Council on Tall Buildings and Urban Habitat
O-14, Dubai

Written by Jesse Reiser, Reiser + Umemoto
Nanako Umemoto, Reiser + Umemoto
Jaime Ocampo, Ysreal A. Seinuk, PC
Posted January 2011

This paper was originally featured as a case study in CTBUH Journal 2010 Issue III and is also available as a PDF download.

O-14 was recognized as a "Best Tall Building Middle East & Africa Finalist" in the 2010 CTBUH Awards Program.

Other Featured Tall Buildings
“The curvaceous, porous form creates a sculptural shell that is monumental and ambiguous on the exterior and intimate and sheltered on the interior.”
- Bruce Kuwabara, CTBUH 2010 Awards Juror, KPMB Architects 
Location
Dubai
Completion
2010
Height
106 m (347 ft)
Stories
24
Area
16,073 sq m (173, 003 sq ft)
Primary Use
Office

Owner/Developer

Creekside Development Corporation
Design Architect
Reiser + Umemoto

Structural Engineer

Ysreal A. Seinuk, PC
MEP Engineer
ERGA Progress
Main Contractor
Dubai Contracting Company

O-14’s façade is an innovative fusion of structure and exterior solar shading that is based on a perforated exoskeleton that dissolves the conventional reading of the building as an “office tower.”  The varying openings in the shell create a dazzling show of natural light, which creates a unique and ever changing sense of interior space. It is a welcomed departure from the standard glass-clad box; a fitting solution given its desert environment.


O-14 is a 24-story commercial tower characterized by 1,326 openings, randomly located and varying in size, throughout the whole exterior shell. O-14, named after its lot designation, is located along the extension of Dubai Creek in the Business Bay area of Dubai, occupying a prominent location on the waterfront esplanade.

Architectural Overview
With O-14, the office tower typology has been turned inside out – structure and skin have flipped to offer a new economy of tectonics and of space. The concrete shell of O-14 provides an efficient structural exoskeleton that frees the core from the burden of lateral forces and creates highly efficient, column-free open spaces in the building’s interior. The exoskeleton of O-14 becomes the primary vertical and lateral structure for the building, allowing the column-free office slabs to span between it and the minimal core. By moving the lateral bracing for the building to the perimeter, the core, which is traditionally enlarged to receive lateral loading in most curtain wall office towers, can be minimized for only vertical loading, utilities, and transportation. Additionally, the typical curtain-wall tower configuration results in floor plates that must be thickened to carry lateral loads to the core, yet in O-14 these can be minimized to only respond to span and vibration.

The shell is organized as a diagrid, the efficiency of which is wed to a system of continuous variation of openings, always maintaining a minimum structural member, adding material locally where necessary and taking away where possible. This efficiency and modulation enables the shell to create a wide range of atmospheric and visual effects in the structure without changing the basic structural form, allowing for systematic analysis and construction. As a result, the pattern design is a combination of a capillary branching field, gradients of vertical articulation, opacity, environmental effects, a structural field, and a turbulence field.

In O-14, the fenestration is not tied to the overall regulating geometry. In a typical office building, the subdivision of form would locate programs in a predictable way, as in larger windows and offices at corners, etc. Here, rather, the pattern seeks to attenuate the monotony, while still preserving a sense of the sublime and the monumental. Its deliberate lack of coordination with the floorplates engenders a randomized connection – all of this confuses legibility and scale, and defeats easy reading of the building’s height and reorganizes the hierarchy of office space.

Structural Design
O-14’s unique perforated concrete tubular shell serves as its main architectural feature, its primary structural system, and an environmentally-smart brise-soleil. This exoskeleton-sunscreen wall features more than 1,326 openings of different sizes
(see Figure 1) in an apparently random pattern but actually creating a diagonal grid to enable its use both as gravity and lateral support. This quality represents concrete at its best.
Figure 1. Elevation
The shell, being a primary structural element, required close collaboration between the architect and structural engineer in order to arrange the entire façade. The sizes and locations of the openings were carefully coordinated in order to make the wall effective in channeling both gravity and lateral loads down to the base of the building. The size and reinforcements of each solid shell element between the openings resulted from several iterative analyses, involving the varying of the openings’ sizes and locations.

The exterior shell of O-14 ends at the ground floor level and is picked up by a continuous 1.20 meter (3’-11”) deep ring beam that follows the irregular outline of the wall. Vertical loads are then transferred through four levels of parking, located underground, to allow for a maximum amount of parking space. The ground floor slab acts as a diaphragm slab, transferring lateral forces to the basement core shear walls, foundation walls, and additional shear walls that are adjacent to the parking access ramps. The gravity and lateral support system is also comprised of the core walls surrounding the main stairs and elevators in addition to the primary exterior shell (see Figure 4). The central core acts as a shear wall up to the 5th level, serving as a transition from the foundation walls and lower level shear walls to the exterior wall above grade.
Figure 2. O-14 Entry
Environmental Effects
The shell acts not only as the primary structure of the building but as a sunscreen open to light, air, and views. The openings on the shell thus modulate according to structural requirements, views, sun exposure, and luminosity. The overall pattern is not in response to a fixed program (which in the tower typology is inherently variable); rather the pattern, in its modulation of solid and void, will affect the arrangement of whatever program comes to occupy the floor plates.
Between the plane of the floor plate and the exterior wall’s vertical opening, each slab edge is set back by one meter from the wall. Since the locations of the openings vary throughout the façade, each floor level is connected differently to the exterior wall at its diagonal grid by tongues extending through the one-meter gap (see Figure 3). Approximately 720 such connections exist between the interior floor slab and the exterior shell (approximately 30 connections per floor).

This one-meter gap between the main enclosure and exterior shell creates a so-called chimney effect, a phenomenon whereby hot air has room to rise and effectively cools the surface of the glass windows behind the perforated shell. This passive solar technique is a natural component of the cooling system for O-14, reducing energy consumption and costs by more than 30%, which is just one of many innovative aspects of the building’s design.
Figure 3. Typical floor plan
Construction Methodology
O-14 is sheathed in a 40-centimeter (1’-4”) thick concrete shell perforated by 1,326 openings that create a lace-like effect on the building’s façade. In order to create the perforated exoskeleton, O-14 uses a slip-form construction technique: modular steel concrete forms are used then moved along the building axis, preventing costly dismantling and setup of complex shapes. The holes are achieved by weaving Computer Numerically Cut (CNC) polystyrene void-forms into the reinforcement matrix of the shell, around which are constructed the slip forms of the interior and exterior surfaces of the shell. Super-liquid concrete is then cast around this fine meshwork of reinforcement and void-forms, resulting in an elegant perforated exterior shell. Once the concrete has cured, the forms are loosened and moved up the tower to the next level, where the process begins again. Dubai Contracting Company worked closely with Beijing Aoyu Formwork Company to systematize the production of the foam pills on site, and to streamline the assembly process of the sheathing, steel reinforcement, and foam pills prior to casting.
Figure 4. Typical reinforcement layout                            Figure 5. O-14 shell stress diagram

From the ground floor to the top of the parapet wall, the total height of the exterior shell is 105.7 meters (346’-9”). The shell thickness is 60 centimeters (2’) from the ground to the 3rd level, and 40 centimeters (1’-3”) from the 3rd to the roof level. A special detail was incorporated into the foam pills at this transition area to accommodate this change on the interior of the façade. Normal weight concrete of 70MPa (10.2 ksi) was used.

In designing the wall, the openings were classified into five different types based on their sizes. The diameter of the largest opening is 8.30 meters (27’-3”) and spans across a two-floor height. The smallest opening diameter is 1.40 meters (4’-7”). The overall void ratio created by the openings is approximately 45%.

With O-14, the strength of the shell is modulated based on mediation between materiality and aperture (see Figure 5). Variable stresses are accommodated by locally increasing and decreasing material so that a uniform strength concrete can be used, simplifying material preparation. Changes in overall opacity can be accommodated by changing the uniform strength of the concrete mix. The mix is a balance between strength and fluidity, as extreme fluidity is necessary for larger contiguous pour segments and slip forming technology. Herein lies the economy of the system, so that within its constraints, a wide spectrum of forms can be possible with little impact to the overall cost or production time.

Figure 6. O-14 Rooftop

Related Links
CTBUH Skyscraper Center Profile:
Visit O-14's profile

O-14 featured as a Case Study:
Download the Paper
2010 CTBUH Journal Issue III

O
-14 recognized as a finalist in the 2010 CTBUH Awards Program:
Download O-14's 2010 CTBUH Awards Book section
2010 CTBUH Awards Book

O-14 featured in
Innovative 20

Download the article
2010 CTBUH Journal Issue II

The CTBUH would like to thank Reiser + Umemoto for their assistance with this article. Images/drawings © Reiser + Umemoto