Dynamic properties and time response of frameworks with semi-rigid and eccentric connections

The paper is considering effects of the semi-rigid and eccentric joint connections of framework structures upon its dynamic properties and the time response due to an earthquake action. The corresponding numerical method representing the linear structural behavior is developed. Semi-rigid connections at beam ends are presented by the rotational springs at beam's ends, with linear moment-rotation relationship. Eccentricity of joint connections is presented by the corresponding short infinitely rigid links at beam's ends. The effect of semi-rigid and eccentric connections is introduced in the numerical model by the corresponding corrective matrix. The corrective matrix is applied upon the conventional stiffness matrix of the beam element with usual rigid and centric connections. As important dynamic properties, the change of the natural circular frequencies and the natural modes, due to variation of joint rigidity and eccentricity of beam-to-column connections, is analyzed. In the time response structural analysis, considering displacements only, dynamic loading due to an earthquake defined by a given accelerogram is considered. The solution of the differential equations of motion is obtained by direct numerical step-by-step integration using the α method (Hilber-Hughes- Taylor). In order to perform the numerical analysis, all considered numerical models and methods are implemented into the corresponding computer code, called ELAN, which is then used for the parametric analyses presented in the paper.