Paleisbrug: Indaten® weathering steel bridges the past and the present

Detailed information

Benthem Crouwel Architects bridge the past and the present

‘s-Hertogenbosch was defended during the Eighty Years’ War (Dutch War of Independence) by temporarily flooding the land around it. Today, a great deal of this land has not yet been developed resulting in ‘s-Hertogenbosch bordering open green landscape known as the Gement. Nowhere else in the Netherlands is an area of such natural landscape so close to a city centre. The architects at Benthem Crouwel ensured that their design connected the beauty of the Gement that was created by the past with the newly developed Paleiskwartier, which is comprised of the municipality’s court building, various applied sciences universities, offices, and residential homes - the present.

Opened in May 2015, the Paleisbrug won the National Steel Prize in 2016.

Views of the Gement

Inspired by the breath-taking views of the Gement from the Paleisbrug, a park was created on the 10-metre-wide bridge that enables people to take in the beautiful landscape while also appreciating the greenery along the Dommel River and the recreational area around the Hofvijver (Court Pond) in Paleiskwartier. By turning the bridge into a park-like area, more than 2500 square metres of park has been added to the centre of 's-Hertogenbosch.

Indaten® weathering steel from ArcelorMittal

The bicycle and pedestrian lanes, plants, trees, benches, and lighting of the Paleisbrug have been integrated in folded plates of Indaten® S355J2W weathering steel from ArcelorMittal. With its improved resistance to atmospheric corrosion, Indaten® forms a changing protective patina that evolves with the environment. The rusty colour of this steel is characteristic for the Paleisbrug.

Weathering steel is a steel alloy with a dense corrosion layer, bringing the corrosion process to a virtual standstill. This means the metal can be left exposed. This steel, which corrodes about 0.5 mm per 100 years, is 1 mm thicker in all areas than would initially be required; after all, steel corrodes on two sides. As such, the bridge has a lifespan of at least 100 years. Furthermore, the robust appearance of the steel fits in well with the atmosphere created by the city's fortifications.

Indaten® weathering steel offers long term durability and no maintenance or painting costs, meaning no disturbance - the bridge will not need to be closed to maintain the weathering steel.

Structure

The Paleisbrug is composed of various sizes of spans that run from column to column. The columns are covered in weathering steel panels so that they form a whole with the spans. The spans are comprised of horizontal weathering steel ducts that cover a concrete compression layer. The longer the span, the higher the ducts. The largest span, measuring 60 metres in length, runs across the railway track. For this span, an additional trussed joint was created on top of the bridge deck. A structure underneath the bridge deck was not possible in this place as the trains require such a large amount of headroom that the entire bridge would have had to be raised by a couple of metres. The trains travel under the bridge with the required 6.75 metres of headroom between the tracks and the bridge, which has a total weight of 1350 tonnes of steel.

The concrete compression layer is perforated in the areas with trees, which has created a tree bed in the steel box girders. The perforations are strategically placed in order to facilitate both the planting scheme and the structure. The concrete is not visible anywhere on the bridge.

Four lanes, each two metres wide and alternately consisting of flower beds and paving, run across the length of the bridge. Strips, sixty centimetres wide and finished with a weathering steel studded sheet, run between the flower beds and the paving. This is where the cables, pipes, and gutters for the rainwater discharge from the street can be found. The setup of the bridge deck and pipework can be replaced, if necessary, without affecting the main supporting structure.

Greenery

The placement of the flower beds and trees on the Paleisbrug was designed in collaboration with landscape architect Piet Oudolf. Divided into three zones, each section of greenery blends into its surrounding area. On the city centre side, the bridge has low, savannah-like plants and individual trees. On the portion of the bridge that covers the railway track below, there are only low plants that allow for clear views of the surrounding landscape. On the Paleiskwartier side, the bridge offers up more of a forest-like character. These three green zones merge to form a new eco system in the heart of the city.

A drip feed watering system with detection was installed in the flower beds on the bridge. The discharge from the planters is fitted with an additional overflow pipe, so that the plants will never receive too much water.

In the evenings, the plants, benches, and paths are lit up by LED lighting, which means the bridge is a pleasant area even after sunset.

An environmentally friendly solution: Solar collection

Keeping the bridge free from ice during the winter cannot be carried out via the typical means of road salt as this would harm the plant life on the bridge. Benthem Crouwel looked for a sustainable and environmentally friendly solution, and they found one in the form of solar collection. The Paleisbrug functions as a giant solar collector during the warm summer months. The floor heating/solar collector is connected to a heat/cold storage unit. During the summer, the bridge retrieves more heat than is needed to heat the bridge in the winter, so it supplies the surrounding district with this extra solar energy. During the winter, the floor heating is connected to an Aquifer Thermal Energy Storage (ATES) system that provides the stored heat (at 10 degrees Celsius) keeping the bridge ice-free.