Maker Maxity

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Mumbai, often referred to as India’s financial and commercial capital, is known as the “City of Dreams.” True to this reputation, the city's projects are often ambitious in both scale and vision. One such landmark development is Maker Maxity, a sprawling 20-acre integrated commercial, entertainment, and hospitality complex located in Mumbai's central business district, the Bandra Kurla Complex (BKC).

The hospitality component of Maker Maxity spans 1.2 million square feet and features two tower blocks, each comprising four interconnected towers. These towers, housing luxury-branded hotels, stand 16 stories tall with a combined total of 475 rooms. Beneath them lies a five-story podium stretching more than 800 feet from end to end—notably designed without expansion joints. The structure also includes three basement levels for back-of-house operations, parking, and services. Atop the podium, a roof deck offers a pool and restaurant with views of the Mithi River. While the design accounted for a future vertical expansion of five additional floors, this plan was ultimately set aside during initial construction.

The project's schematic design was originally based on a structural steel system featuring staggered trusses. However, recognizing that structural steel is relatively uncommon in large-scale hospitality and commercial projects in India, where its use is typically reserved for industrial structures, BASE (the Structural Engineer of Record) and the general contractor, Leighton India Contractors Pvt. Ltd., proposed an alternative solution. They converted the structure into an all-concrete system without altering the original design intent. This revised approach employed long-span post-tensioned beams spanning the building’s width and a distinctive floor system combining composite metal decks with concrete topping supported by the beams. The hybrid system was chosen to reduce or eliminate the extensive shoring and reshoring typically required in conventional concrete construction, ultimately accelerating the project’s timeline.

It's not often that a project begins with a firm "no expansion joint" directive from the client. Their decision was primarily based on the aesthetics of breaking up large open finished lobbies with expansion joints and their expression on the building elevation, in combination with high initial cost and long-term maintenance. Despite numerous discussions and requests early in the design process to incorporate an expansion joint at the podium levels, the response remained a resolute "No."

The podium, overlooking the Mithi River, gracefully follows the river’s flow with an elegant segmented shape. Each tower block comprises four distinct volumes, giving the exterior an architectural expression of independent buildings. The vertical transportation elements, such as elevators and stairs, were strategically clustered within one volume, with corridors extending to the remaining sections. This arrangement effectively reduced restraint to shrinkage and volume changes.

To further minimize restraint, the adjacent interconnected buildings primarily utilized planar shear walls oriented perpendicular to the shrinkage direction. Perimeter beams spanning between the demising walls of hotel rooms, which also supported the tops of large glazed openings, acted as supplementary moment frames along the building's length. These frames offered less resistance to volume changes compared to shear walls, helping to manage structural movement.

To control initial shrinkage in each tower block, a designated shrinkage strip (marked red) remained open for 28 days in the tower and 56 days in the podium. Additionally, a long delay pour strip (marked green) was incorporated into the podium to allow each tower block to undergo long-term volume changes and reduce cracking (Fig. 2). The contractor closely monitored the volume change during construction, and the long delay pour strip was closed shortly after the project was topped out.

In addition to shrinkage control, thermal loading was also considered in the design of the vertical and horizontal framing using a comprehensive 3D ETABS analysis model.

The podium's top at Level 5 was designed to accommodate various functions, including pre-function areas, ballrooms, convention spaces, and indoor pools. Achieving these large open areas using traditional flat slabs or one-way slabs would have required transfer girders at Level 6.

To address this challenge, a unique hybrid floor system was introduced starting at Level 6. This system featured long-span post-tensioned beams with clear spans of approximately 58 feet 6 inches, supporting a metal deck spanning roughly 15 to 16 feet, which served as sacrificial formwork. This one-way spanning metal deck hybrid slab was designed for the design loading with conventional reinforcement placed in the flutes. During construction, the metal deck was temporarily supported at mid-span or one-third points using post shores at a single level (Fig.3).
This hybrid system allowed the temporary shores to be removed within six days—significantly faster than traditional post-tensioned or reinforced concrete frames constructed in India, which typically require reshoring for 12 to 28 days. As a result, the system achieved a 60-75% reduction in framing manpower.

Below Level 5 and in the basement levels, traditional two-way flat plate framing was used.

The podium levels beneath Tower 8, located at the southwest end of the project, extended beyond the tower's footprint. This area housed a large double-height ballroom, with one half positioned beneath the tower and the other half occupying the expanded podium. Above the ballroom, a spacious outdoor amenity deck offered impressive views of the city.
Supporting half the tower's weight with a traditional transfer girder, as a result of single-span beams spanning the width of the building, proved challenging. The ballroom’s high ceiling requirements conflicted with the placement of a girder, and incorporating one at Level 6 interfered with the lobby’s space planning.

To address this, several design alternatives were explored. One option involved a Vierendeel truss extending from Level 6 to Level 20, while another proposed shallower transfer girders placed at four locations between Levels 6 and 20. However, both solutions resulted in beam and column sizes that clashed with the architectural facade, making them less desirable.
In parallel, a traditional transfer truss option was studied. This design featured a full-height transfer truss extending from Level 5 to Level 6, supporting the exterior columns from Level 6 to the roof (Fig. 4). The truss’s bottom chord spanned the entire floor height between Levels 4 and 5, which housed mechanical services. Openings were incorporated into the bottom chord to allow MEP ducts to pass through.

Ultimately, the transfer truss solution emerged as the most efficient option. It was also well-received by the client and architect, who embraced it as a striking design feature of the planned outdoor bar.

The basement levels of the project are situated below the surrounding water table, leading to significant buoyant forces. Based on seasonal fluctuations, the design water table level created a hydrostatic head of approximately 3 meters (10 feet). To manage the water table during construction, an extensive under-raft drainage system, including sumps and pumps, was implemented.

For the final condition, a hydrostatic slab was designed to withstand hydrostatic pressures of around 11.5 kPa (240 psf). The slab was designed to span between the footings, similar to how a reinforced concrete slab spans between drop panels. It was connected to the footing using pull-out dowels cast into the footing. These dowel bars were straightened during concrete placement for the slab, transferring the load from the slab to the footing (Figure 5).

To create a waterproofed basement (bathtub), a mud slab was laid as the bottommost layer, with a waterproofing layer placed on top. This waterproofing layer extended behind the basement retaining walls (on the soil side) up to the ground floor. The stitch slab and footings were installed above this waterproofing layer.

To reduce the hydrostatic head the slab had to support, a ballast layer of compacted fill was added beneath a slab-on-grade (Fig. 5). This fill layer also accommodated various subgrade plumbing, pipes, and other MEP conduits, facilitating easier installation and future access for maintenance or repairs within the waterproofed "bathtub."

The slab-on-grade was 100 millimeters (4 inches) thick and lightly reinforced, while the stitch slab was reinforced similarly to a two-way reinforced concrete slab, with the reinforcement placed in reverse to address uplift loads.

Turning ambitious visions into reality requires comprehensive analysis, careful planning, and purposeful execution. These elements were pivotal in achieving the client's goal. Various structural design solutions were thoroughly explored, with the final selections—including the hybrid floor framing, transfer truss, and stitch slab—chosen through a methodical process of evaluation and continuous collaboration with the architect and contractor. ■