Inclination in design is a remarkable feature that requires careful structural consideration and execution. Let’s investigate 8 unique intentionally inclined structures and understand how they work.
Capital Gate
Architects: RMJM Architects
Completion Year: 2011
Location: Abu Dhabi, United Arab Emirates
Leaning Degree: 18 degrees
Capital Gate, a striking skyscraper in Abu Dhabi, UAE, is renowned for holding a Guinness World Record as the farthest manmade leaning building for its 18-degree lean. Designed by RMJM, the building draws inspiration from its surroundings, particularly the desert and the waves of the nearby sea. Standing 165 meters tall, Capital Gate features 35 floors. The first 18 floors house offices, while the remaining levels are part of the Andaz Hotel. The building’s unique form gives each floor a distinct configuration and layout, adding to its architectural intrigue.
The skyscraper’s lean required its engineers to craft ingenious structural techniques to keep the building standing. Since the building has the tendency to fall towards the side of the lean, the foundation was divided into two parts, made of 490 piles. The first, which is towards the leaning side, is composed of 20m piles under compressions, while the other side is composed of deeper 30m piles to resist the overturning moment, undergoing tension due to the overhang’s stresses. A raft foundation is carried by the piles, forming the building area.
The core of the structure also plays an indispensable role in its stability. Built by pre-cambering, a technique that resulted in a core tilted towards the opposite direction of the lean, the vertical post-tensioning that occurred as a result of adding the floors towards the leaning side aided the core to straighten. Had the core been straight, the loads would have allowed the structure to excessively bend towards the desired lean, causing failure.
Internal and external diagrid systems aid the building’s load transfers to the core, with the help of interconnecting girders, reducing the need for columns.
Puerta de Europa
Architects: Philip Johnson, John Burgee
Completion Year: 1996
Location: Madrid, Spain
Leaning Degree: 15 degrees
The Puerta de Europa towers are the world’s first (purposely) leaning towers. Also referred to as Europe’s Gate or “The Door to Europe,” the towers boast their iconic centric location, symmetric to Madrid’s Plaza de Castilla and the La Castellana axis.
The towers stand 114 meters (377 feet) tall and have a lean of 15 degrees. This required careful structural considerations. The buildings’ 3 basements, weighing 15,400 tons, form an underground ballast that counters the weight of the structure, ensuring stability. Each building’s sturdy concrete core was designed to stabilize the interior floors and was eventually reduced towards the upper floors where the lean shifts to the opposite direction. To support the tilt, a post tensioned steel frame was utilized. The post-tensioning, installed to resist the lean on its opposite side, also helps maintain the core’s stability.
A structural steel diagrid system was also used as the primary structure, functioning with the reinforced core. The diagrid’s facade elements reflect the way the building works, highlighting the core’s central location and the steel frame’s interaction with it.
The towers’ lean resulted in some unusual features. For example, only 4 of the 8 elevators each the top floors, and each floor has a different plan. To differentiate the two towers from above, the east tower is equipped with a red helipad, whereas the west one is topped with a blue helipad.
Montreal Tower
Architect: Roger Taillibert
Completion Year: 1987
Renovation Completion Year: 2019
Location: Québec, Canada
Leaning Degree: 45 degrees
Designed by French architect Roger Taillibert at the request of Mayor Jean Drapeau, Montreal’s Olympic Stadium is an iconic masterpiece, central to the 1976 Games. Known for its impressive and grandiose structure, the stadium is a major symbol of Montreal’s modern heritage. It is the only venue in Quebec large enough to host significant national and international events. The stadium also attracts numerous tourists with its breathtaking views from the Montréal Tower Observatory, which is considered the “tallest manmade leaning tower.”
The Montreal Tower is also renowned for its striking 45-degree incline, an architectural feature that required innovative oblique architecture and prestressed concrete techniques. Prefabricated steel caissons reinforce the upper structure, while its foundation extends 45 meters deep. The tower serves to cover portions of the Sports Center, supporting the Stadium roof, and housing its infamous observatory.
The tower was initially envisioned as a space for sports facilities; however, it remained unused for almost 30 years. It was then renovated to serve as office spaces. This required replacing the heavy concrete panels that limited light penetration for the tower’s initial functions with glass curtain walls for natural light. Due to the tower’s unique curves, the renovation required extensive modifications, such as slab extensions and the use of advanced 3D modeling for more precision. The renovation also involved using Canada’s tallest tower crane, “the giraffe,” which was over 200 meters (656 feet) high and weighed 660 tons.
Aside the 165-meter (541-feet) tower’s iconic lean and unique silhouette, it now hosts well-lit, refined interiors with a striking architectural language that makes its structure transparent and interactive and, of course, much more functional.
Altair Tower
Architects: Safdie Architects
Completion Year: 2021
Location: Colombo, Sri Lanka
Leaning Degree: 13.8 degrees (for the leaning tower)
The Altair tower is Sri Lanka’s tallest residential building. With its striking appearance, composed of a vertical straight tower and one sloped and leaning towards the former, the project offers a spectacular view facing Beria Lake and the Indian Ocean, while providing high-end finishing and numerous recreational facilities.
The 2-leg structural design utilizes a diagrid system which provides similar structures with sufficient structural integrity while providing column-free spaces. The diagrid also facilitated the permeability of the façade and allowed outdoor terracing towards the view.
The towers cater for sustainability concerns by incorporating through-unit designs that allow open plans and natural cross-ventilation in all apartments, enhancing energy efficiency and reducing the need for mechanical ventilation systems.
Wazirabad Signature Bridge
Designers: Schlaich Bergermann und Partner, Germany in JV with Construma Consultancy Pvt Ltd, Mumbai, advised by Ratan J. Batliboi – Architects Pvt Ltd, Mumbai
Completion Year: 2018
Location: Wazirabad, Delhi, India
Leaning Degree: Unspecified
Signature Bridge is a cable-stayed bridge that was constructed to connect North Delhi with East Delhi, taking into consideration the overall population increase and increased transportation demand in the area.
It features a main span of 251 meters (823 feet) and a total length of 675 meters (2215 feet). The bridge’s deck accommodates eight lanes, with four in each direction. Its width is about 35 meters (115 feet), and the structure is supported by lateral cables spaced 13.5 meters (44 feet) apart. The steel tower stands approximately 150 meters tall (490 feet). The pylon’s inclination is used to balance the bridge by resisting the main span’s dead load. The cables to support the main span and backstays are connected to the pylon’s vertical upper part.
The bridge was designed to be a prominent landmark and tourist attraction in Delhi, highlighted by its distinctive slanted pylon, which forms a gateway to New Dehli. The pylon’s upper section features a steel and glass structure, which houses an inspection platform that could also serve as a viewing deck.
Bridge SNP
Designers and Architects: Arpád Tesár and Joseph Zvar and architects Ladislav Kušnír, Joseph Lacko and Ivan Slameň
Completion Year: 1972
Location: Bratislava, Slovakia
Leaning Degree: Unspecified
The Bridge of the Slovak National Uprising, constructed between 1967 and 1972, has been recognized as the city’s most iconic structure. Designed by J. Lacko and A. Tesar, it is a cable-stayed bridge featuring a single pylon. Atop the 80-meter (262-feet) pylon sits a restaurant, accessible by either a lift in one arm or a staircase in the other.
The bridge spans 431.8 meters (1417 feet) in length, 21 meters (69 feet) in width, and the total steel structure, including the pylon, weighs 7,537 tons. The pylon’s inclination along with the attached cables work in a way to resist the dead load of the main span.
Lisbon Harbor Control Tower
Architect: Gonçalo Sousa Byrne
Completion Year: 2001
Location: Lisbon, Portugal
Leaning Degree: Unspecified
The Lisbon Harbor Control Tower is a striking nine-story structure that leans slightly over the water, clad in red copper sheets. The building functions not only as a lighthouse but also as a hub for monitoring shipping traffic, featuring offices, simulators, and seminar rooms arranged around a central hall across its nine floors.
Its unconventional leaning form is complemented by a tripartite vertical structure, echoing the design tradition of Louis Sullivan’s high-rise buildings from the 19th century. The first floor is anchored by light-colored stone, while the upper levels are wrapped in horizontally arranged copper sheets that create a textured effect from a distance. At the top, a glass box, framed by copper slats, gives the tower the appearance of an abstract, modern lighthouse.
Over time, the copper facade has developed a patina, with vertical surfaces turning anthracite-brown and inclined surfaces transitioning to green. This evolving color variation enhances the tower’s unique character, blending formal design with a dynamic, changing exterior.
The Leaning Tower of Gingin
Designers: United Group
Completion Year: 2008
Location: Yeal, WA, Australia
Leaning Degree: 15 degrees
The Leaning Tower of Gingin, located at the Gravity Discovery Center, is designed with a steep 15-degree tilt and is often referred to as the “leaniest” tower in the world. Built in 2008, it replicates Galileo’s gravity experiment, allowing visitors to drop objects from the 45-meter (150 feet) tower and aspires to be a symbol of Galileo’s intellectual and scientific pursuits.
Despite its precarious appearance, the tower is safely supported by 180 tons of concrete. The center also features various exhibits on gravity and the universe, making it a hub for interactive education and exploration.
