Concrete-filled L-shaped steel tube columns can be used to save architectural space at room corners, and may have many advantages of structural behavior of common concrete-filled steel tubes as columns. In this paper, the seismic behavior of concrete-filled L-shaped steel tube columns (CFLSTs) was investigated. Six specimens subjected to a constant axial load and cyclically varying lateral loading were tested to study the effects of width to depth ratio of section, depth to thickness ratio of steel tube and axial load level on the strength, as well as stiffness, ductility and energy dissipation of CFLST columns. Experimental results showed that the displacement ductility of CFLST columns decreased significantly with the increase of axial load level, and the strength and stiffness degradations of CFLST columns were more significant with higher axial load level. With the increase of depth-thickness ratio of steel tube and depth-width ratio of section, the ductility and the lateral ultimate load-carrying capacity of CFLST columns also decreased gradually. All CFLST columns exhibited favorable energy dissipation and ductility, even for the columns subjected to high axial load, which indicates that this type of composite columns is adoptable in practical engineering, especially in seismic regions.
The new staggered story isolated system is developed according to the base isolated system and the mid-story isolated system. Non-linear finite element model of an eighteen stories new staggered story isolated structure is established. For a comparative analysis, the models of a base isolated structure, a mid-story isolated structure, and an aseismic structure are also established, and their shock absorption performances and damages are analyzed for comparison. The results indicate that the new staggered story isolated structure has a small seismic response, good shock absorption performance which is feasible for application. Besides, the shock absorption performance of the new staggered story isolated structure is a little worse than the base isolated structure but slightly better than the mid-story isolated structure. The bottom of core tube and the story below the frame isolated story have large acceleration response which needs to be paid more attention in design.
The inter-story isolated structure is an effective and feasible structure seismic technology and system, but most studies on inter-story isolated structures only consider the mainshock. A strong mainshock is usually accompanied by multiple aftershocks, the structure will be damaged under the action of the mainshock. Because of the short time interval between the main shock and the aftershocks, the structure is often not repaired in time, so it will be further damaged under the action of the aftershock. Therefore, it is meaningful to study the fragility of inter-story isolated structures under the action of main-aftershock sequences. In this study, the incremental dynamic analysis method was used, and the inter-story isolated structure of a frame shear wall was established. The vulnerability curves of each substructure under the action of a single mainshock and main-aftershock sequence were compared. A series structure system was used to calculate the overall vulnerability of the inter-story isolated structure. The vulnerability curves of different isolation layer setting positions and isolation bearing stiffness under the action of a single mainshock and main-aftershock were compared, and the collapse margin ratio (CMR) of the structure given. The results show that aftershocks increase the exceedance probability of each substructure, and with an increase in the limit state, the influence of aftershocks is more obvious. An appropriate isolation layer design reduces the influence of aftershocks and the exceedance probability of the entire structure.
A mid-story-isolated structure is developed from a base-isolated structure. Mid-story-isolated structures located in sloping ground have become a research hotspot in recent years. It is important to consider the soil–structure interaction (SSI) effects and multi-dimensional earthquakes on these structures. This paper established a model of the mid-story-isolated structure considering SSI in sloping ground. An elastic–plastic time history analysis was carried out under the one-dimensional (1D), two-dimensional (2D), and three-dimensional (3D) earthquakes. Under 3D earthquakes, the traditional 2D isolated bearing has limited damping capacity. Therefore, two kinds of 3D isolated bearings were designed. Results show that the seismic response of the mid-story-isolated structure considering SSI in sloping ground can be amplified compared with that of the mid-story-isolated structure without considering SSI. The seismic response of the structure under 3D earthquakes is more significant than that under 2D earthquakes and 1D earthquakes. For the two kinds of 3D isolated bearings, the minimum reduction rate of tensile and compressive stress is about 46% compared with that of the traditional 2D isolated bearings. When the 3D isolated bearings are used, the stress of the soil foundation decreases, which is more conducive to the stability of the soil foundation.
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