Architecture & Art | AUSTRALIA – NEW YORK About the Construction of
KAUST Breakwater Beacon THE STRUCTURAL FORM
The tapered tower is 60m high and divided into three sections, each representing a separate theme. The base is approximately 30m × 25m, reducing to 3m × 2.5m at the top. The first 22m in height is a true shell shape, being anticlastic in form and similar to hyperboloid shapes commonly used in water reservoirs and airport control towers. Beyond that, the spire follows a cone- shaped tapered tower that, at all times, maintains its elliptical form in section. The entire tower is punctuated with hexagonal penetrations that are initially sized up 5m and very irregular in shape at the base, with a transition into a regular size, approximately 0.3m at the apex. There are four doorways as entry points to the internal atrium space, which vary in height up to 12m.
Due to the large number of penetrations and the discontinuities created by the doorways, the structure does not have sufficient continuity to act as a pure structural shell and tends to act like a grillage of continuous beams. The structure was further challenged by the need to split these beams into precast and in- situ concrete components to meet the quality of finishes required.
The lower 22m of the superstructure is comprised of 187 individually-cast hexagonal blocks, each weighing between 2.7 and 18 tons. These blocks were L-shaped in cross-section and, when positioned, formed a U shape with the adjoining hexagonal block. This U was then filled with in-situ concrete to create the structural grillage of beams to support the tower. The outside was covered with precast rings so that only the precast concrete was exposed. The structural sizes for the concrete sections varied from 1m deep × 0.7m wide at the base to 0.55m deep × 0.45m wide at the 22m height.
The framing around the doorways needed to be strengthened due to the concentration of loads and the fact that the doors were a discontinuity in the shell form. These doorways were constructed of structural steel sections fully welded into a continuous frame on-site and then encased in the concrete.
The spire of the tower was made entirely of precast concrete, constructed in complete rings up to 6.9m high or in halves for a similar height. These sections were fully reinforced and then bolted together on-site. The thickness of these sections reduced to 0.18m at the very top.
There was no repetition in the geometry. This presented an extremely complex engineering challenge for Robert Bird Group, which was commissioned to undertake all the engineering for the design, development and construction activities associated with the tower.
About the CONSTRUCTION
The hexagonal elements were constructed using a combination of precast and in-situ poured concrete. First, the internal hexagon was precast off-site in a factory environment and lifted into place on-site using a variety of cranes including one of the largest in the world, a 550-tonne mobile crane. The four teams of surveyors worked on locating the correct positions, within a 20mm tolerance.
Once the internal hexagon was placed, steel reinforcement was then inserted and an in-situ pour completed, stitching each hexagon to its surrounding pieces. When the stitching was completed, the outer skin was then completed by fixing hexagonal biscuits to the outer surface. These slotted into the internal hexagons and concealed the in-situ pour. The dramatic upper spire of the tower is made solely from these precast blocks. The Beacon is located on reclaimed land to form a harbor for the new marina at the university. Construction within the tidal zone required the installation of dams to enable this work to proceed. The footings for the tower consisted of 150 piles, 90 under the Beacon itself and 60 in the outer ring, each with a 750mm-diameter and penetrating an average of 22m deep into the natural dense gravels. These piles and the 2m-deep pile caps were required to support the dead weight of the structure as well as provide a sufficient base for the wind and seismic loads. Additionally, the Beacon is also supported by a 1.5m- thick pile cap ring involving