Capital Gate, Abu Dhabi.

The Capital Gate building in the desert kingdom's capital, Abu Dhabi, has been certified by Guinness
World Records as the "World's Furthest Leaning Man-made Tower."
The 35-story Abu Dhabi building has an 18-degree slope, compared with four degrees for the freestanding bell tower.


But unlike the tower in Pisa, the Capital Gate building has been deliberately engineered to slant.




STRUCTURE
 
From its foundations right through its pinnacle, Capital Gate is a unique building and among the most technically challenging engineering projects in the world. Some key features stand out amongst others:



It’s gravity-defying 18 degree lean, widely believed to be the most inclined in the world The continuous twist of its form which ensures that the tower looks different from every angle The unique nature of the floor plate, each floor is uniqueThe foundation contains an incredibly dense  mesh of reinforced steel that sits above 490 piles, drilled 30 meters underground to accommodate gravitational, wind and seismic pressures.

The core of the building is a pre-cambered, ‘slanting’ core that pulls in the opposite direction to the lean.
 It straightens as the building grows, pulled into a vertical position by the change in the centre of gravity
of the building as concrete was poured onto subsequent floors.

The floor plates up to the 12th level are stacked vertically over one another. Between levels 12th and 29th the floor  plates stagger over each other, in relation to the lean and twist of the shell, by between 800 to 1400mm and then back to 900mm. Between the 29th storey and the top storey, the range is between 900 and 300mm in relation to the line of the façade.

Design


Nothing is standard about Capital Gate. Each room is different. Each pane of glass is different and every angle is different. It was designed to provide no symmetry so it inspires those within and outside the tower. Capital Gate was designed to be the most recognisable icon of the ADNEC/Capital Centre development. Further, it was designed to blend seamlessly with the National Day Grandstand, breathing new life into this historic  landmark for the UAE.

Site Investigations

The type of foundation to be adopted for a building depends upon the load to be transmitted and the bearing capacity of the soil. When the site with a good bearing capacity of reasonable depth is available it is not difficult to design on the type of foundation. On the other hand on certain soil a close investigation is necessary soils of low bearing capacity of bearing depends. Costal areas where the upper stratum is sand and water level is high are cases where investigation is necessary.

 For a large building project such a multi-story structure the site exploration may be both extensive and costly and may include on of the following

1. Trial pits
2. Bore holes
3. Load test

  Trial Pit

A pit dug to a depth on type of foundation expected usually going up to about 3m and rarely to 6m. The pit should be large enough accommodate. A trial pit does exposes a section through the ground revealing for examinations the character and depth of stratum. Sample of soil for caboratory  testing can be readily obtain. A pit also gives the contractor valuable data regarding the cost of excavation of foundations such as foundation. Whether timbering is necessary and whether pumping of underground water is necessary for a building covering a large area four trail pits may be required one near each corners. These pits should not be dug too close to be the proposed building as they would be a source of weakness to the foundation it should be fill with concrete.

Bore hole    

As much work is involve in digging trail pits a simpler method is the use of bore holes. These are used for raising samples of soil for examination. A simple tool for mating bore hole is the Augur which may be operated manually or mechanically.

Load Test

In this method a weight of known cross sectional area dropped from known height. The depth of impression on the soil by the drop of the weight is noted for performing this experiment a pit of the required depth is excavated.

  The depth of pit will be equal to depth of the foundation. After excavating the pit is cleaned and leveled but should not be computed.

The concrete cube block is them drop very gently without impact from the specified height and the impression is noted down. The experiment is repeated at  last 5 times in different pits or along the foundation trench at different poles and the average depth of impression noted. The bearing capacity is worked out as follows.

           Let R is equal to resistance of soil that is resistance to the penetration or resistance to settlement.

H – height through which the weight is dropped

W – weight

D – depth of impression

A – Area of cross section of the weight.

Structural Steel Fire Protection

Fire Resistance Rating for loadbearing (structural) elements is defined as: “the ability of the structural element to withstand the effects of a defined fire (e.g. hydrocarbon time/ temperature profile) for a specified time without loss of the loadbearing function of structural members.” Fire Resistance Rating for loadbearing elements is described by defining the following:

the structural element being considered

 duration of loadbearing ability

 fire load

 restricted critical core temperature

Therefore, every loadbearing member shall be suitably fire protected to meet the requirements of the fire resistance rating. 

Provisional sums

Provisional sums are included in bills of quantities for items of work which cannot be fully described or measured in accordance with the rules of the method of measurement at the time of tender. where these details cannot be supplied,the work is classified as undefined and the contractor will be deemed not to have made any allowance in programming,planing and pricing preliminaries

The following information must be provided with the provisional sum.

The nature of the work

How and where it is to be fixed

Quantities showing the scope and extent of the work

Limitations on method. Sequence and timing.

Example of provisional sum for works.

Provide Provisional sum for construction management services (details of services to be provided by the contractor should be in accordance with minimum requirements specified in the conditions of tender)

Provide  Provisional sum for giving notices, obtaining permits & the payment of fees,deposits (excluding for temporary works & connections), connecting charges incompliance with the requirement of governmental, local authority or other public authorities. The necessary approvals shall be obtained by the Contractor.

Provide Provisional sum for telephone & other services required for carrying out of the works including temporary telephone facility to the Engineer's office.

Provide Provisional sum for Name Board.

Provide Provisional Sum for office accommodation and separate sanitary accommodation including facilities specified in the tender for the use of the Engineer.

Provide Provisional sum for Temporary work and encountered during the construction period and as decided by the Engineer.

Tunnel Ventilation Systems Moving the Air Efficiently

Ventilation Management in long tunnels is the most important requirement not only for the working of machines but also for the sustenance of the personnel. Poisonous gases are generated by blasts in tunnel, exhaust of diesel operated machines, Carbon Dioxide generated by human breathing and besides, a tunnel may cut through strata with trapped foul poisonous gases which would be released on excavation. Arrangement for speedy evacuation of such gases to avoid serious mishaps and sufficient ventilation to counter the effects of heat released by the rocks, exhaust gases, electrical transformers and cables is absolutely necessary. All these factors demand highest standard in design and  performance of the ventilation system. Any shortcoming in the ventilation system can be disastrous and produce long term demoralizing effect on workmen subjected to suffocation resulting in inordinate delay in project execution, ultimately causing huge financial losses. Therefore, ventilation management is the most important aspect of underground  works during construction phase. 

An effective Ventilation System has to ensure the following :

• Air quality 
• Air quantity at the right place
• High reliability  
• Environment   
• Economy

Ventilation theory

• Effective ventilation is expensive 

• Ineffective ventilation, much more expensive
• Expenses include both capital cost and operation cost
• Operation cost is often much higher than capital cost

The quantity of air to be moved is obviously the first choice. At the time of deciding this aspect, one should also consider acceptable tolerances. In general, one may design ventilation for a certain number of air changes at a given situation with considerable range.  It is best to assess the resistance of the air system on the assumption that air of standard density is being handled (i.e. 0.0764 lb. per cu. ft., UK)  Usually, a Return Velocity between 0.3 M/Sec to 0.6 M/Sec is maintained, depending on the length and cross section of the tunnel.

A ventilation system primarily consists of the following :

• A suitable fan with Silencer & Accessories.
• Electrical equipments like Frequency Converter and Control Panel.
• Ducting of correct size and type with necessary accessories for installation.

The Masterbuilder - May 2010