Design and Test of in-Plane Flexural Dampers in a Closed-Form
|關鍵字:||面內撓曲阻尼器;封閉式;曲梁;彎-剪耦合;彈-塑性應力分析;in-plane flexural damper;closed-form;curved beam;bending-shear coupling;elasto-plastic stress analysis|
In this study, the Nested in-Plane Oval Damper (Ni-POD) is proposed by adding to its ancestor, the i-POD, an inner loop to increase its loading capacity. While reserving the merits of i-POD in a closed-form, the descendant improves the efficiency of material utilization in a way to simultaneously meet the desired seismic performance and environmental concerns. Component tests of the dampers indicate that the Ni-POD exhibits higher strength and energy dissipation capacity than those of the previous design, and its mechanical behavior appears primarily in two phases. In the initial phase with both inner and outer loops working in parallel, the damper presents higher stiffness and strength. With higher stress developed, the inner loop of the Ni-POD will be damaged first and enter the second phase where the outer loop continues to sustain loading and deform until the ultimate state. Mechanical characteristics such as ultimate displacement and post-yielding stiffness of the damper at the second phase are closely similar to those of its i-POD counterpart, and therefore the design method for i-POD can be loaned directly. As far as numerical simulation of the cyclic loading tests is concerned, recognizing that ANSYS is unable to discriminate the behavior of the nested damper after damage of the inner loop, a two-stage approach is proposed in this study by analyzing the full model of the nested-type damper and the corresponding inner-loop-only counterpart in parallel under the same loading condition. With the critical displacement corresponding to damage of the inner loop predetermined from the test results, the resisting forces of the full model are deducted from those of the inner-loop-only model as long as the testing amplitude exceeds the critical displacement. Simulation results proved to be adequate. In addition, it is found that mechanical characteristics of the i-POD are related to the dimensionless parameter defined from its design dimensions in a trend of quadratic curves. The empirical formula derived from curve-fitting are eligible for future design references and help in making the practical use of the in-plane flexural dampers a reality. Lastly, component tests of two circular dampers have been conducted to verify the feasibility of the elasto-plastic stress analysis theory for curved beams under bending and shear coupling developed earlier for analyzing the in-plane flexural dampers. The numerical results so obtained, however, deviate from the tests in a great extent and thus considered unreliable. It might be that the curved-beam model is not adequate for structures in a closed-form, or the computer code for elasto-plastic stress analysis contains unfound errors. This requires further investigation.