Bending Moment of Mortise-and-Tenon Joints in a Crossed Chair Base/Moment savijanja spojeva s cepom i rupom na kriznoj potkonstrukciji sjedala stolice

This paper investigated the bending moment of chair base joints. The ultimate bending moments (maximum moment), calculated on the base of the measured maximum applied loads (maximum force), were compared for the front leg and rear leg joints of a chair base. The joints had different angles between the stretcher and the leg (joint angle) as well different tenon lengths (30 mm and 32 mm). The results of the tests indicated that for different test specimen configurations but the same tenon-and-mortise geometry, the maximum force of joints with a smaller value of joint angle (front leg joints) was higher than the force values of joints with a larger angle (rear leg joints) for all tenon lengths. However, the results showed less difference among the calculated bending moments of the analysed sets of joints. A significant difference was not revealed between the bending moments of joints with a smaller value of joint angle and the bending moments of joints with a larger angle for all tenon lengths. A significant difference between the bending moments for the tenon length of 30 mm and tenon length of 32 mm was determined for rear leg joints but not for front leg joints. The presented approach of joint strength analysis through the testing of specimens with different shapes and dimensions are applicable to research and practice. KEYWORDS: chair; mortise-and-tenon joint; bending moment; joint angle; tenon length U radu je proucavan moment savijanja spojeva na kriznoj potkonstrukciji sjedala stolice. Krajnji momenti savijanja (najveci moment), izracunani na temelju izmjerenih najvecih opterecenja (najveca sila), usporedeni su za spojeve prednjih i straznjih nogu krizne potkonstrukcije sjedala stolice. Spojevi su imali razlicite kutove izmedu poveznika i noge (kut spoja), kao i razlicitu duljinu cepova (30 i 32 mm). Rezultati ispitivanja pokazali su da je za razlicitu konfiguraciju ispitnih uzoraka, ali za istu geometriju cepa i rupe, najveca sila bila veca za spojeve s manjim kutom (spojevi prednjih nogu) nego za spojeve s vecim kutom (spojevi straznjih nogu), i to za cepove obiju duljina. Rezultati su takoder pokazali manju razliku izmedu izracunanih momenata savijanja analiziranih grupa spojeva. Nije utvrdena znacajna razlika momenata savijanja spojeva s manjim i vecim kutom za cepove obiju duljina. Znacajna razlika izmedu momenata savijanja za cepove duzine 30 i 32 mm utvrdena je za spojeve straznjih nogu, ali ne i za spojeve prednjih nogu stolice. Prikazani prist