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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 β€œtheConventional Rigid Method” 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 π‘š2Page 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:π‘˜π‘ π‘›π‘œ. π‘œπ‘“ ‘’π‘Ÿπ‘Žπ‘™ π·π‘’π‘Žπ‘‘ π‘™π‘œπ‘Žπ‘‘ π‘ π‘‘π‘Ÿπ‘’π‘ π‘  5 2.5 1 5 42.5 Žπ‘™ 𝐿𝑖𝑓𝑒 π‘™π‘œπ‘Žπ‘‘ π‘ π‘‘π‘Ÿπ‘’π‘ π‘  7 5 35 π‘˜π‘/π‘š2π‘š2πΊπ‘’π‘›π‘’π‘Ÿπ‘Žπ‘™ π·π‘’π‘Žπ‘‘ π‘™π‘œπ‘Žπ‘‘ π‘ π‘‘π‘Ÿπ‘’π‘ π‘  5 2.5 1Page 10

Design of Raft FoundationColumns loads:𝐴π‘₯π‘–π‘Žπ‘™ π·π‘’π‘Žπ‘‘ π‘™π‘œπ‘Žπ‘‘ 𝑆𝑑𝑒𝑠𝑠 π‘π‘’π‘Ÿ 𝑒𝑛𝑖𝑑 π‘Žπ‘Ÿπ‘’π‘Žπ‘˜π‘ π‘‡π‘’π‘Ÿπ‘π‘–π‘‘π‘–π‘‘π‘¦ π‘Žπ‘Ÿπ‘’π‘Žπ‘š2Column 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 design𝑃𝑐 𝑃𝑛 0.7 0.8 (0.85𝑓𝑐′ 𝐴𝑔 𝐹𝑦 𝐴𝑠𝑑 )𝑃𝑐 𝑃𝑛 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‘ˆ π‘π‘œ )(𝑑 (0.34) 𝑓𝑐′11.12.2.1.cWhere,U factored column load Reduction factor 0.85π‘π‘œ The parameter of the sheared aread effective depth of raft𝑓𝑐′ Compressive strengt