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Wcte 2010 tsakanika mouzakis benizelo's mansion


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Wcte 2010 tsakanika mouzakis benizelo's mansion

  1. 1. A POST-BYZANTINE MANSION IN ATHENS. THE RESTORATION PROJECT OF THE TIMBER STRUCTURAL ELEMENTS Eleftheria Tsakanika - Theohari1, Harris Mouzakis2 ABSTRACT: This paper presents briefly the structural system, the pathology, the numerical analysis and the restoration project of a post-Byzantine mansion in Athens, with timber floors and roof that rest on timber frame walls and timber reinforced rubble masonry walls. KEYWORDS: restoration, timber masonry reinforcements (ties, lacings), timber frame walls, fiber carbon bar, FCU. 1 INTRODUCTION 123 An important architectural monument of the Ottoman period in Athens is under restoration since 2008. The monument, a two-story mansion, is a rare example of the post-Byzantine architecture in Greece, since it is the only building of this kind still standing in the area of Athens (Figure 1b, 2b). A preliminary study of this mansion in the framework of a diploma thesis, was presented at the International Timber Engineering Conference in London, in 1991 [1]. be reused. New transversal masonry arches were built, the longitudinal North wall and the quite elaborate North arcade in order to be constructed over them the 1st floor of a new mansion which belonged to a prominent family of Athens (Benizelo’s family) (Figure 3, phase 2). During next centuries, several interventions changed the original mansion causing important architectural and structural problems (Figure 3, phase 3). The North façade of the upper floor was closed (Figures 1a, 1b) and new internal timber walls were built at the 1st floor since the building was divided in 2-4 independent properties. Figures 1a, 1b. The North facade of the building before and after restoration works. Figures 2a, 2b. The South facade of the building before and after restoration works. 2 DESCRIPTION OF THE BUILDING The timber projection, the so-called “sahnisi”, that existed at the center of the South facade was demolished and the gap was closed with rubble masonry. Almost all the original openings (windows and upper course windows) were closed and new ones were opened in different positions (Figures 2a, 2b). 2.1 GENERAL INDORMATION It is a rectangular building, of general dimensions nearly 23.0×9.40m. The South longitudinal rubble wall and the three internal transversal walls of the ground floor belong to an older building or buildings (Figure 3, phase1). During 17th or 18th century these walls were demolished till the level of the existing floor in order to 1 Eleftheria Tsakanika - Theohari, School of Architecture, National Technical University of Athens, Patision Street 42, 10682 Athens, Greece. Email: 2 Harris Mouzakis, School of Civil Engineering, National Technical University of Athens, Heroon Polytechneiou 9 15700, Athens, Greece. Email: 2.2 THE LOAD BEARING STRUCTURE OF THE MANSION The masonry walls of the ground floor (55-60cm wide), and the arcades (35-40cm wide), were made of a threeleaf rubble masonry with clay mortar. On the contrary, only two walls of the upper floor were made of rubble masonry. They had a lot of openings quite close to each other, reinforced with horizontal
  2. 2. N N phase 1 phase 2 phase 3 Figure 3. Ground floor plan (before restoration works), showing the different phases of the building. (G.Kizis, K. Aslanidis, Ch. Pinatsi). timber elements4, embedded in 5 levels, as it can be seen at the East wall (the only wall that was saved intact), giving important information for the architecture and for the original structural system of the building (Figures 5a, 5b). At the South wall the original timber reinforcing system was destroyed after the changes during the last centuries and it could be located only by its remnants (Figures 2a). The 1st level of timber ties exists at the top of all the walls of the ground floor. The 2nd level exists at the level of the sill of all windows, the 3d at the middle of the stone piers between the windows, the 4th exists at the level of the lintel and the 5th at the top of the rubble masonry walls of the upper floor. (Figures 5a, 5b, 6a). The timber reinforcing system is actually a horizontal grid embedded in masonry. It is composed of double longitudinal timbers (16x7cm each), placed at the inner and outer face of the rubble walls, connected through the thickness of the wall with smaller transverse timbers placed over them, every 80-100cm. The connection between longitudinal and transverse timber elements is ensured by a vertical nail. (Figure 6b). The transverse timbers do not exist at the levels of the floor and the roof since in these cases the connection of the longitudinal timbers is accomplished with the beams of the floor and the tie-beams of the roof. As the length of timber elements is smaller than the length of the building, the connection of the longitudinal timbers along the wall, very important for the continuity of the system, is made by a plain scarf joint and one or two nails (Figure 6b). The structural role of the embedded in masonry horizontal timber reinforcements is multiple. The tying of the buildings in several levels as a continuous belt, the tying of the floors and roofs to the walls, the reinforcement of the connection of the walls at different levels along their height, the connection of the outer and inner leaf of the masonry walls, the improvement of the tensile and bending strength of the brittle (by nature) masonry working as reinforcement for in plane and out 4 Different names of the horizontal timber reinforcing system of the masonries are : “timber ties, ring beams, or lacings”, “hatil”, “cator and cribbage” constructions [2], “ιμάντωσις” in ancient Greek and “ξυλοδεσιά” in modern Greek [5]. Figure 4. Plan of the architectural proposal for the 1st floor, (G.Kizis, K. Aslanidis, Ch. Pinatsi). Figures 5a, 5b. The East wall before and during restoration works [1]. Figures 6a, 6b. Typical construction of the horizontal timber reinforcing system embedded in the masonry wall. When the stone piers are in close distances, the timbers at the level of the lintel can be continuous (6a). of plane induced forces, the confining effect (Figure 6a) that is provided at the stone piers between the openings [4], are briefly some of the structural beneficiary for the masonry features of this system, especially for seismic actions [3, 5, 6]. The rest of the upper floor was consisted of a timber colonnade at the main façade (Figure 1b) and two types of timber frame walls filled with solid bricks and lime mortar. Type 1 timber frame had a lot of openings and consequently few diagonal members (Figures 7,8,9a,b), while type 2 had few openings and many diagonal members (Figure 9b, 13c, 23a). In both types, the main load bearing system of the frame was composed by vertical timbers (14x14cm) connected every 70-160cm with two horizontal beams-beddings (14x14cm) at the level of the floor and at the level of the roof. The connection of the vertical posts to these horizontal timbers was accomplished by a round tenon of about
  3. 3. 6.0cm diameter. The same construction detail was used for the connection of the posts of the timber colonnade of the façade to the beams at the upper and lower part (Figure 1a). All other vertical and horizontal timbers had smaller sections (7x12, or 6x13cm) and their joint to each other and to the vertical posts, was in most cases made through shallow grooves and an iron nail. The diagonal timbers were connected just with one iron nail (Figure 22). The timber frame walls where originally tied to the masonry stone walls of the upper floor by nails that connected their last timber post with the embedded in the stone wall, horizontal timbers (Figure 13c,e). The conscious attempt of the builders to use this timber system in order to reinforce and tie efficiently the “vulnerable” upper floor which is composed of differently constructed vertical load bearing systems (timber colonnades, timber frames and stone masonry perforated from openings) with various strength and stiffness properties, is obvious. It must be mentioned though that the rubble walls and arches of the ground floor were not connected to each other since they were built in different phases (Figure 3, phases 1, 2). All the walls (masonry and timber ones) were covered with plaster. only on the outer walls, as king post trusses do, but mainly on the internal ones (Figures 10,11)5. 3 PATHOLOGY The main structural problems of the building were: • The destruction of the continuity of the rubble walls along with the destruction of their horizontal timber reinforcing system, due to the interventions of the 19th and 20th century that changed the position of the openings. During the same interventions some parts of the timber frames were destroyed too (Figures 2a, 7). • The low quality of the rubble walls (three-leaf stone masonry with small stones and clay mortars). • The low quality of the lime mortar used for the brick infill of the timber frame walls, the lack of contact of this filling with the surrounding timber elements and the gaps (loose of contact) at the joints of the timber members (Figures 9b, 12b, 22). Figures 9a, 9b. Timber frame walls before and during restoration works. Figure 7. Longitudinal section showing the type 1 timber frame of the 1st floor before restoration works. The original openings were closed and a part of it was destroyed due to the changes of the last centuries [1]. Figure 8. Longitudinal section showing the proposal for the restoration of the timber skeleton. (based on drawing of G. Kizis, K. Aslanidis, Ch. Pinatsi). The load-bearing structure of the floor was made of simple supported timber beams, placed every 40cm, connected to the rubble masonry under them through the horizontal timber ties on which they were nailed on. The roof is a typical example of the “post and beam” system, a quite common type of roof in Byzantine and post Byzantine buildings in Greece and other countries around Eastern Mediterranean. It’s main structural characteristic is that the vertical loads are transferred from the closely set rafters (every 40-50cm), through a three-dimensional system of beams, posts and struts, not • The excessive deformation of the roof located at the central south part, due to the small section of the longitudinal beams that supported the rafters at the middle of their span. (Figures 10, 11, 19a). • The bending failure of the main horizontal beam on which the central part of the roof was resting on (Figures 11, 20a, 20b). As mentioned before, the loads from the roof are transferred at the outer walls of the building, but mainly at the internal longitudinal timber frame and the beam (19x23cm) which spans the opening that exists at the centre of the building. (Figures 8, 10, 14). It is interesting to be noted, the intelligent solution which the constructors of the roof invented in order to reduce the vertical loads transferred on this beam. The longitudinal timber at the ridge of the roof is supported by posts, every ~1.80m (see Figure 10, Φ1), except in the area over the beam (Φ2), where the posts are replaced by two diagonal timbers. These timbers transfer the loads at the supports of the beam under which the corner posts of the timber frame walls exist, reducing the bending stresses on the beam. It seems that this was not enough since finally a bending failure occurred. • The out of plain deformation of the longitudinal South stone masonry of the 1st floor (about 30cm!), mainly due to seismic action. The wall was kept in that deformed position due to an old retaining scaffolding (Figure 2a, 13a,b) which stopped working some months 5 For more details concerning the description, the pathology and the structural behavior of the “post and beam” system and of this specific roof, see [7].
  4. 4. before the restoration project starts. As a result, the central part of the wall collapsed (Figure 13b). Thankfully, most of this part would be demolished anyway since it was built in the place of the original timber projection “shins” (Figures 2b, 14). It is worth to be noted, that the rigidity of the transverse timber frame walls of the upper floor which were nailed at the timber ties of the South stone wall, was tested on site, since the seismic event/s that caused the detachment of the South masonry left no damages or deformations on the timber frames. The detached nails from the deformed masonry wall could be seen clearly (Figure 13e). a b c d 30cm Transverse timber frame wall (type 2) e Figure 10. Transverse and longitudinal section of the roof [1]. Figures 13a,b,c,d,e. The South masonry wall before restoration works (deformed out of plain and collapsed). 4 METHODS OF ANALYSIS AND NUMERICAL MODEL A detailed finite element model was developed for the numerical investigation of the seismic response of the monument, using linear analysis. The numerical analysis was performed using the ABAQUS software and shell finite elements. Figure 11. Three-dimensional finite element model of the roof. The numerical analysis verified the local structural problems. • The building remained exposed to the weather for several years and all the plaster from the walls was removed due to an unfinished restoration project (Figures 1a, 2a, 9a,9b, 12a,b,c, 18a). As a consequence, many of the timber elements of the roof, the floor and the external timber columns of the main facade suffered a lot from decay, but not from insect attack since the infestation that had occurred in the past was not any more in progress. Timber projection (“sahnisi”) Figure 14. Geometry of the numerical model of the whole building as it would be restored (phase 2). Figures 12a, 12b, 12c. Decayed timbers at the timber façades and the roof. The geometry of the numerical model (Figure 14), included all the architectural details of the 2nd and main phase of monument, as it would be restored. In this Figure, the rubble masonry walls are shown with green
  5. 5. color, the timber frame walls and timber columns are shown with blue color. The seismic vulnerability derived from the absence of connections between walls built at different periods or walls built with different structural systems (masonry and timber frame walls) was taken into account in the model using spring elements (Figure 14, red color). The soil under the footings was taken into account in the model with the depth of 5m in order to describe the soilstructure interaction effects. The soil was modeled as elastic material with Young’s modulus E=12.25MPa and Poisson’s ratio v=0.25 according to the results of the geotechnical investigation and it was considered mass less in order to prevent stationary waves. The walls were assumed elastic with properties depending on the different construction types. For the determination of the mechanical properties of the masonry, the method of homogenization was applied. The stiffness of each composite timber frame wall with infill of mud bricks was determined from the analysis of a standalone finite element model. Afterwards these composite walls were incorporated into the model of the monument with the use of equivalent shell elements. The timber posts of the main façade were taken into account as hinged beam elements constrained in plane by the compact baluster which was also taken into account in the model even though it is a non load bearing element. The roof was analyzed by a separate 3D linear finite element model (Figure 11). The reaction forces of the roof and the floor were applied on the finite element model of the whole structure and their deformable diaphragmatic action was taken into account using shell elements. Linear elastic analysis was applied for the investigation of the seismic response of the structure and for the assessment of the effectiveness of the strengthening measures. This approach is qualitative since linear elastic analysis is not realistic when the developed stresses exceed the tensile strength of the masonry. Elastic analysis cannot predict directly the real forces that will be developed to the horizontal timber reinforcement and the stone part of the masonry, since initiation of cracking leads to the redistribution of the stresses. Nevertheless, the positive effect of timber ties on the seismic behavior of masonry structures was taken into account for the proposed interventions, and consequently for the evaluation of the results of the numerical analysis too, estimating the forces of the embedded timber reinforcements assuming that the tensile strength of the masonry is zero6. According to the Greek Seismic Code, Athens belongs to the seismic zone I, in which the effective peak acceleration is 0.16g for seismic events with a return period of 475 years and 0.21g for a return period of around 1000 years (corresponds to an importance factor of 1.3). The response spectrum method was used for the seismic excitation of the structure for damping ζ=5% and soil category B (TΒ=0.18sec and TC=0.60sec). The natural modes of the structure were calculated and the corresponding eigenperiods were compared to the results from ambient vibration measurements of the real structure. In Figures 15 and 16 the minimum and the maximum principle stresses that were developed on the masonry walls are presented respectively, while in Figure 17 the relative displacements of the structure along X direction are depicted for triaxial earthquake. Figure 15. Minimum principle stresses – General view (combination g + q ± E). Figure 16. Maximum principle stresses – General view (combination g + q ± E). 6 [4], Vintzileou 2008, 970. “The experimental work presented in this paper has proven that timber ties act as confining reinforcement for masonry in compression, thus, enhancing its compressive strength and, much more important, enhancing its deformation at failure. Furthermore, it was demonstrated that timber reinforced masonry may sustain substantially higher shear load than plain masonry; it can also undergo large shear cracks without disintegration. These results seem to be in accordance with the observations made on historic buildings”. Figure 17. Relative displacements of the structure along X direction for triaxial earthquake. Taking into account the beneficial effect of the timber reinforcements, and that the maximum tensile strength of the masonry walls several months after the application of the pozzolan-lime injections, will reach 300kPa (see
  6. 6. 6.5), it is evident that the value of the tensile principle stresses are over the above limit at few and small areas and consequently there is no danger for the integrity of the structure. The minimum compression principle stress (500kPa) is lower than the compression strength of the masonry wall after the injections. The forces that were developed on the springs (Figure 14), were used for the designing of the steel elements that were used for the connection of the different wall systems along their height (see 6.6.1). The maximum developed acceleration at the level of the roof was 1g, considering the roof as an appendix. This value was used for the design of the steel rods that were used to connect the roof through the timber ties to all load bearing walls of the building (see 6.6.2) 5 DIAGNOSTIC METHODS The diagnostic survey was made by a multi-disciplinary team (architects, engineers, conservators, technicians), in order to be determined the condition of all the timber elements, load and non load bearing ones [7]. Various methods were used : ultra-sound, resistograph, along with the visual examination by the engineers and mainly the craftsmen and the conservators that had the opportunity to work on the material. All the above diagnostic procedure provided the necessary documentation for saving timber elements that otherwise could have been replaced with new ones. The examination of timber samples taken from different structural elements, proved that the wood species of the existing timbers was pine7. The systematic measurements of the moisture content of the existing timbers, was about 9-11%. The knowledge of wood moisture content was important because it is a limiting factor for the development of fungi and wood boring insects. Besides that, the new members and parts of members that were going to be used should be of the same species of wood and have almost the same moisture content with the existing ones in order to have similar structural and hygroscopic behavior. This was extremely important for new timbers that substituted decayed parts (wooden prosthesis) especially in areas, as the timber colonnade at the main façade, where the moisture content of the environment and consequently of the timbers has many and often fluctuations. elements (materials and systems in most cases reversible and compatible with the existing ones), avoiding cement or reinforced concrete. • Preservation as much as possible of the authentic material (e.g. minimization of replacements of timbers) using simple techniques in combination with more sophisticated ones [8]. In all cases, the new timber pieces can be easily distinguished from the old ones. A brief description of the most important structural interventions is following : 6.1 ROOF Concerning the reinforcement of the connections which most of them work in compression instead of tension, the use of screws, bolts and timber wedges, can secure the joints while the loads can be transferred through the simple contact of the members without the need of special cuttings. One of the most problematic joint of the roofs is the connection of the rafters to the tie beams, because of the decay problems that occur usually in that area. In “post and beam” roofs, the axial forces of the closely set rafters (every 45cm), are quite small and their joints to the tie-beams at the external walls, carry less loads compared to the loads that usually have the kingpost trusses at the same joint [7]. In some cases, as numerical analysis verified, these forces can be transferred by 2 screws (6-10mm in diameter) without taking into account the contribution of the cuttings. In the cases though that new timbers have to substitute the decayed parts, the formation of the connections can be made using simple methods and not necessarily specialized personnel (Figures 18a,b,c,d). a b c d 6 STRUCTURAL INTERVENTIONS The main principles concerning the restoration of the load bearing elements of the building were the following : • Preservation of the original and authentic structural system, even if it is not visible after the restoration works. • Reinforcement of the original structural system due to the fact that the building is located in a seismic area and its use will change (an old mansion will become a museum, which means high level of safety for the building and visitors), using mainly timber and steel 7 Anastasia Pournou, Department of Conservation of Antiquities and Works of Art, Technological Educational Institute of Athens, Greece. Figures 18a,b,c,d. Intervention proposal (18a) and different ways that the decayed part of the rafters and the tie-beams was substituted. As mentioned in pathology, the numerical analysis of the 3d model of the roof showed that the section of the longitudinal beam at the middle span of the rafters was inadequate. The proposed solution was the addition of new struts (more dense supporting) (Figures 19a, 19b), an
  7. 7. easy to apply and reversible intervention in order to maintain the original beam at its position. b Figures 19a, 19b. View of the deformed beam at the middle span of the rafters (19a) and its reinforcement by adding new timber struts (19b). The main timber beam at the central part of the roof was reinforced with carbon fibres tissues (FCU500/200) due to bending failure (see also pathology), (Figures 20a,b). 6.2 FLOOR The existing timber floors were replaced because of their bad condition ,with new timber ones (beams and planks 3cm thick). 6.3 TIMBER COLLONADE OF THE MAIN FACADE The posts of the main façade of square section (15x15cm) were severely decayed especially at their lower part (Figures 1a, 12a). In order to save as much as possible of the original material, the method of wooden prosthesis was used. The decayed parts, were removed and they were replaced with new timber pieces of the same wood species (pine) and of the same moisture content with the old ones (Figures 21a-d). The geometry of the ends of the connected timbers was decided not to be the same for every post since their decayed parts were different. As a consequence, the final connection for each post was decided after the decayed part was removed and the anaglyph of the sound part was revealed. For the most difficult cases the connection between the old and the new timbers was accomplished with carbon fiber bars (8mm in diameter) fixed 50cm at each piece with a bi-components epoxy resin8. The small c e Figures 20a, 20b. Bending failure of the main timber beam at the central part of the roof (20a). Reinforcement of the beam with carbon fibres tissues (20b). a d Figures 21a,b,c,d,e. Different ways of substituting the decayed parts of posts of the main façade and of a post belonging to a timber frame (21e). diameter of the carbon fiber bars gave the opportunity to have the needed strength and the minimum distances from the edges of timbers with small section, (15x15cm) (Figures 21b, 21c) . As mentioned before, simple techniques (Figures 18) were used in combination with more sophisticated ones depending on the importance of the architectural and structural role of each member, its pathology, its position, and the economy. For example, the connection of the post in Figure 21d was made just with a timber tenon and epoxy resin, while the connection of the posts that belong to timber frame walls (Figure 21d), was accomplished by the suitable formation of the ends of the two pieces, the use of stainless bolts and some times, not always, the use of epoxy resin at their contact area. 6.4 TIMBER FRAME WALLS • Reinforcement of all timber connections using at least 2 stainless steel screws of 6mm diameter9 and timber wedges in order to reestablish the contact of the timber members, where ever was needed. Two types of screws were used : type 1 with only a part of the shank threaded and type 2 with a shank fully threaded (Figure 22). Type 1 screws were used in the cases that a better contact of the timbers had to be assured, since 8 The accuracy of the work, and the specialized knowledge needed for using sensitive epoxy resins dictated after several tests with carpenters, the use of specialized in wood conservators with knowledge of carpentry under the supervision of the engineers. 9 Screws with diameter more than 6mm were causing splitting at the existing (old) timber elements, as the tests on site showed.
  8. 8. type 2 screws though they work better for tensile forces, they keep the distance of the connected members steady. Figure 22. Reinforcement of all the timber / timber connections of the timber frame walls using timber wedges and two types of steel screws. • Reestablishment of the contact (wedging) between the brick infill and the surrounding timber elements, using premixed, cement free, pozzolan-lime mortar. The same mortar was used for the reconstruction of the brick filling in the areas that the timber frame or the infill was destroyed from previous interventions (Figures 23a,b). For the same reason over the straps, a stainless mesh attached by nails was used too (Figures 28b, 28c). 6.5 RUBBLE MASONRY WALLS REINFORCED WITH HORIZONTAL TIMBER ELEMENTS • Consolidation and reinforcement of the rubble walls using premixed, cement free, pozzolan-lime grout for the injections, for the mortars and for the rejointing. • Preservation of the existing timber reinforcing system of the rubble walls of the 1st floor at the areas that the decay was superficial (Figure 5b, East wall). • Reconstruction of the timber reinforcing system of the South wall in places that the masonry had to be built again in order to be restored the original façade of the South wall12 (Figures 2b, 6a, 6b, 24a). The reconstruction of the timber reinforcing system was necessary too in some places at the level of the roof and the floor due to decay problems (Figures 30a, 30b). • Reinforcement of the original connection of the longitudinal timbers along the wall, using additional stainless steel metal plates and screws (Figure 24b). Figures 23a, 23b. Timber frame walls during restoration works. • Reinforcement of the overall behavior of the timber frame walls with an embedded in the plaster mesh of stainless10 steel, nailed every 20-30cm on the timber elements of the frame and occasionally at the mortar of the brick wall. The use of the steel grid was necessary for avoiding cracks at the plaster of a composite wall, made of materials (timber and bricks) with different physical and mechanical properties. Furthermore, its use can improve the in-plane and out-of plane seismic behavior of the timber walls without changing their stiffness properties 11. • The timber skeleton of the projection “sahnisi” that existed at the central part of the South wall (Figure 1b), was reconstructed according to the architectural study, without filling, covered with plywood in both sides (Figure 28a). In order the cohesion of the plaster to be increased, straps of plywood (20mm wide and 9mm thick) were nailed every 20mm on the plywood sheets. 10 The steel mesh had to be stainless because the mortar and the breathable ready-mixed plaster used for the timber frame walls was free of cement, consisted mainly of hydraulic asbestos. 11 The brick infill plays a significant role on the overall load bearing capacity of the timber frames. This role is not easy to be estimated through numerical analysis without experimental data which till now are unfortunately few, taking also in account the variety of the structural systems. (e.g. Santos 1999, Cóias e Silva, Vítor 2002, Ceccotti et al. 2006 [9]). a b c d View of the South wall (24a). Figures 24a,b,c,d. Reinforcement of the longitudinal connection of the timber ties by steel plates and screws (24b). The window frames were nailed to the timber reinforcing system of the wall using timber wedges (filling the gaps) (24c) and screws (24d). • Reinforcement of the rubble masonry around the perimeter of the openings increasing the section of the timber frames of the windows and the shutters, placed in outer and inner face of the walls, from 8x8cm to 8x13cm (Figure 24c). Their connection (their “sewing”) with several screws to the timber reinforcing system of the wall at the level of the lintel, the level of the sill and at the middle height of the piers (Figure 24d), provide 12 According to the architectural proposal, all the external stone masonries and all the internal ones at ground floor should be left without plaster and the wood species of their timber reinforcements should be oak (a more durable species) instead of pine.
  9. 9. additional confinement to the surrounding stone piers and consequently increase the strength of the surrounding masonry wall. The connection and interaction of secondary or non structural members (e.g. window frames) with the main load bearing system, has to be evaluated too even if it is hasn’t been taken into account in the numerical models. Their contribution to the overall behavior of the building may be important, especially as a second line of defence against a strong seismic event [6]. 6.6 Figures 26a, 26b. Plywood sheets were used between the horizontal tie-beams of the roof and the boards of the ceiling. 6.6.1 Reinforcement of the connection of the walls in vertical plane The built in different phases longitudinal and transversal walls of the ground floor were connected with stainless steel rods (d=20cm) every 80-100cm, fixed in masonry with non shrinkage cement mortar. At the level of the floor the arches were connected to the South wall using steel bars anchored in steel angles screwed at the timber ties. The longitudinal and transversal timber frame walls were connected to each other using stainless bolts or screws (d=12cm) every 80cm along their height. The rubble masonry walls of the 1st floor were connected with the timber frame walls using : - carbon steel screws (system WT, d=8cm) driven from the last timber post to the horizontal ties of the masonry (as the original connection was) (Figures 27a, 27b). - stainless steel plates and steel fasteners (bolts and screws) connecting the last timber post, the transverse elements of the timber ties of the masonry and the last post of the new timber skeleton of the timber projection (Figure 28b). As mentioned before, the steel rods were designed in order to withstand the forces that were developed on the springs used at the numerical model for the connection of the different wall systems. Figures 27a, 27b. Connection of last timber post of the timber frame walls with the longitudinal timbers embedded in rubble wall (red dotted lines), using carbon steel screws (system WT). INTREVENTIONS CONCERNING THE OVERALL BEHAVIOR OF THE BUILDING In order to improve the seismic behavior of the building the following measures were taken: 6.6.2 Connections of the walls with the floor and the roof (horizontal plane) The reinforcement of the diaphragmatic action of the timber floor was not proved by the numerical analysis to be necessary, since at the ground floor there are several transversal walls (massive or arched) in close distances 2.70-4.70m improving the out of plane behavior of the longitudinal walls. On the contrary, at the upper floor where less transversal walls exist, the addition of plywood sheets between the horizontal tie-beams of the roof and the boards of the ceiling (Figures 26a, b) was considered necessary in order to improve further the diaphragmatic action at that level even though the existing roof was quite stiff in space because of its structural system and its geometry [7]. The connection of the floor and the roof with the rubble walls of the building was accomplished using the existing horizontal timber system of ties on which the closely set Figures 28a, 28b, 28c. The connection of the timber frame walls with the South masonry wall was improved by the use of the steel plates and the steel mesh that was applied on both new and old timber frame walls. (almost every 40-50cm) horizontal beams of the roof and the floor were screwed on (Figures 30a,b). The horizontal beams of the roof were connected with the same way on the upper beams of the timber colonnade and of the longitudinal timber frame wall of the upper floor. These beams were connected with the transversal timber frame walls too (external and internal ones), with additional timbers and bolts. Special care was taken for the connection of the timber ties to the walls under them in order the seismic forces to be transferred from the horizontal to the vertical load bearing systems. At the level of the floor, the connection of the timber ties was accomplished using stainless steel rods of 12mm diameter every 80-100cm, fixed slightly inclined in the masonry with non shrinkage cement mortar. (Figure 30b).
  10. 10. authenticity of the “invisible” in many cases load bearing system. ACKNOWLEDGEMENTS Figure 29. The connection of the original timber tie with the wall at the level of the roof was not adequate. Authors wish to thank the Archdiocese of Athens for supporting the study and the restoration project, the Hellenic Ministry of Culture, the construction company, and mainly the conservators and the craftsmen that made this restoration work possible. Architectural design: G. Kizis, K. Aslanidis, Chr. Pinatsi. Structural design: E. Tsakanika, H. Mouzakis, E. Zarogianni. Supervision of restoration works: E. Tsakanika, V. Tsouras. REFERENCES Figures 30a, 30b. Connection of the new timber ties at the corner of the roof with half-lap joint secured with screws. The transverse timber pieces under the longitudinal timber ties can be seen too (30a). Connection of the timber ties at the level of the floor with the masonry wall by stainless steel rods (30b). For the design of the steel rods (see chapter 4). At the level of the roof except the above steel rods, an additional measure was taken. Transverse timber elements were embedded in masonry under the longitudinal beams, connected to each other by a screw of 8mm diameter (Figure 30a). This system of anchorage could be used in cases were no metal rods are available. The use the transverse timbers improves the connection of the two faces of the three-leaf masonry and the collaboration and cohesion of the timber grid with the surrounding masonry (a kind of mechanical anchorage in the wall). 7 CONCLUSIONS The positive effect of the timber reinforced or the timber based load bearing systems (horizontal and vertical ones) on the seismic behavior of historical structures, is proven in several cases all over the world for thousands of years. Quite a lot of work has been done concerning their typological and architectural features but less work, mainly in a qualitative way, has been done on their constructional and structural features. A better understanding of this kind of structures based also on experimental and analytical investigations (quantitative way) is very important too, since relative research works are very few especially if one takes into account the variety of the structural systems. The multi-disciplinary team that should work on a restoration project, must have the necessary tools to evaluate the existing condition of a historical building and moreover to select the proper interventions using innovative and/or simple techniques that will save the authenticity of our architectural heritage, including the [1] S. Lazouras, E. Tsakanika. A Traditionally Built House of the 16th Century in Athens. In International Timber Engineering Conference, pages 3.550-3.556, London 1991. [2] R. Hugues. Hatil Construction in Turkey. In International Conference “Earthquake Safe” Lessons to be learned from traditional construction”, Istanbul 2000. [3] P. Touliatos. The box framed entity and function of the structures. The importance of wood’s role, in Conservation of Historic Wooden Structures. In International Conference «Conservation of Historic Wooden Structures”, vol.1, pages 52-64. Florence 2005. [4] E.Vintzileou. Effect of Timber Ties on the Behavior of Historic Masonry. Journal of Structural Engineering, Volume: 134, Issue 6, 961-972, 2008. [5] National Technical University of Athens / Earthquake Protection and Planning Organization EPPO. “Investigation of timber reinforced masonry.” Research Rep., E. Vintzileou, P. Touliatos, and E. Tsakanika, eds. in Greek, 2005. [6] E. Tsakanika, Methodology concerning the restoration of Historical Buildings. Case studies : The Turkish Mansion and the Hagi Mehmet Aga Mosque in Rhodes. In International Conference «Conservation of Historic Wooden Structures”, vol.2, pages 194-203, Florence 2005. [7] E. Tsakanika. Byzantine and Post-Byzantine Historical Timber Roofs in Greece. Typical failures, misunderstanding of their structural behaviour, restoration proposals. In ICOMOS 16th International Conference «From Material to Structure», Florence 2007. [8] C. Bertolini, P. Touliatos, N. Miltiadou, N. Delinikolas, A. Crivellaro, T. Marzi, E. Tsakanika, O. Pignatelli, G. Biglione. The timber roof of Hagia Paraskevi Basilica in Halkida, Greece: Multidisciplinary methodological approach for the understanding of the structural behaviour. Analysis and diagnosis. In International Conference «From Material to Structure», Florence 2007. [9] A. Ceccotti, P. Faccio, M. Nart, C. Sandhaas, P. Simeone P. Seismic Behaviour of historic timber frame buildings in the Italian dolomites. In ICOMOS, 15th International Symposium, Istanbul, 2006.