Germany's Chancellor, Angela Merkel, has cut the ribbon to open the new Bauhaus Museum in Dessau – a building designed to hold the 49,000 exhibits in the Bauhaus Dessau Foundation collection.

Dessau is the German city most closely associated with the Bauhaus school of design, which was operational between 1919 and 1933, and is considered one of the most influential movements in modern design.

Although the original school building in Dessau still stands, it wasn't able to display the entirety of the Foundation's collection, while other Bauhaus buildings in the city could not be adapted to meet the necessary conservation requirements. Consequently an international competition was held to create a new museum, located between the city centre and the municipal park.

The winning entry, chosen from 831 submissions, came from Barcelona-based Addenda Architects, which envisioned a 100-metre long Black Box of reinforced concrete, with no natural light but with optimal climatic conditions to preserve the sensitive items in the collection.

This stands on stilts five metres above visitors' heads and is accessible via two stairwells from the ground floor, where there is the Open Stage, a flexible multipurpose space with a lobby, ticket desk, cafe and shop, and 600sq m (1,970sq ft) of space for changing exhibitions.

All is enclosed within a glass façade, with, on one side, the buildings of the city, and on the other, the park and trees, each reflected in the glass of the museum. This outer "envelope" measures 105m long, 25m wide and 12m high, and required 571 triple-glazed glass panes.

Construction of the building has taken just under two-and-a-half years, with a €28m (US$31m, £25m) project budget.

Roberto Gonzalez of Addenda Architects said: "Our basic concept for the museum was to create a large, flexible space so that exhibitions and workshops can take place without feeling restricted in any way by the architecture. We obviously had to integrate this idea with the requirements for the museum: it had to provide an area of 1,500 square metres for the collection, protect the exhibits from direct sunlight and offer ideal climatic conditions.

"This is how we came up with the idea for the Black Box, a closed concrete cube that floats above the ground. At almost 100 metres in length and 18 metres in width, the Black Box is supported by two staircases, which are 50 metres apart. It doesn't have any supporting columns.

"Of course, we couldn't just leave the space below the Black Box open. We are in Northern Europe where it rains a lot and gets very cold. So we built a kind of winter coat made of glass. This glass façade protects the building, but it also created additional space for exhibitions, events and offices on the ground floor."

Gonzalez also revealed that the Black Box is constructed "like a bridge", in that it is bent upwards at the ends, which will allow it to settle into a horizontal line over a period of years, pulled down by its own weight and that of its exhibits and visitors.

"That's not going to happen immediately but in the course of the next maybe 20 years. Because the Black Box is made of concrete and steel, the outcome can't be calculated exactly. There is some wiggle room – which is much larger than is standard."

Dessau is the second German city to open a Bauhaus museum recently, with Weimar – where the movement began – revealing its new museum less than six months ago, and Berlin – where the Bauhaus movement ended – planning to open a third museum in 2022.