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SWrucWural Analysis of HisWorical ConsWrucWions – Jerzy Jasieńko (ed) © 2012 DPNH ProcławH PolandH ISSN 0860-2395H ISBN 978-83-7125-216-7

pbfpjfC pTrav ANa obpTloATflN miAN lc AalBb Tltbo NlK PO fN Teb BAj CfTAabiI foAN jehrdad eejaziNI eamed jehdadOI Bina eejazi P

ABpToACT qhe world largest adobe citadel in Bam EArgJe BamF was damaged seriously in the OS aecember OMMP earthquakeK pince then many studies and researches have been done to restore this historical complexK Adobe tower koK PO was one the first structures in the citadelI for which a restoration plan was prepared during a projectK lne of the most important purposes of this project was studying the seismic behaviour of the tower to find out answers to the following questionsW

NF thy did this tower experience less damage compared to other towers? OF there are the weakest parts of the structure in future earthquakes? PF that is the best way to improve the seismic performance of the structure? 4F that is the best restoration plan for the tower?

qhis paper presents the study on seismic behaviour of tower koK PO and its restoration planK heywords: Adobe towerI peismic behaviourI oestorationI Bam citadel NK fNTolarCTflN

NKNK The Bam citadel qhe Bam citadel is the largest adobe complex in the world with an area of about OMMIMMM mO EcigK NFK ft has experienced many changes and restorations during past OMMM yearsK rse of weak construction materials to enlarge body shapesI nonJsymmetrical geometric formsI inappropriate restoration methods and successive extensions in some circumstances during different historical periodsI have caused a massive destruction to the largest adobe complex of the world in the OMMP earthquake of BamK xNI OzK

NKOK Tower NoK PO qower koK PO is made of adobe and located at the northJeastern corner of the citadel EcigK NFK ft is round in one side and NR m highK ft is respectively about NRKO m and NMKU m thick at the lower and upper partsI at the middle Ecig OFK A number of shear cracks are seen on its outermost layer EcigK PF and the wall on its eastern side is destructedI but the wall on its western side Ethe northern wallF has undergone no damage in the earthquake EcigK 4FK Archeological findings indicate that tower koK PO and its side walls have an internal main core of adobe with an average thickness of about NKR m xNI OzK

N Associate mrofessorI aepartment of Civil bngineeringI caculty of bngineeringI rniversity of fsfahanI fsfahanI

franI bJmailW mKhejazi]engKuiKacKir C mmKhejazi]yahooKcom O jKpcK in ptructural bngineeringI bmailW hKmehdad]ymailKcom P rndergraduate ptudentI aepartment of ArchitectureI hhorasgan EfsfahanF BranchI fslamic Azad rniversityI

fsfahanI franI bJmailW bbKhejazi]yahooKcom

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cigK N Aerial photo of the Bam citadel xNz

cigK O aimensions of adobe tower koK PO and side walls

cigK P aamaged part of tower koK PO on its outermost layer

cigK 4 qower koK PO and eastern and northern walls

NKPK The phases of restoration plan oestoration plan has been prepared based on relevant charters and recommendations such as the senice Charter xPz and fpCAopAe oecommendations x4zK Charters lay stress upon reaching the adequate safety with the minimum intervention and respecting the originality of the materialsI technologiesI typology and environment of the monument during the restoration workK aurable materialI compatible with original onesI must be usedK qoo much intervention is preventedK fntervention must be reversible as new materials and techniques may be developed in futureK qhe main objective of the restoration plan is to restore the adobe tower koK PO to its state before the earthquakeK cor this purposeI different parts of the existing structure will be restoredI consolidated and strengthenedI and some missing parts will be reconstructed to their original shapesK qhe phases of the restoration plan are presented in qable NK mhases V and NM are described in the followingK

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Table N qhe phases of the restoration plan of adobe tower koK PO

mhase Activity N eistorical survey of the building O Archaeological survey of the building P Architectural survey and documentation of the present state of the building 4 mathology of the building R bxperimental tests for determining mechanical properties of existing materials of the

building S ptudy of vernacular and local techniques for restoration T ptudy of available materials Esuch as soilI adobeI palmJtree fibresI etcKF for restoration

of standing parts and possible reconstruction of missing parts of the building U pelection of techniques and materials for restoration based on related international

charters and laboratory test data V ptructural analysis of original building to evaluate its seismic vulnerability NM aesign of structural strengthening and verification by structural analysis NN mreparation of drawings for restoration and strengthening of standing partsI and

reconstruction of missing parts NO bnd of investigation phase NP fmplementation of restorationI reconstruction and seismic strengthening plan

OK pTorCTroAi ANAivpfp

OKNK jethod of analysis qhreeJdimensional nonlinear time history dynamic finite element analysis has been usedK OKOK ioading According to the franian peismic Code xRz three scaled ground motion records appropriate to design hazard levels have been selectedK qhe design value of stresses and deformations has been taken as its maximum value over all ground motionsK qhese records are as followsW

NK BamJfran westJeast component of OS aecember OMMPI with a SKR oichter magnitude EcigK RF; OK kaghanJfran earthquake longitudinal component of S April NVTT with a S oichter magnitude and

a correction factor of MKU EcigK SF; PK bl CentroJrpA northJsouth component of NU jay NV4M with a TKN oichter magnitude and

a correction factor of NKR EcigK TFK 4K

cigK R dround motion record of Bam OMMP westJeast component xNz

cigK S pcaled ground motions record of kaghan NVTT longitudinal component with a correction factor

of MKU xNz

cigK T pcaled bl Centro NV4M northJsouth component with a correction factor of NKR xNz

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OKPK jaterial properties jaterial properties of adobe shown in qable O are based on a comprehensive study and laboratory tests on adobe bricks in the citadel xSzK ptressJstrain diagram of adobe presented in oeference xSz has been modified and used in alaysis EcigK UF xNzK aynamic properties used in time history analysis are shown in qable PK jaterial properties of com rods and geogrid made of synthetic materialsI used for strengtheningI are presented in qable 4K

Table O jechanical properties of adobe xNI SJUz

Bulk density EkgLmPF NISMM jodulus of elasticity EjmaF NMR moisson’s ratio MKNT Compressive strength EjmaF MKPS clexural tensile strength EjmaF MKMPS Crushing strength EjmaF MK4R Cracking strength EjmaF MKM4R Coefficient of friction of mortar joints MKO

cigK U jodified stressJstrain diagram for old adobe bricks in the Bam citadel xNz

Table P aynamic properties used in analysis xNz

qime history aynamic analysis type T aamping EBF

VKUN dround accelration EmLsOF

Table 4 jechanical properties of com rods and deogrid xNz

com rod with a OO mm diameter qensile strength of area EdmaF N jodulus of elasticity EdmaF 4M

deogrid du RR

Characteristic tensile strength EkkLmF RR Corresponding tensile strain EBF SKR aecrease coefficient in tensile strength MKR

PK ANAivpba jlabip qhe original structureI model NI which consists of the adobe tower and side walls each with half their length EOM mFI has been modelledK aifferent layers of the tower and walls and their interaction using suitable coefficient of friction between the layers have been considered EcigK VFK aynamic structural analysis has been performed for the original structure in order to reach damages similar to the Bam earthquakeK qwo other models have been studied for restorationK fn model OI a MKR m wide expansion joint EcutF along the height of the eastern wall at about R m from the towerI where the eastern wall is partly destructed EcigsK 4 and NMFI is consideredK qhe expansion joint allows independent movements of two parts of the wallK fn model PI the geometry of the walls and tower has been changed; the thickness of side walls has increased in order to make the transition zones from the walls to the tower smoothK

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cigK 9 jodel NI the original structure Ethe tower and two side wallsF with different layers

cigK NM jodel OI the structure with an expansion joint Evertical cutF along the height of the eastern EleftF wall

4K ANAivpfp obpriTp lbtained results from structural analysis due to BamI kaghan and bl Centro earthquakes for models N and O are summerised in qables 4JSK pafety factor contours are shown in cigsK NNJNPK jodel N Ethe original structureF has experienced similar damages to those occurred during the Bam earthquakeK oesults indicate that the weakest part of the structure is the junction of the tower and the eastern wall Eleft wall in cigsK 4I V and NMF; henceI causing the partial destruction of the wallK qhe structural performance of model P Ewith changed geometryF has not improved from that of model N; stillI the connection of the eastern wall to the tower causes structural damageK aisconnecting the eastern wall from the tower Emodel OFI iKeK creating a MKR m wide cut Eexpansion jointF along the height of the wallI decreases the damage dramaticallyK

Table 4 Analysis results of models N and O under the Bam earthquake xNz

ptudied parameter jodel N jodel O Comments

Analysis status kot completed Completed fn model NI due to a weak structural strength the

analysis cannot be completed; iKeK induced stresses are more than adobe strength in some partsK aestruction of eastern wall causes structural analysis for model N to

stop at the time NKVS sK fn model O the separation of the eastern wall from

the tower helped the structure to pass the seismic analysisK

Analysis start time EsF MKMM MKMM

Analysis end time EsF NKVS ORKMO

sibrational period at start time EsF MKPN MKPO fn both modelsI the vibrational period has almost

doubledK ft is due to cracking and crushing that cause a stiffness reductionK sibrational period at

end time EsF MKTO MKSN

jaximum tensile stress during the analysis

EjmaF MKMU MKO Crack has developed in both modelsK

jaximum compressive stress during the analysis EjmaF

MKO MKO

fn model OI the compressive stress is less than compressive strength Eqable OFK qhereforeI there is no crushing in model OK qhere is no comment on model N

because of incomplete analysisK

jaximum displacement during the analysis EmF MKMR MKN

qhe maximum displacement in model O is lower than allowable displacement; iKeK the NLNMM of structureDs height ENR mF xRzK qhere is no comment on model N

because of incomplete analysisK

qhe general status of the structure based on

safety factor diagrams

eigh vulnerable to damage

EcigK NNEaFF

iow vulnerable to damage

EcigK NNEbFF

pafety factor contours EcigK NNF show that model N has been seriously damagedI while the extent of damage to model O is much less; henceI the expansion joint plays an important role in improving the structural behaviorK bxtensive damage of model N indicates that the eastern

EleftF wall been destructed quickly and causes the structural analysis to remain incompleteK

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Table R Analysis results of models N and O under the kaghan earthquake xNz

ptudied parameter jodel N jodel O Comments

Analysis status Completed Completed qhe effect of the kaghan earthquake on models is not as much as the Bam

earthquake; thereforeI the analysis been completed in both modelsK

Analysis start time EsF MKMM MKMM

Analysis end time EsF RKMO RKMO

sibrational period at start time EsF MKPN MKPO fn both modelsI the vibrational period has almost doubledK ft is due to cracking and crushing that cause a stiffness reductionK sibrational period at end time EsF MKRV MKSN

jaximum tensile stress during the analysis EjmaF MKNU MKO Crack has developed in both modelsK

jaximum compressive stress during the analysis EjmaF MKPP MKOS

qhe compressive stress is less than compressive strength Eqable OFK qhereforeI

there is no crushing in models N and OK

jaximum displacement during the analysis EmF MKMRP MKMS

qhe maximum displacement in both models is lower than allowable displacement; iKeK the

NLNMM of structureDs height ENR mF xRzK

qhe general status of the structure based on safety factor diagrams

Almost low

vulnerable to damage

EcigK NOEaFF

kot vulnerable to damage

EcigK NOEbFF

ft can be seen from safety factor contours EcigK NOF that in model N the eastern EleftF

wall has been slightly damagedI but there is no serious damage in the tower and the

northern ErightF wallK jodel O has not been damagedK

qhe kaghan earthquake is much less damaging than the Bam earthquakeK

Table S Analysis results of models N and O under the bl Centro earthquake xNz

ptudied parameter jodel N jodel O Comments

Analysis status Completed Completed qhe effect of the bl Centro earthquake on models is not as much as the Bam

earthquake; thereforeI the analysis is completed in both modelsK

Analysis start time EsF MKMM MKMM

Analysis end time EsF PTKMS PTKMS

sibrational period at start time EsF MKPN MKPO fn both modelsI the vibrational period is almost doubledK ft is due to cracking and crushing that cause a stiffness reductionK sibrational period at end time EsF MKRV MKSN

jaximum tensile stress during the analysis EjmaF MKP MKPN Crack has developed in both modelsK

jaximum compressive stress during the analysis EjmaF MKP MKP

qhe compressive stress is less than compressive strength Eqable OFK qhereforeI

there is no crushing in models N and OK

jaximum displacement during the analysis EmF MKN MKN

qhe maximum displacement in both models is lower than allowable displacement; iKeK the

NLNMM of the structureDs height ENR mF xRzK

qhe general status of the structure based on safety factor diagrams

iow vulnerable to damage EcigK NPEaFF

Almost low vulnerable to damage

EcigK NPEbFF

pafety factor contours EcigK NPF indicate that the tower and its sidewalls in model N

have damaged in some upper partsI whereas in model O the damaged parts have moved

to the lower part of the tower and upper part of the northern ErightF wallK

qhe extent of damage due to the bl Centro earthquake is less than that of the Bam

earthquakeK

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EaF EbF

cigK NN pafety factor contours of the structure due to Bam earthquakeW EaF model NI EbF model O xNz

EaF EbF

cigK NO pafety factor contours of the structure due to kaghan earthquakeW EaF model NI EbF model O xNz

EaF EbF

cigK NP pafety factor contours of the structure due to bl Centro earthquakeW EaF model NI EbF model O xNz

RK obpTloATflN miAN RKNK oeconstruction of the eastern wall with a expansion joint EcutF qhe destructed zone of the eastern wall must be reconstructed with similar adobe bricksK A MKR m wide expansion joint EcutF must be provided along the height of the wall about R m near the towerK ft must be filled with weak materials such as compacted clay EcigK N4FK

cigK N4 oestoration plan for adobe tower koK PO and eastern wall xNz

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RKOK oestoration of the outermost layer of the tower Crushed adobe bricks on the outermost layer of the tower must be removed and replaced by new and similar onesK Cracks on this layer must be restored by com rods with a OO mm diameter and a staggered arrangementK qhe length of each rod must be equal to the thickness of the outermost layer plus NKR m in order to connect the layer to the main coreK eoles for rods are made in the structure by a special drillK qhe space around the rod inside the holes is filled with suitable grout compatible with adobe EcigK N4FK RKPK oeconstruction of stiffened battlements Battlements in most parts of the Bam citadel have been destroyed due to the weakness of materials and inappropriate connection to the top of the wallsK aestructed battlements on the top of the tower and eastern wall must be reconstructed and stiffenedK fn the middle of a battlement a vertical com rod with a diameter of OO mm and NKU m long must be usedK qwo geogrid meshes must be placed on both sides and interconnected by appropriate connectors EcigK NRFK

cigK NR ptrengthening of a battlement using geogrid mesh and com rod xNz ptructural analysis has shown that natural materials such as wood cannot provide required strength; henceI deogrid and com rod Emade of synthetic materialsF have been suggested for restoration of the towerK SK ClNCirpflNp A restoration plan was suggested for adobe tower koK PO in the Bam citadelI which was damaged in the Bam earthquake of OMMPK oestoration project consisted of historicalI archeological and architectural surveyI pathology of the structureI laboratory tests on adobe materialsI structural analysis of the original structureI design and verification of structural strengtheningI and preparation of restoration planK ft was concluded that the junction between the eastern wall and the tower was the weakest partK mroviding a MKR m wide cut Eexpansion jointF along the height of the eastern wall at a distance about R m from the tower would improve structural behavior of the structure dramaticallyK qhe cut is filled with weak materials and the destructed part of the eastern wall must be reconstructedK Adobe bricks of the damaged outermost layer of the tower must be removed and replaced by compatible new onesK qhe cracked area of this layer is strengthened by using com rods with a diameter of OO mm that nail the layer to the main core insideK aestroyed battlements must be reconstructed on the top of the wall and tower and stiffened by com rods and deogrid meshesK AChNltibadbjbNTp qhis work was supported by drant koK UPLV4V from the rniversity of fsfahan and Cultural eeritageI eandicrafts and qourism lrganisation of franK

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obcbobNCbp xNz eejaziI jK EOMNMF ptructural restoration of the adobe tower koK PO of the Bam citadel Ein carsi

and bnglishFK cinal oeportI fsfahanI rniversity of fsfahan and franian Cultural eeritageI eandicrafts and qourismK

xOz eejazi jKI jokhtari bKI qehrani cKI phirazi BKI hhatooni kK EOMMUF mreliminary structural studies of the adobe tower koK PO of the Bam citadelK fnW mrocK NMth fntK ConfK on the ptudy and Conservation of barthen Architectural eeritageK BamakoK

xPz fnternational charter for the conservation and restoration of monuments and sites Ethe senice charterI NVS4FK ENVS4F fnW Ond fntK CongK of Architects and qechnicians of eistoric jonumentsI seniceK

x4z oecommendations for the Analysis and oestoration of eistorical ptructuresK EOMMRF fpCAopAe-fnternational Committee on Analysis and oestoration of ptructures of Architectural eeritageI fCljlpK

xRz franian code of practice for seismic resistant design of buildingsI standard koK OUMM-MR Ein carsiFK EOMMRFI Prd ednI qehranI Building and eousing oesearch CenterK

xSz Consolidation and anchorage of adobe structures in the Bam citadelK EOMMSF oeports koK NJPI qehranI poils bngineering pervices Consulting bngineersK

xTz sargas gKI Blondet jKI qarque kK EOMMSF pummary of building codes for earthen buildings in seismic areasW the meruvian experienceK fnW mrocK Uth rKpK kational ConfK on barthquake bngineeringI pan cranciscoI CaliforniaK

xUz eejaziI jK ENVVTF eistorical buildings of fran: their architecture and structureK pouthampton and BostonI Computational jechanics mublications Etfq mressFK