Prevention, Appraisal, Internal failure, external failure cost
DUCTILITY AND PREVENTION OF STRUCTURAL FAILURE
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Transcript of DUCTILITY AND PREVENTION OF STRUCTURAL FAILURE
DUCTILITY AND PREVENTION
OF STRUCTURAL FAILURE
TOPICS• Types of Loading• Structural Distress under Various Loading Conditions• Ductility Provisions and Structural Repair/Retrofit• Relevant Research at UAP• Conclusions
Types of Loading
Structural Distress under Various Loading
Conditions• Quasi-Static Loads
• Machine Vibration
• Impact Loads
• Blast Loading
• Cyclonic 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-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
Cracks indicating Differential Support Settlement
Extreme Temperature (Fire)
0 100 200 300 400 500 600 700 800 900Temperature C
10
15
20
25
30
35
40
45
50
Co
mp
ress
ive
stre
ng
th (
MP
a)
The age (days)
30
60
90
o
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
Impact LoadsProgressive 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)
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 history
• Extremist views and access to explosives
• Very sudden and very high pressure
Blast Loading
September 11, 2001
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
1.E+07
0 10 20 30 40 50
Distance R (m)
Dyn
amic
Bla
st P
ress
ure
(psi
)
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 country
• Predicament in the demolition of a single building
Cyclones in Bangladesh
Hydraulic 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
May196
1146 2.5~3 11,466
28 May
1963
203 4~5 11,52011
May196
5162 4 19,279
12 Nov
1970
223 6~105,00,0
0025 May
1985
154 3~5 11,06929
April199
1225 6~8
1,38,00015
Nov200
7240 5~6 3,406
25 May
2009
120 2~3 330
Loads due to Surge (BNBC, 1993)
Coastal RegionSurge Height at Sea Coast,
hT (m)T = 50-
yearT = 100-
yearTeknaf 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 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)
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
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 strong
er
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
0
1
10
100
0 1 10
0
1
10
100
0 1 10
ym/y
e
td/Tn td/Tn
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8 0.9
1.0 1.2
1.5
2.0
0.1
0.2
0.3
0.4
0.5
0.6 0.7
0.8 0.9
1.0 1.2
1.5 2.0
Column
k (k/ft) ye (ft)yu (ft)
Ru (k) m (k-s2/ft)
Tn (s) yu/ye
6-00N1.44E+0
31.06E-
020.43 15.2 29.35 0.90 40.3
6-00M1.27E+0
39.45E-
033.83 12.0 29.35 0.96 406
6-1001.33E+0
31.30E-
026.14 17.3 29.35 0.93 472
6-10001.11E+0
31.69E-
026.14 18.7 29.35 1.02 364
W (kg) td/Tn
6-StoriedR = 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
-1500
-1000
-500
0
500
1000
1500
-0.006 -0.003 0.000 0.003 0.006
Curvature (rad/ft)
Mom
ent (
k-ft
)
-0.06
-0.04
-0.02
0.00
0.02
0 40 80 120 160
Time (sec)
GF
Col
umn
Cur
vatu
re (
rad/
ft)
W
WC
WCW
Dynamic Response of RC Railing to Vehicular Impact
2-19mm
290mm
200mm
3-19mm
150mm
190mm
2-19mm 2-19mm
-100
-50
0
50
100
150
-1.0 -0.5 0.0 0.5 1.0
Curvature (rad/m)
Mom
ent (k
N-m
)
Static SR = 100/s
-60
-40
-20
0
20
40
60
-1.0 -0.5 0.0 0.5 1.0
Curvature (rad/m)
Mo
men
t (k
N-m
)
Static SR = 100/s
Moment-curvature relationship of Railing and Rail Post for
different strain rates
Cross-sections of Railing and Rail Post
0.0
0.2
0.4
0.6
0.00 0.02 0.04 0.06 0.08 0.10
Time (sec)
Def
lect
ion
(m)
100, 30 100, 90 50, 30
0.0
0.2
0.4
0.6
0.00 0.02 0.04 0.06 0.08 0.10
Time (sec)
Def
lect
ion
(m)
W = 2 t W = 4 t W = 1 t
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 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
• 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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