351 Feet Tall Lord Shiva Statue in Rajasthan

*Making of a Monument: Engineering tall Steel-Concrete Hybrid Structure at Nathdwara, near Udaipur in Rajasthan

-By Er. Dr. Abhay Gupta, Director, Skeleton Consultants Pvt Ltd, NOIDA

Concept

A Gigantic 351-feet high Shiv statue is being constructed at the top of a 50m high hillock in the sitting position at Nathdwara near Udaipur in Rajasthan. Miraj group of Nathdwara is the sponsor of this 4th tallest statue in World. Originally the statue was proposed in all concrete but owing to geometric complexities and overall performance, Steel was chosen as main frame material on the suggestion of Skeleton. The base of the main statue approx. 60mx45m rectangular shape is representing a hill top. There is a Trishul standing by the side of the statue. The surroundings have been developed as a tourist pilgrimage place.

The main elements for creating this monument are architectural and aesthetics of statue in the desired expressions, Structural Engineering & Design of main frame supporting the external shell and the design of shell itself, site geology and slope stability, a resourceful construction agency with lots of rich experience and capabilities, a well-defined construction methodology for Foundations, main load resisting frame, external shell skin and finally the statue organ shapes.

Important steps

• Statue mockup finalisation


• Site geology and geotechnical investigations to understand the stability of hillock slopes and deciding proper foundations with ground improvement using rock anchors.


• Posture & expressions visualisation when viewed from ground to top and body proportions done by Expert Sculptor.


• Insitu concrete casting for each and every curve & cuts using full scale FRP moulds drawn from EPS foam dummy, employing a 6-arm robotic CNC tool and 3D digitisation.


• Accurate 3D modelling of continuously varying geometry and structural framing to provide stability of large cantilevers, on STAAD & TEKLA.


• Joint less 20000m2 of concrete skin casting using SCC & green cutting


• Integration of structural steel frame and concrete skin to yield a pyramid like rigid structure to last for 250 years.


• A 170-feet high free standing Trident by side of statue, made of Concrete stem and steel top.


• Wind tunnel testing at WindTech Sydney Australia to evaluate complex wind pressure from today to whole design life including future developments, using 726 surface pressure tapings, simultaneously recording and using HFPI.

Posture Finalisation:

The entire process starts with a small 20-30cm high basic conceptual model of statue. The process takes around 4-5 rounds of 3D scanning and digitization in order to properly enlarge the small idol to a gigantic statue in which at every stage 3D scanning, enlargement to next level size, mould making, dummy casting using PoP/ Metal or ABS, and reviewing the next level size, making corrections as per looks, aesthetics and expressions by sculptor. After such 4-5 trials of enlargement, approx. 1:10 to 1: 25 scaled model is achieved which then is used as basic reference for final full scale dummy preparation. 

 

Structural Design Parameters

The monument comes under the category of Irregular configuration buildings as per IS-1893(Part-1):2002. The Irregularity of the structure lies in both the planes, viz., horizontal as well as vertical so; steel members provide flexibility of configuration, construction and behaviour. Therefore, we use the dual system, i.e., Steel Beam-column frame arrangement with Concrete Shear Walls to cater for such an important structure where all lateral forces are resisted by concrete shear walls and steel frame takes gravity loads.

The external skin is a continuous concrete membrane and is subjected to significant temperature changes on outside and inside. No joints can be provided, except at few restricted locations which do not affect the aesthetics. So, the analysis of skin under the self-weight and wind forces shall be done considering the thermal stresses relevant to temperature changes at Nathdwara, which will be ranging from 0 degrees to 50 degrees Celsius. Also, the skin thickness has been designed for thermal gradient for the temperature difference on the outer side and inside. The design life of the structure is 250 years. Concrete for foundation and main internal frame is M30 and for external skin SCC M40 with special emphasis on lowest possible shrinkage/expansion characteristics.

For structural steel high strength (345/350Mpa) rolled steel sections like UB, UCs (from JSPL) with parallel flanges & closed sections has been employed. All connections have been using High Strength Friction Grip bolts with galvanisation. All reinforcement confirms to IS: 1786–2008 having minimum yield strength of 500MPa, but CRS grade.

Structural Planning

Structural frames have been modelled and analysed in ETABS & STAAD as a 3-D model. Based on preliminary calculations and past experience, at this stage, we considered two options, one is Raft Foundation with pedestals and other is Isolated Footings.

There is a huge platform representing Seat for Lord Shiva of about 110feet (33m) height over which Lord Shiva is sitting. The internal space has a Lift and a Stair case system for maintenance and monitoring purpose. Some internal floors also for common public usage and a museum.

External skin of statue has been made through In-situ concrete pouring in specially made glass-fibre moulds. To properly support this skin and transfer the wind forces/self-weight, a special non-corrosive connection has to be conceived and designed. The thickness of skin shell varied from 200mm to 400mm. For analysis and loading on foundations, average 250mm has been considered. External geometry of statue at every 3m interval has been used to prepare structural framing by superimposing all floor plans and arranging RCC walls & steel columns which can be taken through to maximum possible heights. Then individual level plans are reviewed and additional structural members have been introduced. Large cantilevers have been used in many parts using Hilti fasteners.

     

Wind Tunnel Testing

Generally, wind forces on tall structures are obtained from IS875-part.3, depending on the nature of structural system and height. In this case, as per dimensions of statue, the structure is a RIGID body and no dynamic analysis is required. However, the code provides data and information only for regular shapes and wind pressure variations on surface and base bending moments and forces cannot be determined by application of formula and procedure given in codes.

Owing to the complex geometry and several projected elements like Arms, Legs, fingers etc and due to sudden narrowing at neck section, free standing Trishul structure, Wind Tunnel test on a scaled model 1:200 is carried out at WindTech Sydney, Australia to obtain all the required information for design of skin shell, structural frame & foundations. 

Construction

After completing ground improvement using rock anchors, Raft foundations and Footings are cast, with RCC pedestals upto steel column base levels and foundation bolts are installed. RCC walls are also constructed in the shape of base hillock using ply shuttering. For superstructure, 3-4 levels of structural frames, including vertical, horizontal and bracing members, peripheral members should be fixed which controls the external skin shape. RCC shear walls which resist the lateral forces and provide stability to entire structure should also be cast with the steel frame and may advance 3-4 levels than structural frames. FRP moulds are then assembled from the bottom most layer as per identified sequence. These FRP moulds form only external shuttering. For internal shuttering, regular plain shuttering ply is used and arranged in straight lines. Entire perimeter is assembled and properly fixed in position as per designed thickness. Reinforcing steel is prefixed as per design and specifications. It is generally CR grade.

Once all arrangements are done and concrete is ready, SCC is poured in layers of 1.5m height. It is preferred to cast entire skin in lengths of not more than 30m at a stretch and leave gap of about 2m which should be cast later to allow for shrinkage. Then upper 2 more layers without removing the external GFRP moulds, in order to fix properly the lower layer. Curing should continue for 28 days minimum. Green cutting of joints should be adopted. Epoxy bonding agent should be used at all joints, where concrete is continued after a gap of 7-days. All peripheral steel members should be properly embedded with connectors in the skin up to half the thickness. All steel members should be connected to RCC shear walls using Hilti or equivalent post installed anchors.

Casting of special components like fingers, joints and other ornamental items should be taken after casting the primary skin surface. All bolted connections of steel components should be properly tightened once again before casting of RCC skin and any gaps should be packed with MS shim plates.
     

Fire Protection

Exposed steel components should be treated with fire resistant coatings as per statutory safety requirements. Cementitious vermiculite and active Intumescent coatings have been used for 4-hours of fire rating for all the areas where fire hazard is existing.

External Finishing

Once the entire skin casting is done, finishing from top has been started. Concrete skin is first sand blasted and made rough. A base coat of primer is then sprayed followed by protective and aesthetic 50microm copper metallizing spray. External appearance of statue is regularly evaluated by sculptor from all sides in order to make any changes in shape/size during the process.