Bitexco – Symbolizing Vietnam’s Global Emergence through an Iconically Shaped, Structurally Sophisticated, and Sustainable Design

A Beacon for Twenty-First Century Vietnam

Located in Historic District 1 as well as the heart of Ho Chi Minh City’s Financial District, the 263 meter Financial Tower rises as a Beacon towards the future of Vietnam. The tower uses as its reference the Lotus fl ower (a symbol for Vietnam) in a mature blossomed state to build upon Vietnam’s history and make a statement that Vietnam has arrived and is capable of competing with the global marketplace. With the city’s rapid population and business growth, the mixed use development, which includes a 68-story high-rise offi ce building, a fi ve story retail podium, and four basement

areas, eases the demand for commercial space, by providing approximately 93,500, 20,500, and 5,000 square meters respectively for offi ces, retail, and below-grade parking / storage.

Yet even as the tower meets modern day business needs while symbolically speaking to the nation’s future-driven aspirations and the thriving city’s limitless potential, the design respects the historical context of the country’s early beginnings. While the tower is dramatically different in architecture and scale than the surrounding urban milieu (Figure 1), the ground fl oor design and relationship of the lower scale podium is very similar to other iconic and

Bitexco Financial Tower rises above Saigon River, Ho Chi Minh City, VietnamPhoto Courtesy: Bitexco Group

William J. Faschan, P. E., Partner, Leslie E. Robertson AssociatesAnthony Montalto, R. A., Principal, Carlos Zapata StudioNayan B. Trivedi, P. E., Partner, Leslie E. Robertson Associates

Figure 1: Bitexco Financial Tower, view from Historic District 1

Photo Courtesy: Bitexco Group

construction completion in the fall of 2010. The typical lower offi ce fl oors are framed with a conventionally reinforced 10-inch (250mm) thick fl at plate. The upper executive offi ce fl oors are smaller in plan and are framed with a thinner 8-inch (200mm) thick fl at plate (Typical Floor Plans: Podium Figure 3a, on next page - Offi ce, Figure 3b, Ground Floor Figure 3c).

Structural Creativity and High Construction Standards Lead to Completion by Targeted National Celebration

Split-Level Basement Excavation and Donut

In Ho Chi Minh City, where the construction standard is two basement levels for major projects, Bitexco’s small site and tower height increased the requirement to four (Figure 3a). Faced with an aggressive schedule, property constraints, and a high water table, the project team developed a split-four-level basement excavation method

Figure 3a: Retail Podium Elevation with Split-Four-Level Basement Scheme and Shallow Diaphragm Wall

important structures in Ho Chi Minh. The Opera House, a prominent, ornate, and culturally signifi cant building for the city, for example, is isolated from its traditional, French infl uenced neighbors in a very monumental gesture and becomes a focal point for the area.

In similar fashion, the ground fl oor plaza of the Bitexco Financial Tower becomes apublic gathering space that releases the tower from itssurroundings (Figure 2) and allows the structure to be appreciated as a monument as well as a piece of architecture.

The lower scale, glazed retail podium is a modern interpretation of the retail life on the streets of Ho Chi Minh. As opposed to western malls and department stores that turn their back on the sur-roundings and present solid ad-

Figure 2: Street View of Ground Floor Plaza and Public Gathering Space Photo Courtesy: Carlos Zapata Studio

vertising walls, the podium becomes a living window display, merging the traditional street vendor with the modern mall.

The offi ce tower is an all-concrete structure and stands about 50 stories above the surrounding buildings, at least at the time of

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with a shallow diaphragm wall which located the top of the tower mat foundation at the second basement.

The design called for the perimeter diaphragm wall to be 800 mm thick and constructed using the slurry method. To provide a groundwater cutoff for the 14 meter deep excavation, the wall was constructed to a depth of 25 meters below ground.

Because of poor soil conditions, closeness of surrounding buildings, and basement access needs, the structural engineers

Figure 3b (Across): Typical Offi ce Floor Plan

Figure 3c (Below): Typical Ground Floor PlanTypical Offi ce Floor Plan

Figure 5: Construction Site - including Foundation, Diaphram Wall, and Ground Floor Slab (“Donut”)

Figure 4 Basement - Temporary Concrete Slab, Top-Down Erection Column

chose not to use standard temporary bracing practices of tiebacks and rak-ers when building the perimeterdiaphragm wall. Instead, thedesign team devised a partialtop-down slurry method wherethe ground fl oor perimeter slab (“donut”) stabilized the top of the diaphragm wall before basement excavation started (Figure 4). The decision permitted excavation of the tower mat foundation without temporary bracing (Figure 5). After superstructure construction, the tower mat then served as a bracing point for temporary supports for ower excavation of adjacent areas.

Unusually Deep Foundations

The estimated 112.2 million kg weight of Bitexco Financial Tower and poor soil conditions necessitated very deep founda-tions. Design needed as well to address a soil-structure time analysis which predicted an ap-proximately 100 mm settlement.

To compensate, a 4m bored pile supported mat distributes the tower loads from the walls of the narrow services core over the extent of the mat. At the tower, 1500mm diameter bored piles extend to a depth of between 80m to 90m while at the podi-um and underlying basements, 1200mm diameter bored piles go down as far as 63m (Figure 6).

Considerations in mat construction included building the large volume mat in multiple sections, embedding tubing in the mat for a temporary cooling system, and placing insulation on the sides and top of the

mat to limit the potential for cracking from the concrete’s heat of hydration.

In the basement, the one pile per column have a cut-off elevation of the fourth basement level. Within the

top of each pile is a structural steel wide fl ange section which supported the perimeter of the ground fl oor during the top-down excavation and basement construction. Once completed, the fl anges act compositely with the concrete basement columns

Figure 6: Basement and Tower Foundation Piles

Figure 7: Helipad’s ‘Touch-the-Sky’ PanoramaPhotos Courtesy: Carlos Zapata Studio

to support permanent loads.

Despite the extra time required to install the deep foundations, the split-level design and “donut” cut at least a year in excavation and construction time from the four basement design concept by enabling tower construction to start prior to completion of all basement levels.

Helipad Test Assemblage

Consistent with the national fl ower motif, the helipad and sky lounge taper off from the central area near the fi fty-fi fth fl oor, reaching into the atmosphere as if a lotus bud in search of the sun.

Supporting the helipad, with its touch-the-sky panorama (Figure 7) of the growing city,

Figure 9: Helipad Construction - Tapered Steel Cantilever Girders and Platform

Figure 8: Helipad Atypical Floor Plan with Built-Up Sections

Yet, the skyscraper-free views, ovo-tubular design, and high aspect ratio potentially create wind induced building sway problems for Bitexco Tower. To minimize this possible motion, the structural engineering team developed an unconven-

tional steel outrigger truss system. For wind load resistance, the structural design interconnects the outrigger trusses and belt walls to the core walls and perimeter columns at Floors 29 - 30, and allows the outrigger and belt wall system to function with

are a pair of 25 meter long tapered steel cantilever girders which span from the corewalls to the perimeter towercolumns and extend outward to frame the platform (Figure 8). Perpendicularly oriented secondary structural steel beams cantilever beyond the primary girders to support the circular edge (Figure 9).

While the choice of steel produced a lighter structure and sped fabrication, construction of the huge cantilever at thegiven height presented challenges. To ensure that partsintegrated cohesively prior tohoisting in the air, workers testassembled the helipad offsite.

Unconventional Outrigger TrussSystem

the concrete core walls (Figure 10). The outrigger trusses and belt walls stabilize the core by resisting a portion of the overturning moments associated with wind-induced east-west movements.

Within the outrigger system, two of the four sets of double-story trusses align with the two primary core cross walls and the other two trusses align with the fi re stair walls, while connections of the outrigger trusses (1000mm wide) to the cross walls (400mm) effectively transfer forces (Figure 11). Four, one-story tall belt walls, with two on each side of the tower, interconnect pairs of perimeter columns to each outrigger truss. The perimeter columns vary in size from 1400mm (Base Floor) to 850mm (Floors 42-52) with a 1200mm diameter at Floor 29.

Structurally Independent Retail Podium

Steel Vierendeel trusses at levels 2 to 4 act as transfer girders to create a column free space at the entrance for the structurally independent 17000 m2 glazed, steel-framed retail podium. The fi ve-story atrium features a sloping skylight with an 8m cantilever roof. Stainless steel grill panels in the roof which help diffuse the incoming light and three, fi ve story exposed concrete support columns in the atrium create atmospheric and visual ambiance.

Introduction of International Construction Standards

As an irregularly shaped mega-structure, the Bitexco Tower

Figure 10: Outrigger Truss and Belt Wall Systems

Figure 11: Outrigger Truss-Cross Wall Connections

Figure 12: Bitexco Illuminated for 400th Anniversary CelebrationPhoto Courtesy: Carlos Zapata Studio

presented numerous safety challenges to the construction team. The exceptionally high ratios of gross fl oor area to site size as well as the complexity of the ovo-tubular design, which resulted in non-vertical columns and a unique layout for each fl oor, posed particular concern.

Routine inspections of heavy equipment, equipping tower cranes with special collision prevention and wind alarm systems, the implementation of fall prevention policies, and the availability of fi re prevention equipment coupled with fi re drills aided in maintaining a high onsite safety record.

As the fi rst mega-structure in Vietnam, the Bitexco project introduced most of the workers to not only new types of construction but to higher, international safety practices.To garner worker compliance, the construction management team used a three prong approach which included safe practice education, the provision of protective equipment, and an incentive program that rewarded compliant behavior.

Targeted National Celebration Completion Date Achieved

Ultimately, the innovative approaches to the foundation’s excavation, helipad assemblage, and outrigger truss system as well as the high safety standards secured Bitexco’s timely completion, and enabled thebuilding to be part of Vietnam’s 400th anniversary celebration (Figure 12).

Design Considerate of 21c. Sustainablility Needs

To minimize transportation and energy costs while stimulating the regional economy, the Bitexco Financial Center’s structural design called for ahigh strength concrete supplied by the local Vietnamese mar-ket. Since the selected concrete strength of 50 mega-pascals was

not in general use in Vietnam at the time of construction, the decision also helped advance higher strength technology within the country. Structural steel found in the outrigger truss and helipad cantilever offers another sustainable opportunity through the material’s recyclability. At least in the helipad, the choice resulted in a lighter structure and speedier development, which ultimately

Conclusion

An iconic landmark, Bitexco Fi-nancial Tower provides a model for Vietnam’s global emergence through a sophisticated and sustainable structure built with 21c. construction standards. Innovative structural engineer-ing decisions which infl uenced basement excavation, helipad assemblage, and the outrigger truss design as well as high safe-ty practices onsite ensured that construction fi nished before the targeted national celebration.Sustainable materials within the high-rise, such as the LED luminaries, enable the tower to appear as a symbolic beacon towards the future of Vietnam at all hours with an energy and material saving design consid-erate of the world of tomorrow.

cut construction energy costs.

Other sustainable strategies included installation of: a high effi ciency double glazing to reduce solar load, a cooling tower in which the make-up water comes from water fi ltered through an onsite sewage treatment plant, all variable speed fans and pumps with high-effi ciency motors, energy meters for electricity and chilled water on each fl oor to encourage tenants to reduce energy use, and typical fl oor lighting set to the low consumption standard of 10 wm2.

For the tower’s exterior lighting, the pinnacle area holds over 1500 LED fi ttings (Figure 13) which on activation use less than 3500W, yet produce lights visible for miles at night.

Figure 13: Night Time Illumination of Bitexco Financial Tower’s LED Fitted Pinnacle with View from the Saigon River Photo Courtesy: Carlos Zapata Studio

Owner / Developer: Bitexco GroupStructural Designer: Leslie E. Robertson Associates (LERA)Construction Manager: Turner InternationalDesign Architect: Carlos Zapata StudioAssociate Architect: Arep VilleMEP Engineer: DSA EngineeringMain Contractor: Hyundai Engineering & Construction Co. Ltd.

Concrete (m3): 600,000 m3

Reinforcing Steel (t): 5500 tStructural Steel (t): 2700 t

Design Start Date: 2005Construction Start Date: 2007Opening Date: October 2010

Bitexco Financial Tower Data Block