26-07-2012, 11:46 AM
SEISMIC RETROFITTING OF MANI MANDIR COMPLEX AT MORBI
SEISMIC RETROFITTING OF MANI MANDIR COMPLEX AT MORBI,.pdf (Size: 1.05 MB / Downloads: 146)
INTRODUCTION
Morbi is situated in the western region of Gujarat at a distance of about 125 km from the epicenter of the
2001 Bhuj earthquake. The city is famous for its beautiful architecture, which is a harmonious blend of
Gothic, Saracenic, Mughal and Rajput styles. The imposing complex is made up of the Willingdon
Secretariat and the Mani Mandir temple (Figure 1a). It is scenically located on the western banks of the
1 Partner, Vakil Mehta Sheth Consulting Engineers, Mumbai, India and Seismic Engineer for ADB- Capacity Building for
Earthquake Rehabilitation and Reconstruction Project in Gujarat (TA 3644 –INDIA) 2001-2003. Email: alpa_sheth[at]vsnl.com
2 Senior Design Engineer, Vakil Mehta Sheth Consulting Engineers. Email: vmsb[at]vsnl.com
3 Senior Construction Engineer, Vakil Mehta Sheth Consulting Engineers. Email: vmsb[at]vsnl.com
4 Conservation Architect, Indian National Trust for Art and Cultural Heritage, Delhi, India.
Email: inheritarchitects[at]hotmail.com
5 Conservation Architect and Consultant, Indian National Trust for Art and Cultural Heritage, Delhi, India.
Email: malvikab[at]yahoo.com
N
Macchu River, just outside the fortified walls of the old Morbi town. The complex was built in the 1930s
by the ruler of Morbi. It comprises of a very ornate masonry building built in yellow sandstone in the
tradition of the Indo-Saracenic style of architecture. The Secretariat building has a large central courtyard
housing the Mani Mandir temple (Figure 1b). The total area of the Willingdon Secretariat is 4900m2 on
the ground floor and 4150m2 on the first floor. There is a part second floor of about 255m2. Prior to the
earthquake, important government offices occupied a portion of the complex. The extensive damage
suffered during the earthquake has left the building unfit for occupation and some parts of the building are
in imminent danger of collapse.
Seismic retrofit of historic buildings is not often carried out in India and there are no codes to guide such
retrofit. The project brief specified that the buildings be upgraded to meet the current seismic code
specifications. These are stringent and punitive for unreinforced masonry structures and the challenge lay
in a harmonious integration of seismic retrofit program with the architectural restoration and conservation
program (Penelis [1]).
The principles that governed the seismic retrofit program were:
∗ Avoid intervention to maximum extent possible.
∗ Introduce retrofitting measures in consonance with the heritage character and principles of
conservation.
∗ New elements must be non-intrusive and compatible with existing materials.
∗ New elements must not be a cause of further damage (such as corrosion).
∗ Retrofit measures must be easy to implement.
DAMAGE DOCUMENTATION
Original drawings for the building were not available; fresh measured drawings were prepared. Three sets
of condition surveys were carried out with the help of these drawings. Firstly, a macro-survey was carried
out, which helped in identifying grossly the areas of severe, moderate and minor damage, and also the
areas that required emergency interventions. Secondly, a detailed survey was conducted floor-wise, wingwise
to identify the types of damage. Thirdly, a micro-detailed structural survey was carried out room-wise
exhaustively documenting all damages including the extent of corrosion, the location of structural
members and their sizes, and the length and width of cracks.
Fig. 1: Mani Mandir Complex (A) View from Southwest Corner and
(b) Plan of Complex.
(a) (b)
Existing Structure
The Willingdon Secretariat was built originally as a two-storey complex with load bearing walls of soft,
yellow sandstone above plinth and black basalt stone below plinth. The walls are of 450mm thickness
above plinth. The stone is dressed and exposed on the external side and coated with paint or lime wash
internally. The masonry is of Ashlar-type. Stone blocks are not physically bonded to each other by a
clearly identifiable mortar layer and stay in place almost purely by bearing friction. Some of the stones are
locked to each other by means of wooden keys. Such keys are few and far between and were found
primarily in the chhatris (ornamental canopies) and shikhars (decorative towers) above the roof. The stone
blocks of pillars are socketted into each other by a small tongue and groove detail. The walls are
punctured at numerous places for doors and windows.
The floors are built of stone slabs of about 750mm width and of 200mm thickness. These slabs are
wedged between flanges of steel joists (Figure 2a). The joists rest on a stone cornice (made of cornice
pieces) running along wall lengths. A floor finish (of about 150mm thickness) was provided over the stone
slabs. There are arches along the external façade walls and internally across passages.
Damage Prior of 2001 Earthquake
The condition survey showed considerable damage to the buildings even prior to the 2001 earthquake.
General disregard and poor maintenance of the monument had caused deterioration in the form of
corrosion of steel joists, damage to cornice pieces at the steel joist locations, weathering and flaking of
sandstone, roof leakage and peeling of internal paint. The steel joists were corroded in almost all
locations, though to a varying extent. At the roof level, the joists were very heavily corroded and showed
separation of the flanges from the web (Figure 2b). Roof leakage appeared to have been a recurrent
problem. Numerous attempts to remedy this situation were evident; each attempt resulted in the addition
of a fresh layer of waterproofing. Three separate layers of waterproofing were observed, one on top of the
other, together adding up to more than 300 mm thickness. This terrace waterproofing had cracked heavily.
The general damage due to deterioration and weathering was less intensive on the first storey and very
limited on the ground storey.
Fig. 2: Details of Flooring (a) Stone Slab Wedged between Steel Joists, and
(b) Separation of Joist Flanges and Failure of Stone Slab.
(a) (b)
Damage in 1956 Earthquake
The structure appears to have suffered some damage in the 1956 Anjar earthquake (M6.1). The extent of
damage during the earthquake is not known but displacement of keystones of portals, arches and
movement of stones of walls seems to have occurred. Retrofitting measures were undertaken at that time.
Damage in 2001 Earthquake
The earthquake caused severe damage and collapse of a large number of elements above the roof,
extensive damage at the roof level, moderate damage at the first storey and little damage on the ground
storey. Staircase cap slabs, parapets, shikhars, arches, portals and chhatris above the roof were very badly
damaged; a large number of them were partially or completely destroyed (Figure 3a). The bastions at the
extreme corners of the structure sustained severe damage including partial collapse; the portions standing
are precariously balanced and have wide, through-cracks (Figure 3b). Similar observations were noted in
the temple where the corners have been severely damaged (Figure 4a). Stone weather-sheds at the roof
level were broken and destroyed at some places.
Fig. 3: Damage above Roof Level: (a) Destruction of Arches in Elevational Elements,
And (b) Partial Collapse of Bastions.
(a) (b)
Fig. 4: Floor Level Damage: (a) Out of Plane Collapse at Corners of Temple Portion,
And (b) In - Plane Separation in Slab along End Joist.
(a) (b)
Some portions of the roof slab suffered collapse. This was primarily observed in the regions where the
joists supporting the slabs rested on capitals of individual stone columns. These joists were significantly
corroded. A large number of cornice stones at the junction were cracked, locally crushed or dislocated. A
typical crack pattern was observed in the floor slabs: In many bays, there was a crack running parallel to
the joists all along the junction of the end joist (Figure 4b). Weather sheds were broken at this level due to
the falling debris.
At the first storey, almost all joints in arches and pillars opened out (Figure 5a). A large number of the
joints in walls also opened out in a typical diagonal pattern (Figure 5b). Cornices below steel joists were
damaged at many locations (Figure 2a). The arches cracked heavily and the keystone were dislodged in
most arches. Deformation of the arches was also observed. Many decorative galleries and some walls
show a distinct tilt; they have been pushed out and away from the building. Numerous wide cracks were
formed in walls. Many walls opened out at corners.
In the ground storey, there was no major seismic damage; the overall condition is reasonably good except
for minor cracks in walls and a few separation cracks at the crown of the arches. On the south and
southwest walls of the temple, heavy weathering was observed, possibly due to the effects of the
monsoon.
The foundations were excavated at two locations and inspected. No damage or differential settlement was
observed in the structure.
Previous Attempts of Retrofit
As mentioned earlier, there have been some earlier efforts to retrofit the buildings. Keystones of some
arches and stone blocks of a few walls and portals were stapled to adjacent stones, possibly as a response
to the 1956 Anjar earthquake. The steel stitching being stronger than the parent stone, caused local
crushing of the stone even though it prevented complete dislocation of the stone from the adjacent one.
(Figure 6a). There were attempts to contain the weathering of the buildings (Figure 6b). This was done by
insensitively plastering the surface with cement mortar. At one location, some arch pillars that had
weathered badly, had been fully jacketed in concrete.
Fig.: 5 Damage to Vertical Elements: (a) Openings of Joints in Arch, and
(b) Diagonal Cracks in Walls.
(a) (b)
BEHAVIOUR ANALYSIS
Poor Bonding Between Stones
As mentioned earlier, the Secretariat exhibits extensive damage at the roof level, moderate damage at the
first storey and little damage on the ground storey. One of the reasons for such behaviour is the poor
bonding between the stones. There is almost no mortar in the joints and in the absence of a bonding
material, the bond between the stones is derived from bearing friction. At the roof level as there is very
little load on the walls, the friction force will not be sufficient to resist the lateral forces.
Lack of Rigid Diaphragm Action of Slab
The structural system of the floor comprises of stone slabs with steel joists bearing on the cornice. The
cornice is marginally socketted into the wall. There is thus almost no diaphragm action of the floor slab.
As a result, lateral inertia force generated due to the floor mass is not transmitted to the walls in proportion
to their stiffness. Instead, it gets applied as a horizontal thrust to the masonry walls in their weaker
direction. This lateral force is in addition to the lateral force generated due to self-weight of these heavy
walls. The combined lateral forces cause significant out of plane deformations and subsequent damage to
the walls.
Relative Displacement in Slabs
As noted earlier, cracks parallel to joists are seen at some places on the underside of the slab, along the
junction of the joist and stone slab adjacent to wall. These cracks occur due to the relative displacement
between the rigid wall (parallel to the joist) which undergoes very little displacement, and the joist which
undergoes significant displacement (Figure 4b). There is also maximum damage to the cornice at this
location due to local crushing. Shear failure in the form of diagonal cracks (opening out of joints) was
observed in many walls. There was no crushing of stone in the walls. The damage is most severe in walls
that exhibit variation in the stiffness due to random locations of openings on different floor levels.
Reentrant Corners
The Willingdon secretariat is a building of immense proportions with a large central courtyard and several
internal courtyards in each of the wings. There are many reentrant corners thus formed. Expectedly, these
corners suffered damage of much higher magnitude than other areas. The highly stiff bastions at the
extreme corners of the building attracted very large forces and were severely damaged and collapsed
partially.
Fig. 6: Earlier Interventions towards Restoration: (a) Fastening of Stones
Using Mild Steel Staples, and (b) Repairing of Weathered Stone.
(a) (b)
Arches
The arches in the structure have cracked heavily and the keystone has dislodged due to the induced
tension in these arches during reversal of stresses. Dislocation (displacement) of the arch supports have
also caused the first hinge to form at the center of the arch in the seismic event.