Analysis and Description

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

What are the relative magnitudes of the total Dead, Live and Horizontal loads and what implications do these have for the structure of the building?

 

Dead Load =1,811,687,392 LB. To calculate the dead load was found the weights of all materials used in this building, we could find mostly of the materials used: Concrete, Steel Reinforcement, and Glass. Although the Embossed Stainless Steel was not found, we assumed that was a gauge 16 (the most common used gauge). That said the value of Dead Load =1,811,687,392 LB it is very close to the real value.

 

Live Load =238,800,000 LB. To calculate this load, was used the areas that compose the building, the Commercial Floor Area, and Residential Floor Area. The calculations were based in the assignment given by professor Mitchel, using: 40 PSF for residential areas and 80 PSF for commercial areas.

 

Horizontal Load =8,880,000 LB. To calculate this load we performed an estimation to determine the area of one lateral face on the building. To do so, an approximation was made assuming 1/3 of the total of glass utilized corresponds to each lateral face (370,000 SF), also the maximum wind speed used in the calculation was found from local weather records and multiplied by 2 for a conservative result (24 mph Is this the same wind speed number used in the calculation?).

 

 

After getting information directly of the website about the construction of Burj Khalifa, we were able to understand more about the structural system within the building. The spiraling “Y” shaped plan was used to reinforce the structural core of Burj Khalifa.  This design enormously reduce the wind forces on the tower of the building, and also kept the structure simple and fostered constructability. The structural system used in this building can be described as a “buttressed core”, and it consists in a high performance concrete wall construction. Each of the wings buttress the others via a six-sided central core, or hexagonal hub. This central core provides the torsional resistance of the structure, similar to a closed pipe or axle. Corridor walls extend from the central core to near the end of each wing, terminating in thickened hammer head walls. These corridor walls and hammerhead walls behave similar to the webs and flanges of a beam to resist the wind shears and moments. Perimeter columns and flat plate floor construction complete the system. At mechanical floors, outrigger walls are provided to link the perimeter columns to the interior wall system, allowing the perimeter columns to participate in the lateral load resistance of the structure; hence, all of the vertical concrete is utilized to support both gravity and lateral loads. The result is a tower that is extremely stiff laterally and torsionally. It is also a very efficient structure in that the gravity load resisting system has been utilized so as to maximize its use in resisting lateral loads.

 

As the building spirals in height, the wings set back to provide many different floor plates. The setbacks are organized with the tower’s grid, such that the building stepping is accomplished by aligning columns above with walls below to provide a smooth load path. As such, the tower does not contain any structural transfers. These setbacks also have the advantage of providing a different width to the tower for each differing floor plate. This stepping and shaping of the tower has the effect of “confusing the wind”: wind vortices never get organized over the height of the building because at each new tier the wind encounters a different building shape.

 

 

Looking at the foundation load what do you think it means for the type of foundation to be used, and what additional information would you need?

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Foundation Load Calculation= 25,631 LB/SF

Horizontal Load =8,880,000 LB

 

The horizontal load is of great relevance in a choice of the foundation. If this force becomes an issue, you can have your building being supported by a large slab or a mat, which spans a big distance, or can have a deep anchor. As the building is too tall the latter option could not be used, it would require a great depth to maintain the Burj Khalifa stable. The only option was a slab/ mat.

 

The Burj Khalifa is supported by a big reinforced concrete mat, which is in turn supported by bored reinforced concrete piles. Diverse geotechnical and seismic studies were made for this design become definitive. The mat is 3.7 meters thick, and was constructed in four separate pours totaling 12,500 cubic meters of concrete. The 1.5 meter diameter x 43 meter long piles represent the largest and longest piles conventionally available in the region. The foundation was made using a high density, low permeability concrete, also it was used a cathodic protection system under the mat, to reduce corrosive affects that the substructures are exposed to in the local ground water.

 

Would this be an easy or a difficult building for which to develop the structural calculations (assuming you'd already completed the senior year structural sequence)? Why?

 

 

As this is the biggest building in the world of course it had diverse difficulties in its structural calculations. This megastructure is a way to complex to be calculated, it definitely requires more experience and insight than a college degree could supply. Some of the challenges during the structural calculations were for example:

 

 

Wind:

 

As with any tall building, wind plays a major factor in structural calculation process.  The design team of Burj Khalifa conducted over 40 wind tunnel tests to determine the amount of stress that the wind would place on the building. Wind force on the tower was one of the critical stressors considered in the design and features implemented into the tower’s structure. The overall shape of the tower if looking from above resembles the letter “Y”; this three-legged structure was engineer’s solution for the intense wind conditions the tower would face.

 

 

THE STACK EFFECT

 

The stack effect is a common problem in most high rise buildings. The stack effect is the movement of air into and out of buildings. Commonly, the warmer air is lighter and less dense than cold air. Therefore the warm air will rise to the top of the building while the cold air will try to fill the cracks in the bottom of the building. The problem this causes is that the pressure in the bottom can build up and can cause more cracking. This could be disastrous to a building as tall as Burj Khalifa. Cracks in the foundation could cause complete structural failure. 

 

Also many other problems were calculated by the engineers making this structure more complex and difficult to be made such as natural Disasters, earthquakes and tornadoes. This is for sure a complex structure to be calculated.