SUMMARYFloor horizontal accelerations are needed for obtaining forces for the design of diaphragms, for the design of their connections and for the design of non-structural components and equipment supported by structures. Large oor horizontal accelerations have been recorded in buildings during earthquakes. Such accelerations have been responsible for inertia forces causing damage to services and are a major reason for structural damage and even building collapse.This paper describes an analytical investigation into earthquake-induced oor horizontal accelerations that arise in regular buildings built with rigid diaphragms. The paper also describes several methods prescribed by design standards and proposes a new method. The method is based on modal superposition modiÿed to account for the inelastic response of the building's lateral force resisting system. Results obtained from time-history inelastic analysis are compared with the proposed method.

The analytical modelling of infilled frames is a complex issue because these structures exhibit a highly non- linear inelastic behaviour resulting from the interaction of the masonry infill panel and the surrounding frame. This paper presents a general review of the different procedures used for the analysis of infilled frames, which can be grouped in local or micro-models and simplified or macro-models, depending on the degree of refinement used to represent the structure. The finite element formulation and the equivalent truss mechanism are the typical examples of each group. The advantages and disadvantages of each procedure are pointed out, and practical recommendations for the implementation of the different models are indicated.

Reinforced concrete frames infilled with masonry panels constitute an important part of the high-risk structures in different regions of high seismicity. In some developing countries, they are still used as main structural system for low to medium rise buildings. Consequently, reliable methods to analyse infilled frames are required in order to reduce the loss of life and property associated with a possible structural failure. The equivalent strut model, proposed in the 1960s, is a simple procedure to represent the effect of the masonry panel. Several improvements of the original model have been proposed, as a result of a better understanding of the behaviour of these structures and the development of computer software. This paper presents a new macro-model for the evaluation of the global response of the structure, which is based on a multi-strut formulation,. The model, implemented as 4-node panel element, accounts separately for the compressive and shear behaviour of masonry using a double truss mechanism and a shear spring in each direction. The principal premises in the development of the model are the rational consideration of the particular characteristics of masonry and the adequate representation of the hysteretic response. Furthermore, the model is able to represent different modes of failure in shear observed for masonry infills. The comparison of analytical results with experimental data showed that the proposed model, with a proper calibration, is able to represent adequately the in-plane response of infilled frames.

SUMMARYPassive and Semi-Active Tuned Mass Damper (PTMD and SATMD) building systems are proposed to mitigate structural response due to seismic loads. The structure's upper portion self plays a role either as a tuned mass passive damper or a semi-active resetable device is adopted as a control feature for the PTMD, creating a SATMD system. Twodegree-of-freedom (2-DOF) analytical studies are employed to design the prototype structural system, specify its element characteristics and effectiveness for seismic responses, including defining the resetable device dynamics. The optimal parameters are derived for the large mass ratio by numerical analysis. For the SATMD building system the stiffness of the resetable device design is combined with rubber bearing stiffness. From parametric studies, effective practical control schemes can be derived for the SATMD system. To verify the principal efficacy of the conceptual system, the controlled system response is compared to the response spectrum of the earthquake suites used. The control ability of the SATMD scheme is compared to that of an uncontrolled (No TMD) and an ideal passive tuned mass damper (PTMD) building systems for multi-level seismic intensity.

The possibility of foundation rocking of shear wall structures designed to NZS 4203 is discussed. Theory developed by Housner for the free rocking of a rigid block is compared with experimental results from a simple structural model with a number of different foundation conditions. A simple design method for assessing maximum rocking displacements, using equivalent elastic characteristics and a response-spectra approach is proposed, and compared with results from simulated seismic excitation of the model using an electro-hydraulic shake-table. A typical design example is included.

SUMMARY 7This paper presents an innovative set of high-seismic-resistant structural systems termed Advanced FlagShaped (AFS) systems, where self-centering elements are combined in series and/or in parallel with 9 alternative forms of energy dissipation (yielding, friction and viscous damping). AFS systems is developed using the rationale of combining velocity-dependent with displacement-dependent energy dissipation for 11 self-centering systems, particularly to counteract near-fault earthquakes. Non-linear time-history analyses (NLTHA) on a set of four single-degree-of-freedom (SDOF) systems under a suite of 20 far-field and 13 20 near-fault ground motions are used to compare the seismic performance of AFS systems with the conventional systems. It is shown that AFS system with a combination of hysteretic and viscous energy 15 dissipations achieved greater performance in terms of the three performance indices. The use of friction slip in series of viscous energy dissipation is shown to limit the peak response acceleration and induced 17 base-shear. An extensive parametric analysis is carried out to investigate the influence of two design parameters, 1 and 2 on the response of SDOF AFS systems with initial periods ranging from 0.2 to 3.0 s 19 and with various strength levels when subjected to far-field and near-fault earthquakes. For the design of self-centering systems with combined hysteretic and viscous energy dissipation (AFS) systems, 1 is 21 recommended to be in the range of 0.8−1.6 while 2 to be between 0.25 and 0.75 to ensure sufficient self-centering and energy dissipation capacities, respectively.

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SUMMARYSeismic performance attributes of multi-story passive and semi-active tuned mass damper (PTMD and SATMD) building systems are investigated for 12-story moment resisting frames modeled as '10+2' stories and '8+4' stories. Segmented upper portion of the stories are isolated as a tuned mass, and a passive viscous damper or semi-active resetable device is adopted as energy dissipation strategy. The semi-active approach uses feedback control to alter or manipulate the reaction forces, effectively re-tuning the system depending on the structural response. Optimum TMD control parameters and appropriate matching SATMD configurations are adopted from a companion study on a simplified two-degree-of-freedom (2-DOF) system. Statistical performance metrics are presented for 30 probabilistically scaled earthquake records from the SAC project. Time history analyses are used to compute response reduction factors across a wide range of seismic hazard intensities. Results show that large SATMD systems can effectively manage seismic response for multi-degree-of freedom (MDOF) systems across a broad range of ground motions in comparison to passive solutions. Specific results include the identification of differences in the mechanisms by which SATMD and PTMD systems remove energy, based on the differences in the devices used. Additionally, variability is seen to be tighter for the SATMD systems across the suites of ground motions used, indicating a more robust control system. While the overall efficacy of the concept is shown the major issues, such as isolation layer displacement, are discussed in details not available in simplified spectral analyses, providing further insight into the dynamics of these issues for these systems.