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Footing a

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Anas Ramadan
Anas Ramadan

1) Shallow foundations are used when the top soil layers can support applied loads with acceptable settlement. Types include spread footings, combined footings, strap-beam footings, wall footings, strip footings, and raft foundations. 2) Deep foundations are used when top soils are weak and cannot support structural loads. Types include piles, piers, and caissons, which transmit loads to deeper stronger soil layers. 3) The design of an isolated spread footing involves calculating the area and dimensions of plain concrete based on allowable soil bearing capacity, then determining reinforced concrete dimensions, contact pressure, and checking critical sections for moment, shear, and punching.

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‫الساسات الضحلة‬ ‫القواعد المنفصلة‬ SHALLOW FOUNDATIONS ISOLATED FOOTINGS April 5, 2012 Spread Footings 1
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 الحوائط‬ April 5, 2012 ‫أساسات اللبشة‬Footings Spread - ‫- القواعد الشريطية‬ ‫2 - الشدادات‬
Foundations 2) Deep Foundations are used if the top soil is weak and can not support the structure loads. They used to transmit the loads to the stronger deeper soil layers. Forms of deep foundations are piles, 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 السكندرانى‬ April 5, 2012 Spread Footings 3
Wall Footing ‫قواعد الحوائط‬ Wall Reinforced Concrete Plain Concrete April 5, 2012 Spread Footings 4
Isolated Footing P ‫القواعد المنفصلة‬ Reinforced Concrete Plain Concrete April 5, 2012 Spread Footings 5
Combined Footing Pb ‫القواعد المشتركة‬ Pa Reinforced Concrete Plain Concrete April 5, 2012 Spread Footings 6
Pd Strip Footing ‫القواعد الشريطية‬ Pc Pb Pa R.C. April 5, 2012 P. C. Spread Footings 7
Pa Strap Beam Pb ‫الشداد‬ Strap Beam ‫قاعدة جار‬ a Strap Beam b April 5, 2012 Spread Footings 8
- ‫اللبشة المسلحة‬Raft Foundation April 5, 2012 Spread Footings 9
Pile Foundations ‫الخوازيق‬ Very Large Concentrated Large Distributed Weight Weight Low Weight Soft to Firm Clay Dense Sand April 5, 2012 Strong Rock Spread Footings 10
DESIGN OF SPREAD FOOTINGS April 5, 2012 Spread Footings 11
Design Procedure of Isolated Footing Data: Pc : Column load at ground surface, ‫حمل العمود عند سطح الرض‬ a, b : Dimensions of column, (‫أبعاد العمود )طول وعرض‬ B/C of soil: qall or qall net . at foundation level ‫قدرة تحمل التربة المسموح بها عند منسوب التأسيس‬ April 5, 2012 Spread Footings 12
‫‪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.c‬‬ ‫2102 ,5 ‪April‬‬ ‫‪Spread Footings‬‬ ‫31عرض القاعدة العادية‬
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 المسلحة‬ April 5, 2012 Spread Footings 14
- 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
Lp.c. LR.c. P c. c. p. R. B B x1 April 5, 2012 Spread Footings 16
Isolated Footing P Column R.C. Footing P.C. Footing LP.C. LR.C. BP.C. BR.C. b a April 5, 2012 Spread Footings 17
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−I As = k2 d April 5, 2012 Spread Footings x 18
Critical Section for Shear P P fn = AR .C . ( LR .C . - a ) 45o d x1 = -d 2 LR.C. fn Qsh = fn x1 BR.C. Check of Shear: a d b BR.C. Qsh qsh = ≤ 6 kg/cm 2 BR.C. d April 5, 2012 Spread Footings x1 19
Critical Section for Punching P P fn = d/2 d/2 A Punching Section Area: bp = 2 [(a+d) + (b+d)] fn fn Qp = fn [LR.C. BR.C. – (a+d) * (b+d)] LR.C. Check of Punching: d/2 qp = Qp ≤ 8 kg/cm 2 BR.C. bp d d/2 April 5, 2012 Spread Footings 20
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
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 - 0.4 Lp .c . = Ap.c. + = 7.33 + = 2.90 m 2 2 a-b 0.8 - 0.4 B p .c . = Ap.c. - = 7.33 - = 2.50 m 2 2 April 5, 2012 Spread Footings 22
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 m2 April 5, 2012 Spread Footings 23
- 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 2 MI-I = 8.05 t.m 5 M I−I 8.05 x 10 d = k1 = 0.361 = 24.84 cm BR .C . April 5, 2012 170Spread Footings 24
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 /m' April 5, 2012 Spread Footings 25
Critical Section for Moment (Section II-II) ( BR .C . - b ) ( 1.70 - 0.40 ) y= = = 0.65 m 2 2 y 0.65 M 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 10 d = k1 = 0.361 = 24.84 cm LR .C . 210 April 5, 2012 Spread Footings 26
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. a April 5, 2012 Spread Footings 27
Isolated Footing Reinfrocement b a April 5, 2012 Spread Footings 28
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
Check of Punching: Punching Perimeter ‫: المحيط المؤثر للختراق‬ bp = 2[(a + d)+ (b + d)] = 2[(0.8+0.3)+(0.4+0.3)]= 3.60 m Qp = fn [LR.C. * BR.C. – (a+d)* (b+d)] = 22.41 [2.1 * 1.7 – 0.7] = 64.32 ton Qp 64.32 qp = = = 59.56 t/m ≤ 8 kg/cm 2 2 b p d 3.60 * 0.30 April 5, 2012 Spread Footings 30

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Footing a

  • 1. ‫الساسات الضحلة‬ ‫القواعد المنفصلة‬ SHALLOW FOUNDATIONS ISOLATED FOOTINGS April 5, 2012 Spread Footings 1
  • 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 الحوائط‬ April 5, 2012 ‫أساسات اللبشة‬Footings Spread - ‫- القواعد الشريطية‬ ‫2 - الشدادات‬
  • 3. Foundations 2) Deep Foundations are used if the top soil is weak and can not support the structure loads. They used to transmit the loads to the stronger deeper soil layers. Forms of deep foundations are piles, 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 السكندرانى‬ April 5, 2012 Spread Footings 3
  • 4. Wall Footing ‫قواعد الحوائط‬ Wall Reinforced Concrete Plain Concrete April 5, 2012 Spread Footings 4
  • 5. Isolated Footing P ‫القواعد المنفصلة‬ Reinforced Concrete Plain Concrete April 5, 2012 Spread Footings 5
  • 6. Combined Footing Pb ‫القواعد المشتركة‬ Pa Reinforced Concrete Plain Concrete April 5, 2012 Spread Footings 6
  • 7. Pd Strip Footing ‫القواعد الشريطية‬ Pc Pb Pa R.C. April 5, 2012 P. C. Spread Footings 7
  • 8. Pa Strap Beam Pb ‫الشداد‬ Strap Beam ‫قاعدة جار‬ a Strap Beam b April 5, 2012 Spread Footings 8
  • 9. - ‫اللبشة المسلحة‬Raft Foundation April 5, 2012 Spread Footings 9
  • 10. Pile Foundations ‫الخوازيق‬ Very Large Concentrated Large Distributed Weight Weight Low Weight Soft to Firm Clay Dense Sand April 5, 2012 Strong Rock Spread Footings 10
  • 11. DESIGN OF SPREAD FOOTINGS April 5, 2012 Spread Footings 11
  • 12. Design Procedure of Isolated Footing Data: Pc : Column load at ground surface, ‫حمل العمود عند سطح الرض‬ a, b : Dimensions of column, (‫أبعاد العمود )طول وعرض‬ B/C of soil: qall or qall net . at foundation level ‫قدرة تحمل التربة المسموح بها عند منسوب التأسيس‬ April 5, 2012 Spread Footings 12
  • 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.c‬‬ ‫2102 ,5 ‪April‬‬ ‫‪Spread Footings‬‬ ‫31عرض القاعدة العادية‬
  • 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 المسلحة‬ April 5, 2012 Spread Footings 14
  • 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. Lp.c. LR.c. P c. c. p. R. B B x1 April 5, 2012 Spread Footings 16
  • 17. Isolated Footing P Column R.C. Footing P.C. Footing LP.C. LR.C. BP.C. BR.C. b a April 5, 2012 Spread Footings 17
  • 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−I As = k2 d April 5, 2012 Spread Footings x 18
  • 19. Critical Section for Shear P P fn = AR .C . ( LR .C . - a ) 45o d x1 = -d 2 LR.C. fn Qsh = fn x1 BR.C. Check of Shear: a d b BR.C. Qsh qsh = ≤ 6 kg/cm 2 BR.C. d April 5, 2012 Spread Footings x1 19
  • 20. Critical Section for Punching P P fn = d/2 d/2 A Punching Section Area: bp = 2 [(a+d) + (b+d)] fn fn Qp = fn [LR.C. BR.C. – (a+d) * (b+d)] LR.C. Check of Punching: d/2 qp = Qp ≤ 8 kg/cm 2 BR.C. bp d d/2 April 5, 2012 Spread Footings 20
  • 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. 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 - 0.4 Lp .c . = Ap.c. + = 7.33 + = 2.90 m 2 2 a-b 0.8 - 0.4 B p .c . = Ap.c. - = 7.33 - = 2.50 m 2 2 April 5, 2012 Spread Footings 22
  • 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 m2 April 5, 2012 Spread Footings 23
  • 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 2 MI-I = 8.05 t.m 5 M I−I 8.05 x 10 d = k1 = 0.361 = 24.84 cm BR .C . April 5, 2012 170Spread Footings 24
  • 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 /m' April 5, 2012 Spread Footings 25
  • 26. Critical Section for Moment (Section II-II) ( BR .C . - b ) ( 1.70 - 0.40 ) y= = = 0.65 m 2 2 y 0.65 M 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 10 d = k1 = 0.361 = 24.84 cm LR .C . 210 April 5, 2012 Spread Footings 26
  • 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. a April 5, 2012 Spread Footings 27
  • 28. Isolated Footing Reinfrocement b a April 5, 2012 Spread Footings 28
  • 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. Check of Punching: Punching Perimeter ‫: المحيط المؤثر للختراق‬ bp = 2[(a + d)+ (b + d)] = 2[(0.8+0.3)+(0.4+0.3)]= 3.60 m Qp = fn [LR.C. * BR.C. – (a+d)* (b+d)] = 22.41 [2.1 * 1.7 – 0.7] = 64.32 ton Qp 64.32 qp = = = 59.56 t/m ≤ 8 kg/cm 2 2 b p d 3.60 * 0.30 April 5, 2012 Spread Footings 30