Abstract
Wood has been extensively used in Chinese ancient buildings, and it is important to clearly understand the mechanical properties of wood after exposure to elevated temperatures. In this paper, three kinds of tests with 102 clear wood specimens fabricated with Chinese Dahurian larch for each kind of test were conducted. The residual compressive strength, tensile strength, and shear strength parallel to grain of specimens after exposure to different temperatures (100°C, 150°C, 200°C, and 250°C) with various exposure times (15 min, 30 min, and 45 min) and different cooling methods (natural cooling and water cooling) were obtained. Results indicate that exposure to elevated temperatures causes great degradation of compressive strength, tensile strength, and shear strength parallel to grain. When the exposure temperatures exceed 200°C, the relative compressive strength, tensile strength, and shear strength parallel to grain decrease greatly with the increase of exposure time. The residual compressive strength, tensile strength, and shear strength of specimens after water cooling are lower than that after natural cooling. Exposure temperatures also have a great impact on the weight loss and color change of wood. Based on the test data, degradation models for the residual compressive strength, tensile strength, and shear strength of wood were developed. Furthermore, the damage constitutive model of compressive (CDMC) and tensile (CDMT) parallel to grain was established and validated reasonably by tests.
Highlights
In China, Japan, and Korea, ancient timber buildings are extensively used and many have been selected as world material and cultural heritages [1]
Due to the combustible nature of wood coupled with the lack of the fire resistance design, traditional timber structures are made vulnerable to fire, which usually exerts devastating impact on the load-bearing capacity of them [2]
A fire-damaged timber beam in Guardian Angels Church, survived from a fire in 1902, was reused [5], as shown in Figure 2. erefore, correct mechanical properties evaluation of fire-damaged wood is of great significance [6]
Summary
In China, Japan, and Korea, ancient timber buildings are extensively used and many have been selected as world material and cultural heritages [1]. As for precious heritage timber buildings, keeping them as what they are is required by the protection standard GB 50165 [3] It is proved possible by the facts that wood members are usually able to maintain a substantial part of the load-bearing capacity due to an insulating char layer when initially exposed to fire (Figure 1) [4]. Chen et al [14] compared the calculation methods for re rate of timber beams Eurocode, American code, Australia code, and Canada code and found that Australia code prediction including the density e ect of wood species was more closer to test results. Mechanical properties of re-damaged wood have been extensively investigated due to their important roles in the correct prediction of the residual load carrying capacity. (3) Establish a damage constitutive model of high temperature-damaged wood to re ect the deformation characteristics
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