George Jones, BSc C.Eng MICE MIEI, Commercial Design Concepts, UK

There has been continued global growth in tall building construction over recent years. The variation in the use of such buildings is remarkable, from lavish hotels and apartments to socially affordable units. As the world struggles to cope with growing numbers of people, dwindling resources and movements from rural to urban habitats it is unavoidable that population densities will increase, and more efficient use of scarce land and all other resources will be needed. Taller buildings are the inevitable consequence. Tall buildings can use several different types of material to form their framework and envelope. Those materials are mixed to provide an optimum building solution to suit client requirements such as structure, occupancy, vision, affordability, timing, sustainability and quality. Precast concrete is one of those materials, and has been used from whole frameworks to facades, and elements mixed with structural steelwork and cast in place concrete.​

In view of their current popularity several references have been written on the design of tall buildings in steelwork and structural concrete. However, it was felt in fib Commission 6 for Prefabrication that there was not an up to date reference available for the use of precast concrete in tall buildings, that brought together in a single document the modern applications of precast concrete in tall building construction. Task Group 6.7 was therefore set up to address this issue and to prepare a “State of the Art Report” on the subject. This report would focus on how to integrate precast concrete into tall buildings and aims to capture the interest and influence professionals and all parties involved in tall building construction through a single reference without being unduly theoretical in approach. We are also pleased to have had close cooperation with PCI throughout the drafting process and that the Bulletin will be published by both fib and PCI.

Bulletin 101 is divided into four parts. The first four chapters introduce the reader to the benefits that can be achieved with precast concrete and how it can be integrated into any building as individual elements either mixed with other construction forms or as precast systems themselves. Shafts, stair and service cores, division walls, floors and facades are all parts of any functioning tall building and can be provided in precast concrete to act as the structural framework also.

Benefits that can be achieved through using precast concrete in tall building construction, in addition to those from using traditional cast in place concrete, include:

• Offsite dependability.
• Higher strength and more advanced materials.
• The capability to produce components outside the site cycle in advance of construction.
• Greater speed of construction resulting in reduced floor cycle times (critical in tall building construction).
• Time and budget certainty (site climatic and logistical effects are mitigated).
• Assured and improved quality.
• Less clutter on congested floor areas during construction.
• Fewer site personnel with resultant health and safety benefits.
• Ease of demountability and reuse.
• Enhanced performance in earthquakes.
• Automated production processes with great accuracy and less waste.
• Moulding of complex shapes in factory conditions to realise architectural visual intentions more easily.

The next four chapters cover the individual “building blocks” in precast concrete, i.e. floors, columns, walls and stairs. Their application to tall building construction is described with particular attention given to design and detailing and production methodology. There are then three chapters on areas of specific interest. These are building facades, precast in seismic zones and construction itself.

The Bulletin concludes with numerous case studies. The Group particularly wanted to use case studies from as many different regions as possible, and we believe this has been achieved with examples from Europe, North and South America, Australia, Japan, the Middle East and China. Sample case studies illustrating the application and benefits of precast concrete include:

Breaker Tower, Bahrain – Fully Precast Framed

This structure has a full precast concrete framework comprising wall panels, columns, beams and hollowcore floor slabs. The building has 35 storeys and is 165m tall. It has two basic volumes. The high-rise volume has the shape of a vertical “cylinder lock”. Apartments occupy 28 storeys and are situated in the round part of the high rise footprint. Each storey has a free height of 4.2m and apartment residents have an exceptional view of the surroundings. The rectangular part of the high-rise functions as the stabilising “backbone” of the building and houses the elevators and stair cores. The low-rise of the building has a rectangular volume where the 5-storey car park and show room are housed.

Columns are positioned in the round peripheral to allow freedom of placing partition walls. The shear walls at the back of the building form the lateral stability structure. Vertical joints connect the individual shear walls at their intersections. The shear walls act together as stabilizing 3D structures.

Production of the precast elements was always at least two floors ahead of the erection schedule, ensuring that all precast elements were available on time. The contractor carried out precast element installation at an average speed of 2.5 floors per month, which resulted in a floor cycle time of 13 days. Seven days were spent for setting-out, erection and grouting of the precast beams, hollowcore slabs and stairflights. Six days were then needed for installation of the precast columns and shear walls supporting the next floor.

Erasmus Medical Centre, Rotterdam, The Netherlands – Framed by Precast Walls with Innovative Construction Method

The building has 35 storeys and is 120m high. It has a complete precast concrete structural framework. The façade consists of architectural insulated sandwich walls, weighing up to 34 tonnes per element, internal solid walls form the service and circulation shafts, and the floors consist of hollowcore slabs. All walls are loadbearing, and they act together as a tube inside a tube to provide lateral stability. Construction speeds can be maximised if precast element weights are also maximised. Often it is crane capacities, and their susceptibility to high winds, that inhibit speed benefits that can be achieved from precast construction. In this case the contractor decided to use a climbing shed for handling and installation of precast elements instead of the conventional tower crane approach. The elements are installed one floor level at a time and the shed jacked to the next level as the storey is completed. Using the shed it was possible to split vertical and horizontal transport of elements, whereas they are generally combined when using a tower crane. By splitting vertical and horizontal transport a creditable floor cycle time of five days was achieved on a floor area of 43m x 19m. Moreover, the roof of the shed provides cover with consequent health and safety benefits in the closed working environment. Weather, particularly wind, has little effect and there can also be an early start to non-structural work.

The crane operated in a gantry system inside the shed and consequently through direct lifting could also lift heavier precast elements than would have been possible using more traditional craneage.

Urban Dock Park City Toyosu, Japan – Precast Framed and Earthquake Resistant

The larger apartment block has 52 storeys and is 180m high. There is also a second building of 32 storeys on the same site.

The building was designed and constructed using the Sumitomo Mitsui Quick RC Integration Method (SQRIM). This method was developed with the aim of converting all main structural members to fully precast concrete. The method utilises all frame elements to resist lateral forces. This is a seismic damping device equipped structure and uses concrete of 120N/mm² compressive strength for some structural members. The construction period was 33 months with a SQRIM applied floor structural framing cycle of 3-4 days. Seven tower cranes were set up with a capacity of 15 tonnes each. The total number of precast elements was 24,035, which were produced in twelve precast factories. The percentages of insitu concrete elements converted to precast were 100% columns, 95% beams and 74% of floor slabs. This resulted in the on-site labour demand being reduced by 95% for formwork and 97% for rebar fixing.

Premier Tower, Melbourne, Australia – Precast and Insitu Concrete Mixed Construction

As one of Melbourne’s tallest and most prestigious developments, this project is best known for its inspiration: Beyoncé's video ‘Ghost’, which features writhing dancers tightly shrouded in fabric. The result is an elegant, amorphic form, designed by Elenberg Fraser, that sits on an island site opposite Melbourne’s main train terminal, Southern Cross Station. When completed it is expected to rise to 78 storeys (249m tall), comprising 780 one and two-bedroom apartments and 180 hotel suites, as well as a range of leisure facilities.

Melbourne’s construction industry is predisposed to concrete, with precast vertical elements (columns and wall panels) mixed with post-tensioned flat slabs a common method of construction.

To maintain the building’s movement, due to wind, to within acceptable levels, precast mega-columns on the façade maximise the width of the stabilising structure. These are tied to the core by two- or three-storey outriggers concealed in party walls, and secondary outriggers at the mid-height plant floor.

The precast mega columns are sized to carry both gravity and wind loads. The forces generated by the wind loads can be equal to the weight supported by the column. Due to the overall weight of the mega columns, the producer and structural engineer worked closely to create a precast option to form the project’s ‘mega-columns’ within the structure, that could be safely lifted by the site tower cranes.

The result is a composite ‘shell’ column that not only has the required vertical capacity, but also easily accommodates the outrigger connections through the building.

Conjunto Paragon, Santa Fe, Mexico – Architectural Precast Concrete Facade

This hotel of 27 storeys is sited on the highest ground in a recently developed area, making it a prominent landmark. The building façade is formed with architectural precast concrete elements, comprising 520 curved and straight pieces, both concave and convex.

Its relatively massive size was slimmed visually with the undulating design which blends the precast panels with large windows that give expansive views of the landscape.

This building has a winding “S” shaped profile, and consequently precise fabrication of the precast panels was the key to defining the unique shapes needed. High-quality off-site manufacturing ensured achievement of complicated geometry, curved panels, intricate medallions, cubic protruding shapes and balconies.

Panels were erected in a horizontal sequence around the building perimeter. This allowed early phased shell completion at each floor level and release of large sections of the façade for fixing of glazing and protected crews working on interior finishing. The early close-in also meant that hotel owners were able to adapt interiors to specific needs.

Wind, site restraints, building height, the wavy design, protruding windows at the top floors and the construction schedule all created challenges that could only be met with precast architectural panels.