L&T Realty, the real-estate development arm of Larsen & Toubro has a presence in Mumbai, Bengaluru and Hyderabad. Its international presence includes sales and marketing representatives in Singapore, Dubai, UK and the USA.
L&T Realty is committed to creating landmarks of excellence, and aims to enrich people’s lives through sustainable developments. It’s vision is to become the most respected real estate developer of the country by building on its execution leadership and by honouring the dual commitments of quality and delivery timelines. L&T Realty’s portfolio consist of 59 million sq. ft. of residential, commercial, retail and transport-oriented development.
Approximately 25 million sq. ft. is a commercial, retail and transit-oriented development which has a direct link with the use of structural steel.
To make any project successful speed, quality and cost are the three major attributes. When we talk about speed and quality, we believe that there is no match to structural steel as a primary construction material, and as far as cost is concerned, economies of scale (i.e. enhanced usage of structural steel) will certainly help in matching the cost to the conventional RCC construction.
Structural steel also becomes very much important keeping in view the recent changes in public policies. For example, the introduction of MAHARERA (real estate regulation act) ensures that the developers not only deliver on time, but also quality and cost aspect of the product are taken care of with 100 per cent transparency.
In a nutshell speed, quality and cost are three attributes which are going to govern the future of building construction industry in India, and it is safe to trust that the maximization of structural steel consumption will take us closer to the achievement of our business objectives.
L&T Realty realize that before starting conceptual design of any project, the developer should direct the Architectural Consultant, Structural Consultant and Services Consultant to start working closely with the project manager to ensure that the cost, time and quality aspects are maintained during the entire lifecycle of the project.
Let us illustrate with an example. If we look at cost bifurcation of any building project, we realize that approximately 70 to 74 per cent of the total cost is attributed towards core, shell and MEP works. The remaining 26 to 30 per cent of the cost is associated with finishing. We also understand that approximately 85 to 90 per cent of the cost is finalized on design table.
If we co-relate cost, time and quality as variables, it is understood that if we take charge of this 70 to 74 per cent of the cost to achieve desired speed and quality, the same will offer a lot of relief to remaining 25 per cent of finishing work which can be worked out in close co-ordination between project manager and the architectural consultant. This is one reason that Larsen & Toubro have chosen to proceed with development of in-house design teams.
L&T Business Towers
L&T Business Towers are located at the junction of Saki Vihar Road and JVLR (Jogeshvari-Vikhroli Link Road) which is popularly known as gate number 3 of L&T. This project is being constructed for the captive consumption of Larsen & Toubro. These two towers are exclusively designed by Larsen & Toubro and are being constructed by L&T Construction which is the largest construction company in India. These buildings are designed and constructed as per the LEED Gold rating norms.
These buildings consist of:
• 1-basement in RCC with 2-podiums,
• 1-stilt & 16-typical floors in composite structural steel.
• Floor plate area is 30000 sqft.
• Column free space is around 13m.
• Floor to floor height is 4.2 m
Evolution of Design – RCC to Composite Steel
We started designing business towers as conventional RCC buildings. Simultaneously, the soil investigation work was taken up by FUGRO. They investigated 24 boreholes along with the geophysical studies of the plot. As we entered design development, we started understanding the following constraints:
- The senior management of L&T gave us a challenging task of completion of this 11.25 L sq. ft. BUA building with fitouts within 27 months
- The FUGRO investigation revealed that Basalt of very high compressive strength was available at very early depth of 2m from the natural ground level
- In RCC structure it was also realized that reinforcement cutting, bending & placing in vertical elements is going to consume considerable time.
- L&T’s Powai development is in the close vicinity of the Mumbai airport runway & therefore the building height is restricted
- Looking at the plot geometry it was clear that the site was a logistics nightmare.
To summarize the change in design from RCC to composite steel
with concrete filled tubes is helping L&T Realty to achieve
speed & synergy in project and will ensure the delivery of this G+16 storey
high rise commercial tower within a record time of 27 months.Ankur Jadhav, Project Manager, L&T Realty
Overpowering Restraints
The bore logs revealed the presence of high-density basalt rock at very early depth of 2m. We realized that we have to excavate approximately 1.5lakh cum of rock which means approximately 22000 truckload of hard basalt rock.
20-excavators started working on project site and when we realized that the same is not helping the purpose, then controlled blasting was deployed to expedite the excavation process. Further, to protect the soil on one side & the only available route for logistics on other side, we had to carry out shore protection work using 1500 micro-piles which was successfully completed in 90days.
We started excavation activity in January 2018 and the building is to be inaugurated latest by March 2020. Keeping in view the nature of rock, the monsoon & statutory constraints we realized that no matter which technology we use for excavation the same is going to consume at least 7 to 8 months for excavation. This challenge was understood immediately after geotechnical investigation was completed in September 2017 and we started discussing a change from RCC to steel structure; however, it was a little early to conclude and move towards Steel structure.
It was towards early October 2017, when we concluded that we are not going to get any additional time to complete the project and no matter what the buildings must be up & running by March 2020, we seriously started thinking about the steel building option to overcome the time delay in excavation.
L&T design team started working with steel framing along with metal deck slab which resulted in considerable time saving of approximately 3.6months. This resulted in slab cycle time of 7 days. We also opted for triple height concrete filled tube columns (CFT columns) which further helped to reduce the time spent on conventional RCC columns and walls. The prefabricated steel framing also reduced site activities to greater extent. Most importantly when we were carrying out our excavation simultaneously the CFT columns and beams were getting fabricated in shop.
Concrete-filled Tubes – Engineering Marvel in Composite Steel Design
As mentioned earlier, RC design was leading us to a time-consuming reinforcement cutting, bending and placing in columns and RC beams. We introduced RC beams in the system keeping in view the lateral drift requirements stipulated in NBC2016.The large depths of RC beams for 13m span were further adding difficulties in achieving floor to false ceiling height.
In order to resolve these issues, we opted for concrete filled tube (CFT) columns with internal steel ribs which completely eliminated the need of reinforcement in columns. These columns were designed in such a way that these columns can be erected for a height of three floors. The core wall of building was checked for slenderness and we allowed the core jump form for three floors as well. This enabled our construction team to proceed with three slab leading to expedited construction activities.
As compared to large depth RC beams we shifted to relatively low depth steel beams. With the issuance of NBC2016 it has become difficult to design the flat slabs in RCC buildings. The steel deck slab not only provided us with a solution in this regard but also, we could eliminate the use of horizontal formwork in these buildings. Similarly, the use of CFT columns eliminated the use of formwork for columns. The jump form offered us relief on slab cycle time as well. The simple beam to column connections also enabled us to expedite construction activities.
Flexibility for Services Routing
13m span was suggesting large depth RC beams which also created a problem for routing of services in these buildings. The introduction of steel beams not only reduced the beam depth but also provided us with an opportunity to introduce castellations in steel beams which offered a lot of flexibility for services routing.
Overcoming the Logistics Challenges
The plot geometry was a logistics nightmare, having a long tail and most of the plot where the buildings are located provided hardly any space for material storage, enabling works and other site related activities.
The steel structure is being fabricated in shop and transported to site using “Just-in-time” principle which eliminates additional space requirement for storing steel members. Use of composite steel structure also reduces the requirement of reinforcement which results in less space requirement for storing reinforcements.
Steel structure also eliminated the requirement of formwork for beams/columns/roller deck slabs, thus eliminating any need for space provision for formwork as well as labour for formwork.
The time consumed in activities like cutting, bending and placing reinforcement, concrete curing, fixing and removing formwork was brought down to such an extent that this not only provided a saving in time but also allowed us to plan site logistics in a disciplined and organised manner.
Initiatives to Achieve Speed & Synergy
Following are the major initiatives which helped us achieve desired project duration to meet our business objectives:
- Structural steel fabrication in shop during excavation and foundation casting activity at project site ensured that we recover the time lost in excavation.
- Use of CFT columns with no reinforcement and 3 floor erections in one go opened the construction of 3 floors simultaneously resulting in considerable saving in slab cycle time.
- Simple connection designs and details ensured the optimization of construction time.
- Pre-fabricated steel beam with coordinated services cut-outs provided saving in time for MEP work.
- With the use of Intumescent paint over steel column we could get rid of column cladding work which also reduced the finishing timelines to certain extent.
- Optimization of site related activities which are related to reinforcement cutting, bending, placing, formwork, mobilization etc. offered us great deal of time saving.
- In addition to this the skilled manpower requirement reduced drastically due to mechanised construction.
The true success of this project is in the state-of-the-art composite design facilitating large column free spaces along with the optimized floor to floor height, speed of construction & superior quality of final product as formwork is eliminated. The quality of work during the construction and the safety standards followed are typically in line with what L&T is known for.
(Contributed by Sunil Godbole, Senior DGM – Structural Engineering, L&T Realty)
