Industrial bridge construction with cast in place concrete : new production methods and lean construction philosophies
Sammanfattning: The construction industry is associated with high costs, low productivity, a lack of quality and low profit margins. Too often the actual cost for a project exceeds the expected cost. Industrialization of the construction industry is said to be the key to success and its definition is often debated, but what is the meaning of industrialization? How should industrialization be realized in the construction industry? Who is responsible for the change within the industry and which benefits can be achieved by industrialization? These are some of the questions brought up during the course of the research project. The project has been financed by VINNOVA´s research consortium "Road/Bridge/Tunnel" and by Swedish Road Administration Business unit Production and Maintenance, Cementa and Betongindustri. SRA has also contributed with resources from the FUD Program (Research, Development, Demonstration). The project has so far comprised different forms of full scale studies, laboratory studies and theoretical work. In the beginning of the project, interviews were carried out with management of construction sites to lay a foundation for the time and cost apportionment of typical bridges, also to examine which common bottlenecks present in production and to examine how large part of the cast in place concrete the self compacting concrete (SCC) constitutes. The interview gave also an insight in how site management views the possibilities for change in construction today. To further find out the time and cost apportionment, ten bridge projects were examined. The results from this study were studied with regards to new production methods. Unit times for SCC were thus compared with unit times for traditionally vibrated concrete, unit times for rebar carpets were compared with unit times for traditionally clenched reinforcement, and also the effects of left formwork were studied. In these theoretical studies it was clear that great potential for changing today's construction business. To try to verify the theoretical results, mainly two full scale studies have been carried out. Te first was a replacement of an existing bridge on the European road No 4 outside Kalix in the northern parts of Sweden. The project was followed and managed by the research team in close collaboration with the client, contractor, designer and material suppliers. The study was comprehensive and started already in the design phase where the bridge was redesigned for new technical solutions aimed for production enhancement. Here prefabricated reinforcement cages to the foundation and SCC to the whole project were used. Also rebar carpets were used for the superstructure. The reinforcement in a typical bridge superstructure of today most often consists of approximately 80% longitudinal reinforcement and 20% shear force reinforcement. The project aimed at examining if it was technically feasible to use rebar carpets and if there were any economical benefits in using it. The aim was also to examine if it was economical to prefabricate reinforcement cages and transport them to the site for placement in comparison to traditionally fix reinforcement piece by piece. An additional objective was to examine the effect on the working environment imposed by the change in working methods. The other full scale project was concentrated on the use of SCC, but also the rebar carpets were examined to some extent. Here, the design phase was not followed by the researchers and no redesign for maximizing the use of carpets was performed. The aim for the project was above all to examine the economic conditions associated with the use of SCC, and to study the working environment in connection to the casting of SCC compared to traditionally vibrated concrete. The accomplished studies were successful. Especially at the bridge in Kalix, a detailed planning could be realized and Lean Construction philosophies were utilized, this proved to be an important factor for the success. Considerable savings in work efforts at site were realized (approximately 80% of the reinforcement fixing time and approximately 67% of the casting time). The total project time was decreased with approximately 20%. Also a lower total cost for the project was achieved. For the project in Nynäshamn the same effects were not realized since the ideas of new working methods and new planning systems came in to late. However, some positive experiences were gained considering the use of SCC and rebarcarpets. The much important working environment was followed up in the project with a special analytical method, ErgoSAM. Large differences in the workload were measured in a comparison between traditional reinforcement fixing and the handling of prefabricated reinforcement as well as when comparing traditionally vibrated concrete with SCC. The largest economic benefit from introducing SCC to a contractor in civil engineering projects is probably on the superstructure of a bridge, since the largest number of workers is needed during casting of traditional vibrated concrete and it is therefore associated with large casting costs. Hence, the number of workers needed for casting can be markedly reduced if SCC is introduced and proper planning has been carried out. However, controversially it is often easier to introduce SCC for foundations, columns or plate structures since these structural parts are less dominant in the construction and the "risk" related to using SCC is small. However, for these smaller less people demanding castings it is more difficult to achieve economical benefits in using SCC. The overall risk using SCC is that the product it is not robust enough, which might result in the concrete does not enclose the reinforcement satisfactory and rework is needed. Probably the largest benefit with using SCC is, as mentioned earlier, the improvement in working environment. Therefore, the economy of the Swedish construction industry and society can benefit significantly from using the right kind of working method during construction. Finally, it was concluded in the project that, to be able to utilize the "new" and improved production methods in a broader approach, it is of importance to apply Lean Construction philosophies at the planning and construction. Preferably a Lean Design Team should be established.
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