Zeromile Warehousing Pvt. Ltd, a reputed name in the country in warehousing and logistics, approached the Consultant, Epicenter Consulting Engineers Pvt. Ltd., with their intention to develop a 36-acre land near Hyderabad (T.S) into a Warehouse Park. They wanted it to contain 4 giant warehouses, with a cumulative area of around one million square feet, and to be developed in different phases. The plan dimensions of the warehouses were decided by ZMW based on logistics and local regulations among other factors. Consultant was informed that the sub-soil strata consisted of shallow sheet rock for majority of the plot area, and that it was hard soil for remaining area.
As the 2 warehouses in ‘Phase-1’ were to be leased to MNCs that focused on e-commerce, cloud computing, digital streaming and artificial intelligence, Sundeep Reddy – ZMW Director wanted the warehouses and related infrastructure to be designed as per International Standards.
Before the Consultants took on the structural design, they had to work on, and freeze, some important design parameters such as warehouse height, roof slope, column spacing, fire protection methods, solar panel requirements, lighting, ventilation etc. The sub-soil exploration was considered as 10m deep boreholes, and 3m deep trial pits, scattered evenly over the site extent.
In view of the requirements for larger eaves height and greater column spacing, the “steel” gable frame emerged as the clear winner when compared with RCC frame or even composite construction with trusses. It was entirely structural steel from above the warehouse plinth. RCC was confined to sub-structure, while a 5′ high block-wall enclosed each warehouse.
Sundeep Reddy, with his rich experience gained over the years, has been actively involved in the architectural and logistic aspect of the project from the beginning. He made the Architects to work on a variety of options with regards to elevations, fascia, entrance, skylights, mezzanine layouts, canopies, docking and parking facilities from which the final ideas were selected and forwarded to ECE for the next phase viz. Structural Design, Tekla Modeling and Connection Design.
Warehouse in Phase-1 consists of a double-gable space frame with an area of 4,26,000 sq. ft., and had started initially as two independent units, 100mx177m each, spaced 10m apart. Subsequently, the units were merged into a double-gable unit as required by end user. It has already been taken by Mahindra Logistics, who as a 3 PL service provider will house Amazon as the customer.
Six rows of 16m span jack-beams run along the building length supporting rafters for alternate frames. Sheeting consists of seamless profiles from reputed Indian suppliers.
Both the side walls have 5m wide continuous canopies running along the building length in reverse slope. The warehouse has 26,500 sq. ft. of mezzanines, continuous roof monitors, firefighting system, sky lighting, ventilators & dock levelers in addition to an elegant fascia on its front.
Foundation consists of 200 footings, with an equal number of concentric pedestals, resisting wind shear and bending moments, in addition to the usual gravity loads. A 300mm thick RCC wall ties the edge pedestals, thus restricting their bending about their major axes, while retaining the 1.2m deep soil from within the building.
One of the challenges for Consultant was to limit steel tonnage to the least possible. With 13.5m eaves height and huge column free area requirements, this was not easy. The Consultants, therefore, worked with several permutations and combinations, varying support conditions, frame spacing, member profiles and even member releases, to finally arrive at the most economical structural configuration. Member profiles were based on moment envelopes, connections were both ‘shear’ and ‘moment’ type and adequate splices were introduced considering transportation limitations.
Restricting lateral sway, structure drift and rafter deflections to within limits was another big challenge. Structural design was done as per AISC–ASD, while serviceability criteria were based on MBMA-2006
Another design challenge was the fact that the ‘double-gable’ warehouse was to be built as two separate warehouses at different points of time, such that the functioning of the first unit would not have to be interrupted while the second unit was being built. This, therefore, required the structure to be prudently analyzed for below two scenarios:
- As two single units, 100m x 177m each (spaced 10m apart).
- As one single unit, 210m x 177m.
Member sizes governed by the above two cases were considered as the required sizes. Though steel tonnage increased slightly, this was necessary to account for effects of a possible ‘strong wind’ on the first unit until construction of the balance part viz. second unit.
To ensure uninterrupted operation of the first unit, steel brackets were designed and fixed to each column along common line. These would later support rafters of the second unit. Special precautions were taken for design of valley gutter, associated RWPs and internal drains in view of the huge contributory area from adjacent roofs.
Usually, economical configurations require extreme columns to be ‘fixed’, internal columns to be ‘pinned’ and columns for cantilevers to be ‘prismatic’.
Exceptionally high soil SBCs (200 ton/sq. m in present case) help reduce footing and pedestal sizes, even for fixed supports. Fixed column supports result in heavier footings and pedestals (60 per cent heavier in present case), but it brings down the overall warehouse cost by at least 20 per cent.
Though the total duration of Phase-1 including design, construction, fabrication, erection and flooring was initially estimated at 10 months, it is likely to exceed the schedule by at least 50 per cent because of Covid-19 pandemic.
Structural Analysis & Design: STAAD.Pro
Drafting: AutoCAD/ ZWCAD
Detailing/ Modeling: Tekla Structures
Footing & Pedestal Design: ECE Software
Wind Loads: ECE Template
Connection Design: RAM Connection/ ECE Software
Detailed Steel MTO : ECE Template
Client, Developer& PMC: Zeromile Warehousing Pvt. Ltd
Structural Consultant: Epicenter Consulting Engineers Pvt. Ltd
Steel Supplier & Fabricator: Kirby Building Systems
& Structures India Pvt Ltd
Architects: F6 Architects
Steel Tonnage: 2000 MT