Modelling and Seismic Response Analysis of Italian Code-Conforming Base-Isolated Buildings

ABSTRACT

This paper reports on results of nonlinear analyses performed within the RINTC project on an RC building isolated with different systems (High Damping Rubber Bearings, High Damping Rubber Bearings and Flat Sliding Bearings, Friction Pendulum System) and designed according to the Italian design code. The seismic response has been evaluated under different seismic input levels of two sites with different hazard and by considering two Limit States: Global Collapse and Usability-Preventing Damage. The influence of seismic stoppers and modelling uncertainties is also evaluated. Results permit to compute the implicit collapse risk and to identify critical aspects of current design procedures.     

REPEATABLE DYNAMIC RELEASE TESTS ON A BASE-ISOLATED BUILDING

The main activities and the relevant results of an experimental program aimed at evaluating the dynamic characteristics of a large seismically isolated building are described. The building is situated in Potenza (Italy) and is the largest of five seismically isolated blocks of the University of Basilicata. Cyclic shear tests on scaled isolators and some small amplitude free vibration tests were preliminarily carried out. The latter ones were aimed at getting a preliminary linear characterisation of the structure. Finally, many in situ release tests on the isolated structure were carried out, using a mechanical device purposely designed to statically move the building and then suddenly release it, thus making it vibrate freely. The variations of the dynamic characteristics of the system while the oscillation amplitude decreases have been evaluated by using the “Short Time Fourier Transform (STFT)”. The results were elaborated in terms of stiffness and equivalent damping and compared to the results of the laboratory tests on scaled isolators, finding an excellent agreement.     

SEISMIC PROTECTION OF LIGHT SECONDARY SYSTEMS THROUGH DIFFERENT BASE ISOLATION SYSTEMS

The objective of the present work is to examine advantages and drawbacks of different types of isolation systems, when seismic isolation is used as a protection strategy against damage to internal equipment and contents. The starting point of the study is the big experimental program of table tests on reduced-scale R/C structural models, carried out within the MANSIDE (Memory Alloys for New Seismic Isolation DEvices) project. Seven identical l:3.3-scaled, 3-storey frames were tested, including two fixed-base models and four base-isolated models with different isolation systems, namely: (1) rubber isolators, (2) steel-hysteretic system and (3), re-centring SMA (Shape Memory Alloy) system. In this study the internal equipment is regarded as an elastic single degree of freedom, with 2% equivalent viscous damping. Therefore, the capability of fixed-base and base-isolated models with different isolation systems to protect light secondary systems is evaluated by comparing the floor response spectra obtained from the storey accelerations recorded during shaking table tests. Three different PGA's are considered, about 0.15g, 0.3g and 0.5g, respectively. All the shaking table tests are also simulated with an accurate numerical model, to validate and better understand the experimental results. It is found that each type of isolation system reduces considerably the seismic effects on internal equipments in wide frequency regions. However, tuning effects may arise in specific frequency ranges, corresponding to the first mode in structures equipped with quasi-elastic (rubber) isolation systems, and to higher modes in structures equipped with elasto-plastic (steel) and nonlinear re-centering (SMA) isolation systems.     

金陵大报恩寺御碑遗址结构性能及保护技术研究

为了对金陵大报恩寺南北两块御碑遗址进行科学保护,首先通过有限元模拟对南北御碑遗址的现状结构性能进行分析,找出其在正常使用和地震作用时存在的安全隐患;然后根据计算分析结果及整体设计要求提出增设隔震支座的保护技术方案,采用有限元模拟计算对南北两块御碑遗址在增设隔震支座后的结构性能进行分析。计算结果表明:带有御碑的北碑的第一阶自振频率约为不带御碑的南碑的0.087;地震作用下,带有御碑的北碑最有可能破坏的部位是御碑,而不带御碑的南碑最有可能破坏的部位是龟趺头部。施加隔震支座后,南北两块御碑遗址结构的振动频率、最大主拉应力和最大主压应力均明显减小,在7度罕遇地震的情况下均不会发生破坏。研究结果对石碑的结构保护工程研究有参考价值。