Tsakanika_Icomos conference 2005 the turkish mansion the aga mehmet mosque
1. METHODOLOGY CONCERNING THE RESTORATION OF
HISTORICAL BUILDINGS
Case Studies : THE TURKISH MANSION AND THE HAGI MEHMET AGA
MOSQUE IN RHODES
E. Tsakanika Civil Engineer 1 - Lecturer NTUA Athens
Neapoleos 50 – 15123 Nea Filothei – Marousi, Athens
tel: 00301-6890146 e-mail :eletsaka@central.ntua.gr
1. Introduction
Cultural, historical and scientific reasons, dictate the necessity to protect and save our
architectural heritage, including their load bearing system, which is a very important factor
of their architectural value.
Ingenious systems can be found, that can surprise the modern engineer, who in many
cases realises, that he discovers through modern analysis what has been discovered
hundreds, even thousands of years ago with certainly much lesser means of technology.
There is a lot of "hidden knowledge" even in the most poor or humble ones, about the
effort of the traditional builder, to save his building and withstand the forces induced in his
structure with excellent results, giving us ideas and solutions for compatible and successful
interventions. The procedure of analysing and intervening has to be conducted with the
close collaboration from the beginning, of all the professions that must be involved in a
restoration project.
The methodology of studying and assessing the structural systems of the historical
buildings, has to be based on systematic survey, conducted and presented mainly in 3d
axonometric sketches and drawings, of the whole building and its structural details. Non
structural elements, their connection and interaction with the main load bearing system
has to be recorded too, and in some cases taken into account in the numerical models,
because their contribution to the overall behaviour of the building (good or bad) may be
important, especially in seismic areas.
The above described procedure for the evaluation and intervention has been followed in
the 2 case studies that are presented in this paper (constructional analysis and the
recognition of the structural system with detailed axonometric drawings and sketches,
recording of the pathology, and analytical models using finite elements). In these cases, as
in many historical buildings, very interesting constructional details were discovered, that
pointed out the effort of the builders to tie the building, in order to withstand earthquakes,
using, as usually, the timber parts of the structure.
The mentality of the interventions that were proposed was chosen compatible with each
structure avoiding strong interventions, reinforcing them, with light, reversible timber
diaphragms at the roof and the floor, using the existing timber constructional details for
the tying of the building, and the non load bearing parts (windows- partition members) as a
second line of defence against a strong seismic event.
1
2. 2.
THE TURKISH MANSION IN RHODES
2.1. Building’s Description - Pathology – Analysis – Assessment
It is a rectangular two-storied building, of general dimensions nearly 21.0×10.0, with
timber floors and a horizontal timber roof (photo. 1)2.
The present situation of the building has significant problems due :
to the moisture that has penetrated it’s inside causing decay to many timber
elements,
to the degradation of the porous stones,
and mainly, due to the earthquake, which is the most important problem, in a very
seismic area and for a very vulnerable structural system, with which the Turkish
houses of Rhodes are built. In these cases, almost all the masonries of the firstfloor are just ~22cm wide, built by one single porous stone, and completely
perforated due to many openings. (fig. 1)
Almost all these thin walls, have already profound from side-to-side cracks and
detaches, which appear on all the external and transverse walls. The back wall of
the 1st floor is of rubble masonry, about 65 cm width, and fortunately a part of the
façade is made of timber (fig. 1) .
The ground floor, which is made of rubble masonry walls, 60-70 cm wide and a
frontal arcade, of 25 cm wide, has no significant earthquake damages. (fig. 1)
The biggest “headacke” for the civil engineers was the justifiable intention of the architects
and the Supervision’s Committee, to reinstate the authentic morphology of the mansion
and as a result, to open up all the openings of the masonries of the 1st floor, that had been
built up during the last phase of the building and remained closed till now. (Fig. 2).
Usually, walls with so many openings and so closely placed are made of timber.
The building’s pathology was recorded in the corresponding drawings and the
mathematical analysis of masonry’s present situation, with finite elements, verified the
damages, the significant sensitivity of the monument in seismic events and the favourable
influence of forming timber diaphragms at the levels of the 1st floor and the roof (Fig 2).
A parallel systematic constructional analysis was decided to be performed concerning
mainly the timber elements and their structural details, using axonometric 3d drawings
and sketches.
The most important result of the above analysis was, the localization of a very interesting
and ingenious tying system of the building, with timber lacings in three levels of the
vulnerable 1st floor.(Fig 1,2)
2
3. In Detail
The 1st level of timber lacing, is on the top of all the walls of the ground floor (70 cm
wide) where two longitudinal timbers are placed and on which the beams of the floor are
based.
The 2nd level of timber-lacing is on the level of the lintels of the masonry of the first floor.
The timber lacing-lintel, has a cross-section of about 20/7 cm, that covers nearly their
whole width of the wall. Revealing and checking the connection of these timber lacings
atthe corners of all walls, it was found out the conscious attempt of the builders to form a
continuous system along the whole perimeter of the building, that joints efficiently the
corners internal and external, feature that is the main principal of any tying system (Fig 2).
The 3rd and most important level of timber-lacing at the level of the roof , (Fig 1,2), was
revealed after the removal of the earth over the planks.
In the central area of the building, timber elements of great dimensions were found,
with particularly impressive connections. Their existence is justified only as an
attempt to connect and restrain the timber wall of the façade, which has no
transverse walls and therefore, is very vulnerable in forces out of plan.
In Fig 2, the constructional details of the timber elements, revealed again the effort
of the traditional builder to tie his building.
It is worth saying, that in an American Manual for seismic areas, is proposed the
same structural detail for tying the diaphragm timber constructions of the floor and
the roof with the walls that are parallel to the timber beams.
The above mentioned analysis, both structural and mathematical, was the base of
designing the following described interventions. As already mentioned, these local
structural systems, are worth recognised and preserved, not only for theoretical and
historical reasons, but mainly for practical ones, since their study, dictates the appropriate
intervention for each one, avoiding repairs and reinforcements incompatible to the original
and existing structural system of the monument.
2.2. Description of the most important Interventions
Proposals for the masonry structures :
Replacement of all perished porous stones with new ones wherever this is possible.
Grouting and deep rejointing with mortars, whose compositions will be compatible
with the local used materials, without cement.
Good behaviour of the horizontal load-bearing elements and therefore of the whole
construction, mainly depend on the capacity of carrying the vertical loads and the
capacity of carrying and transporting the horizontal loads (earthquake and wind loads) to
the vertical load- bearing elements. Thus, the establishment of the diaphragm action of
the roof and the floo, and their connection to the masonry beneath, can improve the
aseismic behaviour of the building..
3
4. Proposals for the timber parts of the building :
The existing covering of the roof is replaced. The old parts of beams that can be
preserved and have proper dimensions will be reused.
The diaphragm action of the floor and roof is achieved by the use of plywood,
nailed on the main beams (Fig 3). This building, is one of the cases that timber can
be used on the top of the walls instead of the usual reinforced concrete belts, by
repairing the existing timber lacings. Timber connectors instead of steel ones was
proposed to be used, for the connection of the timber lacings to the masonry
beneath, it, because the steel ones in many cases have caused significant problems
to the porous stones of Rhodes (local climate conditions).
All decorative timber frames of the 1st floor, which are non-load bearing elements,
through proper design, are used as additional reinforcing systems of the whole antiseismic behaviour of the building (Fig 2,4)
Finally, on the internal sides of the openings of the 1st floor, the timber perimeter
frames of the windows, will be screwed to the timber lintels –lacings of the walls.
Their section will be increased and the rigidity of their corner will be reinforced
with metal angles. (Fig 5).
Detailed description of the above mentioned interventions can be seen
corresponding Figures and Tables.
on the
3. HAGI MEHMET AGA MOSQUE IN THE MEDIEVAL TOWN OF RHODES
3.1 Building’s Description - Pathology – Analysis – Assessment
Hagi Mehmet Aga mosque is on the first floor of a two storied building (Photoo2 –Fig 6)3.
The vaulted constructions of the ground floor belong mainly to Knight’s Period in Rhodes
and are consisted of masonries 50-80 cm wide, with limited openings and vaults 35 cm
wide. First floor is based on the construction beneath eccentrically.
In the mosque, two main structural phases can be recognized (1820 and 1875). During the
last one, all initial numerous openings were closed, either for architectural reasons or for
improving building’s earthquake behaviour. This intervention was made after repeated
catastrophic earthquakes whose epicentre was in Rhodes (1862, 1863, 1869, 1874).
The mosque, has been built with the typical structural system of the Turkish buildings in
Rhodes ( Fig 6).
This is a very audacious construction, of important height, consisted of walls in large
distance (from one each other), with just one transverse internal wall. All first floor’s walls
are one-stone masonry, by a single layer of local porous stone, 26 cm wide, reinforced in
5 levels by timber lacings. A particular feature of the structural system of the mosque’s
masonries, is the numerous levels (5) that these lacings exist, their connection with all
structural and non structural (morphologic elements) of the building, and their unusually
reinforced connections. The constructional survey and analysis of their structural details is
presented in Fig 6.
4
5. It was proved, that there was an initial design of the building, since a lot of its architectural
parts (external decorative projections, perimeter zones of ceilings e.g.) depend on the
position of structural member (timber lacings) and in many cases protect this system that is
mainly responsible for the safety of the building.
The floor is constructed of timber beams (6×14 cm) every 20-24 cm.
The building has a timber roof based on the last timber lacing on the top of the walls
(Fig 7) .
It has been built, so that the loads from the rafters are transported through the studs and
the struts to the horizontal elements ( tie-beams), which finally bear all the roof’s load
working not only in tension but mainly in bending, spanning 9.5 m. The above is
confirmed from the dimensions of the tie-beams (the cross-section is much bigger (19/25
cm) than the section of the rafters (9/16 cm) and from the way the members are connected
to each other. The studs and the struts are timbers of small cross-section (7×10 cm), their
connection to the rafters and the tie-beams are quite poor, working only in compression
and not in tension. Some of them are missing (Fig 7).
Mosque’s structural behaviour was generally satisfying, with mainly local damages.
The most important are presented consicely : cracks (top of vertical walls, lintels,
opening’s base,) due to earthquake forces in and out of plane. The biggest percentage of
timber lacings seems to be in good condition, although there are locations that appear local
decay. Floor’s condition is generally good.
Mosque’s assessment was completed with the mathematical analysis of the existing
structural system of the whole building (ground and first floor). The damages were
verified. The masonry was modelized by plane finite elements and the major roof’s
members, and timber-lacings by linear elements. At the same time another more detailed
3d mathematical model was used for the roof, using linear finite elements (Table 1). The
most critical parameter for the mathematical analysis of timber structures, is the
appropriate modelization, of the connections. For this roof, the modelization of the
inability to bear tension by the studs and the struts was taken into account using non-linear
analysis, the results of which were compatible to the behaviour and pathology of the roof.
Linear analysis gave false results, since most of the studs and struts were working in
tension suspending the tie-beamw from the rafters.
Through the above analysis it was verified that the structural behaviour of the roof was
generally satisfactory and that the main problems were the deformation of the tie-beams
and the inefficiency of the connections of the studs and struts .
3.2 Description of most important interventions
For the masonry, the decided interventions are almost the same with the ones proposed for
the Turkish mansion.
The basic principle forf the proposed interventions, was the preservation of the existing
load-bearing system, local repairs and minimization of replacements of timbers. For
timber lacings, it was proposed, preservation of their healthy parts, local replacements of
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6. the rotten areas and reestablishment of the continuity of the old and new parts. The timber
floor didn’t need any structural intervention.
The most important problem of the roof, as was mentioned before, was the deformation of
the tie-beam. The proposed interventions were :
Improvement of the original load-bearing system (since both studs and struts did
not function due to poor initial design of their connections) by placing suspension
steel systems to the tie beams, at middle of the roof, so that no bending moments
are introduced to the rafters (photo. 4)
Replacement of the missing struts and studs and reinforcement of their connection
by timber wedges and bolts. (photo. 3)
The connection of the rafter with the tie-beam was reinforced with a screw in order
to carry the additional axial forces that were introduced to the rafters from the new
steel suspension systems.
The above described reinforced structural system of the roof was calculated again, using
new mathematical models. It was found, that the existing cross-sections are now sufficient
and no extra reinforcement or replacements of the timber members is necessary.
For the establishment of roof’s diaphragm action and its connection to the masonry
beneath it was proposed :
The use of plywood instead of timber planks
connection of the roof to the timber- lacings at the top of the walls, by metal plates,
and galvanized screws,
connection of the timber lacing to the masonry beneath, by timber dowels of
diameter not greater than Φ14.
The use of more in number timber dowels and of smaller diameter, was preferred, so that
the seismic forces are spread in a better way, and probably, greater energy absorption
(photo 5).
The use of timber dowels instead of metal ones, was dictated mainly by the poor behaviour
of steel connectors in the porous stone of the constructions in Rhodes, and by the need of
using new methods of reinforcement, more compatible with the existing local traditional
structural systems and with the problems which they present.
Notes
1
2
3
Working group for the restoration of the Turkish Mansion in Rhodes : E.Tsakanika, K.Athanasiadou, Civil
Engineers
Working group for the restoration of Hagi Mehmet Aga Mosque in Rhodes : E.Tsakanika, K.Athanasiadou
Civil Engineers Collaborators: T.Rozos, P.Manolatos, Civil Engineers
Architectural survey of the Turkish Mansion in Rhodes : Mr Pitsinos.
Architectural study for the restoration of the Turkish Mansion in Rhodes : G. Dellas, M Zerledis
Architectural survey and of the Hagi Mehmet Aga Mosque in Rhodes : S. Vogiatzis, R. Oikonomidou
Architectural study for the restoration of the Hagi Mehmet Aga Mosque in Rhodes : R. Oikonomidou
6
7. Bibliography
1) Ε. Tsakanika, S. Lazouras, “A traditionally built house of the 16th century in Athens”
proceedings of the INTERNATIONAL TIMBER ENGINEERING CONFERENCE, London,
1991, vol. 3
2) P. Touliatos “Seismic Disaster Prevention in the History of Structures in Greece”,
Proceedings COST ACTION E5 , “Τimber frame building systems – Seismic behaviour of
timber buildings – Timber construction in the new millennium” Venice 2000.
3) Ε. Tsakanika “THE APPLICATION OF EUROCODE 5 AND 8 IN MODERN AND
HISTORICAL TIMBER STRUCTURES General principles of design» Proceedings COST
ACTION E5 , “Τimber frame building systems – Seismic behaviour of timber buildings –
Timber construction in the new millennium” Venice 2000.
4) P. Touliatos “ The construction as a 3d space unit during the dynamic loading. The role of
wood in the relevant techniques” Proceedings CULTURE 2000, “ WOODEN HANDWORK /
WOODEN CARPENTRY : EUROPEAN RESTORATION SITES ” Porto 2000.
5) P. Touliatos, Ε. Tsakanika, «Examples of the timber construction in Islamic Historical
structures in Greece. Αn Islamic mosque in Kos – A Turkish mansion in Rhodes. Proceedings
CULTURE 2000, “ WOODEN HANDWORK / WOODEN CARPENTRY : EUROPEAN
RESTORATION SITES ” Porto 2000.
7
8. Phot.1
Existing beams of the flat roof
based on the internal timber lacing.
On the only wall of the first floor 65cm wide, two
timber lacings have been placed of a cross-section
nearly 10/10 cm.
Structural model.
(2) Small length timber elements nailed
to the side of the beams and to both
timber tie-beams of the East wall (width
60cm) connecting the construction of the
roof to the walls.
(1) Small timber elements nailed to the last beam
and the to the timber lacing at the top of the wall.
The last beam parallel to the thin wall has grooves
on which timber elements of the same cross-section
are connected in its plane. These transversally
placed elements connect the parallel beams of the
roof to the timber lacing of the one-stone wall. This
structural solution is found rarely and is an attempt
to connect the load-bearing system of the roof to the
transverse walls.
(4) At the place of the fire-place
where the timber tie-beams had to
be cut, metal straps were securing
the continuation of the timber
lacing.
(3)
The use of the diagonal timber element is reinforcing the corner of the building.
Fig.1 The constructional analysis revealed the effort of the traditional builder to tie the walls of the building in order
to withstand the severe eartquakes of the area.
Timber tie beams
Timber wall of the façade
Timber decorative frames
Timber tie beams
Fig.2 Axonometric view of the
existing structural system of the
building
The width of the stone
walls of the first floor
(external and internal) is
25cm and full of openings
Lack of transvere walls
The width of the stone
walls of the ground floor
60-70cm
9. Λ1
Proposed constructional detail for the connection of the timber
roof diaphragm to the East wall (thickness 60cm).
Τimber lacings
10/14 cm.
RC belt.
Μasonry of rubble stone
Back wall of 1st floor.
Λ2 Proposed detail for the connection of the timber roof diaphragm
to the thin internal and external walls (thickness 25cm).
final surface (mortar
reinforced with fibers)
water proof membrane
plywood
battens 6/6-insulation
plywood
roof beams – new ceiling
Different ways of screwing the timber lacings
and the above diaphragm to the walls, using
timber elements.
the decorative
elements help the
collaboration of the
main structural
members.
timber lacing 25/10cm.
Λ3
For the tying of the
walls parallel to the beams,
the
existing
timber
constructional details
are
going to be used.
Λ1
Λ3
Λ3
Λ2
plywood sheets
Fig. 3
Proposals for the establishment of diaphragmatic action at the roof level, using light
reversible diaphragms of plywood, nailed to timber lacings (tie beams) at the top of the walls.
10. Fig 4. Reinforcing of the building using the existing decorative frames.
The frames will be reconstructed
using an one piece strong timber
element for their corner
They frames is proposed to be
connected to the timber lacings of the
longitudinal walls helping their out of
plane behaviour in a seismic event.
Timber decorative frames of poor construction .
Fig 5.
The timber perimeter frames of the windows, will
be screwed to the timber lintels –lacings of the
walls, their section will be increased and the
rigidity of their corner will be reinforced with
metal angles.
The “non load bearing parts” of the building
(windows and partition members Plate 3.)
are used as a second line of defense for a
strong seismic event
Kalamata earthquake – Greece
Photo. P. Touliatos
11. Fig.6.
Axonometric view of the
Mosque of Hagi Mehmet
Aga – Constructional
details of the timber lacing
system of the building.
Structural model
Λ3, Λ4.
Metal plates and nails are reinforcing the connection
of the timber lacings at the corner of the building.
1st, 2nd level of tying
3d, 4th level of tying
5th level of tying
Λ7.
Timber lacings at the level of the floor.
Photo 2.
Λ2.
Longitudinal connections of the timber lacings.
Λ6. The external decorative projection
is based on the 3d lacing. The presense
of this projection is protecting the 3d
and 4th timber lacing
12. Central part of the roof.
Φ1
Φ2
Φ3
Fig 7. Axonometric drawings of the structural system of
the roof and the connections of the timber elements.
1.8
0.5
1.8
-0
The building has a timber roof based on the last timber lacing
on the top of the walls (Fig 7) .
1.8
1.8
0.5
-1.3
-1.3
It has been built, so that the loads from the rafters are
transported through the studs and the struts to the horizontal
elements ( tie-beams), which finally bear all the roof’s load
working not only in tension but mainly in bending, spanning
9.5 m. The above is confirmed from the dimensions of the tiebeams (the cross-section is much bigger (19/25 cm) than the
section of the rafters (9/16 cm) and from the way the members
are connected to each other. The studs and the struts are
timbers of small cross-section (7×10 cm), their connection to
the rafters and the tie-beams are quite poor, working only in
compression and not in tension. Some of them are missing.
-1.5
-1.3
-1.2
-3.4
-6.9
-9.0
-9.9
0
-9.9
-9.0
-6.9
-3.3
Equivalent structural system Φ1
Without studs and struts.
The loads are not transferred from the rafters to
the tie-beam.
0.2
0.7
0.6
2.8
2.9
2.8
2.9
37.1
8.2
8.2
6.2
0
11.3
24.8
33.9
18.4
37.1
11.3
33.9
24.8
Plate 1. Structural model of the roof – Non linear
analysis.
0
For this roof, the modelization of the inability to bear tension
by the studs and the struts was taken into account using nonlinear analysis, the results of which were compatible to the
behaviour and pathology of the roof.
14. Reinforcement of the joints with bolts
Steel suspension system
Photo 3,4.
Τhe proposed interventions for the roof of the Mosque during
the restoration works.
Steel suspension system
Photo 5.
Τimber dowels for the connection of the timber lacings to the masonry below.
