Advancements in Steel and Concrete Manufacture
Figure 1 - Mode Gakuen Cocoon Tower, from Flickr
Technical advancements in the concrete and steel industry have greatly increased the production rate, quality and versatility of these materials over the past century. Factors including pressures from competing materials in the industry, environmental concerns, cost effectivity and structural performance act as a driving force for these advancements to occur.
Figure 2 - First floor plan, Mode Gakuen Cocoon Tower, from CTBUH
Diagrid (DG) systems and self-compacting concrete (SCC) are more recently developed construction methods that overcome many of the limitations the original materials could not. Diagrid systems are commonly used in high rise structures like skyscrapers.
Tokyo’s ‘Mode Gakuen Cocoon Tower’ uses DG systems for both the high-rise skyscraper and low-rise auditorium. With 50 storeys above ground and 3 below, Tange Associates designed this educational building to accommodate 10,000 students. The first-floor plan provides 3 lecture halls and student lounges, surrounding the inner core of the building.
The tower’s complex, tall design, situated in a highly seismic country proved a challenging project for Arup Japan. The complex curved envelope was made possible by the unique compilation of 3 elliptical DG frames and inner core frame. The elliptical frames are positioned at the perimeter of the building allowing a wide stance for efficient transfer of lateral force and earthquake overturning moments. Each storey is a set height to create a clean connection to the proceeding storey’s DG frame. Alongside the installed cogeneration system, the elliptic shape allows for an even distribution of natural light as well as aerodynamic wind dispersion. This intelligent design is in response to the environment reducing unnecessary greenhouse gas emission and heat radiation. Strong winds need to be further dissipated evenly to avoid structural damage.
A “diagonal” “grid” system acts as a form of bracing while eliminating the need for vertical columns. Isotropic materials, like steel are often favoured for this construction method as the bracing members are used to resist both compression and tension. The structural stability of this is made possible by the triangular configuration of the grid. It enables the effective distribution of dead loads on top of the lateral load through the frame.
Regarding construction, the core frame is constructed primarily. This requires precision and accuracy before being welded into place. Next the DG members are assembled into place, using temporary works to form initial connections. Floor beams are then erected and aligned, finally, permanent bolts replace the temporary works and the DG structure is welded together.
Figure 3 - Lincoln City & Country Museum interior, from Panter Hudspith
In contrast SCC is often used for low-rise buildings. Developed in Japan in the 1980’s, SCC is a high strength concrete. It has a much higher cement content than traditional concrete, through the addition of a water-reducing admixture. The electrostatically charged cement particles are neutralised by the admixture, thereby reducing friction allowing greater flow between the particles, avoiding the negative impacts of adding excess water to the mixture. Superplasticisers are now used for higher efficiency, causing repulsion between the cement particles. To prevent instability a viscosity modifying agent is added to hold the structure well throughout its lifetime.
Benefits of this construction method include faster and safer on-site construction as no vibration is required, increased workability as the concrete mix flows easily around heavy, complex reinforcements, a higher quality finish and reduced labour and plant costs during construction which usually offsets the increased price of SCC to traditional concrete.
SCC is a self-levelling material making it perfect for the construction of sloping roof slabs exemplified in the ‘City and County Museum’ in Lincoln. The roofs used complicated bulky reinforcements that most concretes would fail to produce a perfect finish over, SCC however presented a consistent high-quality finish either side of each slab. The high fluidity of SCC makes it excellent for detailed design. Boardmark effects and textures are achieved throughout the museum mimicking the use of different materials. Brick texture can be seen in the interior of the museum, as shown in Figure 3.
Concrete and steel have developed into uniquely useful materials over the past century, exhibiting properties suitable for a variety of different types of construction. Technical advancements exemplify these changes and have allowed many of the ground-breaking structures standing today to be erected. Perhaps the most structurally sound designs incorporate the use of both these materials. Neither material has reached it full capability, however, environmental sustainability has become a priority in recent years forcing the high embodied energy and carbon of concrete and steel to be taken more into consideration. For this reason current research is focused on increasing the efficiency of timber and other more eco-friendly materials. Nevertheless, due to the economic sustainability of concrete and steel, further advancements have yet to come.
Bibliography
CTBUH, Case Study: Mode Gakuen Cocoon Tower, CTBUH Journal, 2009, pp. 16-19
Crompton S., Advances In Concrete Technology, ICT, December 2010, pp. 16-20
Shri Purvansh Shah B., Advancements in Concrete Technology, AJER, Vol. 4, 2015, pp. 36-40
Fu F., Design and Analysis of Tall and Complex Structures, February 2018, chpt. 2.3, 2.4 & 5.4
Szolomicki J. and Golasz-Szolomicka H., Technological Advances and Trends in Modern High-Rise Buildings, August 2019
Rich, D. et al., Optimising construction with self-compacting concrete. Proceedings of the Institution of Civil Engineers - Construction Materials 170 (2), 2017, pp. 104-114
ConcreteCentre, Self-Compacting Concrete, MPA
