摩擦型基础隔震建筑在近场地震作用下的保护性评估

1
INTRODUCTION
Heavy earthquakes in recent years, such as that happened in Lomaprite in 1989, Northridge in 1994, Kobe in 1995, and chi-chi in 1999, have caused great damages. In these earthquakes, the faults, such as strike-slip, dip-slip, and vertical faults, move quickly towards one direction with high-peak-ground acceleration. Particularly for base-isolated building with a long natural period, this fault motion may cause large bottom displacement to collide with the limit devices, such as the foundation ditch and limit damper. This collision was observed accompanying with great increase in shearing force and acceleration at the upper structure(Nagarajaiab, 2001). To solve the above problem, the ponding of the base-isolated buildings have attracted great interests(Malhotra, 1997; Tsai, 1997). The upper structure was assumed as an elastic shearing beam, while the foundation ditch as a spring-damper. The pounding responses were investigated under different spring stiffness and different distance between the foundation slab
Abstract: Different pounding models were used to investigate the dynamic response characteristics of friction base-isolated building (P-F, R-FBI and FPS) pounding response when it collided with the limit device under near-fault ground motions. Mathematical equations of different types of poundings and the parameters in each model were presented. Upon pounding, inter-storey shearing force and acceleration response were found to be greatly increased, and higher modes of vibration of the structure were evoked. The discrepancy of computation structures of different pounding models was under 10% whereas nonlinear pounding models would be more time-consuming in calculation. Therefore, Kelvin linear model was recommended in practice. protective measures were put forward to reduce pounding response of base-isolated building by using higher damping rubber impact damper, and the feasibility of such measures were validated. Keywords: Friction base-isolated building, near-fault ground motions, structural pounding, protective measures
2 ESTABLISHMENT OF MOTION EQUATIONS CONSIDERING POUNDING EFFECTS
The computational diagram of collision between P-F and R-FBI (or FPS) in base-isolated buildings and limit devices are as in Figure 1 and Figure 2. Their equations of motion are as follows.
The equation could be simpxg b 2 s 2bb s
n Fc ri xi (4) M z i1 In Eq.(2) and (4), u stands for friction coefficient, Fc indicates the friction force. represents the total mass of the structure, And sign () stands for sign function. The rest signs can be found in Figure 1 and Figure 2. The upper structure motion equation of mass i is as follows: mi xi f d i f i f i1 mi ( s xg ) (i 1, 2,, n)
Jian Fan1, Xiaohong Long2 ¹ School of Civil Engineering & Mechanics, Huazhong University of Science and Technology, Wuhan 430074, P.R. China 2 School of Civil Engineering & Mechanics, Huazhong University of Science and Technology, Wuhan 430074, P.R. China

Figure 1. computational diagram of P-F base-isolated building
(5) where fdi stands for damping force on mi., In the present study, linear viscous damping is used. fi stands for inter-storey restitution force on storey i, which is related with inter-storey relative drift. Moreover, both conditions when the damping is linear and nonlinear are taken into account. In the following part, the value of fi will be deduced in detail. As to linear inter-storey restitution force, the following equation is as follows. f i ki ( xi xi 1 ) (6) Wher’e ki stands for inter-storey stiffness on storey i. Wen’s differential hysteresis model is used to imitate nonlinear inter-storey restitution force, and the equation of fi is as follows. f i i ki yi (1 i )ki Dy i vi (7) where i stands for the ratio of post-yielding stiffness to pre-yielding stiffness, ki equals elastic inter-storey stiffness on storey i, D yi is yielding displacement on storey i, yi xi xi1 is relative displacement on storey i, i is dimensionless parameter which means hysteresis component of deformational parameter on storey i of the structure. i is described in the following equation. n 1 n i Dy i 1 Ai y i y i vi i vi ri yi vi i (8) v i where, Ai , i , ri , ni are constants related to hysteresis shape. Equation motion of P-F and F-RBI could be worked out when Equations (2)(5)(8) or (4)(5)(8)are combined together, with state vector Z (t ) being introduced into them. (t )},{V (t )}] ,{ X (t )},{ X (9) z (t ) [ s, s