ABSTRACT
ABSTRACT: This paper continues the historical analysis of tall wooden buildings started in the author’s ICSA2 010 Key note pap er, Better than Steel? Th e use of timber for large an d ta ll buildings from Ancient Times until the Present (Langenbach 2010) The Industrial Re volution began in Great Britain with the me chanized manufacture of te xtiles, which led to changes in both the scale and technology of building construction. In the United States, where wo od was p lentiful, the inte rior stru cture of th e multi-sto ry textile mills was o f timber hidden behind the brick or stone exterior walls. The need for water power to drive the machines prior to electricity demanded that the construction be located in multistory buildings adjacent to rivers, wh ich dic tated th eir form . Durin g the 1820’s and 30’s, tradition al timber framing with beams and closely-spaced joists was rapidly replaced with heavy timber construction in which joists were eliminated in favor of 2.5 to 3 inch (6 cm-7.5cm) planks grooved and splined together and spanning from beam to beam, a distance of about 8 to 10 feet (2.4-3.0m) on center. To qualify as slow-burning, the beams were a minimum of 12 inches (30cm) thick in either vertical or horizontal thickness. This system of construction was later identified and promoted as “slow-burning,” also referred to as “mill construction”. Historically, the risk of fire in cotton mills was high because friction and freq uent sparks from foreign matter getting into the rotating machines would easily ignite the cotton dust. Al-though this multi-story heavy timber construction has been commonly thought to have been developed because of it s fire-re sistive q ualities, h istorical re search ap pears to su pport th e find ing tha t it originally e merged b ecause o f its ec onomy and practicality, even with th e increase in the amount of wood it used. At this same time there was a need for the increased strength and stiffness that it provided. The historical records show that it was somewhat later that it was found to offer significant advantages in reducing the spread of fires as we ll as significantly delaying the collapse of burning floors in mills, after which it became known as “slow-burning construction”. This paper describes the attributes and the history of what is th e precursor of “Type IV, Heavy Timber” in the IBC, the current building code in North America.
