Direct stiffness method

About: Direct stiffness method is a research topic. Over the lifetime, 2584 publications have been published within this topic receiving 53131 citations.

Actuation of the Kagome Double-Layer Grid. Part 2: Effect of imperfections on the measured and predicted actuation stiffness

Abstract: The actuation stiffness of a set of steel Kagome Double-Layer Grid (KDLG) structures with brazed joints is measured experimentally and compared with predictions by the finite element method. The predicted actuation stiffnesses for the perfect KDLGs much exceed the measured values, and it is argued that the low values of observed actuation stiffness are due to the presence of geometric imperfections introduced during manufacture. In order to assess the significance of geometric defects upon actuation stiffness, finite element calculations are performed on structures with a stochastic dispersion in nodal position from the perfectly periodic arrangement, and on structures with wavy bars. It is found that bar waviness has the dominant effect upon the actuation stiffness. The predicted actuation stiffness for the imperfect structures are in satisfactory agreement with the measured values assuming the same level of imperfection between theory and experiment.

Stiffness Modeling of Reinforced Concrete Beam-Columns for Frame Analysis

Abstract: In defining member stiffness coefficients, simple distinctions between beams or columns can be misleading, especially for frames governed by earthquake or wind loads where column compression loads may be small relative to column strengths. In this paper, factors influencing beam-column stiffness in frame analysis are reviewed and simple formulas are proposed to determine effective flexural and shear stiffness coefficients of beam-columns as a function of the applied axial compression. The proposed stiffness coefficients represent conditions at incipient yield, and are applicable for linear analyses and the linear preyield region of nonlinear analyses. Proposed stiffness coefficients are compared to test data and alternative recommendations from several sources. More test data is needed for refinement of available models, particularly in the area of shear stiffness.

Stiffness control and transformation for robotic systems with coordinate and non-coordinate bases

Abstract: In this paper, the application of the conservative congruence transformation (CCT) to the stiffness mapping between non-coordinate basis and coordinate basis systems is studied and presented. Through the stiffness transformation between the 2 degree-of-freedom cylindrical and joint spaces, we illustrate that the CCT can be applied either directly or indirectly to the stiffness transformation between any two systems with either coordinate basis or noncoordinate basis. It is found that the same stiffness control for a conservative system will render a symmetric stiffness matrix with respect to a coordinate basis, but an asymmetric matrix with respect to a non-coordinate basis. The direct and indirect CCT methods are presented, with the latter requiring an intermediate coordinate system with a generalized coordinate basis. The relationships of the effective K/sub g/ matrices between the direct and indirect CCT methods are found and validated.