UNDERSTANDING RESPONSE SPECTRUM & PROVISIONS OF BNBC-2014

UNDERSTANDING RESPONSE SPECTRUM&PROVISIONS OF BNBC-2014

OUTCOME AT THE END OF THIS TRAINING/WORKSHOP/DISCUSSION YOU WILL UNDERSTAND:

WHAT IS AN EARTHQUAKE RESPONSE SPECTRUM RESPONSE SPECTRUM AS PER BNBC/14, AND HAVE A DISCUSSION GROUP TO SHARE YOUR IDEAS

AND CONFUSIONS

CONTENT PART – I UNDERSTANDING EARTHQUAKE RESPONSE SPECTRUM

PART – II RESPONSE SPECTRUM PROVISION OF BNBC/2014

PART – III : GROUND MOTION SIMULATION

RECAP - STRUCTURAL DYNAMICS

EQUATION OF MOTION

Summing forces along the x-axis is p(t) - fS – fD –fI = 0

EQUATION OF MOTION (Earthquake Excitation)

Single-Degree-of-Freedom System

2

secnn

T

n

rads/sec

k

m

n2

cps (Hz)nf

NATURAL PERIOD OF VIBRATION

DAMPED FREE VIBRATION

EFFECT OF DAMPING ON FREE VIBRATION

DAMPED FREE VIBRATION

EFFECT OF DAMPING ON THE NATURAL VIBRATION FREQUENCY

PART - IUNDERSTANDING RESPONSE SPECTRUM

ORIGIN OF THE RESPONSE SPECTRUM METHOD • Response Spectrum Method began in 1932, in the doctoral dissertation of M.A. Biot (1905–

1985)

• The RSM remained in the academic sphere of research for many years and did not gain widespread engineering acceptance until the early 1970s.

• First, the computation of the response of structures to earthquake ground motion led to “certain rather formidable difficulties” (Housner 1947), and,

• second, there were only a few well-recorded accelerograms that could be used for that purpose.

• Then, in 1971, with the occurrence of the San Fernando, California, earthquake, the modern era of RSM was launched. This earthquake was recorded by 241 accelerographs, and by combining these data with all previous strong-motion records it became possible to perform the first comprehensive empirical scaling analyses of response spectral amplitudes (Lee 2002).

TIME HISTORY DATA THE MOST DIRECT DESCRIPTION OF AN

EARTHQUAKE MOTION IN TIME DOMAIN IS PROVIDED BY ACCELEROGRAMS THAT ARE RECORDED BY INSTRUMENTS CALLED STRONG MOTION ACCELEROGRAPHS.

THE ACCELEROGRAPH RECORDS THREE ORTHOGONAL COMPONENTS OF GROUND ACCELERATION AT A CERTAIN LOCATION.

THE PEAK GROUND ACCELERATION, DURATION, AND FREQUENCY CONTENT OF EARTHQUAKE CAN BE OBTAINED FROM AN ACCELEROGRAMS. AN ACCELEROGRAM CAN BE INTEGRATED TO OBTAIN THE TIME VARIATIONS OF THE GROUND VELOCITY AND GROUND DISPLACEMENT.

TIME HISTORY DATATime, sec Acceleration, g

0.00 0.006300.02 0.003640.04 0.000990.06 0.004280.08 0.007580.10 0.010870.12 0.006820.14 0.002770.16 -0.001280.18 0.003680.20 0.008640.22 0.013600.24 0.007270.26 0.000940.28 0.004200.30 0.00221

http://peer.berkeley.edu/smcat/

http://db.cosmos-eq.org/scripts/default.plx

El Centro ground motion (N-S Component)May 18, 1940

TIME HISTORY DATA

FOR EARTHQUAKE EXCITATION – i. ANALYTICAL SOLUTION IS NOT POSSIBLE; ii. NUMERICAL METHODS ARE EMPLOYED TO FIND OTHER QUANTITIES LIKE a. VELOCITY; b. DISPLACEMENT ETC. DIFFERENT NUMERICAL METHODS ARE:

CENTRAL DIFFERENCE METHOD

AVERAGE ACCELERATION METHOD

NEWMARK’S METHOD ETC.

TIME HISTORY DATA ANALYSIS

RESPONSE SPECTRUM

DEFORMATION RESPONSE SPECTRUM

VELOCITY RESPONSE SPECTRUM

Plot of V vs. TN

ACCELERATION RESPONSE SPECTRUMPlot of A vs. TN

COMBINED D-V-A SPECTRUM

A V D

nn

Tn A V 2

D2

Tn

RESPONSE SPECTRUM CHARACTERISTICS

Response spectrum ( = 0,2,5, and 10%) and peak values of ground acceleration, ground velocity, and ground displacement for El Centro ground motion.

RESPONSE SPECTRUM CHARACTERISTICS

Response spectrum for El Centro ground motion plotted with normalized scale A/ϋgo , V/ůgo , and D/ugo ; = 0, 2 , 5 and 10%.

RESPONSE SPECTRUM CHARACTERISTICS

Response spectrum for El Centro ground motion shown by a solid line together with an idealized version shown by a dashed line; = 5%

ACCELERATION RESPONSE SPECTRUMEL CENTRO EARTHQUAKE 5% DAMPING

IT IS NOT PRACTICALLY

POSSIBLE TO CALCULATE

EXACT STRUCTURAL PERIOD

.

SPECTRAL ACCELERATION

FOR SHORT PERIOD IS VERY

IRREGULAR.

FOR PRACTICAL USE IT HAS

TO MADE ‘SMOOTH’

DESIGN RESPONSE SPECTRUM

PART - IIRESPONSE SPECTRUM PROVISIONS OF BNBC/14[PART 6, CHAPTER 2 – ARTICLE 2.5.6]

DEVELOPMENT HISTORYEARTHQUAKE ZONING MAP OF BANGLADESH

EARTHQUAKE ZONING MAP 1972Adopted from East Pakistan MapDEVELOPED BY METROLOGICAL DEPARTMENT OF BANGLADESH IN 1972THE COUNTRY WAS DIVIDED IN FOUR ZONES

•ZONE 1 : Seismic factor 0.2g ~ 0.1g

•ZONE 2 : Seismic factor 0.1g ~ 0.067g

•ZONE 3 : Seismic factor 0.067g ~ 0.05g

•ZONE 4 : Seismic factor < 0.05g

ZONING MAP 1978PREPARED BY GEOLOGICAL SURVEY OF BANGLADESH THE COUNTRY WAS DIVIDED IN THREE ZONES

•ZONE 1 : Seismic coefficient 0.08g

•ZONE 2 : Seismic coefficient 0.05g

•ZONE 3 : Seismic coefficient 0.04g

BNBC – 1993Housing and Building Research Institute (HBRI)

FIRST SCIENTIFIC APPROACH ADOPTED IN PREPARING SEISMIC ZONING MAPTHE COUNTRY WAS DIVIDED IN THREE ZONES

•ZONE 1 : Seismic coefficient 0.2g

•ZONE 2 : Seismic coefficient 0.15g

•ZONE 3 : Seismic coefficient 0.075g

PROBABILITY OF EXCEEDANCE 20% IN 50 YEARS.

BNBC – 2014 being updatedHousing and Building Research Institute (HBRI)

SEISMIC ZONING MAP PREPARED FOR 2475 YEARS HAZARD LEVEL (PROBABILITY OF EXCEDENCE 2% IN 50 YEARS)THE COUNTRY IS DIVIDED IN FOUR ZONES

•ZONE 1 : Seismic coefficient 0.36g

•ZONE 2 : Seismic coefficient 0.28g

•ZONE 3 : Seismic coefficient 0.20g

•ZONE 4 : Seismic coefficient 0.12g

EARTHQUAKES1973-2013

http://earthquake.usgs.gov/

EARTHQUAKES1973-2013

Historical earthquakes of 1973~2013 (source http://earthquake.usgs.gov/earthquakes/search/)

superimposed on proposed on BNBC seismic zoning map

BNBC/14 EARTHQUAKE DEFINITION 2% Probability of Exceedence in 50 Years (2,475 Year Return

Period) – MAXIMUM CONSIDERED EARTHQUAKE (MCE)

Design Ground Motion 2/3rd of MCE

Design Ground Motions are Set at 2/3rd of MCE Ground Motion Levels, With The Reasoning That Any Structure Designed With The Provision Shall Have A Minimum Margin Against Collapse of 1.5

PEAK GROUND ACCELERATION (PGA)AN INFINITELY RIGID STRUCTURE

– HAS ZERO NATURAL PERIOD (T=0)

– DOES NOT DEFORM:

• NO RELATIVE MOTION BETWEEN ITS MASS AND ITS BASE

• MASS HAS SAME ACCELERATION AS OF THE GROUND

HENCE, PEAK GROUND ACCELERATION REPRESENTS STRUCTURAL RESPONSE OF A STRUCTURE OF ZERO PERIOD

PARAMETERS DEFINING ELASTIC RESPONSE SPECTRUM

ACCELERATION RESPONSE SPECTRUM

TB = Lower limit of the period of the

constant spectral acceleration branch as a function of site class (Table 2.5.4 )

TC = Upper limit of the period of the

constant spectral acceleration branch as a function of site class (Table 2.5.4 )

TD = Lower limit of the period of the constant

spectral displacement branch as a function of site class (Table 2.5.4 ).

PARAMETERS DEFINING ELASTIC RESPONSE SPECTRUM

Table 2.5.4: Site dependent soil factor and other parameters defining elastic response spectrum

Soil type S TB(s) TC(s) TD(s)

SA 1.00 0.15 0.4 2.0

SB 1.20 0.15 0.5 2.0

SC 1.15 0.20 0.6 2.0

SD 1.35 0.20 0.8 2.0

SE 1.40 0.15 0.5 2.0

MAY BE THIS VALUE IS WRONG !!!!!!!!!!!!

ELASTIC RESPONSE COEFFICIENT, CS

• SOIL TYPE = SA (ROCK)• DAMPING = 5%• ZONE = DHAKA (0.2g)

DESIGN RESPONSE SPECTRUM

STRUCTURE IMPORTANCE FACTOR, AS DEFINED IN SECTION 2.5.7.1

OCCUPANCY CATEGORY

IMPORTANCE FACTOR, I

I OR II 1.0III 1.25IV 1.5

Table 2.5.5 Importance Factors for Buildings and Structures for Earthquake design

RESPONSE REDUCTION FACTOR

AN EXAMPLE

Table 2.5.4: Site dependent soil factor and other parameters defining elastic response spectrum

Soil type S TB(s) TC(s) TD(s)

SA 1.00 0.15 0.4 2.0SB 1.20 0.15 0.5 2.0SC 1.15 0.20 0.6 2.0SD 1.35 0.20 0.8 2.0SE 1.40 0.15 0.5 2.0

AN EXAMPLE - Continued• ELASTIC SEISMIC RESPONSE COEFFICIENT FOR “0” PERIOD (PGA FOR THE SITE)

• ELASTIC SEISMIC RESPONSE FOR SHORT PERIOD

• ELASTIC SEISMIC RESPONSE COEFFICIENT FOR CONSTANT ACCELERATION ZONE

• ELASTIC SEISMIC RESPONSE COEFFICIENT FOR VELOCITY SENSITIVE ZONE

• ELASTIC SEISMIC RESPONSE COEFFICIENT FOR DISPLACEMENT SENSITIVE ZONE

AN EXAMPLE - ContinuedT CS

0.000 1.1500.100 2.0130.150 2.4440.200 2.8750.300 2.8750.400 2.8750.500 2.8750.600 2.8750.700 2.4640.800 2.1560.900 1.9171.000 1.7251.100 1.5681.200 1.4381.300 1.3271.400 1.2321.500 1.1501.600 1.0781.700 1.0151.800 0.9581.900 0.9082.000 0.863

ELASTIC RESPONSE COEFFICIENT, CST B =

0.2

sec

T C = 0

.6 s

ec

T D =

2 s

ec

AN EXAMPLE - Continued

DESIGN RESPONSE SPECTRUM, Sa

0.000

0.050

0.100

0.150

0.200

0.250

0.300

0.350

0.400

0.450

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0

SPEC

TRAL

ACC

ELER

ATIO

N, S

a

PERIOD T, SEC

T Original (Rock site)

Soil Amplicatio

n

Design, Sa

(Reduced by R)

0.000 0.133 0.153 0.0310.100 0.267 0.268 0.0540.150 0.333 0.326 0.0650.200 0.333 0.383 0.0770.300 0.333 0.383 0.0770.400 0.333 0.383 0.0770.500 0.267 0.383 0.0770.600 0.222 0.383 0.0770.700 0.190 0.329 0.0660.800 0.167 0.288 0.0580.900 0.148 0.256 0.0511.000 0.133 0.230 0.0461.100 0.121 0.209 0.0421.200 0.111 0.192 0.0381.300 0.103 0.177 0.0351.400 0.095 0.164 0.0331.500 0.089 0.153 0.031

Original on Rock

Amplified for Soil Type

Reduced by Response Reduction Factor, R

PART - IIIGROUND MOTION SIMULATION

SEISMIC INSTRUMENTATION ERA, BANGLADESH ONE ANALOGUE SEISMOGRAPH WAS INSTALLED IN 1954 IN BALU-BAGAN CHITTAGONG. INSTRUMENTATION ERA STARTED BY INSTRUMENTATION OF JAMUNA BRIDGE. JAMUNA MULTIPURPOSE BRIDGE AUTHORITY COMPLETED THE INSTRUMENTATION WORK IN 2003. SIXTY MORE ACCELEROGRAPHS WERE OBTAINED FROM SAFER CITIES PROJECT OF COSMOS—WSSI TO DEPLOY IN THE FREE-FIELD AT DIFFERENT LOCATION OF BANGLADESH. THIRTY FOUR (34) STRONG MOTION ACCELEROGRAPHS (SMA) ARE INSTALLED IN DIFFERENT LOCATIONS OF PWD OFFICE AND BUET CAMPUS IN 2006.

NO TIME HISTORY DATA AVAILABLE

BANGLADESH STRONG MOTION DATAat Station ID: ALTUS S/N 2928 Channel 1: EW 07/05/2008 16:55:52 (GMT) – AT NATORE

0 10 20 30 40 50

Time [sec]

-0.006

-0.004

-0.002

0.000

0.002

0.004

0.006

Acc

ele

ratio

n [g

]

Max : -0.00380 (19.07 sec)

0 1 2 3 4

Period [sec]

0.000

0.005

0.010

0.015

0.020

Acc

eler

atio

n [g

]

GROUND MOTION SIMULATIONSPECTRUM COMPATIBLE TIME HISTORY DATA GENERATION• STANDARD PROCEDURES AVAILABLE

Linear scaling Frequency content modification Frequency domain techniques Time domain techniques

• COMPUTER ROUTINE NEEDED TO CALCULATE THE MATCHING. COMMONLY AVAILABLE SOFTWARE ARE RspMatch SeismoMatch SIMQKE SYNTH EZ-FRISK

EL-CENTRO EARTHQUAKE STRONG MOTION DATA HAS BEEN SCALED DOWN BY A FACTOR OF 0.41716 TO MAKE MAXIMUM ACCELERATION OF 0.133g

GROUND MOTION SIMULATION1. LINEAR SCALING OF A KNOWN STRONG MOTION DATA

RESPONSE SPECTRUM OF THE SCALED STRONG MOTION DATA

COMPARISON OF SCALED DATA – BNBC/14 SPECTRUM

STRONG MOTION SIMULATION2. SPECTRA MATCHING IN FREQUENCY DOMAIN TECHNIQUES

EL-CENTRO SPECTRUM PLANNED TO MATCH WITH THE BNBC SPECTRUM

SPECTRUM MATCHED

COMPARES OF THE SPECTRUMS

MATCHED TIME HISTORY GRAPH

THANKS&

WELCOME TO OPEN DISCUSSION