Behavior of Bidirectional Spring Unit in Isolated Floor Systems

Engineering Structures, 1992

Results of an experimental testing are presented for a five-storey steel frame model, subjected to horizontal and vertical earthquake vibrations with varying intensities. The dynamic testing included the fixed base conditions, as well as full isolation by means of neoprene pads and helical springs, coupled with or without viscous dampers. The response of the structural model to both horizontal and vertical vibrations has been thoroughly recorded, and these records have been correlated with those of the analytical investigations. The main conclusion of the study is that the vertical vibrations may unexpectedly cause response amplifications at very high undesirable levels, especially when the structure is base isolated by means of rubber pads. No such deficiency occurs, however, when helical springs and viscodampers are used.

Base isolation or seismic isolation enables the reduction in earthquake forces by lengthening the natural time period of structure; hence it is significantly effective in low and mid-rise buildings with less than 10 stories. Taller building with height more than 10 storey already have larger time period and the effectiveness of base isolation is reduced., In this paper an attempt has made to study the feasibility of sliding isolation at intermediate floor levels. Two R.C.C. building 12 storey and 18 storey are analyzed by dividing each building into different segment and each segment is isolated with Friction Pendulum isolators. The response of structure with isolators at multiple floor levels are studied with 1940 El Centro, 1994 Northbridge and 1995 responses are compared to the conventional fixed base structure and with structures isolated at base. Considerable reduction is observed in the building isolated at intermediate floor level.

Engineering Structures, 2001

A viable non-linear dynamic design procedure for fluid viscous spring-dampers used in base-isolation systems of building structures is presented herein. The procedure consists of a preliminary design phase developed for a single-degree-of-freedom idealisation of the structural system, and in a final verification phase. The damping coefficient values ensuring achievement of the basic performance levels hypothesised in the design problem are estimated at the first stage. An explicit relationship interpolating the damping coefficient demand curves traced out as functions of damper loss factor, and dynamic input frequency composition and amplitude, is proposed as the basic design equation to this aim. This relationship, derived from previous analytical studies, is further validated herein against the results of experimental forced-vibration tests conducted on a steel frame mock-up. A first demonstrative application of the procedure is then carried out on a simple building with very stiff superstructure. Doubled calibration of the damping coefficient under normative-generated and pulse-type input ground motions, and evaluation of the influence of the pre-stress load imposed on several types of fluid viscous devices in the manufacturing process, are included. Selected case studies are discussed in the accompanying paper. 

Engineering Structures, 2001

The non-linear dynamic design procedure of fluid viscous spring-dampers proposed in the accompanying paper is applied to two selected case studies, represented by a reinforced concrete and a steel five-storey frame building with identical global dimensions. The fundamental vibration periods of the two structures in fixed-base conditions, equal to 0.58 s and 1.08 s, respectively, fall within the range of technical interest for use of base isolation. The reliability of the analytical relationship by which the damping coefficient is estimated in the preliminary design phase is further verified by comparing its predictions with the loss factor values calculated from the results of numerical integration of the equations of motion. The final verification phase of the procedure is then developed with regard to a double design performance objective, for which immediate occupancy and life safety levels are targeted under the "basic design" and "maximum considered" earthquakes, respectively. 

2016

The double-shoe braking system used in elevators of buildings with the purpose of mechanical braking behavior are used an experimental method for the preparation of the dynamic model in this study. The double-shoe braking system is used in many mechanisms. The double-shoe braking system is a complex structure consisting of many parts, so that it is difficult to create a model with a theoretical approach to make the right contact definitions. Therefore, experiments were performed by creating experimental model in this study and the results of these experiments have shown that the structural noise and vibrations were significantly affected by the speed, and braking and takeoff acceleration of the engine.

Earthquake Engineering & Structural Dynamics, 2008

An experimental investigation on a base isolation system incorporating stainless steel–Teflon bearings as sliders, and pressurized fluid viscous spring dampers, is presented in this paper. In the system examined, dampers are connected to the base floor of an isolated building to provide the desired passive control of response in the superstructure, as well as to guarantee that it re-centres completely after the termination of a seismic action. Two types of experiments were conducted: sinusoidal and random cyclic tests, and a pseudodynamic test in ‘substructured’ configuration. The cyclic tests were aimed at characterizing what follows: the hysteretic and strain-rate-dependent response of the considered highly non-linear spring dampers; the normal pressure- and strain-rate-dependent frictional behaviour of steel–Teflon bearings, manufactured in compliance with the latest standards for this class of sliders; and the combined response of their assembly. The pseudodynamic test simulated the installation of the protection system at the base of a 2:3-scale three-storey steel frame structure, already tested in unprotected conditions by an earlier experimental campaign. Among other findings, the results of the performed tests, as well as of relevant mechanical interpretation and numerical simulation analyses, confirmed the linear additive combination of the dissipative actions of spring dampers and sliders in this mixed installation, and the high protective performance of the considered base isolation/supplemental damping system in a realistic earthquake simulation. Copyright © 2007 John Wiley & Sons, Ltd.

Advances in Mechanical Engineering, 2019

The article deals with investigations of a prototype single and double multi-leaf spring composed of a four-leaf main spring and a double-leaf supporting spring subjected to the cyclic loads. A methodology of a measurement conducted during experimental tests and a set of research instruments used in the stand research allow evaluation of the effects of friction and the accompanying heat stress of the leaf spring in the quasi real operating conditions. The role of clearances and friction in operation of this type of construction as well as analytical, numerical, and bench testing methods used in the research on the effect of energy dissipation due to friction on operation of the leaf spring are discussed. Dynamic elastic characteristics with hysteresis loops and identification of leaf cooperation areas are presented for the single and double multi-leaf springs tested under different conditions.

Earthquake Engineering & Structural Dynamics, 2003

This paper presents a two-dimensional numerical study on the nonlinear seismic response of buildings equipped with two types of energy dissipators: Constant Friction Slip Braces (CFSB) and Adding Damping and Stiffness (ADAS). Three types of reinforced concrete buildings with 3, 7 and 15 storeys, representatives of the short-medium-and long-period ranges, are considered. Dissipators are placed in steel diagonal braces in all the floors. The sliding threshold (or yielding) forces for each mechanism are selected using two different criteria: (i) they are taken as 50, 75 and 100 per cent of those generated by the equivalent static lateral forces recommended by the UBC-91 for a ductile moment resisting frame and (ii) they are constant in the whole building (this constant value is chosen equal to the maximum forces obtained with the previous criterion). The input consists of ten recorded earthquakes (normalized with respect to their Housner intensity) corresponding to medium and stiff local soil conditions. Average values on the ten registers are given for the maximum horizontal displacement, the base shear, the energy dissipated and the interstorey drift. The possibility of failure in some devices has been numerically simulated to assess the robustness of the system. The obtained results show that both devices are useful to reduce the response compared to the bare frame and that CFSB is more efficient than ADAS; for 7and 15-storey frames the lateral displacement with CFSB is even smaller than the one for the braced frame (rigid connections instead of dissipators). The conclusions are expected to provide simple design guidelines.

The Structural Design of Tall and Special …, 2010

The performances of variable curvature sliding isolators like variable frequency pendulum isolator (VFPI) and variable curvature friction pendulum system (VCFPS) installed in the base-isolated benchmark building subjected to bi-directionally acting seven strong earthquakes have been studied. The shear type base-isolated benchmark building is modelled as three-dimensional linear elastic structure having three degreesof-freedom at each fl oor level. Time domain dynamic analysis of the building has been carried out with the help of constant average acceleration Newmark-Beta method and non-linear isolation forces has been taken care by fourth-order Runge-Kutta method. The force-displacement responses of the VFPI and VCFPS are studied under parametric variations of their key characteristics for the comparative performance evaluation. The time history variations of response characteristics and peak response evaluation criteria are also investigated for overall comparison of their performances. The performance of VFPI and VCFPS are observed both in uniform and hybrid isolation systems. The force-displacement responses of both VFPI and VCFPS subjected to strong near-fi eld earthquakes show excessively large isolator displacements at higher initial radii of curvature of sliding surface. The large isolator displacements of VFPI and VCFPS can be restrained effi ciently by addition of viscous fl uid dampers in comparison to the increase in coeffi cient of friction of isolators.

Precision Engineering, 2016

We define isotropic springs to be central springs having the same restoring force in all directions. In previous work, we showed that isotropic springs can be advantageously applied to horological time bases since they can be used to eliminate the escapement mechanism [7]. This paper presents our designs based on planar serial 2-DOF linear isotropic springs. We propose two architectures, both based on parallel leaf springs, then evaluate their isotropy defect using firstly an analytic model, secondly finite element analysis and thirdly experimental data measured from physical prototypes. Using these results, we analyze the isotropy defect in terms of displacement, radial distance, angular separation, stiffness and linearity. Based on this analysis, we propose improved architectures stacking in parallel or in series duplicate copies of the original mechanisms rotated at specific angles to cancel isotropy defect. We show that using the mechanisms in pairs reduces isotropy defect by one to two orders of magnitude.