Free vibrations of a pultruded GFRP frame with different rotational stiffnesses of bolted joints

Experimental and numerical results for the dynamic response of an all-FRP (fiber-reinforced polymer) two-dimensional frame in free vibration are presented. The frame was assembled of pultruded glass-fiber-reinforced polymer (GFRP) profiles and bolted beam-to-column connections with GFRP angles. To give a variable rotational stiffness to the four beam-to-column major-axis joints, all bolts were tightened by a constant torque of 10, 25, or 40 N · m. Experimental measurements were performed on the three configurations to identify the natural frequencies of the first vibration mode in the plane of the frame and to determine the ability of each structure to dissipate the initial acceleration imposed on it through damping. The results obtained are compared with analytical and finite-element calculations.
It was found that an increased bolt torque improved the dynamic response of the GFRP frame by reducing its vibration time and maximum displacements and by enhancing its dissipation capacity.