The level of high rise construction we see today is a result of series of construction process and development carried throughout years. Initially, it was heavy and sturdy structures, which with time have changed to lightweight structures as we see today.
the high-rise buildings we see presently and those undergoing construction is the fourth generation of high rise buildings. The high-rise building in the fourth generation have strong emphasis building safety and protection along with the life safety factors.
We will see through the different generation of high rise building construction briefly in the coming section.
High-Rise Building Construction in First Generation
The high-rise building that were constructed during the first generation take walls that are heavy in weight. The exterior wall was constructed by means of stones or bricks.
When considering the thickness of the wall, they were given in a larger thickness. This is to ensure that the complete load over the building is carried properly by the walls.
An example of first generation high rise building is the Monadnock Building in Chicago. This was built from 1889 to 1891. The building is 16 stored and is considered as the tallest load bearing structure in the world. The walls at the base have a thickness of 6 feet. This thickness was a way to carry the loads from the upper floors.
Most of the authorities in the first generation came up with a recommendation that a thickness equal to 12 feet is necessary to support the load from the first story. This thickness value was added with four inches with each increase of story.
This hence limited the construction of stories greater than 10. The Monadnock Building mentioned above was an exception at that period.
Many first-generation high-rise building were characterized by their facades made from cast iron. Some of the buildings has columns made from cast iron but were unprotected. Even the wrought iron columns and steel beams were employed.
Most of the floor during the period where made from wood. This was a weak link during a fire attack. This had resulted in numerous building collapse.
Vertical openings that were unprotected was a common construction practice in the high-rise building construction. Everywhere in a high rise building the use of open stairways, elevator shafts and the light wells were common. These features are restricted in the modern high-rise construction of buildings.
Fig.1: Monadnock Building in Chicago
Second Generation of High-Rise Building Construction
The high-rise construction in second generation can also be called as pre-world war II High rise construction. This era has given rise to the development of the protected steel frame structures.
The following were the features that characterized the high-rise building in this generation:
- Assembly of fire resistance
- Shaft enclosures
- Use of non-combustible materials
Masonry enclosure were provided for all kind of metal structural members. This was also provided for vertical shafts that was enclosed by masonry and tiles.
The floor construction was carried out by having concrete floors that were constructed on brick or arches of hollow tile. The floor areas were subdivided. The use of combustible materials was limited in the construction as a step to improve fire resistance.
The buildings constructed in the Pre-world war II were considered to be most excellent buildings. In order to have closer access to the natural ventilation and lighting, the building have floor spaces that were small. It was common in the building.
More open floor areas were derived in the modern high-rise buildings with the invention of central heating system, air conditioning systems (HVAC), fluorescent lighting systems etc.
The high-rise building in this period had floors that were well segregated fire area. The Empire State building in New York is the best example of second generation high rise building construction.
Fig.2: The Empire State building in New York
Third Generation High Rise Building Construction
The third-generation construction of high rise buildings are known as post-world War II high rise construction. This have resulted in the evolution of much more lighter construction methods and materials.
This era was the rise of steel frame type structure with core, or in other words, center core construction technique. A common exterior wall surrounded the inner core structure.
The exterior wall is either glass or some sort of stone material. The exterior steel frame has curtain wall that are attached to it by fastening. The fastening is done such a way that a gap exists between the structural frame and the curtain walls.
Within this gap, a fire stopping material is placed or a kind of vertical fire extension have chances to occur. This is a major problem behind fires in major high rise buildings.
The method and type of stopping used are similar to that used to fill the gap as mentioned above, is very important. Many buildings have used friction fire stopping material like rock wool to be placed in the curtain wall gap. This is held in place by means of friction.
When the material becomes wet due to any reason of rain or air conditioning water or any other reason, this material absorbs the water and become heavy. Once it become too heavy it falls out. Such situation makes the curtain wall gap unprotected. This creates an open path for the spreading of vertical fire.
This generation makes use of central heating as well as ventilation system (air conditioning etc.) inside the building very significantly. This is more related to the air movement and the extension of smoke and fire related issues. These third-generation buildings can be defined as windowless as the common HVAC system is used.
The occupants faced the problem of egress due to the lack of fire towers and less remote scissor stairs. The modern high rise construction has the stair in the core structure that they no longer will remain remote for access. As these cores have most of the stair arrangement, it was observed that they were more contaminated by the smoke and product of combustion when a chance of serious fire issue is commenced.
Pressurization for the stairwells were provided by many of the modern high rises, but they were futile. During a mass evacuation, the pressurization to the stair well become of no use as there is multiple opening of door quickly.
Many mega high-rise structures followed unique construction features to reach the desired heights. The Seas Tower and the former World Trade Center used the tubular construction design.
The tubular structural design makes use of high load bearing members to bound and surround the buildings. The interior members have to take less load. The sections and designs are hence placed based on this criteria in a tubular building construction. In order to support the floor, truss combination is used.
Fig.3: Seas Tower in Chicago
Fourth Generation of High Rise Construction
This generation of high rise building construction have begun and are on its course. This is also called as the post-9/11 high rise construction. This generation structures make us see the resurrection of many features that are seen in the second generation.
Considering all the limitation of past generation construction, the newer high-rise construction considers a means of egress through a stairwell. This also consider a means for assisting the fire departments by means of logistical operations.
For examples, the use of elevators carried in a heavy enclosure which is resistant to fire, explosion, collapse and smoke.
These robust construction techniques come out to be costly. But the concern about fire and life safety compromise with the cost.
Fig.4: Burj Khalifa, Dubai – Fourth Generation High Rise Construction