ABSTRACT
It is known that the environmental changes, in tropical area impact significantly the mechanical behavior of timber structures. Indeed, Gabon, with more than 1900 m3 of annual precipitations, around 85% relative humidity and a mean temperature near 27°C, does not break with this rule. The objective of the present study is to perform a comparative experimental test, of cyclic compressive loading on Milicia Excelsa (Iroko), Aucoumea Klaineana Pierre (Okoume) and Pterocarpus Soyauxii (Padouk), at different internal moisture content stages. 150 samples of these three species, dimensioned according to standard NF EN 408 were loaded. The specimens have been loaded in static compression test until their collapse in order to obtain the mechanical characteristics of each species as: (i) the modulus of elasticity, (ii) the maximal strength and (iii) the stress at the yield point. Then, they had loaded (loading-unloading-reloading), five times, in cyclic compressive loading at different internal moisture content rates. The applied force was taken at 10% of the maximum rupture force of Okoume specie and kept constant at each cycle. The results show a stiffening of the three types of specimens with the loading cycles. The stiffening is faster from the densest species to the least dense species, respectively. In addition, the phenomenon of densification, that occurs during the five loading-unloading cycles, it is done with constancy of compressive strength in the three species studied.
