DUCTILITY AND PREVENTION

OF STRUCTURAL FAILURE

TOPICSTypes of LoadingStructural Distress under Various Loading ConditionsDuctility Provisions and Structural Repair/RetrofitRelevant Research at UAPConclusions

Types of Loading

Structural Distress under Various Loading Conditions

Quasi-Static LoadsMachine VibrationImpact LoadsBlast LoadingCyclonic Storm Loading

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

Support Settlement

Overloaded super-structure and sub-structureFilling up lands, ponds, with soft infillNo/inaccurate soil test and no soil improvement

(a) Building before support settlement, (b) Uniform settlement, (c) Differential settlement

Cracks indicating Differential Support Settlement

Extreme Temperature (Fire)

Fig. 7(a): The effect of fire flame on the compressive strength at 1-hour of exposureEffect of temperature on

(a) Steel yield strength, (b) Concrete compressive strength

Steel melts as in September 11, 2001Dehydration of paste in the concrete matrix

Impact LoadsProgressive Failure of Slabs

Progressive Failure of slabs in (a) USA, (b) Bangladesh

Sudden drop of top slab causes a large impact loadCreates a series of slab failures heaped like a pack

of cards (called a pancake failure)

Vehicular Impact on Bridge Railings

Railing crash involving (a) smaller vehicle, (b) larger vehicle

Vehicular Impact on Bridge Railings

Arrangements for vehicular-impact test of RC railings

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

One blast can change historyExtremist views and access to explosivesVery sudden and very high pressure

Blast Loading

September 11, 2001

1 kg

10 kg 100 kg

10000 kg

1000 kg500 kg

0 10 20 30 40 50

Distance R (m)

Distance R (m)

Fig. 14: Variation of blast pressure with distance, for explosives of different weightsVariation of Blast Pressure with Distance

Nature of Blast Loading

Controlled Demolition

Controlled Demolition

Ever-changing urban infrastructure in this countryPredicament in the demolition of a single building

Cyclones in BangladeshHydraulic Loading

Date Year Max. Wind Speed(Kmph)) Storm Surge Ht. (m) Deaths09 Oct 1960 162 3 3,00030 Oct 1960 210 4.5~6 5,14909 May 1961 146 2.5~3 11,46628 May 1963 203 4~5 11,52011 May 1965 162 4 19,27912 Nov 1970 223 6~10 5,00,00025 May 1985 154 3~5 11,06929 April 1991 225 6~8 1,38,00015 Nov 2007 240 5~6 3,40625 May 2009 120 2~3 330

Loads due to Surge (BNBC, 1993)

Coastal RegionSurge 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

Ductility Provisions and Structural Repair/Retrofit

Ductility Provisions in Structural Design

Methods of Structural Retrofitting

Ductility Provisions in Structural DesignProvisions for Quasi-Static Load

Steel yielding preferred to Concrete crushingBalanced 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)

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

Provisions for Machine Vibration

Fig. 19: Machines supported on shock-absorbing springs

Provisions for Cyclone Load

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

Blast Resistant Design

Pair of Links

Pair of Links

(a) Beam-Column connection details (b) CFRP wrapped Column

Blast Resistant Planning

Methods of Structural Retrofitting

Jacketing and Confinement

Steel jacketed columns (a) circular, (b) rectangular with elliptical jacket

FRP jacketed (a) Circular Columns, (b) Square Columns

Jacketing and Confinement with transverse ties

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

Jacketing of Columns

Retrofitting Beam-Column Frames

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

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

k c

m y(t), F(t)

y

R

k

ye ym

t

F(t)

Fm

td

Column k (k/ft) ye (ft) yu (ft) Ru (k) m (k-s2/ft) Tn (s) yu/ye

6-00N 1.44E+03 1.06E-02 0.43 15.2 29.35 0.90 40.3

6-00M 1.27E+03 9.45E-03 3.83 12.0 29.35 0.96 406

6-100 1.33E+03 1.30E-02 6.14 17.3 29.35 0.93 472

6-1000 1.11E+03 1.69E-02 6.14 18.7 29.35 1.02 364

W (kg) td/Tn6-Storied

R = 3m R = 10m R = 30m

1000.0125 356 0.68 0.0160.0250 847 1.55 0.0330.0500 1859 4.57 0.069

10000.0125 5242 51 0.1940.0250 11423 142 0.4160.0500 23818 347 0.857

100000.0125 55190 1246 6.910.0250 118559 2802 22.970.0500 245327 5943 65.90

Ductility Demand (ym/ye) for Different Loading Conditions

Ductility Ratio (yu/ye) for 6-Storied Building

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

Dynamic Response of RC Railing to Vehicular Impact

2-19mm

290mm

200mm

3-19mm

150mm

190mm

2-19mm 2-19mm

Moment-curvature relationship of Railing and Rail Post for different strain rates

Cross-sections of Railing and Rail Post

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

Maximum Deflections (mm) from Parametric Studies

Dynamic Response showing effect of (a) Vehicular Weight, (b) Velocity and Angle

Experimental Work on Column Retrofit

Careful assessment of structural loads, and better construction practice necessary Member jacketing and confinementProper 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

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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