Systematic development of a new hysteretic damper based on torsional yielding: part I—design and development

Abstract

Analytical and experimental studies into the behavior of a new hysteretic damper, designed for seismic protection of structures is presented in two papers. Although the subject matter of the papers is a specific system, they are also intended as an illustration of practical application of diverse engineering tools in systematic development of an anti-seismic product. The Multi-directional Torsional Hysteretic Damper (MTHD) is a recently patented invention in which a symmetrical arrangement of identical cylindrical steel energy dissipaters is configured to yield in torsion while the structure experiences planar movements due to earthquake shakings. The device has gone through many stages of design refinement, prototype verification tests and development of design guidelines and computer codes to facilitate its implementation in practice. The first of this two-part paper summarizes the development stages of the new system, conceptual and analytical. The experimental phase of the research is the focus of the accompanying paper. The new device has certain desirable properties. Notably, it is characterized by a variable and controllable-via-design or adaptive post-elastic stiffness. This feature gives the isolated structure the capability to evade the dominant period of the ground motion leading to reduced displacements while having force levels comparable to regular bilinear isolation systems. The device has already been applied to four major bridges.The appropriate numerical solution procedure of the above equations depends on the form and nature of torque-twist angle (T-θ) relationships, which will be discussed in Section 6. 850 A. SALEM MILANI AND M. DICLELI Figure 10. Displacement-dependent variation in tangent stiffness-based period of an isolated structure equipped with MTHD + sliding bearings (μ = 0.01), in case of a typical MTHD with (a) HI = 1.5; (b) HI = 2.0. 858 A. SALEM MILANI AND M. DICLELI Figure 12. Effect of displacement direction in MTHD: (a) angle, α to characterize the orientation of the imposed displacement relative to the configuration of the EDs, (b),(c): properties of the MTHD versus angle α.860 A. SALEM MILANI AND M. DICLELI Figure 13. (a) FE model. Distribution of plastic strain in peripheral elements over the height of the ED (along the uniform part) at increasing twist angles (θ): (b) E t /E = 0.0002 (nearly elasto-plastic) with the presence of bending, (c) E t /E = 0.002 with the presence of bending, (d) E t /E = 0.002 with pure torsion (no bending)

Systematic development of a new hysteretic damper based on torsional yielding: part II—experimental phase

“…Following the verification tests, the fatigue and fracture behavior of the cylindrical EDs of the device is studied by subjecting certain numbers of them to further cyclic tests up to failure, and observations on their fatigue/fracture behavior are reported. The experimental verification test results proved the validity of the developed theory and component design assumptions presented in a companion paper . Furthermore, the EDs are found to exhibit excellent torsional low‐cycle fatigue performance.…”

“…However, one should keep in mind that although MTHD is designed to provide lateral and rotational stiffness for the cylindrical EDs, component flexibility and manufacturing tolerances will prevent realization of pure torsion in EDs in practice. The real value of maximum strain is thus affected by the presence of some bending moment and associated shear, as well as strain concentration near the neck region, as laid out in the companion paper . Furthermore, cyclic localization of damage gradually changes the general state of strain in the damaged region.…”

“…For design purposes, it is advisable to consider the strain concentration factor, estimated based on FEM (see the companion paper ), in case of C45 steel, which shows concentrated damage near the neck region. In the case of S355J2 + N and 42CrMo4 + QT steels, however, although strain concentration may exist, evidence suggests that its ultimate impact on cyclic life should be small.…”

“…The multidirectional torsional hysteretic damper (MTHD) is a recently patented invention in which a symmetrical arrangement of identical cylindrical steel energy dissipaters (EDs) is configured to yield in torsion while the structure experiences planar movements due to earthquake shakings. The conceptual and theoretical development stages of this new damper are presented in a companion paper . The focus of this paper is to report on the experimental studies carried out on a prototype of the newly developed damper.…”

“…Guidelines in EN 15129 are consulted in conducting the experimental studies reported in this paper. The main goal of the experimental studies is to test the validity of the theory developed in a companion paper and to evaluate the low‐cycle fatigue performance of the EDs of the damper. Force–displacement (F–D) response of the MTHD is studied through fully reversed cyclic displacement‐controlled tests that were carried out in compliance with EN 15129.…”