Construction investment has been on the rise since 2011. However, the lack of construction workers and engineers is a serious problem. As the amount of construction project is forecasted to increase until 2020, securing the construction workers and engineers is an immediate agenda for the government, local government, and construction industries.
On the other hand, since 2010, usage of “Cross Laminated Timber (CLT)” has started in Japan. It is attracting attention to reduce carbon emissions by utilizing timber resources as an alternative material for building structures. The authors focused on the fact that assembly construction methods including CLT could shorten the construction period that would lead to saving the workforce and improving the construction work environment.
Fukushima Prefecture decided to develop a total number of 4, 890 public housing, and by 2017, 4707 were built. One project has been constructed by CLT structure with a short construction period of 5.5 months.
This research is about the efficient construction by CLT panel on a low-rise residential building. An actual project “Iwaki CLT public housing for revitalization” had been analyzed which has 57 units on four divided buildings by three stories. Previous researches mainly focus on the structure of the CLT construction, but analysis of planning methods and especially on the productivity of CLT constructions are also in need.
To realize “Iwaki CLT Public Housing for Revitalization”, the authors have proposed several manifests for efficient construction. The hypotheses on design methods and construction schemes were made with the design and building team KIAMI (Fukushima CLT Society), together with two previous researches on “YUGAWA CLT Collective House (2015)” and “TSUKUBA CLT Test House (2015)”.
CLT panel construction had been carried out smoothly from 24th November to 29th December 2017. To prove the hypotheses, a man-hour survey had been conducted during the panel construction process on site. As the research results show, a total of 1, 875 CLT panels (933 wall panels, 499 slab panels, 443 appended walls) have been measured. “Panel setting time” and “crane-up time” for each panel and the number of workers who handled the process was recorded. Finally, design method theories and construction management schemes were created by analyzing research data and documents.
As a result, it is possible to show the agenda for CLT building to improve construction efficiency by introducing CLT.
< Design method theories on panel structure planning >
1. Adequate panel clearance should be chosen. It should be set to 1mm for each CLT panel. Excessive clearance between panels for allowance of panel settings are likely to hinder construction accuracy.
2. The joining method choice by accuracy is more critical than flexibility to have trouble-free construction.
3. Reducing the number of panels is effective for shortening the construction period, and it is practical to design by large panels.
<Guidelines for construction planning and management>
4. Work time tends to converge due to learning effects. Target operating time of CLT wall panels installation can be set to 5 minutes 20 seconds.
5. It is important to manage the order of installation for each work and panels. The panel set order should be planned without panel supports.
