The Mani Mandir complex (100m×100m in plan) is an important historic monument of the town of Morbi
in the western state of Gujarat, which suffered significant damage during the M7.7 Bhuj earthquake of
2001 in India. As part of the earthquake reconstruction program, the Government of Gujarat decided to
seismically retrofit this complex. The project was divided into two phases of design and execution; this
paper discusses the evaluation and design procedures recommended for exeuction. A detailed condition
survey was carried out and measured drawings were prepared. A comprehensive retrofit program was
formulated. Conservation principles, minimum intervention and consonance with the heritage character of
the building were important considerations in selecting the retrofit program. The complex was modeled
using finite elements and behaviour was studied of the existing structure as well as retrofit structure. The
retrofit measures recommended included discriminate use of internal reinforced concrete skin walls,
providing a rigid diaphragm behaviour mechanism in existing slabs, introducing stainless steel
reinforcement bands in the existing masonry walls, cross-pinning and end-pinning in walls and pillars,
and strengthening of arches and elevation features.
2. 100m×100m in plan
Historic monument
125 km from the epicenter of the 2001
Bhuj earthquake
Morbi in the western state of Gujarat
Western banks of the Macchu River
Built in the 1930s by the ruler of Morbi
Very ornate masonry building
INTRODUCTION
2
3. Contd.
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
Total area of the Willingdon Secretariat is;
- 4900m2 on ground floor
- 4150m2 on first floor
- 255m2 a part of second floor
Fig. 1: Mani Mandir Complex
3
4. Principles that Governed The Seismic Retrofit Program
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
4
5. DAMAGE DOCUMENTATION
Macro Survey
Identifying the areas of
severe, moderate and
minor damage
Areas that required
emergency
interventions
Detailed Survey
Floor-wise and Wing-
wise
To identify the types of
damage
Micro-Detailed Structural
Survey
Room-wise
Documenting all
damages including the
extent of corrosion, the
location of structural
members and their
sizes, and the length
and width of cracks.
5
6. Two – storey complex
Load bearing walls of soft,
- yellow sandstone above plinth
- black basalt stone below plinth
Stone is dressed and exposed on external side
- coated with paint or lime wash internally
Ashlar-type masonry
Fig. 2: Plan of Mani Mandir Complex
EXISTING STRUCTURE
6
7. No physical bonds between stone blocks
Stay in place by bearing friction
Some stones locked by wooden keys – Chhatris ( ornamental canopies)
- Shikhars ( decorative towers)
The stone blocks of pillars are socketed into each other by a small tongue and groove
detail
Floors are built of stone slabs
750mm width and 200mm thick.
Slabs wedged between flanges of steel joist
Fig. 3: Stone Slab Wedged between Steel Joists
7
8. Joist rest on stone cornice
Floor finish – 150mm thick
Arches along external façade walls
and internally across passages
Fig. 4: Separation of Joist Flanges and Failure of
Stone Slab
8
9. Damage Prior of 2001
Earthquake
Corrosion of steel joists
Damage to cornice pieces at the
steel joist locations
Weathering and flaking of
sandstone
Roof leakage
Peeling of internal paint
Damage in 1956
Earthquake
Displacement of keystones of
portals, arches
Movement of stones of walls
9
10. Damage in 2001 Earthquake
Severe damage and collapse of a large number of elements
Extensive damage at the roof level
Moderate damage at the first storey
Little damage on the ground storey
Staircase cap slabs, parapets, shikhars, arches, portals and chhatris above the roof
were very badly damaged
Bastions at the extreme corners of the structure sustained severe damage
10
11. Fig. 5: Damage above Roof Level: (a) Destruction of Arches in Elevational Elements,
(b) Partial Collapse of Bastions
11
12. Fig. 6: Floor Level Damage:
Fig. 7: Damage to Vertical Elements: (a) Openings of Joints in Arch;
(b) Diagonal Cracks in Walls
12
13. Previous Attempts of Retrofit
Keystones of some arches and stone blocks of a few walls and portals were stapled
to adjacent stones
Plastering the surface with cement mortar
Arch pillars had been fully jacketed in concrete
13
14. Fig. 8: Earlier Interventions towards Restoration: (a) Fastening of Stones Using Mild Steel Staples;
(b) Repairing of Weathered Stone.
14
15. BEHAVIOUR ANALYSIS
Poor Bonding Between Stones
Lack of Rigid Diaphragm Action of Slab
Lack of Rigid Diaphragm Action of Slab
Reentrant Corners
Arches
15
16. STRUCTURALANALYSIS
Material Tests
Modeling and Analysis of the Existing Structure
- Design Force Level for the Buildings
- Modeling
Verification of the Analysis and Structural Adequacy
16
17. METHODOLOGIES FOR REPAIR,
RESTORATION AND RETROFITTING
Elements to be Added/Enhanced for Improved Seismic Behaviour of Structure
- Introducing rigid diaphragm action of slab
- Enhancing Strength of the Structure
- End-pinning of Wall Corners
- Introducing Horizontal Reinforced Bands To Existing Masonry Walls
- Strengthening of Arches
- Cross-Pinning of Corridor Columns
- Stitching and Grouting of Cracks in Walls
17
18. Fig. 7: Location of Proposed Bracings and R.C. Skin Walls at First
Floor Level
18
19. Fig. 8: Sectional Details of Anchoring of Diagonal Floor Bracing in Walls
19
20. FIG. 9: Details of New R.C. Skin Wall (a) R.C. Skin Wall Nogged in to Masonry Wall;
(b) New R.C. Skin Wall Foundation
(a) (b)
20
21. Fig. 10: Intervention in Walls: (a) End Pining at Wall Corners;
(b) Seismic Reinforcement Bands
(a) (b)
21
22. Fig. 11: Detail of Interventions in Arches: (a) Strengthening of Arches Using Ties;
(b) Strengthening Of Arches by Pining And Reinforcement Band.
22
23. Fig. 12: Interventions in Vertical Elements: (a) Cross Pining of Corridor Columns
(b) Detail of Stitching Cracks in Walls
23
24. Areas Requiring Demolition and Rebuild
- Roof Slab
- Bastions
- Elevation Features above Roof (Chhatris and Shikhars) and Decorative Balconies
- Roof Parapets
- Weather Sheds
24
27. Conclusions
The total area of new reinforced concrete skin walls introduced is less than 10% of
the area of the existing masonry walls
The estimated cost of the proposed retrofit worked out to less than Rs. 4300/m2
Reinforced concrete skin walls, diagonal bracing on the underside of the floor slabs
for diaphragm action, horizontal stainless steel reinforcement bands in existing
masonry walls have been proposed to improve lateral strength and behaviour
Cross-pinning and end pinning have been recommended to improve the seismic
behaviour of walls, weather sheds and stone pillars
27
28. REFERENCES
Alpa Sheth et. al., (2004), “Seismic Retrofitting of Mani Mandir Complex at
Morbi, Gujarat, India”, World Conference on Earthquake Engineering, 2430;1-6
28