Physics of a celestial structure

  Pillar of strength

The structure had to support the weight of more than 800 people, including 700 members of the choir and orchestra. The weight of the altar itself, including the sacrificial table, chairs, pulpit and musical instruments, also had to be taken into account. Peri Polska, which produced the platform, used a SkyDeck floor shoring, covering the steel truss with aluminium panels measuring 75x150cm. The top side of the panels was coated with a fine plywood layer, while the structure was reinforced with additional 21mm thick wooden boards produced in Finland.

The Holy Cross

Only a few people were aware that the structure was shifted 60cm towards the centre of the square at the very last moment. The geodetic sleepers used by the designers proved to be insufficiently precise – huge columns supporting the main illumination system of the square were in the place where the altar’s foundation was supposed to be.

Stanisław Końsko, director of the Transport and Ancillary Production Plant of Mostostal Warsaw, reveals that: “Both cross and roof were anchored using additional loading of the base with 50-ton ballast. The result was a structure which coped well with weather changes without damaging the surface of the square.”

 Attention was also directed at removing water should rain occur. The plan was for it to flow down a gutter installed along the lowest edge of the roofing to two 5cm thick ‘leksan’ drainage pipes, i.e. made of transparent polycarbonate. The same material was used for the plates suspended from the structure of the roofing above the papal throne. A stained glass figure of the Holy Ghost was fixed to modules of 2x6m in area and 8mm thick.

But the effect of this struggle with gravitation terrified the graphic designer, who argued that the densely dispersed screws destroyed the composition of the stained glass window on the leksan material. Ultimately, the number of screws hidden in the picture’s background was reduced.

 We asked a construction specialist to estimate how much the investment might have cost. He assessed the cost of materials based on the project’s technical data and on widely accessible price catalogues:

waluminium panels to cover the cross – around PLN 30,000

wplywood on the platform which cannot be reused – around PLN 100,000

For ever and ever?

The cross, altar and stained glass image will be donated to Polish parishes as precious souvenirs of the papal visit. The scaffold and floor panels of the platform were made of multiple-use elements, which means they will surely be used again on many construction sites. The same is true of the plywood sections which were not destroyed during assembly or dismantling and will be used again for other boarding purposes.

The future of the steel roofing structure is still unclear. The initial plan was to give it up for scrap, but then the organisers received an offer to deliver the whole structure to a company which would use it as the skeleton structure of a standard all-year roof. Tomasz Kosma Kwieciński of ATJ Architekci, however, appeals for caution: “The fact which must be remembered is that we did not take into consideration the load on the structure resulting from snowfalls, as they do not tend to occur in May.”  

Tomasz Cudowski