Efficient structural design and good construction.ppt
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EFFICIENT STRUCTURAL DESIGN &
GOOD CONSTRUCTION
Engr. Sabbir Siddique,PEngSeptember 4, 2013
Comilla
Organized by
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DISCUSSION TOPICS STRUCTURAL DESIGN
– Discussion on Earthquake Loading- Ductility in structure
- Common design mistakes & key points
GOOD CONSTRUCTION – Water/Cement ratio- Compaction- Curing
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EARTHQUAKE LOADING
Seismic Zone
Location Seismic Intensity
Seismic Zone Coefficient, Z
1 Southwestern part including Barisal, Khulna, Jessore,
Rajshahi
Low 0.12
2 Lower Central and Northwestern
part including Noakhali, Dhaka,
Pabna, Dinajpur, as well as Southwestern corner
including Sundarbans
Moderate 0.20
3 Upper Central and Northwestern
part including Brahmanbaria, Sirajganj, Rangpur
Severe 0.28
4 Northeastern part including Sylhet,
Mymensingh, Kurigram
Very Severe 0.36
The Seismic Zoning Map – BNBC/2013
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BASIC INFORMATION ON EARTHQUAKE DESIGN
Values of the contour is Peak Ground Acceleration (PGA) in g for Maximum Considered Earthquake (MCE).
MCE is an earthquake which has 2% probability of exceedance in 50 years.
The MCE earthquake has a return period of 2,475 years; and
There is 36% probability that this MCE ground motion shall not occur in the 50 years period.
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BASIC INFORMATION ON EARTHQUAKE DESIGN
Structural design to be done using Design Basis Earthquake (DBE) which is of 2/3 MCE.
It may be noted that the earlier version of the code (BNBC/93 Art. 2.5.7.1) it was 225 years mean return period earthquake (20% probability of exceedance in 50 years).
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HOW TO INPUT EARTHQUAKE LOAD ?
BETTER WAY TO INPUT EARTHQUAKE LOAD IS AS – RESPONSE SPECTRUM FUNCTION.
IT CONSIDERS THE DYNAMIC MODE SHAPES OF THE BUILDING.
EASY TO INPUT – IF YOU HAVE LITTLE UNDERSTANDING ON STRUCTURAL DYNAMICS.
EARTHQUAKE DESIGN
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For Comilla
PGA for MCE = 0.2g
PGA for DBE = 2/3x0.2 = 0.133g
Very roughly this Design Basis Earthquake PGA has a return period of 475 years.
EARTHQUAKE DESIGN
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EARTHQUAKE LOADGROUND ACCELERATION OF EL-CENTRO EARTHQUAKE
RESPONSE SPECTRUM OF EL-CENTRO EARTHQUAKE FOR 5% DAMPING
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EARTHQUAKE LOAD
A TYPICAL RESPONSE SPECTRUM CURVE FOR COMILLA ZONE
SOIL- ROCK AS PER BNBC/2013
Design Acceleration Response Spectrum
0.000
0.050
0.100
0.150
0.200
0.250
0.300
0.350
0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 2.2 2.4 2.6 2.8 3 3.2 3.4 3.6 3.8 4
Period, sec
Spe
ctra
l acc
eler
atio
n,sa
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EARTHQUAKE LOAD
Design Acceleration Response Spectrum
0.000
0.020
0.040
0.060
0.080
0.100
0.120
0.140
0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 2.2 2.4 2.6 2.8 3 3.2 3.4 3.6 3.8 4Period, sec
Spe
ctra
l acc
eler
atio
n,sa
A TYPICAL RESPONSE SPECTRUM CURVE AS PER BNBC/2013
Seismic zone coefficient, Z = 0.20
Structure importance factor, I = 1.0Soil coefficient, S = 1.15
Force-Resisting Structural System = OMRF
Response reduction factor , R = 3.0
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EARTHQUAKE LOADArt. 2.5.4 EARTHQUAKE RESISTANT DESIGN- BASIC CONCEPT
PROJECT LOCATION Comilla Art. 2.5.6.2 Seismic zone coefficient for Maximum Considered Earthquake , Z 0.2 gArt. 2.5.7.1 Structure importance factor, I 1
Seismic Force-Resisting Structural System Ordinary reinforced concrete moment framesTable 2.5.7 Response reduction factor , R 3
Table 2.5.4 Lower llimit of the period of the constant spectral accleration branch, TB 0.2 sec
Table 2.5.4 Upper llimit of the period of the constant spectral accleration branch, TC 0.6 sec T Sa
Table 2.5.4 Lower llimit of the period of the constant spectral displacement branch, TD 2.0 sec 1 0 0.051Table 2.5.4 Site dependent soil factor defining elastic response spectrum, S 1.15 2 0.05 0.070Eqn. 2.5.6 Damping correction factor, 1.0 3 0.1 0.089
Viscous damping, 5 % 4 0.15 0.109Art. 2.5.6.3 Coefficient used to calculate lower bond for Sa , 0.2 5 0.2 0.128Table 2.5.1 Site classification based on soil properties SC 6 0.4 0.128
7 0.6 0.1288 0.8 0.0969 1 0.077
10 1.2 0.06411 1.4 0.05512 1.6 0.04813 1.8 0.04314 2 0.03815 2.2 0.03216 2.4 0.02717 2.6 0.02318 2.8 0.02019 3 0.01720 3.2 0.01521 3.4 0.01322 3.6 0.01223 3.8 0.01124 4 0.010
Table 1 Acceleration response spectrum data
Design Acceleration Response Spectrum
0.000
0.020
0.040
0.060
0.080
0.100
0.120
0.140
0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 2.2 2.4 2.6 2.8 3 3.2 3.4 3.6 3.8 4Period, sec
Spe
ctra
l acc
eler
atio
n,sa
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EARTHQUAKE LOAD
IF WE ARE LITTLE COURAGEOUS – WHY NOT USE ‘TIME HISTORY DATA’ FOR OUR BUILDING ANALYSIS ?
WE CAN GENERATE A RESPONSE SPECTRUM COMPITABLE TIME HISTORY DATA WITH LITTLE EXPERTISE IN NUMERICAL MATHEMATICS.
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EARTHQUAKE LOAD
-0.6
-0.4
-0.2
-0.0
0.2
0.4
0.6
0 2 4 6 8 10 12 14 16 18 20
t (s)
Time history 1
TIME HISTORY CURVE FOR BNBC/2013 RESPONSE SPECTRUM CURVE AS SHOWN BEFORE
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EARTHQUAKE LOAD
0.00
0.02
0.04
0.06
0.08
0.10
0.12
0.14
0.16
0.18
0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0
T (s)
Response Spectrum 1
TIME HISTORY DATA MATCHING TARGET SPECTRUM
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DUCTILITY IN STRUCTURE
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DUCTILITY IN STRUCTURE
WE CAN MAKE A CONCRETE STRUCTURE DUCTILE BY -
USE DUCTILE REINFORCING MATERIAL
MAKE DUCTILE DETAILING OF JOINTS
IN SIMPLE WORD DUCTILITY MEANS – ABILITY TO DEFORM
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GENERALIZED FORCE DEFORMATION CURVE OF STRUCTURES
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COMPARISON OF MEMBER DUCTILITY FOR DIFFERENT STEEL MATERIAL
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COMPARISON OF MEMBER DUCTILITY FOR DIFFERENT STEEL MATERIAL
500 GRADE GENERAL STEEL
500 GRADE BSRM EXTREME
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COMMON MISTAKES IN STRUCTURAL DESIGN OF BUILDING
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BASIC LIMITATON OF THE PRACTICING CIVIL ENGINEER?
TOO DEPENDENT ON SOFTWARE FOR DESIGN OF STRUCTURAL MEMBERS
DO NOT UNDERSTAND MATERIAL SPECIFICATION
DO NOT UNDERSTAND CONTRACT
CAN NOT WRITE REPORTS
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LOADS IN BUILDING WE HAVE GOOD UNDERSTANDING OF PERMANENT GRAVITY LOADS (DEAD & LIVE).
WE HAVE LESS UNDERSTANDING ON ENVIORNMENTAL LOAD e.g. WIND & EARTHQUAKE.
WE HAVE NO UNDERSTANDING ON SECONDARY LOADS e.g. CREEP, SHRINKAGE.
DID YOU KNOW ? FOUNDATION SETTLEMENT IS A LOAD THAT NEED TO BE CONSIDERED IN DESIGN.
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COMMON MISTAKES WE DO IN FOUNDATION DESIGN
SOIL INVESTIGATION - WE NEVER SAY WHAT TO INVESTIGATE
WE SELDOM CONSIDER WATER TABLE IN FOUNDATION DESIGN
WE SELDOM CONSIDER SURCHARGE LOAD FROM GR. FLOOR ON
FOUNDATION
WE NEVER CALCULATE SETTLEMENT
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BEAM DESIGN
TORSION IS AN IMPORTANT ISSUE BUT USUALLY NOT CONSIDERED IN RC DESIGN – BECAUSE GENERAL PURPOSE ENGINEERING SOFTWARE ONLY CONSIDER STRONG AXIS MOMENT/SHEAR FOR RC DESIGN. – THIS IS A GREAT MISTAKE.
NEVER CHECK REINFORCEMENT DETAILING AT JOINTS.
NEVER CHECK CRACK WIDTH, DEFLECTION & VIBRATION.
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COLUMN DESIGN
COLUMN FAILS IN SHEAR DURING EARTHQUAKE – COMMON PRACTICE IS TO DESIGN COLUMN FOR AXIAL FORCE AND MOMENT ONLY.
WHAT ABOUT MOMENT MAGNIFICATION IN COLUMN DESIGN? OR OTHERWAY TO CONSIDERE GEOMETRIC NON-LINEARITY?
DID YOU KNOW- STIFFNESS OF THE STRUCTURE REDUCE FOR AXIAL COMPRESSION?
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Good ConstructionResults in Safe Structure
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Three most important Issues for Good Concrete Construction
Water-Cement Ratio
Compaction
Curing
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Never just add water to the concrete to make it more workable, always use a mix of cement paste (i.e. water AND cement).
Dry Concrete?
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COMPRESSIVE STRENGTH OF CONCRETE
Water Cement Ratio VS Compressive Strength
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Compaction is done by shaking, or vibrating, the concrete which liquefies it, allowing the trapped air to rise out.
Compaction must be done as concrete is placed, while it is still plastic. Never let concrete dry-out and stiffen because it will be too hard to compact.
Properly compacted concrete is more dense, strong and durable. Off-form finishes will also be better.
Compaction of Concrete
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Compaction of Concrete
Put the poker into the concrete QUICKLY.
Take the poker out very SLOWLY
The area vibrated at one time is called theRADIUS OF ACTION. This can be seen by over what radius air bubbles rise to the surface.The radius of action will be greater with aLARGER poker and more-workable concrete.
Always compact in a definite pattern so the radius of action overlaps and covers the whole area of the concrete.
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Compaction of Concrete
NEVER touch the form face with the poker as it can damage the formwork and the concrete.
NEVER spread or move concrete sideways with the poker, always use a shovel.
NEVER touch the reinforcement with the poker.
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COMPRESSIVE STRENGTH OF CONCRETE
Strength VS Compaction
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Curing of Concrete
WHAT IS CURING ?Curing means to cover the concrete so it stays MOIST. By keeping concrete moist the bond between the paste and the aggregates gets stronger. Concrete doesn’t harden properly if it is left to dry out.
WHEN TO CURE?Curing is done just after finishing the concrete surface, as soon as it will not be damaged.
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Curing of Concrete
The simplest method of APPLYING WATER is to put a continuous fine, misty spray of water over the concrete.
BEWARE: The spray must be a very fine mist or else it will damage the surface of the concrete.Concrete will dry out more quickly in hot weather. Keep the concrete continuously moist.
The most important thing in curing is to keep the concrete moist at all times. Hosing in the morning and again at night and letting the concrete dry out in between is not good.
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Curing of Concrete
Another way to cure concrete is to cover with PLASTIC SHEETS to slow down water loss.
Concrete may also be cured by applying a CURING COMPOUND [EVAPORATIVE RETARDANT (Aliphatic Alcohol)] which slows water loss.
Recent example is 3rd Karnafuly Extra dosed Cable Stayed Bridge.
Another passive way of Curing is to keep the formwork for long time.
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COMPRESSIVE STRENGTH OF CONCRETE
Strength VS Curing
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LAST BUT NOT THE LEAST
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NEVER EVER DO THESE MISTAKES
Any design work without calculation. Left you drawing incomplete thinking that it would be done at site during construction.
Provide a drawing without necessary information in it.
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Do not make a ‘KICKER’ for Column Casting. If you need something like a
‘KICKER’ to place the formwork – make it at least 300mm high so that you can vibrate it with Poker Vibrator. And NEVER use hand-
mix concrete for such construction.
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Do not add cement grout on old concrete to pour new concrete.
Fresh water is good enough. If required use jointing material e.g.
SIKADUR-31 or other similar.
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CIVIL ENGINEERING IS NOT A WHITE COLLAR JOB.
WITHOUT PROPOER CONSTRUCTION KNOWLEDGE & EXPERIENCE YOU WILL NEVER BE GOOD DESIGNEER.
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FURTHER QUESTIONS?
Feel free to knock me at:
www.sabbirsiddique.com