Meidling Emergency Hospital Helipad

The air ambulance intervenes around 120 times a year after accidents and brings patients to the Meidling Emergency Hospital. However, due to new legal requirements, the size and structural load-bearing capacity of the helipad of the hospital no longer complied with the legal framework. An enlargement of the existing landing area on the roof was out of the question for structural reasons. The client, AUVA decided to develop the new landing site as an independent structure right next to the existing one and to connect it with a bridge.

Furthermore, the patient transfer room was to be equipped with a new facade, a new sliding door, new drywall and tiled flooring, and the route from the new landing site was to be adapted accordingly. The individual levels of the rising building components had to be aligned with the approach path of the helicopter. The challenging electrical system included landing lights in line with flight safety requirements, the heating of the around 750m² landing area, lightning protection and the integration of all of this into the higher-level control technology of the Meidling Emergency Hospital.

This challenging construction project, commissioned by AUVA, therefore comprised the steel construction, the drilled piling, the foundations, the manufacture of the composite slab, the electrical engineering and the renovation of the entrance areas. Several departments at PORR performed all the work here. In addition to the steel construction department, the railway and civil engineering, specialist civil engineering, IAT and ELIN (Ortner Group) were also involved.

A double helix made of steel tubes.

PORR’s scope of services included the detailed planning for the steel construction, the manufacture and assembly of the helipad as the general contractor. When planning the construction, every single step was structurally calculated and drawn in order to be able to evaluate the forces and deformations in detail.

During the development of the steel construction details and their calculation, the main focus was on structural boundary conditions on the one hand, and the manufacturability and ease of construction on the other. The central part of the project was a double helix composed of welded steel tubes. This was made in so-called ladders in the factory on specially developed templates, then delivered to the construction site by special transport and positioned with the help of a mobile crane. The individual ladders were then connected to one another by fitted pipe segments, called cross bars.

Construction in two floors.

After an extensive study of options, the decision was made to erect the helix in two floors. The reason for this was that a ladder element with a total length of 30 metres undergoes very large deformations in the assembled state and could only have been controlled with difficulty on the construction site due to the three-dimensional geometry. With special, longitudinally adjustable connections to the central assembly tower, the cross bars could be installed without tension, thereby ensuring the plan geometry. Now in its final state, the double helix is a component with great rigidity in all directions. A bolted platform that is rigid in the radial and tangential directions was then placed on the welded double helix. The node formations and tolerances had to be chosen so that on the one hand the boundary conditions from the structural design and the execution standards were met,

but on the other hand simple and quick assembly without reworking on the construction site was guaranteed. For this purpose, a bolt connection was chosen between the double helix and the platform at a total of twelve contact points.

The radially running girders were connected to a central ring. A splice joint allowed both the bending moments to be transferred and the geometric tolerances to be compensated for by utilising the existing hole tolerance. The radial and tangential rows of beams were connected by means of head plates, and the safety net was attached to the ring beam. The seats of the connecting bridge are designed in such a way that independent movement to the existing structure is possible even in the event of an earthquake. Finally, the entire double helix was given a fire protection coating. At the outermost edge of the platform, we implemented lighting effects that set off the structure perfectly.

Drainage options and complex scaffolding.

The drainage of the platform leads in an architecturally inconspicuous way along a strand of the double helix to the foundation. In the event of a damaged helicopter, the escaping kerosene would also be discharged via the sewers and collected via separators installed in the foundation.

A bituminous seal is applied over the primary concrete. This is where residual water that cannot be diverted on the top level is discharged. A level with heating mats is arranged in the secondary concrete. This heating level ensures that no snow remains on the platform and that the surface does not ice up. In the secondary concrete there are also drainage gullies, beacons, temperature sensors and lightning protection devices.

A particular challenge in this construction scheme was planning and executing the scaffolding. An internal scaffolding tower was necessary for the attachment and installation of the ladder elements. An external scaffolding with a height of 25m and a diameter of 36m was required to access every single point of the double helix and for the assembly of the platform. The scaffolding company carrying out the work had little experience with constructing the double-cantilevered scaffolding needed due to the cramped structural conditions.

Elaborate planning with successful completion.

With regard to the plateau levels and the base area, the scaffolding had to be planned in such a way that the complex three-dimensional geometry of the double helix did not collide with the straight system scaffolding. One of the first subsections started with the scaffolding with an octahedron base. It was then gradually expanded with the installation of the ladders. Therefore, the accessibility for the assembly of the steel structure, the welding sequence and the site corrosion protection had to be fully planned before construction began.

The helipad went into operation on schedule in autumn 2021, and the contractually agreed total completion date, including the inventory and outdoor facilities, was achieved according to plan. This success was made possible by the excellent cooperation between several PORR departments working together to overcome the structural challenges.