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Title: Energy Based Approach for Post Seismic Structural Health Monitoring of A Four Span Bridge

Authors: Seyed A. Bassam (Contact person, Presenter)Graduate student

Department of Civil and Materials Enineerin

!niversity of "llinois at C#icao

$%& '. aylor Street

&*+ Enineerin esearc# -acility, MC &%

C#icao, "/ 0P#one1 (23&)**42+$

-a51 (23&)**4&%&

E4Mail1 s6assa&7uic.edu

Amir#ossein "ranmanes#

Graduate student

Department of Civil and Materials Enineerin

!niversity of "llinois at C#icao $%& '. aylor Street

&*+ Enineerin esearc# -acility, MC &%C#icao, "/ 0

P#one1 (23&)**42+$

-a51 (23&)**4&%&

E4Mail1airanm&7uic.edu

-ar#ad Ansari

Professor and 8ead

Department of Civil and Materials Enineerin!niversity of "llinois at C#icao

$%& '. aylor Street

&*+ Enineerin esearc# -acility, MC &%C#icao, "/ 0

P#one1 (23&)**4&%20

-a51 (23&)**4&%&

E4Mail1 fansari7uic.edu

mailto:airanm2@uic.edumailto:airanm2@uic.edu

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Energy Based Approach for Post Seismic Structural

Health Monitoring of a Four Span Bridge

Seyed A. Bassam, Amir#ossein "ranmanes# and -ar#ad Ansari

ABSTRACT

#is study reports on t#e development of a structural #ealt# monitorin met#odoloy fordetection of various staes of damae in 6rides follo9in eart#:ua;es. #e results are ac:uired

from s#a;in ta6le tests of a %4span lare Scale Bride su6ones. An enery 6ased damae evaluation tec#ni:ue 9as developed for t#e evaluation of t#e

6ride interity at various amplitudes of seismic motions to aue t#e damae assessmentcapa6ility of t#e met#od. -ollo9in eac# seismic motion, t#e structural interity of t#e 6ride

9as investiated 6y t#e enery 6ased met#od. esults from t#is study indicated t#at it is

possi6le to detect damae at early staes of development t#rou# a com6ination of #i#resolution sensors and advanced structural #ealt# monitorin met#odoloies.

?????????????

Seyed A. Bassam, P#D, !niversity of "llinois at C#icao, $%& '. aylor Street, &*+ Enineerin esearc# -acility,

M@C &%, C#icao, "/ 0

Amir#ossein "ranmanes#, P#D Candidate, !niversity of "llinois at C#icao, $%& '. aylor Street, &*+ Enineerin

esearc# -acility, M@C &%, C#icao, "/ 0-ar#ad Ansari, Professor and 8ead, !niversity of "llinois at C#icao, $%& '. aylor Street, &*+ Enineerin esearc#

-acility, M@C &%, C#icao, "/ 0

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!TR"#$CT"!

Brides in seismic >ones face various types of round motions and s#a;in intensities.Seismic desin codes #ave one t#rou# a num6er of transformations in order to assure safety 6y

preventin collapse and maintainin structural performance (Caltrans &%). "n t#is respect, t#e

piers are allo9ed to o t#rou# inelastic deformations in order to dissipate enery. Servicea6ility is#o9ever remains to 6e an issue since t#is approac# renders t#e columns vulnera6le to lare lateral

displacements causin damae in t#e plastic #ine >ones at t#e 6ase and t#e pier cap connections

(Elnas#ai et al. 3*$*). "n order to properly evaluate t#e condition of t#e 6rides in t#e aftermat# ofeart#:ua;es and to address 6ot# safety as 9ell as servicea6ility concerns, it is essential to develop

deterministic met#odoloies t#at 9ould o 6eyond visual inspections (Buc;le 3**%). ne met#od

for :uantification of t#e state of damae in reinforced concrete 6rides is t#e use of a damae inde5

(D"). "n eneral, damae indices #ave 6een 6ased on a set of structural response parameters suc# asdisplacements, forces and #ysteretic eneries.

raditional damae inde5 models used t#e ma5imum displacement of t#e columns to

estimate t#e damae (Po9ell, 3*$$). 8o9ever, damae accumulated durin t#e cyclic loadin

reduces t#e ultimate ductility ratio of t#e structure and t#erefore, t#e damae estimated 6y t#edisplacement 6ased met#ods underestimate t#e level of damae. Panaiota;is and -ardis (&3)

t#rou# la6oratory e5periments o6served t#at t#e deformation at failure of reinforced concreteelements su6

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n normali>ed a5ial stress,

w confinement ratio

Par; and An damae inde5 is e5tensively used in performance 6ased seismic desin (-aero. Moreover, it 9ould yield a damae inde5 of reater t#an 3. for t#e

monotonic loadin at ultimate, u (Bo>ornia and Bertero &3). o overcome t#e second

dra96ac;, C#ai et al. (3**+) incorporated only portion of dissipated enery a6ove t#at of monotonic

loadin as contri6utin to damae, t#at is, modifyin E:uation (3) to t#e form

( )m h hmCH

u y u

E EDI

Q

= + (2)

9#ere

hmE = Dissipated enery 6y t#e structure for a monotonic loadin

"n t#is case, t#e model converes to one at failure for monotonic loadin. can 6e

calculated as

.

(3 )

m

m m

=

+ (%)

9#ere

@m u y = is t#e monotonic displacement ductility.

8o9ever, damae inde5 6y E:. (2) is still larer t#an >ero 6efore concrete crac;in. o

alleviate t#is pro6lem, a modification can 6e made to E:. (2) as1

m cr h

u cr y u

EDI

Q

= +

(+)

#e proposed met#od results in damae inde5 of >ero 6efore concrete crac;in, andradually increases 9it# t#e proression of t#e damae until unity at collapse. Scope of t#e researc#

descri6ed in t#is paper includes investiation of damae in a %Hspan 6ride under proressively

increasin round motions 6ased on t#e s#a;e ta6le tests and recorded displacement time #istory oft#e =ort#ride eart#:ua;e. Development and application of surface ad#ered fi6er optic

displacement sensors for measurin t#e 6ent deformations, and application of proposed damae

inde5 met#odoloy to assess t#e e5tent of damae are descri6ed in t#e su6se:uent sections of t#ispaper.

E%PERME!TA& PR"'RAM

#e e5perimental proram included a :uarter scale %4span 6ride 9#ic# 9as desined and

constructed per current provisions of t#e =ational Cooperative 8i#9ay esearc# Proram

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(AC@MCEE &3) 6y t#e !niversity of =evada in eno researc#ers (=elson et al. &0). #e

6ride 9as su6

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-iure &. Modified =ort#ride round accelerations used as t#e reference e5citation

Sensors And Instrumentation

A specially desined -i6er Bra Gratin (-BG) surface ad#ered displacement sensor 9asfa6ricated for t#e 6ride test. #e strain transduction mec#anism in -BG sensors is 6ased on t#e

s#ift in t#e central 9avelent# of t#e Bra ratins in t#e optical fi6er. By careful selection of t#e

Bra 9avelent#, and considerin t#e ma5imum levels of e5pected strains, it is possi6le tointerroate many -BGs on a sinle fi6er. #e -BG interroation system used in t#e present study

9as specially desined to accommodate many -BGs 6y 9idenin t#e spectral rane to * nm.

"nterroation unit scanned t#e dynamic strains at t#e rate of &+ 8>.#e -BG 9as attac#ed to a special stainless steel arc# 9it# a aue lent# of 3 mm, and

9as protected 9it# plastic ru66er (-iure 2). By usin t#is approac#, t#e dynamic rane of t#e

sensor 9as mec#anically increased ( to I+ mm). #e sensor sensitivity 9as o6tained as +picometer@millimeter, 9it# t#e operatin temperature of 4%J$ oC. !p to si5 sensors 9ere serially

multiple5ed on a lead line.

#e sensors 9ere ad#ered to t#e column surface and 9ere a6le to monitor 6ot# tensile and

compressive displacements. #e stainless steel arc# ensured t#e sensor capa6ility to monitor crac;openin displacements as lare as + mm 9ide. 8avin t9o connectors at t#e ends of t#e

displacement sensors made it possi6le to multiple5 several sensors in series on a sinle lead line.

Sensor locations are sc#ematically s#o9n in -iure %.

-iure 2. -i6er ptic displacement sensor ad#ered to t#e surface of t#e 6ride column

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-iure %. Deformation sensor arranement and num6erin

E%PERME!TA& RES$&TS

A procedure developed 6y Bassam (&$) 9as used to calculate t#e 6ent displacementsfrom t#e curvatures measured 6y t#e -i6er ptic sensors. #e sensors 9ere a6le to ac:uire #i#

resolution sinals 6ot# at lo9 and #i# amplitudes of loadin. ypical time deformation responseof t#e columns is s#o9n in -iure + correspondin to t#e last event (severe loadin) causin

crac; openin displacements as lare as 2mm 9#ic# is rat#er lare.

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0 5 10 15 20 25 30 35

-0.1

-0.05

0

0.05

0.1

0.15

time (s)

displacement(in)

-iure +. ypical time #istory of t#e sensor displacements, /ast event, Sensor =o. +

Pus#over analysis 9as performed to determine t#e strent# of t#e desined 6ride for t#evarious staes of damae, i.e. at first crac;in, yieldin of t#e re6ars, and at t#e ultimate

deformation capacity of t#e columns. #is analysis 9as necessary to determine t#e lateral

displacement response parameters cr , y , u , and yQ for t#e computation of t#e damae inde5,

i.e. E:. (+) in t#is study.

-ailure 9as assumed to occur 9#en t#e confined concrete at t#e e5treme compression fi6erof t#e core concrete reac#ed t#e ultimate concrete compressive strain. #e pus#over analysis 9as

performed 6ot# for lonitudinal as 9ell as t#e transverse directions. Since t#e cap 6eams 9ere riid,

t#e lonitudinal and transverse response for t#e individual 6ents yielded similar results. #e loaddisplacement response of t#e 6ents 6ased on t#e pus#over analysis is s#o9n in -iure +, and t#e

specific lateral displacement and load parameters are s#o9n in a6le ".

AB/E ". PAAMEES BA"=ED -M 8E P!S8KE A=A/LS"S

element 6ent 3 6ent & 6ent 2

cr (mm) .* $. 0.33

y (mm) &3.$ 2&.%3 &0

u (mm) 32$.+ 3*+.$2 3.&%

yQ (=) 3*3.&0 3&.3 3+.0

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-iure +. -orce Displacement curves for t#e 6ents 6ased on pus# over analysis

o esta6lis# t#e load displacement response and for computation of dissipated enery it 9as

necessary to ac:uire t#e load #istory durin t#e s#a;in events. o ac#ieve t#is, t#e 6ent forces, bF

9ere estimated indirectly follo9in t#e procedure suested 6y o#nson et al. (&)1

( ).b a f s c sF F F M M a= + ()

'#ere

aF S#a;e ta6le actuator force

fF -riction of t#e s#a;e ta6le $.*KN

sM "nertial mass of t#e s#a;e ta6le

cM Mass of t#e footin, spacer 6loc;, safety frames and #alf of t#e 6ent columns

sa S#a;e ta6le acceleration

By usin t#is approac#, t#e force time #istory responses of t#e 6ents 9ere computed 6ased

on t#e s#a;in ta6le accelerations. nce t#e force time #istory for all t#e s#a;in events 9as

ac:uired, it 9as possi6le to esta6lis# t#e force4displacement #ysteresis plots to compute t#e

#ysteretic enery, as 9ell as t#e lo6al force4displacement envelopes for t#e ma5imum force andt#e correspondin displacements. ypical force4displacement #ysteresis plot are s#o9n in -iure .

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-60 -40 -20 0 20 40 60-250

-200

-150

-100

-50

0

50

100

150

200

250

Displacement (mm)

Force(KN)

-iure . ypical -orce4Displacement diaram of 6ent 2, lonitudinal (Event +)

#e lo6al force4displacement relations#ip provides a tool for measurin t#e performanceand a direct means for t#e evaluation of t#e proposed damae assessment met#od. #e lo6al

force4displacement responses of all t#e 6ride 6ents are s#o9n in -iure 0. #e tic; mar;s in

-iure 0 correspond to t#e ma5imum loads and correspondin displacements for eac# individual

event. #e o6served damae states, i.e. first crac;in, yieldin, spallin, etc. are also identified in-iure 0.

-iure 0. Glo6al -orce4Displacement envelope diarams

#e damae inde5 9as evaluated for t#e 6ride 6ents usin t#e proposed approac# 6y E:.

(+). esults are s#o9n in -iure $ in terms of t#e damae inde5 as a function of t#e 6ent

displacements.

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0

0.2

0.4

0.6

0.8

1

1.2

0 20 40 60 80 100 120 140 160

Maximum bent displacement (mm)

bent 1

bent 2

bent 3

-iure $. Damae inde5 variation 9it# event

Computation of t#e damae inde5 6ased on t#e proposed met#od in t#is study yield results

compara6le 9it# t#e o6served damae state in -iure 0. As can 6e seen, t#e damae inde5 increases

from >ero to t#e ma5imum one at t#e events 9#ere t#e 6ents 3 and 2 fail. Bent 2 did not reac# tofailure due to its #i#er lent#. Also, for t#e first & events 9ere t#e displacements 9ere 6elo9

crac;in, t#e damae inde5 remains >ero.

Based on t#e proposed met#od and t#e o6served damae levels for t#e 6ride investiated #ere, aenerali>ed damae scale can 6e suested as1

DI = =o damae

.3DI< Minor damae4li#t crac;in, development of yieldin

.3 .2DI< Moderate damae4locali>ed spallin.2 3DI< < Severe damae4 plastic #ines are formed

3DI = -ailure

#ese values are 6ased on t#e limited test data, and at t#is point, furt#er e5perimentation isnecessary to esta6lis# t#e re:uired data 6ase to support t#e scales mentioned a6ove.

C"!C&$S"!S

Scope of t#e investiation in t#is study included t#e application and evaluation of a

deterministic damae assessment met#od for post seismic evaluation of 6rides. #e e5perimentalportion of t#e researc# involved s#a;e ta6le tests of a four span 6ride usin t#e recorded round

motions of t#e 3**% =ort#ride eart#:ua;e. #e 6ride 9as su6

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#e -i6er ptic sensors used in t#is study could survive even follo9in t#e full scale

seismic loads e5perienced 6y t#e 6ride. Considerin t#eir #i# resolutions toet#er 9it# lare

dynamic rane, and #i# resistance in #ars# environmental conditions, usin t#ese types of sensorsis recommended for t#e #ealt# monitorin applications 9#ere #i# relia6ility of t#e measurin

sensor is re:uired.

AC(!")&E#'EME!T

#is pro