A new coupled vibration control system is proposed for a group of slender buildings constructed closely in urban areas.
The connection dampers which can move in vertical, not in lateral are set between the adjacent buildings. Also, to
concentrate the earthquake input energy to the connection dampers, a rocking structural system is applied to each
connected building. This proposed system can introduce a kind of 'smart' self-centering system for target buildings. To
verify the earthquake reduction effects of the proposed system, some numerical analyses are executed to real scale
building frame models. In the analyses, two buildings are connected by the vertical dampers. That is the simplest
application of the coupled vibration control system. Their responses are compared with those of a single fixed base
frame model and a single rocking frame model. The analysis results successfully demonstrated that the new coupled
vibration control system has high performance for seismic response reduction of target slender buildings.
It has pointed out that uplifting response can reduce seismic force of buildings. In this paper, to understand this phenomenon from the point of view of modal analysis, vibration characteristics and dynamic behavior of multiple story buildings allowed to uplift are investigated. Analytical models are simplified 2-dimensional multiple story buildings with vertical springs at the bottom, where uplifting is allowed. Models are assumed to be elastic and have no damping. At first, eigenvalue analysis is carried out to clarify the vibration characteristics, that is, natural period and participation vector. Eigenvalue problem is solved utilizing reduced formula for tridiagonal matrix. Next, dynamic behavior is investigated to clarify the effects of higher modes on responses, distribution of shear force along the height and the amount of energy which can be stored as potential energy of self-weight. Dynamic behavior is initiated by means of just adding a certain level of initial horizontal velocities to the model at rest. The distribution of initial velocities along the height is proportional to the 1st mode shape of fixed base model. Analysis is carried out between the initiation of uplift and landing, that is, half cycle of uplifting behavior. From the results of some examples, it is concluded that higher modes have much effect on story shear force responses and distribution of shear force along the height differs from that of ordinary fixed base model.
To reduce seismic responses of steel building structures, we are now developing the base plate yielding system (BPY system). This system has base plates yielding in the uplift direction at each column base. When the base plates yield, the structure can cause rocking. As some researches have pointed out, rocking effects can reduce seismic damage of buildings under some conditions. In this paper, to improve the seismic performance of the BPY system, conventional or adaptive viscous dampers are attached at each column base besides yielding base plates. Using the adaptive dampers, we can change the damping coefficient according to a sign of vertical velocity at each uplifting part. When a building starts uplifting, and when the sign of vertical velocity is plus, we should set moderate damping coefficient to the damping devices so that they do not restrain a building from uplifting. When the building is landing, and when the sign of the vertical velocity is minus, we can set larger damping coefficient to them so that they can dissipate seismic energy as much as possible. To examine the effect of these additional dampers, numerical tests are carried out. A building structure is replaced by a one-mass system with a footing beam. The height and width of the one-mass system are 30 m and 8 m respectively. The 1995 Kobe NS and an artificial ground motion are used for seismic analyses. It is concluded that the seismic responses of the BPY system can be reduced using the adaptive dampers effectively.
The shaking table tests are carried out to examine the seismic responses of rocking structural systems with yielding base plates (base plate yielding systems). When subjected to a strong earthquake ground motion, these systems can cause rocking vibration with base plate yielding to reduce the seismic responses of buildings. In the tests, the seismic responses of test frames are compared with those of fixed-base systems and simple rocking systems. The test frames are the steel frames of one-third scale which have one bay and five stories. The total height and width are 5 and 2 meters, respectively. In tests of the base plate yielding systems, the yielding base plates are attached at the bases of these frames. Furthermore, to predict the seismic responses of base plate yielding systems, such as up-lift displacements, base shears and roof displacements, we propose a simple prediction method using an equivalent single degree-of-freedom (SDOF) system. It is concluded that the base plate yielding systems can reduce effectively the seismic response of building structures and their seismic responses are predicted by the proposed method appropriately.
We are developing the rocking structural systems that can reduce earthquake responses of buildings by causing rocking vibration. This paper aims to examine the effects of the rocking system. To cause rocking vibration under appropriate control, weak base plates are attached at the bottom of each steel column at the first story. When the weak base plates yield during a strong earthquake, the building causes rocking vibration. In this paper, the earthquake responses of this rocking system (the base plate yielding system) are examined comparing with those of the simple rocking system and the fixed-base system by nonlinear time history analyses. The results are summarized as follows: 1) Story shear forces of the base plate yielding systems are reduced as much as those of the simple rocking system. The roof displacements and axial forces are less than those of the simple rocking system. 2) The roof displacements and axial forces of the base plate yielding systems are almost similar to those of the fixed-base system under a certain input level. It is concluded that the rocking system with weak base plates can reduce earthquake responses of buildings.
The final purpose of our study is development of the structural health-monitoring technique for the real existing buildings. In this paper, the results of the analytical studies are shown as the first step of our health-monitoring scenario. One of the purposes of the first step is to make the analytical models for evaluating the structural performance.