seismic protection of cultural heritage

Seismic Protection of Cultural Heritage

WCCE-ECCE-TCCE Joint Conference

October 31 November 1, 2011

DRAFT FOR SCIENTIFIC COMMITTEE APPROVAL 1

Project Name: Restoration of Ay Monastery Chapel, Ayvalk, Turkey Author: Ahmet Topba, MSc Architect: Ersen Grsel, MArch, Haluk Erar, MArch, EPA Mimarlk Structural Engineer: Ahmet Topba, MSc, ATB Yap Mhendisleri Re-construction Drawings: Cenk ztibet, MArch General Contractor: Koray naat, A.. Master Mason: Sleyman Sar Ta Sanatlar Abstract:

The Restoration Project of Ay Monastery is a case study of restoration for adaptive future re-use of a historic structure. In this paper, aside from the architectural, cultural, and historic significance of the structure, challenges of restoration design and the execution of the design will be discussed. The focus of the paper will be the Chapel structure restoration, since this was the only restorable structure on the Monastery site. The other structures were un-repairable and they were re-constructed. Reinforcements and re-constructions against possible seismic events as well as gravity loading on the structure will be depicted. The existing condition of the structures was investigated as of the end of 2008, and drawings and reports of the architectural, structural, and material-wise condition of the structure were documented in the beginning of 2009. Subsequently, re-construction (restitsyon) drawings were made. In May 2009 restoration design was completed. After it was approved by the authorities, construction started toward the end of the same year.

Fig.1.a) A 1908 postcard picture of the Monastery Fig.1.b) Existing condition in 2008

Introduction and history:

The Monastery is located in the township of Ayvalk, Balkesir. Located 2.5m above water level on the northern coast of the Island of Cunda, it is a 40 minute trail walk amongst the olive orchards. It is presumed that, Ay Monastery (Agios Dimitrios Ta Selina) was built in the 17. Century by Ayranoz Monks. The years 1771 and 1795 on the various entrances are presumed to be the dates when the Monastery was repaired. It is one of the 7 Monasteries on the Island of Cunda. The layout of the Monastery had been shaped by need over time with various one-to-two-story structures surrounded by perimeter walls. These structures all opened to a common inner





courtyard. Typical to monastery construction, in the center of the courtyard was its church. The structures that formed the complex were made with rubble stone salvaged from the surroundings and had earth for mortar. After 1865, during a serious renovation period, lime mortar was used in stone walls. During the same period, the central Chapel, which seems to be the most well-built structure of them all, was built in the Byzantine style with stone and solid brick. The restoration design team devised a project which foresaw strengthening for the restorable structures and reconstructing the un-restorable to the original condition. For the engineering design, the 2007 Turkish Seismic Code, other relevant Turkish Codes, and national and international literature were studied. During the field measurement and re-construction design periods, existing masonry materials were investigated for physical and mechanical properties by Mimar Sinan University. The restoration work started in the autumn of 2009 and scheduled to be completed in June 2011.

Fig.2. An elevation photo from 2008. Priest Rooms is completely destroyed. Facades of Structures 1,2, and 3 partially remain

Fig.3. The Structures that constituted the Monastery complex

Priest Rooms Structure

Structure 1

Structure 2

2

Structure 3 Chapel





Existing Condition in 2008:

The Monastery structures had been repaired during different periods of time. Except for some parts of the Chapel structure, in part due to poor repairs, the existing condition of the structures is a mix of masonry construction put together without high-quality workmanship or meticulousness. For masonry units, rough basalt stones, rough-cut sandstones, and solid bricks were used. Usually basalt and sand stones were in good condition, however historic brick not protected with plaster had decomposed or softened. Original or as an old-period repair, the rubble stone construction had earth fillings for insulation or for mortar in both interior and exterior leaves of walls as seen in Figs.5.c and 6.a. The solid brick construction was done with lime mortar reinforced with dried plant fibers, a traditional and historic mortar called Horasan. Where the brick construction had been protected with plaster, it was in good condition.

Fig.5.a) Front facade. Broken tie caused shear

cracks and displacement.

Fig.5.b) Chapel perimeter

wall- beachside

Fig. 5.c) Large hole with plants growing in

earth mortar on Chapel perimeter wall-hillside

The relatively new, patchy repairs were done with lime-mortar which was in a better condition. This kind of repair is evident on the beachside walls as seen in Fig.5.b. However, these repairs were only superficial patches with mortar joints only 5-7cm deep into the 75cm to 90cm thick

Fig.4.a) Plan of Chapel. A structure with 13.5m by 5.8m

plan dimensions

Fig.4.b) Section of Chapel. The top of Cupola is 10.6m-high from

the ground .





walls. While the bonding of units of the seemingly older or original construction wasnt sufficient and stone units had been laid randomly, no toothing to the older, existing masonry was observed in the repairs either. In addition, the protective plaster had been long removed. Abuse had taken place, and many holes were made by people as well. As a result, perimeter wall masonry was completely dissolved with stones lost over time or had fallen and formed heaps next to the walls as evident from photos in Figs. 5.c and 6.a. The Chapel vaulted roof, cupola, columns, and arches had been made with solid brick and lime mortar, and they had been protected with plaster. In general, the arches and vaults were in good condition with one large crack through the apex of one of the four arches. Of the five 24mm x 96mm steel ties, three of them were tying the cylindrical roof vaults, and the other two were ties between the arched columns, all in the short direction of the structure. None of them were functioned due to breakage and heavy corrosion. In fact, the rupture of the front facade tie caused the sliding of the beach-side support of the facade arch, creating continuous shear cracks and displacements up to 4cm on the top of the facade and support walls. (Fig.5.a) It was concluded by the restoration design team that the perimeter walls had to be reconstructed, while columns, vaults, arches, and the cupola shall have been strengthened and restored.

Fig.6.a) Chapel interior wall. Rubble stone construction had

crumbled and formed heaps next to walls.

Fig.6.b) In spite of the un-repairable condition of the perimeter

walls, the brick vaults, arches, columns, and the cupola was in

a restorable condition.

According to the Kandilli Earthquake Observatory Records, between 1919 and 1944 there had been three major earthquakes in the Ayvalk area with magnitudes 6.5 to 7 Richter scale. In addition, the material found on ground suggested that over the steep slope on the hillside behind the Priest Rooms structure, landslides had occurred causing much damage. In fact, this structure was completely destroyed by 2008. The re-constructive drawings could have only been made from historic documents and pictures.

Geotechnical Investigation:

Sites soil was investigated in two ways. First, the soil was investigated on the grounds where the foundations of the structures would be placed. 10 borings were made on the site within the Monastery perimeter walls, and the soil profile was obtained. Second, a slope stability study was





made based on the thought that the steep slope curbing the Monastery from behind eroded in time. Based on the borings and the stability study, the earth formation was captured with geological sections through the site. The sections as seen in Fig. 8, also helped the contractor prepare for the safety precautions to be taken temporarily while excavating for foundations. In general, the Monastery soil condition was as follows: the top layer was eroded or fallen material (soil layer a), under this layer was weathered-rock and hard-clay (soil layer b), and beneath this formation was volcanic rock (soil layer c). See Table 1. for properties of the layers.

Parameters Layer: a b c Internal Friction Angle, (deg) 20 32 45 Cohesion, c (KPa) 30 50 50 Friction Coef. btwn. Soil and Structure, d(deg) 17 22 28

Table 1.Geotechnical parameters of Soil Layers a, b, and c that constitute the layers on the site.

The soil was classified as Soil Class Z2 and Local Soil Group B1-C1 per the 2007 Turkish Seismic Code.

Fig.8. Section showing the geological formations and excavations of the slope during construction.

Seismic and FEM Analysis:

The Chapel structure was modeled as a masonry structure in SAP2000 FEM software with shell and frame elements. Un-reinforced and reinforced iterations were made with the models, and strengthening was designed based on the comparative studies. A Response Spectrum Analysis was made based on the 2007 Seismic Code with Spectrum Coefficient taken as S(T)=2.5 and Structural Behavior Factor as R=2. As prescribed in the geotechnical reports, the site was as in Seismic Zone 1, so the Effective Ground Acceleration Coefficient was A0=0.4 and Spectrum Characteristic Periods were Ta=0.15 and Tb=0.4. The elastic moduli and allowable compressive stresses were taken as listed in Table 2 below. Laboratory data, 2007 Seismic Code, a literature

a Eroded-Fallen material over time

b Weathered Rock Hard Clay

c- Volcanic Rock (Hard Yuntda Formation)

Chapel Foundation





survey for comparative properties, and past experience with historic structures were used to determine these values.

Masonry Type Elastic Modulus, 200 x fd (MPa)

50% of Block Comp. Strength, fd (MPa)

Allow. Comp. Strength, fem (MPa)

Historic rubble stone 220 11 0.6 Strengthened historic solid

brick 2000 10 2.5

Reconstructed rough stone + solid brick multi-wythe wall

1600 8 2

Table 2.Assumed compressive strengths and elastic moduli of various masonry construction types used in Chapel FEM analysis The Priest Rooms and Structures 1, 2, and 3 were analyzed and built in either of two ways. First type of design was masonry load-bearing walls strengthened with RC. Second were RC structures clad with 30-50cm thick brick or stone masonry facades. A total of 100 modes were considered in the analysis with SAP 2000. The high number of modes were necessitated due to the requirement of gathering a minimum of %90 mass participation in the spectral analysis in both x and y axis. A large number (7910 shells) of small shell elements, thereby a fine FE mesh was used partly because some of the details, such as the interaction between the column-cupola frame and the perimeter walls, had to be studied in detail for the strengthening strategy. In addition, this was a small structure with 13.5m x 5.8m plan dimensions, so the computation time was not considerable. Therefore, using many but small elements did not result in analysis inefficiencies. Neither the capturing of the global behavior of the structure was compromised, since the entire structure was modeled the same way.

Fig. 9. Exterior and interior views of the Chapel FEM model. As seen from the results of the spectral analysis in Figure 11.a, when assumed existing masonry properties from Table 2 are used for the perimeter walls, the maximum compressive/tensile stress was 3.5MPa while the displacement on the top of Cupola is 1.5cm. When the reconstructed masonry properties as per Table 2 of the multi-wythe wall are used, the stress levels drop to 1.3MPa with displacements in the range of 0.6cm on top. (See stress distribution in Fig.11.b)





Fig. 10.a) First mode shape. Weak (governing) direction. T=0.14sec Fig. 10.b) Second mode shape. T=0.09sn

Due to the increased elastic modulus and the bond provided by the RC tie beam placed at the support level of the vaults, the walls in the weak-direction were engaged more in the seismic loading in this governing direction. Stresses at the four corners of the weak-direction walls were increased to 0.8-1MPa, making these corners the walls tension/compression zones. This action was much like a concrete shear walls response to lateral forces. And hence the reinforcement for these corners was designed as vertical RC columns with ties to the new mat foundation.

Fig. 11.a) Compressive/Tensile stresses. Max=3.5MPa. Perimeter

walls are modeled w/exist. rubble stone wall properties. Fig. 11.b. Max=1.3MPa. Perimeter walls are modeled w/re-

constructed multi-wythe wall properties and RC tie beam.

Design of Strengthening and Re-construction:

A multitude of strengthening elements and reconstructive measures were designed for the Chapel. These measures can be viewed in Figures 12 through 21:

Reconstruction of the perimeter walls with 35cm rough stone exterior + 40cm solid brick interior multi-wythe walls.

50cm x 30cm RC tie beam along the perimeter at the vault support level.





Vertical L-shaped 25cm x 60cm RC elements at wall corners. Horizontal reinforcements within masonry wall to take tensile stresses where the cupola

pendentives butt against the perimeter wall (blue in Figure 12.a)

Fig. 12.a) Strengthening elements used in Chapel restoration are

shown in color.

Fig. 12.b) Reconstructed perimeter walls supported by

the new 30cm mat foundation

Steel plates, pins, and anchors tying cupola columns and arches to the perimeter walls. Various steel mesh and connectors, between leaves of the multi-wythe walls and

foundation dowels to the mat. A 30cm mat under the entire structure was designed due to the weak material at the base. 5mm galvanized steel mesh laid on the exterior of the vault w/ 7cm structural topping. Epoxy injection of the vaults, columns, cupola to fill existing cracks. 10mm rebars embedded and anchored around the edges of windows of the cupola.

Fig. 13.a) RC tie beam and vault strengthening Fig. 13.b) RC vertical column at wall corners





Temp. Shoring & Execution of Design:

To implement the reconstruction, inventive methods and substantial team effort between the design and construction teams were required. First, the solid brick vaults and cupola were temporarily shored by scaffolding. Then double UPN350s connected with M24 bolts at 35cm sandwiching the 75cm perimeter walls were installed as temporary tie beams. (Fig. 15) When the bolts were tightened, the rubble above the tie beam level would not fall while the wall underneath was removed and reconstructed above a new mat foundation.

Fig.14. Sketching the restoration scheme. FEM model print-out was

used as the base.

The double UPN350s were also tied across inside the Chapel with four L100x100x10 cross ties which could work both in tension and compression should the vault move in either direction laterally during construction. When the steel temporary ties and scaffolding were in place, began the removal and reconstruction of the perimeter walls up to the bottom elevation of UPN ties. This was done in 2m-3m sections not to compromise the safety of masons underneath and not to risk displacement of the vaults. Figures 16-17 show these stages in detail. During the works, constant visual monitoring for possible vault movements was done by the masons crews.

Fig.15.a)Temporary scaffolding to hold the vaults Fig.15.b) Detail of temp. steel tie-beam

This inventive staged construction also allowed for the foundation betterment of the Chapel. A new 30cm mat foundation with dowels into the reconstructed walls was installed in stages. For continuity of the mat, shear keying of 10cm between mat sections were used and bent rebar from the previous section was extended into the next section at every stage.





Fig.16.a) Temporary steel tie beam in place along

the perimeter.

Fig.16.b) Detail of the reconstructed multi-

wythe wall and dowels to mat.

Fig.16.c) Wall and mat are

being constructed in stages

below the steel beam.

After the mat was poured, and wall below the steel tie beam was reconstructed, (Figure 17) the wall section above the tie beam was replaced. Removing of rubble and placing the permanent RC tie was done meticulously without compromising the vault supports. The temporary steel was also removed after this stage. The structural mortar used in the reconstructed walls was lime-cement mix mortar Type B4 per TS 2510 or M11 (1:1:4) per TS EN 1996. The lime content was particularly desired to provide similar behavior to the existing.

Fig.17.a) Section below UPN350to be reconstructed in the

next stage.

Fig.17.b)The same section from Fig 17.a completed and tied to

previous stage.

The staged construction was specially planned for the facades and the corners. (Fig. 18-19) A survey and tagging of the existing corner stones were done prior to the repair. Initially, the part below the arched timber scaffolding was replaced. The corner stones were dismantled, repaired, and re-assembled with necessary replacements above the corner portion of the new mat. The crown arch was held in place partly by the double cantilevering action of steel tie beams in the corner. In addition, the timber scaffolding was replaced with the new brick facade in 3 stages, providing extra temporary support for the crown arch. When the reconstruction of the walls and restoration of the vaults were finished, a complete and seamless solid brick structure was formed inside. The new brick of the walls were connected with the existing brick of the vaults.





Fig.18. Schematic drawing showing stages of front facade reconstruction

In addition, the vaults were strengthened against tensile stresses form spectral analysis with 5mm galvanized 5cm x 15cm steel wire mesh. The 7cm structural topping increased the vaults effective thickness to 20cm. Conclusions:

The project was a challenging restoration to provide an adaptive future re-use of this historically and culturally important Monastery. Many challenges existed in design and construction stages. The existing condition of the walls required reconstruction while roof vaults, cupola, pendentives, and columns needed to be restored in place. Inventive methods had to be used during the temporary shoring and staged reconstruction of the structure.

Fig.19.a) Front wall below steel is removed.

Corners would be next.

Fig.19.b) Last stage of facade reconstruction.

Top of the wall corner held by tie beam

cantilevers

Fig.19.c) Corner stone repair process.

Reinforcement from RC vertical element can be

observed in the photo.





Fig.20.a) Reinforcements

around window openings

of Cupola

Fig.21.b)Reinforcement of vaults with steel

mesh and structural topping

Fig.22.c) Walls & Vault: Continuous solid brick

shell is formed inside of the Chapel when the

wall reconstruction is completed.

Results of the spectral seismic analysis were interpreted and applied as various practical strengthening elements. Historic fabric was respected and traditional methods were combined with modern methods.

References:

Binda L., et al, Repair and Strengthening of Historic Masonry Buildings in Seismic Areas, 12th Int. Brick/Block Masonry Conf., 2000

Butenweg, C., et al, Modeling Methods of Historic Masonry Buildings under Seismic Excitation, Journal of Seismology, 2006

Celep Z., Gedik, Y. H., Earthquake Analysis and Strengthening of the Historical Mehmet Aa Mosque, The 14th World Conf. on Earthquake Engineering, 2008

elik, O. C., Sesigr, H., Observations from April 2009 LAquila Earthquake, Seminar at Istanbul Chamber of Civil Engineers, 2009

Fig.22. Restoration progress photo from Spring 2011

Grsel E., Erar H., Restoration of Ay Monastery, EPA Architecture Report for

Landmarks Commission, 2009

Habibullah, A., Wilson, E.L., SAP2000, Structural Analysis Program, Computers and Structures, Inc., 2008

Koyunlu, K., zturk, H., Ay Monastery Geotechnical Report, Geosan A.., 2010 Menegotto, M. Seismic Repair and Upgrading of a Dome Lantern in Assisi, Structural

Engineering International, IABSE, 1993 Tahir, , Ay Monastery Slope Stability Assessment Report, 2009 Turkish Seismic Code, Ministry of Reconstruction and Resettlement, 2007

nay, A. . Seismic Resistance of Historic Structures, METU Dept. of Architecture, 2002

seismic protection of cultural heritage

Documents