Method of constructing a supporting structure in arched form, the supporting structure comprising a plurality of sequential overlapping frame structures, the method comprising: providing a first initially straight or pre-curved frame structure (10,30,70,80) having a first end and a second opposite to said first end, said first and second ends being separated from one another by an initial distance; pivotally supporting said first and second ends; pushing the first and second ends towards one another to achieve a displacement of said first and second ends relative to one another, thus causing the first and second ends to pivot and said first frame structure to progressively and flexibly bend against a resiliency thereof into a final arched form, wherein the displacement of said first and second ends relative to one another amounts to at least 1% of the initial distance between said first and second ends; and fixing said first and second ends relative to one another in their displaced position so as to preserve the final arched form of said first frame structure; providing a second initially straight or pre-curved frame structure (82, 84) extending alongside the first frame structure, each of the first and second frame structures comprising an intrados surface and an extrados surface; causing said second frame structure to progressively bend concomitantly with said first frame structure in such a way that one of the intrados (90,94) and extrados (88,92) surfaces of the first frame structure contacts the other of the intrados and extrados surfaces of the second frame structure at the latest when said first frame structure is in its final arched form; and fixing said second frame structure to said first frame structure so as to prevent relative movement between them; and wherein each of the first and second frame structures comprises a fibre-reinforced polymer hollow formwork into which concrete can be poured and allowed to set. providing a first initially straight or pre-curved frame structure (10,30,70,80) having a first end and a second opposite to said first end, said first and second ends being separated from one another by an initial distance; pivotally supporting said first and second ends; pushing the first and second ends towards one another to achieve a displacement of said first and second ends relative to one another, thus causing the first and second ends to pivot and said first frame structure to progressively and flexibly bend against a resiliency thereof into a final arched form, wherein the displacement of said first and second ends relative to one another amounts to at least 1% of the initial distance between said first and second ends; and fixing said first and second ends relative to one another in their displaced position so as to preserve the final arched form of said first frame structure; providing a second initially straight or pre-curved frame structure (82, 84) extending alongside the first frame structure, each of the first and second frame structures comprising an intrados surface and an extrados surface; causing said second frame structure to progressively bend concomitantly with said first frame structure in such a way that one of the intrados (90,94) and extrados (88,92) surfaces of the first frame structure contacts the other of the intrados and extrados surfaces of the second frame structure at the latest when said first frame structure is in its final arched form; and fixing said second frame structure to said first frame structure so as to prevent relative movement between them; and wherein each of the first and second frame structures comprises a fibre-reinforced polymer hollow formwork into which concrete can be poured and allowed to set.