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DUCTILITY AND PREVENTION OF STRUCTURAL FAILURE. TOPICS Types of Loading Structural Distress under Various Loading Conditions Ductility Provisions and.

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Presentation on theme: "DUCTILITY AND PREVENTION OF STRUCTURAL FAILURE. TOPICS Types of Loading Structural Distress under Various Loading Conditions Ductility Provisions and."— Presentation transcript:

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 Vertical Loads Overload from service requirement and careless use Poor construction practices and material quality Quasi-Static Loads 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 Extreme Temperature (Fire) Fig. 7(a): The effect of fire flame on the compressive strength at 1-hour of exposure Effect of temperature on (a) Steel yield strength, (b) Concrete compressive strength Steel melts as in September 11, 2001 Dehydration of paste in the concrete matrix

9 Impact Loads Progressive Failure of Slabs Progressive Failure of slabs in (a) USA, (b) Bangladesh 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)

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

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

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

15 Cyclones in Bangladesh Hydraulic Loading DateYearMax. Wind Speed(Kmph))Storm Surge Ht. (m)Deaths 09 Oct196016233,000 30 Oct19602104.5~65,149 09 May19611462.5~311,466 28 May19632034~511,520 11 May1965162419,279 12 Nov19702236~105,00,000 25 May19851543~511,069 29 April19912256~81,38,000 15 Nov20072405~63,406 25 May20091202~3330

16 Loads due to Surge (BNBC, 1993) Coastal Region Surge Height at Sea Coast, h T (m) T = 50-yearT = 100-year Teknaf to Cox's Bazar4.55.8 Chakaria to Anwara, Maheshkhali-Kutubdia Islands7.18.6 Chittagong to Noakhali7.99.6 Sandwip, Hatiya and all islands in this region7.99.6 Bhola to Barguna6.27.7 Sarankhola to Shyamnagar5.36.4

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 Fig. 18: Arrangements of free fall tests on concrete slabs without and with a gravel cushion Arrangements of free fall tests on concrete slabs

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

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

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

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

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

25 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 Seismic Retrofitting Makes stiffer Makes stronger

26 Jacketing of Columns Retrofitting Beam-Column Frames

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 Numerical Study on Design of Blast Resistant Buildings 0.18 SecSec StoreyStorey Detailing Options NoModMaj maxmax NN KK maxmax NN KK maxmax NN KK B(sup)B(sup) 6 1.651.65 0.160.16 0.120.12 1.651.65 0.150.15 0.130.13 1.651.65 0.150.15 0.180.18 1212 1.651.65 0.270.27 0.510.51 1.651.65 0.240.24 0.420.42 1.651.65 0.260.26 0.340.34 2424 1.651.65 0.200.20 0.410.41 1.651.65 0.240.24 0.300.30 1.651.65 0.200.20 0.290.29 6 0.340.34 0.400.40 0.510.51 0.630.63 0.360.36 0.490.49 1.041.04 0.230.23 0.410.41 1212 0.200.20 0.120.12 0.360.36 0.350.35 0.130.13 0.310.31 0.470.47 0.140.14 0.220.22 2424 0.120.12 0.120.12 0.250.25 0.090.09 0.170.17 0.330.33 0.120.12 0.170.17 Response to Blast Load for R u /F m = 0.10~2.0 and Damping Ratio (a) 0%, (b) 5% (a) Damped SDOF system with elastic fully- plastic k, (b) Blast Loading k c m y(t), F(t) y R k yeye ymym t F(t) FmFm tdtd

29 Columnk (k/ft)y e (ft)y u (ft)R u (k)m (k-s 2 /ft)T n (s)yu/yeyu/ye 6-00N1.44E+031.06E-020.4315.229.350.9040.3 6-00M1.27E+039.45E-033.8312.029.350.96406 6-1001.33E+031.30E-026.1417.329.350.93472 6-10001.11E+031.69E-026.1418.729.351.02364 W (kg)td/Tntd/Tn 6-Storied R = 3mR = 10mR = 30m 100 0.01253560.680.016 0.02508471.550.033 0.050018594.570.069 1000 0.01255242510.194 0.0250114231420.416 0.0500238183470.857 10000 0.01255519012466.91 0.0250118559280222.97 0.0500245327594365.90 Ductility Demand (y m /y e ) for Different Loading Conditions Ductility Ratio (y u /y e ) for 6-Storied Building

30 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 W WC WCW

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

32  ult  Ref of various Posts Damping RatioWeight (ton) Velocity (kmph), Angle(  ) TopMiddleSide4%2%41 100, 90  50, 30  250330168187377390413244517193 Maximum Deflections (mm) from Parametric Studies Dynamic Response showing effect of (a) Vehicular Weight, (b) Velocity and Angle

33 Experimental Work on Column Retrofit

34 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 Conclusions

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

36 THANK YOU


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