# Parallel-to-Grain Compressive and Tensile Behavior of Paulownia Wood at Elevated Temperatures
###### Abstract  
Fast-grown Paulownia wood is extensively used as construction material in China. The mechanical properties of Paulownia wood at room temperature are well known. However, investigations of its mechanical behavior at elevated temperatures are very limited. To address this issue, thermal analysis was conducted to investigate the mass loss and reaction heat during water evaporation and thermal decomposition. Moreover, parallel-to-grain compressive and tensile tests were conducted on clear Paulownia wood specimens at temperatures ranging from 20 \({}^{\circ}\)C to 220 \({}^{\circ}\)C. It was found that kinking is the main failure mode of the compressive specimens, while transverse rupture was frequently observed in the tensile specimens. At 220 \({}^{\circ}\)C, the retention rates of the average parallel-to-grain compressive and tensile strengths were 38% and 42%, respectively. However, the strengths significantly increased as the temperature increased from 100 \({}^{\circ}\)C to 140 \({}^{\circ}\)C, due to the moisture evaporation and the hardening of the dry lignin. The design curve suggested by EN 1995-1-2 was very conservative (as much as 76%) at estimating the parallel-to-grain compressive strengths. However, the design curve was slightly nonconservative (less than 6%) at predicting the parallel-to-grain tensile strengths when the temperature was below 60 \({}^{\circ}\)C. Furthermore, a significant reduction (approximately 40%) in the deformation capacity was found when the temperature was higher than 180 \({}^{\circ}\)C.  
Paulownia wood; elevated temperature; tensile behavior; compression behavior; thermal analysis +
Footnote †: journal: _Applied_  
between 25 \({}^{\circ}\)C and 288 \({}^{\circ}\)C. It was found that the tensile strength decreased slightly from room temperature to 175 \({}^{\circ}\)C, and then reduced significantly when the temperature was higher than 175 \({}^{\circ}\)C. [PERSON] [9] reported the parallel-to-grain tensile properties of spruce at temperatures between 25 \({}^{\circ}\)C and 250 \({}^{\circ}\)C. It was found that the tensile strength of spruce at 250 \({}^{\circ}\)C is 35% of that at room temperature while the tensile modulus is 53% of that at room temperature. [PERSON] [10] conducted parallel-to-grain tensile experiments on larch and Douglas-fir wood at temperatures from 20 \({}^{\circ}\)C to 250 \({}^{\circ}\)C, considering three temperature durations of 60, 120 and 180 min. A nonlinear relationship was found between the ultimate tensile strength and the temperature. The reduction in the tensile strength was slight in the range of 100 to 150 \({}^{\circ}\)C and the peak tensile strength was found in the range of 150 to 200 \({}^{\circ}\)C. When the temperature was higher than 200 \({}^{\circ}\)C, the tensile strength decreased rapidly. For the specimens with a temperature duration of 60 min, the average tensile strength of Douglas fir and larch at 250 \({}^{\circ}\)C was 33% of that at room temperature. [PERSON] et al. [11] studied the influence of moisture content and temperature on the tensile properties of New Zealand pine, and the tensile stress-strain relationship under different moisture content and temperature was presented and discussed. [PERSON] et al. [8] reported the compressive properties of dried Douglas-fir wood at elevated temperatures. The results showed that the compressive strength decreased slowly as the temperature rose from room temperature to 288 \({}^{\circ}\)C. [PERSON] [10] studied the parallel-to-grain compressive strength of Douglas fir and larch wood at elevated temperatures. It was found that the failure mode of the specimens at temperatures from 20 \({}^{\circ}\)C to 130 \({}^{\circ}\)C was kinking. As the temperature increased from 130 \({}^{\circ}\)C to 250 \({}^{\circ}\)C, end crushing was the typical failure mode. [PERSON] et al.