Footing a

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Footing a

  1. 1. ‫الساسات الضحلة‬ ‫القواعد المنفصلة‬ SHALLOW FOUNDATIONS ISOLATED FOOTINGSApril 5, 2012 Spread Footings 1
  2. 2. Foundations Foundations are usually divided into: :‫تنقسم الساسات عادة إلى‬ • Shallow Foundations are used when the top layers of soil can support the applied loads with accepted settlement. They can take any form of the followings: ‫1( أساسات ضحلة: ويتم استخدامها عندما تكون طبقات التربة العلوية قادرة‬ ،‫على تحمل الحمال الواقعة عليها من المنشأ بأمان وبقيم مقبولة للهبوط‬ :‫ومن أنواعها‬ - Spread (isolated) Footing, - Combined Footing, - Strap – Beam Footing - Wall Footing, - Strip Footing, - Raft Foundation. ‫- القواعد المنفصلة- القواعد المشتركة- قواعد الحوائط‬April 5, 2012 ‫أساسات اللبشة‬Footings Spread - ‫- القواعد الشريطية‬ ‫2 - الشدادات‬
  3. 3. Foundations2) Deep Foundations are used if the top soil isweak and can not support the structure loads.They used to transmit the loads to the strongerdeeper soil layers. Forms of deep foundations arepiles, piers, and caissons ….etc. ‫2( الساسات العميقة: وتستخدم عندما تكون طبقات التربة القريبة‬ .‫من سطح الرض ضعيفة أو ل تستطيع تحمل أحمال المنشأ‬ ‫وتستخدم الساسات العميقة لنقل الحمال إلى طبقات التربة القوية‬ – ‫التى تستطيع تحملها. ومن أنواعها: الخوازيق – الدعائم‬ .‫القيسونات – البار السكندرانى‬April 5, 2012 Spread Footings 3
  4. 4. Wall Footing ‫قواعد الحوائط‬ Wall Reinforced Concrete Plain ConcreteApril 5, 2012 Spread Footings 4
  5. 5. Isolated Footing P ‫القواعد المنفصلة‬ Reinforced Concrete Plain ConcreteApril 5, 2012 Spread Footings 5
  6. 6. Combined Footing Pb ‫القواعد المشتركة‬ Pa Reinforced Concrete Plain ConcreteApril 5, 2012 Spread Footings 6
  7. 7. Pd Strip Footing ‫القواعد الشريطية‬ Pc Pb Pa R.C.April 5, 2012 P. C. Spread Footings 7
  8. 8. Pa Strap Beam Pb ‫الشداد‬ Strap Beam ‫قاعدة جار‬ a Strap Beam bApril 5, 2012 Spread Footings 8
  9. 9. - ‫اللبشة المسلحة‬Raft FoundationApril 5, 2012 Spread Footings 9
  10. 10. Pile Foundations ‫الخوازيق‬ Very Large Concentrated Large Distributed Weight Weight Low Weight Soft toFirm Clay Dense SandApril 5, 2012 Strong Rock Spread Footings 10
  11. 11. DESIGN OF SPREAD FOOTINGSApril 5, 2012 Spread Footings 11
  12. 12. Design Procedure of Isolated FootingData:Pc : Column load at ground surface, ‫حمل العمود عند سطح الرض‬a, b : Dimensions of column, (‫أبعاد العمود )طول وعرض‬B/C of soil: qall or qall net . at foundation level ‫قدرة تحمل التربة المسموح بها عند منسوب التأسيس‬April 5, 2012 Spread Footings 12
  13. 13. ‫‪Step by Step Design Procedure‬‬‫‪-Load P at the foundation level is 1.10 x Pc‬‬ ‫-الحمل عند منسوب التأسيس ))‪ × = 1.1P‬حمل العمود )‪،(cP‬‬ ‫- حيث 01.0 من حمل العمود تكافئ وزن القاعدة‬ ‫‪Design of Plain Concrete Footing‬‬ ‫تصميم قاعدة الخرسانة العادية‬ ‫مساحة الخرسانة العادية ,‪- Area of plain concrete‬‬ ‫.‪Ap.c. = P / qall = Lp.c. x Bp.c‬‬ ‫حيث:‬ ‫‪ A.p.c‬مساحة القاعدة العادية ‪ L.p.c‬طول القاعدة العادية ‪B.p.c‬‬‫2102 ,5 ‪April‬‬ ‫‪Spread Footings‬‬ ‫31عرض القاعدة العادية‬
  14. 14. Step by Step Design Procedure a-b ‫ طول العمود‬a ‫حيث‬ Lp .c . = Ap.c. + 2 a-b ‫ لقرب‬B.p.c ‫ و‬L.p.c ‫يتم تقريب‬ B p .c . = Ap.c. - ‫5 سم بالزيادة‬ 2 Plain Concrete Thickness ‫تخانة الخرسانة العادية‬ - t p.c. = 30 cm if P < 40 ton - t p.c. = 40 cm if P > 40 ton- Projection distance, x1 = 0.80 – 1.00 tp.c. ‫إلى 1 تخانة العادية‬x1 = 0.8 ‫رفرفة الخرسانة العادية عن المسلحة‬April 5, 2012 Spread Footings 14
  15. 15. - Reinforced Concrete Dimensions: :‫أبعاد الخرسانة المسلحة‬ LR.C. = Lp.c. – 2 x1 ‫طول الخرسانة المسلحة‬ BR.C. = Bp.c. – 2 x1 ‫عرض الخرسانة المسلحة‬ - Reinforced Concrete Footing Area: :‫مساحة قاعدة الخرسانة المسلحة‬ AR.C. = LR.C. x BR.C. - Contact Pressure (fn): Pc :‫ضغط التلمس بين العادية والمسلحة‬ fn = AR.C.April 5, 2012 Spread Footings 15
  16. 16. Lp.c. LR.c. P c. c. p. R. B B x1April 5, 2012 Spread Footings 16
  17. 17. Isolated Footing P ColumnR.C. FootingP.C. Footing LP.C. LR.C. BP.C. BR.C. b aApril 5, 2012 Spread Footings 17
  18. 18. Critical Section for Moment P I Pc fn = AR .C . ( LR .C . - a ) x= 2 x fn LR.C. MI-I = fn x BR.C. 2 M I−I a d = k1 BR.C. BR .C . b I M I−IAs = k2 dApril 5, 2012 Spread Footings x 18
  19. 19. Critical Section for Shear P P fn = AR .C . ( LR .C . - a ) 45o d x1 = -d 2 LR.C. fnQsh = fn x1 BR.C.Check of Shear: a d b BR.C. Qshqsh = ≤ 6 kg/cm 2 BR.C. dApril 5, 2012 Spread Footings x1 19
  20. 20. Critical Section for Punching P P fn = d/2 d/2 A Punching Section Area: bp = 2 [(a+d) + (b+d)] fn fnQp = fn [LR.C. BR.C. – (a+d) * (b+d)] LR.C.Check of Punching: d/2qp = Qp ≤ 8 kg/cm 2 BR.C. bp d d/2April 5, 2012 Spread Footings 20
  21. 21. Example Design an isolated footing to support a column load of 80 ton, knowing that the soil allowable bearing capacity, qall = 1.20 kg/cm2, and the column dimensions are 80 x 40 cm.April 5, 2012 Spread Footings 21
  22. 22. Solution- P at F.L. = 1.10 x Pc = 80 x 1.10 = 88 ton (cP) ‫1.1 = × حمل العمود‬P)) ‫-الحمل عند منسوب التأسيس‬ Design of Plain Concrete Footing ‫تصميم قاعدة الخرسانة العادية‬ Ap.c. = P / qall = 88.0 / 12.0 = 7.33 m2 a-b 0.8 - 0.4Lp .c . = Ap.c. + = 7.33 + = 2.90 m 2 2 a-b 0.8 - 0.4B p .c . = Ap.c. - = 7.33 - = 2.50 m 2 2April 5, 2012 Spread Footings 22
  23. 23. Plain Concrete Thickness ‫تخانة الخرسانة العادية‬ P > 40 ton, then t p.c. = 40 cm-Projection distance, x1 = 0.80 – 1.00 tp.c.- x1 = tp.c. = 0.40 m = 40 cm - Reinforced Concrete Dimensions: LR.C. = Lp.c. – 2 x1 = 2.90 – 2 x 0.40 = 2.10 m BR.C. = Bp.c. – 2 x1 = 2.50 – 2 x 0.30 = 1.70 m AR.C. = 2.10 x 1.70 = 3.57 m2April 5, 2012 Spread Footings 23
  24. 24. - Contact Pressure (fn): ‫ضغط التلمس بين العادية والمسلحة‬ Pc 80.0 fn = = = 22.41 t/m 2 AR.C. 3.57 Critical Section for Moment (Section I-I) ( LR .C . - a ) ( 2.10 - 0.80 ) x= = = 0.65 m 2 2 x 0.65 M I − I = f n x BR.C. = 22.41 * 0.65 * 1.70 * 2 2MI-I = 8.05 t.m 5 M I−I 8.05 x 10d = k1 = 0.361 = 24.84 cm BR .C .April 5, 2012 170Spread Footings 24
  25. 25. Take d = 30 cm, and t = 35 cm 5 M I − I 8.05 x 10 As = = = 21.08 cm 2 k 2 d 1273 x 30 As = 11 φ16 = 7 φ16 /mApril 5, 2012 Spread Footings 25
  26. 26. Critical Section for Moment (Section II-II) ( BR .C . - b ) ( 1.70 - 0.40 ) y= = = 0.65 m 2 2 y 0.65M II − II = f n y LR.C. = 22.41 * 0.65 * 2.10 * 2 2 MI-I = 9.94 t.m 5 M II − II 9.94 x 10d = k1 = 0.361 = 24.84 cm LR .C . 210April 5, 2012 Spread Footings 26
  27. 27. Take d = 30 cm, and t = 35 cm 5 M II − II 9.94 x 10 As = = = 26.03 cm 2 k2 d 1273 x 30 As = 13 φ16 = 7 φ16 /m LR.C. y II II b BR.C. aApril 5, 2012 Spread Footings 27
  28. 28. Isolated Footing Reinfrocement b aApril 5, 2012 Spread Footings 28
  29. 29. Check of Shear ( LR .C . - a ) ( 2.10 - 0.8 ) x1 = -d = - 0.30 = 0.35 m 2 2 Qsh = fn x1 BR.C. = 22.41 * 0.35 * 1.70 = 13.33 ton Qsh 13.33 qsh = = = 26.1 t/m 2 BR .C . d 1.70 * 0.30 qsh = 26.10 t/m2 = 2.61 kg/cm2 < 6.0 kg/cm2 O.K.April 5, 2012 Spread Footings 29
  30. 30. Check of Punching:Punching Perimeter ‫: المحيط المؤثر للختراق‬bp = 2[(a + d)+ (b + d)] = 2[(0.8+0.3)+(0.4+0.3)]= 3.60 mQp = fn [LR.C. * BR.C. – (a+d)* (b+d)] = 22.41 [2.1 * 1.7 – 0.7] = 64.32 ton Qp 64.32qp = = = 59.56 t/m ≤ 8 kg/cm 2 2 b p d 3.60 * 0.30April 5, 2012 Spread Footings 30

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