Recently, some weaknesses of a lead rubber bearing (LRB) have been identified such as excessive tensile stress at some basemat-edge isolators and degradation of lead plug damping performance by temperature rising due to responses during the large and long duration earthquakes. The degradation of lead plug damping performance has become a design factor and a concern with response evaluation method to consider the thermal effect to lead plug has been growing. In this paper, to study the degradation of lead plug damping performance, firstly loading tests (a multi-cyclic loading tests to get thermal conditions of the lead plug, and a horizontal/vertical directional loading tests to get mechanical behaviors of the LRB under multiple degree of freedom loading) for LRB specimens were performed, then an analysis program to simulate the tests are newly developed that are validated by comparing to the test results. By these tests and analyses, some new findings are given on heat generation characteristics of the lead plug along with its thermal boundary conditions. By checking the LRB performance after the loading tests, another finding is given that mechanical characteristics are almost recovered when the lead plug temperature is enough cooled even that was once heated up to 300 degrees Celsius.
A darnping vibration experiment was carried out on an actual shell structure (a PC cylindrieal shell) to clarify damping characteristics of the shell structure, and also to aid in preparing a data base on darnping ratios of shell and spatial structures for use in dynamic response analysis. The experimental methods used were microtremor observation and a hurrian exchation experiment.
The analytical methodsused for evaluating damping ratios were the randorn decrement technique (RD technique) and the halfipower method, Kej, werds: Damping, Cylindrical shell, Reinforced concrete, Random decrement technique(RD technique), Halfpower method, Microtremor observation, Human power excitation experiment University's Tsudanuma campus, with its prestressed concrete (PC) cylindrical shell roof, Using random decrement technique and halfipower method, the data obtained is used to find estimates ofthe damping ratio, and the differences between these two techniques are considered, PC structures entered experimental use in 1928, and with Freyssinet's introduction of tensioning wires, fixing cones and stressingjacks in 1939, they could enter widespread use.The use of PC in spatial structures has also been experimented with, In 1940, the Freyssinet system was used to construct an aircraft hangar in Karachi with a parallel cylindrical shell stmcture.
This paper provides a series comprising the “Development of Evaluation Method for Seismic Isolation Systems of Nuclear Power Facilities”. Part 6 presents scaled tests for Lead Rubber Bearing (LRB) newly developed for this project.
Following tests are performed to obtain the basic characteristics of LRB,.
(1) Horizontal and Vertical Simultaneous Loading Test:
LRBs with diameter of 250mm are tested dynamically under simultaneous axial and lateral loading. The hysteresis characteristics is not changed under compressive load although it is changed under tensile load.
(2) Basic Break Test:
LRBs with a diameter of 800mm are tested statically under various combinations of axial and lateral forces. The hysteresis characteristics model of LRB is determined by this test. It is confirmed that the breaking strain of LRB under compression load exceeds 450%.
(3) Horizontal Hardening and Vertical Softening Test:
For LRBs with a diameter of 1200 mm, 75% scale of actual LRB are tested statically for horizontal hardening and vertical softening regions. It is confirmed that the hysteresis model which is developed by smaller LRBs is applicable to these large scale models.
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