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 .
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
Eleftheria Tsakanika - Theohari, School of Architecture,
National Technical University of Athens, Patision Street 42,
10682 Athens, Greece. Email: email@example.com.
Harris Mouzakis, School of Civil Engineering, National
Technical University of Athens, Heroon Polytechneiou 9
15700, Athens, Greece. Email: firstname.lastname@example.org.
2.2 THE LOAD BEARING STRUCTURE OF THE
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
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
Different names of the horizontal timber reinforcing system
of the masonries are : “timber ties, ring beams, or lacings”,
“hatil”, “cator and cribbage” constructions , “ιμάντωσις”
in ancient Greek and “ξυλοδεσιά” in modern Greek .
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 .
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
, 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
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
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
only on the outer walls, as king post trusses do, but
mainly on the internal ones (Figures 10,11)5.
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
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 .
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
For more details concerning the description, the pathology
and the structural behavior of the “post and beam” system and
of this specific roof, see .
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).
Transverse timber frame
wall (type 2)
Figure 10. Transverse and longitudinal section of the
Figures 13a,b,c,d,e. The South masonry wall before
restoration works (deformed out of plain and collapsed).
4 METHODS OF ANALYSIS AND
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
Figure 11. Three-dimensional finite element model of the
roof. The numerical analysis verified the local structural
• 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
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
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
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).
, 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
6.5), 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 . 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
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 . 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 :
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 . 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).
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
• 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
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
easy to apply and reversible intervention in order to
maintain the original beam at its position.
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).
The existing timber floors were replaced because of their
bad condition ,with new timber ones (beams and planks
TIMBER COLLONADE OF THE MAIN
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
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).
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.
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
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.
Screws with diameter more than 6mm were causing splitting
at the existing (old) timber elements, as the tests on site
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
• 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.
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.
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 ).
View of the South wall (24a).
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
• 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
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
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 .
Figures 26a, 26b. Plywood sheets were used between
the horizontal tie-beams of the roof and the boards of the
6.6.1 Reinforcement of the connection of the walls in
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 . 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).
authenticity of the “invisible” in many cases load bearing
The connection of the
original timber tie with
the wall at the level of
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.
Figures 30a, 30b. Connection of the new timber ties at
the corner of the roof with half-lap joint secured with
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 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
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