Direct estimation of the seismic demand and capacity of oscillators with multi‐linear static pushovers through IDA

SPO2IDA is introduced, a software tool that is capable of recreating the seismic behaviour of oscillators with complex quadrilinear backbones. It provides a direct connection between the static pushover (SPO) curve and the results of incremental dynamic analysis (IDA), a computer‐intensive procedure that offers thorough demand and capacity prediction capability by using a series of nonlinear dynamic analyses under a suitably scaled suite of ground motion records. To achieve this, the seismic behaviour of numerous single‐degree‐of‐freedom (SDOF) systems is investigated through IDA. The oscillators have a wide range of periods and feature pinching hysteresis with backbones ranging from simple bilinear to complex quadrilinear with an elastic, a hardening and a negative‐stiffness segment plus a final residual plateau that terminates with a drop to zero strength. An efficient method is introduced to treat the backbone shape by summarizing the analysis results into the 16, 50 and 84% fractile IDA curves, reducing them to a few shape parameters and finding simpler backbones that reproduce the IDA curves of complex ones. Thus, vast economies are realized while important intuition is gained on the role of the backbone shape to the seismic performance. The final product is SPO2IDA, an accurate, spreadsheet‐level tool for performance‐based earthquake engineering that can rapidly estimate demands and limit‐state capacities, strength reduction R‐factors and inelastic displacement ratios for any SDOF system with such a quadrilinear SPO curve. Copyright © 2006 John Wiley & Sons, Ltd.     

Buckling and vibration analysis of flexible beams resting on an elastic half-space

The present paper deals with the buckling and vibration of prismatic beams resting on an elastic half-space. The computational procedure developed herein utilizes the advantages of both an analytical approach and a finite element scheme. This is accomplished by deriving exact frequency and axial force dependent stiffness matrices using the analytical solutions of the governing differential equation as ‘shape functions’. The major advantages of the proposed approach over previous ones are pointed out and discussed in detail. Numerical results demonstrating the performance of the proposed method are presented in the final part of the paper.     

Dynamic effects of moving loads on road pavements: A review

This review paper deals with the dynamic response of road pavements to moving loads on their surface. The road pavement can be modeled as a beam, a plate, or the top layer of a layered soil medium. The foundation soil can be modeled as a system of elastic springs and dashpots or a homogeneous or layered half-space. The material behavior of the pavement can be elastic or viscoelastic, while that of the foundation layers elastic, viscoelastic, water-saturated poroelastic or even inelastic. The loads are concentrated or distributed of finite extent, may vary with time and move with constant or variable speed. The analysis is done by analytical, analytical/numerical and purely numerical methods, such as finite element and boundary element methods, under conditions of plane strain or full three-dimensionality. A number of representative examples is presented in order to illustrate the problem and the methods of analysis, demonstrate the dynamic effects of moving loads on the layered soil medium and indicate the implications of the results on road and airport pavement design.     

Sand fabric evolution effects on drain design for liquefaction mitigation

This paper revisits the seminal work of Seed and Booker (1977) [21] on the design of infinitely permeable drains for liquefaction mitigation. It is shown that their basic mathematical assumption for the rate of earthquake-induced excess pore pressure generation overlooks sand fabric evolution effects during cyclic loading and eventually leads to underestimation of the drain effectiveness. This is because such effects cause peak excess pore pressures to be attained at the early stages of partially drained shaking, followed by a gradual attenuation even if shaking continues undiminished, a response feature not predicted by the original formulation. In addition, special emphasis is given to the analytical relation describing the excess pore pressure build-up until liquefaction in undrained tests. This relation was considered unique in the original work, for reasons of simplicity, thus neglecting sand fabric evolution effects that may differentiate it for various sands, densities and loading conditions. Hence, a revised analytical formulation is proposed, which takes into account both above effects of sand fabric evolution. The paper provides a quantitative assessment of their influence on drain effectiveness and establishes a new set of charts for drain design. Experimental measurements from shaking table tests, as well as robust numerical simulations are shown, which underline the necessity for the revised solution and design charts.     

A methodology for the performance evaluation of low-cost accelerometer and magnetometer sensors in geomatics applications

This paper presents a methodology and its software implementation for the performance evaluation of low-cost accelerometer and magnetometer sensors for use in geomatics applications. A known mathematical calibration model has been adopted. The method was completed with statistical methodologies for adjusting observations and has been extended to calculate accuracies for the attitude, heading, and tilt angles estimation that are of interest to geomatics applications. The evaluation method consists of two stages. First, the evaluation method reviews the total magnitude of acceleration or the strength of the magnetic field. Second, the evaluation is more detailed and concerns the determination of mathematical parameters that describe both accelerometer and magnetometer working model. A software tool that implements the evaluation model has been developed and is applied both in accelerometer and magnetometer measurement data-sets acquired from a low-cost sensor system.     

Near‐optimal piecewise linear fits of static pushover capacity curves for equivalent SDOF analysis

The piecewise linear (‘multilinear’) approximation of realistic force‐deformation capacity curves is investigated for structural systems incorporating generalized plastic, hardening, and negative stiffness behaviors. This fitting process factually links capacity and demand and lies at the core of nonlinear static assessment procedures. Despite codification, the various fitting rules used can produce highly heterogeneous results for the same capacity curve, especially for the highly‐curved backbones resulting from the gradual plasticization or the progressive failures of structural elements. To achieve an improved fit, the error introduced by the approximation is quantified by studying it at the single‐degree‐of‐freedom level, thus avoiding any issues related to multi‐degree‐of‐freedom versus single‐degree‐of‐freedom realizations. Incremental dynamic analysis is employed to enable a direct comparison of the actual backbones versus their candidate piecewise linear approximations in terms of the spectral acceleration capacity for a continuum of limit‐states. In all cases, current code‐based procedures are found to be highly biased wherever widespread significant stiffness changes occur, generally leading to very conservative estimates of performance. The practical rules determined allow, instead, the definition of standardized low‐bias bilinear, trilinear, or quadrilinear approximations, regardless of the details of the capacity curve shape. Copyright © 2012 John Wiley & Sons, Ltd.     

Derivation of new SAC/FEMA performance evaluation solutions with second‐order hazard approximation

A novel set of SAC/FEMA‐style closed‐form expressions is presented to accurately assess structural safety under seismic action. Such solutions allow the practical evaluation of the risk integral convolving seismic hazard and structural response by using a number of idealizations to achieve a simple analytical form. The most heavily criticized approximation of the SAC/FEMA formats is the first‐order power‐law fit of the hazard curve. It results to unacceptable errors whenever the curvature of the hazard function becomes significant. Adopting a second‐order fit, instead, allows capturing the hazard curvature at the cost of necessitating new analytic forms. The new set of equations is a complete replacement of the original, enabling (a) accurate estimation of the mean annual frequency of limit‐state exceedance and (b) safety checking for specified performance objectives in a code‐compatible format. More importantly, the flexibility of higher‐order fitting guarantees a wider‐range validity of the local hazard approximation. Thus, it enables the inversion of the formulas for practically estimating the allowable demand or the required capacity to fulfill any design objective. Copyright © 2012 John Wiley & Sons, Ltd.     

Potential suitability for urban planning and industry development using natural hazard maps and geological–geomorphological parameters

During the planning of an urban environment, usually only economic and social parameters are taken into account. As a result, urban areas are susceptible to natural disasters, which cause extensive damages in them, because the cities or towns have been repeatedly located in vulnerable areas. In this study, for the protection of human environment, is proposed a unique approach of urban planning and sustainable development. The study area is Trikala Prefecture (Western Thessaly, Central Greece). An integrated evaluation of the suitable areas for urban growth and light industry development is proposed by using mainly natural hazards as well as geological–geomorphological–geographical characteristics of the study area. The used parameters were correlated by using the analytical hierarchical process (AHP) method and incorporated into a geographic information system (GIS) in order to produce the corresponding suitability maps. The study area is classified in five categories of very high, high, moderate, low, and very low suitability for urban growth and industrial development. Moreover, the spatio-temporal changes of the urban limits are studied since 1885 for the three major towns (Trikala, Kalambaka and Pyli) of the study area. These changes sketch out the urban growth trend. The comparison between the urban growth trend with the potential suitability for urban growth and industrial development of these towns lead to discrepancies. These can be attributed mainly to the fact that in the majority of cases, only geographical, social, and economical factors were used for urban development, whereas in our study, natural hazards, geomorphological, and geographical parameters were quantified and taken into account.     

Erratum to: Geotechnical and mineralogical properties of weak rocks from Central Greece

The original version of this article was published in Central European Journal of Geosciences volume 1, issue 4 (2009), pp 431–442, DOI:10.2478/v10085-009-0029-0. Unfortunately the original version of this article contains mistakes in authors names which we correct here. Editorial staff of the journal apologise for any inconvenience that may result from the oversight.