FAÇADE ENGINEERING AND RECYCLED GLASS

Inference: Recycled glass has been innovatively used in the country for a long time now. So where is it now?

Though glass as a construction material in cladding and insulation applications has definitely come of age in the country, there is no really significant progress when it comes to recycled glass product innovations or applications. Recycled glass seems to be a phenomenon essentially in the container and packaging industry or heading towards landfills. The world over awareness of the potential of this material doesn't seem to be significantly seen in the Indian construction industry.

Environmental concerns

With the rising consciousness of environment conservation and green construction recycled glass has come up in several innovative and decorative construction products. Recycling of glass seriously cuts costs of raw materials and energy/fuel. Since glass can be recycled indefinitely as its structure does not deteriorate when reprocessed. Countries like Switzerland and Finland recycle more than 90% of their container waste.

The process

Waste glass is collected from various sources and collection schemes like bottle banks, kerbside schemes or directly from parties using large quantities of glass containers. In India the kabbadiwala is a major link in this chain. These collections and glass rejected due to breakages and manufacturing defects together form glass cullet. Cullet may have added materials in the form of plastic, aluminum etc. that can change the properties of the cullet. After pulverization, the aggregate has a texture similar to natural sand and is as hard-grained.

Combined with concrete it produces a material with a higher abrasion resistance than similar mixtures using quartz sand. There is also often a reduced drying shrinkage in these mixes. Powdered glass is polozzolanic, or it contributes to strength development by reacting with lime. Though these strengths are lower than Portland cement alone there are distinct economic advantages of using the material.

Product Innovations

Glass aggregates: Recycled glass used in new construction products includes new window glazing, wall and floor tiles and fiberglass insulation. It also goes into concrete towards making tiles, terrazzo flooring, pavers, wall finishes, pipe bedding and concrete as exposed aggregate. The decorative elements are accentuated by the colors and sparkle of the original glass. They also have the scope to meet special requirements of custom design-on-order products architectural accents. 

Tumbled glass: These are recycled glass pieces that have a frosted surface and rounded edges. These pieces widen the scope for innovation in interior design, mosaics and landscape accenting. They are suitable for incorporation into tiled surfacing, architectural glass designs or to feature in reflecting pools and fountains. Tumbled glass may also be used as ballast gravel in green roof and other green building applications. 

Abrasive/ blasting media: Crushed recycled glass is a safe and effective medium to substitute natural sand and slag. It is applicable for sandblasting work like surface preparation, removal of rust or paint, etc. With its lower weight it is easier to use and dispose off.

Water Filteration media: Finely crushed recycled glass presents itself as a direct replacement for silica sand. It has shown its advantages in being lighter, more hygienic and safer to use than silica sand. As a light weight product it provides more filter volume per unit weight. These products have no crystalline silica and do not trap bacteria resulting in lowered requirements of chlorine and coagulants.

Bent glass

Bent glass has been on the building scene since the early 19th century. This dynamic product is growing in proportion of its use with the development of glass technology, improving safety properties and the energy saving properties available in glass.

Bent glass adds greatly to the aesthetic potential of design. The curved surfaces give a building its own personality, creating the whole or a part of the façade. 

With a growing proportion of bent glass been processed to make safety glass, bent glass can also be laminated for specialized categories like bullet resistant. There is also widening scope of available products in terms of available sizes. This may then be increasingly used in both facades and interior architecture.

So far bent glass has primarily been used in public buildings, office complexes and for corporate facility facades. Interior architecture applications for bent glass include railings for staircases, walkways, partitions and elevator glass panels.

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Article by,

Ms.Soma Soundharya

Asst.Prof.

Department of Civil Engineering

Sphoorthy Engineering College, Nadergul

Sphoorthy Engineering College

NUCLEAR REACTORS

Nuclear Reactor Technology has found potential in this era where innovation and development are keys to build a brighter future. The massive abundance of energy released through the process of fission, as well as fusion, are being harnessed and used at constantly increasing efficiencies. The first artificial nuclear reactor, called the Chicago Pile-1, was constructed at the University of Chicago, by a team led by Enrico Fermi, in late 1942.  This was the seed that led to the growth and understanding of nuclear energy technology all over the world, utilizing newer and better ways to increase the efficiency and safety of the Nuclear Reactors as a whole.

The total installed capacity for electricity generation in the country has increased from 16,271 MW as on 31.03.1971 to 206,526 MW as on 31.03.2011. (Energy Statistics, 2012)

Nuclear power is the fourth-largest source of electricity in India. As of 2010, India has 20 nuclear reactors in operation, in six nuclear power plants, generating 4,780 MW while seven other reactors are under construction and are expected to generate an additional 5,300 MW.

As in previous years, during the year 2010–11, demand for electricity in India far outstripped availability, both in terms of base load energy and peak availability. Base load requirement was 861,591 (MU) against availability of 788,355 MU, an 8.5% deficit. During peak loads, the demand was for 122 GW against availability of 110 GW, a 9.8% shortfall (Central Electricity Authority, Govt. of India Ministry of Power, 2011). 

Power Plants Located Across India 

• Narora Atomic Power Station

• Rajasthan Atomic Power Station

• Tarapur Atomic Power Station

• Kakrapar Atomic Power Station

• Kudankulam Nuclear Power Plant

• Madras Atomic Power Station (Kalpakkam)

• Kaiga Nuclear Power Plant

India, like rest of the world, faces a high demand for energy that needs to be satisfied by the end of this decade, and Nuclear Technology is our best option in achieving such a goal. There have been incidences of public outcry pertaining to the safety of the Nuclear Containment Structure. The mass protests against the French-backed 9900 MW Jaitapur Nuclear Power Project in Maharashtra and the 2000 MW Koodankulam Nuclear Power Plant in Tamil Nadu, and the state government of West Bengal state refusing permission to a proposed 6000 MW facility near the town of Haripur that intended to host six Russian reactors are some examples of such problems that hinder the development of this energy technology.

The reasons and vacillations regarding its safety have been considered by scientists and engineers, and are found to be manageable, solutions of which, can be resolved through proper analysis and design.

A common misconception about a nuclear power plant’s containment structure is that their massive concrete construction is a protection against the release of radioactive products in the case of a postulated accident. Such a task is achieved by the overall containment system as a collection of the “Engineered Safety Features,” not just by the concrete shell alone. It must be understood that the concrete component is meant as a biological shield against gamma-ray radiation and a protection of the reactor internals against damage from the effects of nature like that of an earthquake and the effects of the outside elements including missiles such as light posts driven by tornado or hurricane 100-miles per hour winds, and even the direct impact by a massive aircraft such as a Boeing-747. The concrete shell in fact is strong at its exterior curvature, and weak at its interior curvature. This is an inherent characteristic of shell structures. Think about how difficult it is to crush an egg by squeezing it in one’s hand, yet it is easy for the weak and helpless chick to peck its way out of the interior of an egg’s shell. The concrete shell is designed to withstand the direct impact of an aircraft on its exterior, but miserably fails a build-up of stress at its interior. An increase of stress by steam release, if unquenched, at its interior will eventually cause it to fail; much like a chain at its weakest link. The weakest links in that case occur at the coolant inlet and outlet pipes and the instrumentation cabling and electrical power penetrations.

Pre-stressed concrete (PSC) structures, the best example of engineering structure that has excellent structural efficiency, are widely used in various engineering works. As PSC structures are economic and have fine shape, increasing number of engineering works are being conducted using PSC structures. Since the 1960s, many have tried to analyze complex structures in a more substantial way using finite element method. It is almost impossible to conduct experiment on every structure because each structure is different in its structural type, materials, and surrounding conditions. Experiment under specific conditions also should risk failures and high costs. In this regard, finite element method can be a good alternative because it enables easy control of various conditions such as shape, load, and boundary. Using the method, it is also possible to check the internal stress of a structure. With the continuous methodological improvement and development of high-performance computers, finite element method is now widely used in analyzing complex structures. It is also now possible to take in various other factors into the analysis so as to attain more realistic data regarding the structures behaviour. The elastic behaviour of concrete comprises of the linear phase, which have been studied and used as a means of design, and a non-linear phase. Structural nonlinearities are encountered on a routine basis. For instance, whenever two pieces of paper are stapled together, the metal staples are permanently bent into a different shape you heavily load a wooden shelf, it will sag more and more as time passes. As weight is added to a car or truck, the contact surfaces between its pneumatic tires and the underlying pavement change in response to the added load. If a plot of the load-deflection curve for each of these examples were to be drawn, it would discovered that they all exhibit the fundamental characteristic of nonlinear structural behaviour - a changing structural stiffness.

The potential of the non-linear phase has not been completely utilized in structures due to its complexity and enormous time consumption. The development of analysis softwares has changed this view and now, it is possible to reap benefits from even the non-linear phase of concrete behaviour. A nonlinear analysis is necessary in this order to study, understand and improve the capability of the structure to resist these loads.

In conclusion, the importance of nuclear technology has been recognized world over and being in possession of such technology it is only natural that we use it for the development of our nation. As civil engineers it is in our interest to find ways to ensure safety and security in that regard through research and application of technology and analytical that are already out there in the world.

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Article By:

Mr.Nishanlulu Mohd Jaleel

Asst. Prof.

Department of Civil Engineering

Sphoorthy Engineering College

Sphoorthy Engineering College

THE THIN SHELL

Shell structure, in building construction, is a thin, curved plate structure shaped to transmit applied forces by compressive, tensile, and shear stresses that act in the plane of the surface. They are usually constructed of concrete reinforced with steel mesh. The shells are most commonly flat plates and domes, but may also take the form of ellipsoids or cylindrical sections, or some combination thereof.

Types and Forms of Shell Structure
• Folded Plates
• Barrel Vaults
• Short Shells
• Domes of Revolution
• Folded Plate Domes
• Intersection Shells
• Warped Surfaces
• Combinations
• Shell Arches

Folded Plates

The elements of a folded plate structure are similar to those of a barrel shell except that all elements are planar, and the moments in the slab elements are affected by the differential movement of the joints.

For the structure shown, the end supports and the side supports are both complete walls +

Barrel Shells

The elements of a barrel shell are: 

(1) The cylinder, 

(2) The frame or ties at the ends, including the columns, and 

(3) The side elements, which may be a cylindrical element, a folded plate element, columns, or all combined.

For the shell shown in the sketch, the end frame is solid and the side element is a vertical beam. 

A barrel shell carries load longitudinally as a beam and transversally as an arch. The arch, however, is supported by internal shears, and so may be calculated. 

The elements of a folded plate structure are similar to those of a barrel shell except that all elements are planar, and the moments in the slab elements are affected by the differential movement of the joints. 

For the structure shown, the end supports and the side supports are both complete walls 

The elements of a short shell are the barrel, which is relatively short compared to radius, the element at the base of the cylinder to pick up the arch loads, and the arches or rigid frame to pick up the entire ensemble. In this case it is a rigid frame arch. The size of the arch could have been reduced by horizontal ties at the springings. There may be multiple spans.

The short shell carries loads in two ways: 

(1) As an arch carrying load to the lower elements. and 

(2) As as a curved beam to the arches. 

The thickness of the shell can be quite thin due to these properties.

Domes

Domes are membrane structures, the internal stresses are tension and compression and are statically determinate if the proper edge conditions are fulfilled. In a dome of uniform thickness, under its own weight, the ring stresses are compression until the angle to the vertical is about 57 degrees. If the dome is less than a full hemisphere, a ring is required at the base of the dome to contain the forces.

Translation Shells

A translation shell is a dome set on four arches. The shape is different from a spherical dome and is generated by a vertical circle moving on another circle. All vertical slices have the same radius. It is easier to form than a spherical dome. 

The stresses in a translation shell are much like a dome at the top, but at the level of the arches, tension forces are offset by compression in the arch. However there are high tension forces in the corner. 

Advantages of Concrete Shells

Like the arch, the curved shapes often used for concrete shells are naturally strong structures, allowing wide areas to be spanned without the use of internal supports, giving an open, unobstructed interior. The use of concrete as a building material reduces both materials cost and a construction cost, as concrete is relatively inexpensive and easily cast into compound curves. The resulting structure may be immensely strong and safe; modern monolithic dome houses, for example, have resisted hurricanes and fires, and are widely considered to be strong enough to withstand even F5 tornadoes.

Disadvantages of Concrete Shells

Since concrete is porous material, concrete domes often have issues with sealing. If not treated, rainwater can seep through the roof and leak into the interior of the building. On the other hand, the seamless construction of concrete domes prevents air from escaping, and can lead to buildup of condensation on the inside of the shell. Shingling or sealants are common solutions to the problem of exterior moisture, and dehumidifiers or ventilation can address condensation.

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Article By:

Mr.Nishanlulu Mohd Jaleel

Asst. Prof.

Department of Civil Engineering

Sphoorthy Engineering College

Sphoorthy Engineering College