Raft foundation is a thick concrete slab reinforced with steel which covers the entire contact area of the structure like a thick floor. The bearing capacity increased by combining all individual footings in to one mat since bearing capacity is proportional to width and depth of foundations. The extensive foundation which is usually called raft foundation, is a unified foundation that extends throughout the entire area of the columns. A raft or mat foundation is a large concrete slab used to interface columns in several lines with the base soil. The piled raft foundation utilises the pile group for the control of settlement, with the piles providing most of the stiffness at the service loads while the raft elements provide. Compensated foundation structural design of mat foundations 2. Instructional materials complementing fema p751, design examples foundation design 3. Determine the stress distribution beneath the foundation. Here is the list of some of the major aspects, when to use or choose a mat foundation. The raft will be used for economical consideration. We are currently based in the east of pretoria, gauteng.
A raft foundation may be used where the base soil has a low bearing capacity andor the column loads are so large that more than 50 percent of the area is covered by conventional spread footings. Design of raft foundation excel sheet raft foundation is a thick concrete slab reinforced with steel which covers the entire contact area of the structure like a thick floor. Determine the stress distribution beneath the foundation 5. Usually large concrete slab supporting many columns. To get a better idea about when to use raft foundation, it is important to understand how raft foundation works. Download excel sheet to design raft foundation easily. Design of mat foundations 1 design of mat foundations hemant kumar bhaskar roll no0610421 2 types of foundations. The behaviour of the raft foundation resembles the behaviour of a strip foundation grid. Winner of the standing ovation award for best powerpoint templates from presentations magazine. The book gives many examples of project applications covering a wide range of structural forms and ground conditions. Solid slab rafts, slab beam rafts, cellular rafts, piled raft foundations. Worlds best powerpoint templates crystalgraphics offers more powerpoint templates than anyone else in the world, with over 4 million to choose from. This foundation will be used for a loose sand soil. The first type solid slab rafts can be further divided as flat raft mats, wide toe rafts, blanket rafts and slip plane rafts.
Jan 4, 2018 download excel sheet to design raft foundation easily. A very good reference the piled raft foundation for the burj dubai design and. Sachpazis date 230420 chkd by date appd by date raft foundation design bs8110. When column loads are unequally distributed or where the foundation is a very heavy structure where stiffness is principal requirement to avoid excessive distortion of the structure as a result of variation in the load distribution on the raft, in such case slab and beam type raft foundation is provided. In this particular post we are going to consider the analysis and design of the same foundation using manual calculations according to the principles of the eurocodes.
Design of raft foundation excel sheet online civilforum. Consider the average uniform value of pressure act on each continuous slab. A raft foundation is a reinforced concrete slab under the whole of a building or extension, floating on the ground as a raft floats on water. The maximum differential settlement in foundation on clayey soils and sandy soils should not exceed 40mm and 25mm respectively. The maximum settlement should generally be limited to the following values. Which software is better for raft analysis safe, staad. Raft foundation design and analysis with a practical. Commonly used type of raft is the solid slab raft without downstand beam. It explores the assumptions that are made in the analysis of soil structure interaction, together with the associated calculation methods.
As a rule, raft foundation is used as a buildings foundation when the soil has a low bearing capacity. Between the geotechnical design parameters of bearing capacity and settlement, which are independent, if the design just satisfies bearing capacity, settlement will be over satisfied i. Sketchup 3d animation of basement details duration. Undoubtedly safe is the best software for raft foundation analysis and design in fact,best for any horizontal member design,punching and deflection check has been examined excellent in safe and even variable depth local thickening raft for sam. Raft foundation a mat foundation is a thick reinforced concrete slab supporting arrangement of columns or walls in a row and transmitting. Kousik deb,department of civil engineering,iit kharagpur. Design of raft foundations methods and calculations. Mat foundations are sometimes preferred for soils that have low loadbearing capacities, but that will have to support high column or wall loads. Raft foundation design requirements and applicability. Available textbooks, handbooks, various publications and papers give widely different approaches for design of raft foundations. Please wash your hands and practise social distancing. The system of beamslab roof consists of slab, main beams in short and long directions, and secondary beams may also be used.
Raft foundation is generally used to support structures like residential or commercial buildings where soil condition is poor, storage tanks, silos, foundations for heavy industrial equipment etc. Curve 3 represents the case in which piles are positioned in such a way to act as a settlement reducers. A foundation system in which essentially the entire building is placed on a large continuous footing. Introduction a raft or mat foundation is a large concrete slab used to interface columns in several lines with the base soil. For a moment frame, the column vertical loads are the resultants of base overturning. The bearing capacity increased by combining all individual footings in to one mat since bearing capacity. If a single square footing need to be designed under the maximum axial load that is occurred in columns type 4. Raft foundation when to use, types, construction civil. The raft, or spread, foundation spreads the load of the building across the ground. Force on a pile eq on unloaded pile pile supporting structure. Ppt design of mat foundations powerpoint presentation.
This book examines alternative design procedures for plain and piled raft foundations. The scope of this session includes design of mat foundations for both. Sometimes area covered by raft may be greater than the contact area depending on the bearing capacity of the soil underneath. Plain slab raft which are flat concrete slab having uniform thickness throughout. Mat raft foundation 7 types of mat foundations 8 to design mat foundation. A structural designer engaged in the design of raft foundations finds it hard to select the method that can be carried out. This is an alternative if you cant use a traditional strip or trench fill foundations. The design of raft foundations involves a number of disciplines. A piled raft foundation combines two foundationbuilding techniques into a hybrid design suitable for specialized circumstances. Raft foundation is a thick concrete slab reinforced with steel which ppt presentation summary. On the base of structural system adopted for the structure of the raft, these can be classified as. Check out our resources for adapting to these times. Types of raft foundation raft support on the soil, 2.
Mat foundation raft foundation it is a combined footing that may cover the entire area under a structure supporting several columns and walls. Structural design of raft foundation pe civil exam. Oct 08, 2017 mat raft foundation modeling, input,check for soil pressure,punching check,deflection check. Instructional materials complementing fema 451, design examples foundation design 1416 reduction of overturning moment nehrp recommended provisions allow base overturning moment to be reduced by 25% at the soilfoundation interface.
The reinforcing bars runs normal to each other in both top and bottom layers of. Mat or raft foundation is a large concrete slab supporting several columns in two or more rows. What is the process for constructing a raft foundation. Design the structural component of the mat foundation using the stress distribution obtain from 4. Aug 12, 2017 design of raft foundation excel sheet raft foundation is a thick concrete slab reinforced with steel which covers the entire contact area of the structure like a thick floor. This paper sets out some principles of design for such foundations. The piled raft foundation utilises the pile group for the control of settlement, with the piles providing most of the stiffness at the service loads while the raft elements provide the additional capacity at the ultimate load levels. To begin constructing the solid slab raft foundation, the vegetative top soil original soil is removed then the soil left behind is compressed.
Ppt design of raft foundation based on geotechnical. Design of beamslab raft foundation bending moment and shear force diagrams for each slabs and beams in the short direction. The raft foundation is a kind of combined footing that may cover the entire area under the. Ppt shallow foundation analysis and design powerpoint. This type of foundation spreads the load of the building over a larger area than other foundations, lowering the pressure on the ground. What is the difference between pad foundation, strip foundation and raft foundation. Raft foundations sometimes referred to as raft footings or mat foundations. In conjunction with professional consulting engineers we provide a complete design and construction service for raft foundations.
Think of it as a raft floating on the ground supporting a structure. It is used where the supporting soil has low bearing capacity. The design of the foundation to satisfy the local shear failure criteria. For foundations of such high rise building, normally raft foundation, pile foundation or piledraft foundation are used. Apr 23, 2016 raft foundation r a f t f o u n d a t i o n s 8 9. Theyll give your presentations a professional, memorable appearance the kind of sophisticated look that todays audiences expect. Optimal cost design of rigid raft foundation report page link. Raft foundations e optimized design of piled raft foundations has been actively investigated in recent years 1920 21 22, focusing on the mechanisms of different pile arrangements and. It may occupy the entire foundation area or only a part of it. Raft foundations sometimes referred to as raft footings or mat foundations are formed by reinforced concrete slabs of uniform thickness typically 150 mm to 300 mm that cover a wide area, often the entire footprint of a building.
The properties used in the analysis and the design of this raft foundation are shown in table 4. Design philosophy of piled rafts concept of piled raft. What is the purpose of setting minimum amount of longitudinal steel areas for columns. For building foundation design, it is one of the most important aspects is to choose the right foundation.
Optimal cost design of rigid raft foundation report posted by. May 05, 2017 undoubtedly safe is the best software for raft foundation analysis and design in fact,best for any horizontal member design,punching and deflection check has been examined excellent in safe and even variable depth local thickening raft for sam. Raft foundation design for a typical 2 storey house example bs8110. The mat foundation, which is sometimes referred to as a raft foundation. For foundations of such high rise building, normally raft foundation, pile foundation or piled raft foundation are used. Piled raft foundations are increasingly being recognised as an economical and effective foundation system for tall buildings.
In order to transfer these loads properly to the soil, footings must be design to prevent excessive settlement minimize differential settlement, and. A raft foundation is essentially a reinforced concrete slab on the ground foundation designed for the specific soil conditions on the stand. The session describes the uses of mat foundations, historical perspectives that. Conventional rigid method structural design of mat foundations the conventional rigid method of mat foundation design can be explained.
Design of raft foundations as of american concrete institute committee 336, 1988 prepared by. Raft foundation design requirements and applicability a raft or mat foundation is a sizable concrete slab or slabandbeam system which supports all the loads of superstructure through walls or columns in two or more rows and rests on soil layer or rock. Footings are structural elements, which transfer loads to the soil from columns, walls or lateral loads from earth retaining structures. In case of prf of oil tank on nonliquefiable sand, the main concern in the rational design of the foundation is piles design and their punching effect on the raft, while the major critical. A conventionally reinforced mat raft foundation is selected, proportioned and designed, such as to.