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


DISCUSSION TOPICS STRUCTURAL DESIGN

– Discussion on Earthquake Loading- Ductility in structure

- Common design mistakes & key points

GOOD CONSTRUCTION – Water/Cement ratio- Compaction- Curing


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


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.


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).


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


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


EARTHQUAKE LOADGROUND ACCELERATION OF EL-CENTRO EARTHQUAKE

RESPONSE SPECTRUM OF EL-CENTRO EARTHQUAKE FOR 5% DAMPING


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


EARTHQUAKE LOAD


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


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


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


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.


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


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


DUCTILITY IN STRUCTURE


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


GENERALIZED FORCE DEFORMATION CURVE OF STRUCTURES


COMPARISON OF MEMBER DUCTILITY FOR DIFFERENT STEEL MATERIAL


COMPARISON OF MEMBER DUCTILITY FOR DIFFERENT STEEL MATERIAL

500 GRADE GENERAL STEEL

500 GRADE BSRM EXTREME


COMMON MISTAKES IN STRUCTURAL DESIGN OF BUILDING


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


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.


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


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.


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?


Good ConstructionResults in Safe Structure


Three most important Issues for Good Concrete Construction

Water-Cement Ratio

Compaction

Curing


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?


COMPRESSIVE STRENGTH OF CONCRETE

Water Cement Ratio VS Compressive Strength


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



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.



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.



Strength VS Compaction


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.


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.


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.



Strength VS Curing


LAST BUT NOT THE LEAST


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.


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.


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.


CIVIL ENGINEERING IS NOT A WHITE COLLAR JOB.

WITHOUT PROPOER CONSTRUCTION KNOWLEDGE & EXPERIENCE YOU WILL NEVER BE GOOD DESIGNEER.


FURTHER QUESTIONS?

Feel free to knock me at:

www.sabbirsiddique.com

Efficient structural design and good construction.ppt

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