Award: City of Oulu
Year: 2021
Partner: Sitowise
Dimensions:
Length: approx. 190,00 m, longest span approx. 80,00 m
Width: 4,50 m
Construction: Block girder bridge with glulam deck and natural stone decking
Our services: Design, static preliminary design, cost estimate
Description
The city of Oulu held a competition in February 2021 to design a bridge for the new Hartaanselänranta area, one of the youngest neighbourhoods in the growing city, where preparations for the 2025 housing fair are underway. The new residential area is crossed by the mouth of the river Toppilansalmi which is crossed by the proposals of the design competition.
For the design competition, Sitowise assembled its own team of experts: "Natural materials fit the spirit of the area and the design goals. That is why we wanted to design the bridge as a wooden structure, as there are no similar bridges in Finland. To bring in new ideas and up-to-date know-how for wooden bridge solutions, we invited a German timber construction pioneer to join us. IB-Miebach was an important part of our team," says Ari Savolainen from Sitowise.
Sitowise participated with two timber construction designs - an arch bridge and the log girder bridge here. The structure's supporting framework, a two-strut beam structure in timber construction, spans five spans as a continuous structure with Gerber joints. The main girders are connected by steel cross frames and have high vertical and horizontal stiffnesses. The glulam beams are stepped according to their load: the highest cross-section results above the four-armed supports. Due to a sensible arrangement of the joints in the moment-zero passages, all elements can be prefabricated. The resulting forces and moments on the foundation bodies are transferred via pile foundations. The deck made of large-format natural stone slabs corresponds optimally with the material wood and is very durable. The slabs are maintenance-free and develop a natural patina over time. The slab surface is sandblasted for slip resistance and designed as a waterproof covering, as the joints are underlaid with drainage channels and closed by a permanently elastic jointing.
The service life of the superstructure - assumed to be 100 years - is determined by the structural wood protection. The upper and lateral protection against weathering, moisture ingress and UV exposure is ensured by the tight roofing with lateral overhang and redundant protection in the form of waterproofing on the upper side of the beam. The external driving rain protection of at least 45° inclined rain direction is achieved by the projection of the closed covering in combination with the recessed step of the cross section to the lower edge of the beam. The design takes into account good air circulation in all areas so that drying is favoured. All components are easily accessible and can be inspected and tested by hand. The components exposed to direct weathering are made of durable materials such as steel, stainless steel or reinforced concrete.
