III. Technical similitudes and differences between the two skyscrapers

A) Techniques of construction and foundations :

FOR THE SHARD :

The "lift function" developed by KONE

The first challenge was to limit the ground movements during demolition and excavation. This was done by carrying out rigorous tests at the foundation stage because of the old ground used for the Shard.

-The area of the building site had to be secured by a wall of concrete secant  900mm and 1,500mm diameter piles.

- The next operation was to install 68 plunge piles. First, 1,800mm diameter piles were excavated up to 60m and then reinforcement cages were inserted and filled with concrete. When the concrete was dry they add piles (25m) to this.

-The 400mm ground floor was then cast, they began the excavation..

-The B2 slab, 350mm , they were using the 'slip form process during the construction of the core with concrete and a mould.

-Excavation continued until the B3 slab was cast, with thickness varying from 3m beneath the core, 4.5m in the lift pits and 1.5m for the perimeter. A thousand tonnes of reinforcement bar were used and 5,500 cubic metres of concrete were used during 36 hours to create the largest single pour in the UK.  

A short video about the Shard

As for The Freedom Tower :

The cornerstone was laid down on 4 July of 2004. During the 2006 summer, explosives were used to destroy the rest of the foundations of the first World Trade Center.

Then 310 Cubic meters of concrete were brought by 40 trucks to make the base foundations. The first girder of steel was put ( People could sign their names in it). They made a circle of girder of steel and poured the concrete into it. Later, they put another circle of girders of steel on the first one. They built concrete columns in the middle.

The workers built 2 cranes and they put them on a steel platform which grew up floor after floor to enable the workers to build the towers safely.

For the foundations 9400 tons of steel were used.

The spire weighs fifty tons and is 408-foot tall. It was transfered into place as soon as it arrived. As for the Freedom Towers some radio antenna  was installed on the top of the spire to conduct radio signals. Usually, the height of a tall building is measured to the top of its spire, but not to the top of its antenna but in the case of the One World Trade Center the maximum height is calculated from its base to the top of the antenna.

A short video about theOne world trade center

In this video we can see a timelapse of the construction of the Freedom Tower from A to Z.

We can see the foundation, the walls, the workers etc.

B) Structures and materials of the towers :

Materials :

Glass :

Glass

The most common and the most consensual definition of glass is that of Jerzy Zarzycki " glass is a robust non-lens presenting the phenomenon of glassy transitions ", completed also by J.Barton and C.Guillemet as regards the glazing: a glazing plan subjected to an effort of flexion (effect of the wind, the snow) has a face in compression and a face in extension.
The constraint in the break is of the order of:
- 4 dan / mm ² ( 40 Mpa) for an annealed roaming glazing.
- 12 in 20 dan / mm ² (120 to 200 Mpa) for a tempered glazing
The high value of the fold resistance of the toughened glass is due to the fact that the treatment of tempering, be it either thermal or chemical, compresse s the faces of the glazing .

Concrete :

Concrete

Majorities :

The concrete used in the building, as well as in public works in general includes several categories.

Generally the concrete can be classified in three groups (NF standard IN 206-1 articles 3.1.7 - 3.1.9), according to its density:
 
Basic concrete: Between 2 000 and 2 600 kg / m3;

Heavy concrete: > 2 600 kg / m3;

Light concrete: Between 800 and 2 000 kg / m3.

The most common concrete can also be classified according to the nature of its dispositions (binders):

Concrete of cement;Concrete  silicate (Lime);

Concrete of gypsum ;

Concrete asphalts.
 
Concrete can vary according to the nature of aggregates, additives, colouring agents, surface treatments and can so adapt to the requirements of every realization, thanks to its proprieties and aspect.
 
Basic concretes are most used for building and public work. They present a 2 300 kg / m3 density approximately. They can be armed or not, and when they are requested in flexion, prestressed.


Various calculations bound to the resistance of the concrete:


Fresh concrete: measure (Control of the actual dosages), plasticity measure(control of the consistency) measure content in air(sight) (control of the space)

Manufacturing test tube (control of ß means)

Hardened concrete: Measure ß cube, evolution scléromètre, evolution try(essay) frost(gel), permeability, special tries(essays)...


Resistance :



Numerous tests and studies concern the durability of concretes. In particular, the characterization of materials by acoustic ultrasounds enables to detect structural changes in the material.


What affects the concrete most is the carbonation which is a chemical reaction between Co2 the steel of the structure anymore afterwards, which affects armature and corrupts the mechanical resistance

Steel :

Majorities :

Steel 

Steel is elaborated to resist mechanical or chemical constraints, thus chemical elements can be added to its composition, besides carbon. These elements-- manganese ( Mn), chromium ( Cr), nickel (Nor), molybdenum (Mb), mainly -- are called elements of addition.
Steel is very interesting when it is a question of being worked because it deforms rather easily: 
resistance in the elastic deformation: module of elasticity E;
Hardness, resistance in the irreversible deformation, in the break: elastic limit Re, minimal resistance in the break Rm, the hardness H;
Shock resistance: impact strength K.

Various types of steels :

There are various types of steel that depend especially on the country where they are made: non-allied steels of general use (construction); special non-allied steels, for heat treatment, moldable, weldable, forgeable low alloy steels, for tempering and returned; the elements of alloy favor the hardenability and enale to have interesting structures.

 

These are the three main materials of the modern architecture. Before, the buildings were principally made of wood or stones.

C) Energy and Sustainable Development :

       These towers are recent and with the newly developping interest of the people in the protection of environment, new standards are implemented in the building of new skyscrapers.

      -Thus in the case of The Freedom Tower and The Shard, the same standards and the same numbers have been applied, it is due to the fact that the architecs used the same standards and they inspired each other. The architects focused on environement-friendly and energy saving points:

     -The buildings are made with glass facades, thus providing a big source of natural light. Besides, 90% of the light inside the towers is provided by the sun, there is therefore almost no need to lighting. In the case of the Shard, Renzo Piano uses a system of blinds to retain heat at night and let the light pass through the day.

        -The skyscraper The One World Trade Center, is equipped with an energy saving system which enables it to reduceits energy needs by 21% (for example thanks to low consumption bulbs).

In the Freedom Tower and also in the Shard 100% of the rainwater is collected via a rainwater collecting system  named:"redundant water tanks". It enables to feed the sprinkler system. It's efficient.
Here we can see a sprinkler system. The Sprinkler system  aims at using rain water in the fireproof system and for daily use: the water falls into gutters which carry it into pipes which filter it and take it to other pipes to feed some systems like the fire alarms, the toilets, the bathrooms etc... )

 Example of a prinkler  system.

      -The building is partially powered by 12 hydrogen fuel cells. They aims at generating 4.8 megawatts of energy to the tower and other towers of the New World Trade Center.  Here is a diagram of the batteries to show the operation :

Hydrogen fuel cell

In short, Hydrogen passes from the top to the bottom on the left of the fuel cell and this fuel passes trough Anode, PEM and Cathode atoms to make an electric current.

Note that the cement used for the construction of the towers emit less CO2 than a basic cement and 95% of the materials used in the construction of the building are recycled. The numbers vary somehow on the tower.

The Shard in its design includes a gas engine, and a central heating system that reduces by 10% the need for electricity and gas.

Finally, on the set of two skyscrapers, the energy consumed is 30% renewable energy, like most of the new towers.

Today and since few years, people have finally undertood that the world needs to save more energy. So a lot of new standards are adopted all over the world. For example, the two towers we studied use the same standards that is why we find the same reduced consumption of energy. Before that, the architect didn't really care about the environment and built towers without any standard.

D) Security of the towers :

 As The Freedom Tower ( Also called :" The One World Trade Center ) was built on the site of the former World Trade Center that was destroyed due to a terrorist attack( Cf :   ), that is why, many measures were taken during the construction and that was also true for the Shard. So both towers are made with a huge pillar of reinforced concrete where emergency stairs are located and  reserved for firefighters. The stairwells are pressurized with anti-fire systems. The two towers are equipped with systems of air filtration to "cleanse" the towers in case of chemical attacks. Both towers mainly use the same way to securise the first twenty to thirty floors.

The two towers were built in a period where the fear of terrorism was high.

The 1WTC reinforced floors

For the protection of the first floors, the architect of the towers used layers of prismatic glass (glass with properties common to the prism), aluminum and reinforced concrete, these materials are used to counter any explosion of vehicule or something like that.

Example of a part to a water walls

In the case of the One World Trade Centre the underground car parks are equipped with metal detectors to scan all incoming vehicules.

The top and the bottom of the 1WTC are equipped with redundant water tanks to feed sprinkler systems and to protect it from flood.

The visitors of the 1WTC building may pass through airport-style metal detectors and X-ray machines. Every bag, briefcase, delivered parcel is screened and before that visitors walk through a garden which is watched by some 400 cameras.

The elevators are also subject to a very important safety.

A worker, who was working on them said :

Basically, the elevator operation—the individual cabs—are controlled by software that determines very quickly—within seconds—which cab is most efficient to serve a particular call based on other calls that have been registered by the system at the turnstiles. So really it's the turnstile that sends the signal to the destination dispatch software and that then manages—digitally-the elevator that is assigned to a group of people or you individually, depending on your destination. That maximizes the service capacity of the elevators and minimizes the use of electricity and power so that elevators are not dispatched at random or by the demand of a single caller

As we can see the buildings of today are subjet to a lot of security systems whereas in older buildings security was not so much important. It is obviously a consequence of terrorism.