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Need for prefabrication – Principles – Materials – Modularcoordination Standardization – Systems – Production – Transportation – Erection.
Behavior of structural components – Large panel constructions – Construction Ofroof and floor slabs – Wall panels – Columns – Shear walls
Disuniting of structures- Design of cross section based on efficiency of material used – Problems in design because of joint flexibility – Allowance for joint deformation.
Joints for different structural connections – Dimensions and detailing – Design of expansion joints
Progressive collapse – Code provisions – equivalent design loads for considering abnormal effects such as earthquake , c clones, etc., - Importance of avoidance of progressive collapse.
The first three types are mainly classified according to their degree of precast elements used in the construction. For example brick is small unit of pre casted material and used in buildings. This is called as small prefabrication and the degree of precast element is very low.
Suppose the roofing systems and horizontal members are provided with pre casted elements. These constructions are known as medium prefabricated construction. Here the degree of precast elements is moderate.
In large prefabrication most of the members like wall panels, roofing / flooring systems, beams and columns are prefabricated. Here the degree of precast elements is high. One of the main factors which affect the factory prefabrication is transport. The width of the road, mode of transport vehicles are the factors which determines the prefabrication which is to be done on-site or in factory. Suppose the factory is situated far away from the construction site and the vehicle needs to cross congested traffic areas with heavy weighing elements the cast in-site prefabrication is preferred. Even though the same condition as the cast in site prefabrication is preferred only when umbers of houses are more for small elements the conveyance is easier with normal type of lorry and tractors. We can adopt factory or off- site prefabrication for this type of construction.
In the total prefabrication systems, the space frames are casted as a single unit and erected at the site. The wall fitting and other fixing are done on site. This type of construction is known as open system of prefabrication.
In this system the whole things are casted with fixing and erected on their position.
In this method of construction, the building elements required are precast and then erected. Since the casting of horizontal elements (roof / floor) often take more time due to erection of frame work, the completion of the building is delayed and hence this method is restored. In most of the building sites, this method is popular, so in industrial buildings where the elements have longer spans. Use of double tees, channel units, cored stabs, slabs, hyperboloid shells, etc, are some of the horizontal elements used. This method is efficient when the elements are readily available and the building has reached the roof level. The delay caused due to erection of framework, delay due to removal of framework is eliminated completely in this method of construction suitable for any type of building provided lifting and erection equipment’s are available.
####### Total prefabrication:Very high speeds can be achieved by using this method of construction. The method can be employed for frame type of construction or for panel type; the total prefabrication is done on-site or off-site. The choice of the two methods depend on the situations when the factory produced elements are transported and erected on site, we call it off-site prefabrication. If this method is to be adopted we should have a very good transportation facility for the products to be transported to the site of construction. If the elements are cast near the building site and erected, the transportation of elements can be eliminated, but we have to co nsider the space availability for establishing such facilities though it istemporary.
Modular coordination means the interdependent arrangement of a dimension based on a primary value accepted as a module. The strict observance of rules of modular coordination facilitated, 1. Assembly of single components into largecomponents. 2. Fewest possible different types ofcomponent. 3. Minimum wastage of cuttingneeded. Modular coordination is the basis for a standardization of a mass production of component. A set of rules would be adequate for meeting the requirements of conventional and prefabricated construction. These rules are adaptable for, a. The planning grid in both directions of the horizontal plan shallbe 1. 3m for residential and institutionalbuildings, 2. For industrialbuildings, 15m for spans up to12m 30m for spans between 12m and18m 60m for spans over18m The centre lines of load bearing walls shall coincide with the grid lines. b. In case of external walls the grid lines shall coincide with the centre line of the wall ora line on the wall 5 cm from the internal face of thewall. c. The planning module in the vertical direction shall be 1m up to and including a height of2.8m. d. Preferred increments for the still heights, doors, windows and other fenestration shall be 1m. e. In case of internal columns the grid lines shall coincide with the centre lines of columns. e. In case of external columns, the grid lines shall coincide with the centre lines of the columnsin the storey or a line in the column from the internal face of the column in the topmoststorey. A basic module can be represented as module and for larger project modules are represented Mp. For eg: For a project module in horizontal coordination, the component can be of 30cm and for vertical component size be of 10cm. The storey height is fixed between finished floor levels as 2.8m and if the thickness of slab is<15cm storey height is fixed as 2.7m. The Centre distance between the load bearing walls can be chose from a set of modules. The use of other dimensions is not allowed. In the design of a building, modular grid can be used consisting of parallel line spaced at a value of module M or Mp and a grid line chosen as a base for setting out a part of a building becomes a modular axis. In the fig (a), a typical grid is chosen for load bearing walls without duct. The interior walls are placed so that their centerlines coincide with the modular axis. In the fig (b), a grid is shown for load bearing walls with hollow ducts in between. The centre line of the grid is found by deducting the size of duct.
System is referred to a particular method of construction of buildings using the prefabricated components which are inter related in functions and are produced to a set of instructions. With certain co strains, several plans are possible; using the same set of components, the degree of flexibility varies from system to system. However in all the systems there is a certain order and discipline. The system of prefabricated construction depends on the extend of the use of prefab components, their characteristics to be considered in devising a system: a. Intensified usage ofspaces b. Straight and simple wallingscheme c. Limited sizes and numbers ofcomponents d. Limited opening in bearingwalls e. Regulated locations ofpartitions f. Standardized service and stairunits g. Limited sizes of doors and windows with regulatedpositions h. Structural clarity andefficiency i. Suitability for adoption in low rise and high riseblocks j. Ease of manufacturing storing andtransporting k. Speed and ease oferection l. Simple jointingsystem
Design for prefabrication, preassembly and modular Construction. Simplify and standardize connectiondetails. Simplify and separate building systems. Consider w orker safety during Deconstruction Minimizebuilding Components andmaterials. Select fittings, fasteners, adhesive and sealants that allow for quicker assemblyand facilitate the removal of reusablematerials. Design to accommodatedeconstruction Logistics. Reducebuildingcomplexity. Design for reusablematerials. Design for flexibility andadaptability.
o Self supporting readymade components are used, so the need for formwork, shuttering and scaffolding is greatlyreduced. o On-site construction and condition is minimized. o Less waste mayoccur. o Construction time is reduced and buildings are completed sooner, allowing an earlier return of the capitalinvested. o Quality control can be easier in a factory assembly line setting than a construction sitesetting. o Prefabrication can be located where skilled labour is more readily available and costs of labour, power materials, space and overheads arelower. o Time spoil in bad weather or hazardous environments at the construction site is minimized. Saving in cost, material, time & manpower. Shuttering and scaffolding is not necessary. Independent of weathercondition. o
Careful handling of prefabricated components such as concrete panels (or) steel and glass panels is reduced. Similarly leaks can form at joints is prefabricated components. Attention has to be paid to the strength and corrosion resistance of the joining of prefabricated sections to avoid failure of the joint. Transportation costs may be higher for voluminous prefabricated sections than for the materials of which they are made, which can often be packed more efficiently. Large group of buildings from the same type of prefabricated elements tend to look drab and monotonous Local jobs are lost.
1. Prefabricated structures are used for sites which are not suitable for normal construction method such as hilly region and also when normal construction materials are not easilyavailable. 2. PFS facilities can also be created at near a site as is done to make concrete blocks usedin plane of conventionalknick. 3. Structures which are used repeatedly and can be standardized such as mass housing storage sheds, godowns, shelter, bus stand security cabins, site offices, Fool over bridges road bridges. Tubular structures, concrete building blocks etc., are prefabricateds tructures
The term production of systems is describes a series of operation directly concerned In the process of making or more apply of moulding precast units on the face of it there are very many techniques since almost every type prefabricates requires a Specific series of operation in its production. These techniques however may be grouped into three basic method of production. These are 4. The standsystem 5. The conveyor belt or production linesystem 6. The aggregatesystem 7. Stand system In the stand system the prefabricates mature at the point where they were moulded While the production team moves to successive stands the bed on which prefabricates. Conveyor belt The conveyor belt system of production splits the whole production process in to a series of operation carried out at a separate successive and permanent point to the heat may be by means of conveyor belt trolleys & craneetc. Aggregate system The word aggregates describes a large, complex permanently installed set of machines and mechanical application which can carry out most of the separate operation invo lved in casting concrete components.
The location of pre casting yards consist of storage facilities suitable for transporting and erection equipments and availability of raw materials are the critical factors which should be carefully planned and provided for effective and economic use of pre-cast concrete components in construction. The manufacture of the components can be done in a centrally located factor of in a site where pre casting yards set-up at or near the site of work.
Factory prefabrication is restored in a centrally located plant for manufacture of standardized components on a long form basis. It is a capital intensive production where work is done throughout the year preferably under acovered shed to avoid the effects of seasonal variations high level of mechanization can always be introduced in this system where the work can be organized in a factory like manner with the help of constant team of workmen. The basic disadvantage in factory prefabricated, is the extra cost in occurred in transportation of elements from plant to site of work sometimes the shape and size of prefabricable are to be limited due to lack of suitable transportation equipment roads controls etc.
In this scheme, the components are manufactured at site near the site of work as possible. This system is normally adopted for a specific job order for a short period. The work is normally carried out in open space with locally a valuable labour force. The equipment machinery and moulds are of mobile nature. Therefore there is a definite economy with respect to cost of transportation. This system suffers from basic drawback of its non-suitability to any high degree of mechanization. It has no elaborate arrangements for quality control.
The various processes involved in the manufacture of precast elements are classified as follows: 1) Mainprocess 2) Secondary (auxiliary)process 3) Subsidiaryprocess MAIN PROCESS: It involves the following steps. 1) Providing and assembling the moulds, placing reinforcement cage in position forreinforced concrete work, and 2) Fixing of inserts and tubes wherenecessary. 3) Depositing the concrete in to themoulds. 4) Vibrating the deposited concrete into themoulds. 5) Demoulding theforms. 6) Curing (steam curing ifnecessary) 7) Stacking the precastproducts. SECONDARY (AUXILLARY) PROCESS: This process is necessary for the successful completion of the process covered by the main process. 1) Mixing or manufacture of fresh concrete (done in a mixing station or by a matchingplant). 2) Prefabrication of reinforcement cage (done in a steel yard ofworkshop) 3) Manufacture of inserts and other finishing items to be incorporated in the main precastproducts. 4) Finishing the precastproducts. 5) Testing the precastproducts. STAGES OF PREFABRICATED CONCRETE PRODUCT: FLOW DIAGRAM OF STAGES OF PROCESSING CONCRETE---------MOULD-----------------STEEL MIXING--------------PREPARATION--------CUTTING FILLING----------------------------------------REINFORCING COMPONENT COMPACTION CURING DEMOULDING STORAGE TRANSPORT Transport of prefabrication elements must be carried out and with extreme care to avoid any flock and distress in elements and handled as far as possible to be placed in final portion. Transport of prefab elements inside the factory depends on the method of production selected for the manufacture. Transport of prefab elements from the factory to the site of action should be planned in conformity with the trafficable rules and regulations as stipulated by the authouriticthe size of the elements is often restricted by the availability of suitable transport equipment, such as tractor-am-tailor, to suits the load and dimension of the member in addition to the load carrying capacity of the bridges on theway. While transporting the prefab elements in various systems, such as wages, trucks, bullock cards etc. care should be taken to avoid excessive cantilever actions and desired supports are maintained. Special care should be taken in negotiating sharp beds uneven of slushy roads to avoid undesirable stresses in elements and in transport vehicles. Before loading the elements in the transporting media, care should be taken to ensure the base packing for supporting the elements are located at specified portion only.
ERECTION It is the process of assembling the Prefabrication element in the find portion as per the drawing. In the erection of prefab elements the following items of work are to be carried out. 1).Slinging of the prefab elements. 2).Tying up of erection slopes connecting to the erection hooks. 3).Cleaning the elements and the site of erection. 4).Cleaning the steel inserts before incorporation in the joints lifting and setting the elements to correct position. 5).Adjustments to get the stipulated level line and plumb. 6).Welding of deats. 7).Changing of the erection tackles. 8).Putting up and removing the necessary scaffolding or supports. 9).Welding the insorts laying the reinforced in joints. The erection work in various construction jobs by using prefab elements differs with risk condition, hence skilled foremen, and workers to be employed on the job. Equipments required for erection Equipments required for the prefab elements in industry can be classified as. 1) Machinery required for quarrying of course and fineaggregates 2) Conveying equipment, such as but conveyor, chain conveyorsetc. 3) Concretemixers 4) Vibrators 5) Erection equipment such as cranes, derricks, chain pulleyetc. 6) Transportmachines 7) Work shop machinery for fabricating and repairingsteel. 8) Bar straitening, bending and weldingmachines 9) Minor tools and takes, such as concrete bucketsetc… 10) Steam generation a plant for acceleratedcuring Planning co-ordination It is important to have the pre caster erector/installer and builder working together to achieve best performance. Site Access and storage • Check for site accessibility and precast panels deliveryto site especially low bedtrailers • Check whether adequate space for temporary storage before installation andground conditions. (firm ground &leveled) • Uneven ground will cause overstress & crackpanels. Planning crane Arrange ment • Plan the crane capacity and lifting gears basedon • Heaviest weight of precastpanels • Liftingheights. • Workingradius • Position of crane in relation to final panellocation Plan othe r equipments • Boom lift and scissor lift for unhooking installedpanels. • Liftinggears Skilled personnel’s • Competent craneoperators • Rigger • Signaledetc General considerations for crane selection • Total liftingweight • Cranemodel • Crane safe working load (SWL) (i.e) Based on 15% capacity buildin F.O.S. 1.33 o Lifting capacity must be 1.5 times the total weight i.e) F.O.S 1.5 • Lifting and swingradius • Crane countereight • Crane boom length is relation to the vertical and horizontal clearance from thebuilding. Installation Process Installation of vertical components Verification of Delivered Panels • Check the panels delivered for correct marking lifting hook and positionetc. • Surface finishingcondition • Pc Dimensioncompliance • ReinforcementProvision/position • Architectural Detailcompliance 1. Settingout • Check the panels delivered for marking, lifting hook andcondition. • Set the reference lines &grids • Check starter bars for vertical components before hoisting forinstallation 2. Setting out Quality controlpoint • Ensure correct offsetline • Check shim pedal/plate level andfirm • Rubber gasket propertysecured • For external wall/column place backerrod. 3. Hoisting, Rigging andInstallation • While tilting provide rubber pad to avoid chipoff. • Lift and rig the panel to designatedlocation • Adjust the panel in position andsecure • Lifting of space adding items with balanced centre of gravity. • Ensure horizontal alignmentcorrect • Ensure panel vertically to correctplumb • Check panel to panel gap consistency • Check stability of prop before releasing hoistingcable. 4. Groutingworks • Prepare and apply non shrink mortars toseal • For corrugated pipe sleeve on spliced sleeve pour NSGT or proprietary grouts into pipeslab. • Keep installed panels undisturbed for 24hrs. • Check joint widths are consistent beforegrouting • Grout used should be same grade of components and self compacting to preventcracking. • Collect test cube sample for testing for critical element or load bearingelements 5. Connecting joints • Cast in situ joints install rebars asrequired • Set up forms for castingjoints • Do Concreting • Remove forms after sufficientstrength • For external connections sealant shall beused • Panel with welded connections welding asrequired Installation of Horizontal Elements 1. Settingout • Set reference line/offset line to required alignment and level of slab/beam duringinstallation • Put temporary prop to support the precast slab/beamelements • Before Hoisting chem.Dimensions • Check level and stability ofshim • Check protruding/ starter bars are within the Specified tolerance to prevent anyobservation during the erectionprocess 2. Hoisting & Installation • Put temporary props to supportslab/beam • Lift and rig the elements in designatedlocation • Align and check the level beforeplacement • The beams shall prop at least 2location • Balcony planter box and shall be supported more than 2 location based on designconsiderations • Check level of precastelements 3. Connections/Jointing • Precast w ith cast-in-situ joints place the lap rebars asrequired • Set formwork for castingjoints • Remove formwork after concrete strength isachieved • Supporting beams shall be designed to form part of formworkjoints • The connecting/lapping rebars tied &secured • Same grade of concrete 10 to be used that of pael. 4. Installation using Bigcanopy • Big canopy high rise precast concrete constructionsystem • This is used for faster andefficient 5. ErectionPurpose • In Japan o Used to construct the 26 storey pre-cast concrete30,763m 2 o The system realized 60% reduction inlabor requirement for the frameerection. • InSingapore o DBS China square used the system to erect is efficient andfaster
The word system is referred to a particular method of construction of buildings using prefabricated components which are inter-related in functions and are produced to a set of instructions with certain constraints. Several plans are possible using the same set of components. The degree of flexibility varies from system to system.
The following characteristics among others are to be consideration devising a system. 1) Intensified usage ofspaces. 2) Straight and simple wallingscheme. 3) Limited sizes and number ofcomponents. 4) Limited opening in bearingwalls. 5) Regulated locations ofpartitions. 6) Standardized service and stairunits. 7) Limited sizes of doors and windows with regulatedpositions. 8) Structural clarity andefficiency. 9) Suitability for adoption in low rise and high riseblocks. 10) Ease of manufacturing, storing and transporting. 11) Speed and ease oferection. 12) Simple jointing system.
The system of prefabricated construction depends on the extent of the use of prefabricated components, their material, sizes and the technique adopted for their manufacture and use in building. The various prefabrication systems are outlined below. 1) Smallprefabrication 2) Mediumprefabrication 3) Largeprefabrication 4) Open prefabricationsystem a. Partial prefabrication opensystem b. Full prefabrication opensystem 5) Large panel prefabricationsystem 6) Wallsystem a. Cross wallsystem b. Longitudinal wallsystem 7) Floorsystem 8) Stair casesystem 9) Box type system
The first 3 types are mainly classified according to their degree of precast elements using in that construction. for eg:- brick is a small unit precasted and used in buildings. This is called as small prefabrication. That the degree of precast element is verylow.
Suppose the roofing systems and horizontal member are provided with precast elements. These constructions are known as medium prefabricated construction. Here the degree of precast elements are moderate.
In large prefabrication most of the members like wall panels, roofing/flooring systems, beams and columns are prefabricated. Here degree of precast elements are high.
One of the main factors which affect the factory prefabricate on is transport. The width of road walls mode of transport vehicles are the factors which factor the prefabrications which is to be done on site or factory. Suppose the factory situated at a long distance from the construction site and the vehicle have to cross a congested traffic with heavy weighed elements the cost in-situ prefabrication is preferred even though the same condition are the cast in site prefabrication is preferred only when number of houses are more for small elements the conveyance is easier with normal type of lorry and trailers. Therefore we can adopt factory (or) OFF site prefabrication for this type of construction.
This system is based on the use of the basic structural elements to form whole or part of a building. The standard prefabricated concrete components which can be used are, 1) Reinforced concrete channelunits 2) Hollow coreslabs 3) Hollow blocks andbattens 4) Precast plank andbattens 5) Precast joists andtiles 6) Cellular concreteslabs 7) Pre stressed / reinforced concreteslabs 8) Reinforced / pre stressed concretecolumns 9) Precast lintels andsunshades 10) Reinforced concrete waffle slabs / shells 11) Room size reinforced / pre stressed concretepanels 12) Reinforced / pre stressed concrete wallingelements 13) Reinforced / pre stressed concretetrusses The elements may be cost at the site or off thesite. Foundation for the columns could be of prefabricated type of the conventional cast in situ type depending upon the soil conditions and loads. The columns may have hinged or fixed base connections depending upon the type of components used and the method of design adopted. There are two categories of open prefabricated systems depending on the extent of prefabrication used in the construction as given below. 1) Partial prefabrication opensystem 2) Full prefabrication opensystem
The system basically emphasizes the use of precast roofing and flooring components and other minor elements like lintels, sunshades, kitchen sills in conventional building construction. The structural system could be in the form of in situ frame work or load bearingwalls.
In this system, almost all the structural components are prefabricated. The filler walls may be of bricks or of any other local materials.
This is based on the use of large prefabricated components. The components used are precast concrete large panels for walls, floor roofs, balconies, stair cases etc. The casting of the components could be at the site or off the site. Depending upon the context of prefabrication, this system can also lend it self to partial prefabrication system and full prefabrication system.
Structural scheme with precast large panel walls can be classified as 1) Cross wallsystem 2) Longitudinal wallsystem
In this system the cross walls are load bearing walls. The facade walls are non-load bearing. This system is suitable for high rise buildings.
In this system, cross walls are non-bearing, longitudinal walls are load bearing. This system is suitable for low rise buildings. A combination of the above systems with all load bearing walls can also be adopted. Precast concrete walls could be 1) Homogeneouswalls 2) Non-homogeneouswalls Homogeneous walls: The walls could be solid or ribbed. Non-homogeneous walls : Based on the structural functions of the walls, the walls could be classified as a. Load bearingwalls b. Non-load bearingwalls c. Shearwalls Based on their locations and functional requirements the walls are further classified as (i) External walls which can be load or non- load bearing depending upon the layout. They are usually non- homogeneous walls of sandwiched type to impart better thermalcomforts. (ii) Internal walls which provide resistance against verticalloads, horizontal loads, fire etc. and are normallyhomogeneous.
Depending upon the composition of units, precast flooring units couldbe homogeneous ornon- homogeneous. 1) Homogeneous floors could be solid slabs, cored slabs, ribbed or waffleslabs. 2) Non-homogeneous floors could be multilayered ones with combinations light weight concrete or reinforced / pre stressed concrete with filledblocks. Depending upon the way, the loads are transferred the precast floorscould be classified as one way or two waysystems.
One way system transfers loads to the supporting members in one direction only. The precast elements of this category are channel slabs, hollow core slabs, hollow blocks and hollow plank system, channels and tiles system, light weight cellular concrete slab etc.
Transfer loads in both the direction imparting loads on the four edges. The precast element under this category are room sized panels two way ribbed or waffle slab system etc..
Stair case system consists of single flights with inbuilt risers and treads in the element only. The flights are normally unidirectional transferring the loads to supporting landing slabs or load be ring walls.
In this system, room size unit are prefabricated and erec ted at site. This system derives its stability and stuffiness from the box limits which are formed by four adjacent walls. Walls are joined to make rigid connections among themselves. The box unit rest as plinth foundation which may be of conventional type of pre-casttype.
Prefabricated building materials are used for buildings that are manufactured off site and shipped later to assemble at the final location some of the commonly used prefabricated building. The materials used in prefabricated components are many. The modern trend is to use concrete steel, treated wood, aluminum cellular concrete, light weight concrete, ceramic products etc. While choosing the materials for prefabrication the following special characteristics are to beconsidered. • Light weight for easy handling and transport and to economic ansections and sizes offoundations • Thermal insulationproperty • Easyworkability • Durability in all weatherconditions • Non combustibility • Economy incost • Soundinsulation
• Easyavailability • Light weight for easy handling and transport and to economies onsections and seizes offoundations. • Thermal insulationproperty • Easyworkability • Durability to all weatherconditions • Non combustibility • Economy incost
behavior of large panel construction Large panel structure All the main part of a building, including exterior wall and interior wall, floor slab, roofs, and staircase, may be made up from large panel structure are used in two main design schemes, frame-panel and panel building. In frame-panel building, all the base loads are borne by the building’s frame, and as enclosure element. Frameless buildings are a ssembled from panels that perform the load bearing and enclosing functions simultaneously. • Large panel structure for Exteriorwall • Large panel structure for Interiorwall. • Large panel structure for floorslab • Large panel structure for Roofelement. a) Large panel structure for Exteriorwall; • Large panel structure for exterior walls consist of panel one or two stories in height and one or two rooms in width. The panel may be blind (without openings) or with window or door openings. • In terms of design, the wall panels may be single layer (solid) and multilayer(sand witch) Solid panels are manufactured from materials that have insulating properties and at the same time can perform supporting functions for example, light weight concrete, cellular concrete, and hollow ceramic stone. • Sandwich wall panels are made with two or three layers: their thickness depends on the climate conditions of the regions and the physic technical properties of the materials used for the insulating layer and for the exteriorlayer. • The surface of exterior wall panels is covered with decorative mortar or isfaced with ceramic or other finishingtiles. • After assembly, the joints between panel are filled with mortar orwith lightweight or ordinary concrete and then sealed with packing and specialmastics. b) Large panel structure for Interiorwalls: • The large panel structure of interior walls may be non load bearing or loadbearing. • In the first case, they are made from gypsum slag concrete or fromother materials that act as enclosures. In the case of load bearing structure, the wall panels, which combine enclosing and load bearing function, are made from heavy or lightweight, silicate or cellular concrete, or vibration set brick or ceramicwork. • The dimensions of the panels are determined by the dimensions of the rooms (in apartment houses), their height is equal to the height of a story, the width is equal to the depth or width of a room, and the thickness of the walls between rooms is usually 10-14 cm(between apartment 14-18cm) 25 c) Large panel structure for floorslab: • The large panel structure of floor slabs are usually made from reinforced concrete, the area of the floor slabs in apartment buildings usually equals the area of one room and be as great as 30 sq.m. • Flagging panels have an area of 5-8 sq m. The large panel floor slabs of housing public, and administrative building are of both the solid and sandwich types in the latter, provision is made for a sound insulation layer to reduce air and impactnotice. • Composite floor panels, consisting of a load bearing reinforced concrete panel combined with a floor or ceiling panel and soundproofing, insulating, and other lay r, a e often used in housing construction. d) Large panel structure for RoofElement: • The large panel roof elements are used in housing and public buildingsmainly in the form of combined articles roofs, and in industrial buildings the roof panels have a span of up to 12m. • The weight of large panel structure depends on the method of dividingthe building into prefabricated element; it is usually 1.5-7.5tons. • Large panel structure of a high rise apartment building consist of (1) foundation slab,(2) exterior wall panel,(3) interior wall panel, (4) floor slab,(5) deck ,(6) exterior panel in the process ofinstallation • At the joints, the panels have to which steel connecting pieces are welded, thus linking together all the panels and providing general stability of thebuilding. • Large panel structures are used in the construction of high risebuilding. roof and floor slabs construction and precaststructure Behavior of roof and floor slabs: • The roofing / flooring system consist of RC planks andjoists. • The planks are casted to a standard size and they are connected with RCCjoists which are provided at a regularinterval. • The loads from planks are transmitted to RCC joists and then to mainbeams. • The main beams are provided with channel sections 10cm projections on the necessary side with the spacing ofjoist. • The joists are seated in the channel and boltedtogether. • The loads from slabs to the main beam will come as pointloads. • The roofing / flooring slabs system consists of planks which are supported overRCC joist. • The planks can be made in any one of the following form with orwithout prestressing. According to the span andloads. • The usual width of these of slabs is 0.5m and spanning to the requirement up to a maximum limit of 5m withoutprestressing. • The thicknesses of planks are casted in two steps with different mould to access monolithic action with adjacent slab by putting necessary reinforcement andconcreting. Structural Behavior Of Precast Structure: 1. The design load-carrying structure advantage from the viewpoint ofprefabrication. 2. Principles of structuralanalysis. 3. Variousspecifications. 4. Dimensioning ofjoists. 5. Elimination of handlingstresses. 6. Redistribution of stresses in jointedstructure. 7. Calculation of reinforced concrete structure co-operating with strengthening concrete layercast- in-situ. 8. Influence of the sequence and the method of placing on the stressof the state of thestructure. 9. Stability of precast structuralmembers. 10. Quality of materials used for precast reinforced concretestructure.
In Floor and Roof: • Structural floor / roof account for substantial cost of a building in normal situation. Therefore, any saving achieved in floor/roof considerably reduce the cost ofbuilding. • Use of standardized and optimized roofing components where shuttering is avoided prove to be economical, fast and better inquality. • Some of the prefabricated roofing/flooring components found suitable in many low-cost housing projectsare Precast RC planks: Precast RC planks Prefabricated brick panels. Precast RB curved panels. Precast RC channel roofing. L panel roofing. Trapezon panel roofing Unreinforced pyramidal brick roof. Precast concrete panels. • This system consists of precast RC planks supporting over partially precast joist. RC planks are made with thickness party varying between 3 cm and 6cm. • There are haunches in the planks which aretapered. • When the plank is put in between the joists, the space above 3 cm thicknessis filled with in-situ concrete to get tee-beam effect of thejoists. • The planks are made in module width of 30 cm with maximum length of 150cm and the maximum weight of the dry panel is 50kg. • Precast joists are rectangular in shape, 15 cm wide and the precast portion is 15cmdeep. • The main reinforcement of the overhang provided at the top in the in-situ concrete attains sufficientstrength. • The savings achieved in practical implementations compared with conventional RCC slab about25%. Prefabricated brick panel: • The prefabricated brick panel roofing system consist of is made of first class brick reinforced with two MS bars of 6mm dia and joists filled with either1:3 cement mortar or M15concrete. • A panel of 90cm length requires 16 bricks and a panel of 120cm requires 19bricks. • Partially precast joist it is a rectangular shaped joist 13cm wide and 10cm to12.5cm deep. • The overall depth of joist with in-situ concrete becomes 21cm to 23.5cm, it is designed as composite tee-beam with 3.5cm thickflange. • The partially precast RC joist, is designed as simply supporting tee-beam with 3,5cm thick flange. Precast curved brick arch panel: • This roofing is same as RB panel roofing except that the panels do not have an yreinforcement. • A panel while casting is given a rise in the centre and thus an arching action is
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