Lighthouse

Projects

Denmark’s tallest residential building – the Lighthouse at Aarhus Docklands (Aarhus Ø) – requires Denmark’s greatest precision in building set-out.

LE34 shows the way

PROJECT DETAILS

Client:

Per Aarsleff A/S

Periode:

2019 - 2022

Ydelser:

Fixed point network
Setting out for buildings
Levelling
Plotting based on 3D, IFC files
Monitoring of set-out
As-built documentation

At 142 meters, the building is a lighthouse in more than one sense. It is a guiding light for Aarhus, for urbanisation of the harbour areas and for how to build a high-rise building – from 3D design to technical set-out that takes into account the massive pressure of the concrete, wind and sun on the structure. As well as the water that surrounds it.

Out of the ordinary

Water and unobstructed views of Aarhus Bay and Kalø Vig are the watchwords for the views of the future residents. But they are also the key words for all the parties involved in the construction, because the combination of the surrounding water and the record high altitude make many aspects of this project a bit extraordinary.

As a land surveying company, we normally place prisms and fixed points on neighbouring properties to create a fine-meshed fixed point network that ensures the accuracy of our setting-out work. However, on the Lighthouse construction this option is limited to only nine prisms on the roof of the few neighbouring properties. In the other places we would have placed them, there is water. This creates a one-sided geometry, which we have compensated for using advanced GNSS technology.

Precision at sea using active GNSS fixed points

On each floor, we have set up four large prisms fitted with a GNSS receiver. These are also known as active GNSS fixed points. Combined with the measurement of the five prisms on the roofs of the neighbouring properties, we get a position within 2–3 mm.

When prism and GPS are securely tightened, they run for an hour and collect GNNS data, which is subsequently processed and netted. We repeated this process three times per floor – the first time as a check of the location of the large form for the “core” of the construction, the second time as a check of the precast core and the third time as plotting fixed points for casting a new deck.

In addition to ensuring a high level of precision in set-out, the frequent use of GNSS technology also ensures the executing contractor Per Aarsleff A/S a continuous overview of any deviations from the design, so that the casting for the next part of the building can be adapted to the real conditions.

Light in the morning darkness

LE34's fixed points and set-out show the path forward in terms of where and how the next contractors in the process are to complete their work on the floor. Therefore, we often start working quite early in the morning – floor after floor.

Light in the morning darkness

Mikkel Langrebe Kolding, surveying technician, LE34

“It is great to be part of – Denmark’s tallest residential building project. I was assigned to the project in the beginning, in 2019, and have worked closely with per Aarsleff A/S, because it is the same people over such a long period of time. It is set-out work where you constantly have to think five steps ahead and work independently, so everything is ready for the next team to take over.”

Precision, floor after floor

Since the construction of the Lighthouse began in 2019, LE34 has set out thousands of points: Set-out for the pillars on which the foundation is laid, set-out for each of the 45 floors, set-out for façades, walls, fixtures and more.

We watch for wind and sun

The advanced builder’s level, inclinometer, is set up every 10 floors and shows exactly how much wind and sun cause the building to bend in either direction.

The only time when the building is straight, in principle, is when it is calm and the sun is not shining. The inclinometer is read and we compensate for the current deflection when we set out.

We collect documentation

During the construction process, we have set out thousands of points – for the large structures such as a new floor and detail set-out, such as mounting of façade elements. In total, we have set out over 15,000 points.

After each new floor, we create as-built documentation to verify that the building is built as designed, including as-built scans of lift shafts and steel mounting.

Extensive monitoring of potential set-outs

Sun and wind are not the only things that constantly affect the Lighthouse building. So too does the building’s own weight. This impact is something LE34 also watches through extensive monitoring of potential set-outs.

We do this by continuously levelling to mainland bolts. Due to the surrounding water and due to the fact that the Lighthouse is built on old seabed, monitoring is carried out from established points several kilometres away – from existing bolts from the official Danish levelling network. The building is designed with the lower floors shrinking and settling under the heavy pressure of the concrete and with the upper floors becoming 2–3 mm higher than the lower floors.

The as-built documentation and the monitoring of set-offs are an important element for the builder and contractor’s overview and ensure a factual knowledge and data basis at all stages of the construction.

Multifunktionel jordfordeling på Femern 2

Rene Bundgaard Christensen, chartered land surveyor, LE34

“Lighthouse is the first building where we set off a large number of the points based on 3D files. This allows us to see the entire construction from all angles on the controller to the total station when we work, and gives a good sense of context.”