Intricate And Challenging Projects In Prefabricated Concrete

 

Infosys Multi Level Car Park, Pune, India

Ajit Vasant Bhate

Managing Director,

Precast India Infrastructures Pvt Ltd

 

The Infosys Multi Level Car Park, Pune, India was a truly challenging project, constructed fully in concrete, without any other materials or finishes, with prefabricated elements and in-situ concrete combination. All aspects of design, viz architectural, structural, façade landscape and MEP services were tested to perfection and accuracy in a sustainable manner.

The execution of this project was a challenge under critical site side margins for construction (Use of a 50 ton rail mounted tower crane inside the footprint) and complex transportation requirements. There was a total of 3,500 elements in the building, consisting of 16 m span precast TT slabs, 15 m PC columns, and 1,300  façade elements around 7 m long and weighing 2.5 tons, triangular in profile, fixed in around 160 days on site. The challenges involved complex structural design in seismic zone 3 (Standard), amalgamating the structural and façade elements, methodical connections between column and column, beam and column, column and spandrel, spandrel and façade element, and façade element to element. The special challenges were overcome to transport elements from factory to site. With a very unique self-designed and electronically managed factory and site construction site coordination, culminating in the installation of all 3,700 elements within an erection tolerance limit of +/- 10 mm made this unique structure a truly award winning entity internationally, and ultimately featured it on the cover page of fib bulletin 78. In addition, describing this experience to all concrete lovers would also be a great challenge.

Introduction

With the steady rise in the Indian economy, the construction industry has become the second largest industry, which contributes to the country’s growth. This growth magnified demands for quick, clean and hassle free construction technologies and has thus, laid ‘concrete’ foundations for the precast technology in India.

The experience of evolution from conventional labour oriented projects to mechanized/industrialized construction techniques was path breaking. It commenced from the onset of investments, styles and processes of architectural design, execution of the project, mindsets of Consultants, technology transfer, and technical approvals, apart from maintaining quality, speed, and overcoming logistical constraints in India.

 

 

Precast India IPL, pioneering the Indian scenario in precast technology has always prided in accepting such challenges and exceeding expectations by creating exquisite structures despite all the odds; one such marvel is the Multi-Level Car Park built for their prestigious client, Infosys Ltd., in their Pune campus. This eye-catching half million sq. ft multi-level car park appeared as the cover page of fib Bulletin 78 and was also named as ‘The Outstanding Concrete Structure of India - 2016’ by Indian Concrete Institute (ICI), apart from winning numerous other awards.

The precast concrete elements in the building speak volumes about the innovations and the cutting edge technologies used for the construction of this magnificent structure. Concrete was chosen over glass after multiple considerations and advantages of sustainability, which resulted in excellent natural lighting and ventilation factors, minimizing future maintenance costs and enhancing safety. This project won special awards in architectural, structural, and precast construction categories, since each aspect was the culmination of a unique and detailed plan, from inception, to architectural design, structural design, production, planning, transportation, quality control, installation and handing over.

 

International Architectural Design Competition

To meet the client’s requirements of creating an exquisite structure and to elevate their internal performance benchmark, Precast India conducted an International Design Competition for the facade. Master Architects from countries like India, Peru, Germany, Spain and Greece brought out their best, and within 45 days, the winning entry from Arch Domingo Seminario was selected and signed off by the
Hon. Shri Narayan Murthy of Infosys, for execution.

 

 

The architecture of this structure is a perfect example of how uber modern structures can be designed to blend with the basic Architectural concept evolved from and resembling the warmth of woven wool, with a virtue of maintaining the architectural view and unharmed air circulation along with sufficient mild sun light entrainment in all the area.

The parking structure comprises of a basement + ten floors with parking capacity of around 1,300 cars. In addition to precast concrete columns, beams, double tee slabs, hollow core slabs, staircases, and spandrels, the uniqueness of the building lies in its stupendous
1,300 odd, 100 mm thick precast concrete façade elements[5], all of which were produced and transported from Precast India’s plant 45 km away from the site.

 

        

 

This is a one of its kind structure in India, with structural concrete prefabricated elements used so extensively for a façade, instead of glass or aluminium composite panels which are standards for external cladding or facades. Therefore, the execution of this project at the nascent stage of birth of Precast India Infrastructures Pvt. Ltd. was a huge challenge, successfully met.

Structural Design

The whole structure in seismic zone 3[1] was designed and analyzed in-house, by a team of experienced structural designers, led by
Prof. Sypros Tsoukantas and Mr. Tryfon Topintzis from Greece, with whom the credit lies. The structural design of the precast elements[4] was complex, as it involved intricate connections between prefabricated basement walls-columns/rafts, and floor to façade elements. The connections are ductile[3], sturdy, unyielding, and boast of a spandrel-façade element couple action with shear forces borne by the monolithic corbels in the spandrels, and interlocking of each facade element against overturning of the individual elements, weighing around 2.5 tons each.

 

 

The ductile[3] connection of façade element with building spandrell was achieved by the use of mild steel bolts forming couple to offer moment of resistance for 1.5 m cantilevering façade element. The use of mild steel bolts offer enough warning before failure in the seismic event.

Integrated IT Systems

Having a reputation for extensive integration of IT systems into all processes[9] and at all levels, the infusion of which has led into designing and executing many prefabricated concrete structures with great accuracy and precision, the complexity of this project was reduced to some extent with such integration. A 3D Tekla model including all reinforcements and precast connections was made; highly accurate production drawings were generated from this model and production of the elements was carried out accordingly.

Complete developed in-house, cloud based planning and tracking software – Protrak, generated production and erection schedule, along with sequence for installation and a full-fledged data base of elements. SuperSaas and Precast Logistics Software (PLS), the other in-house developed IT systems, facilitated online booking of resources (RMC, trailers, cranes) and logistics management respectively. Fully configured in-house version of SAP helped in purchase orders, material management and budget tracking. 3D BIM Tekla modelling helped in pre-engineering of mechanical electrical plumbing services in elements during planning which reduced mismatches on site.

Production

Believing firmly in preplanning of even the smallest details/activities well in advance before production drawings and unique element IDs, were generated in Protrak, to pinpoint the life cycle stages of everyone expedited from design stage up to final installation on site. Tracking and controlling quality with requisite record submittals to the client, transporting, stacking locations, installation, etc., in a unique self-designed web based format, fully acknowledged the strong and weak points of the internal execution system at that stage.

The state-of-the-art production facility, consisting of a hollow cores lab unit, carousel unit (for solid slabs and walls), mechanically and hydraulically operated adjustable beam and column moulds, giving smooth surface finish, special batching plants, tilting tables, shear cut bend lines (steel cutting), gantry cranes, steam curing facilities, etc., produced the entire 3,700 precast elements used in the project with utmost efficiency and quality, with a concrete grade of M40, similar to concrete in-situ.

All the risks and challenges like demoulding, lifting, installation and anchoring, etc., were eliminated, and structurally approved by casting sample prototypes multiple times, and subjecting mock-up representative elements to ultimate load application till failure.

 

Complex Elements Demanding High Accuracy

 

Quality Control Systems

Each element produced had to pass 10 stages of inspection before finally being installed at the site; the stages are- pre concreting, during concreting[6], demoulding, lifting, stacking pre delivery, pre transportation, unloading stage, pre erection, and post grouting.

Multiple tests on raw materials and load tests for representative elements were done and certified by third party testing agencies, before full scale production began. Each test and control greatly helped in achieving the high quality and consistency with regards to strength and finish, resulting in the life cycle of this award winning project today.

Stacking

Long spans and critical geometry of elements were a concern while stacking. A separate special support lifting system was designed in-house to de-mould and stack the elements, avoiding lifting and handling stresses; consequently, the façade elements were lifted delicately and quickly.

 

 

 

 

Transportation To Site

Transportation of delicate and fragile elements 45 km through the existing narrow and choked roads was a definite challenge, considering the road conditions; the lifting and handling stresses prompted attention to the economics in transporting multiple elements.

Consequently, transportation experts at PIIPL innovated a double decker transport assembly system, designed and fabricated as a removable attachment. Thus, shifting eight façade elements per trip improved installation speed to meet the target dates.

 

 

Installation On Site

The entire erection of the 3,700 elements was a perfectly pre-planned activity, even before the production planning, considering all the major constraints at site, like restricted side margin availability, limited access, availability of special tools and tackles, etc. The installation of the 1,300 odd façades was propitiously accomplished with an average erection time of
25 min per façade element.

For installation of TT slabs, columns, beams and other elements of the structure, a 50 MT rail mounted Liebherr tower crane was set up on rails in the centre of the building, considering element weight and available crane capacity at the required radius (16 Tons at
48 metres). Installation was done in three parts, each of which was checked for structural stability, even for seismic actions possible during construction phase. A 50 ton and 120 ton mobile crane was also used.

Accuracy, Tolerances And Precision

An overall accuracy between 10 mm and 15 mm was achieved without any adjustment anywhere, despite the complex nature of all the precast elements, especially the facade element used in this project. The 20 mm bolt in the façade element passing through the spandrel sleeve of 40 mm had an overall tolerance of 20 mm only, which had also already accounted for other tolerances during erection of foundations, columns, beams, etc.

 

 

 

This came as a result of constant coordination and exchanges between all the stakeholders[9], including design, planning, production, transportation and installation of all the elements.

Conclusion
Perfect coordination between all stakeholder teams ensured the creation of a milestone and a unique game changer in the Indian precast industry.

 

 

References

  1. BIS, I. (2000). Indian Standard (IS) Plain and RC-Code of Practice 2000. Bureau of Indian Standards.
  2. Standard, I. (1893). Criteria for earthquake resistant design of structures. Indian Standards Institution, IS, 1975.
  3. BIS, I. (1993). 13920 Ductile Detailing of Reinforced Concrete Structures subjected to Seismic Forces–Code of Practice. (India): Bureau of Indian Standards.
  4. Handbook, PCI Design. “Precast/Prestressed Concrete Institute.” Chicago 11 (1985): 11-18.
  5. BSI, B. S. 8110-1: 1997 Structural use of concrete–Part 1: Code of practice for design and construction.
  6. ACI Committee, & International Organization for Standardization. (2008). Building code requirements for structural concrete (ACI 318-08) and commentary, ACI.
  7. Ajit V Bhate, Jt. MD, Bhate and Raje Construction Co. Pvt. Ltd and MD, Precast India Infrastructures Pvt. Ltd., 2010-present.
  8. Precast India QAQC Manual, 2015
  9. Precast India MPFC (Meta Process Flow Chart) Document, 2015