The most important bearing systems were developed in the mosques involving
the widest spans. The bearing system is inseparable from the interior space.
Designing the space implies conceiving how it will be structured and how it will
be covered. In Sinan's mosques, the bearing system is particularly clear and
rational. The outer shell and the interior space reflect each other. The bearing
elements do not turn into meaningless forms on the outer facade, neither
are they used for mere decoration. Sinan of course borrowed elements from
buildings erected before him, but he managed to develop new compositions and
variations out of these elements. The spaces he designed are usually covered by
domes, semidomes and trompes. At times, flat roofed cloister, but also cloister,
groin and cross vaults are used.
The dome is the uppermost element. It consists of a semi-sphere ending with a
circular base, which is placed over a cylindrical drum. It is supported by
exterior buttresses or small buttressed arches called flying buttresses. Most
often, the drum is not noticeable from the inside, although visible from the
outside. It is usually also pierced all around with a quasi rhythmic sequence of
filled and open windows. In the majority of Sinan's mosques, the domes are
between 11 and 14 m. in diameter.
The semidome functions as a sheltering element but also as a kind of prop
supporting the arch which bears the dome.
The dome usually covers a square, sometimes a hexagonal or octagonal prism.
The development of the polygon based dome plan in Islamic architecture owes much
to Sinan. The transition from the square or polygonal structure to the dome
circumference is provided through transitional elements. In the case of a square
base, these elements will be either trompes (Haseki, Hadim Ibrahim) or
pendentives (Uskudar Mihrimah, Edirnekapi Mihrimah, Sehzade, Suleymaniye, Kilic
Ali, Zal Mahmud).
In hexagonal based systems (Kara Ahmet, Molla Celebi, Kadlrga Sokollu, Atik
Valide), the transition to the dome's circumference will be ensured by small
pendentives, the main dome and the two trompes on each side of it covering a
rectangular surface. The transitional elements from an octagonal based structure
to the dome circumference (Rustem Pasha, Selimiye, Azapkapi Sokollu,
Nisanci) is achieved through little pendentives, the dome and its neighbouring: trompes this time covering a square surface. Sinan has enriched these
transitional elements with different variations. Trompes may be linked to wall
corners through pendentives (Molla Celebi, Atik Valide) or their typical
variant, stalactite vaultings or muqarnas (Kadirga Sokollu, Rustem Pasha). The
trompes themselves may vary, some of them being fluted (Haseki, Hadim Ibrahim).
Semidomes are linked to the bearing system with pendentives (Atik Valide,
Azapkapi Sokollu) or trompes (Uskudar Mihrimah, Sehzade, Suleymaniye). Windows
are placed at the bottom of the semidomes and trompes. If the span is very wide,
it is reinforced with iron beams.
In Sinan's works, this elaborate gradual rise from the external main walls up
to the, main dome is an important development which reinforces the relationship
between wall and dome from a structural point of view, and the relationship
between prism and semi or quarter sphere from a visual point of view. On the
exterior, the whole upper structure spreads out from the top like a pyramid
until it reaches the outer walls. It spreads from the main dome flanked with its
flying buttresses, the top part of the arches supporting it -which are often
graded (Suleymaniye, Edirnekapi Mihrimah, Luleburgaz Sokollu) -and the
stabilising turrets, down through the trompes and semidomes, all the way to the
cupolas capping the; galleries and the latecomers porch. This gradation has the effect of
emphasising the dominance of the dome without exaggerating it. Prisms,
cylinders, and semi and ; quarter spheres fuse together in harmonious rhythm and
symmetry. The whole weight of the structure is easily distributed onto the
ground, without the use of discordant elements of support tiring the eye or
confusing the mind.
Arches transfer the weight they receive from the dome, pendentives and walls
above them to vertical bearing elements. In Sinan's works, the dome lies on a
prism formed by arches. The number of these arches is four, six or eight. Some
semidomes and vaults seem to act like buttresses supporting the arches. Large
arches have their bay filled in with a windowed wall, so that light can
penetrate the interior. The Edirnekapi Mihrimah offers the most impressive
example of the use of such windowed walls, followed by the Suleymaniye and the
Selimiye. As the bay of the arch increases so does its soffit (in the
Suleymaniye, the bay is of 21.60, and the soffit of 3.35 meters). Arches are
interconnected with iron tie beams. On the exterior of the building, they are
made particularly apparent, which rhythmically enhances the general modular
system. Sinan mostly uses pointed arches in his works. They are double centred
or double centred tangent arches, their centers situated at a distance corresponding to three fifths
of their bay at spring line level. A study made on the windows in the
arch-bay-walls shows that 60% of them are situated slightly below, 20%
slightly above, and 20% t just on the springing line.
VERTICAL SUPPORT ELEMENTS
WALL AND PROPS
Only in narrow spanned mosques do we see Sinan use the walls
alone to support the dome, and even here, the presence of arches can be traced
on the inner wall surfaces. While the general bearing system consists of a
masonry wall structure, the load distribution is quite clearly defined, from the
covering elements downwards. This definition implies what may be called a
"masonry carcass" system, in which the weight of the dome is
transmitted to the large arches rising between their piers, and from there to
the piers themselves, as well as to the pilasters and buttresses. A system
which, in many places, I practically eliminates the need for bearing walls.
Walls are reinforced by pilasters especially where the arches are based. Such
props can be internal or external or situated on both sides. They can also be
linked to each other by arches. Mihrab protrusions reinforce the piers on which
the arches are based, as do the graded buttresses, which are more or less,
hidden within the galleries and porticoes. From the Sehzade onward, Sinan brilliantly manages to cloak the buttresses with the galleries and arcades he
designs on the lateral facades (also on the mihrab facade in the Selimiye).
Selimiye the stairs too are situated inside the buttresses.
In polygon based mosques especially, piers which are close to a wall are
reinforced by a special arch linking them to the said wall. In Sinan's mosques,
the mihrab wall is thicker because of the niche (the thickest is found in the
Suleymaniye, measuring 266 cm, the thinnest, at the Azapkapi Sokollu measuring
106 cm). In the side walls, the thickness is usually between 118 and 130 cm,
reaching a maximum of 230 cm at the Suleymaniye, and 106 cm at the .Azapkapi Sokollu.
The walls erected within the bays of the arches or between the buttresses are
usually pierced with numerous windows, their function being practically reduced
to that of partition walls. Sinan was particularly skillful at composing the
window layout between the arches. Such walls were also very skillfully used to
hide the thickness of arches or buttresses.
PIERS AND COLUMNS
Domes are most often supported by piers in Sinan's mosques. These piers are
in turn linked to the walls, pilasters or buttresses through arches. As the
number of piers increases, their cross-section gets narrower. Only in a few
buildings (the Kara Ahmet Pasha and Atik Valide mosques, and the Kanuni and Selim
II tombs), are domes supported by columns.
The larger polygon shaped piers or pillars (7.5 x 7.5 m. at the Suleymaniye)
may have their corners indented or a mihrab niche lodged into them, or else be
profiled, in order to be given a slimmer appearance.
ST ABILISING TURRETS
Sometimes piers may rise higher than the covering elements, and form
stabilising turrets which are usually crowned with a fluted dome. Weight towers
were erected to counteract the possible destabilising effects of lateral forces
on the piers.
Ottoman minarets are of an elegance rarely found in other Islamic countries, soaring like lances towards the sky. They are decked with one to three
balconies, which are reached by inner staircases. The steps of these Staircases
are shaped out of a single stone, with one of their sides forming a kind of ;
vertical core cylinder as they pile up in the axis of the minaret. The steps are
held together with tenons on the centre side which forms the core cylinder
while their other side is clamped to the minaret wall, the leaden binders used e
to reinforce the joints also serving to soften the horizontal strain caused by
wind or earthquakes. In the Selimiye, and for the first time, Sinan built
three separate staircases which reach each of the three balconies of the four
minarets without ever intersecting. The minaret's conical roof or spire is made
of timber rafters covered with roof boarding and sheet of lead, the spire cover
rest on a wooden pole planted in the central axis of the minaret.
BUILDING TECHNIQUES AND MATERIALS USED
The construction technique of the period basically perpetuated pre-existing
traditional stone and brick masonry practices.
Domes and vaults: They are made of special bricks and their thickness increases with their span. The thickness of the dome moreover gradually increases as
we near its bottom. Iron bands surround and reinforce the dome at the level of
the windows situated in its lower part, where they counteract its tendency to
widen. The outer surface of the dome is plastered with earth and then covered
with leaden sheets.
Transitional elements: Pendentives and trompes are made of stone, bricks or
alternate rows of each brick surfaces are covered with plaster or ceramic
tiles. Stone, bricks or plaster is used for the muqarnas or stalactite
Arches: Wide spanned arches are made of hewn stones, sometimes in alternate
rows of different colour. Arches with smaller bays are made of alternate rows of
stones and bricks or only bricks. Arches are linked to each other and on the
other sides with iron beams attached at the top of their supporting columns or
piers. Window arches have their outer side filled in with marble or stone panels
or geometrical lattices carved out of marble, while the inside is decorated with
geometrical motifs made of plastered bricks or a combination of stone, brick and
plaster, or else with tile panels or gypsum framed stained glass.
Eaves: In some buildings, very large eave overhangs supported by long iron props
can be seen in entrance porches.
Columns and piers: Columns used in porticoes and galleries are usually made of a
single piece of granite, serpantin, porphyry, pudding or breccia stone, often
brought from antique buildings. Newly made columns are made of Marmara marble or
Kestanbol granite. The ratio of their diameter to their length is approximately
5-7.7 in the galleries, 6-7.7 in latecomers' porches, 6-7 in courtyards
porticoes and 6-9 in external porticoes. Their capital and base are decorated
with a variety of diamond or stalactite (mukarnas) motifs. A rich diversity of
these motifs are readily used in a single portico's row of columns. Capitals in
late comers' porches are usually of the stalactite kind. The typical height of a
capital corresponds to 1.2-1.5 times the diameter of its column. A bronze ring
links the capital and base to the body of the columns. In 40% of the cases,
columns have no base.36 Certain base profiles resemble antique motifs while
others are of the stalactite type. As for piers, they are of a round or
polygonal shape, and made of quality hewn stones.
Walls: In large and quality buildings, both sides of the walls are made of hewn
stones, with the gap left in between filled with mortared rubble stone. The
stones of a facade may reach 40 cm in height. In buildings other than large
mosques, alternate rows of stones and bricks are sometimes used. The most common
recurring order consists of two rows of bricks, followed by one row of stones
and then three rows of bricks. Coarse Limestone, called kufeki or Bakirkoy stone
was mostly used, with lime mortar mixed with powdered brick serving as a binder.
Stones are also tied together with iron clamps. Horizontal reinforcing beams are
mostly wooden, with iron beams also used at times. A green colored tuff is used
for the foundations, which are widened towards the bottom. When the soil is poor
or loose, wooden stakes are planted and linked together with a system of wooden
beams, which is covered by a layer of mortar and then by the foundations proper.
Although it is built on solid ground, the Suleymaniye is supported by such a
grid of wooden beams.
Floors: Marble slabs cover exposed surfaces like courtyards. These slabs do
not usually form regular geometrical designs. The material is parsimoniously
used, chipped slab corners being frequently cased with correspondingly shaped
neighbouring slabs (casing technique). Inside the buildings, hexagonal, square
or rectangular shaped terra-cotta tiles are used.
Above text and pictures are from the book titled "Turkish Art and Architecture in Anatolia and Mimar Sinan".
You can purchase "Turkish Art and Architecture in Anatolia and Mimar Sinan" book and other Turkey related books from Explore Turkey Bookstore.