1. Singly curved shells like cylindrical shells 2. Doubly curved or spherical shells

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1 UNIT IV PART A 1. What are shells? (N/D 16), (M/J 12) Shells are three dimensional structures constructed as storage tanks or roof for large column free areas, such as exhibition halls, sports complex or theatres. 2. What are launching girders? (N/D 16) For erection of large beams in buildings or bridges, temporary girders are used. Such girders are called launching girders. Launching girders are usually of steel as it would be light compared to concrete girders 3. Write a note on offshore platform (M/J 16) Offshore platforms are structures constructed in the ocean to explore or to produce oil and gas from the sources found below the sea. Offshore platforms are in steel or in concrete 4. Define articulated structures (M/J 16) A structure in which relative motion is allowed to occur between parts, usually by means of a hinged or sliding joint or joints. 5. What are the precautions to be taken while erecting light weight components on tall structures? (M/J 12) The precautions to be taken while erecting light weight components on tall structures are, a) Excellent coordination and site organization have to be maintained b) All heavy equipments like generators, lightning system, twists, etc., are to be in working condition c) Adequate communication facility should be coordinated between ground level, crane drivers, ship format and twist operators. 6. What are the three common tower crane configurations? (N/D 11) The three common tower crane configurations are, a) Static tower cranes b) Travelling tower cranes c) Climbing tower cranes

2 7. What are cooling towers? (N/D 10) Cooling Towers are used to cool the water that is used to recon dense the steam that is used to generate electricity. 8. Define Braced Domes. (N/D 10) Braced domes are composed either of members lying of a surface of revolution of straight members with their connecting points lying on such a surface, an arrangement which avoids any obstruction of the inner space. This arrangement generally results in a dome of circular tone or in one truncated into a polygonal base, domes with elliptical or oval plan have been used in rare cases. 9. What are the systems of pre stressing? (N/D 11) 1. Freyssinet System 2. Magnel-blaton System 3. Lee-Mc. Call or stress steel system 1. What are the advantages of pre stressed cement concrete? (N/D 15) 1. It is possible to take the full advantage of compressive strength of concrete and high tensile strength of the steel used to 30% of the concrete is saved to 80% of the steel is saved. 4. Prestressed concrete members are thinner in section and hence there is greater reduction of the self-weight of the member. 2. How are domes erected? (N/D 12) Domes are usually erected with a central temporary support on which the supporting ring rests. If the span is greater than 40 50m, the tower of an erecting frame serves the support. 3. What are shells? (N/D 16) Shells are three dimensional structures constructed as storage tanks or roof for large column free areas, such as exhibition halls, sports complex or theatres. 4. How are shells classified? (N/D 11) 1. Singly curved shells like cylindrical shells 2. Doubly curved or spherical shells 5. What is a sky scraper? (N/D 15) A skyscraper is a tall, continuously habitable building of many storeys, usually designed for office and commercial use. There is no official definition or height above which a building may be classified as a skyscraper. One common feature of skyscrapers is having a steel framework that supports curtain walls. These curtain walls either bear on the framework below or are possibly suspended from the framework above, rather than load-bearing walls of conventional construction.

3 6. What are tall structures? (N/D 13) Transmission towers are tall structures with relatively small cross section and with a large ration between the height and the maximum. Tall buildings are generally multi storeyed structure where greater part of the construction is composed of beams and stancheons. 7. Define Braced Domes(A/M 11) Braced domes are composed either of members lying of a surface of revolution of straight members with their connecting points lying on such a surface, an arrangement which avoids any obstruction of the inner space. This arrangement generally results in a dome of circular tone or in one truncated into a polygonal base, domes with elliptical or oval plan have been used in rare cases 8. Distinguish between silos and bunkers. (N/D 11) Silos A silo is a structure for storing bulk materials. Silos are used in agriculture to store grain or fermented feed known as silage. Silos are more commonly used for bulk storage of grain, coal, cement, carbon black, woodchips, food products and sawdust. Silos are mostly above the ground Bunkers A bunker is a defensive military fortification designed to protect the inhabitants from falling bombs or other attacks. They were used extensively in World War I, World War II, and the Cold War for weapons facilities, command and control centers, and storage facilities. Bunkers are mostly below the ground PART B 1. Describe in detail about shell roof structures (N/D 16) (M/J 15) Shells are 3d structures constructed on storage tanks or roof for large column area such as indoor stadiums, exhibition halls, theatres, complex churches etc Classification Singly curved Double curved Cylindrical shells Singly curved It can be used for rectangular shape buildings, shells represents the roof of the building Dome storage

4 tank for water and petroleum is example for single curved Doubly curved For doubly curved structures the super structure should be in hexagonal or circular shape Cylindrical shape These are just modification of pitched roof and frequently employed in modern age construction It has two types North light shell roof Barrel vault shell roof Both are different to provide lighting effect in factories In barell vault ventilation s provided in middle Special Forms for Concrete Shells A thin shell concrete structure, is a structure composed of a relatively thin shell of concrete, usually with no interior columns or exterior buttresses. 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

5 Barrel Shells The elements of a barrel shell are: (1) The cylinder, (2) The frame or ties at the ends, including the columns, and

6 (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. 1. Explain Domes (N/D 11) [N/D- 14] Domes

7 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.

8 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 3.. Explain the general requirements in launching girders. (M/J 16)[N/D-13] Launching girders are most commonly used for placing pre-cast post-tensioned concrete box segments to form viaducts and bridges and are especially useful for lofty structures in marine or congested urban conditions due to their ability to move themselves forward to the next span - hence they are particularly economic for multi-span structures. Curvature can be accommodated by moving laterally on crossbeams and modest gradients can also be accommodated. For most situations the balanced cantilever method is the favoured sequence of construction. Description and Sequence: LGs are relatively large pieces of equipment, their size being based on the maximum spans and segment weights to be erected. A large LG might typically weigh in excess of 800 tonnes and be in the order of 150 to 180 metres in length (as a rule of thumb just over twice the length of the main spans unless intermediate temporary support systems are to be used). Regular inspection maintenance of this equipment to an approved schedule is fundamental to ensure trouble-free and safe operation. Once the LG is in place the basic steps for a typical span construction are:- Delivery of a segment to the LG (at deck level or from ground level) Pick-up and winching of segment into its approximate position Application of epoxy resin to segment faces to be joined Final positioning and temporary stressing for self-support (allowing the segment to be released from LG) Internal permanent post-tensioning sufficient to allow placing of the next segment Repetition for further segments until completion of the cantilevers

9 Form and stress a concrete stitch at mid-span to complete the span Launch the LG to next span Final post-tensioning possibly continuous through more than one span Launching the girder to the next span is usually a multi-stage process involving tiedowns, counterbalancing with pre-cast segments and winches and the use of temporary support legs but the precise procedure to be followed will vary from one piece of equipment to another and must be clearly set out in method statements, and preferably certified by an independent checking engineer. Launching girder in balanced cantilever mode Insurance Aspects: For insurance purposes launching girders may be considered either as contractor s plant or temporary works and this can be an important factor when preparing the policy documents. However, whether treated as plant or temporary works, a failure can have very serious insurance implications including:- Injury or loss of life by operatives and members of the public Third party property damage Damage and delay to the contract works Clearance of debris Claims can arise, and have arisen, either as a result of procedures not being strictly followed or due to failure of the equipment itself and hence the development of detailed procedural steps and their very strict implementation using experienced operatives is essential to reduce the risks to their lowest achievable level. Training and Access: Operating and moving LGs is a specialised process requiring staff with extensive training and experience. Whilst main contractors might wish to allocate some staff to the erection process they should be under the direct command of a specialist from the manufacturer or a company specialising in this type of work. In addition to the task of lifting and placing the segments these workers need to receive training in several related operations including gluing and post-stressing of the segments together with the numerous safety requirements for standard construction such as ventilation requirements, working at height, PPE and communications. All trained staff (including resident site staff) who are permitted to access the LG working areas, should be clearly identifiable (usually by means of a truss permit label on their helmets) without which access to the fenced-off working areas above and below should be denied. In the case of shift-working a period of supervision hand-over is important to ensure on-going operations follow the correct sequence and the agreed procedures.

10 Detailing the Erection Procedures: Method statements, including risk assessments, should set out the procedural steps to be followed in detail and it is considered important for the manufacturer or specialist company to be directly involved in this process. Setting out the multi-stage operations is best undertaken by means of a general method statement which can then be developed into a more detailed and specific MS. These statements will invariably require diagrammatic as well as descriptive elements covering the erection sequence for each span and highlighting the particular stressing required at different times, as certified by the independent checking engineer. 4. Write a note on bridge decks (M/J 12) (N/D 10) BRIDGE DECKS The principal function of a bridge deck is to provide support to local vertical loads (from highway traffic, railway or pedestrians) and transmit these loads to the primary superstructure of the bridge, (1). As a result of its function, the deck will be continuous along the bridge span and (apart from some railway bridges) continuous across the span. As a result of this continuity, it will act as a plate (isotropic or orthotropic depending on construction) to support cal patch Continuity ensures that whether or not it has been designed to do so, it will participate in the overall structural action of the superstructure. The overall structural actions may include: Contributing to the top flange of the longitudinal girders, Contributing to the top flange of cross girders at supports and, where present in twin girder and cross girder structures, throughout the span, Figure 1(3). Stabilising longitudinal and cross girders Acting as a diaphragm to transmit horizontal loads to supports. Providing a means of distribution of vertical load between longitudinal girders, It may be necessary to take account of these combined actions when verifying the design of the deck. This is most likely to be the case when there are significant stresses from the overall structural actions in the same direction as the maximum bending moments from local deck actions, e.g. in structures with cross girders where the direction of maximum moment is along the bridge. The passage of each wheel load causes a complete cycle of local bending stresses. The number of significant stress cycles is, therefore, very much higher for the deck than for the remainder of the superstructure. In addition, some of the actions of the deck arising from its participation in the overall behavior are subject to full reversal; an example is the transverse distribution of vertical load between girders. For both these reasons, fatigue is more likely to govern the design of

11 the bridge deck than the remainder of the superstructure. 5. What are the different Types of Material Handling Equipment? (N/D 10) (M/J 14) Material handling equipment encompasses a diverse range of tools, vehicles, storage units, appliances and accessories involved in transporting, storing, controlling, enumerating and protecting products at any stage of manufacturing, distribution consumption or disposal. Categories of Material Handling Equipment The four main categories of material handling equipment include: storage, engineered systems, industrial trucks and bulk material handling. Storage and Handling Equipment Storage equipment is usually limited to non-automated examples, which are grouped in with engineered systems. Storage equipment is used to hold or buffer materials during downtimes, or times when they are not being transported. These periods could refer to temporary pauses during long-term transportation or long-term storage designed to allow the buildup of stock. The majority of storage equipment refers to pallets, shelves or racks onto which materials may be stacked in an orderly manner to await transportation or consumption. Many companies have investigated increased efficiency possibilities in storage equipment by designing proprietary packaging that allows materials or products of a certain type to conserve space while in inventory. Examples of storage and handling equipment include: Racks, such as pallet racks, drive-through or drive-in racks, push-back racks, and sliding racks Stacking frames Shelves, bins and drawers Mezzanines Engineered Systems Engineered systems cover a variety of units that work cohesively to enable storage and transportation. They are often automated. A good example of an engineered system is an Automated Storage and Retrieval System, often abbreviated AS/RS, which is a large automated organizational structure

12 involving racks, aisles and shelves accessible by a shuttle system of retrieval. The shuttle system is a mechanized cherry picker that can be used by a worker or can perform fully automated functions to quickly locate a storage item s location and quickly retrieve it for other uses. Other types of engineered systems include: Conveyor systems Robotic delivery systems Automatic guided vehicles (AGV) Industrial Trucks Industrial trucks refer to the different kinds of transportation items and vehicles used to move materials and products in materials handling. These transportation devices can include small hand-operated trucks, pallet-jacks, and various kinds of forklifts. These trucks have a variety of characteristics to make them suitable for different operations. Some trucks have forks, as in a forklift, or a flat surface with which to lift items, while some trucks require a separate piece of equipment for loading. Trucks can also be manual or powered lift and operation can be walk or ride, requiring a user to manually push them or to ride along on the truck. A stack truck can be used to stack items, while a non-stack truck is typically used for transportation and not for loading. There are many types of industrial trucks: Hand trucks Pallet jacks Pallet trucks Walkie stackers Platform trucks Order picker Sideloader Many types of AGV Bulk Material Handling Equipment Bulk material handling refers to the storing, transportation and control of materials in loose bulk form. These materials can include food, liquid, or minerals, among others. Generally, these pieces of equipment deal with the items in loose form, such as conveyor belts or elevators designed to move large quantities of material, or in packaged form, through the use of drums and hoppers. Conveyor belts Stackers Reclaimers Bucket elevators Grain elevators Hoppers Silos

13 6 Explain in detail, the process of in-situ pre-stressing of high rise structures? (A/M 10) (N/D 12) PRESTRESSING METHOD IN MULTI-STORIED BUILDING FRAME History of Pre-stressing The art of pre-stressing concrete evolved over many decades and from many sources, but we can point to a few select instances in history that brought about this technology. In the United States, engineer John Roebling established a factory in 1841 for making rope out of iron wire, which he initially sold to replace the hempen rope used for hoisting cars over the portage railway in central Pennsylvania. Later, Roebling used wire ropes as suspension cables for bridges, and he developed the technique for spinning the cables in place. During the 19th century, low-cost production of iron and steel, when added to the invention of portland cement in 1824, led to the development of reinforced concrete. In 1867, Joseph Monier, a French gardener, patented a method of strengthening thin concrete flowerpots by embedding iron wire mesh into the concrete. Monier later applied his ideas to patents for buildings and bridges. Swiss engineer Robert Maillart s use of reinforced concrete, beginning in 1901, effected a revolution in structural art. Maillart, all of whose main bridges are located in Switzerland, was the first designer to break completely with the masonry tradition by putting concrete into forms technically appropriate to its properties yet visually surprising. His radical use of reinforced concrete revolutionized masonry arch bridge design. The idea of pre-stressing concrete was first applied by Eugene Freyssinet, a French structural and civil engineer, in 1928 as a method for overcoming concrete s natural weakness in tension. Pre-stressed concrete can now be used to produce beams, floors or bridges with a longer span than is practical with ordinary reinforced concrete. PRE-STRESSED CONCRETE Pre stressed concrete, like reinforced concrete, is a composite material which uses to advantage the compressive strength of concrete, whilst circumventing its weakness in tension. Pre

14 stressed concrete is made from structural concrete, usually of high strength, and high strength steel tendons which may or may not be grouped together. Prior to external loading the tendons are tensioned in one of two ways. With pretensioning the tendon are tensioned prior to the casting of the concrete and using post tensioning techniques the tendons are tensioned after the concrete has hardened. Some ordinary reinforcing steel is also often included both as subsidiary longitudinal reinforcement and as transverse stirrups to resist shear. Pre-stressed concrete is a method for overcoming concrete's natural weakness in tension. It can be used to produce beams, floors or bridges with a longer span than is practical with ordinary reinforced concrete. Pre-stressing tendons (generally of high tensilesteel cable or rods) are used to provide a clamping load which produces a compressive stress that offsets the tensile stress that the concrete compression member would otherwise experience due to a bending load. Traditional reinforced concrete is based on the use of steelreinforcement bars, inside poured concrete. The basic purpose of pre-stressing is to improve the performance of concrete members and this is achieved by inducing in the beam initial deformation and stresses which tend to counteract those produced by the service loads. Since concrete is weak in tension in normal reinforced concrete construction cracks develop in the tension zone at working loads and therefore all concrete in tension is ignored in design.

15 Pre-stressing involves inducing compressive stresses in the zone, which will tend to become tensile under external loads. This compressive stress neutralizes the tensile stress so that no resultant tension exists, (or only very small values, within the tensile strength of the concrete). Cracking is therefore eliminated under working load and all of the concrete may be assumed effective in carrying load. Therefore lighter sections may be used to carry a given bending moment, and pre-stressed concrete may be used for longer span than reinforced concrete. The pre-stressing force also reduces the magnitude of the principal tensile stress in the web so that thin-webbed I - sections may be used without the risk of diagonal tension failures and with further savings in self-weight. The pre-stressing force has to be produced by a high tensile steel, and it is necessary to use high quality concrete to resist the higher compressive stresses that are developed. As the name itself suggests pre-stressing is the technique of stressing a structural member prior to loading to resist excessive tensile stresses. The advantages of pre-stressed concrete as a construction material in multi storied frame can be listed as follows: Maximum utilization of provided section of the member. Provision of slender member for long span beams as compared to RCC. Use of high strength materials contribute to the durability of the structure. Pre-stresses concrete has considerable resilience and impact resistance. Proves to be economical only in long span beam-column frames compared to other materials. The intermediate distance between the columns can be in increased by using prestressed concrete as compared to reinforced cement concrete. Architectural design provisions and specifications can be achieved using pre-stressed concrete. Dead weight of concrete is reduced to a higher rate using pre-stressed concrete. PRINCIPLE OF PRESTRESSING The function of pre-stressing is to place the concrete structure under compression in those regions where load causes tensile stress. Tension caused by the load will first have to cancel the compression induced by the pre-stressing before it can crack the concrete. Figure (a) shows a plainly reinforced concrete simple-span beam and fixed cantilever beam cracked under applied load. Figure (b) shows the same unloaded beams with pre-stressing forces applied by stressing high strength tendons. By placing the pre-stressing low in the simple-span beam and high in the cantilever beam, compression is induced in the tension zones; creating upward camber. Figure (c) shows the two pre-stressed beams after loads have been applied. The loads cause both the simple-span beam and cantilever beam to deflect down, creating tensile stresses in the bottom of the simple-span beam and top of the cantilever beam. The structural Designer

16 balances the effects of load and pre-stressing in such a way that tension from the loading is compensated by compression induced by the pre-stressing. Tension is eliminated under the combination of the two and tension cracks are prevented. Also, construction materials (concrete and steel) are used more efficiently; optimizing materials, construction effort and cost. Fig 1. - Comparison of Reinforced and Prestressed Concrete Beams Pre-stressing can be applied to concrete members in two ways, by pre-tensioning or posttensioning. In pre-tensioned members the pre-stressing strands are tensioned against restraining bulkheads before the concrete is cast. After the concrete has been placed, allowed to harden and attain sufficient strength, the strands are released and their force is transferred to the concrete member. Pre-stressing by post-tensioning involves installing and stressing pre-stressing strand or bar tendons only after the concrete has been placed, hardened and attained a minimum compressive strength for that transfer. METHODS AND SYSTEM OF PRE-STRESSING There are two methods of pre-stressing concrete: - 1) Pre-cast Pre-tensioned 2) Pre-cast Post-tensioned Both methods involve tensioning cables inside a concrete beam and then anchoring the stressed cables to the concrete.

17 Pre-cast Pre-tensioned: - Pre-tensioning is a method of pre-stressing in which the steel tendons are tensioned before the casting of the member. In this method the tendons are tensioned using hydraulic jacks, which bear on strong abutments between which the moulds are placed. After the concrete attains full strength the tendons are released and the stress is transferred to the concrete by bond action. Procedure of precast pre-tensioned concreting Stage 1 Tendons and reinforcement are positioned in the beam mould. Stage 2 Tendons are stressed to about 70% of their ultimate strength. Stage 3 Concrete is cast into the beam mould and allowed to cure to the required initial strength. Stage 4 When the concrete has cured the stressing force is released and the tendons anchor themselves in the concrete.

18 1. Explain in detail, the merits and demerits of various types of shells. (A/M 11) (N/D 12) 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