Archive for the ‘Civil Engineering’ Category

Precast Concrete

WHEN used as a construction system, precast concrete offers several advantages that range from improved quality to safer, long-lasting structures, says the Riyadh-based Al Rashid-Abetong (ARA), which has been serving the Saudi market for more than three decades.

The advantages of precast construction, coupled with the inherent benefits of concrete, provide a superior building material that has been proven the world over for several decades.

“Precast systems offer significant savings in construction, thanks to earlier completion dates, inbuilt fireproofing, reduced formwork, scaffolding, reduced wet trades and increased budget control,” says Munir Sultan, assistant sales and marketing manager. (Read more..)

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How to write an Academic Essay?

Written work is the dominant means of assessment required of a student. This note is intended to assist you in preparing and presenting essays and reports for all of the modules you take. It will also assist you in preparing papers for tutorial discussions, in writing essay-type examination answers, and in the final year dissertation. (Read more..)

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Contex a weapon against corrosion

Contex a weapon against corrosion
Hempel has been on the road promoting its solution to the harmful environmental effects on reinforced concrete. Its anti-carbonation coating system Contex is a proven ‘first line of defence’ against corrosion, says the leading paints and coatings manufacturer.
HEMPEL, a global leader in the production and sales of protective and decorative coatings, recently organised a Middle East roadshow as part of its efforts to communicate with specifiers and customers and introduce new solutions to solve certain engineering problems.
The roadshow seminars, held last month (May 4 to 17) in Kuwait, Bahrain and Saudi Arabia (Riyadh, Jeddah and Makkah), covered two topics that concern both civil and architectural interests – concrete protection and colour trends.
Moataz Kamel, marketing manager for Hempel Middle East (West), spoke about concrete protection, focusing on the aggressive environmental elements that concrete is exposed to and the damage that can occur through exposure to these aggressive agents.
He also presented Contex, Hempel’s highly effective solution for the protection of reinforced concrete against these elements.
A proven ‘first line of defence’, Contex is an anti-carbonation coating system that provides proactive protection to concrete against a wide range of possible attacks and in turn protects steel rebar from corrosion, maintaining both the compressive and tensile strengths of the concrete structure.
Says Kamel: “Reinforced concrete, as an engineering material, is widely used in most civil structures. When used in various structural elements, it needs to withstand various loads that the skeleton of the building is subjected to.
“Reinforced concrete consists of concrete mix comprising cement, water and aggregate in addition to steel rebar. After hardening and curing, the concrete mix acts as a passive layer protecting the steel rebar from corrosion. This protection comes mainly due to the alkalinity of the concrete, which exceeds pH12.”
Reinforced concrete in buildings may come under attack from a number of elements in the environment. These include liquid water, intrusion of carbon dioxide (CO2) and chloride ions, and sulphate attack.”
Carbonation
Elaborating on the process of carbonation, he says: “Carbon dioxide ingresses through pores in the concrete and in the presence of liquid water, it reduces the pH value of the concrete down to pH9. This reduced alkalinity makes the media aggressive on the steel rebar, which starts to corrode.
This apart, the CO2 reacts with calcium hydroxide (CaOH3), one of the chemical compounds in concrete, to produce calcium carbonate (CaCO3), which weakens the material and causes spalling of the concrete cover.
“Also when steel rebar corrodes, its cross-section increases, resulting in internal stresses, which in turn causes cracks in the concrete cover. This process leads to cracking and spalling of the concrete cover, which will further expose the steel rebar to the environment.”
Chloride intrusion
The highly alkaline environment of good quality concrete forms a passive layer surrounding the embedded rebar, which normally prevents the steel from corroding. However, chloride ions if present in the concrete facilitate a local breakdown of the passive layer when the pH value is reduced, resulting in pitting of the steel rebar. Pitting is a form of localised corrosion and occurs mainly in the presence of neutral or acidic solutions containing chlorides or other halides.
Other factors
Concrete surfaces may also crack due to various reasons, such as volumetric changes taking place due to drying of concrete; thermal cracks and tension cracks due to tensile stresses, says Kamel.
“These cracks also contribute the process of corrosion by allowing aggressive elements to get inside the concrete section and reach the steel rebar,” he adds.
Contex’s range of acrylic coating systems provides the most comprehensive solution for these problems within the civil industry, providing both water-borne and solvent-borne systems in a wide variety of finishes.
“Contex prevents liquid water, CO2 and chlorides from reaching both the concrete and steel rebar, thus preventing all expected chemical reactions that could cause concrete degradation and initiate steel rebar corrosion,” says Kamel.
At the same time, Contex allows the entrapped humidity to be released from the concrete section, facilitating the breathability of the building.
Finally, Contex has a crack-bridging ability to overcome cracks which may occur on the concrete surface due to previously-mentioned causes. This ability ensures the integrity of the coating system, preventing it from cracking and leaving the concrete section exposed to aggressive environmental effects.
Each of Hempel’s Contex anti-carbonation coating systems has been independently tested and certified by Taylor Woodrow laboratories in the UK, as being able to provide proactive protection to concrete structures against a wide range of possible attacks and defects, he says.
These include chloride intrusion, concrete carbonation, alkali degradation, rebar corrosion, water/vapour entrapment, crack-bridging ability, ultraviolet degradation, and mechanical/impact damage.
Colour trends
As part of the road show, Hempel also focused on the latest colour trends, which will shape the fashion, interiors and many other disciplines during autumn/winter of this year. Mohamed Baitie, regional brand manager, Hempel Middle East (West), presented four main trends to the audience – Contour, Punch, Opal and Roma.
With his presentation, Baitie took the audience on a journey of how the trends were identified before they were finally presented to designers. This was achieved through workshops that brought together selected designers from different industries to create colour palettes to represent the colour trends.
The workshops were conducted by the UK-based Global Colour Research Company, which is one of the leading colour research bureaus in the world in the field of shaping the colour trends globally.
Baitie also went through the concept of every colour trend and its main elements, pointing out however that these trends do not represent certain colour schemes and hence cannot be used directly as colour cards by designers. The four palettes represent the trends of colour, texture, transparency and glossiness, which Hempel takes and translates into its colour proposition through different colour cards that are provided to its customers.
“Hempel as a worldwide leader in the paint industry is keen to base its colour proposition on the latest colour trends created by the most reliable colour research company worldwide,” Baitie concluded.

Hempel has been on the road promoting its solution to the harmful environmental effects on reinforced concrete. Its anti-carbonation coating system Contex is a proven ‘first line of defence’ against corrosion, says the leading paints and coatings manufacturer. (Read more..)

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Mega structures: Construction of Burj Dubai

Episode 1

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Megastructures: Construction of Burj Al Arab

Episode 1

http://www.youtube.com/watch?v=ow321Ximh70 (Read more..)

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Mega Structures: Dubai’s Palm Island

Episode 1

http://www.youtube.com/watch?v=WybVe8eXXqw (Read more..)

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Construction Management technology Education

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Building Design

Building designs
by Dennis Brand
Perhaps the best way to describe design and build contracts is to explain what they are not. The traditional design-bid-build contract is a sequential process of phases or stages in which the owner or developer first contracts with a design professional to prepare a concept or basic design, then later a detailed design that is suitable for construction. This will include plans and specifications that when complete will be used to solicit competitive bids and finally the award of a construction contract to the lowest bidder.
In design and build contracts, one entity performs both the design and construction under a single contract. Often the contract is awarded by some process other than competitive bidding, thus it differs from traditional design-bid-build in two ways. First, the design and construction components are packaged into a single contract; second, it is not necessarily awarded to the lowest bidder after competitive bidding.
Why use design and build?
Design and build contracts have the potential to reduce the overall project costs as the contractor performing the design has a better appreciation of the construction costs of the various alternatives. They can therefore produce a design that is less expensive to build and they have an incentive to do so.
Another way to look at this advantage is that it moves value engineering from after the contract award, where the contractor proposes cost reduction ideas and shares the savings with the owner, to pre-award, where the owner enjoys most of the savings.
Design and build contracts may also result in the earlier completion and occupancy of a project as there is no downtime between the completion of a design and start of construction. Furthermore, the contractor can begin construction of early phases of the project, such as grading and foundations, before the design of later phases like the building envelope and MEP systems are complete.
This process is sometimes referred to as fast-track. It eliminates the traditional liability gap that can occur when the design is produced by a consultant and the contractor constructs the design under a separate contract. Design professionals can obtain insurance coverage for professional liability insurance only, which covers negligence, error and omissions. Virtually all design contracts limit their liability to this.
However, there can be non-negligent errors and omissions on the part of the designer that cost the owner money, but for which the designer is not liable. One example of this is where the designer undertakes reasonable subsurface investigations but fails to detect a rocky outcrop that will require additional work on the part of the construction contractor.
In the traditional design-bid-build approach, the owner warrants the correctness of the plans and specifications to the construction contractor. In the event of an error where the contractor incurs additional costs, these are met by the owner with little prospect of recovery from the designer. Design and build contracts eliminate this gap because the is solely responsible for defective plans, specifications or differing site conditions.
When a project is designed around current generation products, any proposed substitution of new or alternative items following bidding may require revisions to the structure, mechanical or electrical components to accommodate the new design. In such occasions the question arises: who will pay for the resulting charges? Design and build contracts solve this problem: the contractor selects the equipment then designs the building around this, which seems a more logical way to proceed.
The traditional design-bid-build method of contracting can suffer from under-optimisation when individual project participants seek to optimise their own positions. For example, the total cost to the owner of a building’s steel frame includes the cost of the engineering to determine the required steel sections plus that of the steel. The designer has little incentive to minimise the amount of structural steel, their concern is only to spend sufficient design time to ensure that there is enough steel to meet both gravity and seismic loads.
With design and build contracts, the contractor has an incentive to use additional engineering in order to achieve the optimum amount of steel required for the structure. That is not to say that this type of contract results in unsafe or less efficient structures, rather that it reduces unnecessary quantities of materials and equipment that do not necessarily add to the robustness of the structure.
Design and build contracts may reduce the administrative burden on the owner as there is one award and one contract to administer. The total cost of the project becomes apparent earlier. In traditional design-bid-build jobs, construction costs are not known until bid opening and it is possible to spend money on a design that the owner may not be able to build. Frequently construction bids exceed the project budget, which results in it having to be redesigned, thus delaying completion.
The risk factors
Under a traditional design-bid-build contract arrangement the owner has full control over the details of the plans and specifications. It does not publish them for bids until it is satisfied that they reflect their requirements. With design and build contracts the owner gives up some of this control.
Moreover, the owner must confirm its needs much earlier. With traditional design-bid-build contracts, if the owner is indecisive on its needs, it can clarify them during the design phase. With design and build projects, however such changes can be very expensive and disruptive, impacting on both costs and completion.
To summarise, if the owner is not certain what they want, due to the expense in making changes after contracts are awarded, the more traditional design-bid-build method may be the best choice.

Building designs

by Dennis Brand

Perhaps the best way to describe design and build contracts is to explain what they are not. The traditional design-bid-build contract is a sequential process of phases or stages in which the owner or developer first contracts with a design professional to prepare a concept or basic design, then later a detailed design that is suitable for construction. This will include plans and specifications that when complete will be used to solicit competitive bids and finally the award of a construction contract to the lowest bidder. (Read more..)

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Asbestos management in the UAE

Asbestos management in the UAE
by Charles Faulkner
Each year almost 100,000 people die worldwide due to asbestos related disease, which is more than the number of lives taken by skin cancer. Asbestos related diseases are now the greatest occupational killer in world history and the figures continue to rise.
In the UAE there is a commonly-held belief that asbestos is only a problem in Europe and North America, where the horror stories of exposure, litigation, compensation and death – not necessarily in that order – are well publicised. But, asbestos is not perceived as an issue for the Emirates.
As a construction risk management consultant, it initially shocked me to find out that there was not an absolute prohibition against the use of all Asbestos Containing Materials (ACMs) in the UAE as recommended by the World Health Organisation, especially as the UAE is at the forefront of many aspects of building design and new technology. It is still legally permitted to import asbestos for the manufacture and subsequent use of asbestos cement pipes for the purpose of water supply and sewerage.
Furthermore the use of asbestos board in the Emirates has only been banned since November 2006, shattering the myth that asbestos is only present within older buildings. In fact over 17,000 tonnes of asbestos was imported and consumed in the UAE in 2007* – its most evident utilisation being the construction industry.
Any work with ACMs can present a risk to human health, and it is well established that there is no known safe level of exposure to any type of asbestos fibre. Those most at risk from the harmful effects of asbestos include construction workers, particularly those involved in demolition and refurbishment activities and asbestos water pipe installation, and tradesmen such as electricians, plumbers and carpenters.
It is not uncommon for those unknowingly exposed to asbestos to spread the deadly fibre through contaminated equipment and clothing, leading to the so called “secondary exposure” of work colleagues, family and friends. The American and European press regularly report the tragic stories of families whose lives have been devastated by asbestos related deaths, usually in women and children, attributed to contaminated clothing and second hand asbestos exposure.
The only way to reduce the hazards of ACMs in the construction industry is to prohibit the use of ACMs (voluntarily and legislatively), use safer substitute materials, and proactively manage the remaining residual risk from each of the activities that are associated with asbestos exposure.
From a legal and ethical point of view, employers must understand that prevention to exposure is paramount and where this is not possible they must assess the work and provide their employees with the appropriate procedures, control measures, personal protective equipment and respiratory protective equipment. Current legislation must be adhered to, and a best practice guideline implemented.
WSP Environment and Energy in association with the non-profit health and safety organisation Buildsafe UAE will form a focus group this month to produce workable guidelines that will not only comply with both local and federal legislation but also develop industry health and safety best practice procedures. The procedures will detail the safe systems of work for asbestos related activities and then be distributed to Buildsafe UAE members.
Only by collectively acknowledging that there is a risk from ACMs in the UAE construction industry and addressing that risk can we play our part in putting an end to unnecessary asbestos related deaths.

by Charles Faulkner

Each year almost 100,000 people die worldwide due to asbestos related disease, which is more than the number of lives taken by skin cancer. Asbestos related diseases are now the greatest occupational killer in world history and the figures continue to rise. (Read more..)

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Building Failure

by Mohammed Azad Hossain

Building components tend to fail depending on materials, designs, method of construction, environmental conditions and the use to which the building is put. Substandard materials and design errors are major causes of component failure. (Read more..)

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