BNBC 2017: Evaluation of Seismic Load using Equivalent ......Earthquake force •Inertia force...

Equivalent Static Analysis: BNBC 2017 1

74

Dr. Tahsin R. Hossain Dept. of Civil Engg. BUET

BNBC 2017: Evaluation of Seismic Load using Equivalent Static Force Method

Dr. Tahsin Reza Hossain Professor Department of Civil Engineering, BUET


74


Outline of Lectures • Lecture 1- Seismic loading concept of BNBC 2017; estimation of

seismic loading using equivalent static force method (ESFM) and Computer application

• Lecture 2- Dynamic Analysis as per BNBC 2017, Response spectrum method (RSM) and Time History method (TH), computer applications

• Lecture 3- Seismic design and detailing of concrete structure for IMRF structures with Computer applications

• Lecture 4- Seismic design and detailing of concrete structure for SMRF structures with Computer applications


74


Lecture 1:

• Basic Philosophy of earthquake resistant design

• Equivalent Static Analysis method as in BNBC 2017 section 2.5.9

• Computer application(ETABS) to design a RC building


74


What causes Earthquake?


74


Earthquake effects

Four basic causes of earthquake damage

• Ground shaking

• Ground failure

• Tsunamis

• Fire

• Our concern is ground shaking


74


Earthquakes do not kill people, buildings do


74


Earthquake force

• Inertia force throughout the mass

• Distinctly different from DL, LL, WL

• Reversible force

• Complex, random

• Difficult to predict

• Dynamic


74


Inertia force and relative motion

• Frame structure

• Inertial force at roof transfer through column

• Larger u larger internal force


74


Simultaneously in three directions

Equivalent Static Analysis: BNBC 2017 10 74


Generation of seismic force

• Inertia force flows through all structural components

• All components need to be sufficiently strong to transmit the force



Philosophy of seismic design

11



Lateral Force Method

• Equivalent Static Force Method

• Dynamic Response Method –Response Spectrum Method

–Time History Method


Dr. Tahsin R. Hossain Dept. of Civil Engg. BUET 15

WR

ZICV

amF

Sir Isaac Newton

1642-1727



Z coefficient and C curve



Factor of 2 hidden in old BNBC

17

WR

ZICV

2



Seismic Zoning Map: 1993 and 2017



Design Earthquake Force, BNBC 2017

sa CR

ZIS

3

2

Spectral Acceleration

0.11



Base shear

V = SaW

0.044



Vertical Distribution of base shear

V

F1

F2

F3

F4

F5

F6

F7

k=1 k >1

k = 1 for structure period 0.5 = 2 for structure period ≥ 2.5s = linear interpolation between 1 and 2 for other periods.

n

i

k

ii

k

xxx

hw

hwVF

1



Soil type S TB

(s) TC (s)

TD (s)

SA 1.0 0.15 0.40 2.0

SB 1.2 0.15 0.50 2.0

SC 1.15 0.20 0.60 2.0

SD 1.35 0.20 0.80 2.0

SE 1.4 0.15 0.50 2.0

Site dependent soil factor and other parameters defining elastic response spectrum

0for15.21 BB

s TTT

TSC

TTTSη.C CBs for52

DCC

s TTTT

TSC

for5.2

sec 4for5.22

TT

T

TTSC D

DCs

Normalized acceleration response spectrum, Cs

55.0)5/(10 η

Here is structural damping expressed as a percentage of critical damping.



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

Description of Seismic Zones



The seismic zoning map divides the country into four seismic zones with different expected levels of intensity of ground motion. Each seismic zone has a zone coefficient which provides expected peak ground acceleration values on rock/firm soil corresponding to the maximum considered earthquake (MCE). The design basis earthquake is taken as 2/3 of the maximum considered earthquake.

MAXIMUM CONSIDERED EARTHQUAKE (MCE): The most severe earthquake ground motion considered by this code.

DESIGN EARTHQUAKE: The earthquake ground motion considered (for normal design) as two-thirds of the corresponding Maximum Considered Earthquake (MCE).

The intent of the seismic zoning map is to give an indication of the Maximum Considered Earthquake (MCE) motion at different parts of the country. In probabilistic terms, the MCE motion may be considered to correspond to having a 2% probability of exceedance within a period of 50 years.



Nature of Occupancy

Occupancy Category

Buildings and other structures that represent a low hazard to human life in the event of failure

I

All buildings and other structures except those listed

in Occupancy Categories I, III, and IV

II

Buildings and other structures that represent a substantial hazard to human life in the event of failure, including, but not limited to:

• W here more than 300 people congregate in one area • Daycare facilities with a capacity greater than 150 • S chool facilities with a capacity greater than 250 • C olleges or adult education facilities having more than 500 students. • Health care facilities with a capacity of 50 or more resident patients but nor

surgery facility. • Jails and detention facilities

III

Buildings and other structures designated as essential facilities, including, but not limited to:

• Hospitals and other health care facilities having surgery or emergency treatment facilities

• Fire, rescue, ambulance, and police stations and emergency vehicle garages • Designated earthquake, hurricane, or other emergency shelters • Designated emergency preparedness, communication, and operation

centers and other facilities required for emergency response • Power generating stations and other public utility facilities required in an

emergency • Ancillary structures (including, but not limited to, communication towers,

fuel storage tanks, cooling towers, electrical substation structures, fire water storage tanks or other structures housing or supporting water, or other fire-suppression material or equipment) required for operation of Occupancy Category IV structures during an emergency

IV

Occupancy Category of Buildings and Other Structures

Occupancy Category

Importance factor

I

I or II 1.0

III 1.25

IV 1.5

Importance Factors for Buildings and Structures for Earthquake design



Occupancy Category I, II and III Occupancy Category IV

Site Class Zone 1

Zone 2

Zone 3

Zone 4

Zone 1

Zone 2

Zone 3

Zone 4

SA B C C D C D D D

SB B C D D C D D D

SC B C D D C D D D

SD C D D D D D D D

SE, S1, S2 D D D D D D D D

Seismic Design Category of Buildings

Seismic design category controls the building height limit and permissible framing type.



Site Class

Description of soil profile up to 30 meters depth

Average Soil Properties in top 30 meters Shear wave velocity 𝑽 𝒔 (m/s)

Standard Penetration Value, 𝑵 (blows/30cm)

Undrained shear strength, 𝑺 𝒖 (kPa)

SA Rock or other rock-like geological formation, including at most 5 m of weaker material at the surface.

> 800 -- --

SB Deposits of very dense sand, gravel, or very stiff clay, at least several tens of metres in thickness, characterised by a gradual increase of mechanical properties with depth.

360 – 800 > 50 > 250

SC Deep deposits of dense or medium dense sand, gravel or stiff clay with thickness from several tens to many hundreds of metres.

180 – 360 15 - 50 70 - 250

SD Deposits of loose-to-medium cohesionless soil (with or without some soft cohesive layers), or of predominantly soft-to-firm cohesive soil.

< 180 < 15 < 70

SE A soil profile consisting of a surface alluvium layer with Vs values of type C or D and thickness varying between about 5 m and 20 m, underlain by stiffer material with Vs > 800 m/s.

-- -- --

Site classification based on soil properties



Natural Period mnt hCT

hn = Height of building in metres from foundation or from top of rigid basement. This excludes the basement storeys, where basement walls are connected with the ground floor deck or fitted between the building columns. But it includes the basement storeys, when they are not so connected.

Ct and m are obtained from Table 6.2.20

Structure type Ct m

Concrete moment-resisting frames 0.0466 0.9

Steel moment-resisting frames 0.0724 0.8

Eccentrically braced steel frame 0.0731 0.75

All other structural systems 0.0488 0.75 NOTE: Consider moment resisting frames as frames which resist 100% of seismic force and are not enclosed or adjoined by components that are more rigid and will prevent the frames from deflecting under seismic forces.



BNBC 2017 PROVISIONS

1. 1.4D 2. 1.2D + 1.6L 3. 1.2D + (L or 0.8W) 4. 1.2D + 1.6W + L 5. 1.2D + E + L 6. 0.9D + 1.6W 7. 0.9D + E

D = Dead load E = Seismic Load F = Fluid pr. H = Soil pr. L = Live load

Lr = Roof live load R = Rain load T = Thermal load W = Wind load

1. 1.4D 2. 1.2D + 1.6L 3. 1.2D + L 4. 1.2D + 0.8W 5. 1.2D + L + 1.6W 6. 1.2D + L + E 7. 0.9D + 1.6W 8. 0.9D + E

For Typical Building Analysis



RC design in BNBC 2017 is similar to ACI318-2008



EXAMPLE: ETABS PROBLEM



DESIGN SPECIFICATION Dhaka City: Seismic Zone 2, Z=0.2 (Table 2.5.2, 2.5.3) Site Class: SC (Table 2.5.1) Occupancy Category: II (Table1.2.1) Importance Factor: 1 (Table2.5.5) Seismic Design Category: C (Table 2.5.6) Frame Type: Intermediate Moment Frame, R=5 (Section 8.3.3.1)



DESIGN SPECIFICATION Live load: 40psf residential, multi family (Table 2.3.1) Floor finish: 30psf (estimated) Partition wall: 80psf (assumed, estimated) Live load on stair: 100 psf(Table 2.3.1) Number of floors: GF+8 fc’= 3ksi, fy=60ksi



H WX Wxhx^k V

96 582.15 164405 0.209262 52.54357

86 582.15 143499 0.182652 45.86204

76 582.16 123163 0.156767 39.3627

66 582.15 103447.3 0.131672 33.06158

56 582.15 84429.57 0.107466 26.98355

46 582.15 66201.63 0.084264 21.15793

36 582.15 48893.07 0.062233 15.62615

26 582.16 32697.56 0.041619 10.45009

16 582.15 17939.44 0.022834 5.733415

6 105.49 966.7574 0.001231 0.308974

Sum 5344.86 785642.3 1 251.09

0

10

20

30

40

50

60

70

80

90

100

0 20 40 60



Soil Type Zone-1 Zone-2 Zone-3 Zone-4

SA 0.0121 0.0201 0.0281 0.0362

SB 0.0145 0.0241 0.0338 0.0434

SC 0.0139 0.0231 0.0324 0.0416

SD 0.0163 0.0271 0.0380 0.0488

SE 0.0169 0.0281 0.0394 0.0507

Lower Cut-off: Minimum percentage of load,

V= value x W

Values are 0.06035 times Appendix-C Table- 6.C.4

Note: lower cutoff will NOT work if ASCE 7-02 is

selected in ETABS



Upper Cut-off: Maximum percentage of load

V= value x W / R Soil Type Zone-1 Zone-2 Zone-3 Zone-4

SA 0.2000 0.3333 0.4667 0.6000

SB 0.2400 0.4000 0.5600 0.7200

SC 0.2300 0.3833 0.5367 0.6900

SD 0.2700 0.4500 0.6300 0.8100

SE 0.2800 0.4667 0.6533 0.8400

Note: Upper cutoff will WORK if ASCE 7-02 is

selected in ETABS

Values are same as Appendix-C Table - 6.C.4



Stiffness in Strength Analysis • Use reduced moment of inertia of beam, column and

wall • Elastic Second order analysis • The reduction represent ultimate state and used for

design

• For lateral deflection under service load multiply these stiffness values by 1.4



Wind drift and sway



SWAY CHECK FOR WIND • For occupant comfort • Use reduced moment of inertia of beam, column and wall

• For lateral deflection under service load multiply these stiffness values by 1.4



Storey drift for earthquake



BNBC 2017 SEISMIC PROVISIONS Vertical Earthquake Loading, Ev (sec. 2.5.13.2 ) The maximum vertical ground acceleration shall be taken as 50 percent of the expected horizontal peak ground acceleration (PGA). The vertical seismic load effect Ev may be determined as: 𝐸v = 0.5(𝑎ℎ)𝐷 Eqn. (6.2.56) Where, 𝑎ℎ = expected horizontal peak ground acceleration (in g) for design = (2/3)𝑍𝑆 if Z corresponds to MCE (2500 yr return period) = ZS if Z corresponds to DBE (500 yr return period) 𝐷 = effect of dead load, S = site dependent soil factor (see Table 6.2.16).




Load Effect Combinations for LRFD/USD (Sec. 2.7.3): 1. 1.4(D+F) 2. 1.2(D+F+T) + 1.6(L+H) + 0.5(Lr or R) 3. 1.2D + 1.6(Lr or R) + (L or 0.8W) 4. 1.2D + 1.6W + L + 0.5(Lr or R) 5. 1.2D + E + L 6. 0.9D + 1.6W + 1.6H 7. 0.9D + E + 1.6H

D = Dead load E = Seismic Load F = Fluid pr. H = Soil pr. L = Live load Lr = Roof live load R = Rain load T = Thermal load W = Wind load

Definition of Seismic Load, E

Total load effects of earthquake that include both horizontal and vertical, or related internal moments and forces.




1. 1.4D 2. 1.2D + 1.6L 3. 1.2D + (L or 0.8W) 4. 1.2D + 1.6W + L 5. 1.2D + E + L 6. 0.9D + 1.6W 7. 0.9D + E

D = Dead load E = Seismic Load F = Fluid pr. H = Soil pr. L = Live load

Lr = Roof live load R = Rain load T = Thermal load W = Wind load


For Typical Building Analysis




1. 1.4D 2. 1.2D + 1.6L 3. 1.2D + L

4. 1.2D + 0.8Wx

5. 1.2D - 0.8Wx

6. 1.2D + 0.8Wy

7. 1.2D - 0.8Wy

8. 1.2D + L + 1.6Wx

9. 1.2D + L - 1.6Wx

10. 1.2D + L + 1.6Wy

11. 1.2D + L - 1.6Wy

12. 1.2D + L + Ex + D 13. 1.2D + L - Ex + D 14. 1.2D + L + Ey + D 15. 1.2D + L – Ey + D

16. 0.9D + 1.6Wx 17. 0.9D - 1.6Wx 18. 0.9D + 1.6Wy 19. 0.9D - 1.6Wy

4

5

7

6

20. 0.9D + Ex - D 21. 0.9D - Ex - D 22. 0.9D + Ey - D 23. 0.9D - Ey - D

8

Expanded Combinations for 3D Analysis of Typical Buildings (SDC B) 𝐸v = 0.5(𝑎ℎ)𝐷 Eqn. (6.2.56), Let Ev = D where = 0.5(𝑎ℎ)





1. 1.4D 2. 1.2D + 1.6L 3. 1.2D + L

4. 1.2D + 0.8Wx

5. 1.2D - 0.8Wx

6. 1.2D + 0.8Wy

7. 1.2D - 0.8Wy

8. 1.2D + L + 1.6Wx

9. 1.2D + L - 1.6Wx

10. 1.2D + L + 1.6Wy

11. 1.2D + L - 1.6Wy

12. 1.2D + L + Ex + 0.3Ey

13. 1.2D + L + Ex - 0.3Ey

14. 1.2D + L - Ex + 0.3Ey

15. 1.2D + L - Ex - 0.3Ey

16. 1.2D + L + Ey + 0.3Ex

17. 1.2D + L + Ey - 0.3Ex

18. 1.2D + L - Ey + 0.3Ex

19. 1.2D + L - Ey - 0.3Ex

20. 0.9D + 1.6Wx 21. 0.9D - 1.6Wx 22. 0.9D + 1.6Wy 23. 0.9D - 1.6Wy

24. 0.9D + Ex + 0.3Ey

25. 0.9D + Ex - 0.3Ey

26. 0.9D - Ex + 0.3Ey

27. 0.9D - Ex - 0.3Ey

28. 0.9D + Ey + 0.3Ex

29. 0.9D + Ey - 0.3Ex

30. 0.9D - Ey + 0.3Ex

31. 0.9D - Ey - 0.3Ex

4

5 7

6 8

Expanded Combinations for 3D Analysis of Typical Buildings

(SDC C and D) Vertical seismic effect not yet shown





12. 1.2D + L + Ex + 0.3Ey + D 13. 1.2D + L + Ex - 0.3Ey + D 14. 1.2D + L - Ex + 0.3Ey + D 15. 1.2D + L - Ex - 0.3Ey + D 16. 1.2D + L + Ey + 0.3Ex + D 17. 1.2D + L + Ey - 0.3Ex + D 18. 1.2D + L - Ey + 0.3Ex + D 19. 1.2D + L - Ey - 0.3Ex + D

24. 0.9D + Ex + 0.3Ey - D 25. 0.9D + Ex - 0.3Ey - D 26. 0.9D - Ex + 0.3Ey - D 27. 0.9D - Ex - 0.3Ey - D 28. 0.9D + Ey + 0.3Ex - D 29. 0.9D + Ey - 0.3Ex - D 30. 0.9D - Ey + 0.3Ex - D 31. 0.9D - Ey - 0.3Ex - D

6 8

Expanded Combinations for 3D Analysis of Typical Buildings Vertical seismic effect considered (SDC C and D) 𝐸v = 0.5(𝑎ℎ)𝐷 Eqn. (6.2.56) Let Ev = D where = 0.5(𝑎ℎ) Combination group 8 and 9 can be re-written...



Seismic detailing is given in section 8.3 of part 6



Buildings are to be designed in accordance with Seismic Design Category (SDC).

Seismic Design Category vs RC design requirement. SDC Severity Design requirement B Low Ordinary reinforcement design provisions considering code specified

seismic and other loads. Use of reinforcement up to Grade 80 is possible for main reinforcement.

C Medium Reinforcement design provisions considering code specified seismic and other loads.

Use of reinforcement up to Grade 80 is possible for main reinforcement. Specific detailing of reinforcement at joints are required (no special

calculation needed). D High Special seismic design provisions considering code specified seismic and

other loads for reinforcement design. Maximum Grade 60 steel is allowed for main reinforcement. Rebar must

have fu/fy>1.25 as well as meet specified ductility requirement. Reinforcement design and detailing at joints are required based on special

design calculations specific for joints. This is essential.

BNBC 2017 SEISMIC PROVISIONS



Thank you

Ref: 1. Manual for Seismic Design of Reinforced Concrete Building, PWD 2. Seismic Design of Reinforced Concrete Special Moment Frames-NEHRP 3. 2009 NEHRP Recommended Seismic Provisions- Training and Instruction Manual 4. EQTIPS-www.nicee.org 5. Seismic Detailing of Concrete Buildings- David Fanella 6. Bangladesh National Building Code 2015, HBRI

BNBC 2017: Evaluation of Seismic Load using Equivalent ......Earthquake force •Inertia force...

Documents

Transcript of BNBC 2017: Evaluation of Seismic Load using Equivalent ......Earthquake force •Inertia force...