. At the top of the stroke, or at a lesser height which can be controlled by the operator, the steam is cut off and the cylinder falls freely on the pile helmet. 
  2. Double-acting pile hammers; can be driven by steam or compressed air. A pilling frame is not required with this type of hammer which can be attached to the top of the pile by leg-guides, the pile being guided by a timber framework. When used with a pile frame, back guides are bolted to the hammer to engage with leaders, and only short leg-guides are used to prevent the hammer from moving relatively to the top of the pile. Double-acting hammers are used mainly for sheet pile driving. 





Diesel hammers 
Also classified as single and double-acting, in operation, the diesel hammer employs a ram which is raised by explosion at the base of a cylinder. Alternatively, in the case of double-acting diesel hammer, a vacuum is created in a separate annular chamber as the ram moves upward, and assists in the return of the ram, almost doubling the output of the hammer over the single-acting type. In favourable ground conditions, the diesel hammer provide an efficient pile driving capacity, but they are not effective for all types of ground. 

Pile driving by vibrating
Vibratory hammers are usually electrically powered or hydraulically powered and consists of contra-rotating eccentric masses within a housing attaching to the pile head. The amplitude of the vibration is sufficient to break down the skin friction on the sides of the pile. Vibratory methods are best suited to sandy or
gravelly soil.

Jetting: to aid the penetration of piles in to sand or sandy gravel, water jetting may be employed. However, the method has very limited effect in firm to stiff clays or any soil containing much coarse gravel, cobbles, or boulders.
complete vibration hammer kit, just need a heavy excavator to attach the hammer


Boring methods ( non-displacement piles) 

Continuous Flight Auger (CFA) 
An equipment comprises of a mobile base carrier fitted with a hollow-stemmed flight auger which is rotated into the ground to required depth of pilling. To form  the pile, concrete is placed through the flight auger as it is withdrawn from the ground. The auger is fitted with protective cap on the outlet at the base of the central tube and is rotated into the ground by the top mounted rotary hydraulic motor which runs on a carrier attached to the mast. On reaching the required depth, highly workable concrete is pumped through the hollow stem of the auger, and under the pressure of the concrete the protective cap is detached. While rotating the auger in the same direction as during the boring stage, the spoil is expelled vertically as the auger is withdrawn and the pile is formed by filling with concrete.In this process, it is important that rotation of the auger and flow of concrete is matched that collapse of sides of the hole above concrete on lower flight of auger is avoided. This may lead to voids in filled with soil in concrete. 

The method is especially effective on soft ground and enables to install a variety of bored piles of various diameters that are able to penetrate a multitude of soil conditions. Still, for successful operation of rotary auger the soil must be reasonably free of tree roots, cobbles, and boulders, and it must be self-supporting.

During operation little soil is brought upwards by the auger that lateral stresses is maintained in the soil and voiding or excessive loosening of the soil minimise. However, if the rotation of the auger and the advance of the auger is not matched, resulting in removal of soil during drilling-possibly leading to collapse of the side of the hole. 



Underreaming 
A special feature of auger bored piles which is sometimes used to enable to exploit the bearing capacity of suitable strata by providing an enlarged base. The soil has to be capable of standing open unsupported to employ this technique. Stiff and to hard clays, such as the London clay, are ideal. In its closed position, the underreaming tool is fitted inside the straight section of a pile shaft, and then expanded at the bottom of the pile to produce the underream Normally, after installation and before concrete is casted, a man carrying cage is lowered and the shaft and the underream of the pile is inspected. 


C.H.D.P 
Continuous helical displacement piles: a short, hollow tapered steel former complete with a larger diameter helical flange, the bullet head is fixed to a hallow drill pipe which is connected to a high torque rotary head running up and down the mast of a special rig. A hollow cylindrical steel shaft sealed at the 
lower end by a one-way valve and fitted with triangular steel fins is pressed into the ground by a hydraulic ram. There are no vibrations. Displaced soil is compacted in front and around the shaft. Once it reaches the a suitably resistant stratum the shaft is rotated. The triangular fins either side of its leading edge carve out a conical base cavity. At the same time concrete is pumped down the centre of the shat and through the one-way valve. Rotation of the fins is calculated so that as soil is pushed away from the pile base it is simultaneously replaced by in-flowing concrete. Rates of push, rotation and concrete injection are all controlled by an onboard computer. Torque on the shaft is also measured by the computer. When torque levels reach a constant low value the base in formed. The inventors claim that the system can install typical pile in 12 minute. A typical 6m long pile with an 800mm diameter base and 350mm shaft founded on moderately dense gravel beneath soft overlaying soils can achieve an ultimate capacity of over 200t. The pile is suitable for embankments, hard standing supports and floor slabs, where you have a soft silty layer over a gravel strata.



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Saturday, April 28, 2012

How to select the type of light reflector for home



Electric (Artificial) Lighting


Lamp types
(1) Incandescent lamps produce a warm light,are inexpensive and easy to use but have limited lumination per watt (20 to 40) and a short life. Normal voltage lamps produce a point source of light. Most common shapes are A, R, and PAR. Low voltage lamps pro- duce a very small point of intense brightness that can be focused into a precise beam of light (for merchandise or art).These are usually PAR shapes or designed to fit into a parabolic reflector. Sizes are designated in 1⁄8 inch of the widest part of lamp.Tungsten-Halogen (quartz) and low voltage are a special type of incandescent. Quartz is another type of incandescent that has high-intensity white light with slightly longer life.

(2) Gaseous discharge lamps produce light by passing electricity through a gas. These lamps require a ballast to get the lamp started and then to control the current.

  1. Fluorescent lamps produce a wide, linear, diffuse light source that is well-suited to spreading light downward to the working surfaces of desks or displays in a commercial environment with normal ceiling heights (8′ to 12′). Lamps are typically 17, 25, or 32 watts. The deluxe lamps have good color-rendering characteristics and can be chosen to favor the cool (blue) or the warm (red) end of the spectrum. Dimmers for fluorescent are expensive. Fluorescent lamps produce more light per watt of energy (70–85 lumens/watt) than incandescent; thus operating costs are low.The purchase price and length of life of fluorescent lamps are greater than for incandescent and less than for HID. Four-feet lamp lengths utilize 40 watts and are most common. Designations are F followed by wattage, shape, size, color, and a form factor.
  2. High-intensity discharge (HID) lamps can be focused into a fairly good beam of light. These lamps, matched with an appropriate fixture are well-suited to beaming light down to the working place from a high ceiling (12′ to 20′).Dimming HID lamps is difficult. The lamps are expensive but produce a lot of light and last a long time. If there is a power interruption, HID lamps will go out and cannot come on again for about 10 minutes while they cool down.Therefore,in an installation of HID lamps, a few incandescent or fluorescent lamps are needed to provide backup lighting. Since they operate at high temperatures, they would be a poor choice for low ceilings, wall sconces, or any other close proximity light source. They would also be a poor choice in assemblies and other occupancy where power outages could cause panic. Mercury vapor (MV; the bluish street lamps). Because they emit a blue-green light, they are excellent for highlighting foliage, green copper exteriors, and certain signage. Deluxe version is warmer. 35 to 65 lumens/watt. This is not much used anymore. Metal halide (MH) are often ice blue cool industrial-looking lamps. Deluxe color rendering bulbs are 50 to 400 watts, and almost as good as deluxe fluorescent for a warmer effect. Efficiency is 80 lumens/watt. High-pressure sodium (HPS) produces a warm golden yellow light often used for highways. Bulbs are 35 to 400 watts. Deluxe color rendering is almost as cool as deluxe fluorescent for a cooler effect. Efficiency is 100 lumens/watt. Low-pressure sodium (LPS) produces a yellow color which makes all colors appear in shades of grey. They are excellent for promoting plant growth indoors. Bulbs are typically 35 to 180 watts. Used for parking lots and roadways. Efficiency is 150 lumens/watt.
  3. Cold cathode (neon) has a color dependent on the gas and the color of the tube. Can be most any color. Does not give off enough light for detailed visual tasks, but does give off enough light for attracting attention, indoors or out.



Types of reflectors

Common types of reflectors


Lighting systems and fixture types

Note: Costs include lamps, fixture, and installation labor, but not general wiring. As a rule of thumb, fixtures are 20% to 30%, and distribution (not included in following costs) is 30% to 70%.

(1) General room lighting; A large proportion of commercial space requires even illumination on the workplace.This can be done a number of ways.

  1. Direct lighting is the most common form of general room lighting.
  2. Semidirect lighting; All systems other than direct ones necessarily imply that the lighting fixtures are in the space, whether pendant-mounted, surface-mounted, or portable. A semidirect system will provide good illumination on horizontal surfaces, with moderate general brightness.
  3. General diffuse lighting; A general diffuse system most typically consists of suspended fixtures, with predominantly translucent surfaces on all sides.Can be incandescent,fluorescent,or HID.
  4. Direct-indirect lighting; A direct-indirect will tend to equally emphasize the upper and lower horizontal planes in a space (i.e.,the ceiling and floor). Typical fixture:same as semidirect.
  5. Semi-indirect lighting; A semi-indirect system will place the emphasis on the ceiling, with some downward or outward-directed light.
  6. Indirect lighting; A fully indirect system will bounce all the light off the ceiling, resulting in a lowcontrast environment with little shadow. Typical fixture:Same as Direct-Indirect.
  7. Accent or specialty lighting; Used for special effects or spot lighting, such as lighting art objects or products on display.


Friday, April 27, 2012

How to grade bitumen



Bitumen used for paving grades are categorized according to viscosity (degree of fluidity) gradings. The higher the grade, the stiffer the bitumen gets.

Viscosity is a measure of the resistance of a fluid which is being deformed by either shear or tensile stress. In everyday terms (and for fluids only), viscosity is "thickness" or "internal friction". Thus, water is "thin", having a lower viscosity, while honey is "thick", having a higher viscosity. Put simply, the less viscous the fluid is, the greater its ease of movement (fluidity).


The test procedures used for paving grades of bitumen are as follows:

  • Penetration Test;  used to determine the consistency of bitumen by measuring the distance that a standard needle will penetrate vertically into a sample
  • Viscosity Test; is a more scientific measure of consistency than Penetration. Various tests are used to measure the resistance to flow of bitumen and to thereby define its consistency.
  • Flash Point: used to measure the temperature to which a sample of bitumen may be safely heated by establishing the temperature at which a small flame causes the vapour above the sample to ignite or flash.
  • Ductility: gives an indication of the extent to which a sample of the material can be stretched before breaking. A standard briquette of bitumen, placed in a mould in a water bath heated to 15°C, is pulled apart, usually at a speed of 5 cm per minute. The length of the thread of bitumen at the moment when it breaks, expressed in centimetres, is the ductility of the sample.
  • Solubility and the Presence of Insolubles: indicates the degree of contamination of the bitumen by other matter and therefore the presence of pure bitumen. The Australian test measures the percentage of matter that is insoluble in toluene.
  • Effect of Heat and Air: is determined to simulate the conditions obtained when the bitumen is used to manufacture hot-mix. In the Rolling Thin Film Oven Test a moving film of bitumen is heated in an oven at 163°C for 60 minutes. The viscosity is measured before and after treatment.
  • Softening Point: a measurement of the temperature at which a sample of bitumen held in a ring in a water bath allows a steel ball of specified weight to fall to a point at a specified distance below it.


The chart below shows typical applications for paving grade of BP bitumens:

Applications for Bp class
Bitumen class Sprayed Sealing Asphalt
Light Medium Heavy Extra Heavy
Class 170 ok ok      
Class 320   ok ok ok  
Class 600       ok ok




AASHTO M 226 and ASTM D 3381 Viscosity Grades
Standard
Grading based on Original Asphalt (AC)
Grading based on Aged Residue (AR)
AASHTO
M 226
AC-2.5
AC-5
AC-10
AC-20
AC-30
AC-40
AR-10
AR-20
AR-40
AR-80
AR-160
ASTM
D 3381
AC-2.5
AC-5
AC-10
AC-20
AC-30
AC-40
AR-1000
AR-2000
AR-4000
AR-8000
AR-16000






Following table is the specification for performance grade bitumen


PROPERTY
GRADES
STANDARD

PG 76-10
PG 82-10


Min
Max
Min
Max

Flash Point, COC, °C
230
-
230
-
T48
Viscosity @ 135°C, Pa·s
135°C
3.0
135°C
-
ASTM D4402
Dynamic Shear @ 70°C, G*/sin d, kPa
1.00
-
-
-
-
After RTFO
-
-
-
-
-
Dynamic Shear @ 70°C, G*/sin d, kPa
2.20
-
-
-
-
Mass Loss, %
-
1%
-
1%
-
After PAV @ 100°C
-
-
-
-
-
Dynamic Shear @ 28°C, G*·sin d, kPa
-
5000
-
-
-
Creep Stiffness @ -12°C, S, MPa
-
300
-
-
-
Creep Stiffness @ -12°C, M-value
0.300
-
-
-
-









Thursday, April 26, 2012

Problems Caused due to Lateral Deflection of Tall Buildings - wind load



Wind loading on a high-rise building can have a dominant influence on its structural arrangements and design. Lateral deflection due to wind load actions on tall buildings has become a major concern for the designers of today’s high-rise buildings and it is one of the key important factor that must be considered in the structural design of a tall building.

In contrast to vertical loads, lateral load effects, such as the forces exerted by wind on buildings are quite variable and increase rapidly with increase in height. Further, such lateral forces tend both to snap(shear)  and push over (bending) the tall buildings. Excessive or uncontrolled lateral deflection may cause extensive structural, non structural, constructional damages and discomfort to building occupants leading both extensive economic and social damages. It may cause cracking of partitions and external cladding, misalignment of mechanical systems and doors, and possible permanent deformations.

Lateral defections must be limited to prevent second-order P-Delata effects due to gravity loading being of a such a magnitude to precipitate collapse. Further, it must be limited or maintained at a sufficiently low level to allow the proper functioning of non structural components , to avoid distress in the structure, to prevent excessive cracking and consequent loss of stiffness, to avoid any redistribution of load to non-load-bearing components and to prevent dynamic motions becoming large enough to cause discomfort to occupants, to prevent delicate work being undertaken, or effect sensitive equipment.

In recent years the subject of tall building motion and its reduction has received considerable attention. With present trends towards taller, lighter, and more flexible structures, the importance of study and research on this topic is ever-increasing. Of particular interest are methods to reduce the lateral deflection due to wind load actions.


 Reasons for Tall Buildings

Ancient tall buildings and structures are primarily solid structures serving as monuments rather than space enclosures. By contrast, contemporary tall buildings and structures are human habitats, conceived in response to rapid urbanization and population growth.

There are various reasons for construction of tall buildings. The growth in modern tall building construction has been largely for commercial and residential purpose.   However, ego and competition still play a part in determining a building’s height. In addition, various other social and economic factors, such as increase in land value in urban areas and high density of population have lead to a great increase in the number of tall buildings all over the world. Further, the business and tourist community , with its increasing mobility, has fuelled a need for more frequently high-rise , city centre hotel accommodation. The high cost of land, the desire to avoid continuous urban sprawl, and the need to preserve important agricultural production have all contributed to the increasing number of tall buildings.



 Early Tall Building Versus Modern Tall Buildings

As mentioned in the previous section, ancient tall buildings are primarily solid structures rather than space enclosures. By contrast modern tall buildings are human habitats. The difference in the usage of buildings, from solid monumental structures to space enclosures, in itself has not changed the basic stability and strength requirements; the structural issues are still the same, the materials and methods are different.

In the design of early monuments, consideration of spatial interaction between structural sub systems was relatively unimportant, because their massiveness provided for strength and stability. Comparatively, with evolution of radically new structural systems the size and density of structural elements of modern tall building are strikingly less and continue to be diminish motivated by real-estate market, aesthetic aspects and innovative and challenging structural solutions powered by the immense analytical backup provided by computers. Early tall buildings are either prismatic, square or round. The modern tall buildings are better designed and takes more varied and irregular external architectural shapes. 



In recent decades there have been great advances in the design and construction of tall buildings throughout the world, and in the associated development of analytical techniques. The progress in reinforced concrete was slow and intermittent. The inherent advantages of the concrete which could be readily formed to simultaneously satisfy both aesthetic and load –carrying requirements, were not fully appreciated until the end of World War I. Since then significant developments in reinforced concrete occurred. Rather than bringing significant increases in height, these modern developments comprised new structural systems, improved material qualities and services and better design and construction techniques.

The constant search for more efficient solutions led to the innovative designs and new structural form of recent years. The taller and more slender a building, the more important the structural factors become, and more necessary it is to choose an appropriate structural form or system.

This chapter provides a comprehensive literature review on the research subject. It describes various important aspects that is related to the research subject and must be considered in executing the research. Further, apart from a general outline of the structural systems for concrete buildings, special attention is devoted to the structural systems those are studied under this research. These structural systems are described in detail.


Structural Concept of tall building

With regard to lateral loading, a high-rise building is essentially a vertical cantilever beam from the earth. This is the key idea in conceptualizing the structural system for a narrow tall building. This conceptualized cantilever may comprise one or more individually acting vertical cantilevers, such as shear walls or cores, each bending about its own axis and acting in unison only through the horizontal in-plan rigidity of the floor slab. Alternatively the cantilever may comprise a number of columns or walls that are mobilized to act compositely , to some degree, as the chords of a single  massive cantilever, by vertically shear resistant connections such as bracing or beams.

The laterally directed forces due to wind load actions tends to snap the building and push the building over. Hence, the building must have a system to resist both the shear and bending. In resisting the shear forces, the building must not break by shearing off and must not strain beyond the limit of elastic recovery. Also the system resisting the bending must ensure that the building is not overturned and is not broken by premature failure of columns. In addition its bending deflections should not exceed the limit of elastic recovery.

On the other hand when the structure resists to bending and shear, this may set the building in motion, creating an other engineering problem; motion perception or vibrations. As mentioned earlier, excessive or uncontrolled dynamic motions will cause discomfort to the building occupants and extensive socioeconomic damages.  


Different types of wind load on buildings






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