Transcript Ductility and Prevention of Structural Failure
DUCTILITY AND PREVENTION OF STRUCTURAL FAILURE
TOPICS
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Types of Loading
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Structural Distress under Various Loading Conditions
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Ductility Provisions and Structural Repair/Retrofit
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Relevant Research at UAP
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Conclusions
Types of Loading
Structural Distress under Various Loading Conditions
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Quasi-Static Loads
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Machine Vibration
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Impact Loads
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Blast Loading
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Cyclonic Storm Loading
Quasi-Static Loads Vertical Loads
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Overload from service requirement and careless use
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Poor construction practices and material quality
Cracks in Beams and Columns Ultimate Collapse of Structure
Support Settlement
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Overloaded super-structure and sub-structure
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Filling up lands, ponds, with soft infill
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No/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)
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Steel melts as in September 11, 2001
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Dehydration of paste in the concrete matrix 50 45 40 35 30 The age (days) 30 60 90 25 20 15 10 0 100 200 300 400 500 600 o Temperature C 700 800 900
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
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Impact Loads Progressive Failure of Slabs Sudden drop of top slab causes a large impact load
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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
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
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Blast Loading Nature of Blast Loading One blast can change history
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Extremist views and access to explosives
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Very sudden and very high pressure
Distance
R
(m) 40 50 1.E+07 0 1.E+06 1.E+05 1.E+04 1.E+03 1.E+02 1.E+01 1.E+00 1.E-01 1.E-02 1.E-03 1.E-04 1.E-05 1.E-06 0 10 20 30 10 20 30 10000 kg 500 kg 10 kg 40 September 11, 2001 1000 kg 100 kg 50 Distance
R
Variation of Blast Pressure with Distance Fig. 14: Variation of blast pressure with distance, for explosives of different weights 1 kg
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Controlled Demolition Ever-changing urban infrastructure in this country
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Predicament in the demolition of a single building
Controlled Demolition
Date 09 Oct 30 Oct 09 May 28 May 11 May 12 Nov 25 May 29 April 15 Nov 25 May Year 1960 1960 1961 1963 1965 1970 1985 1991 2007 2009
Hydraulic Loading Cyclones in Bangladesh
Max. Wind Speed(Kmph)) 162 210 146 203 162 223 154 225 240 120 Storm Surge Ht. (m) 3 4.5~6 2.5~3 4~5 4 6~10 3~5 6~8 5~6 2~3 Deaths 3,000 5,149 11,466 11,520 19,279 5,00,000 11,069 1,38,000 3,406 330
Loads due to Surge (BNBC, 1993)
Coastal Region Teknaf to Cox's Bazar Chakaria to Anwara, Maheshkhali-Kutubdia Islands Chittagong to Noakhali Sandwip, Hatiya and all islands in this region Bhola to Barguna Sarankhola to Shyamnagar Surge Height at Sea Coast, h
T
(m) T = 50-year T = 100-year 4.5
7.1
7.9
5.8
8.6
9.6
7.9
6.2
5.3
9.6
7.7
6.4
Ductility Provisions and Structural Repair/Retrofit
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Ductility Provisions in Structural Design
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Methods of Structural Retrofitting
Ductility Provisions in Structural Design
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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)
Provisions for Impact Load
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
Blast Resistant Planning Pair of Links Pair of Links (a) Beam-Column connection details (b) CFRP wrapped Column
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
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) Makes stiffer Local Strategies - Jacketing of Beams, Columns, Joints - Strengthening of individual footings Makes stronger
Retrofitting Beam-Column Frames Jacketing of Columns
Relevant Research at UAP
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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
F m k R m k c
Numerical Study on Design of Blast Resistant Buildings
y(t), F(t)
0.1 0.3 0.5 0.7 0.1 0.3 0.5 100 100 10 1 0.2 0.4 0.6 0.8 0.9 1.0 1.5 1.2 2.0 10 1 0.2 0.4 0.6 0.8 0.7 0.9 1.0 1.2 1.5 2.0
y F(t) y e y m t
0 0 0 0 1 10 1 10
t d /T n t d /T n
Response to Blast Load for R
u
/F
m
= 0.10~2.0 and Damping Ratio (a) 0%, (b) 5%
t d
(a) Damped SDOF system with elastic fully plastic k, (b) Blast Loading
Column 6-00N 6-00M 6-100 6-1000
Ductility Ratio ( y u / y e ) for 6-Storied Building
k (k/ft) 1.44E+03
y e
(ft) 1.06E-02
y u
(ft) 0.43
R u
(k) 15.2
m (k-s 2 /ft) 29.35
T n
(s) 0.90
1.27E+03 1.33E+03 1.11E+03 9.45E-03 1.30E-02 1.69E-02 3.83
6.14
6.14
12.0
17.3
18.7
29.35
29.35
29.35
0.96
0.93
1.02
y u
/y
e
40.3
406 472 364
Ductility Demand ( y m / y e ) for Different Loading Conditions
6-Storied W (kg)
t d
/T
n
R = 3m R = 10m R = 30m 0.0125
356 0.68
0.016
100 1000 10000 0.0250
0.0500
0.0125
0.0250
0.0500
0.0125
0.0250
0.0500
847 1859 5242 11423 23818 55190 118559 245327 1.55
4.57
51 142 347 1246 2802 5943 0.033
0.069
0.194
0.416
0.857
6.91
22.97
65.90
Dynamic Response of Coastal Structures to Ocean Wave Loading
0.02
1500 1000 0.00
0 40 80 120
W
160 500 -0.006
-0.003
0 0.000
-500 0.003
0.006
-0.02
WC
-0.04
-1000
WCW
-0.06
-1500 Time (sec) Curvature (rad/ft) (a) Moment-Curvature Relationship, (b) Curvature vs. Time for GF column of 6-Storied Building for 50-Year Storm
Dynamic Response of RC Railing to Vehicular Impact
Static SR = 100/s 190mm 60 150mm 2-19mm 290mm 2-19mm -1.0
-0.5
40 20 0 -20 0.0
-40 -60 0.5
SR = 100/s 1.0
150 100 200mm 50 -0.5
0 -50 0.0
3-19mm 2-19mm -1.0
0.5
1.0
Cross-sections of Railing and Rail Post -100 Curvature (rad/m) Moment-curvature relationship of Railing and Rail Post for different strain rates
W = 2 t W = 4 t W = 1 t 100, 30 100, 90 50, 30 0.6
0.6
0.4
0.4
0.2
0.2
ult 250 0.0
0.00
0.0
0.02
0.04
0.06
0.08
0.10
0.00
0.02
0.04
0.06
Time (sec) Time (sec) Dynamic Response showing effect of (a) Vehicular Weight, (b) Velocity and Angle 0.08
0.10
Maximum Deflections (mm) from Parametric Studies
Ref of various Posts Damping Ratio Weight (ton) Velocity (kmph), Angle( ) Top Middle Side 4% 2% 4 1 100, 90 50, 30 330 168 187 377 390 413 244 517 193
Experimental Work on Column Retrofit
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Conclusions Careful assessment of structural loads, and better construction practice necessary – Member jacketing and confinement
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Proper assessment of soil properties necessary from accurate soil testing – Soil strengthening measures
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Member detailing measures and shock absorbing devices can be used to improve structural performance to Impact loads
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Machine Vibrations should either be transferred to rigid sub-structure or supported on flexible spring/damper
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Large stand-off distance, shock absorbers and member ductility necessary for Blast Resistant Design
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Measures to resist cyclonic storms (combination of wave, current and wind forces) include protective vegetation and member ductility