Supertall Jakarta Tower Driven by Sustainability
Source: ASCE’s Civil Engineering Magazines (May 20, 2014)
By Jenny Jones
Constructing a highly sustainable 530 m tall tower in Jakarta, Indonesia, presents significant challenges that engineers are resolving through performance-based design.
A 530 m tall skyscraper in Jakarta, Indonesia, will be the world’s first “supertall” tower—defined by the Council on Tall Buildings and Urban Habitats in Chicago as those more than 300 m tall—to feature sustainability as its primary design driver. Intended to be a net-zero-energy building, the tower will boast a host of energy-saving and energy-generating features, including an array of wind turbines at its crown. But constructing the supertall building in a highly seismic area and on a site with poor soil conditions is creating an array of challenges that engineers are resolving through performance-based design.
The tower will be at the center of a new campus that is being developed and will be occupied by the Indonesian state-owned energy company Pertamina. One of five buildings on the campus, the 99-story tower will house the company’s offices. Other buildings will include a mosque, a fitness center, and a publicly accessible multipurpose performance hall. A covered walkway, which designers call the “energy ribbon,” will weave through the campus, protecting Pertamina’s nearly 20,000 employees from the elements as they navigate between the buildings. The walkway’s canopy and all of the other horizontal surfaces throughout the campus will be covered by photovoltaic panels.
Pertamina is constructing the campus to consolidate its operations, which are currently dispersed among several buildings throughout Jakarta. The company wanted the campus to reflect its progressive approach to energy consumption and invited several international architecture firms to submit design proposals for the project. As a result of that competitive process, it selected a team from the multidisciplinary design firm Skidmore, Owings & Merrill (SOM) to provide the architectural design; the structural and civil engineering; the sustainability features; and the mechanical, electrical, and plumbing design for the project. The team includes members of SOM’s Chicago and New York City offices. Scott Duncan, AIA, LEED-AP, a design director and lead of the architecture team for SOM, says that because this will be an owner-occupied building, the team could be exceptionally innovative with the design. “Historically, supertall buildings have been designed based on [a] formal expression or on a structural concept,” he says. “We wanted to rethink the supertall building to be designed in response to environmental factors and saving energy.”
A series of site-specific parametric studies were conducted to determine the best shape and orientation of the tower. That process revealed that counter to conventional wisdom, which suggests that a building located in such an intense solar environment as Jakarta should be elongated in form and oriented on an east-west axis, a compact and rounded building on a north-south axis would actually perform better. As a result, the building will have a curved geometry, its primary facades facing north and south. Those facades will be covered by aluminum sun-shading fins to reduce solar gain, while the east and west facades will be more opaque. “This building is very close to the equator, so it will receive almost equal amounts of high-angle sun from the north and south,” Duncan explains. “Its design is specific to Jakarta’s location on the planet.”
Test borings have shown that the site has poor soil as far down as 120 m, a condition not uncommon in the region. As a result, the building will be founded on a pile-supported raft. The piles will be roughly 1.8 m in diameter and descend to a depth of approximately 100 to 120 m. “There are definite layers of bad soil even down at one hundred-twenty meters that we’re trying to avoid so we can maintain the support that we need for a tower this large,” says Charles Besjak, P.E., S.E., M.ASCE, AIA, the director of structural engineering for the New York City office of SOM. The walls of the building’s five basement levels will have egg crate-shaped walls to effectively distribute the building’s gravity loads to the concrete raft, which extends beyond the footprint of the tower itself, Besjak explains. “This essentially reduces the concentrated forces in the piles under the tower core to a larger area,” he says.
Engineers are using the International Building Code and plan to conduct a dynamic time-history analysis to establish the tower’s performance-based design criteria. Jakarta is in a highly seismic zone, so earthquake loads are the controlling factor of the structural design, Besjak notes. The tower will have a reinforced-concrete, shear-wall core and a structural-steel flooring system to reduce its overall weight while maximizing its stiffness. Outrigger trusses between the 33rd and 35th floors and the 62nd and 64th floors will tie the tower’s core to megaflange columns at its perimeter. Interconnected by a belt wall, the megaflange columns will distribute the loads uniformly through the structure while keeping the column sizes to a minimum. Web walls located throughout the structure will provide additional shear stiffness. “We plan to go beyond the prescriptive code requirements and develop a performance-based design approach, which will help reduce the overall seismic and foundation forces, resulting in a more efficient, cost-effective structure,” Besjak says.
The tower’s north and south facades will extend beyond the top of the tower and will have a void between them, extending in the east-west direction. A hat truss will connect all of the columns at the top of the tower to provide enough stiffness to frame the void. “The hat truss is like a donut with a truss structure that goes all the way around and distributes loads to the perimeter columns and the core,” Besjak explains. The void will create a “wind funnel” that will accelerate even a gentle breeze, making it ideal for producing wind-generated power. “By studying the velocities of wind, it became clear that with the building’s height we gained access to greater wind velocities and therefore a great potential for energy generation,” Duncan says. “And it just so happened that the prevailing wind is from the east, so the orientation of the building allowed the funnel and turbines to align with the optimal wind path.” As many as four vertical-axis wind turbines will be located inside the void, the floor of which will be glass so people can view the turbines from below. The turbines will also be visible from an observation deck and restaurant at the top of the building.
The project is still in the schematic design phase, but ground has already been broken on the campus. The tower should be completed in 2020. The design of the entire campus is meant to reflect Pertamina’s concern for the environment, while also helping to advance sustainable design practices—especially those for tall buildings. “We’re going to see a shift where energy becomes a primary driver for building forms, whether that be generating energy, or saving energy, or both,” Duncan explains. “We’ve had the unique opportunity to really push these ideas on this project, which is well supported by a very forward-thinking client, so we hope this project will serve as a prototype for sustainable building design.”