Advantages and Applications of Post-Tensioning

There are post-tensioning applications in almost all facets of construction. In building construction, post-tensioning allows longer clear spans, thinner slabs, fewer beams and more slender, dramatic elements. Thinner slabs mean less concrete is required. In addition, it means a lower overall building height for the same floor-to-floor height. Post-tensioning can thus allow a significant reduction in building weight versus a conventional concrete building with the same number of floors. This reduces the foundation load and can be a major advantage in seismic areas.

A lower building height can also translate to considerable savings in mechanical systems and façade costs. Another advantage of post-tensioning is that beams and slabs can be continuous, i.e. a single beam can run continuously from one end of the building to the other. Structurally, this is much more efficient than having a beam that just goes from one column to the next.

Post-tensioning is the system of choice for parking structures since it allows a high degree of flexibility in the column layout, span lengths and ramp configurations. Post-tensioned parking garages can be either stand-alone structures or one or more floors in an office or residential building. In areas where there are expansive clays or soils with low bearing capacity, post-tensioned slabs-on-ground and mat foundations reduce problems with cracking and differential settlement.

Post-tensioning allows bridges to be built to very demanding geometry requirements, including complex curves, variable superelevation and significant grade changes. Post-tensioning also allows extremely long span bridges to be constructed without the use of temporary intermediate supports. This minimizes the impact on the environment and avoids disruption to water or road traffic below. In stadiums, post-tensioning allows long clear spans and very creative architecture. Post-tensioned rock and soil anchors are used in tunneling and slope stabilization and as tie-backs for excavations. Post-tensioning can also be used to produce virtually crack-free concrete for water-tanks.

Structural engineering

Structural engineering is a field of engineering dealing with the analysis and design of structures that support or resist loads economically. Structural engineering is usually considered a specialty within civil engineering, but it can also be studied in its own right.

Structural engineers are most commonly involved in the design of buildings and large nonbuilding structures but they can also be involved in the design of machinery, medical equipment, vehicles or any item where structural integrity affects the item’s function or safety. Structural engineers must ensure their designs satisfy given design criteria, predicated on safety (e.g. structures must not collapse without due warning) or serviceability and performance (e.g. building sway must not cause discomfort to the occupants).

Structural engineering theory is based upon physical laws and empirical knowledge of the structural performance of different geometries and materials. Structural engineering design utilises a relatively small number of basic structural elements to build up structural systems that can be very complex. Structural engineers are responsible for making creative and efficient use of funds, structural elements and materials to achieve these goals.

Structural engineering dates back to at least 2700 BC when the step pyramid for Pharaoh Djoser was built by Imhotep, the first engineer in history known by name. Pyramids were the most common major structures built by ancient civilizations because the structural form of a pyramid is inherently stable and can be almost infinitely scaled (as opposed to most other structural forms, which cannot be linearly increased in size in proportion to increased loads).

Throughout ancient and medieval history most architectural design and construction was carried out by artisans, such as stone masons and carpenters, rising to the role of master builder. No theory of structures existed, and understanding of how structures stood up was extremely limited, and based almost entirely on empirical evidence of ‘what had worked before’. Knowledge was retained by guilds and seldom supplanted by advances. Structures were repetitive, and increases in scale were incremental.

No record exists of the first calculations of the strength of structural members or the behaviour of structural material, but the profession of structural engineer only really took shape with the industrial revolution and the re-invention of concrete (see History of concrete). The physical sciences underlying structural engineering began to be understood in the Renaissance and have been developing ever since.

Prefabricated construction method

Prefabricated construction is a building process in which elements or modules of the structure are prefabricated at plants, then transported to the construction site for installation. Using this method can reduce  the time of building, also saving construction cost. Prefabricated construction is now widely applied for new houses or other building structures like bridge, tunnels,  culverts, water supply system…

The benefits of prefabricated construction method is from the  fabrication of standard components on factory floor. This  production is less time consumption compared to actual condition of construction process. The prefabricated elements are transported to the site for installing process. At the site, the modules are unloaded, moved into position with the support of heavy cranes, and assembled to form a designed building.

Together with the fast assembly, prefabricated construction also saves a lot of money on the construction project. By using standard patterns, the building materials are saved at the manufacturing factories. This help to reduce the waste in formwork and other materials that can occur during traditional building procedures.

Another considerable  profit using prefabricated construction method is the energy efficiency. Because the prefab elements of a panelized home are precut, they fit snugly together, making for a tighter edifice. This means less effort for heating and cooling, resulted  in lower energy bills.

The rapid development of prefabricated houses has led to the increasing of construction templates that homeowners have more choice for designs of their houses. By combining these templates, it is possible to design the layout of the house, specify the dimensions of each room, and build a home that is exactly to the specification of the owners. There are also complex building plans for prefabricated construction that can be adjusted slightly and still have the benefit of using materials of standard lengths, widths, and textures.

Prefabricated houses are not the only type of construction structures that can be produced using prefabrication construction method. As mentioned above, this method is widely used in many types of constructions like bridges, culverts or even swimming pools.

Tests for Surface cracking in concrete structures

Problem of concrete cracking

The wing wall to a highway bridge abutment shows random surface cracks and spalling several years after construction.

Aims of testing

The principal aim will be identification of the cause of deterioration followed by an assessment of present and future serviceability. Appointment of blame may follow.

Proposals

Visual inspection of crack patterns, and their development with time, may permit preliminary classification of cause as (a) structural actions, (b) shrinkage, or (c)material deterioration. This may be followed by strength assessment as in A2 if structural actions are suspected, or chemical/petrographic testing if material deterioration is likely. Cores may conveniently be used to provide suitable samples and should be taken from the areas most seriously affected. Chemical testing to detect chlorides or sulfates will be selected according to the crack pattern whilst microscopic examination can check for frost action, alkali/aggregate reaction and entrained air content.
Serviceability will be determined on the basis of the extent of deterioration and the ability to prevent worsening of the situation.

Interpretation of testing results

Shrinkage cracks are likely to occur at an early age and follow a recognizable pattern, as do cracks due to structural actions. Material deterioration is therefore indicated in this case, and may be due to chemical attack from internal or external sources or due to frost action. Chloride attack is unlikely since the cracks do not follow the pattern of reinforcement, thus initially test for sulfate and cement content. If the results ofthese tests indicate acceptable levels, petrographic examination will be necessary to attempt to identify aggregate/ alkali attack or frost action. If frost action is indicated, micro-metric examination will yield an estimate of the entrained air content for comparison with the specified value.

Expansion and alkali-immersion tests on cores may be required if alkali/aggregate reaction is found. If future deterioration can be prevented by protection of the concrete from the source of attack, this should be implemented after such cutting out and making good as may be necessary. If the source of deterioration is internal and not of a localized nature it may prove necessary to replace the member once it reaches a condition of being unfit for use.

Chemical testing to harderned concrete and allied techniques

Chemical testing of hardened concrete is mainly limited to the identification of the causes of deterioration, such as sulphates or chlorides, or to specification compliance, involving cement content, aggregate/cement ratio or alkali content determination. Water/cement ratio, and hence strength, is difficult to assess to any worthwhile degree of accuracy, and direct chemical methods are of limited value in this respect. Some chemical tests are expensive, and will often only be used in cases of uncertainty, or in resolving disputes, rather than as a means of quality control of concrete.

Specialist laboratory facilities are required for most forms of chemical testing. Basic procedures for the principal tests are outlined below, and emphasis has been placed on the interpretation and reliability of results. Techniques and procedures are generally complex, and extreme care must be taken both during sampling and testing if accuracies are to be achieved which are of practical value. One of the major problems of basic chemical testing is the lack of a suitable solvent which will dissolve hardened cement without affecting the aggregates, and if possiblesamples of the aggregates and cement should also be available for testing. Other instrumental techniques, such as differential thermal analysis, requires expensive and complex equipment together with a high degree of skill and experience, but growing in usage. The range of techniques available to the cement chemist is wide, and many are of such a highly specialized nature that they are outside of the scope of this chapter. Attention has therefore been concentrated on those methods which are most commonly used for in-situ investigations, whilst the more important of the other techniques are indicated together with their most commonly used applications.

ASTM standards are available for commonly used chemical tests, but BS 1881: Part 124 (302) provides more comprehensive guidance and procedural details for many tests. These include cement content, aggregate content and grading, aggregate type, cement type, original water content and bulk density, as well as chloride, sulphate and alkali contents. These procedures apply to calcareous cements, and to natural or inorganic artificial aggregates. Additional background information and details are given by Figg and Bowden , and a comprehensive Concrete Society Technical Report offers further detailed guidance. It is particularly important that an engineer requiring chemical analysis of concrete should be aware of the limitations of the methods available, and in particular the effect that some materials’ properties may have on the accuracy of analysis. The most likely causes of lack of accuracy are:

(i) Inadequate sampling or testing
(ii) Aggregates contributing to the analysis
(iii) Cements with unusual and unknown composition
(iv) Changes to the concrete from chemical attack or similar cause
(v) Presence of other materials.

It is also essential that an experienced concrete analyst should be employed. He must be given a clear brief of the information required from testing, and all relevant data concerning the constituents and history of the concrete must be made available.

Time Estimates and Planning in Project Management

Accurate time estimation is a skill essential for good project management. It is important to get time estimates right for two main reasons:

1. Time estimates drive the setting of deadlines for delivery and planning of projects, and hence will impact on other peoples assessment of your reliability and competence as a project manager.
2. Time estimates often determine the pricing of contracts and hence the profitability of the contract/project in commercial terms.

Often people underestimate the amount of time needed to implement projects. This is true particularly when the project manager is not familiar with the task to be carried out. Unexpected events or unscheduled high priority work may not be taken into account. Project managers also often simply fail to allow for the full complexity or potential errors and stuff ups, involved with a project. The 2004-2006 Wembley Stadium project in London is often used as an example, although there are countless others of less profile.

Time estimates are important as inputs into other techniques used to organise and structure all projects. Using good time estimation techniques may reduce large projects to a series of smaller projects.

Step 1 – Understand the Project Outcome

First you need to fully understand what it is you need to achieve. (Refer to my article; Project Management – Begin with the end in mind). Review the project/task in detail so that there are no “unknowns.” Some difficult-to-understand, tricky problems that take the greatest amount of time to solve. The best way to review the job is to just list all component tasks in full detail.

Step 2 – Estimate Time

When you have a detailed list of all the tasks that you must achieve to complete the project then you can begin to estimate how long each will take.

Make sure that you also allow time for project management administration, detailed project, liaison with outside bodies resources and authorities, meetings, quality assurance developing supporting documentation or procedures necessary, and training.

Also make sure that you have allowed time for:

* Other high urgency tasks to be carried out which will have priority over this one.
* Accidents and emergencies.
* Internal/external meetings.
* Holidays and sickness in key staff/stakeholders.
* Contact with other customers, suppliers and contractors.
* Breakdowns in equipment.
* Missed deliveries by suppliers.
* Interruptions by customers, suppliers, contractors, family, pets, co-workers etc.
* Others priorities and schedules e.g. local government planning processes.
* Quality control rejections etc.
* Unanticipated events (e.g. renovating the bathroom finding white-ants/termites in the walls).

These factors may significantly lengthen the time and cost needed to complete a project.

If the accuracy of time estimates is critical, you will find it effective to develop a systematic approach to including these factors. If possible, base this on past experience. In the absence of your own past experience, ask someone who has already done the task or project to advise what can go wrong; what you need to plan for; and how long each task took previously.

You can lose a great deal of credibility, and money, by underestimating the length of time needed to implement a project. If you underestimate time, not only do you miss deadlines, you can also put other people under unnecessary stress.

Step 3 – Plan for it Going Wrong

Finally, allow time for all the expected and unexpected disruptions and delays to work that will inevitably happen. Sickness, strikes, materials not available, poor quality work, bureaucratic bungling etc

Gantt Chart for Plan and Schedule Projects

Gantt charts are useful tools for analysing, planning and controlling complex multi-stage projects. It very helpful for a manager for his project management.

Gantt charts can:

* Assist in identifying the tasks and sub-tasks to be undertaken
* Help you lay out the tasks that need to be completed
* Assist in scheduling when these tasks will be carried out and in what order
* Assist in planning resources needed to complete the project
* Assist in working out the critical path for a project where it needs to be completed by a particular date

When a complex or multi-task project is under way, Gantt charts assist in monitoring whether the project is on schedule, or not. If not, the Gantt chart allows you to easily identify what actions need to be taken in order to put the project back onto schedule.

An essential concept behind project planning is that some activities depend upon other activities being completed first. For example, it is not a good idea to start building the walls in an office block before you have laid the foundations; neither is it a good idea to put the cake mix into the tin without greasing the tin first.

These are dependent activities which need to be completed in a sequence, with each stage being more-or-less completed before the next stage can begin. We can call such dependent activities ‘sequential’.

Non-sequential activities are not dependent on the completion of any other tasks. These activities may be done at any time before or after a particular stage in the project is reached. These activities are called are non-dependent or “parallel” tasks.

To create a Gantt chart:

Step 1. List all Activities/Tasks in the Plan

For each task, show the earliest possible start date, how long you estimate the length of time it should take, and whether it is parallel or sequential. If tasks are sequential, show which stages they depend on.

Head up a sheet of graph paper (using pencil and a ruler) with the days, weeks or months through to task completion on the top x-axis. The y-axis can be used to itemise each task in its order. You may want to use a spreadsheet for this instead of graph paper if you prefer.

Step 2. Plot the Tasks onto the Plan

Next list the tasks in the first column on the left hand side of the page, the y-axis. To draw up a rough first draft of the Gantt chart; plot each task on the plan, showing it starting on the earliest possible date. Draw each task as a horizontal bar, with the length of the bar being the length of time you estimate the task will take. Above each task bar, mark the estimated time taken to complete the task. At this stage there is no need to include scheduling – all you are doing is setting up the first draft.

Step 3. Schedule the Tasks/Activities

Now on a fresh sheet redraw the Gantt chart to schedule actions and tasks. Schedule these in such a way that sequential actions are carried out in the desired sequence e.g. dig holes, lay foundations, begin construction. Ensure that these dependent activities do not start until the activities they depend on have been fully completed.

Where possible, schedule parallel tasks so that they do not interfere with sequential actions on the critical path. While scheduling, ensure that you make best use of the time and resources you have available. Do not over-commit resources and allow some time in the schedule for holdups, overruns, quality rejections, failures in delivery, etc.

Once the Gantt chart is drawn, you can see how long will it take to complete your project. The key steps to be carried out to ensure successful completion of the project should be clearly visible.

In practice professional project managers use sophisticated software like Microsoft Project or Microsoft Excel to create Gantt charts. Not only do these packages make the drawing of Gantt charts easier, they also make subsequent modification of plans easier and provide facilities for monitoring progress against plans. Tables and spreadsheets can also be used to create simple and easy to change charts without Microsoft Project. Spreadsheets with coloured bars are most useful for the simplest projects.

What is Gantt Chart

The Gantt chart is a type of bar chart that is helpful in laying out the tasks associated with a given project. When executed properly, the Gantt chart helps to ensure that the project schedule is maintained at a reasonable pace, and that the individual tasks that make up the work breakdown schedule logically progress in a manner that moves the project closer to completion. A Gantt chart can be used for just about any type of project, from laying out a marketing strategy or planning a building project.

The chart is named after Henry Laurence Gantt, who refined the concept of using a bar chart to control steps relevant to the process of shipbuilding. During the 20th century, the essentials of his process chart were applied to projects that had nothing to do with the building of ships. Today, the Gantt chart is used to establish a precedence network that determines the priority level of each task associated with the project. At the same time, the chart also evaluates the dependency relationships of each of the tasks. Together, these two aspects of the Gantt chart make it possible arrange and project the completion time of various tasks in a manner that shows a logical progression toward the successful completion of the project.

In most cases, the Gantt Chart appears as a horizontal bar chart. Each task associated with the project is accounted for on the body of the chart. Because the Gantt chart is concerned with executing the project in the most efficient manner, it also helps to define the amount of time required to complete each individual task. The chart also helps to define tasks that can be completed concurrently and which tasks cannot be addressed until other tasks are fully complete. This function helps to project both the sequence and the duration of each task involved in the project.

One of the main advantages of preparing a Gantt chart is that it provides an easy reference for how to carry out a given project by breaking it down into specific phases and tasks. This visual charting often helps to identify potential bottlenecks in the project, as well as make it easier to identify tasks that may have been overlooked in the original layout of the project. As with any type of planning tool, it is also possible to adjust the components of a Gantt chart to accommodate any unforeseen circumstances that take place during the life of the project.

Quality Control and Safety Concerns in Construction

Quality control and Construction Safety represent increasingly important concerns for project managers.

Weak quality control leads to defects or failures in constructed facilities, thus result in very large costs. Even with minor defects, re-construction may be required and facility operations impaired. Increased costs and delays are the result. In the worst case, failures may cause personal injuries or fatalities. Accidents during the construction process can similarly result in personal injuries and large costs. Indirect costs of insurance, inspection and regulation are increasing rapidly due to these increased direct costs. Good project managers try to ensure that the job is done right the first time and that no major accidents occur on the project.

As with cost control, the most important decisions regarding the quality of a completed facility are made during the design and planning stages rather than during construction. It is during these preliminary stages that component configurations, material specifications and functional performance are decided. Quality control during construction consists largely of insuring conformance to these original design and planning decisions.

While conformance to existing design decisions is the primary focus of quality control, there are exceptions to this rule. First, unforeseen circumstances, incorrect design decisions or changes desired by an owner in the facility function may require re-evaluation of design decisions during the course of construction. While these changes may be motivated by the concern for quality, they represent occasions for re-design with all the attendant objectives and constraints. As a second case, some designs rely upon informed and appropriate decision making during the construction process itself. For example, some tunneling methods make decisions about the amount of shoring required at different locations based upon observation of soil conditions during the tunneling process. Since such decisions are based on better information concerning actual site conditions, the facility design may be more cost effective as a result.

With the attention to conformance as the measure of quality during the construction process, the specification of quality requirements in the design and contract documentation becomes extremely important. Quality requirements should be clear and verifiable, so that all parties in the project can understand the requirements for conformance. Much of the discussion in this chapter relates to the development and the implications of different quality requirements for construction as well as the issues associated with insuring conformance.

Safety during the construction project is also influenced in large part by decisions made during the planning and design process. Some designs or construction plans are inherently difficult and dangerous to implement, whereas other, comparable plans may considerably reduce the possibility of accidents. For example, clear separation of traffic from construction zones during roadway rehabilitation can greatly reduce the possibility of accidental collisions. Beyond these design decisions, safety largely depends upon education, vigilance and cooperation during the construction process. Workers should be constantly alert to the possibilities of accidents and avoid taken unnecessary risks.

Traffic Engineering – Traffic Control Devices

GENERAL

Traffic control devices are signs, signals, markings or other devices used to regulate, warn or guide highway traffic. When properly used they promote safe orderly and convenient movement of traffic, both motorized and non-motorized. All necessary devices should be in place on any highway open to traffic.

Uniformity of traffic control devices and their application enables highway users to quickly recognize and interpret devices and to react correctly to them. Uniformity means treating similar situations in the same way. Effective traffic control devices meet five basic requirements. They fulfill a need; command attention; convey a clear, simple meaning; command the respect of road users; and give adequate time for proper response.

The application of traffic control devices should be based on sound engineering principles in conjunction with studies of traffic flow, accidents, speeds, delays, and physical conditions. Once a determination has been made, the devices used must conform to the Manual of Uniform Traffic Control Devices.

SIGNS (GENERAL)

Signs are essential to inform highway users of specific regulations and to call attention to hazards that are not self-evident. They also inform drivers about highway routes, directions, destinations, and points of interest. When considering the need for warning or guide signs, the needs of highway users unfamiliar with the area should be a major consideration.

Traffic signs are standardized in terms of shape, color, legend and symbols to enable highway uses to quickly and correctly comprehend the sign message.  There are some signs that do not follow these basic shapes and colors. For example, the STOP sign (Regulatory) is an octagon shape with a white legend on a red background.

Standard signs are specified in a variety of sizes to provide suitable target value and legibility for each type highway environment and condition. Sign size is identified by a letter (usually A, B, C, D, or E).

The minimum height of a roadside sign (difference in elevation between the edge of the roadway and the bottom of the sign) on conventional highways and expressways is seven feet. Where there are multiple signs on the same support, the lowest sign should be at least six feet. At locations where it is considered unlikely that signs would interfere with pedestrians or be blocked by parked vehicles, these minimum heights are reduced to five feet and four feet respectively.

SIGNS (REGULATORY)

Regulatory signs inform highway users of traffic regulations. They are sometimes used to advise of statutory rules which may not be apparent or which require emphasis. Unlike regulations, however, statutory rules are in effect even if not posted.

Stop and Yield signs may be used to assign right of way at intersections. Sight distance across the corners of the intersection and the prevailing approach speed on the major highway are significant in determining whether a Stop or Yield sign should be used.

There are two types of speed limits: linear (along a portion of a highway) or area (all highways within a specified area, except those specifically excluded). Investigations to determine appropriate speed limits should include: the existing speed pattern, intersections and roadside development, traffic volumes, accident experience, and physical conditions of the highway.

For linear speed limits longer than 1100 feet, multiple speed limit signs are required. The first sign shall be placed at the beginning of the limit. The second sign should be placed within 1100 feet of the first with additional signs being placed at distances equal to 100 times the numerical value of the speed limit.

Basic Types of Construction Equipment

Construction Equipment is one of those things where the overall influence it has primarily rests on other factors on construction sites. So then what you simply must do is gather as many details as possible and think about them. Therefore you do have to be cautious about what you choose and dismiss. When you are satisfied that your research is thorough, then that is the time to evaluate the possibilities.

We know you would like to choose what is right and best, and to that end we gladly give you some exceptional guidelines concerning Construction Equipment.

Construction equipment types cover from the very heavy equipment to the portable and mobile lighter equipment, some of them with a precise description of their functions are detailed below.

• Backhoe loader: Engineering equipment with a front bucket/shovel and a small backhoe in the rear combined with a tractor is known as backhoe loader. It is mostly used in small construction sites and in urban engineering such as fixing city roads.

• A crawler, which is very powerful and attached with a blade, is called a bulldozer. Even though any heavy engineering vehicle is known as bulldozer, it is actually a tractor with a dozer blade.
• A compact excavator is a wheeled or tracked vehicle with a backfill blade and swing boom. It is also known as mini excavator. The functions and movements of the machines are carried out by transferring hydraulic fluid. This makes a compact hydraulic excavator different from other construction equipment. (See this text for full understand on compact excavator machine)
• To compact gravel, dirt, asphalt and concrete in construction work and road laying a road roller which is also known as roller-compactor would be used.
• A motorized cultivator with a rotating blade to work in the soil is known as rotary tiller. They are either drawn behind a tractor or self-propelled.
• A crane is a derrick or tower equipped with pulleys and cables for lowering and lifting materials. The cranes used in construction industry are mostly temporary structures.
• Dragline excavation systems are heavy equipment mostly used in surface mining and civil engineering. The smaller type of dragline excavator is used for port and road construction. The larger type dragline excavator is used in strip-mining operations for coal extraction.
• In the building industry, to make foundations, a drilling machine is used. It is also used in oil wells and water wells.
• An excavator commonly known as a digger is an engineering vehicle, with a cab mounted on a rotating platform or pivot, and a backhoe on top of an undercarriage with wheels or tracks.
• In untamed regions which are being reclaimed for construction, a feller buncher, a machine having an attachment, which fells trees, is used.
• A forklift, lift truck or forklift truck is an industrial truck used to pick up and transport heavy material using steel forks under the material to be lifted. The most common usage of a forklift is to move materials stored on pallets.
• A loader also known as a bucket loader, front-end loader, scoop loader, shovel, or front loader is a type of tractor using buckets, which can be tilted to lift and move material.
• A paver is used to spread asphalt on roadways.

We have covered a few basic items about Construction Equipment, and they are important to consider in your research. Of course we strongly recommend you discover more about them. We believe you will find them to be very helpful in a lot of ways. Do take the time and make the effort to discover the big picture of this. Continue reading because you do not want to miss these critical knowledge items.

Truly, what we have offered you here, today, is by no means the end of the learning process about Construction Equipment and Machines. These are powerful points, to be sure, and you can realize excellent results as well. However, be careful thinking there is no more outstanding information, either. There are certain areas that you need to learn more about if you want real success with Construction Equipment management. That is what is can be achievable when you go on to discover more.

Introduction to Prestressed Concrete

Plain concrete, commonly known as concrete, is an intimate mixture of binding material, fine aggregate, coarse aggregate and water. This can be easily moulded to desired shape and size before it looses plasticity and hardens. Plain concrete is strong in compression but very weak in tension. Strength of concrete in tension is very low and hence it is ignored in reinforced cement concrete (R.C.C) design. Concrete in tension is acting as a cover to steel and helping to keep steel at desired distance. Thus in R.C.C. lot of concrete is not properly utilized. Prestressing the concrete is one of the method of utilizing entire concrete.

The principle of prestressed concrete is to introduce calculated compressive stresses in the zones wherever tensile stresses are expected in the concrete structural elements. When such structural element is used stresses developed due to loading has to first nullify these compressive stresses before introducing tensile stress in concrete.

Thus in prestressed concrete entire concrete is utilized to resist the load. Another important advantage of pre-stressed concrete (PSC) is hair cracks are avoided in the concrete and hence durability is high. The fatigue strength of PSC is also more. The deflections of PSC beam is much less and hence can be used for longer spans also. PSC is commonly used in the construction of bridges, large column free slabs and roofs. PSC sleepers and electric piles are commonly used.

The material used in PSC is high tensile steel and high strength steel. The tensioning of wires may be by pretensioning or by post tensioning. Pretensioning consists in stretching the wires before concreting and then releasing the wires. In case of post tensioning, the ducts are made in concrete elements. After concrete of hardens, prestressing wires are passed through ducts. After stretching wires, they are anchored to concrete elements by special anchors.

The Tallest Buildings in the World

When speaking of the tallest buildings in the world, it is important to specify exactly what is being measured. Listers must decide if the building is to be measured from sidewalk level or below, whether or not TV towers or masts are included, and whether an antenna, flagpole, or spire should count. A building is considered to differ from a tower in its primary use, being designed for residential, business, manufacturing, or mixed use, whereas a tower is not.

The Council on Tall Buildings and Urban Habitat, formerly the Joint Committee on Tall Buildings in conjunction with Emporis Buildings, is the authoritative source for information about the tallest buildings in the world, and their list of the tallest buildings, drawn from an extensive database, is based on the height of the building to the structural or architectural top, which includes spires and pinnacles, but does not include antennas, masts, or flagpoles. Prior to 9/11, the twin towers of the World Trade Center in New York City, New York were ranked fifth – 1,368 ft (417 m) – and sixth – 1,362 ft (415 m) – on the list of the tallest buildings in the world.

Interesting facts:

• The tallest building in the world, Taipei 101, is nearly 200 feet (61 m) taller than the next tallest building.
• Of the top ten tallest buildings in the world, all are either in Asia or the United States.
• Of the top 20 tallest buildings in the world, the most, five, are in China, with four in Hong Kong, three in Chicago, and two each in Taiwan and Kuala Lumpur.
• In the top 100 tallest buildings in the world, the only ones completed prior to 1969 are all in New York City and were completed between 1930 and 1932. They are: the Trump Building, originally called the Bank of Manhattan Trust Building, and the Chrysler Building – 1930; the Empire State Building – 1931; and the American International – 1932.
• In the top 200 tallest buildings in the world there are:
  • 25 in New York City
  • 17 in Hong Kong
  • 13 in Shanghai
  • 12 in Chicago.
  • 8 in Dubai
  • 7 in Singapore
  • 6 each in Tokyo, Seoul, Sydney and Houston
  • 5 in Kuala Lumpur and Shenzhen, China
  • 4 each in Los Angeles and Melbourne and Toronto and Atlanta

TALLEST BUILDINGS IN THE WORLD
Number	Building	City	Height	Floors	Year	Architect
1.	Taipei 101	Taipei , Taiwan	1,671 ft (509 m)	101	2004	C.Y. Lee & Partners
2.	Petronas Tower 1	Kuala Lumpur, Malaysia	1,483 ft (452 m)	88	1998	Cesar Pelli & Associates Architects, Adamson Associates, RSP Architects Planners & Engineers Private Limited
3.	Petronas Tower 2	Kuala Lumpur, Malaysia	1,483 ft (452 m)	88	1998	Cesar Pelli & Associates Architects, Adamson Associates, RSP Architects Planners & Engineers Private Limited
4.	Sears Tower	Chicago, IL USA	1,451 ft (442 m)	108	1974	Skidmore, Owings & Merrill LLP
5.	Jin MaoTower	Shanghai, China	1,380 ft (421 m)	88	1998	Skidmore, Owings & Merrill LLP, The Shanghai Institute of Architectural Design (SIADR), East China Architectural Design & Research Institute Co. Ltd.
6.	Two International Finance Centre	Hong Kong	1,362 ft (415 m)	88	2003	Rocco Design Limited, Cesar Pelli & Associates Architects
7.	CITIC Plaza	Guangzhou, China	1,283 ft (391 m)	80	1997	DLN Architects & Engineers
8.	Shun Hing Square	Shenzhen, China	1,260 ft (384 m)	69	1996	K.Y. Cheung Design Associates
9.	Empire State Building	New York City, NY, USA	1,250 ft (381 m)	102	1931	Shreve, Lamb & Harmon Associates
10.	Central Plaza	Hong Kong	1,227 ft (374 m)	78	1992	DLN Architects & Engineers

Ebooks

• Engineering books
• Indian Engineerings book 
• Analysis $ Design of beams for B.M.1
• Analysis $ Design of beams for B.M.2
• Analysis of statically Determinate structures
• Beams1
• Beams analysis using Deflection method
• Beams2
• Beams Formula
• Beams3
• Beams4
• Bending in Practical
• Bending of beams
• Benefits $ concern about Dam
• Continious beams1
• continious beams2
• Design Aid for continious beams
• Dictionary for building of civil engineering1
• Dictionary for building of civil engineering2
• Fixed beams1
• Fixed beams2
• Fixed beams3
• Guidelines for Dam
• Two span continious beams
• Basic Differentitation Formula
• Formula onTrigonometry
• Integration Formula
• linear Algebra,Determinant,Inverse,Rank 
• Method of Superposition
• Relative motion using Translating motion
• Relative Velocity
• Surveying Measurements
• Surveying Levelling
• Young Trigonometry 3D
• Electrical Technology
• Strength of Material

Production of RCC

Production of RCC is done according to the Client’s schedule and request. The concrete is produced continuously. However there are at times some breaks during operation. Some of these breaks are planned, like planned stops of concrete placement, regular maintenance of the equipment, meals, interferences with other activities in the Project, etc. Some others are not; for example, bad weather conditions, power cuts, etc.

The production at the RCC plant consists of the production of the following sub-systems:

(a) The water supply system.

Water is pumped from the river and cleaned and treated with a sedimentation and filtration system and is delivered to the main storage tank at a rate of 200 m3 per hour. It is then stored in the main storage tanks at the plant which has a storage capacity of 300,000 gals. The treated water is delivered to the plant accordingly.

(b) The cooling system.

The clear water that is delivered to the plant is chilled by the three Water Chillers and the temperature of water is lowered down to 4 deg C and pumped to the wet belt where the aggregates which are transported by a very slow conveyor are sprayed with chilled water. The dirty water is collected at the sedimentation tank and the sediments are separated and cleaned water is again recycled back to the water tank where the water is chilled and pumped back to the wet belt again for cooling and cleaning the aggregates. Additionally two ice plants are constructed inside the plant with a total capacity of 200 tons per hour and a variable amount if ice is added to the mixing concrete accordingly to get the required temperature of concrete.

(c) The conveying system.

The aggregates are transported by two lines of inclined and horizontal conveyors with a speed of about 1.67 m/s.

Three sizes of coarse aggregates are loaded onto the horizontal conveyor belt each separated by a spacing of 75 secs to deliver 400 tons per hour for each line. For the two lines the quantity that can be delivered is about 800 tons per hour, meeting the expected peak production demand. The aggregates are then transported by inclined conveyors and collected inside the inline silos by means of the distributing belts which deliver the different sizes of aggregates to different compartment inside the silos. The fine aggregate is separately transported by a different line of conveyor to its own compartment inside the silo. The whole system is automatically controlled from a control room.

(d) Storage and conveyance of cementitious materials.

Cementatious materials such as cement and pozzolan which are used in the RCC are produced and obtained from different locations and transported to the plant and are stored in 10 x 1000 ton cement and pozzolan silos.

They are conveyed to the 150 ton working silos from the plant by means of pneumatic blowing system which has a total capacity of 120 tons per hour and then delivered from the working silos to the mixers by means of screw conveyors.

(e) Concrete Mixing.

According to the mix design, the aggregates are automatically weighed on the weighing belts underneath the inline silos. Ice is weighed and added whenever necessary at the end of the weighing belt. Cement, Pozzolan, water and admixture are weighed separately and fed into the mixers. A very uniform concrete with a temperature of not more than 18 deg C and consistency (VeBe time) of 8 to 12 secs is produced to deliver to the placement site by trucks or by the RCC conveyor system.

Measures to avoid cracking in fresh concrete

Generally, the contractor shall allow for all necessary measures to monitor and avoid cracking in fresh hydrating concrete, regardless the size or volume of the pour. Such measures shall be to the satisfaction of the Engineer and shall be such that maximum surface crack width on hardened concrete measure immediately after the pour does not exceed 0.004 times the nominal cover of the main reinforcement.

The contractor shall allow for and provide approved instrumentation for the measurement of internal temperature changes in large pours. The maximum concrete temperature at the point of delivery shall not in general exceed the lower of either 37 degree C, or 6 degree C above the prevailing shade temperature in accordance with the recommendations of ACI. The limiting internal temperature differential measured across the extreme faces of concrete mass shall not exceed 25 degrees C at any time.

Curing of hardened concrete shall be executed in accordance with the curing specification. Generally, the element surface shall not be cooled to dissipate heat from the concrete. Curing methods, such as the wetting of heated concrete elements exposed to prolonged and direct radiation, which induce temperature gradients within the concrete mass are strictly prohibited.

For large pours, the contractor shall allow for and take extra precautions to reduce concrete temperature gradient and to prevent the loss of surface moisture. Such measures include but are not limited to:

• Keeping all mix constituents shaded where possible to reduce their temperatures in the stockpile

• Cooling of mixing water and/or replacing part or whole of the added water with ice.

• Reducing the cement content by the use of admixtures (but not below that required for the durability)

• Using a cement with a lower heat of hydration

• Injecting liquid nitrogen after mixing of concrete

• Restring the time between mixing and placing of the concrete to not more than 2 hours

• Providing approved surface insulation continuously over all exposed surfaces to prevent draughts and to maintain uniform temperature through the concrete mass

• Initiating curing immediately after final tamping and continue until the approved surface insulation system is fully in place

• Providing shade to the concrete surface to prevent heat gain from direct radiation.

If the surface exhibits crack after compaction, it shall be retamped to close the cracks while the concrete is still in plastic stage.

Bridge plans

Bridge plans are generally attached as supplements to the roadway construction plans. The basic types of sheets in a set of bridge plans include the following.

TITLE AND INDEX SHEET
The title and index sheet identifies the bridge by contract number and location and contains an index of all other sheets in the plans.

BORING DATA SHEETS
The boring data sheets indicate the results of soil borings made at the bridge site prior to construction. The Bridge Technician uses these sheets to identify the types of soils that are encountered during structure excavation, and to determine the approximate depths at which the types of soils occur.

LAYOUT SHEET
The layout sheet consists primarily of a topographical situation plan of the bridge site and a profile view of the proposed bridge grade. The situation plan identifies the landowners and natural and manmade features in the contract area. The plan also delineates right of way limits, limits of construction, and the locations of benchmarks used for grade control. The layout sheet also may include a list of utilities in the contract area that may be affected by the contract.

GENERAL PLAN
The General Plan sheet includes a plan view, which is the bridge seen from above, and an elevation view, which is the bridge seen from the side.

The plan view identifies:

1) The exact location of the bridge in terms of the contract station numbers and the obstacle the bridge is intended to cross

2) The degree of skew, if any

3) All important centerlines for the structure, roadway, and bearing

4) The overall length of the bridge and the lengths of all intermediate spans

5) All significant widths for the “out to outs,” roadways, shoulders, sidewalks, and parapets

The elevation view identifies:

1) Original and projected ground lines

2) Elevations of railroads, low water lines, highways, etc., to be crossed and any minimum vertical clearance requirements

3) Minimum tip elevation for piling, if used, and the planned bottom-of-footing elevations
4) The locations of fixed and expansion bearings

Shotcrete Components

Shotcrete has been widely used for tunneling works and slope protection, it is also used for architectural purposes. There are two types of shotcrete application, the wet and dry process. Shotcrete is a concrete transported by means of air under pressure with high velocity. It is applied and compacted in the same time against a surface.

Shotcrete components

As mentioned earlier, shotrete differ from normal concrete by the way to apply it.
Here below some points that should be observed and respected when producing shotcrete mixes.

Cement

It is obvious that the cement quality properties play a dominant role in the high early strength behaviour. The specific surface (Blaine value) should be not lower than 3500 cm2/g. Compressive strength of the cement lime should be more than 10 MPa after 2 days and more than 35 MPa after 28 days.

First stiffening of the cement lime should not be before 1,5 hours and not after 4 hours from the start of the mixing with water.
The choice of cement however is at all the time governed by the required properties of the hardened concrete and not for their suitability for spraying.
The early strength requirement would determine the cement content. Usually for dry process we dose 280-350 kg for 1 m3 of dry bulk mix. For wet process, cement content can vary from 425 kg/m3 to 500 kg/m3. Suitable cement content regarding the strength required can be verified only by shotcrte trial. A slight retardation of the setting time is observed by the tri-calcium aluminates in case of sulfate resistant cement. Blast furnace cements cause the same problem.

Water

All water use for mixing cementitious components must be clean as it occurs naturally. Spring, waste- water must be analyzed in order to determine their compatibility with the other components of the mix. The water cement ratio should not exceed 0,40 if high strength or durable shotcrete is required.

Sand

Sand must be clean. It is always combined with aggregate. The S/A ratio varies from 55% – 65%. Despite to specify the sand grading itself according to a certain grading refereeing to a certain standards, it is the combination of the sand and aggregate together that must comply with the standard used.

Aggregate

Aggregate would be mostly crushed aggregate considering that they could be produced from the excavated material. However we should avoid flaky elongated aggregate.

Sand / Aggregate ratio

This ratio must satisfy a few conditions. The S/A ratio must allow easy shotcrete pumping or rotor filling. As a rule it is clear that mixes containing fines in excess would cause dust, increase the water demand. A contrary, mixes containing aggregates in excess would increase rebound.
It has been observed that good pumping properties are achieved when the particles smaller than 1.18 mm represent around 40% of the sand / aggregate combination.

Superplasticiser / stabilizer:

They are taken in consideration for the production of wet mix only.
They are usually Naphthalene or polycarboxylate base superplasticiser.
Only some special modified Lignosulfate base superplasticiser could be used.
As normal concrete, their use allows a reduction of the water by still keeping suitable workability. However, it must be noted that lower the W/C is faster early strengths are reached. Dosage would depend on the workability required.
Usually they are dosed from 1,0-1,7 %.

Accelerator

They are definitely required for wet mix application. They are used in certain cases for dry process application too.
They are added for various reasons. They allow the spraying of thick layer when out-put is high and consequently the shotcrete reaching the substrate would not fall down. They allow developing early strength that would minimize surrounding rock deformations. They limit the rebound formation. Certain type of accelerators allows sealing work when substrate shows water leakage. They exist in powder or liquid form. They are either Alkali or Alkali Free. Typical dosages of modern accelerator are from 3-8% by weight of cement

Important Requirements for Concrete Inspection and Acceptant

Inspecting the concrete quality inclusive the inspection of materials, equipments, production process and the characteristics of the already solidifying concrete The slump of the concrete mixture is inspected at the Site in accordance with the following regulations:

• For the concrete mixed at Site, need to inspect immediately after mixing the initial batch

• For the pre-cast concrete at the concrete mixing station (commodity concrete), need to inspect for each delivery at the concrete placing site

• When mixing concrete under the stable weather condition and material moisture, inspect once per shift

• When there is change in type and moisture of the material as well as change the compositions for providing & mixing concrete, need to inspect at once the initial mixing batch, then, further inspecting at least once per shift.

The testing samples for determining the concrete strength need to be taken according to each group. Each group will include three units of sample taken at the same time at one position in accordance with the regulations. The quantity of sample group will be regulated according to the weight as follows:

For the great concrete block, take one sample group per 500 m3 when the weight  in one placing block greater than 1000 m3 and take one sample group per 250 m3 when the concrete weight in one placing block less than 1000 m3.

• For the big foundation, take one sample group per 100 m3 but not less than one sample group per one foundation block

• For the concrete of machinery foundation, take one sample group for the placing block greater than 50 m3 but still take one sample group for the block less than 50m3

• For the frame and structures of foundation (column, girder, plate, arch …), take one sample group per 20 m3 of concrete 

• In case of placing concrete for single structures with less weight, still take one sample group if necessary;

• For the concrete of floor, road surface (car road, runway, …, take one sample group per 200 m3 of concrete but if the concrete block is less than 200 m3, still take one sample group.

• In order to check the water proof of concrete, take one sample group per 500 m3. but if the concrete block weight is less than this, still take one sample group

The strength of concrete during construction after inspected at the age of 28 days by pressing the casting sample at the Site is considered to meet the designing requirements when the average value of each sample group is not less than designing grade and no sample in the sample group getting the strength below 85% of designing grade