National Institute of Forest Science recognizes ‘structural glued laminated timber’ as a standard fire-resistant structure
Structural glued laminated timber now allows construction of up to 12 stories without fire-resistance testing
The National Institute of Forest Science (Director Jeon Beom-gwon) under the Korea Forest Service announced that, now that structural glued laminated timber has been recognized as a standard fire-resistant structure, the fire-resistance testing that previously required substantial cost and long waiting periods can be omitted, which is expected to greatly facilitate the spread of medium- and large-scale timber construction.
Generally, buildings above a certain scale are required to use fire-resistant structures in their main structural elements so that occupants can evacuate in the event of a fire. To be recognized as a fire-resistant structure, a full-scale structure must pass a fire-resistance test in which it is exposed to standard fire conditions of 1,000℃ or higher for a certain period of time.
Existing concrete and steel-frame structures offer a very wide range of usable fire-resistant structures, and even the 3-hour fire-resistant structures required for buildings of 13 stories or more are available on the market. However, it was not until November 2020 that the 18 m height limit was abolished for timber structures, and currently only the 1-hour fire-resistant structure, which permits construction of up to 4 stories, is produced and supplied by three companies.
Accordingly, since 2019 the National Institute of Forest Science has conducted joint research with the Korea Institute of Civil Engineering and Building Technology (the agency for fire-resistance testing and fire-resistant structure recognition) to standardize the fire-resistance performance of structural glued laminated timber — a representative member of heavy timber structures. Through this research, basic combustion characteristic data were established, and based on this the Korea Institute of Civil Engineering and Building Technology pursued standard recognition of the fire-resistant structure, which was recognized and announced on December 22 last year.
With this standard recognition, producers of KS F3021 structural glued laminated timber (species group A, including larch species) can now obtain fire-resistant structure recognition for columns and beams through factory inspection alone, without fire-resistance testing. As a result, the fire-resistant structure recognition procedure, which used to take more than a year, has been shortened to about one month, and once granted, the recognition can be used permanently.
In addition, performance-based fire-resistance design of up to 2 hours is now possible based on the charring depth of the timber, allowing buildings of up to 12 stories to be freely constructed. This is a result that proves timber structures can be sufficiently safe against fire depending on the design.
To expand the use of domestic timber and promote eco-friendly timber construction, the National Institute of Forest Science has developed medium- and large-scale timber construction technology, and on this basis completed the 5-story ‘Hangreen Timber Hall,’ the tallest timber structure in Korea, in Yeongju, Gyeongsangbuk-do, in 2019.
During construction, in carrying out the 2-hour fire-resistant structure recognition test for the timber structure required for the 5-story ‘Hangreen Timber Hall,’ it experienced testing costs of about 15 million won per structural element and a long waiting period of about one year.
This standard recognition is the result of regulatory innovation achieved when the National Institute of Forest Science — which had confirmed that fire-resistance testing was an obstacle to the spread of medium- and large-scale timber construction — and the Korea Institute of Civil Engineering and Building Technology — which had directly confirmed the stability of timber structures in 2-hour fire-resistance tests — jointly recognized the need for standard recognition of fire-resistant structures for timber.
Shim Kuk-bo, head of the Wood Engineering Division, said, “We expect this to make fire-resistance design easier for timber public buildings, which have recently been growing larger and taller. Going forward, for timber buildings of 13 stories or more, we plan to continue expanding the scope of standardization and conducting follow-up research on 3-hour fire-resistance performance.”
▲ As the Korea Institute of Civil Engineering and Building Technology pursued standard recognition of the fire-resistant structure and structural glued laminated timber was recognized as a standard fire-resistant structure, timber buildings of up to 12 stories can now be constructed. The photo shows Hangreen Timber Hall (photographer Park Young-chae)