Tuesday, June 15, 2021

Cover Story

Up, Above & Beyond!

 

Fast paced urbanization has resulted in over-crowded urban spaces, which has ultimately resulted in the vertical expansion of the building in the urban towns of the world, which we fondly call – Skyscrapers or Tall Buildings. While the looks of them might be fascinating for all, but what goes behind developing them is nothing short of an architect’s nightmare and years of dedication. With the overriding factors such as wind, shape and sustainability, tall buildings of tomorrow are bound to be the FUTURE of the URBAN spaces! Married by technological and material innovations, these buildings or rather super structures reflect draftsmen’s vision and their might in making it a reality! writes PRERNA SHARMA

 

A new generation of landmark mega-towers and super-slender buildings is rising across the globe.The pandemic has put the pause button on a lot of new construction in 2020, including that of the tallest buildings. According to the Council on Tall Buildings and Urban Habitat (CTBUH), only 106 buildings of 200 meters (656 feet) or more were built on the planet last year, the fewest since 2014.

 

One of the famous high-rise builders, Kamran Moazami, General Director, Property and Buildings, WSP UK, has aptly said, “The art of building high isn’t only about design, but about the efficiency of material, speed of construction, maximum achievable space, seamless coordination of engineering and architecture, thereby achieving optimal cost and performance as well as an iconic and elegant building.”

 

The passion, obsession and necessity of building supertall and mega tall structures continues to challenge engineers and architects to reach new heights and ‘go where no man has gone before’.Professor Kourosh Kayvani, one of Australasia’s leading structural engineers, highlights that the increasing rate of urbanization in recent decades has seen an accelerated trend in the construction of high-rise and tall buildings worldwide, particularly in the emerging economies of the world. A fundamental economic driver for the growth of tall (particularly residential) buildings is the scarcity of land in the densely urbanized parts of the world. The competition for constructing the tallest building in a city, country, region or the world has acted as another driver for the growth of tall buildings worldwide. In the past two decades or so, the race for constructing the tallest has been extended to include the contest for constructing the most iconic and spectacular high-rise buildings often characterized by complex geometries and leaning/twisting forms.

 

From a structural engineering point of view, as high-rise buildings get taller and slender, their design becomes increasingly (and fundamentally) influenced by specific behavioral factors that are much less significant for shorter buildings. These factors include the dynamic response of tall buildings to wind loads both in the ultimate and serviceability limit states, and the differential axial shortenings of the vertical elements of tall buildings under gravity load effects. As far as these factors are concerned, the absolute height of the building is not necessarily the best measure for “tall behavior”. In particular, the magnitude of the dynamic wind response is more significantly influenced by the overall slenderness of the building and the natural frequencies of its fundamental modes (i.e., the first two sway modes about the principal axes of the building and its first torsional mode) than its absolute height.

 

The overall slenderness of a tall building is usually defined by its “height-to-base ratio”, being the height of the building divided by its narrowest plan dimension. Essentially, higher height-to-base ratios and lower natural frequencies increase the dynamic component of the response to wind. A building with a height-to-base ratio of more than around 5 and/or a fundamental natural frequency of less than approximately 0.2 Hz is expected to respond to wind loads in a significantly dynamic way (where building inertial effects are significant) or even in a potentially aero-elastic fashion (where building motion interacts with and influences the wind flow).

 

 

Battling Building Sway

AEC professionals calculate estimated building sway from wind as a function of height and incorporate that into the plan. For the Burj Khalifa, two to four meters of movement was designed into the structure. Buildings are usually over-designed to withstand 500- to 1,000-year weather events. Aside from noise, the biggest problem from building sway is occupant comfort. Humans can detect slight movements that pose no threat to the building. A light breeze at ground level may feel like a hurricane 150 floors above, whipping the building enough to make people feel ill. There are two basic approaches to battling the wind: dampen it or confuse it. The other approach is not to fight the wind but confuse or redirect it. Buildings incorporate aerodynamic features to ensure the wind can build up dangerous levels of pressure. The main enemy is vortex shedding when wind passes the sharp edges of buildings. This condition creates eddies of air that batter the structure in unpredictable ways. Air currents can tune into the building’s resonant frequency leading to vibrations or cyclic swaying that can worsen until the structure collapses. Architects are learning to direct the wind through and around the building use channels, fins and soft curves. Slavish devotion to symmetry could lead to catastrophic consequences.

 

 

When designing a building, the Mean, Background, and Resonant wind loads need to be considered:

Mean wind load: Steady drag and lift forces due to dynamic pressures arising from the mean wind speed.

Background wind load: Non-steady drag/lift forces due to additional dynamic pressures arising from gust wind speed.

Resonant wind load: Transient inertial forces generated by the dynamic responses of the structure to wind (both direct and interference effects), which is negligible for low-rise buildings but dominant in tall buildings.

 

 

Controlling wind motion or acceleration to acceptable levels for human comfort is often a critical aspect of tall building design. As is the case with other resonant dynamic effects, increasing damping is often the most effective method in controlling wind motions. However, the issue is that a reliable level of damping in buildings is often quite limited (i.e. equal or less than 1% of critical damping). Therefore, additional dampers would often be required. A common approach is to add tuned mass dampers (TMDs) at or near the top of the tall building. Many modern tall buildings incorporate a tuned mass dampener, a counterweight that helps balance the force of movement on the building’s exterior. For example, the Taipei 101 tower in Taiwan houses a 730-spherical pendulum that sways back and forth, balancing the force of the wind from storms and typhoons.

 

 

 

Seismic engineering of high-rise buildings

The prime objective of seismic design is clearly to provide life safety. The common practice to achieve economic and safe design is to dissipate seismic energy in the structure during an earthquake by forming controlled and stable “damages” in the structure (in the so called “plastic hinges”).To ensure that damage is distributed rather uniformly among floors and that the gravity load path is not compromised, engineers often use what is called a “strong column/weak beam” design philosophy, which stipulates that the columns of a joint needs to be at least 20% stronger than the beams framing the same joint. While this philosophy provides life safety, the implication of widespread plastic hinges is extensive damage throughout the structure to the extent that the building might be damaged beyond repair due to an earthquake.

 

According to a research paper,‘Technological Advances and Trends in Modern High-Rise Buildings’ by Jerzy Szolomicki,Faculty of Civil Engineering, Wroclaw University of Science and Technology, Poland and Hanna Golasz-Szolomicka, Faculty of Architecture, Wroclaw University of Science and Technology, the least-resistant construction for an earthquake is a skyscraper, which is a certain paradox in comparison with their number in the world. The most modern skyscrapers in Tokyo are able to withstand earthquakes of over seven degrees on the Richter scale. Of course, more forces affect a building with a larger earthquake, and its construction therefore experiences larger displacements. A building’s response to earthquakes is vibrations in the form of sinusoidal motion. In order to counteract both these forces and the impact of wind, apart from a rigid construction, very advanced technologies of damping devices are used. For example, the foundations of these buildings (Maison Hermes Tokyo) are mounted with a system of spring or elastomer vibration dampers, due to which tectonic movements affect the upper part of the building to a lesser extent. In addition, as presented by the characteristics of high-rise buildings, viscous oil dampers (Mode Gakuen Cocoon), anti-buckling steel stabilizers (Midtown Tower, Roppongi Hills, Kabukiza Tower) and tuned mass dampers (Tokyo Tree Tower) are used in various levels of these buildings. When using all these supporting elements, it is most important that the location of the center of gravity of the building does not change during earthquakes.

 

A very important aspect associated with the technological development of high-rise buildings is the safety of their users. One World Trade Center in New York is the most advanced building in the world when it comes to security technology, setting new standards for the design of high-rise buildings.

 

 

Rethinking Structural Design

The shape of today’s skyscraper is particularly notable. The advances in technology and materials have allowed erection not only of very high buildings but also allowed them to take on new and exciting shapes. Today high-rise buildings can twist, lean and turn back on themselves. These shapes are chosen for visual effect, but occasionally they contribute to minimizing wind loads by improving a building’s aerodynamic properties.

 

As building and material science advanced, tall buildings were designed on a tube system rather than a rectangular design of the earliest skyscrapers. The tube works well to a point – the width and depth must rise in proportion with the height. The Burj Khalifa used a new approach — the buttressed core. A central hexagonal concrete core is supported by three triangular buttresses, like the fins on a rocket.

 

Designed by Architect Adrian Smith, who also led design on the Burj Khalifa, the tower is supported by a central core, which is braced by 2-foot-thick concrete walls that line the double-loaded corridors in each of the three wings in the tripodal structure. One variation under consideration would use a hollow base, like the Eiffel Tower. The bottom would be open; otherwise, the ground floors would be too big to make effective use of as the building rose to the sky.

 

 

Raising Elevator Expectations

Researchers at Columbia University found that office workers in New York City spent 16.6 years collectively waiting for elevators, but only 5.9 years actually traveling in them. The system effectively sidesteps the limits that cable-based elevator systems place on building heights. Right now, elevator runs are limited to about 1,600 feet because traditional wire suspension ropes can’t support their own weight and the weight of the cabin beyond that length. That means building multiple elevator lobbies in supertall buildings that take up valuable floor space for mechanical systems. Finnish elevator company Kone developed an ultra-lightweight carbon fiber cable, UltraRope, that could double the distance of an elevator’s ride. ThyssenKrupp eliminated cables altogether. Each cabin in the MULTI elevator design is outfitted with a stack of permanent magnets that interact with electric coils on the hoistway. The coils pulse on and off to push the car in the right direction. Without cables confining one elevator cabin per shaft to vertical movements, multiple cabins could move through a building in a loop like a bus system. The system can be built with fewer and smaller shafts than conventional elevators, increasing a building’s useable area by up to 25%.Getting occupants to higher floors without it taking forever or having to stop at multiple sky lobbies to switch elevators is challenging. Double-decker elevator cars and computerized controls are used to efficiently get passengers to their desired floors while minimizing wait times. New breakthroughs in vibration reduction and pressure regulation are making faster travel speeds more comfortable and less vomit-inducing.

 

 

A look into the future: Material, technology and sustainability

The global impact of buildings means that engineers and designers need to start creating more sustainable high-rise buildings. Currently, buildings account for 40% of global energy use, 15% of water use and 30% of the waste that is generated. Although the drive to deliver good, functional and economical designs for high-rise buildings is not changing fundamentally, the focus on produce energy efficient and sustainable designs is expected to increase at an accelerating pace. Tall buildings are proportionally more material- and energy-hungry than lower rise buildings. In high-rise buildings, the structure is a large portion of the overall cost and embodied energy, and hence, the structural engineer can significantly influence the overall sustainable design outcome.

 

Sustainable structural design goals can be achieved by addressing the following three objectives: reduce, reuse and recycle. Advanced analysis and design methodologies allow us to design increasingly more efficient structures (with just the required amount of material and no more). Also, new material technology is opening the way for the reduction of the embodied energy per unit of material (in terms of transport energy, sustainable supplies, and the like). The use of industrial by-products such as fly-ash, slag and silica fume as a cement substitute can drastically reduce the embodied energy of concrete.

 

“Reuse” is about adapting the use of a high-rise building while keeping the original structure. There are growing examples of adaptive reuse of high-rise buildings globally. To achieve future reusability of high-rise buildings, an important design consideration is the provision of “planning flexibility”. This can be achieved in the design phase by a generous choice of structural grid, live load allowances and the like (i.e. use longer spans and larger live loads that are more adaptable to future reuse). The emergence of building information modelling (BIM) as a repository of information for asset management (as-built drawings, mill certificates and the like) is also expected to facilitate future reuse opportunities. Future high-rise buildings are likely to be designed with more consideration given to the recyclability of structural components (beams, columns, etc.).

 

Szolomicki and Golasz-Szolomicka also emphasize that sustainability is a major issue concerning high-rise buildings. It is strongly required to use sustainable concepts and applicable technology for reducing energy consumption and CO2 emissions. Covering the walls of a building with greenery affects the changing of microclimate, produces oxygen, absorbs CO2 and captures particles of pollution. Currently, plants are becoming an appropriate facade material in the creation of architecture. Their use is planned and dedicated to achieving both a specific aesthetic and ecological effect.

 

By the nature of high-rise buildings, it is very difficult to achieve a low energy building. High energy consumption in high-rise buildings has influenced the search for innovative solutions aimed at improving energy efficiency in this area. Currently, photovoltaic panels and wind turbines are primarily used to produce electricity for a building’s own needs. Designing the building together with an integrated wind turbine constituted a major design challenge for the Bahrain World Trade Center building. The project had to take into account the wind speed and direction, which occur in a given area, and as a result change parameters depending on the geometry of the building. There are many factors that affect the flow of wind in these installations. Among them are not only the location and occurring terrain, but also the shape of the building and its dimensions. Skyscrapers not only favor the development of innovative solutions, but also aim to improve human comfort when visiting a building or the safety of people residing in it. For example, the HMS (home management system) system is used, which integrates the majority of installations in an apartment. The organization of operation and modern equipment of high-rise buildings means that they belong to the category of “smart buildings”.

 

While the trend in the development of higher strength steel and concrete is not stopping, use of new material with superior performance (like fibre reinforced concrete) and/or superior sustainability (such as engineered timber) is gaining significant momentum. While timber buildings of taller than ten stories have already been achieved, there are significant research and development projects underway globally aiming to construct buildings as tall as 40 stories in steel-reinforced timber.

 

The other growing trend is in offsite fabrication of high-rise buildings. As labor costs escalate relative to material costs and as the construction safety and quality gain increasing attention, solutions involving prefabricated or manufactured structural components and building modules are gaining increasing popularity. There is a growing trend in construction of high-rise buildings from fully modular systems.

 

 

Newer innovations

To prepare for the next generation of supertall buildings – those over 300 meters or 984 feet – engineers are working on innovations such as carbon fiber cables for elevators and mass dampers, weights that reduce sway from the wind. An elevator that uses magnets instead of cables could move through buildings sideways like the Wonkavator from “Willie Wonka and the Chocolate Factory.”

 

Researchers City, University of London are developing new vibration-control devices based on Formula 1 technology so “needle-like” high-rise skyscrapers, which still withstand high winds can be built. Current devices called tuned mass dampers (TMDs) are fitted in the top floors of tall buildings to act like heavyweight pendulums counteracting building movement caused by winds and earthquakes. But they weigh up to 1,000 tons and span five storeys in 100-storey buildings -- adding millions to building costs and using up premium space in tight city centres.

 

Recent research work published by Dr Agathoklis Giaralis (an expert in structural dynamics at City, University of London), and his colleagues, published in the November 2019 edition of the Engineering Structures journal (Optimal tuned mass damper inter design in wind-excited tall buildings for occupants’ comfort serviceability, preferences and energy harvesting) found that lightweight and compact inerters, similar to those developed for the suspension systems of Formula 1 cars, can reduce the required weight of current TMDs by up to 70%.

 

Dr Giaralis said, “If we can achieve smaller, lighter TMDs, then we can build taller and thinner buildings without causing seasickness for occupants when it is windy. Such slender structures will require fewer materials and resources, and so will cost less and be more sustainable, while taking up less space and also being aesthetically more pleasing to the eye. In a city like London, where space is at a premium and land is expensive, the only real option is to go up, so this technology can be a game-changer.”

 

Tests have shown that up to 30% less steel is needed in beams and columns of typical 20-storey steel building thanks to the new devices. Computer model analyses for an existing London building, the 48-storey Newington Butts in Elephant and Castle, Southwark, had shown that “floor acceleration” – the measure of occupants’ comfort against seasickness – can be reduced by 30% with the newly proposed technology.

 

“This reduction in floor acceleration is significant,” added Dr Giaralis. “It means the devices are also more effective in ensuring that buildings can withstand high winds and earthquakes. Even moderate winds can cause seasickness or dizziness to occupants and climate change suggests that stronger winds will become more frequent. The inerter-based vibration control technology we are testing is demonstrating that it can significantly reduce this risk with low up-front cost in new, even very slender, buildings and with small structural modifications in existing buildings.” Dr Giaralis said there was a further advantage:

 

“As well as achieving reduced carbon emissions through requiring fewer materials, we can also harvest energy from wind-induced oscillations -- I don’t believe that we are able at the moment to have a building that is completely self-sustaining using this technology, but we can definitely harvest enough for powering wireless sensors used for inner building climate control.”

 

 

Up, Above & Beyond!

The skyscraper of the future will have a mixed-use function. The increasing popularity of mixed-use complexes, and in particular the growth in residential towers, has left its mark on every aspect of skyscraper design and construction. In terms of structure, concrete has now overtaken steel as the most prevalent skyscraper material. In terms of construction, mixed-use buildings are more difficult and costly to erect than single-purpose one. In terms of design, mixed-use buildings present the added complexity of segregating users and uses, taken into account pedestrian flows, vertical transportation, loading and other services. In designing these buildings, architects must often deal with multiple building code provisions, as standards for commercial and residential occupancy often differ.

 

Fast Facts

  • Raising a supertall building will require rethinking materials. High-tech concrete reinforced with microfibers in a complex recipe of super materials could rival the compressive strength of structural steel. Because it’s more massive, a concrete tower can have the same resistance to the wind in a thinner profile. Engineers are looking at aerospace materials like carbon fiber. It’s very light, very strong, and also very expensive.
  • 3D printing technology has allowed engineers to easily prototype multiple building components and test them in wind tunnels.
  • Building Information Modeling (BIM) and 3D computer modeling allow architects and engineers to accurately assess how the building will perform in real-world environments, which can lead to a reduction in redundant structural elements that skyscrapers of the past had to rely on.
  • Wind has always been an important consideration when erecting tall buildings and it becomes more important and complex as the height increases.

 

 

All major cities in US like New York, Los Angeles to far East like Singapore & KL and Dubai , Super high rises define the horizon… Mumbai also does the same , Kolkata is catching up so other cities it’s a matter of time. With habitable land area shrinking and more and more population flocking to cities, people will choose tall buildings as default options. Also from city pollution point of view, higher elevation means lesser pollution is added bonus other than better views.

ANI RAY, MANAGING DIRECTOR, ACC INDIA

 

 

Being one of the leading manufacturers of chemical solutions and products for construction, we work in close relations with the industry. We have collaborated with leading Real Estate developers in both residential and industrial segments. ECMAS offers broad spectrum of end-to-end solutions for modern high-rise structures. Our products include Admixtures for high performance concrete and SCC , a wide variety of Waterproofing solutions, Repair & Strengthening solutions, Floorings, Sealants, Adhesives, Thermal insulation, Protective coatings, Synthetic structural fibres, meeting specific project requirements and enhancing durability of construction.

RAJEEV GUPTA, BUSINESS HEAD & CMO, ECMAS CONSTRUCTION CHEMICALS

 

 

Building technology has evolved rapidly much faster than the standards of cement, steel, concrete, and admixtures. DCP aims to enhance its business process, using the latest developed technologies putting DCP in a leading position. DCP is dedicated to providing continuous customer service and support throughout every stage of the construction process. The DCP team will always work hand-in-hand with all parties to ensure all client needs are met without any delays.

MOH’D YAGHMOUR, MARKETING SUPPORT MANAGER, DON CONSTRUCTION CHEMICALS




Leave a Comment

Name  
Email Address
(will not be published)    
Website
Comment