This paper presents the results obtained from tests of a new friction damping system, which has been proposed in order to improve the response of steel Moment Resisting Frames (MRF) and Braced Moment Resisting Frames (BMRF) during severe earthquakes. The system consists of a mechanism containing brake lining pads introduced at the intersection of frame cross-braces. Seismic tests of a three storey Friction Damped Braced Frame (FDBF) model were performed on an earthquake simulator table. The experimental results are compared with the findings of an inelastic time-history dynamic analysis. The results clearly indicate the superior performance of the FDBF compared to conventional building systems.
SUMMARYValuable insights on the problem of seismic pounding have been obtained recently from analytical studies. So far, the proposed analytical models have not been validated experimentally. This paper presents the results of shake table tests of pounding between adjacent three-and eight-storey single-bay steel framed model structures. The pounding response of the frames was measured for various earthquake intensities and initial separations. The experimental results were compared to the predictions resulting from two existing pounding analysis programs. The solution strategy of the first program, SLAM-2, is based on a modal superposition technique. The second program, PC-ANSR, is a non-linear timestep analysis code in which an elastic gap element has been included. Modelling the pounding effect by elastic gap elements in the two programs produced accurate displacement and impact force results. Amplitudes of short acceleration pulses were not well predicted, however, for practical time-step increments. Relative rotations between adjacent floors induced grinding contacts which cannot be captured by uni-axial gap elements.
In the last decade, many energy dissipating systems have been proposed to raise the seismic design of structures beyond the conventional ductility design approach. Among these new systems, friction damping has shown some great potential. In a friction damped system, friction damping devices are inserted in a structure and slip at a predetermined optimum load during severe seismic excitations, before any yielding of the structural members has occurred. Slipping of the devices allows the structure to dissipate the input seismic energy mechanically by friction rather than by inelastic deformation of the structural elements. This paper presents an overview of the recent research and development in Canada on a particular type of friction damped bracing. Analytical and shake table test results are first summarized to illustrate the earthquake performance of friction damped structures compared to the performance of conventional building systems. The development of a design slip load spectrum for the rapid estimation of the optimum slip load distribution is then presented. Finally, two practical examples of the implementation of this system are described: (1) the design of a reinforced concrete library building; and (2) the retrofit of a precast concrete school building.
Recent earthquakes have caused unacceptably high death tolls. We, the editors of the World Housing Encyclopedia, believe that reducing such an unacceptably high loss of life from earthquakes is the most important challenge facing the global earthquake engineering community. This paper acknowledges the continuing disparity between life loss from earthquakes in developing and developed countries, and the increasing vulnerability in developing countries. A sampling of current efforts to improve construction practices includes the publication of earthquake tips in India, construction manuals in Colombia, and the formation of various international networks to promote collaboration and information sharing. Future possibilities include more rewards for research into inadequately engineered construction, greater emphasis on small-scale, local efforts, and a stronger emphasis on advocacy. We believe that all of us, as earthquake professionals, have a responsibility to make the built environment safer worldwide.
The recently proposed mega-sub controlled structure (MSCS), a new type of structure associated with the design and construction of super-tall buildings, has attracted the attention of designers for use in enhancing the control effectiveness in mega-frame buildings. In this paper, a dynamic equation and method to assemble parameter matrixes for a mega-sub controlled structure under random wind loads is presented. Semi-active control using magnetorheological dampers for the MSCS under random wind loads is investigated, and is compared with a corresponding system without dampers. A parametric study of the relative stiffness ratio and relative mass ratio between the mega-frame and the substructures, as well as the additional column stiffness ratio that infl uences the response control effectiveness of the MSCS, is discussed. The studies reveal, for the fi rst time, that different control mechanisms exist. The results indicate that the proposed structure employing semi-active control can offer an effective control mechanism. Guidelines for selecting parameters are provided based on the analytical study.
SUMMARYA trilinear model is used to simulate the seismic resisting mechanism of a single-degree-of-freedom friction-damped system to re#ect the situation in which both dampers and frame members lose their elastic resistance. The seismic response of the friction-damped system is normalized with respect to the response of its corresponding linear system by an approach that incorporates a credible equivalent linearization method, a damping reduction rule and the algebraic speci"cation of the design spectrum. The resulting closed-form solutions obtained for the normalized response are then used to de"ne a force modi"cation factor for friction-damped systems. This force modi"cation factor, together with the condensation procedure for multi-degree-of-freedom structures, enables the establishment of a quasi-static design procedure for friction-damped structures, which is intended for the bene"t and use of structural practitioners. A curve-"tting technique is employed to develop an explicit expression for the force modi"cation factor used with the proposed design procedure; it is shown that this simpli"cation results in satisfactory accuracy. Finally, a design example is given to illustrate the validation of the proposed design procedure.
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