DUCTILITY AND PREVENTION OF STRUCTURAL FAILURE

1. DUCTILITY AND PREVENTION OF STRUCTURAL FAILURE

2. TOPICS • Types of Loading • Structural Distress under Various Loading Conditions • Ductility Provisions and Structural Repair/Retrofit • Relevant Research at UAP • Conclusions

3. Types of Loading

4. Structural Distress under Various Loading Conditions • Quasi-Static Loads • Machine Vibration • Impact Loads • Blast Loading • Cyclonic Storm Loading

5. Quasi-Static Loads Vertical Loads • Overload from service requirement and careless use • Poor construction practices and material quality Cracks in Beams and Columns Ultimate Collapse of Structure

6. Support Settlement • Overloaded super-structure and sub-structure • Filling up lands, ponds, with soft infill • No/inaccurate soil test and no soil improvement (a) Building before support settlement, (b) Uniform settlement, (c) Differential settlement

7. Cracks indicating Differential Support Settlement

8. Fig. 7(a): The effect of fire flame on the compressive strength at 1-hour of exposure Extreme Temperature (Fire) • Steel melts as in September 11, 2001 • Dehydration of paste in the concrete matrix Effect of temperature on (a) Steel yield strength, (b) Concrete compressive strength

9. Impact Loads Progressive Failure of Slabs • Sudden drop of top slab causes a large impact load • Creates a series of slab failures heaped like a pack of cards (called a ‘pancake’ failure) Progressive Failure of slabs in (a) USA, (b) Bangladesh

10. Vehicular Impact on Bridge Railings Railing crash involving (a) smaller vehicle, (b) larger vehicle

11. Vehicular Impact on Bridge Railings Arrangements for vehicular-impact test of RC railings

12. Dynamic Amplification of Machine Vibration Fig. 11: Dynamic amplification of machine vibration Machine Vibration • Machines and Power Generators • Careless Placement and Design • May cause Resonance and Fatigue

13. September 11, 2001 Variation of Blast Pressure with Distance Distance R (m) 0 10 20 30 40 50 10000 kg 500 kg 1000 kg 100 kg 10 kg 1 kg Distance R (m) Fig. 14: Variation of blast pressure with distance, for explosives of different weights Blast Loading Nature of Blast Loading • One blast can change history • Extremist views and access to explosives • Very sudden and very high pressure

14. Controlled Demolition Controlled Demolition • Ever-changing urban infrastructure in this country • Predicament in the demolition of a single building

15. Date Year Max. Wind Speed(Kmph)) Storm Surge Ht. (m) Deaths 09 Oct 1960 162 3 3,000 30 Oct 1960 210 4.5~6 5,149 09 May 1961 146 2.5~3 11,466 28 May 1963 203 4~5 11,520 11 May 1965 162 4 19,279 12 Nov 1970 223 6~10 5,00,000 25 May 1985 154 3~5 11,069 29 April 1991 225 6~8 1,38,000 15 Nov 2007 240 5~6 3,406 25 May 2009 120 2~3 330 Hydraulic Loading Cyclones in Bangladesh

16. Coastal Region Surge Height at Sea Coast, hT (m) T = 50-year T = 100-year Teknaf to Cox's Bazar 4.5 5.8 Chakaria to Anwara, Maheshkhali-Kutubdia Islands 7.1 8.6 Chittagong to Noakhali 7.9 9.6 Sandwip, Hatiya and all islands in this region 7.9 9.6 Bhola to Barguna 6.2 7.7 Sarankhola to Shyamnagar 5.3 6.4 Loads due to Surge (BNBC, 1993)

17. Ductility Provisions and Structural Repair/Retrofit • Ductility Provisions in Structural Design • Methods of Structural Retrofitting

18. Ductility Provisions in Structural Design Provisions for Quasi-Static Load • Steel yielding preferred to Concrete crushing • Balanced Steel Ratio (b), Maximum (max) and Minimum Steel Ratio (min) • Column Ties and Spirals, latter is more ductile Behavior of tied and spirally reinforced columns (Nilson)

19. Provisions for Impact Load Arrangements of free fall tests on concrete slabs Fig. 18: Arrangements of free fall tests on concrete slabs without and with a gravel cushion

20. Fig. 19: Machines supported on shock-absorbing springs Provisions for Machine Vibration

21. Provisions for Cyclone Load Coastal forest and vegetation (a) diminished tsunami wave height, (b) prevented destruction of houses at West Java

22. Pair of Links Pair of Links Blast Resistant Design Blast Resistant Planning (a) Beam-Column connection details (b) CFRP wrapped Column

23. Steel jacketed columns (a) circular, (b) rectangular with elliptical jacket Methods of Structural Retrofitting Jacketing and Confinement

24. FRP jacketed (a) Circular Columns, (b) Square Columns Jacketing and Confinement with transverse ties

25. Seismic Retrofitting Global Strategies - Adding shear wall, infill wall, wing wall - Adding bracing - Wall thickening - Mass reduction (using lighter materials) - Supplemental damping (TMD, TLD) - Base Isolation (shock absorber) Local Strategies - Jacketing of Beams, Columns, Joints - Strengthening of individual footings Makes stiffer Makes stronger

26. Retrofitting Beam-Column Frames Jacketing of Columns

27. Relevant Research at UAP • Numerical Study on Design of Blast Resistant Buildings • Dynamic Response of Coastal Structures to Ocean Wave Loading • Dynamic Response of RC Railing to Vehicular Impact • Transverse/Compression Reinforcement in RC Beams

28. Sec Storey Detailing Options No Mod Maj max N K max N K max N K B(sup) 6 1.65 0.16 0.12 1.65 0.15 0.13 1.65 0.15 0.18 12 1.65 0.27 0.51 1.65 0.24 0.42 1.65 0.26 0.34 24 1.65 0.20 0.41 1.65 0.24 0.30 1.65 0.20 0.29 6 0.34 0.40 0.51 0.63 0.36 0.49 1.04 0.23 0.41 R 12 0.20 0.12 0.36 0.35 0.13 0.31 0.47 0.14 0.22 y(t), F(t) m 24 0.12 0.12 0.25 0.09 0.17 0.33 0.12 0.17 k c k y ym ye F(t) Fm t td Numerical Study on Design of Blast Resistant Buildings Response to Blast Load for Ru/Fm = 0.10~2.0 and Damping Ratio (a) 0%, (b) 5% (a) Damped SDOF system with elastic fully-plastic k, (b) Blast Loading 0.18

29. Column W (kg) td/Tn k (k/ft) 6-Storied ye(ft) yu (ft) Ru (k) m (k-s2/ft) Tn (s) yu/ye 6-00N 1.44E+03 R = 3m 1.06E-02 0.43 R = 10m 15.2 R = 30m 29.35 0.90 40.3 100 6-00M 0.0125 1.27E+03 356 9.45E-03 3.83 0.68 12.0 0.016 29.35 0.96 406 6-100 0.0250 1.33E+03 847 1.30E-02 6.14 1.55 17.3 0.033 29.35 0.93 472 6-1000 0.0500 1.11E+03 1859 1.69E-02 6.14 4.57 18.7 0.069 29.35 1.02 364 1000 0.0125 5242 51 0.194 0.0250 11423 142 0.416 0.0500 23818 347 0.857 10000 0.0125 55190 1246 6.91 0.0250 118559 2802 22.97 0.0500 245327 5943 65.90 Ductility Ratio (yu/ye) for 6-Storied Building Ductility Demand (ym/ye) for Different Loading Conditions

30. W WC WCW Dynamic Response of Coastal Structures to Ocean Wave Loading (a) Moment-Curvature Relationship, (b) Curvature vs. Time for GF column of 6-Storied Building for 50-Year Storm

31. 290mm 190mm 150mm 200mm 2-19mm 2-19mm 2-19mm 3-19mm Dynamic Response of RC Railing to Vehicular Impact Cross-sections of Railing and Rail Post Moment-curvature relationship of Railing and Rail Post for different strain rates

32. ult Ref of various Posts Damping Ratio Weight (ton) Velocity (kmph), Angle() Top Middle Side 4% 2% 4 1 100, 90 50, 30 250 330 168 187 377 390 413 244 517 193 Dynamic Response showing effect of (a) Vehicular Weight, (b) Velocity and Angle Maximum Deflections (mm) from Parametric Studies

33. Experimental Work on Column Retrofit

34. Conclusions • Careful assessment of structural loads, and better construction practice necessary – Member jacketing and confinement • Proper assessment of soil properties necessary from accurate soil testing – Soil strengthening measures • Member detailing measures and shock-absorbing devices can be used to improve structural performance to Impact loads

35. Machine Vibrations should either be transferred to rigid sub-structure or supported on flexible spring/damper • Large stand-off distance, shock absorbers and member ductility necessary for Blast Resistant Design • Measures to resist cyclonic storms (combination of wave, current and wind forces) include protective vegetation and member ductility

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