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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

TAA awlNd lc TolNdpA – obcibCTflN lN Teb ob-rpb lc A BerTANbpb tATCeTltbo Matthias BeckhN ABpToACT qhe paper deaäs with the construction of a unique Bhutanese tower structure and its conversion into a modern museum. fn the first partI the history of the qaa azong in qrongsaI the geographicaä center of BhutanI wiää be expäicated. qhe fortified watch towerI which was used to protect the grand main azong Efortified monasteryF situated beäowI was buiät in the seventeenth century. qhe medievaä construction was converted into a museum dedicated to the history of Bhutan within the recent years EOMMRJOMMUF. qhe main part of the paper wiää focus on medievaä Bhutanese construction materiaäs and techniques at the exampäe of qaa azong – construction methods that haven”t changed much for ages in this secäuded eimaäayan kingdom. As Bhutan is äocated aäong the eimaäayan fauät äineI some of the historicaä components were upgraded to meet the safety expectations of a museum. qhe paper wiää concäude with a discussion about the sometimes confäicting design aspects of turning a historic and basic structure äike qaa azong into a modern museum. heywords: Bhutan, barthquake, Masonry, oetrofitting, mreservation, Museum NK fNTolarCTflN

NKNK Trongsa – focal point of Bhutanese history qrongsaI a smaää viääage and capitaä of the correspondent districtI is äocated in the geographicaä center of Bhutan. qhe verdant vaääey and its surroundings were cruciaä for the founding of BhutanI as many decisive events took päace here. qhe main azong – a fortified monastery – can be traced back to Shabdrung kgawang kamgyel ENRV4JNSRNFI or simpäy ShabdrungI the äegendary unifier of the country. fn the first haäf of the seventeenth century he had succeeded in bringing the western haäf of Bhutan under his controä. ee then estabäished qrongsa azong in NSROI which was buiät by one of his confidants at the päace of a former tempäe. qhe azong served as a base for seizing the eastern parts of the country. Buiät strategicaääy on a mountain spur separated from the mountain range and high above the wiäd gorge of Mangde Chhu riverI the massive azong dominated the entire vaääey. qherebyI it controääed the trading routes from eastern to western Bhutan and in the northJsouth direction from qibet to fndia. rntiä the time of phabdrungI the azongs served soäeäy as miäitary stronghoäds for the ruäers of smaää kingdomsI thereby foääowing qibetan modeäs. rnder the ruäe of the phabdrungI howeverI the purpose of the azongs deveäoped from a hitherto miäitary one to a more muätifaceted usage. pince thenI the azongs are centers of both reäigious and secuäar power. qhe space of the azong and its many courtyards is shared between the administrative and the reäigious sphere. fn the case of qrongsa azongI for exampäeI these spheres are distinctäy separated with quarters for about SM civiä servants of the province administration and the premises of the monk body with 4MM peopäe and OT tempäes. ft was customary to päace watchtowersI caääed qaa azongsI next to the azongs to safeguard them. eoweverI onäy very few of these watchtowers stiää exist today. qhe qaa azong of maroI which today houses the kationaä juseumI is one of these rare exampäes. qhe construction work of the qaa azong

N ar.Jfng. jatthias BeckhI aepartment of ptructuraä aesignI cacuäty of ArchitectureI qechnische rniversität

jünchenI m.beckh]ärz.tum.de

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in qrongsa started presumabäy in the same year äike the azong. fts historyI constructionI restoration and adaptive reJuse are expäained in the foääowing parts of this paper.

cigK N qaa azong and one of the two äower singäe standing towers EOMMRF NKOK Taa azong – the watchtower of Trongsa azong qhe qaa azong of qrongsa was buiät at the same time äike the main azong at the beginning of the second haäf of the seventeenth century. ft was buiät as a defense structure to protect the main azong beäow. aue to its strategic positionI attacks on the azongI which were onäy possibäe from the mountainsI couäd be warded off from its massive waääs. qhe compäex consists of a circuäar fiveJstoried towerI caääed rtseI fäanked by two äower towers. fn päanI the three towers form an isosceäes triangäe. qhe äower towers are connected to the rtse by narrow threeJstoried side wings. qhe rtse – the centraä eäement of the buiäding – is the oädest part of qaa azong. qhe two äower towers were added äater. ApparentäyI the wings between the towers must have been buiät more recentäyI as there is no interäocking of the masonry between the wing structures and the towers on either side. qaa azong had been severeäy damaged by the great NUVT Assam earthquake and had been repaired and partäy rebuiät in its aftermathI just äike the main azong beäow. fn NVVMI a heavy storm äed to the coääapse of many of the roofs. fn the foääowingI the traditionaä roofs made of wood shingäes were repäaced by corrugated steeä paneäs. lriginaääy constructed as a pure defense structureI the buiäding was used for reäigious purposes since the mid nineteenth centuryI when peace came to Bhutan. At the beginning of the twentieth centuryI two tempäes were buiät within the structureI and äittäe äater two hermits with their caretaker monks moved into the buiäding. NK3K The restoration and adaptive re-use of Taa azong fn the year OMM4I it was decided to restore and reuse qaa azongI as part of a BhutaneseJAustrian cooperation project. A group of foreign consuätants prepared the restoration päan and museum designI advising the Bhutanese counterpartI who was in charge of impäementing the project. qaa azongI with its two important tempäes and its unique significance for BhutanI caääed for two main objectives of the project. cirst of aääI it required to preserve qaa azong as a päace of worship for Bhutanese Buddhists. qhis aäso meant that the two monk hermits shouäd keep their space in the restored buiäding. qhe second aim was to estabäish a modern museum dedicated to the rich historicaä and reäigious heritage of qrongsa. qhusI qaa azong shouäd retain its spirituaä aspects whiäe being adapted to the requirements of a museum. ConsequentäyI it was decided to divide the buiäding spatiaääy into two separated spheresI with the museum occupying the centraä towerI north towers and north wing. qhe two hermits and their caretaker monks as weää as the office spaces were moved to the south wing and south tower. As a side effect of the projectI it was intended to draw more visitors to qrongsa and thereby generate more income for äocaä business.

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cigK O pection and eäevation drawing of the north towerI north wing and rtse Ecentraä towerFI drawing by dötz eagmüääer

OK ClNpTorCTflN ANa obpTloATflN lc TAA awlNd

OKNK Constituting structural elements qhe construction of qaa azong is characteristic for azong buiädings of this era. fn the foääowingI the constituting eäements of the structure wiää be briefäy expäained. 2KNKNK oubble stone masonry walls jost exterior waääs of the structure consist of heavy rubbäe stone masonryI with thicknesses ranging from UM to PMM cm in the case of the rtse. qhe rough stones of the masonry are äaid in mud mortar. As it is usuaääy the caseI the waääs säightäy säope inwards over the height of the buiäding. Aää waää faces are covered with a traditionaä whitewash made of äime. taää openings for doors or äoophoäes are typicaääy bridged by square oak äinteäs.

2KNK2K bkra walls qhe exterior waääs of the highest two stories of the north and south wings are made of wattäe and daub waääs. qhe haäfJtimbered construction comprises a centraä äayer of wattäeI which is typicaääy made of a weaving of späit bamboo. qhe pockets are packed with an earthen infiää and a cäay render provides a smooth finish for the whitewash cover. 2KNKPK cloor construction fn the case of the rtseI the fäoor framing is done by massive timber äogsI which have been stripped off their bark. qhe spacing is typicaääy very tight; in most cases the cäearance is just as wide as the äogs. At the bearingsI the äogs are embedded within the waääsI often äeading to wet rot. At the north and south wingsI the fäoor framing consists of joists made of dressed pine woodI with an aämost square cross section. A heavy äayer of cäay upon the wooden päanking provides the fäoor finish. 2KNK4K ooof structure qhe north and south wings are covered with the typicaä traditionaä Bhutanese system of säightäy incäined pitched roofs. Basicaääy consisting of a type of puräin roofI massive horizontaä beams support stocky round piääars of varying height that support the puräins. At either endI the piääars are bifurcated to provide the joint to the horizontaä beam and respectiveäy to the puräin. qhe round rafters consist of undressed members of pine woodI which carry the roof cover made of wood shingäes.

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OKOK ptructural fabric – existing condition auring the initiaä inspectionI the structuraä fabric proved to be in a depäorabäe condition. qhe heavy rubbäe stone masonry waääs were made of pooräy fitted rough stones äaid in a thick bed of mud mortar. rnäike in the main azong beäowI where the stones of good quaäity where brought to the site from distant quarriesI soft mica schist from the äocaä hiääs was used for the waää construction of the qaa azong. qhe soft stones and the poor quaäity of construction had äed to an abundance of cracks and deep fissures – a situation that had certainäy been aggravated by the weak foundations. jost of the foundations were extremeäy shaääow for a buiäding of this size. ppot checks unveiäed a foundation depth of äess than RM cm and cracked stones at many äocations. caiäing foundations had äed to substantiaä settäements particuäaräy at the korth and pouth towers. jost of the buiädings structuraä timbers were severeäy damaged by pest infestation or dry and wet rot. kone of the structuraä timbers predated the OMth century. jost of the aäready rotten fäoor beams must have been äess than 4M years oädI indicated by the marks of modern saw bäades from the miää beäow. ApparentäyI the äast structuraä renovation had been carried out in a haste with no or onäy äittäe time to dry the wood properäy. fn a simiäaräy speedy mannerI the traditionaä roof structure had been entireäy repäaced after storm damage with a makeshift roof truss and corrugated steeä. fn generaäI most of the decayed structuraä timbers had to be repäaced; the roof systems were to be rebuiät foääowing the historic bäueprint with wooden shingäes. OK3K peismic Activity iocated aäong the eimaäayan fauät äineI Bhutan is exposed to strong seismic activity. Aäthough the country has not suffered a major earthquake in recent yearsI smaääer tremors are experienced about every year. qhe most devastating earthquakeI with its epicentre in nearby AssamI happened in NUVT. qhe tremors couäd be feät as far as Ahmedabad and meshawar. qrongsa azong was badäy damaged during this eventI but was repaired shortäy afterwards. qhe äast powerfuä earthquakes happened in NVSM and NVUMI when many buiädings äike memayangtse monastery were severeäy damaged. fn generaäI the centraä and eastern parts of Bhutan a more prone to strong seismic activity than the western parts. ff the seismic zones of the fndian codes and reguäations were extended over into BhutanI the centraä and eastern parts of the country wouäd be in wone s – the most endangered one. jaximum ground acceäeration can range from M.O g up to M.4 g. An essentiaä part of the structuraä restoration was therefore the incäusion of precautionary measures to address the risk of an earthquake. coääowing the maxim “minimum intervention – maximum protection”I a variety of smaääJscaäe interventions was incorporated to upgrade the structuraä resistance of the buiäding. Aää interventions are unobtrusive and äowJtechI an absoäute precondition under the various constraints of the project. qhe key eäements of the structuraä upgrade range from foundation underpinnings and tie beams beäow grade äeveä to conceaäed ring beams at the top of the three towers. qhese eäements can be an effective device to increase the shear resistance of the existing waääs and prevent outJofJpäane damage. fn additionI the fäoor päanes were stiffened by two äayers of päywood paneäs with staggered joints to create rigid horizontaä päates. qhe impäemented strengthening measures increase the cohesiveness of the buiäding by tying some of the weaker parts more firmäy together. By doing thatI differentiaä movement of the structuraä parts during seismic motion wiää be reduced and the buiäding wiää be more apt to act as one singäe unit. OK4K eistory of the restoration Before restoration work couäd startI the site stiää had to be deveäoped to provide basic access. Being onäy accessibäe by a footpathI a cabäe car was instaääed to bring construction materiaä from the main road to the site. juch of the required materiaäI howeverI stiää had to be carried by workers. Construction work in Bhutan is stiää dominated aämost excäusiveäy by manuaä äabour. At peak timesI more than NRM workers were empäoyed to work on the siteI in the quarries and the saw miää. oestoration work started in lctober OMMR with the repair of the north wing and north tower. aue to uneven subsidenceI the äower haäf of the korth tower’s existing foundation had to be underpinned and enäarged with reinforced concrete. curthermoreI the weak condition of some parts of the masonry of the north tower required the partiaä removaä and rebuiäding of some masonry sections. qhe restoration of the pouth wing foääowed in a simiäar fashion. fn guäy OMMSI whiäe the restoration of the rtse had aäready commencedI huge cracks deveäoped in the massive waääs of the tower. fn the foääowingI the waää progressiveäy disintegrated and a substantiaä portion of the waää sheared off. qhe damage was most äikeäy triggered by the repäacement of decayed wooden äinteäs and fäoor beams in the rtse’s

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ground fäoorI which had caused a shift of the stress distribution within the masonry. iuckiäyI no one was injured during the coääapse of the waää portion.

cigK 3 martiaä Coääapse of the rtse waää qhe severe damage raised serious questions about the stabiäity of the masonry waääs. Controversiaä discussions about the safety of the buiädingI possibäe strengthening measures and the further restoration strategy foääowed. qhe key arguments in the debate revoäved around the authenticity vaäue of the structure and the required safety äeveä for a museumI which wouäd eventuaääy house important artistic and historicaä treasures of Bhutan. fntricate and costäy strengthening measuresI äike grout injections or the äikeI that are commonpäace at comparabäe projects in more deveäoped äocations had to be precäuded due to the remoteness of the siteI the technoäogy at handI as weää as financiaä constraints. After the carefuä weighing of aää optionsI the very poor quaäity of the waääs as weää as the required safety äeveä for a museum finaääy äet to the decision to dismantäe and reconstruct the rtse.

cigK 4 siew of the compäeted “qower of qrongsa Art juseum” EOMMUF

After four years of restoration workI the qower of qrongsa Art juseumI as it is officiaääy caääed todayI opened in OMMU.

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3K ClNCirpflNp auring the process of päanning and constructionI the originaä maxim to preserve as much as possibäe of the structuraä fabric as possibäeI had to be surrendered to the goaä to achieve an appropriate äeveä of safety for the museumI its visitorsI and the exhibited objects. qhereforeI more historic fabric was affected than originaääy anticipated. diven the constraints and äimiting factors of project and siteI the author stiää deems the decisions taken the best under the circumstances. Adaptive reJuse of historicaä buiädings as museums aämost aäways caääs for extensive interventions. qhe unavoidabäe äoss of historicaä traces is often depäorabäe. fn the case of qaa azongI howeverI the conversion of this rare buiäding type into a museum prevented it from the foreseeabäe fate of further decay and uätimate äoss. AChNltibadbMbNTp qhe main consuätants for the project were Christian pchickägruberI dötz eagmüääerI and qhomas pchrom for the museum design and architecture. qhe author was in charge of the structuraä engineering and retrofitting of the project. qhe author wishes to thank qhomas pchromI the project coordinator of the qaa azong restorationI for his heäp in the preparation of this articäe. obcbobNCbp xNz pchickägruberI Ch. EOMMVF qhe tower of qrongsa – oeligion and mower in Bhutan. dhentI pnoeck

mubäishers. xOz qenzingI a.I bd. ENVVPF An introduction to traditional architecture of Bhutan. pingaporeI tah

jee mress.