The general trends of the inelastic behaviour of plan-asymmetric structures have been studied. Systems with structural elements in both orthogonal directions and bi-axial eccentricity were subjected to bi-directional excitation. Test examples include idealised singlestorey and multi-storey models, and a three-storey building, for which test results are available. The response in terms of displacements was determined by nonlinear dynamic analyses. The main findings, limited to fairly regular and simple investigated buildings, are: (a) The amplification' of displacements determined by elastic dynamic analysis can be used as a rough, and in the majority of cases conservative estimate in the inelastic range. (b) Any favourable torsional effect on the stiff side, which may arise from elastic analysis, may disappear in the inelastic range. These findings can be utilised in the approximate pushover-based seismic analysis of asymmetric buildings, e.g. in the N2 method. It is proposed that the results obtained by pushover analysis of a 3D structural model be combined with the results of a linear dynamic (spectral) analysis. The former results control the target displacements and the distribution of deforrn&ions along the height of the building, whereas the latter results define the torsional amplifkations. The proposed approach is partly illustrated and evaluated by test examples.

A non‐parametric empirical approach, called the conditional average estimator (CAE) method, has been implemented for the estimation of the flexural deformation capacity of reinforced concrete rectangular columns expressed in terms of the ultimate (‘near collapse’) drift. Two databases (PEER and Fardis), which represent subsets of the original databases, were used. Four input parameters were employed in the basic model: axial load index, index related to confinement, shear span index, and concrete compressive strength. The results of analyses suggest that, in general, ultimate drift decreases with increasing axial load index, and increases with better confinement. An increase in the shear span‐to‐depth ratio has a beneficial effect until a turning point is reached. After that the opposite trend can be observed, i.e. a decrease in the ultimate drift with further increasing of the shear span‐to‐depth ratio. No clear trend is observed in the case of concrete compressive strength. The predictions, obtained by using the Fardis database are in general somewhat larger than the predictions from the PEER database, due to the difference in the definition of ultimate drift. The scatter of results is large. The local coefficient of variation, which is a measure for dispersion, amounts to about 0.2–0.5. The ultimate drifts obtained by using the two databases, were compared with the values predicted by the Eurocode 8 empirical formula. Copyright © 2006 John Wiley & Sons, Ltd.

SUMMARYAn attempt has been made to explore the general trends in the seismic response of plan-asymmetric structures without any restrictions imposed by a particular code. Systems with structural elements in both orthogonal directions under bi-directional excitation were studied. Idealized single-storey models with bi-axial eccentricity were employed. The systems were torsionally sti and, in the majority of cases, mass-eccentric. The main ÿndings are: in general, inelastic torsional response is qualitatively similar to elastic torsional response. Quantitatively, the torsional e ect on the exible side, expressed as an increase of displacements due to torsion, decreases slightly with increasing plastic deformation, unless the plastic deformations are small. The response on the sti side generally strongly depends on the e ect of several modes of vibration and on the in uence of the ground motion in the transverse direction. These in uences depend on the structural and ground motion characteristics in both directions. Reduction of displacements due to torsion, typical for elastic torsionally sti structures, usually decreases with increasing plastic deformations. As an additional e ect of large plastic deformations, a attening of the displacement envelopes in the horizontal plane usually occurs, indicating that torsional e ects in the inelastic range are generally smaller than in the elastic range. The dispersion of the results of inelastic torsional response analysis is generally larger than that of elastic analysis.

Recently, several new ground-motion prediction equations (GMPEs) have been developed in the U.S.A. (the NGA project) and elsewhere. Unfortunately, the predictions obtained by using different models still differ considerably, although starting from the same database. In this paper, a non-parametric approach, called the Conditional Average Estimator (CAE) method, has been used for ground-motion prediction. The comparison between the CAE results and the predictions obtained by five NGA and one European model suggest that the model predictions depend substantially on the selection of the effective database and on the adopted functional form. Both decisions rely to some extent on judgement, and their influence is especially important at short distances from the source. The differences between the results obtained from the European and NGA databases seem to be of the same or even smaller magnitude than the differences observed between different NGA models, at least at short and moderate distances. Aftershocks in the database generally decrease the median values and increase dispersion. The non-parametric CAE method has proved to be a simple but powerful tool for ground-motion prediction, especially in a research environment. It can be used for quick predictions with different databases and different input parameters within the range of available data. It is easy to add to or remove data from the database, and to check the influence of additional input parameters. With availability of high quality data, the non-parametric approach will become more reliable and more attractive also for practical applications.I. PERUŠ AND P. FAJFAR and evaluation of important structures. Seismic hazard usually makes a large contribution to the total risk of a structure in seismically active regions, so the selection of appropriate GMPE's could have a substantial influence on the safety and economy of structures and equipment.Recently, five different groups of US researchers developed new ground-motion models (AS-Abrahamson and Silva [1]; BA-Boore and Atkinson [2]; CB-Campbell and Bozorgnia [3]; CY-Chiou and Youngs [4]; and I-Idriss [5]) within the NGA project [6]. New GMPEs have also been proposed in other parts of the world. Douglas [7-9] has kept track of the developments worldwide. There have been indications that models developed by using regional data can be transferred to other regions. Stafford et al. [10] made comparisons of recent European (AB-Akkar and Bommer [11] and ADSS-Ambraseys, Douglas, Sarma and Smit [12]) and NGA models.Their results indicate that, for most engineering applications, the NGA models may confidently be applied within Europe. A similar conclusion was drawn by Campbell and Bozorgnia [13]. Douglas [14] concluded that it is currently more defensible to use well-constrained models, possibly based on data from other regions, than to use predicted motions from local, often poorly constrained, models.The new models, especially the NGA ones, represent a significant advance in the state-of-the-art of empirical ground...

SUMMARY A web‐based methodology for the prediction of approximate IDA curves, which consists of two independent processes, is proposed. The result of the first process is a response database of the SDOF model, whereas the second process involves the prediction of approximate IDA curves from the response database by using n‐dimensional linear interpolation. Such an approach enables user‐friendly prediction of the seismic response parameters with high accuracy. In order to demonstrate the capabilities of the proposed methodology, a web application for the prediction of the approximate 16th, 50th and 84th fractile responses of an RC structure was developed. For the presented case study, the response database was computed for a set of 30 ground motion records and the discrete values of six structural parameters. Very good agreement between the computed and the approximated IDA curves of the four‐storey RC building was observed. Copyright © 2012 John Wiley & Sons, Ltd.

BackgroundThis study aimed to externally validate and upgrade the recent difficulty scoring system (DSS) proposed by Halls et al. to predict intraoperative complications (IOC) during laparoscopic liver resection (LLR).MethodsThe DSS was validated in a cohort of 128 consecutive patients undergoing pure LLRs between 2008 and 2019 at a single tertiary referral center. The validated DSS includes four difficulty levels based on five risk factors (neoadjuvant chemotherapy, previous open liver resection, lesion type, lesion size and classification of resection). As established by the validated DSS, IOC was defined as excessive blood loss (> 775 mL), conversion to an open approach and unintentional damage to surrounding structures. Additionally, intra- and postoperative outcomes were compared according to the difficulty levels with usual statistic methods. The same five risk factors were used for validation done by linear and advanced nonlinear (artificial neural network) models. The study was supported by mathematical computations to obtain a mean risk curve predicting the probability of IOC for every difficulty score.ResultsThe difficulty level of LLR was rated as low, moderate, high and extremely high in 36 (28.1%), 63 (49.2%), 27 (21.1%) and 2 (1.6%) patients, respectively. IOC was present in 23 (17.9%) patients. Blood loss of >775 mL occurred in 8 (6.2%) patients. Conversion to open approach was required in 18 (14.0%) patients. No patients suffered from unintentional damage to surrounding structures. Rates of IOC (0, 9.5, 55.5 and 100%) increased gradually with statistically significant value among difficulty levels (P < 0.001). The relations between the difficulty level, need for transfusion, operative time, hepatic pedicle clamping, and major postoperative morbidity were statistically significant (P < 0.05). Linear and nonlinear validation models showed a strong correlation (correlation coefficients 0.914 and 0.948, respectively) with the validated DSS. The Weibull cumulative distribution function was used for predicting the mean risk probability curve of IOC.ConclusionThis external validation proved this DSS based on patient’s, tumor and surgical factors enables us to estimate the risk of intra- and postoperative complications. A surgeon should be aware of an increased risk of complications before starting with more complex procedures.

A non-parametric empirical approach, called the conditional average estimator (CAE) method, has been applied for the prediction of the normalized lateral force-drift envelope of reinforced concrete (RC) rectangular columns, as well as their characteristic drifts (effective yield drift, capping drift and ultimate drift), and drift-related parameters (the ratio between the effective yield drift and elastic drift, and two ductility measures). A subset of the PEER RC column database was used. Five input parameters were employed: axial load index, index related to confinement, shear span index, concrete compressive strength, and longitudinal reinforcement index. The results suggest that the relations between the input and output parameters are complex, and that it is difficult to isolate the influence of a single parameter. Nevertheless, some trends were observed. The axial load index is the most influential input parameter. All the results decrease with an increasing axial load index, whereas they increase with an increasing longitudinal reinforcement index. An increase in the index related to confinement results in increases in the ultimate drift and in ductility. The influence of the shear span index is the most complex. The influence of the concrete strength is small with the exception of two output parameters related to elastic drift, which substantially decrease with increasing strength. The dispersion of the results is relatively large. The results of the predictions can be used for mathematical modelling of moment-rotation backbone curves for plastic hinges, and for the estimation of the deformation capacity of columns in seismic performance assessments. I. PERUŠ AND P. FAJFAR are required. A simple, robust and rational model, which is able to simulate the actual structural behaviour of frame structures quite well [1], is the lumped plasticity model. It employs the concept of plastic hinges. Such a model is typically defined by the moment-rotation backbone curve and hysteretic rules. Analytical and semi-empirical approaches are available for the determination of moment-rotation backbone curve (e.g. [2,3]). Due to the complexity of the problem, empirical approaches have also been developed. Mostly, only partial problems have been investigated. For example, Sugano [4] formulated an empirical expression for the ratio of the secant stiffness at yielding to the initial stiffness. Simple equations for this ratio have been recently proposed by Elwood and Eberhard [5]. Fardis and co-workers [6, 7] have developed empirical formulas for yield and ultimate drifts. A version of their expressions has been incorporated into Eurocode 8, Part 3 [8].Very recently, Haselton [9] has proposed empirical expressions for several drift-related parameters, which allow the construction of the complete backbone curve, including the strength-degrading part. Moreover, in [9] an empirical expression has also been defined for energy dissipation capacity, which is required for the definition of hysteretic rules in the Ibarra et al. model [10...

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