Structural Design Of Raft Foundation - PE Civil Exam
QATAR UNIVERSITYCOLLAGE OF ENGINEERINGCOURSE: DESIGN OF REINFORCED CONCRETE STRUCTURESStructural Design ofRaft FoundationSubmitted to:Dr. Mohammed Al-ansariPrepared by:Haytham Adnan SadeqMohammed Saleem TahaDate of submission:01-01-2009Page 1
Acknowledgment:After completing this special project in Design of raft foundation for the course of Design ofreinforced concrete structures, we are deeply indebted to the people who contributed invarious ways towards its progress and completionWe are grateful to Dr. Mohammed Al-Ansari for his continuous goodness andencouragement. We would also like to express our deepest for our families and friends whohelped in the success of this project.Page 2
Abstract:In this report, a full discussion and clarification of the design of Raft foundation in loose sandwill be shown in details. The columns loads calculation for this raft is also will be shown interms of the turbidity area of the columns. Final design and detailing will be shown at theend of this report with SAFE software design out file attached.Page 3
Table of Contents:Acknowledgment: . 1Abstract: . 3List of Figures: . 5List of Tables: . 61. Introduction: . 72. Objective: . 83. Raft Modeling and Analysis: . 93.1.0 Raft dimensions: . 93.2.0 Columns loads in Raft:. 103.3.0 Why Raft should be used: . 133.4.0 Raft thickness: . 143.5.0 Raft Depth check: . 153.5.1 One way shear: . 153.5.1 Two way shear (interior column): . 163.5.2 SAFE Punching Shear check: . 163.5.0 Soil Pressure Check: . 173.6.0 SAFE Settlement Analysis: . 203.7.0 Moments Strips SAFE results: . 213.7.1 X direction strips . 213.7.2 Y direction strips . 224. Manual & Computer Design: . 234.1.0 X-strip Design: . 234.2.0 Y-strip Design: . 254.3.0 Comparison Table: . 274.4.0 Detailing: . 275. Conclusion: . 286. References: . 297. Index: . 30Page 4
List of Figures:Figure 1, Raft layout . 9Figure 2, Raft dimension and column spacing . 10Figure 3, Column design . 12Figure 4, Diagonal tension shear area . 14Figure 5, C4 shear diagram . 15Figure 6, maximum shear in strips CSY3 . 15Figure 7, two way shear area . 16Figure 8, punching shear factors for the raft . 16Figure 9, resultant position due to column loads . 17Figure 10, columns total service loads (DL LL) . 18Figure 11, corners of raft . 19Figure 12, settlement of Raft using SAFA software. 20Figure 13, X-strip moment diagram . 21Figure 14, Y-strip moment diagram. 22Page 5
List of Tables:Table 1, parmaters used in Raft Design . 8Table 2, design loads . 10Table 3, all columns loads . 11Table 4, Properties taken in Raft Design . 13Table 5, x-strips moments values . 21Table 6, y-strips moments values . 22Table 7, comparison between manual and computer design . 27Page 6
Design of Raft Foundation1. Introduction:This foundation will be done for a storage 5 story building. The raft will be used foreconomical consideration. The justification of using raft foundation will be discussed incolumns loads section 3.2.0.The raft foundation is a kind of combined footing that may cover the entire area under thestructure supporting several columns in one rigid body. In this project, the soil profile showsthat the bearing stress is around 100 kN/m 2 . The raft foundation is usually used with thiskind of soil. The columns have high axial loads. If spread footings used, the area of thefooting required will be big as will be shown in column load section 3.2.0. In this big spreadfooting condition, the raft foundation could be much practical and economical.In this project, the raft will be designed as flat plate, which has a uniform thickness andwithout any beams or pedestals.Page 7
Design of Raft Foundation2. Objective:This report shows the structural design of the raft foundation. The raft is modeled in SAFEsoftware. All analysis and design are based on the ACI code. Raft foundation can be designusing several methods. In this special project the method used in the design called βtheConventional Rigid Methodβ and all design steps will be shown in the report.All design parameters are shown in table 1.ParameterYield strength of steelStrength of concreteYoung modules of elasticityDear load factorLive load factorSoil Unit weightAllowable Bearing stressConcrete Unit weightNotationFyfcED.L.FL.L .FΞ³ soilqaΞ³ concreteValue400 MPa30 MPa20000001.21.615 kN/m3100 kN/ m225 kN/ m3Table 1, parmaters used in Raft DesignPage 8
Design of Raft Foundation3. Raft Modeling and Analysis:3.1.0 Raft dimensions:Raft foundation has been modeled in SAFE software. The raft has x side spacing of 7 metersand y-side spacing of 6 meters. One meter edge is around the edges columns. The plan ofthe raft is shown in figure 1.Figure 1, Raft layoutThe total area of the raft 3 7 1 1 3 6 1 1 23 20 460 π2Page 9
Design of Raft Foundation3.2.0 Columns loads in Raft:The industrial building that this raft is designed for has 5 stories with dead and live loadswhich are shown in table 2.Load typeServicesSlab own weight assumedFlooringLive loadsLoad caseDeadDeadDeadLiveLoad value (kN/m2)2.5 kN/m2(25kN/m3)(0.2m) 5 kN/m21 kN/m27 kN/m2Table 2, design loadsFigure 2 shows the columns notation and the yellow lines shows the turbidity areas that arecovered by the columns.Figure 2, Raft dimension and column spacingLoads per square meter are calculated as:ππ ππ. ππ οΏ½οΏ½οΏ½πππ π·πππ ππππ π π‘πππ π 5 2.5 1 5 42.5 οΏ½π πΏπππ ππππ π π‘πππ π 7 5 35 ππ/π2π2πΊππππππ π·πππ ππππ π π‘πππ π 5 2.5 1Page 10
Design of Raft FoundationColumns loads:π΄π₯πππ π·πππ ππππ ππ‘ππ π πππ π’πππ‘ ππππππ ππ’ππππππ‘π¦ πππππ2Column type (1):Axial unfactored Dead load 42.5 kN/m2 4 4.5 m2 765 kNAxial unfactored Live load 35 kN/m2 4 4.5 m2 630 kNTotal Sevice Axial load 765 630 kN 1395 kNUltimate axial load 1.2 765 1.6 630 1926 kNColumn type (2):Axial unfactored Dead load 42.5 kN/m2 4 7 m2 1190 kNAxial unfactored Live load 35 kN/m2 4 7 m2 980 kNTotal Sevice Axial load 1190 980 kN 2170 kNUltimate axial load 1.2 1190 1.6 980 2996 kNColumn type (3):Axial unfactored Dead load 42.5 kN/m2 4.5 6 m2 1148 kNAxial unfactored Live load 35 kN/m2 4.5 6 m2 945 kNTotal Sevice Axial load 1148 945 kN 2093 kNUltimate axial load 1.2 1148 1.6 945 2889 kNColumn type (4):Axial unfactored Dead load 42.5 kN/m2 7 6 m2 1785 kNAxial unfactored Live load 35 kN/m2 7 6 m2 1470 kNTotal Sevice Axial load 1785 1470 kN 3255 kNUltimate axial load 1.2 1785 1.6 1470 4494 kNExtra Column loads:These columns are placed in the right edge of the raft, and they are external columns thatare carried by the raft and will cause moments around x-axis and y-axis as will be shown.The axial loads of the original columns and extra columns are shown in the table 3.Column no.Dead load (kN)Live load 300250200150C4 (maximum)C5 (extra)C6 (extra)C7 (extra)C8 (extra)Total service load(kN)1395217020933255800700600500Total factoredload (kN)19262996288944941080940800660Table 3, all columns loadsPage 11
Design of Raft FoundationColumns Dimensions and Reinforcement:Columns have been designed using the PCA columns. All columns have dimensions of 500mm by 500 mm with 12 22 as shown in figure 3. This design of column will resists allcolumns loads up to the maximum load of 4494 kNFigure 3, Column designππ ππ 0.7 0.8 (0.85ππβ² π΄π πΉπ¦ π΄π π‘ )ππ ππ 0.7 0.8 (0.85(30)(500)(500) (400)(4562)Pc 4592 kN Pu 4494 kNPage 12
Design of Raft Foundation3.3.0 Why Raft should be used:If a single square footing need to be designed under the maximum axial load that isoccurred in columns type 4.This foundation will be used for a loose sand soil. The properties used in the analysis and thedesign of this raft foundation are shown in table 4.Soil typeEffective bearing stress for the soilSub-grade modulesConcrete strength of raftReinforcement Steel strengthLoose sandq e 100 kN/m220,000 kN/m330 MPa400 MPaTable 4, Properties taken in Raft Designq e 100 kN/m2Total Maximum Sevice Axial load 1785 1470 kN 3255 kN1.1 3255Area of single sqaure footing 35.8 m2100B X B 35.8 B 35.8 6 m by 6 mThis area is considered to be very big to be excavated under one column. So the raftfoundation will be much efficient and more economical for this foundation.Page 13
Design of Raft Foundation3.4.0 Raft thickness:In Raft foundation, the thickness can be determined by checking the diagonal tension shearthat will be imposed in the raft. The maximum ultimate column load will be used in thecalculation.π ππ )(π (0.34) ππβ²11.12.2.1.cWhere,U factored column load Reduction factor 0.85ππ The parameter of the sheared aread effective depth of raftππβ² Compressive strength of concreteIn this Raft,π 4494 kN 4.494 MNππ 4 0.4 π 1.6 4πFigure 4, Diagonal tension shear areaAnd by using the equation above, the requireddepth of the raft can be determined.π ππ )(π (0.34) ππβ²ACI-05 11.12.2.1.c4.494 1.6 4π)(π 0.75 (0.34) 304.494 1.6π 4π 2 1.3973.2169 1.6π 4π 20 4π 2 1.6π 3.21690 4π 2 1.6π 3.2169Solving equation for dd 0.689 m 689 mm 700 mmThickness of the raft 700 75 25 (assumed bar diameter)Thickness 800 mmPage 14
Design of Raft Foundation3.5.0 Raft Depth check:3.5.1 One way shear:ππ’ πππ₯πππ’π π πππ π (π€π πππ )To determine the π€π πππ , the average soil pressure should bedetermined in the maximum loads stripes.For the y-strips, CSY4 have maximum shear value in C4. Which is equalto 2173.51 kNFigure 5, C4 shear diagramCSY3 will be analyzed separately to calculate the ultimate bearingstress of the soil.πππ‘ππ ππππ‘ππππ πππππ ππ π π‘πππ πΆππ3ππππ‘ π΄πππ ππ π‘ π π π‘ππππΆ2 πΆ4 πΆ4 πΆ2ππππ‘ (π€πππ‘ ππ π π‘πππ)(πππππ‘ ππ π π‘πππ)2996 4494 4494 2996ππππ‘ 214 ππ/π2(3.5)(20)ππππ‘ 214 ππ/π2π€π πππ (214 ππ/π2 ) π€πππ‘ ππ π π‘πππ (214 ππ/π2 )(3.5)π€π πππ 749ππ/πAssumingπ 800 75 725 ππππ’ πππ₯πππ’π π πππ π (π€π πππ )ππ’ 2173.5 0.725 749ππ’ 1630.5 ππππ’ 10001630.5 1000π 680.4 ππ110.75ππβ² 6 π΅0.7530 6 3500π 680.4 ππ π 725 ππFigure 6, maximumshear in strips CSY3Page 15
Design of Raft Foundation3.5.1 Two way shear (interior column):ππ’ πΆπππ’ππ π΄π₯πππ πΏπππ π π 2 (π€π πππ )To determine the π€π πππ , the average soil pressure should bedetermined in the maximum loads stripes.ππππ‘ 214 ππ/π2Assumingπ 800 75 725 ππππ’ πΆπππ’ππ π΄π₯πππ πΏπππ π π 2 (π€π πππ )ππ’ 4494 0.725 0.5 2 214 4172.9 ππππ 4 π π 4 500 725 4900 ππππ’ 10004172.9 1000ππΌπΌπΌ 110.75ππβ² 3 ππ0.7530 3 4900ππΌπΌπΌ 622.6 πππ 622.6 ππ π 725 ππFigure 7, two way sheararea3.5.2 SAFE Punching Shear check:Safe software has command of checking the punching shear of the raft or any slab that ismodeled in safe. And in this project, the punching shear has been checked using the SAFEsoftware and all the factors are less than 1. This means that the load shear is less than theraft shear resistance. The punching shear factors are shown in the following figure:Figure 8, punching shear factors for the raftPage 16
Design of Raft Foundation3.5.0 Soil Pressure Check:In this section, the soil net pressure should be checked in each point of the raft foundation.The raft foundation is not symmetric around x-axis nor y-axis due to difference in thecolumns positions and loads. Moments effects on the raft should be checked to assure thatthe stresses of the raft under all columns are less than the net allowable stress which isequal to 100 kN/m2 .π π ππ¦ π₯ ππ₯ π¦ π΄πΌπ¦πΌπ₯π΄ π΄πππ ππ π‘ π πππ‘ 7 3 1 1 6 3 1 1 23 20π΄ 460m2π 3 23(20)3πΌπ₯ 15333.3 m41212π 3 20(23)3πΌπ¦ 20278.3 m41212π π π’π ππ πππ π πππ£πππ ππππ’ππ πππππ π 4 πΆ1 4 πΆ2 4 πΆ3 4 πΆ4 ππ₯π‘ππ ππππ’ππ πππππ π 4 1395 4 2170 4 2093 4 3225 800 700 600 500π 38252 ππFigure 9, resultant position due to column loadsPage 17
Design of Raft FoundationFigure 10, columns total service loads (DL LL)Calculate My:ππ₯ π β² 10.5π π β² π1 π₯ β² 1 π2 π₯ β² 2 π1 π₯ β² 1 π2 π₯ β² 2 πβ² π1πβ² 7 2170 3255 3255 2170 14 2170 3255 3255 217038252 17.5 800 700 600 500 21 (1395 2093 2093 1395)1πβ² 227850 45500 14649638252π β² 10.976 πππ₯ 10.976 10.5 0.4758 πππ¦ πππ₯ 38252 0.4758 18200 ππ. πCalculate Mx:ππ¦ π β² 9π π β² π1 π¦ β² 1 π2 π¦ β² 2 π1 π¦ β² 1 π2 π¦ β² 2 πβ² πPage 18
Design of Raft Foundation118 1395 2170 2170 800 139538252 12 2093 3255 3255 700 2093 6 (2093 3255 3255 600 2093)1πβ² 142740 136752 6777638252π β² 9.07843 πππ¦ 9.07843 9 0.07843 πππ₯ πππ¦ 38252 0.07843 3000 ππ. ππβ² Calculate Soil pressure due to total service axial loads and moments:π ππ¦ π₯ ππ₯ π¦ , π 1, 2, 3 πππ 4π΄πΌπ¦πΌπ₯where (-) minus signs refers to compression stress.Soil pressure will be checked in the four corners of the raft. Soil pressure should not bemore than the allowable stress of the soil and not less than 0 ππ/π2 , to make sure that notension could occur in any part of the raftππ π ππ¦ π₯ ππ₯ π¦ π΄πΌπ¦πΌπ₯38252 18200 11.53000 10.5 46020278.315333.338252 18200 11.53000 10.5 46020278.315333.3 83.157 10.321 2.054 95.532 ππππ‘ 100 ππ/π2 okππ π1π1π1π138252 18200 11.53000 10.5 46020278.315333.3π2 83.157 10.321 2.054π2 75.265 ππππ‘ 100 ππ/π2 okπ2 Figure 11, corners of raft38252 18200 11.53000 10.5 46020278.315333.3π3 83.157 10.321 2.054π3 70.89 ππππ‘ 100 ππ/π2 okπ3 38252 18200 11.53000 10.5 46020278.315333.3π4 83.157 10.321 2.054π4 91.424 ππππ‘ 100 ππ/π2 okπ4 All pressure values are in compression and they are less than the net bearing stress of thesoil which is equal to 100 ππ/π2Page 19
Design of Raft Foundation3.6.0 SAFE Settlement Analysis:SAFE software has been used in the modeling of the raft, because the SAFE is specified slabs,footing and mat foundations modeling. Figure 11 shows the settlements contours that areanalyzed by SAFE software. The maximum settlement occurred is equal to 28.5 millimeter.Settlement of 28.5 millimeters is considered to be acceptable, because the maximumallowable settlement is equal to 100 mm.Figure 12, settlement of Raft using SAFA softwarePage 20
Design of Raft Foundation3.7.0 Moments Strips SAFE results:In SAFE software, the raft is automaticity divided to different strips. Each direction has acolumn strip and middle strips. The moments analyzed by SAFE software are the stripmoments per one meter width of the strip.3.7.1 X direction stripsIn x-strips, the column strips have a dimension of 2.5 meter width and the middle stripshave a dimension of 3 meters width. Moments computed are analyzed base on one meterunit width of the strip. Moment Diagram of x-strips are shown in figure 13.Figure 13, X-strip moment diagramTable 5 shows the analysis outputs for x-strip moments. Negative moments will be designedfor Top Reinforcement, and Positive moments will be designed for Bottom Reinforcement.Strip notationStrip FieldCSx1MSx1CSx2MSx2CSx3MSx3CSx4Column stripMiddle stripColumn stripMiddle stripColumn stripMiddle stripColumn stripMaximum Moment Value 2.0476.61039.015231142.3303.41064.311191052.2Table 5, x-strips moments valuesPage 21
Design of Raft Foundation3.7.2 Y direction stripsIn y-strips, the column strips have a dimension of 2.75 meter width and the middle stripshave a dimension of 3.5 meters width. Moments computed are analyzed base on one meterunit width of the strip. Moment Diagram of x-strips are shown in figure 14.Figure 14, Y-strip moment diagramTable 6 shows the analysis outputs for Y-strip moments. Negative moments will be designedfor Top Reinforcement, and Positive moments will be designed for Bottom Reinforcement.Strip notationStrip FieldCSY1MSY1CSY2MSY2CSY3CSY4CSY5Column stripMiddle stripColumn stripMiddle stripColumn stripMiddle stripColumn stripMaximum Moment Value 66.2948.314451230.33441193.0939.71117.5Table 6, y-strips moments valuesPage 22
Design of Raft Foundation4. Manual & Computer Design:Using the SAFE software analysis, the moments of x and y strips will be used to design thetop and the bottom reinforcement for the raft. The maximum moments in each directionwill be used to design the reinforcement in all raft strips. SAFE software design output willbe compared with the manual design for those maximum positive and negative moments4.1.0 X-strip Design:4.1.1 Positive moments (Bottom Reinforcement):Design of reinforcement will be based on one meter unit of the strip. The distance to therebar center is equal to 75 mm, so effective raft depth equal toπ 800 75 725 ππππ’ πππ₯πππ’π 1532 ππ. π/mππ’ 1532π6 3.2382 ππ0.9 1000 725 2 πΊπ π‘π ππ’ π‘ππππ π 0.0088 ππππ 0.0035 π 0.0088 ππππ₯ 0.0244π΄π 0.0088 π π 0.0088 1000 725π΄π 6380 ππ2 /muse 13 25/m π΄π 6381 ππ2 /m1000π 83 π’π π π 80 ππ ππππ₯ 450 ππ13 1Use 25@80ππCheck Mc:As Fy6381 400a 100.1 mm0.85 fc b 0.85 30 1000a100.1c 117.7 mmB10.85d h cover 800 75 725 mmd c725 117.7 t 0.003 0.003 0.0154 0.005 Tension Controlc117.7then use 0.9aMc As Fy d 2100.1 6Mc 0.9 6381 400 725 e2Mc 1550.4 kN. m ππ’ 1532 kN. m okUse 25@80mm for positive moments x direction bottom ReinforcementPage 23
Design of Raft Foundation4.1.2 Negative moments (Top Reinforcement):Design of reinforcement will be based on one meter unit of the strip. The distance to therebar center is equal to 75 mm, so effective raft depth equal toπ 800 75 725 ππππ’ πππ₯πππ’π 1142.3 ππ. π/mππ’ 1142.3π6 2.4152 ππ0.9 1000 725 2 πΊπ π‘π ππ’ π‘ππππ π 0.0064 ππππ 0.0035 π 0.0064 ππππ₯ 0.0244π΄π 0.0064 π π 0.0064 1000 725π΄π 4640 ππ2 /muse 10 25/m π΄π 4909 ππ2 /m1000π 111.1 π’π π π 110 ππ ππππ₯ 450 ππ10 1Use 25@110 ππCheck Mc:As Fy4909 400a 77 mm0.85 fc b 0.85 30 1000a77c 90.6 mmB1 0.85dbd h cover stirrups 800 75 725 mm2d c725 90.6 t 0.003 0.003 0.021 0.005 Tension Controlc90.6then use 0.9aMc As Fy d 277 6Mc 0.9 4909 400 725 e2Mc 1213.2 kN. m ππ’ 1532 kN. m okUse 25@110mm for negative moments x direction top ReinforcementPage 24
Design of Raft Foundation4.2.0 Y-strip Design:4.2.1 Positive moments (Bottom Reinforcement):Design of reinforcement will be based on one meter unit of the strip. The distance to therebar center is equal to 75 mm 25 mm, because y-direction reinforcement will be underthe reinforcement of x-direction, so effective raft depth equal toπ 800 (75 25) 700 ππππ’ πππ₯πππ’π 1532 ππ. π/mππ’ 1450π6 3.2882 ππ0.9 1000 700 2 πΊπ π‘π ππ’ π‘ππππ π 0.009 ππππ 0.0035 π 0.009 ππππ₯ 0.0244π΄π 0.009 π π 0.009 1000 700π΄π 6300 ππ2 /muse 13 25/m π΄π 6381 ππ2 /m1000π 83 π’π π π 80 ππ ππππ₯ 450 ππ13 1Use 25@80ππCheck Mc:As Fy6381 400a 100.1 mm0.85 fc b 0.85 30 1000a100.1c 117.7 mmB10.85d h cover 800 75 725 mmd c725 117.7 t 0.003 0.003 0.0154 0.005 Tension Controlc117.7then use 0.9aMc As Fy d 2100.1 6Mc 0.9 6381 400 725 e2Mc 1550.4 kN. m ππ’ 1450 kN. m okUse 25@80mm for positive moments Y direction bottom ReinforcementPage 25
Design of Raft Foundation4.2.2 Negative moments (Top Reinforcement):Design of reinforcement will be based on one meter unit of the strip. The distance to therebar center is equal to 75 mm 25 mm, because y-direction reinforcement will be underthe reinforcement of x-direction, so effective raft depth equal toπ 800 (75 25) 700 ππππ’ πππ₯πππ’π 1532 ππ. π/mππ’ 1230.3π6 2.7902 ππ0.9 1000 700 2 πΊπ π‘π ππ’ π‘ππππ π 0.0076 ππππ 0.0035 π 0.0076 ππππ₯ 0.0244π΄π 0.0076 π π 0.0076 1000 700π΄π 5300 ππ2 /muse 11 25/m π΄π 5400 ππ2 /m1000π 100 π’π π π 100 ππ ππππ₯ 450 ππ10 1Use 25@100 ππCheck Mc:As Fy5400 400a 84.7 mm0.85 fc b 0.85 30 1000a84.7c 99.6 mmB1 0.85d h cover stirrups db 800 75 25 700 mmd c700 99.6 t 0.003 0.003 0.0181 0.005 Tension Controlc99.6then use 0.9aMc As Fy d 284.7 6Mc 0.9 5400 400 700 e2Mc 1278.5 kN. m ππ’ 1230.3 kN. m okUse 25@100mm for negative moments Y direction top ReinforcementPage 26
Design of Raft Foundation4.3.0 Comparison Table:Moment ValuekN.m/mManual DesignSAFE designX-stripBottom AsTop As15321142.3 25@80ππ 25@110ππ6381 ππ2 /π4909 ππ2 /π13 25 6381 ππ2 /π10 25 4909 ππ2 /π14501230.3 25@80mm 25@100mm6381 ππ2 /π5400 ππ2 /π12 25 5890ππ2 /π11 25 5400ππ2 /πY-stripBottom AsTop AsTable 7, comparison between manual and computer design4.4.0 Detailing:Reinforcement detailing will be shown in the next page.Page 27
Design of Raft Foundation5. Conclusion:At the end of this special project, we are really happy that we have been involved in the Raftmanual design. The raft foundation is considered to be a very common foundation typeespecially here in Qatar.We also have been involved in using SAFE analysis and design software which is reallyprofessional and helped us for this project.Page 28
6. References:-MacGregor, Wight, Reinforced Concrete Mechanics And Design, 4th edition, University ofMichigan,-Braja M.Das, Principles of Foundation Engineering, 6th edition, 2007 by Nelson, Chris Carson-Al-Ansari notes in Course: Design of Reinforced Concrete Structure, Fall 2008, QatarUniversityPage 29
7. Index:π ππππ‘ ππ ππππ‘ππππ’πππ π π‘πππ π πππ π‘ππππ’π‘πππ ππππ πππππππ π πππ πππππ π‘ππππ π‘ππππ π½1 ππ΄π ππππ ππ π‘πππ πππ π π‘ππππ΄π ππππ ππ πππππ£πππ’ππ ππππ΄π ,πππ ππππππ’π π‘πππ πππ οΏ½οΏ½π π€πππ‘ ππ πππππππ π πππ ππππππ πππππππ‘ππ ππ ππππ‘ππππ π πππ‘πππ πππ π‘π€π π€ππ¦ π πππ ππ π ππππ πππ ππππ‘ππππ , πππΆπ πππππππππππ‘ ππ ππ‘πππ£π ππππ‘ ππππ π π’πππΆπ πππππ πππ£ππ ππππ π‘ π ππππππ π‘ π π’πππππ ππ π‘πππ πππ π‘π π‘ π π π’πππππ ππ π‘ π οΏ½οΏ½ππ οΏ½οΏ½, πππΆπ ππππ‘ππ πππππ‘πππ π‘ π πππ‘π’ππ ππππππ‘ πππππππ ππ π οΏ½οΏ½ π‘π ππ πππ’ππ£πππππ‘ π’ππππππ ππππππ‘ ππππππππΆπ ππππππ‘ οΏ½οΏ½ πππππππππππ‘ ππ πππ π ππ ππππ‘ ππππ π π’πππ ππππππ‘ππ£π ππππ‘ ππππ πππππππ π πππ π π’πππππ π‘π ππππ‘ππ ππ π π‘πππ ππ π‘πππ πππ π§πππ.πβ² πππ π‘ππππ ππππ ππ₯π‘ππππ πππππππ π πππ πππππ π‘π ππππ‘ππππ ππ οΏ½οΏ½πππππππππ‘, ππππ πππππππ ππππππ‘ππ ππ πππ , π€πππ , ππ ππππ π‘πππ π πππ π π‘ππππ , πππ· ππππ πππππ οΏ½οΏ½πΈπ ππππ’ππ’π ππ ππππ π‘ππππ‘π¦ ππ πππππππ‘π πππ ππππ2πΈπΌ πΉπππ₯π’πππ π π‘ππππππ π ππ πππππππ π πππ ππππππ , π ππ2ππΈπ ππππ’ππ’π ππ ππππ π‘ππππ‘π¦ ππ οΏ½οΏ½ πππ ππππ2β²ππ πππππππ π ππ£π π π‘πππππ‘ ππ πππππππ‘π ππ’π 28 πππ¦, ππ π ππ πππππ πππππ’πππ‘ππ π π‘πππ π ππ οΏ½οΏ½ ππ‘ π πππ£πππ πππππ , πππ ππ π/ππ2ππ¦ π¦ππππ π π‘πππππ‘ ππ οΏ½οΏ½π οΏ½οΏ½ ππ£πππππ ππππ‘ ππ π‘ ππππππ π ππ π πππ ππ πππππΌ ππππππ‘ ππ πππππ‘ππ ππ π π πππ‘πππ , ππ4ππ πππ π‘ππππ πππ‘π€πππ π‘ π πππ π’ππ‘πππ‘π ππ π‘ π πππ‘πππππ πππππππ π ππ£π ππππ‘πππ πππ πππππ ππ ππππ π π πππ‘ππππ ππππππ‘ππ£π πππππ‘ ππππ‘ππππ πππ πππππππ π πππ πππππππ π πππ πππππ‘ ππ ππππ ππ πππ π€ππ¦ π πππ , πππππππππ¦ ππππ‘ππ π‘π ππππ‘ππ ππ π π’πππππ‘π ππ πππ£ππππππππ‘ πππππ‘ ππ πππππ π πππ ππππ π’πππ ππππ π‘π ππππ ππ π π’πππππ‘π .Page 30
π ππππππ‘ππ ππππ‘ππππ ππππππ‘ π‘π ππ π’π ππ πππ πππ πππ ππ π π ππππππ πππππππ π πππ ππππππ πΎπ πππ’ ππππ‘ππππ ππππππ‘ ππ’π π‘π ππππ‘ππππ ππππππ ππππ‘ππππ ππππππΈ ππ’ππππππ ππππ ππ ππ ππππ π‘ππ , πππππ πππ ππππ’ππππ πππππππ ππ₯πππ ππππ π π‘πππππ‘ ππ‘ πππ£ππ οΏ½οΏ½π πππππππ ππ₯πππ ππππ π π‘πππππ‘ ππ‘ π§πππ οΏ½οΏ½π’ ππ₯πππ πππππ ππ’π π‘π ππππ‘ππππ πππππ π ππππππ πππ‘π€πππ ππππ ππ πππππππ π πππ π π‘πππππ‘ ππ πππππππ‘πππ’ π πππ πππππ ππ’π π‘π ππππ‘ππππ πππππ π€πππ π‘π½1 πππ‘ππ ππ ππππ‘ ππ ππππ‘ππππ’πππ π π‘πππ π πππππ , π, π‘π ππππ‘ π‘π πππ’π‘πππ ππ₯ππ , ππΎ πππ‘ππ ππ π‘ π πππ π‘ππππ πππ‘π€πππ π‘ π ππ’π‘ππ πππ¦πππ ππ οΏ½οΏ½ ππ π ππππ’ππ π‘ππ‘ π ππ£πππππ ππππ‘ ππ π‘ π ππππ’ππ .π πππ‘ππ ππ π‘πππ πππ π π‘πππPage 31
Total Sevice Axial load 765 630 kN 1395 kN Ultimate axial load 1.2 765 1.6 630 1926 kN Column type (2): Axial 2unfactored Dead load 42.5 kN/m2 4 7 m 1190 kN Axial unfactored Live 2load 35 2kN/m 4 7 m 980 kN Total Sevice Axial load 1190 980 kN 2170 kN Ultimate axial load 1.2 1190 1.6 980 2996 kN
analyses of un-piled and piled raft foundations with sandy soil. For the un-piled raft, the normalized settlement parameter (IR) for the raft sizes of 8mx8m and 15mx15m ranged as 1.03-1.17mm and 0.66- 0.83mm respectively. In the case of the piled raft with raft thickness of 0.25, 0.40, 0.80, 1.50, 3.0m, the corresponding maximum settlements
, respectively. Raft foundations fail when the resistance of the raft is less than the action caused by the applied load. The raft resistance is measured using the design moment strength M c while the raft action is measured by the external bending moments M e as shown in Figure 1. The raft limit state function is given by the following equation:
analysis and design. For foundations of such high rise building, normally raft foundation, pile foundation or piled-raft foundation are used. The raft will be used for economical consideration. The raft foundation is a kind of
As with any foundation system, a design of a piled raft foundation requires the consideration of a number of issues, including: 1. Ultimate load capacity for vertical, lateral and moment loadings 2. Maximum settlement 3. Differential settlement 4. Raft moments and shears for the structural design of the raft 5.
the design requirements, piled raft foundations come out as an economical foundation option under such circumstances. Different methods of analysis of piled raft foundations have been developed, but there is only limited information about comparative performances of the piled raft foundation under various parameters.
these systems can be combined and one can have a more efficient, safe and economical design. Thus, piled raft foundation system is one of those combined systems. In designing raft foundations, engineers frequently encounter situations in which the bearing capacity of the raft is quite adequate, but the settlements are estimated to be excessive.
A Review on Pile-Raft Foundation Rahul Solanki* Civil engineer, L&T Construction, India. E-mail id: rahul.solanki310@gmail.com Sagar Sorte Civil engineer, Tata Housing, India. E-mail id: sagar.sorte19@gmail.com Abstract The design concepts given by various researchers on pile-raft foundation is reviewed and described in this paper.
the relationship between raft thickness and the number of design parameters, including soil type [9-10]. 3 TYPES OF FOUNDATION The most common forms of deep foundations are piles, pillars and caissons. The mechanism for shifting the weight to the ground is basically the same in these types of foundations. Raft.
