MODELLING OF RC MEMBERS UNDER CYCLIC BIAXIAL FLEXURE AND AXIAL FORCE

A model is proposed for the incremental force-deformation behaviour of reinforced concrete sections and members, under generalised load or deformation histories in 3D, including cyclic loading, up to ultimate deformation. At the section level the model is of the Bounding Surface type and accounts for the coupling between the two directions of bending and between them and the axial direction. For the construction of the member tangent flexibility matrix on the basis of the section tangent flexibility matrix, a piecewise-linear variation along the member is assumed for the nine terms of the tangent section flexibility matrix. Model parameters are derived on the basis of available test results for: (a) the force-deformation response under cyclic biaxial bending with normal force; (b) the hysteretic energy dissipation; (c) the secant-to-yield member stiffness, and (d) the ultimate deformation of the member under cyclic biaxial load paths.     

SLIDING MODE CONTROL OF BUILDING FRAMES UNDER RANDOM GROUND MOTION

A sliding mode control theory is presented to control the response of building frames to predominant frequency components of the random ground motions. The control algorithm is derived based on a sliding surface which is a function of a state vector containing the structural displacements and velocities and variables that dictate the predominant frequency components of the excitation. Three control mechanisms are employed to control the response of the building frame namely, (1) active mass damper (AMD) placed at the top storey of the building, (2) an actuator placed at a storey level and, (3) an actuator placed at a storey level along with a tuned mass damper (TMD) situated at the top storey level. Responses obtained by the proposed control strategy are compared with those obtained by the linear feedback and feedforward-feedback control strategies (conventional control strategies). Also, they are compared with those obtained by the sliding mode control strategy that considers in its state vector only structural displacements and velocities. It is shown that the proposed control strategy generally performs better than other control strategies in the higher range of control forces. For the lower range of control forces, conventional control strategies are more effective.     

MODELLING OF STRUCTURAL ACCELERATIONS AND APPLICATION TO CONTROLLER DESIGN

In this paper a method for the identification of simplified linear models for building structures is applied to the case when acceleration, rather than displacement, is measured. A frame from benchmark structural controller studies is simulated, and from the input-output data of these simulations, simplified models for the acceleration response of the frame are obtained that have far fewer degrees of freedom. One of these simplified models is used to design a controller, which is tested using an evaluation model from the benchmark controller studies and found to be effective.     

A COMPARATIVE STUDY OF STRENGTHENING AND RETROFITTING MEASURES FOR UNREINFORCED BRICK MASONRY MODEL UNDER CYCLIC TESTING

An experimental study on half-scale brick-masonry models with different strengthening and retrofitting measures has been studied under cyclic loading in a quasi-static test facility. The strengthening measures undertaken for the studies axe the horizontal bond beam at the lintel and sill level with a combination of vertical reinforcement at corners and openings. The retrofitting measures studied are grouting with epoxy-sand-mortar and cement-grout-injection with welded wire mesh in the cracked region. The tests reveal that the horizontal bond beam at lintel level with vertical reinforcement is effective in reducing the cracking above the lintel level. The insertion of an additional sill-band signi-ficantly reduces the cracking in walls. The epoxy-sand-mortar techniques for retrofitting of cracked regions prove to be effective enough to restore the initial strength, stiffness and deformation capacity. Although specimen retrofitted with cement-grout-injection with welded wire mesh is effective to regain the ultimate strength yet the brittle failure is observed as the specimen is stressed beyond the elastic limit.     

ADVANTAGES AND LIMITATIONS OF ADAPTIVE AND NON-ADAPTIVE FORCE-BASED PUSHOVER PROCEDURES

The recent drive for use of performance based methodologies in design and assessment of structures in seismic areas has significantly increased the demand for the development of reliable nonlinear inelastic static pushover analysis tools. As a result, the recent years have witnessed the introduction of the so-called adaptive pushover methods, which, unlike their conventional pushover counterparts, feature the ability to account for the effect that higher modes of vibration and progressive stiffness degradation might have on the distribution of seismic storey forces. In this paper, the accuracy of these force-based adaptive pushover methods in predicting the horizontal capacity of reinforced concrete buildings is explored, through comparison with results from a large number of nonlinear time-history dynamic analyses. It is concluded that, despite its apparent conceptual superiority, current force-based adaptive pushover features a relatively minor advantage over its traditional non-adaptive equivalent, particularly in what concerns the estimation of deformation patterns of buildings, which are poorly predicted by both types of analysis.     

Design Methodology for Seismic Upgrading of Substandard Reinforced Concrete Structures

This article presents a design methodology for seismic upgrading of existing reinforced concrete (RC) buildings. The methodology is based on the modification of the deflected shape of the structure so as to achieve a near-uniform distribution of interstorey drift along the building height, thereby eliminating damage localization. Yield Point Spectra are utilized for the definition of demand and a direct displacement-based design approach is implemented. The fundamental steps of the method are described in detail, including a systematic evaluation of assumptions and limitations. A full-scale tested structure is used as a case study for assessment and verification of the proposed methodology. Alternative retrofit scenarios are set according to target response and performance levels. The role of the target deflected response shape and its influence on the outcome of the retrofit strategy is investigated. The viability of the alternative retrofit scenarios is studied for different ground motions including near-fault earthquake records.     

A Fast and Efficient Simulation of the Far-Fault and Near-Fault Earthquake Ground Motions Associated with the June 17 and 21, 2000, Earthquakes in South Iceland

The two M_w 6.5 earthquakes on June 17 and 21, 2000, respectively, in the populated South Iceland Seismic Zone (SISZ) significantly augmented the Icelandic database of strong ground motions, and several strong velocity pulses were recorded at near-fault sites. The strong motions are interpreted via the Specific Barrier Model (SBM) and a mathematical model of near-fault velocity pulses. The data indicates self-similar source scaling and significantly greater attenuation of seismic waves than in other interplate regions. Through inversion of the data a new attenuation function for the SISZ has been adopted, which results in unbiased simulations. For the first time, the characteristics of the recorded near-fault pulses have been identified and compared to the worldwide database of such records. The SBM and the near-fault pulse model combine naturally in a fast and efficient synthesis of realistic, broad-band strong ground motions in the far-fault and near-fault region. Such simulations are showcased for the June 2000 earthquakes and indicate that the modeling approach adopted in this study is an effective tool for the estimation of realistic earthquake ground motions in the SISZ.     

EVALUATION OF CONVENTIONAL AND ADAPTIVE PUSHOVER ANALYSIS I: METHODOLOGY

In this paper, a methodology is suggested and tested for evaluating the relative performance of conventional and adaptive pushover methods for seismic response assessment. The basis of the evaluation procedure is a quantitative measure for the difference in response between these methods and inelastic dynamic analysis which is deemed to be the most accurate. Various structural levels of evaluation and different incremental representations for dynamic analysis are also suggested. This method is applied on a set of eight different reinforced concrete structural systems subjected to various strong motion records. Sample results are presented and discussed while the full results are presented alongside conclusions and recommendations, in a companion paper.     

Chemical Alteration and Use of Beeswax Through Time: Accelerated Ageing Tests and Analysis of Archaeological Samples from Various Environmental Contexts

In order better to interpret the chemical composition of ancient organic residues and artefacts containing beeswax, the degradation of this raw material was accelerated in the laboratory by controlled heating. During the course of degradation, deposits were condensed above the beeswax. Both degraded beeswax and these deposits were analysed. These experiments definitively proved that n‐alkane depletion is due to a sublimation process that depends on the molecular weight of these hydrocarbons. The formation of benzoic and cinnamic derivatives due to the degradation of flavonoid precursors initially present in beeswax has also been highlighted for the first time. The analysis of samples from Neolithic and Roman periods led to the identification of beeswax characterized by different degradation patterns linked to their environmental context.     

Local Government Portfolios and Regional Growth: Some Combined Dynamic CGE/Optimal Control Results

A theoretical policy model is presented that combines regional dynamic CGE modeling and optimal control to explore the role of local government taxation and expenditure in enhancing regional growth. It contributes to the regional CGE literature by explicitly solving for an optimal policy and augments earlier regional optimal control models by adding endogenous optimization of producer and consumer agents in response to endogenously determined prices. Results of three policy regimes are analyzed in terms of gains in the objective function, impacts on income inequality, and sensitivity to model parameterization.