Konstantinos Morfidis

Formulation of a generalized beam element on a two-parameter elastic foundation with semi-rigid connections and rigid offsets

A new, generalized Bernoulli/Timoshenko finite beam element on a two-parameter elastic foundation is presented. The element stiffness matrix is based on the exact solution of the differential equation governing displacements, and possesses the ability for an optional consideration of shear deformations, semi-rigid connections, and rigid offsets. In addition to the proposed stiffness matrix, equivalent element nodal load vectors are developed for handling the external uniform loading and linear temperature variations. The usefulness of the new element in the analysis of reinforced concrete or steel structures is documented by three numerical examples.

Seismic parameters’ combinations for the optimum prediction of the damage state of R/C buildings using neural networks

Abstract The aim of the present paper is to investigate the number and the combination of 14 seismic parameters through which an optimum prediction for the damage state of r/c buildings can be achieved using Artificial Neural Networks (ANNs). Multilayer perceptron networks are utilized. For the training of the ANNs a data set is created using results from Nonlinear Time History Analyses of 30 r/c buildings with different structural dynamic characteristics, which are subjected to 65 actual ground motions. The Maximum Interstorey Drift Ratio is used as the damage index. Two versions of the “Stepwise method”, i.e. the Forward Stepwise Method and the Backward Stepwise Method, as well as the “Weights Method”, are adopted as methods for the investigation of the most effective combinations of the examined seismic parameters. The most significant conclusion that turned out is that ANNs can predict adequately the seismic damage state of r/c buildings if at least 5 seismic parameters are used as inputs. The classification of the seismic parameters on the basis of their correlation with the damage state is not unique, since it depends to the configuration and the training algorithm of ANNs as well as the method which is utilized for the classification.

Eurocode-compliant seismic analysis and design of R/C buildings:

This chapter provides a concise qualitative overview of the philosophy for earthquake resistant design of ordinary structures adopted by relevant international codes of practice, including Eurocode 8. The aim is to facilitate practicing engineers with the interpretation of the code-prescribed design objectives and requirements for the seismic design of ordinary reinforced concrete (r/c) building structures which allow for structural damage to occur for a nominal design seismic action specified in a probabilistic manner. In this regard, the structural properties of stiffness, strength, and ductility are introduced along with the standard capacity design rules and requirements. Further, the role of these structural properties in the seismic design of r/c building structures following a force-based approach in conjunction with equivalent linear analysis methods is explained. Emphasis is placed on delineating the concept of the behaviour factor, or force reduction factor, which regulates the intensity of the seismic design loads and ductility demands. Moreover, the development and current trends in the emerging performance-based design approach for earthquake resistance are briefly reviewed. Lastly, practical recommendations to achieve higher-than-the-minimum-required by current codes of practice structural performance within the force-based design approach are provided.

Effects of nonlinear soil–structure-interaction on seismic damage of 3D buildings on cohesive and frictional soils

The present paper investigates the impact of nonlinear soil–foundation–structure-interaction (NLSFSI) on the damage response of 3D R/C buildings supported on different soil types with varying flexibility. The main goal of the paper is to present a first approach towards the possible quantitative differentiation, with respect to fixed base conditions, on the overall damage level when NLSFSI effects are accounted for. To accomplish this purpose nine buildings with various heights and structural systems are studied. For the foundation of the buildings two different soil types are considered, namely cohesive and frictional ones. Moreover, the soil flexibility is taken into account by using two different values of the soil’s shear wave velocity. The buildings are subjected to 65 bidirectional earthquake records, for which nonlinear time history analyses are conducted. The accelerograms of each record are scaled to two different seismic intensities corresponding to certain performance levels using appropriate scaling factors. The damage state of the buildings is expressed through the maximum interstorey drift ratio. The assessment of the results revealed that the role of soil–foundation–structure-interaction (SFSI) is not necessarily beneficial. In order to assess the SFSI effects a number of parameters are important as the frequency content of the earthquake ground motion, the building’s structural system, the foundation soil flexibility as well as the earthquake intensity.

Design of R/C Buildings to EC8-1: A Critical Overview

This chapter provides practical recommendations for the preliminary seismic design and the finite element modeling of reinforced concrete (r/c) building structures assumed to behave linearly. It also discusses and provides commentary on structural seismic analysis methods adopted by Eurocode 8 (EC8). Specifically, the main principles of conceptual design for achieving well-qualified lateral load-resisting structural systems for earthquake resistance are briefly reviewed. Further, capacity design rules and local detailing practices for enhanced ductility capacity in r/c buildings are presented. Different types of structural analysis methods commonly employed in code-compliant seismic design of structures are outlined and focus is given to the EC8-prescribed equivalent linear analysis methods for forced-based seismic design, namely, the lateral force method and the modal response spectrum method. In this context, the EC8-compatible seismic design loading combinations and the EC8 design spectrum for elastic analysis are also presented. Moreover, the most commonly used finite element modeling practices for linear analysis of r/c multi-storey buildings are detailed, including the modeling of floor slabs, frames, planar walls, cores, and footings resting on compliant soil. Finally, brief comments are included on the proper use and quality verification of commercial seismic design software using benchmark structural analysis and design example problems.

Fundamental Principles for the Design of Earthquake-Resistant Structures

This chapter provides a concise qualitative overview of the philosophy for earthquake resistant design of ordinary structures adopted by relevant international codes of practice, including Eurocode 8. The aim is to facilitate practicing engineers with the interpretation of the code-prescribed design objectives and requirements for the seismic design of ordinary reinforced concrete (r/c) building structures which allow for structural damage to occur for a nominal design seismic action specified in a probabilistic manner. In this regard, the structural properties of stiffness, strength, and ductility are introduced along with the standard capacity design rules and requirements. Further, the role of these structural properties in the seismic design of r/c building structures following a force-based approach in conjunction with equivalent linear analysis methods is explained. Emphasis is placed on delineating the concept of the behaviour factor, or force reduction factor, which regulates the intensity of the seismic design loads and ductility demands. Moreover, the development and current trends in the emerging performance-based design approach for earthquake resistance are briefly reviewed. Lastly, practical recommendations to achieve higher-than-the-minimum-required by current codes of practice structural performance within the force-based design approach are provided.

EC8-Compliant Seismic Analysis and Design Examples

This chapter presents three numerical benchmark example problems considering three different structures to illustrate the implementation of various clauses of Eurocode 8 (EC8) for the seismic design of ordinary reinforced concrete (r/c) buildings. Pertinent numerical input data and selected output data are reported in tabular form to facilitate the use of these example problems as tutorials for commercial seismic structural analysis and design software packages according to EC8. In particular, the first example problem involves undertaking EC8-compliant seismic analysis and deformation-based verification checks using both the lateral force and the modal response spectrum methods for a 5-storey dual r/c building with a single in-plan symmetry and with fixed support conditions. The outcomes from each analysis method are juxtaposed and compared. Further, the second example problem considers a 5-storey dual torsionally sensitive r/c building with fixed support conditions to perform seismic analysis using the modal response spectrum method along with post-analysis deformation-based verification checks. Finally, the third example considers a 4-storey dual r/c building with an r/c core and one underground storey (basement) resting on compliant soil. Emphasis is placed on the modelling of the box-type foundation, including pad and strip footings, and of the supporting ground using linear translational and rotational springs. The modal response spectrum method of analysis is used for the EC8-compliant design of the structure. Complete detailing and design verification checks according to Eurocode 2 and Eurocode 8, including capacity design rules, are presented in detail for selected r/c structural members, namely, for two beams, one column and a wall.

Practical Implementation of EC8 for Seismic Design of R/C Buildings – Flowcharts and Commentary

This chapter delineates all the required computational and logical steps involved in the analysis stage of seismic design of ordinary reinforced concrete (r/c) buildings according to Eurocode 8 (EC8) by means of detailed self-contained flowcharts and pertinent comments. Special focus is given to verification checks for structural regularity in plan and elevation, on the classification of building structures based on torsional sensitivity, on the determination of the maximum allowed behavior factor by EC8, and on the selection and implementation of the two equivalent linear methods of analysis considered by EC8, namely the lateral force method and the modal response spectrum method. Furthermore, additional flowcharts and comments are included for the implementation of EC8-prescribed post-analysis verification checks based on deformations, that is, verification check of second-order effects via the interstorey drift sensitivity coefficient and verification check for maximum interstorey drift to ensure that damage limitation requirements of EC8 are met. Practical recommendations expediting the implementation of EC8-compliant analysis of ordinary r/c buildings are provided. Finally, the required detailing and verification checks for the design of r/c structural members according to Eurocode 2 and Eurocode 8 are presented in the form of self-explanatory flowcharts, along with the special requirements for the determination of seismic design bending moment and shear force diagrams.