The aim of this research was to build a chair resistant to force from front to back. To achieve this goal, poplar wood was treated with heat and steam, and then curved at an angle of 90°. Curved frame was used for manufacturing chairs. In this study, three different designs of chairs were used. Control sample is a chair of custom type. The first design was a chair with a curved frame forming the structure back down to bottom (one-piece type) and the second design with two curved parts (twopiece type). Front to back load tests were conducted by mechanical universal testing machine in accordance with DIN EN 1729-2 standard. For each design, the test was repeated three times. The results of the experiment showed that differences between the designs were significant. The full type chairs were broken at the load about 1725 N, but the partial type chairs at about 1421 N. For the top to bottom load test, the full type chairs were broken at about 1052 N, other chairs were more resistant. In general, by introducing a design using the curved frame made of treated poplar, the resistance of chairs is improved. Keywords Wooden chairs Á The maximum front to back load Á The maximum top to down load Á Curved poplar wood & Ali Bayatkashkoli

Expanding the service life length of wooden made furniture, and consequently decreasing the demand for raw wood could help the economy of the world society and environmental safety. In this research, an experimental inquiry was conducted to determine the effects of curved members, the frame integrity, chair scheme, and rehabilitation of even the failed chairs on the behavior of chairs. The flexural properties of the curved specimens were firstly determined using the ASTM D143-94 test. Then, three layouts of chairs (A, B, and C) made from poplar wood were examined under the DIN EN-1729-1&2 standard. Finally, the failed chairs were rehabilitated using the sheets of glass fiberreinforcing polymers (GFRP) and re-tested. The results showed that the rehabilitation of the curved samples causes rebounding of their mechanical properties. Besides, the rehabilitated samples are more flexible than primary ones. Furthermore, the results demonstrate that the capability of the proposed normalized modulus of rupture (NMOR) criterion, in contrast to the current modulus of rupture (MOR) one, for predicting the failure modes and regions of the wooden and composite structures. The experiments on the chairs showed that all rehabilitated patterns are more robust than primary schemes. That means, the discarded (or discarding) chairs (due to failure of joints, legs, or, in general, a part of the chairs) return to their service life, and massively reduce the demand for wood, which is strongly favored by environmental aspects. Moreover, rehabilitated layout B (RB), which has two continuous-main-curved members is at least 2.4 times stronger than other rehabilitated patterns, and rehabilitated layout C (RC) having three continuous-main-curved members is about 40% stronger than a rehabilitated custom chair (RA), that illustrates more integrity and strength. Besides that, the strength of RB is 2.22 and 2.04 times that of the corresponding primary chairs, depending on front-to-back and up-to-down loading, respectively. Finally, univariate analyses of variance and least significant difference (LSD) showed the high precision of the results. Consequently, the research provides a facility not only to save original material resources, but also to eliminate furniture waste going in the landfill.