L&T-S&L have been involved in 2×660 MW Thermal Power Project as an architect engineer to a major EPC contractor in power industry. This project is based on environment-friendly supercritical technology which consumes less coal for unit power generation. It is one of the large projects in central India. As an architect engineer for the entire power project, the scope of structural engineer includes design of various buildings, facilities and equipment foundations namely: turbine building, turbo generator foundation, pipe racks and other plant and non-plant structures. Major portion of the total scope of steel is consumed in turbine building (TG Building) itself (approximately 65-70 per cent) of total 19,000 MT scope.
Picture Perfect
TG building – a 270m long, 42m wide and 33m high building – is the heart of the power plant housing major equipments like steam turbine, generator, condenser, boiler feed pumps, deaerator, cranes, etc. Geometrically, the building mainly comprises of two bays – turbine bay of 30m span and heater bay of 12m span. There are several equipment floors in the building to support equipment and piping. The turbine bay hall is provided with 30m roof girder. Moreover, for plant services, a cantilever steel support is provided outside the building. For operation and maintenance of the equipment, two cranes of 220 MT in simultaneous operation in Turbine Bay and single crane of 45MT in heater Bay is provided.
Steely Push
Due to large length, the building is divided into three portions namely Unit 1, Control Bay and Unit 2 by two expansion joints. The primary frame consists of moment resisting frame along transverse direction and braced frame along longitudinal direction. The secondary frame consists of floor/roof framing. High strength structural steel of grade E350 is used for columns, roof girders and framing beams along transverse direction. Structural steel of grade E250 is used for vertical bracings, tie beams, crane girders, floor/roof framing members, girts / side runners / wall beams, purlins and staircases.
The TG Building is built using approximately 13,500 MT of structural steel totally shop fabricated by an Indian supplier. Usually, client specification recommends use of steel as major part of building material for TG Building because of its high strength to weight ratio, high speed of erection, low maintenance costs and good behavior under cyclic (wind and seismic) / fatigue (crane) loads. Using structural steel as material, it is easy to ensure quality and consistency.
Color coated insulated sandwich panel is being used as façade of TG Building. RCC deck slab over truss/girder is provided as roofing system of the building. Structural slope and adequate waterproofing is provided to prevent ingress of water through roof slab. Internal floors/platforms consist of RCC deck slab/grating/chequered plate on steel floor framing.
A challenge of simultaneous engineering and fabrication for a heavy and complex bolted structure was attempted with positive spirit, collaboration with stakeholders and passion to achieve something which has no visible past references. A success was visible at every stage like engineering, procurement, management, fabrication, transportation, erection and quality assurance. Each stakeholder could benefit in terms of completion of scope in time, controlled cost and required quality. It also reassured the spirit of engineering profession “everything is possible… just attempt it with plan and zeal to achieve.
JIGNESH CHOKSHI, Sr. Dy. General Manager, L&T-Sargent & Lundy Ltd.
Changing Trend
Usually for an architect-engineer like us, the scope such TG building includes the detailed engineering and preparation of design drawings. These design drawings are then used by detailer to make the steel shop drawings to be used by fabrication workshop. Traditionally, especially in India, this building has been constructed with field weld connections. As labor requirement is substantial for field welding of the members and due to scarcity and increased cost of skilled welder, the trend has been changing slowly over past few years where the contractors have started relying on bolted connections.
As this is one of the long lead items and its erection needs to start within 10 months from the project award date, the fabrication needs to start quite early so that material can be shipped to site in time. This is one of the reasons due to which the choice for bolted structures is gaining popularity.
Timely Challenge
A major challenge for the bolted structures is that the member sizes are required to be finalized quite early so that the bolt holes at correct locations are punched. This results in limited flexibility to engineer and the task is to finalize most of the members in first place itself. Due to large size of the building and late procurement of critical equipment and associated piping and electrical services, the engineering of such building is done in progressive manner and usually, the entire building is progressively completed. Conversely, the bolted construction requires early completion of the engineering so that correct members are erected at site.
Innovative Solutions
To resolve this issue of progressive engineering, yet moving ahead for construction to meet project schedule, scope of making fabrication drawing was also included as part of detailed engineering. This has been a unique attempt that was planned to be implemented in a live project, which required unique and innovative approach. Probably, simultaneous engineering of the building with bolted connections and issuance of fabrication drawings has no past references.
A meticulous plan was made to meet such requirement, where there was no prior experience or references, we adopted latest technology of making fabrication drawings, unified design and erection drawings and also progressed on deciding connections for items that will be engineered progressively. To cater the needs of large volume of the work like updating the member sizes based on latest design, generation of design drawings for client submission, application of connections and generation of fabrication drawings, the work was performed on a shared platform. A proper control and monitoring mechanism was implemented to avoid discrepancies between engineered items and fabricated items.
This unique attempt has greatly benefited us, both in terms of time and cost, as entire work was done within same roof and did not required frequent communication with external detailers for design changes. No expediting was required from client side with external detailer or with engineer like us, as they got everything from one stop. This one stop solution resulted in a good progress on fabrication front and less involvement of multiple agencies. It took around 11 months to complete the detailed engineering of major portion of building and issuance of its fabrication drawings. A novel and unique approach adopted for assembly tagging and part tagging resulted in smooth fabrication at shop and uninterrupted erection at site. The initial planning with all the stakeholders of this task greatly benefited in making right sequences for each activity, thus resulting no excess material at shop or site as well as just in time material availability.
Fact File
Function: Power Plant
Architect: L&T-Sargent & Lundy Ltd.
Structural Consultant: L&T-Sargent & Lundy Ltd.
Tonnage: 13,500 MT
Status: Ongoing