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Sunday, December 28, 2008

Types of Steel sections

Saturday, December 27, 2008

what are the Basic types Bridge

In general there are five types of bridge;
1. Girder Bridge
2. Arch Bridge
3. Cable Stayed
4. Rigid Frame Bridge
5. Suspension Bridge


1. Girder Bridge

A girder bridge is perhaps the most common and most basic bridge. A log across a creek is an example of a girder bridge in its simplest form. In modern steel girder bridges, the two most common girders are I-beam girders and box-girders.

If we look at the cross section of an I-beam girder we can immediately understand why it is called an I-beam (illustration #1.) The cross section of the girder takes the shape of the capital letter I. The vertical plate in the middle is known as the web, and the top and bottom plates are referred to as flanges. To explain why the I shape is an efficient shape for a girder is a long and difficult task so we won't attempt that here.

A box girder is much the same as an I-beam girder except that, obviously, it takes the shape of a box. The typical box girder has two webs and two flanges (illustration #2.) However, in some cases there are more than two webs, creating a multiple chamber box girder.

Other examples of simple girders include pi girders, named for their likeness to the mathematical symbol for pi, and T shaped girders. Since the majority of girder bridges these days are built with box or I-beam girders we will skip the specifics of these rarer cases.

Now that we know the basic physical differences between box girders and I-beam girders, let's look at the advantages and disadvantages of each. An I-beam is very simple to design and build and works very well in most cases. However, if the bridge contains any curves, the beams become subject to twisting forces, also known as torque. The added second web in a box girder adds stability and increases resistance to twisting forces. This makes the box girder the ideal choice for bridges with any significant curve in them.

Box girders, being more stable are also able to span greater distances and are often used for longer spans, where I-beams would not be sufficiently strong or stable. However, the design and fabrication of box girders is more difficult than that of I beams. For example, in order to weld the inside seams of a box girder, a human or welding robot must be able to operate inside the box girder.


2. Arch Bridge

After girders, arches are the second oldest bridge type and a classic structure. Unlike simple girder bridges, arches are well suited to the use of stone. Many ancient and well know examples of stone arches still stand to this day. Arches are good choices for crossing valleys and rivers since the arch doesn't require piers in the center. Arches can be one of the more beautiful bridge types. Possibly the oldest existing arch bridge is the Mycenaean Arkadiko bridge in Greece from about 1300 BC.

3. Cable Stayed

A cable-stayed bridge is a bridge that consists of one or more columns (normally referred to as towers or pylons), with cables supporting the bridge deck. A typical cable stayed bridge is a continuous girder with one or more towers erected above piers in the middle of the span. From these towers, cables stretch down diagonally (usually to both sides) and support the girder.

4. Rigid Frame Bridge

Rigid frame bridges are sometimes also known as Rahmen bridges. In a standard girder bridge, the girder and the piers are separate structures. However, a rigid frame bridge is one in which the piers and girder are one solid structure.


5. Suspension Bridge

Suspension bridge: construction that allows automobiles to travel between two points separated by an obstacle.
Side span: segment between two pylons at the ends of a bridge.
Centre span: segment between two pylons at the centre of a bridge.
Side pylon: tower-like vertical construction situated at the side, usually supporting the cables of a suspension bridge or a cable-stayed bridge.
Foundation of a pylon: very durable lower part of a tower.
Suspender: support cable.
Suspension cable: set of braided wire that supports a bridge.
Pylon: tower-like vertical support that usually supports the cables of a suspension bridge or a cable-stayed bridge.
Stiffening girder: tightener beam.

Friday, December 26, 2008

concrete testing ; Aims of in-situ testing


Three basic categories of concrete testing may be identified.

(i) Control testing is normally carried out by the contractor or concrete producer to indicate adjustments necessary to ensure an acceptable supplied material.

(ii) Compliance testing is performed by, or for, the engineer according to an agreed plan, to judge compliance with the specification.

(iii) Secondary testing is carried out on hardened concrete either in, or extracted from, the structure. This may be required in situations where there is doubt about the reliability of control and compliance results or they are unavailable or inappropriate, as in an old, damaged, or deteriorating structure. All testing which is not planned before construction will be in this category, although long-term monitoring is also included.

Control and compliance tests have traditionally been performed on ‘standard’ hardened specimens made from samples of the same concrete as used in a structure; it is less common to test fresh concrete. There are also instances in which in-situ tests on the hardened concrete may be used for this purpose. This is most common in the pre casting industry for checking the quality of standardized units, and the results can be used to monitor the uniformity of units produced as well as their relationship to some pre-established minimum acceptable value. There is, generally, an increasing awareness amongst engineers that ‘standard’ specimens, although notionally of the same material, may misrepresent the true quality of concrete actually in a structure. This is due to a variety of causes, including non-uniform supply of material and differences of compaction, curing and general workmanship, which may have a significant effect on future durability. As a result, a trend towards in-situ compliance testing, using methods which are either non-destructive or cause only very limited damage, is emerging, particularly in North America and Scandinavia. Such tests are most commonly used as a back-up for conventional testing, although there are notable instances such as the Storebaelt project where they have played a major role (1). They offer the advantage of early warning of suspect strength, as well as the detection of defects such as inadequate cover, high surface permeability, voids, honeycombing or use of incorrect materials which may otherwise be unknown but lead to long-term durability problems. Testing of the integrity of repairs is another important and growing area of application.

The principal usage of in-situ tests is nevertheless as secondary testing, which may be necessary for a wide variety of reasons. These fall into two basic categories.

reference;
(1) Petersen, C.G. and Poulsen, E. Pull-out testing by Lok-test and Capo-test. Dansk Betoninstitut A/S, 1992.

Thursday, December 25, 2008

Drinking water plant and how drinking water is treated

The importance of good drinking water in maintaining human health was recognized early in history. However, it took centuries before people understood that their senses alone were not adequate judges of water quality.

Drinking water is so important for good health. Your body is estimated to be about 60 to 70 percent water. Blood is mostly water, and your muscles, lungs, and brain all contain a lot of water. Your body needs water to regulate body temperature and to provide the means for nutrients to travel to all your organs. Water also transports oxygen to your cells, removes waste, and protects your joints and organs.
The reason for having drinking water treatment is because of the appearance of particles in water. Filtration was established as an effective means of removing particles from water and widely adopted in Europe during the eighteenth century. As so it followed to asia and different parts of the world.

The origin of drinking water to your taps
Our Drinking water comes from the water in lakes or rivers (surface water), or from water that comes from wells (groundwater) and some times the sky (rain water). Many people who live in large cities or towns get their water for drinking from lakes and rivers.

Contaminants that may be found in drinking water


There is no such thing as naturally pure water. People are increasingly concerned about the safety of their drinking water. As improvements in analytical methods allow us to detect impurities at very low concentrations in water, water supplies once considered pure are found to have contaminants. We cannot expect pure water, but we want safe water. The health effects of some contaminants in drinking water are not well understood, but the presence of contaminants does not mean that your health will be harmed.

Drinking water can become contaminated at the original water source, during treatment, or during distribution to the home.
• If your water comes from surface water (river or lake), it can be exposed to acid rain, storm water runoff, pesticide runoff, and industrial waste. This water is cleansed somewhat by exposure to sunlight, aeration, and micro-organisms in the water.
• If your water comes from groundwater (private wells and some public water supplies), it generally takes longer to become contaminated but the natural cleansing process also may take much longer. Groundwater moves slowly and is not exposed to sunlight, aeration, or aerobic (requiring oxygen) micro-organisms. Groundwater can be contaminated by disease-producing pathogens, leachate from landfills and septic systems, careless disposal of hazardous household products, agricultural chemicals, and leaking underground storage tanks.

In general all water contains some impurities
• Erosion of natural rock formations
• Substances discharged from factories
• Discharged from farmlands
• used by consumers in their homes and yards

Drinking water treatment Process

The process flow diagram illustrates a municipal water treatment plant that is used for the removal of taste and odour compounds. Water is pumped from the river into a flotation unit, which is used for the removal of suspended solids such as algae and particulate material. Dissolved air is injected under pressure into the basin through special nozzles. This creates microbubbles which become attached to the suspended solids, causing them to float. The result is a layer of suspended solids on the surface of the water, which is removed using a mechanical skimming technique.

water coagulation & flocculation is used for removal of natural organic matter (NOM) from surface waters.

Ozone is produced on site by passing high tension, high frequency electrical discharges through air in specially designed equipment. Ozone is injected into the water to provide a powerful bactericidal action and to break down the natural humic compounds that are the cause of the taste and odour problem.

Coagulation, flocculation and sedimentation
In traditional water treatment, certain chemicals are added to raw water to remove impurities. While some particles will spontaneously settle out from water on standing (a process called sedimentation), others will not. To cause particles that are slow to settle or are non-settling to settle out more readily, a soluble chemical or mixture of chemicals is added to the water. Such a chemical is called a coagulant and the process is called coagulation.
The coagulant reacts with the particles in the water, forming larger particles called flocs, which settle rapidly.

Flocs can also be effectively removed by passing the water through a filter. The process is controlled so that the coagulant chemicals are removed along with the contaminants.
Coagulation/flocculation processes generally use aluminium sulphate (alum) or ferric chloride as the coagulant.

• Filtration
One of the oldest and simplest processes used to treat water is to pass it through a bed of fine particles, usually sand. This process is called sand filtration. In its simplest form, the water is simply passed through the filter with no other pre-treatment, such as the addition of a coagulant. Usually this type of filter will remove fine suspended solids and also some other particles such as larger microorganisms.

Sand filtration is even more efficient when the water being treated passes through the sand filter very slowly. Over time the sand particles become covered with a thin surface layer of microorganisms. Some might refer to this layer as a slime but water scientists call it a biofilm. Even very small particles stick to this biofilm and are held, while water of greatly improved quality passes out through the filter.

• Disinfection
Disinfection is carried out to kill harmful microorganisms that may be present in the water supply and to prevent microorganisms regrowing in the distribution systems.
Good public health owes a lot to the disinfection of water supplies. Without disinfection, waterborne disease becomes a problem, causing high infant mortality rates and low life expectancy. This remains the situation in some parts of the world.

Key factors considered by a water authority in selecting a disinfection system are:
• Effectiveness in killing a range of microorganisms.
• Potential to form possibly harmful disinfection byproducts.
• Ability of the disinfecting agent to remain effective in the water throughout the distribution system.
• Safety and ease of handling chemicals and equipment.
• Cost effectiveness.

Distribution
Water is distributed after all this process to our taps.

Reference
Introcduction to envirometal engineering, 2nd edition, P.Aarne Vesilind | Susan M. Morgan
http://www.epa.gov/rgytgrnj/kids/drnk_b.htm
http://courseweb.unt.edu/rhondac/spring2006/webpages/Watercyclegraphic1.gif
http://epa.gov/safewater/dwh/contams.html
http://www.bigatoll.com/Industrial.html
http://www.bae.ncsu.edu/programs/extension/publicat/wqwm/he393.html
http://www.waterquality.crc.org.au

Soil Compaction for better construction project


What is soil Compaction?
Soil compaction is when soil particles are pressed together making the air voids minimum as possible.


reasons why we need to compact soil ;
  • Increases load-bearing capacity
  • Prevents soil settlement and frost damage
  • Provides stability
  • Reduces water seepage, swelling and contraction
  • Reduces settling of soil
Machines used for compaction;
  • Smooth wheel Rollers
  • Sheepsfoot Rollers
  • Rubber- tiered Rollers
  • Vibratory Rollers
  • Stumpers
  • Walk-Behind Roller
Smooth wheel Rollers
Smooth wheel Rollers suitable for proof rolling sub grades and for finishing.














Sheepsfoot Rollers
This roller is most effective to compact Clayey soils.














Smooth wheel Rollers
This type have the most advantage because it can compact both soil and clayey soils















what are Cables, Arches, Trusses, Beams, Surface; Membranes, plates and shells


Cables are usually flexible and carry their loads in tension, cables are commonly used to support bridges and building roofs. When we use cables fro these purposes , the cable has an advantage over the beam and the truss, specially for spans that are greater than 46m, because they are always in tension, cables will not become unstable and suddenly collapse, as may happen with beams or trusses.


Arches
achieves its strength in compression, since it has a reverse curvature to that of the cable. The arch must be rigid, however, in order to maintain its shape, and this results in secondary loadings involving shear and moment, which must be considered in its design. Arches are frequently used in bridge structures, dome roofs and for opening in masonry walls.


Truss is a structure comprising one or more triangular units which are constructed with straight slender members whose ends are connected at joints. A plane truss is one where all the members and joints lie within a 2-dimensional plane, while a space truss has members and joints extending into 3 dimensions.

There are two basic types of trusses. The pitched truss or common truss is characterized by its triangular shape. It is most often used for roof construction.

Beams are primarily designed to resist bending moment; however, if they are short and carry large loads, the internal shear force may become quite large and this force may govern their design.

A beam is a structural element that carries load primarily in bending (flexure). Beams generally carry vertical gravitational forces but can also be used to carry horizontal loads (i.e. loads due to an earthquake). The loads carried by a beam are transferred to columns, walls, or girders, which then transfer the force to adjacent structural compression members.

In Light frame construction the joists rest on the beam.

Beams are characterized by their profile (the shape of their cross-section), their length, and their material. In contemporary construction, beams are typically made of steel, reinforced concrete, or wood. One of the most common types of steel beam is the I-beam or wide-flange beam (also known as a "universal beam" or, for stouter sections, a "universal column"). This is commonly used in steel-frame buildings and bridges. Other common beam profiles are the C-channel, the hollow structural section beam, the pipe, and the angle.

Surface structure; A surface structure is made from a material having a very small thickness compared to its other dimensions.


Membranes; The most commonly specified sheet materials are self-adhering rubberized asphalt membranes. These 60-mil-thick membranes are composed of rubberized asphalt laminated to a waterproof polyethylene film. The asphalt side is incredibly sticky but is covered by a release paper, which you remove during application.


Plates; A surface plate is a solid, flat plate used as the main horizontal reference plane (datum) for precision inspection, marking out (layout), and tooling setup.

Surface plates must be calibrated on a regular basis to ensure that chipping, warping or wear has not occurred. A common problem with surface plates are specific areas or a section that is frequently used by another tool (such as a height gage) that will cause wear to a specific point resulting in an uneven surface and reduced overall accuracy to the plate. Tools and workpieces may also cause damage when dropped on the surface plate or when material chips have not been removed. This will result in erroneous measurements and can only be fixed by resurfacing the plate.


Shells; Surface structure may also be made of rigid material such as reinforced concrete. As such they may be shaped as folded plates, cylinders, or hyperbolic paraboloids, and are referred to as thin plates or shells.

Reference;

• Structural analysis / R.C Hibbeler / 6th edition
• www.maplevalleytruss.com
• www.glenbrook.k12.il.us
• www.concretenetwork.com/

what is Consolidation - Consolidation of soil for soil investigation


Consolidation is a process by which soils decrease in volume. It occurs when stress is applied to a soil that causes the soil particles to pack together more tightly, therefore reducing its bulk volume. When this occurs in a soil that is saturated with water, water will be squeezed out of the soil. The magnitude of consolidation can be predicted by many different methods. In the Classical Method, developed by Karl von Terzaghi, soils are tested with an oedometer test to determine their compression index. This can be used to predict the amount of consolidation.

When stress is removed from a consolidated soil, the soil will rebound, regaining some of the volume it had lost in the consolidation process. If the stress is reapplied, the soil will consolidate again along a recompression curve, defined by the recompression index. The soil which had its load removed is considered to be overconsolidated. This is the case for soils which have previously had glaciers on them. The highest stress that it has been subjected to is termed the preconsolidation stress. The over consolidation ratio or OCR is defined as the highest stress experienced divided by the current stress. A soil which is currently experiencing its highest stress is said to be normally consolidated and to have an OCR of one. A soil could be considered underconsolidated immediately after a new load is applied but before the excess pore water pressure has had time to dissipate.

How many days is it for curing?


The recommended minimum curing time is 28 days, but most contractors typically wait only 7 to 14 days just to save time and money, but depending on the size of the concrete its very important to cure for 28days cos it will gain full or almost full strength.


pouring water (curing) of concrete after it been poured

What is the name given for the procedure of pouring water on concrete?
its called curing, a processed where concrete is left moist due to the exothermic reaction that takes place which may give cracks on the concrete.

Why Cure?
The major objective of concrete curing applications is to prevent the rapid loss of water from the concrete. As concrete loses water due to evaporation from the top surface, differential drying shrinkage can occur. This is a major contributor to shrinkage cracking. The application of curing methods reduces the loss of water from the surface of the concrete. It also permits more complete hydration of cement in the concrete itself. Minimizing evaporation also helps control the temperature of the concrete during its early-age stage.

Curing operations should begin after the water sheen disappears from the surface, and after any texturing operations have been completed. In the case of a curing compound, the membrane formed by the compound should not be disturbed after it is placed.

Rapid Drying Conditions
In rapid drying conditions, a light water fog may be necessary to maintain moist surface conditions prior to the application of curing methods. Light water fogging can be accomplished during a short period of time when the concrete surface begins to dry but before the curing operations can begin, such as prior to texturing operations have been completed.

Use of Ambient Weather Condition Information
Ambient weather conditions, such as wind speed, relative humidity, and air temperature can interact with the temperature of the concrete to cause excessive water evaporation from the concrete surface. Since different curing methods provide different levels of protection, knowing the amount of protection required is important in determining the method to use. In order to know the required level of protection, the ambient conditions and concrete temperature must be known. A portable weather station that records the ambient conditions and automatically predicts evaporative water from the concrete surface can be an invaluable tool for controlling water loss from the concrete surface. Such a tool can also warn in advance when conditions approach predefined limits of evaporation.
Curing Methods
Various concrete curing methods are available, and each provides different levels of protection. A single coat of liquid curing compound generally provides the least protection, but additional coats can improve its performance. Polyethylene sheets, cotton mats and wet burlap provide additional protection.

Liquid Curing Compound

White-pigmented, liquid membrane curing compound is used most often due to its low cost and ease of application. It does not require great amounts of labor, nor does it expensive, bulky material, such as cotton mats. It's disadvantages are that it provides the least amount of protection, and the membrane can be ruptured inadvertently.

The liquid curing compound should be white, to avoid excess heat absorption from the sun (Figure 4.1). Also, the white color enables construction workers to check more easily for coverage uniformity and gaps in the coverage. The liquid compound must be constantly agitated during application to ensure that the mixture is applied correctly. The curing compound spraying operation should be shielded from the wind throughout the process.

The compound must cover all exposed surfaces, including the sides of the pavement slab. The compound should not, however, be applied into any joints in the pavement. For ultra-thin whitetopping, curing compound should be applied at twice the normal application rate, due to its extra sensitivity to drying shrinkage.


Figure 4.1 - White-Pigmented, Liquid Membrane Curing Compound.

Plastic or Waterproof Paper

Plastic, or polyethylene, sheeting provides good protection to the concrete from water evaporation from the surface (Figure 4.2). It requires more labor than liquid curing compound, yet it is not as bulky as cotton mats or burlap. Waterproof paper may also be used in the same manner described here for plastic sheeting, but is not as common.

The plastic sheeting must not have any rips or tears through which water can escape. The sheets should overlap to provide full coverage for the concrete surface. Just as with curing compound, the sheeting should cover all exposed concrete surfaces, including the edges of the pavement slab. Active methods must be used to hold the sheeting in place. Do not assume that they will remain in place of their own accord.

Figure 4.2 - Polyethylene Sheeting Used as a Curing Method.

Cotton Mats or Burlap

Cotton mats represent a great increase in evaporation protection, both by providing additional moisture if needed, and by protecting the concrete from ambient conditions such as low humidity, high wind speeds, and high temperatures. Cotton mats and wet burlap must be kept continually moist. When the mats get dry they can become more harmful than without them due to "wicking" action which draws moisture from the concrete into the mat.

FAULTS (EARTHQUAKE) IMPACT TOWARDS BUILDING FOUNDATION

A fault is a fracture in the crust of the earth along which rocks on one side have moved relative to those on the other side. Most faults are the result of repeated displacements over a long period of time.

TYPES OF FAULT;
1. Dip Slip Faults
The movement is up or down parallel to the dip of inclined faults surface



2. Strike slip fault

A fault where movement(or slip) is predominantly horizontal and therefore parallel to the strike of the fault
3. Oblique-Slip Fault
A fault where movement of both strike-slip and dip-slip components

IMPACTS OF FAULT
Earthquake-induced ground shaking can pose threats to people and structures (specially foundation of the building which leads to collapse the buildings) even at distant locations from the fault on which the earthquake event is occurring. Ground shaking at a particular location depends on the earthquake magnitude (e.g., a measure of total energy released by fault rupture); epicenter distance (e.g., the distance from the center of the fault rupture to the location of interest); and, subsurface conditions of the geologic and soil units at the location of interest.
EFFECTS OF EARTHQUAKE TOWARDS BUILDING FOUNDATION

Ground motion

  • Is the trembling and shaking of the land
  • can cause building to vibrate
  • can be large enough to topple large structures such as bridges and office and apartment buildings
Landslide
  • can be triggered by shaking of the ground
  • can cause extensive damage
Liquefaction
  • occurs when a water saturated soil or sediments turns from a solid to a liquid as a result of earthquake shaking
  • causes building to sink and underground tanks to float as once-solid segments flow like water.
LOCATING AND MONITORING
Earthquakes can be monitored using the instrument that could accurately record seismic waves. The instruments measure the ground motion and can be use to find the location, depth and size of an earthquake.
- seismometer
- seismograph
- seismogram

MINIMIZE BUILDING FAILURE
  • construction must meet the building codes(strictly enforced in earthquake-prone areas)
  • control the location of the buildings.(building built on soft sediment are damaged more than building on hard rock)
  • firmly attach house to the foundation with anchor bolts.
  • Repair any deep cracks in foundations

Importance of a geologist in construction project


An engineering Geologist is an individual who applies geologic data, principles, and interpretation so that geologic factors affecting planning, designing, construction and maintenance of civil engineering works and properly recognized and utilized.

They also advise on procedures required for such developments and the suitability of appropriate construction materials. Majority of subsurface exploration for civil engineering project is performed by engineering geologist.

In a construction project an engineering geologist needs are a lot, and plays a very major role in a project, they can predict or forecast of future events and conditions that my develop, they can recommend ways to handling and treating various earth material and process, even provide criteria for excavation and also they can do inspection during construction to confirm conditions of geological environment patterns.

Typical Work Activities Typical activities cover three key areas:

Office-based activities, including:

• consulting geological maps and aerial photographs to advise on site selection;
• undertaking desk studies and assessing sources of site information prior to field investigations;
• assisting with the design of built structures, using specialised computer software or calculations;
• assessing findings for construction engineers;
• collating data and producing reports;
• undertaking additional project management duties;
• overseeing the progress of specific contracts.

Site-based activities, including:

• planning detailed field investigations by drilling and analysing samples of deposits/bedrock;
• supervising site/ground investigations;
• maintaining technical control of a site;
• making visits to new project sites.

Liaising with staff and clients, including:

• advising on and testing a range of construction materials, for example sand, gravel, bricks and clay;
• making recommendations on the proposed use of a site;
• advising on problems such as subsidence;
• providing information and advice to clients as required;
• ensuring that a site investigation progresses to budget;
• managing staff, including other engineering geologists, geotechnical engineers, consultants and contractors;
• attending professional conferences and representing the company or organisation at other events.

When building a tunnel, Prior to tunnel inspections, a general site reconnaissance should be performed by a geologist to observe the existing ground surface

conditions and geology in the vicinity of the tunnel portals and ventilation building located on the side of the tunnels. The purpose of the site reconnaissance is to evaluate the existing surface conditions in an attempt to identify possible causes of the groundwater infiltration experienced within the tunnel structures.

Reference:

- Geotechnical and foundation Engineering Design and Construction, Robert W.Day, New York.

- Journal of Geotechnical and Geoenvironment Engineering, November 2006. volume 132, number 11, American society of civil engineers.

- http://www.prospects.ac.uk/cms/ ShowPage/Home_page/Explore_ types_of_jobs /Types_of_Job/p!eipaL?state=showocc&pageno=1&idno=111
- OCCUPATIONAL PROFILE, Engineering geologist
- 57th ANNUAL HIGHWAY GEOLOGY SYMPOSIUM HOSTED BY :The Colorado Geological Survey, The Colorado Department of Transportation.

Engineering Drawing and inside of Haram kaba




Air-conditioning Systems for buildings - how ari condition works

Air conditioning is a process of controlling and treatment of all air content for space or for closed space.

In the broadest sense air conditioning can refer to any form of cooling, heating, ventilation or disinfection that modifies the condition of air, typically for thermal comfort.
Engineers define the process of air-conditioning as one in which a system of mechanical components-usually including a compressor, a fan, condenser coil, evaporator coil and a chemical refrigerant - extracts heat from indoor air and transfers it to outside, leaving the cooled indoor air to be re-circulated.

The Cooling Cycle Works as Follows

-The compressor compresses cool Freon gas, causing it to become hot, high-pressure Freon gas.
-From the compressor, this hot and high pressure gas passes into the condenser where this gas runs through a set of coils so it can dissipate its heat, and it gradually condenses inside the condenser into a liquid.
-The high pressure Freon liquid runs through an expansion valve, the expansion valve acts to lower the pressure of the liquid thereby reducing the boiling point temperature of the liquid.
-The low pressure liquid then passes through the evaporator and in the process it evaporates to become cold, low-pressure Freon gas . This cold gas runs through a set of coils that allow the gas to absorb heat and cool down the air inside the building.

what are the INSTRUMENTS USED FOR TACHEOMETRY

Theodolite






Is an instrument for measuring both horizontal and vertical angles



Prism for leveling



The prism is used to return the transmitted beam to the instrument to allow a distance to be determined by time of flight or phase comparison.



Tripod

Tripod is an adjustable three legged stand, as for supporting theodolite, prism etc.




Measuring tape

It is used to measure the distance between two stations.




Staff

A leveling staff is the equivalent of a long ruler and it enables distances to be measured vertically from the horizontal plane established by a level to points where heights are required.



Staff bubble

The Staff bubble is attached to the level staff while taking level readings. The staff bubble should be centered in the circle as shown in the picture here. A centered staff bubble indicates that the staff is being held vertical and accurate staff readings can be made at this time.

What are the Failure Of Engineering Material


Various theories of failure have been proposed, their purpose being to establish, from the behavior of a material subjected to simple tension or compression tests, the point at which failure will occur under any type of combined loading.

Structural Failure; many materials such as brick, glass, concreate and some metals are brittle, generally implying that when the limit of elasticity is reached they are close to disintegration or failure. Acceptable

Working stress for such material are obtained by loading them to destruction and then applying a suitable safty factor, this factor of safety should take into account that failure may be sudden or dramatic since plastic flow in them is not normally possible.

Often, a deficiency in engineering ethics is found to be one of the root causes of an engineering failure. An engineer, as a professional, has a responsibility to their client or employer, to their profession, and to the general public, to perform their duties in as conscientious a manner as possible. Usually this entails far more than just acting within the bounds of law. An ethical engineer is one who avoids conflicts of interest, does not attempt to misrepresent their knowledge so as to accept jobs outside their area of expertise, acts in the best interests of society and the environment, fulfills the terms of their contracts or agreements in a thorough and professional manner, and promotes the education of young engineers within their field.

Structural failure refers to loss of the load-carying capacity of a component or member within the structure or of the structure itself. Structural failure is initiated when the material is stressed to its strength limit, thus causing fracture or excessive deformations. The ultimate failure strength of the material, component or system is its maximum load-bearing capacity. When this limit is reached, damage to the material has been done, and its load-bearing capacity is reduced significantly and quickly. In a well-designed system, a localized failure should not cause immediate or even progressive collapse of the entire structure. Ultimate failure strength is one of the limit states that must be accounted for in civil engineering.

In conection with tests to failure of materials and of structural parts or members it is important to observe and record the type of failure and the characteristics of the fracture. Such observation shoiuld include not only the phenomena associated with final rupture but also all evidences of change of condition such as yield, slip, scaling, necking down, localized crack development, etc..

Two modes of fracture may occur in a metallic or crystalline material- a separation fracture as a shear or sliding fracture.

It is based on the assumption that failure occurs when the maximum principle. Sharp on an element reaches a limiting value.

Primary Causes of Engineering Disasters

The primary causes of engineering disasters are usually considered to be;

* human factors (including both 'ethical' failure and accidents)
* design flaws (many of which are also the result of unethical practices)
* materials failures
* extreme conditions or environments, and, most commonly and importantly
* combinations of these reasons

A recent study conducted at the Swiss federal Institute of technology in Zurich analyzed 800 cases of structural failure in which 504 people were killed, 592 people injured, and millions of dollars of damage incurred.

Almost any component that fails in service does so because it wore out, it corroded, or it broke. Some components surfer two or more modes of deterioration.

Many years of failure analysis work have shown that most service failure did not occur because of bad material. More often than not, some common-sense design factor was ignored of there was an error in fabrication.


Common problems and preventive measures

Underground piping- check soil conditions; use cathodic protection, plastic or bitumanstic coated pipe, or polyethylene wrapping if the soil shows conductivity. This type of soil produces abnormal potential for corrosion of ferrous pipes.

Under deposit attack- Design equipment to be cleanable. If chemical handling equipment is difficult to clean thoroughly, chances are it will not be cleaned. When chemicals are allowed to accumulate on surfaces, severe local corrosion can occur the deposit.

Water coolant system- wherever possible use a recirculating system and add proper corrosion inhibitors to the water.

Oil sumps- use vapor space inhibitors in the oil to prevent corrosion in the tank space above the oil level.

Corrosion in storage- use vapor space inhibitors inert gas shielding, desiccants, hermetically sealed containers, or moisture- displacing oils on metal surface that may be stored for long periods of time before use. Keep storage container full whenever possible.

Coating- when using metallic coating for corrosion protection, try to use a metal that is anodic to the substrate so that pitting will not occur in pinholes and scratches. Nonmetal coating should be checked for pinholes and scratches.

Stress corrosion cracking- the most common causes of Stress corrosion cracking is chlorides in contact with austenitic stainless steels. Stress corrosion cracking will not occur if welds are stress relieved or if operating stress levels are kept low by design.

Environmentally assisted cracking- plastic failure studies shows that 30% of plastic failure is due to environmental stress cracking. Some corrosion engineers believe that all plastic will eventually develop environmental stress cracks.

Intergranular corrosion: use low-carbon or stabilized grades of austenitic stainless steel when welding processes can cause sensitization; check welded tubing and pipe for sensitization (in manufacture) before use (ASTM A 708). Avoiding use of stainless steels sensitizing range from 800 to 1650 F.

High temperature Oxidation: avoid the use of metals at temperatures in excess of the maximum use temperature in air. Temperature above the maximum use temperature cause excessive scaling.

Welding- Avoid incomplete penetration welds. Unfused part of the joint can become a concentration cell. Invert gas backing or pickling after welding should be used to prevent weld-contamination corrosion of s.s.


Some concepts;

- premature wear failures can be minimized by designing parts to resist specific modes of wear.

- corrosion failure can be minimized by using materials with documented ability to withstand a particular environment.

- Mechanical failure can be minimized by calculating operating stresses cad keeping these stress rupture of the materials involved. It is also imperative to prevent the introduction of geometric stress concentrating should also be used to ensure that flaws from fabrication or service conditions do not exist.

- Nothing has to fail. Roads paved by the Romans 2000 years ago are still in use; many modern highways in the northeast united stated last less than 10 years. The difference is ,very simply, proper design, and Quality workmanship.



Reference:

-Material in construction, G.D Taylor.
-Engineering Material properties and selection, 7th edition, Kenneth G. budinski, micheal K. budinski.
-Strength of materials, 2nd edition.
-The testing and inspection of Engineering material, Harmer E. Davis, Consulting Edition.
-http://www.matscieng.sunysb.edu/disaster/

what are ceramic material and its uses ?


When we just hear the term Ceramic, the term ceramic comes to mind as dish, porcelain figures, and the like. A typical dictionary definition of ceramic is “ the art of work of making pottery, like, porcelain, etc..

Original definition of ceramic: compound composed of metallic and non metallic elements with strong ion, ionic or covalent bond between atoms.

The most significant property is common to ceramic as well as to cemented carbide, glasses, and carbon-graphite is brittleness. Most of ceramic materials are brittle: concrete blocks , ceramic tile, carbide tools, ceramic wear pants, glasses, pottery, computer chips, bricks.


Technical Ceramics can also be classified into three distinct material :

* Oxides: Alumina, zirconia

* Non-oxides: Carbides, borides, nitrides, silicides

* Composites: Particulate reinforced, combinations of oxides and non-oxides.

Each one of these classes can develop unique material properties. Below is some details about categories.

Oxide ceramics: Oxidation resistant, chemically inert, electrically insulating, generally low thermal conductivity, slightly complex manufacturing and low cost for alumina, more complex manufacturing and higher cost for zirconia.

Non – oxide ceramics: Low oxidation resistance, extreme hardness, chemically inert, high thermal conductivity, and electrically conducting, difficult energy dependent manufacturing and high cost.

Ceramic – based composites: Toughness, low and high oxidation resistance (type related), variable thermal and electrical conductivity, complex manufacturing processes, high cost.

The most used material of any type of structure application are ceramic type of material, concrete, to glasses.

In the early 1990s’,many material research laboratories in industry had programmes trying to develop application for which ceramics will be cost effective and provide a service advantage over other materials, only few ceramics emerged as contenders for industrial applications; Aluminium oxides, silicon carbides, also cemeted carbides and in some cases the machinable ceramic(glass-bonded micas) are candidates.

Ceramic Industry manufacture of useful and ornamental articles from clay by shaping and hardening it in high temperature. The industry is basically a development of indigenous pottery works. Broadly, ceramics denote the manufacture of any product made from a non-metallic mineral hardened at high temperatures. Industrial ceramics comprise all industrially used solid materials that are neither metallic nor organic. Major ceramic products include glass, earthenware, porcelain, and white-ware, porcelain enamels, brick tiles and terracotta, refractories, cement, lime and gypsum and certain abrasives.

In a Industry ceramic materials play a very large roll, from walls to electrical ware, ceramic is used world wide, industrial uses of ceramic are;

Bricks (mostly aluminium silicates), used for construction, building walls as partitions as protections and many more used in a ceramic brick.

Earthenware, which is often made from clay, quartz and feldspar.

Ferrite (Fe3O4), which is ferrimagnetic and is used in the core of electrical transformers and magnetic core memory.

Zirconia, which in pure form undergoes many phase changes between room temperature and practical sintering temperatures, can be chemically "stabilized" in several different forms. Its high oxygen ion conductivity recommends it for use in fuel cells. In another variant, metastable structures can impart transformation toughening for mechanical applications; most ceramic knife blades are made of this material.

Clay products of all kinds can be used for interior finishing, ceramic wall tile in various sizes and shapes is used in kitchens, bathrooms, wash rooms, labouratires, for a feature wall, or as a dadu or wainstoria with another material covering the upper part of the wall.

In the early 1980s, Toyota researched production of an adiabatic ceramic engine which can run at a temperature of over 6000 °F (3300 °C). Ceramic engines do not require a cooling system and hence allow a major weight reduction and therefore greater fuel efficiency. Fuel efficiency of the engine is also higher at high temperature. In a conventional metallic engine, much of the energy released from the fuel must be dissipated as waste heat in order to prevent a meltdown of the metallic parts.

Recently, there have been advances in ceramics which include bio-ceramics, such as dental implants and synthetic bones. Hydroxyapatite, the natural mineral component of bone, has been made synthetically from a number of biological and chemical sources and can be formed into ceramic materials. Orthopedic implants made from these materials bond readily to bone and other tissues in the body without rejection or inflammatory reactions. Because of this, they are of great interest for gene delivery and tissue engineering scaffolds. Most Hydroxyapatite ceramics are very porous and lack mechanical strength and are used to coat metal orthopedic devices to aid in forming a bond to bone or as bone fillers. They are also used as fillers for orthopedic plastic screws to aid in reducing the inflammation and increase absorption of these plastic materials. Work is being done to make strong-fully dense nano crystalline Hydroxapatite ceramic materials for orthopedic weight bearing devices, replacing foreign metal and plastic orthopedic materials with a synthetic natural bone mineral. Ultimately these ceramic materials may be used as bone replacements or with the incorporation of protein collagens, synthetic bones.

Until the mid 1980s’ the electroic industy multichip substance needs were normally met by ceramic based hybrid intergrated circuits (HICs) HICs were the first widely used mem technology, whose biggest strength lays in its extensive passive component capability.

In electronic circuits, last packing processes step is package sealing. Ceramic packages use two basic process: glass and solder sealing. Welding is used in very high reliability applications typically with metals packages. There are various ceramic packages construction and sealing techniques. Glasses may also be used to attach the package lid to the seal ring solder attachment of metal hide to a moralized seal ring is widely used in military applications.

In paint industry ceramic as a surface coating offer high coating offer high hardness, resistance to abrasion and corrosion protection as well as high temperature properties considerably superior to those of there materials. Their main disadvantages are their liability to crack under conditions of mechanical and thermal shock and their cost.

Reference:

-Engineering material, 5th edition, Kenneth G. budinski.
-Material of construction,2nd edition, R.C smith.
-Ceramic Fabrication Technology; Roy Rice
-Building services materials hand book, E & F.N spon
-Materail scince & technology,vol16,R.W cahn,p.haasan, e.j kraner.

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