UNDERSTANDING RESPONSE SPECTRUM & PROVISIONS OF BNBC-2014

OUTCOME WHAT IS AN EARTHQUAKE RESPONSE SPECTRUM 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    

NATURAL PERIOD OF VIBRATION k n  rads/sec m  2 T sec n  n  n f cps (Hz) n 2

EFFECT OF DAMPING ON FREE VIBRATION DAMPED FREE VIBRATION     EFFECT OF DAMPING ON FREE VIBRATION

EFFECT OF DAMPING ON THE NATURAL VIBRATION FREQUENCY DAMPED FREE VIBRATION EFFECT OF DAMPING ON THE NATURAL VIBRATION FREQUENCY

PART - I UNDERSTANDING 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.

El Centro ground motion (N-S Component) TIME HISTORY DATA El Centro ground motion (N-S Component) May 18, 1940 Time, sec Acceleration, g 0.00 0.00630 0.02 0.00364 0.04 0.00099 0.06 0.00428 0.08 0.00758 0.10 0.01087 0.12 0.00682 0.14 0.00277 0.16 -0.00128 0.18 0.00368 0.20 0.00864 0.22 0.01360 0.24 0.00727 0.26 0.00094 0.28 0.00420 0.30 0.00221 http://peer.berkeley.edu/smcat/ http://db.cosmos-eq.org/scripts/default.plx

TIME HISTORY DATA CENTRAL DIFFERENCE METHOD 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 SPECTRUM Plot of A vs. TN  

COMBINED D-V-A SPECTRUM A  V   D n n Tn A  V  2 D 2 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 SPECTRUM EL 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 - II RESPONSE SPECTRUM PROVISIONS OF BNBC/14 [Part 6, chapter 2 – article 2.5.6]

DEVELOPMENT HISTORY EARTHQUAKE ZONING MAP OF BANGLADESH

EARTHQUAKE ZONING MAP 1972 Adopted from East Pakistan Map DEVELOPED BY METROLOGICAL DEPARTMENT OF BANGLADESH IN 1972 THE 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 1978 PREPARED 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 – 1993 Housing and Building Research Institute (HBRI) FIRST SCIENTIFIC APPROACH ADOPTED IN PREPARING SEISMIC ZONING MAP THE 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 updated Housing 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

EARTHQUAKES 1973-2013 http://earthquake.usgs.gov/

EARTHQUAKES 1973-2013 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 0.5 SC 1.15 0.20 0.6 SD 1.35 0.8 SE 1.40 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 Table 2.5.5 Importance Factors for Buildings and Structures for Earthquake design OCCUPANCY CATEGORY IMPORTANCE FACTOR, I I OR II 1.0 III 1.25 IV 1.5

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 2.0 SB 1.20 0.5 SC 1.15 0.20 0.6 SD 1.35 0.8 SE 1.40

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 - Continued ELASTIC RESPONSE COEFFICIENT, CS T CS 0.000 1.150 0.100 2.013 0.150 2.444 0.200 2.875 0.300 0.400 0.500 0.600 0.700 2.464 0.800 2.156 0.900 1.917 1.000 1.725 1.100 1.568 1.200 1.438 1.300 1.327 1.400 1.232 1.500 1.600 1.078 1.700 1.015 1.800 0.958 1.900 0.908 2.000 0.863 ELASTIC RESPONSE COEFFICIENT, CS TB = 0.2 sec TC = 0.6 sec TD = 2 sec

AN EXAMPLE - Continued    

DESIGN RESPONSE SPECTRUM, Sa Original (Rock site) Soil Amplication Design, Sa (Reduced by R) 0.000 0.133 0.153 0.031 0.100 0.267 0.268 0.054 0.150 0.333 0.326 0.065 0.200 0.383 0.077 0.300 0.400 0.500 0.600 0.222 0.700 0.190 0.329 0.066 0.800 0.167 0.288 0.058 0.900 0.148 0.256 0.051 1.000 0.230 0.046 1.100 0.121 0.209 0.042 1.200 0.111 0.192 0.038 1.300 0.103 0.177 0.035 1.400 0.095 0.164 0.033 1.500 0.089 Amplified for Soil Type Original on Rock Reduced by Response Reduction Factor, R

PART - III GROUND 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 DATA at Station ID: ALTUS S/N 2928 Channel 1: EW 07/05/2008 16:55:52 (GMT) – AT NATORE

GROUND MOTION SIMULATION SPECTRUM 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

GROUND MOTION SIMULATION 1. LINEAR SCALING OF A KNOWN STRONG MOTION DATA EL-CENTRO EARTHQUAKE STRONG MOTION DATA HAS BEEN SCALED DOWN BY A FACTOR OF 0.41716 TO MAKE MAXIMUM ACCELERATION OF 0.133g

RESPONSE SPECTRUM OF THE SCALED STRONG MOTION DATA

COMPARISON OF SCALED DATA – BNBC/14 SPECTRUM

STRONG MOTION SIMULATION 2. 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

WELCOME TO OPEN DISCUSSION THANKS & WELCOME TO OPEN DISCUSSION