“What we usually consider as impossible are simply engineering problems… there’s no law of physics preventing them.”

Nearly four years ago, I attended a meeting between Tata Steel and OVAL trust regarding finalizing a sculpture location in a City area of Mumbai which was being developed as a Garden for public. This Garden was being developed by my company for OVAL trust. Meeting got over after finalizing the location and with an instruction to do Soil Investigation at the location for the foundations for the sculpture. We finished the Soil Investigation and submitted the report to Tata Steel team.

After around 10 months later, I received a mail from one of the trustees Nayana Kathpalia that the sculpture would not see the light of the day as the agency which had taken the project for execution had declined to do the project. She did know that I was a practicing Engineer and possibly that’s the reason she asked me whether I would see if it was possible for me to take up the sculpture project which included design and installation. Accordingly, the concept line diagram was forwarded to me by the team. As an initial observation I realised that the sculpture in its present form had basic difficulties in being fabricated and built in the real world. Primarily it did not have a central axis to begin with around which the triangles would rotate.Moreover, there was no longitudinal continuity in the members i.e. triangles were disconnected from each other.

The constraints were also explained that the sculpture had be made in Hollow Steel Tubes “Tata Structura” of sizes readily available with the clients.

It was time to get into an agreement and start the project design. Costing and Agreement formalities took around three months and project started in February 2011.

The sculpture was finally put on to the design program input with sections as follows:

• The main central spine: Hollow Circular tube of 8mm thick 200mm diameter.
• Other three runners at each triangle ends: Hollow Circular tube of 8mm thick 200mm diameter.
• Triangles: 122×61 5.4 mm thick rectangular Box sections
• Foundations: Rectangular RCC pad of 9mx9mx1.0m depth

The real challenge were:

• How to build a 3-D structure with an available line diagram? Since the structure geometry was such that no two points were following a pattern, each node/ joint was unique
• The pipes were rotating through its central axis and the behaviour of the sections had to be analysed as a spring.
• Even if I understood how it would be executed, the same had to be translated into a working detail so that workers understand how the structure had to be built without which it all will remain on the drawing board only.
• The geometry defied an accepted principle of Design that the sections which carry more stress should have more cross sectional area. In the the case of Charkha, the initial parts were the smallest in dimension while the end cantilevered portion were the largest.
• There is an issue with pipes getting welded to the surface of another pipe with high stress concentration. This also had to be resolved.Locally the pipe could itself bend/ deform with compression. This was eventually resolved with grouting of the pipes reinforcements with Non-Shrink grout till 1/4th of the length of the each pipe from both supports. This also ensured that the moments got transferred to the base properly.

Modelling on computer:

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The execution team decided to build a 1-1 scale structure off site at our own workshop at Cotton Green, Mumbai. Base foundations were cast. On the foundation plane, a grid was marked as per the node points of sculpture as x-y axis. for the z dimension a 20 mm steel rod was used as a vertical bar( z axis) to locate the node.

It was time to start bending the pipes as per the curvature in 3-D. Main central spine Pipes were bent to shape and erected first. These pipes had to be supported on a rectangular steel cribs( trestles) as seen above. The second layer of three circular pipes rotating around the central spines were bent and erected supported again on cribs.

Now, finally the triangles had to be cut to shape and welded to the main spine. The issue with the triangular framing was that its plane was not orthogonal to the main spine and every triangle plane was at a varying angles. It also meant that the contact area would not be much and welding had to be very very accurate.

But the team was determined to bring this sculpture to shape and it is with this determination that next stages were achieved. Each stage was achieved with precision and supporting the each stage on cribs. The stages are

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In the end, entire 28 Tonnes of steel pipes were put in position and welded leaving some end parts to be fabricated at site. The next in line was to de-assemble this unit into transportable pieces as the site of work was around 6 kms away and through very heavy traffic. Moreover, at each cut location, pipe end portions a thick plate with pre-drilled holes had to be welded as collars so that this assembly could be put together again at site without much effort. Any directional change in the collars meant more problems in aligning at site due to the nature of the sculpture. The painting had to be done as well before transporting.

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After the painting, it was now time to transport the units( 7 in total) to site at Cross Maidan and finish the installation with final welding. The time of inauguration was nearing.

After the painting, it was now time to transport the units( 7 in total) to site at Cross Maidan and finish the installation with final welding. The time of inauguration was nearing.

The stages of erection at site

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The entire team worked continuously 24×7 for nearly a week to finish the erection, welding and Painting sequence to finally finish it on 2nd October, the Gandhi Jayanti when this sculpture, Charkha was slated to be inaugurated. There was a time during this period when the event management team, lighting and civil engineering team were working together.

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Inaugaration:

The completed sculpture “Charkha” in its full glory

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The team which brought this all together:

Sushil Singh, Shreepraksh D. Singh, Afrat Ali, Chandrashekhar Yedve, Sanjay Dalvi

Tata Steel: V Murali Krishnan, Girish Joshi, Kulvin Suri, Shenoy.

OVAL trust: Shirin Bharucha, Nayana Kathpalia