Building with Technology

Technology has permeated all walks of life. Can construction be far behind? Madhavi Gokhlay gets some answers.With a name like CONSTRUCTION WORLD, you'd be forgiven for thinking that our universe revolves only around bare bones like brick, mortar, steel and cement, not to forget the sweat and toil. But you couldn't be more mistaken, for construction has evolved considerably with the passage of time, embracing futuristic technologies and materials along the way.In India too, with construction being the second largest economic activity after agriculture, and the country fast emerging as a powerful new economy on the global stage, it is imperative that we adopt newer, better construction technologies to meet our ambitious goals of infrastructure and habitat construction. In a bid to learn more about the latest technologies in building construction in India and overseas, we sifted through an earlier cover story on building tall, caught up with some experts, and gleaned valuable insights into the topic.FoundationNeedless to say, any structure must have a strong foundation for it to last. Although, there hasn't been much change in foundation technologies in India and overseas. In Mumbai, mostly thick raft foundations are built whereas in other parts of the country, bored piles are used. As Mark Griffith, Building Operation Manager, Leighton Contractors (India) Pvt Ltd, tells us, We see a huge opportunity for grout injected piling, especially down south, where there is black soil. Unlike traditional piling, in this method you drill and pump grout on the drilling so even as the dirt is pulled out, it doesn't collapse. In terms of excavation, rock saws mounted on a minimum 20-tonne excavator are used to cut straight through hard rock. While this isn't a new excavation technology, it isn't commonly used in India, reveals Griffith.For multi-storeyed buildings, below the ground, there is something called a diaphragm wall, whereby you enclose your foundation line and people can then go inside and do the excavation, says S A Reddi, Management Consultant. There is one more method called top-down construction, where you start from the ground level, and continue construction downwards.According to Satish Dhupelia, Consulting Structural and Civil Engineer, Satish C. Dhupelia Engineers, Earlier, the foundation was considered good only if it rested on tough rock. However, in terms of soil strata, you might get anything: clay, sand, soft murrum, hard murrum, soft rock or hard rock; each with varying load-bearing capacities. In fact, in places like Mexico, where it is hard to find good strata even for a few 100 ft, floating raft foundations are preferred instead of conventional foundations.PilingIn India, only one type of piling equipment has been in use, i.e. bored piles. While some vendors have introduced innovative piling methods and equipment in recent months, the overall situation seems skewed in favour of bored cast-in-situ piling.The other issue is that both custom and economics warrants the use of piles that are only around 1.2 to 1.5 m in diameter. In other parts of the world, in Chicago for instance, the piles have diameters up to 5 to 6 m, says Dr Joseph Colaco, President, CBM Engineers, and Structural Concept Consultant. Also, in India we tend to use straight shafts, whereas in other parts of the world, like Houston where I live, belled piles are used that are built straight but have an angular flare toward the bottom, ideal for piling in clay type soil.Meanwhile, experts suggest the use of faster and cheaper piling and geotechnical systems that are already in practice in the developed world (See Futuristic foundation technologies). It is critical however that the introduction of new technologies be coupled with the right kind of equipment, and the right kind of skills required to handle such equipment.ShutteringShuttering is basically formwork or a temporary confinement of a certain shape and size for concrete to be poured in, till it sets and gains strength. Typically, wet concrete is very heavy and does not have any strength; it is known to gain strength around three to seven, to a maximum of 28 days, after depositing.In the olden days, wooden formwork was used to build concrete structures. Then came Doka, and in the last few years, newer technologies such as Meva, Mivan, Teri, etc. have been brought in. These shuttering technologies have now become fairly common in most construction projects in India, says Dr Colaco. In fact, we have even forced shuttering on a three-day cycle, where we cast the concrete, and start pulling out the formwork just three days later, leaving the props and back shoring in place. Nowadays, shuttering can be done in a matter of three to five days.Explaining what Mivan is, Venkatraman B, Sr. Vice President - Projects, Peninsula Land Ltd, says, Mivan, which is fairly common, is basically aluminium formwork where the corners and snap are tied together, avoiding external plaster, enabling faster internal finishing. It saves about 30 per cent of time.CranesBuilding vertical necessitates the use of cranes as you go higher and higher. For Griffith, the ideal craning solution for taller towers is luffing cranes vis-a-vis traditional hammer head tower cranes as these provide greater flexibility of operation in confined spaces. Dhupelia, however, believes cranes are relevant only in precast building construction, where you are building 20 storeys and above, and all the structural components need to be lifted to those heights. Having worked as a structural engineer on Palais Royale, one of the country's tallest buildings with several firsts to its credit, Dr Colaco reveals that a lot of tower crane technologies developed in Europe and the US are now being imported into India.Significantly, the placement booms that come along with tower cranes are used to transport concrete from the batching plant on site to exactly where you want to drop it in place.  Meanwhile, the taller the tower, tower cranes tend to become an expensive proposition. In such cases, climbing cranes that have to be moved up every 10 storeys are considered a more viable option.Pumping concreteWe are using the latest pumping technology available in India from Schwing Stetter, says Griffith. These high-capacity concrete pumps are capable of pumping concrete up to heights of 400 m and above. Not only in terms of pumping but even in the case of concrete, higher grades of concrete are being developed; and the process of making concrete itself has evolved, with a lot of admixtures being used to enhance its properties.According to Dr Colaco, While there have been advancements in the pumping of concrete, we still don't have lightweight concrete in India. Typically, concrete weighs around 150 pounds but in Europe and the US, they make concrete that weighs around 20 per cent less. As such, the major columns and foundations of concrete buildings in India are heavier compared to the western world. Currently, the Palais Royale team is exploring the possibility of introducing such lightweight concrete in similar projects. Pumping concrete is not a big issue but the shuttering should be capable of taking it, says Venkatraman B. It is important to connect the pump to the concrete that is already done, and not to the shuttering. Otherwise, beyond say  12 storeys, the vibration becomes too much to handle and can cause the shuttering to give way.ReinforcementTo make up for the lack of tension in concrete, reinforcement in the form of steel bars is used in slabs, columns and beams. Nowadays, you have separate bar cutting and bar bending machines, where the steel you purchase is cut, bent and given back to you in readymade form, thereby increasing capacity and reducing wastage, reveals Venkatraman B. In fact, this is how Dubai's Al Burj Tower was constructed, with the contractor having a capacity of 30,000 tonne per month.Reddi adds to this, saying, Traditionally, straight bars were brought to site, cut, bent and assembled, making it a really tedious process. Now you have factory-produced reinforcement, where bars are cut and bent in the factory and possibly, assembled outside before bringing to the construction site, where they are lifted by cranes and placed into position. While there are very few factories producing reinforcement, their number will hopefully increase over time. Also, when you go for standard length columns, the floor-to-floor height coupled with slabs increases wastage. As such, that length of the steel bar that cannot be used for tying the column is then sliced. Slicing is thus a structurally approved technology that helps avoid wastage of reinforcement bars.Post-tensioning of slabsEarlier, pre-stressed concrete construction was applied mainly to bridges with longer spans, explains Dhupelia. However, with larger spans in today's buildings, people don't want beams protruding down. As such, post-tensioning of slabs (PT slabs) is done using pre-stressed concrete.With concrete very weak in tension, reinforcing steel bars or rebars (or salia as they are called in India) are put in beams, columns, etc. In regular concrete structures, rebars are round rods placed in the shuttering before concrete is placed, explains Dr Colaco. They are generally bought in 12 m lengths. In pre-stressed concrete, however, rebars are smaller in diameter and very long high-strength cables are used. They are placed in plastic sheathing to break any bond to the concrete. They are generally 'draped' so they are low in the middle of the slab and anchored at one end. In around three to seven days after the concrete is cast, the other end of the steel cable is pulled to very high stress levels and then anchored. When the cables are pulled, they compress the concrete and thereby counteract the loads placed on the slab. The advantages are less thickness and less vertical deflection of the slab, more watertight and -free slabs, and generally faster construction. While pre-stressing has been in India for a long time, post-tensioning of slabs is fairly new.For his part, Venkatraman B says, Nowadays, with people preferring wider rooms with more options to design, flat slabs are being used, and it is mostly pre-stressed concrete that helps to do these flat slabs.Hollow core slab constructionThis technology was used in Bengaluru nearly 15 years ago, and is now being used in some recent projects in Mumbai, according to Venkatesh Raghavan, Senior Director - Technical Services, Tishman Speyer India Pvt Ltd. Hollow core slabs or hollow core planks are precast slabs of pre-stressed concrete used in the construction of floors in multi-storeyed buildings. Hollow core slab construction has been especially popular in low seismic zones in Northern and Eastern Europe. The slabs have tubular voids extending across their length, making them much lighter than massive floor slabs of equal thickness or strength. Typically, the hollow core slabs are about 120 cm wide and around 15 to 50 cm thick.Glass facadeBy virtue of its unique properties, glass is more suitable for colder climes. However, glass facades are increasingly finding use in building construction in India. Typically, coatings are used to make glass more reflective and less heat absorbing. From a structural point of view as well, glass has the advantage of being lightweight.Unitised panels - a technology developed mostly in the US - are being used, where an aluminium picture frame is taken, glass is put in place, and the whole thing is lifted as a unit and erected on the construction site, explains Dr Colaco, adding, that a lot of unitised construction systems are now being imported into India from China, Japan and Europe. Rakesh Sharma, Managing Director, Tishman Speyer India Ltd, argues, Although a lot of design is happening using glass as material, it needs to be done more intelligently. For instance, if there is too much glass on the east or west side of a building, you are essentially trapping a lot more heat, and placing a greater load on your air-conditioning system.Fire safetyIn India, fireproofing technology is essentially unheard of because it is mostly used with steel structures, and a majority of our buildings are made of concrete. However, that's about to change. We just finished a steel building called Sun Shine Parkway Tower in Dadar and there's another one coming up at Century Mills in Worli, reveals Dr Colaco. These steel buildings will import fireproofing technology, where cement slurry will be sprayed on steel to form a coating that is fire resistant. The US trademark name of the technology is 'Monokote' although it is being manufactured by other companies as well.Meanwhile, concrete structures happen to be inherently fireproof; the only cause for worry is when you cut holes in the floors either for ventilation shafts or plumbing, as these could become potential fire chimneys. A technology increasingly making inroads into India is sprinkler systems, where pipes full of water run through the ceiling, so they can douse any fire that may occur, adds Dr Colaco.Wind resistanceWith rapidly mushrooming high rises, especially in metros such as Mumbai, the High Rise Committee (a technical committee on high rise construction in Mumbai, which looks into areas such as structural design, foundation adequacy and environmental impact), insists that all proposed buildings over a certain height should first undergo a wind tunnel test before being designed. A model of the high rise and its surroundings is placed in a chamber, and air is blown over it. The pressure caused is measured and the actual design has to make an allowance for this. In Europe, the US and Australia, there are wind tunnels for real. In India, though, wind tunnel labs are only now being built, with one in Chennai already, says Dr Colaco.Additionally, there's also a wind or war test, where a sample of the building's facade - say, one storey, around 15 ft long - is tested in a chamber for variables like dynamics and rain penetration.Another technology - impact tests on glass - already in vogue in some parts of the US, might soon come to India. Basically, when there's a cyclone, debris from the street and other buildings may fly around and hit other buildings causing damage, like breaking glass. These tests pre-empt the impact of such conditions on window walls.Seismic resistanceIn terms of seismic design, India still uses slightly outdated methodologies compared to the rest of the world. However, new technologies like damping systems might soon come here. Buildings in seismic zones can be helped through some form of damping, where instead of a conventional water tank sitting atop a building, the same can be built like a rectangular swimming pool, which is long and shallow, with vertical pieces of wood, plastic, etc, called 'baffles' inside. In the event of an earthquake, the building begins to sway and so does the water in the swimming pool, foaming owing to the presence of baffles, creating what is called white water. This absorbs some of the wind pressure on the building. Say, the wind pressure on the building is 100, the dampness takes 20 to 30, so the building has to withstand only 70 to 80.In Mumbai, while constructing 20 storeys and above, you automatically design for seismic zone three (India has been divided into different zones ranging from zone one to zone five depending on the intensity of earthquakes experienced over a few hundred years), and there is a municipal certificate awarded as proof of seismic resistance being built into your design.ElevatorsCurrent technologies are all about increasing the speed and capacity of elevators. In China, elevators ride at the speed of 5-6 m per second. On the anvil are even more evolved elevator systems. For instance, Japanese engineers are experimenting with a system, where elevators will be able to change hoistways the way railway trains change tracks. At present, elevators move vertically up and down within one hoistway in the building. In future, they will be able to move horizontally, and swing over to the next hoistway whenever it is vacant. Also, the elevators of the future will be pressurised so they can work at very high speeds. The flipside, though, is that people may feel uncomfortable as the elevator moves higher up through the hoistway.There is a significant change on the cards. Right now, you are asked to take the stairs instead of the elevator if there is a fire. Elevators in future will work when there is a fire, says Dr Colaco. These are being developed especially for all those firemen who have to drag their equipment up and down the building whenever a fire breaks out. India will have such elevators possibly in the next 20 years or so.Another trend you see in Dubai, Europe and the US is a vertical post on the outside of a building, where you push the button to indicate the floor you want to go to. The post responds, telling you to take a certain elevator, after which you walk into the building to that particular elevator, and get transported to the floor of your choice.As Raghavan tells us, Several new elevator technologies are gaining popularity in India, including destination controls, high-speed elevators particularly in taller buildings, segregation between parking and office levels, automatic variable voltage elevators, variable frequency control elevators that are energy-efficient, and so on.Prefabricated structuresPrefabrication is viewed as an opportunity to use specialised equipment to produce standardised building components that can be quickly assembled and erected. While the prefabricated industry in India is still in its fledgling state, an increasing number of vendors are taking complete responsibility for the design, detailing, manufacturing and installation of prefabricated components such as pre-insulated panels and ancillary materials. Today, there are quite a few factories that specialise in the prefabrication of wall panels, roofing sheets, hollow core slabs, etc, as per predetermined specifications. This not only helps in the timely completion of projects but also eliminates cost overruns. According to Venkatraman B, prefabricated structures seem to be catching up mainly because of the huge labour shortage all over the country.Steel structuresTraditionally, steel buildings have been a rare sight in India. And while Dr Colaco has completed a 30-storey steel building in Dadar, with another 50-storey one coming up in Worli, he feels that the supply of structural steel is limited although it is manufactured in India and that the prices are very high. Further, auxiliary industries including metal deck manufacturing, shear studs and fire-proofing are in their infancy. Most important, Indian engineers have very limited knowledge and experience in designing structural steel buildings.DemolitionEssentially, demolition of buildings is a controlled processed, where the building is first brought down to its raw structure. Then, explosives are placed in different areas and timed, such that the interior columns go down first followed by exterior ones. Finally, the whole building implodes or caves in. Thanks to our congested cities, we need controlled demolition, where you can preserve the surroundings, keeping them intact even as the structure is demolished, says Raghavan. Meanwhile, in Sharma's opinion, One way of demolishing is through mechanisation, where you pulverise everything, break it and dump it. However, this may not find favour with the developed world, where sustainability requires you to salvage as much material as possible.The verdictIn sum, while many of the latest technologies in building construction are already in use in India, there are some grey areas where the country has some catching up to do. As Raghavan says, Talking about fabricated, non-RCC structures, the western world is far ahead of us and they also have the kind of skilled labour required for the job. However, Sharma is quick to point out the difference: buildings in the West are designed for cold environments unlike ours; thus, the entire design and what goes into construction is different. His take: Maybe the solution lies in not aping the West blindly but in selectively and intelligently adopting technologies that are suitable and useful to us in terms of improving overall quality and speed of construction.Watch out for...Cyrus Pithawalla, Director, Hiranandani Group of Companies, lists emerging trends in building construction in India and internationally:Dry wall constructionDue to various constraints like time, skilled labour and speed of construction, dry wall construction will be playing a very important role throughout the world, in the near future. Dry wall construction offers various advantages including less supervision and faster erection.ShutteringA lot of development is taking place in the field of shuttering. Many companies are coming up with technologies that help construction meet the required deadlines with reduced labour requirement as well as the desired finish and accuracy. Almost every dream of an architect can come alive with shuttering designs. Some of the companies supplying effective shuttering systems include Doka, Mivan, Sten, Fuvi, etc.Self compacting concreteVery complex construction involves high rebar requirement and thus, congestion of rebar is becoming inevitable. In this scenario, it is very important to introduce self compacting concrete, which helps civil engineers carry out concreting without worrying about compaction of the same. Large foundations, where it is difficult to ensure proper compaction in every part, can be cast using self compacting concrete.CranesCranes are now becoming an integral part of any construction activity. Old, conventional ways to transfer materials and concrete, especially in high rise structures, is almost impossible using manual labour. Thus, cranes are becoming a boon for construction industry. A wide range of choices are available to suit different construction requirements.RMC concrete pumpingNow, engineers have the choice to pump concrete up to 2.2 km horizontally (relay pumping) or 715m vertically, and this makes the task of construction easy in case of special projects like railway bridges or construction of chimneys. Thus, length and height is no longer a restriction in the world of construction.Use of super plasticisers and retardersIn the current market scenario, with the concreting of higher grades and transportation issues of RMC concrete, the use of appropriate super plasticiser with retarder, will be one of the most promising trends, especially in India, where construction activities are increasing and reaching a peak, with no space availability for raw materials to be stocked, even for plastering purpose.Use of mineral admixturesDurability of concrete is a major concern for any structure, and mineral admixtures like fly ash, GGBFS, Micro silica, Rice husk, Metakaolin, etc are now important ingredients of concrete. Addition of these mineral admixtures not only improves the properties of concrete, but also helps consume waste products, thus helping the environment.Going greenWater and energy are important aspects of green. Energy efficient, pollution free, recyclable products with minimal water consumption can all be termed as green. Green is sustainable. It is about meeting today's needs without compromising the ability of future generations to meet their needs. Some green measures in construction include:Use of hollow, concrete blocks with fly ashUse of over-deck/under-deck insulationUse of high performance glassConstruction waste managementConstruction CategoriesConventional RCC frame constructionUsed in buildings that are a few storeys high, where the walls themselves are load bearing, and floors can be constructed using different materials. The walls get thicker as you go higher as they have to bear the load of the floors above them. For instance, the buildings in the Fort area of Mumbai have mostly been built in the early part of the 20th century and have external walls that are load bearing. Even the Art Deco type sea-facing buildings on Marine Drive fall under this category.Pre-cast reinforced concrete frame constructionSimilar to conventional reinforced concrete frame construction, except that it uses precast elements, including precast columns, beams and slabs. For instance, Pune-based BG Shirke and Company has developed a system for precast reinforced concrete frame construction up to 24 storeys. Here, columns are precast in the yard, transported to site, raised up by cranes, and placed in position. The same is done for precast beams and slabs. The company is engaged in a lot of work, more residential than commercial. On one site, it has managed to put up 25 floors in a matter of just five months.Steel frame constructionTill recently, this method of construction was not very popular in India. For whatever reasons, steel mills were rolling out limited sections for construction; mainly industrial sheds and not multi-storeyed buildings. But with developments such as Tata's acquisition of Corus, mills will possibly now develop higher grade, higher strength steel, bringing out rolled sections suitable for steel frame building construction for malls, etc. Russia has many malls built in this manner, where steel is rolled out in mills, sections taken, cut, erected and assembled, and the floor is ready and this process continues. Going forward, there will be more steel frame buildings constructed in India but they will essentially be commercial buildings and shopping malls because planning parameters for residential buildings are such that they render steel frame construction uneconomical.Pre-engineered buildingsReadymade structures are either available or structures are designed to meet your requirements. All the fabrication, cutting, etc, is done in the factory, and then transported to site, where it is assembled. Done largely for industrial requirements, pre-engineered buildings come mostly in the form of standard size industrial sheds with sloping roofs, and are anywhere between 40-100 ft wide.Futuristic foundation technologies:Precast piling with factory made piles, mechanical pile splices and integrated piling rigs equipped with energy-efficient impact hammers and data logging and monitoring systemsDriven cast-in-situ piling with integrated piling rigs equipped with energy-efficient impact hammers, casing extraction systems and data logging and monitoring systemsSheet piling, a form of driven piling, performed by driving thin interlocking steel sheets into soil to obtain a continuous barrier in the ground. The most common use is within temporary deep excavations, where retention of higher earth pressures of soft soil is required, in retaining walls and cofferdams erected to facilitate more permanent worksContinuous flight auger (CFA) piling, a rapid and cost-effective open site method of constructing load-bearing and retaining structure piles, where the ground is composed of soft rock and/or non-cohesive sands, gravels or silts, where otherwise long casings or drilling fluids would be required. Most effective for sensitive sites, where it provides a quiet and vibration-free piling techniqueDeep soil mixing to improve strength of soils in-situ.Jet grouting, which involves injecting ultra high-pressure fluids or binders into the soil at high velocities to break up the soil structure, and mix the soil particles in-situ to create a homogeneous mass, which in turn solidifies to form soilcrete with high strength and low permeability characteristics. This ground modification technique has many applications in foundations, excavations, tunnel support, seepage cut-off, walls for dams, etcRapid impact compaction (RIC) system to provide controlled impact compaction of the earth-usually a 7 tonne or heavier hydraulic impact hammer is used to impart blows to increase the density of the soil up to a depth of 6 m, thereby enhancing the bearing capacity and stiffness of soilMass stabilisation with automatic dosing, mixing and monitoring systems of high productivityHydraulic pile head breakers, especially for a wide range of concrete piles, both cast-in-place and precastScrew piles/helical piles, which involve screwing special types of piles into the ground, using either machine-mounted or hand-held hydraulic drill equipment. Helical piles are useful for both tension and compression loads, and for transmission towers, anchoring and foundation rafts to overcome uplift forcesSelf-compacting concrete for deep foundations, which uses a highly flowable, non-segregating concrete, that spreads into place, fills the complete space and encapsulates the reinforcement without any mechanical consolidationGround improvement with vibro vompaction (in coarse-grained soils)/vibro replacement (in fine-grained soils), which has wide applications to support wide area loads, embankments, control of liquefaction, etc. It is a faster and cheaper method, either to replace and/or provide additional support to deep foundationsGive us your comments on this article at feedback@ASAPPmedia.com