Asimina Athanatopoulou

Equivalent Static Eccentricities in the Simplified Methods of Seismic Analysis of Buildings

The equivalent static eccentricities of seismic forces are usually defined by codes with simple expressions of the static eccentricity. This paper presents certain formulae for the exact calculation of these eccentricities on the basis of the dynamic response of a simplified model. From the parametric analysis of such formulae the determinative role of the torsional and lateral stiffness of the system becomes obvious for the correct evaluation of the equivalent static eccentricities. Finally, a proposal is made for the improvement of the static torsional provisions of the current codes.

Static Pushover Analysis Based on an Energy-Equivalent SDOF System

In this paper, a new energy-based pushover procedure is presented in order to achieve an approximate estimation of structural performance under strong earthquakes. The steps of the proposed methodology are quite similar to those of the well-known displacement modification method. However, the determination of the characteristics of the equivalent single-degree-of-freedom (E-SDOF) system is based on a different rational concept. Its main idea is to determine the E-SDOF system by equating the external work of the lateral loads acting on the multi-degree-of-freedom (MDOF) system under consideration to the strain energy of the E-SDOF system. After a brief outline of the theoretical background, a representative numerical example is given. Finally, the accuracy of the proposed method is evaluated by an extensive parametric study which shows that, in general, it provides better results compared to those produced by other similar procedures.

Evaluation of inelastic response of 3D single-story R/C frames under bi-directional excitation using different orientation schemes

The aim of the present paper is to evaluate by means of nonlinear dynamic analysis four different procedures for the selection of sectional forces needed for the design of R/C frames. For this purpose, a single-story building is designed using four different procedures to select the sets of internal forces needed for the calculation of longitudinal reinforcement. All the four procedures are based on the results of linear response history analysis. Nonlinear dynamic analyses under 16 bi-directional ground motions are performed for 4 different seismic intensity levels. The two horizontal accelerograms of each ground motion are applied along horizontal orthogonal axes forming with the structural axes several incident angles. The results of this study demonstrate that one of the investigated procedures that takes into account the critical seismic angle is more efficient for the design of R/C frame elements.

Scalar Structure-Specific Ground Motion Intensity Measures for Assessing the Seismic Performance of Structures: A Review

ABSTRACT The assessment of the seismic performance depends on the choice of the earthquake Intensity Measure (IM). During the past years many IMs, which take into account not only earthquake characteristics but also structural information, have been proposed. However, no consensus on which IM is the best predictor of the seismic response exists. Along these lines, the objective of this paper is to present the various developed scalar structure-specific seismic IMs and the problems associated with their use in practice, so that the engineer may become familiar with them and their implications in the context of Performance-Based Earthquake Engineering.

CODE PROVISIONS AND ANALYTICAL MODELLING FOR THE IN-PLANE FLEXIBILITY OF FLOOR DIAPHRAGMS IN BUILDING STRUCTURES

In this paper a review of the provisions of some modern seismic codes for the analytical modelling of the floor diaphragm action is made and a methodology using simplified 2-D finite elements models for monolithic floors is suggested, taking into consideration the in-plane flexibility of them. The simplified models use the coarsest discretisation mesh possible, simply taking into account all the connection points of the vertical structural elements on the diaphragm of each storey. The efficiency of the proposed simplified F.E. models is tested with comparative response-spectrum dynamic analyses of various building structures with different plan shapes, according to EuroCode 8 [EC8, 1994]. The simplified models provided excellent results for the dynamic characteristics of the entire building and the stress state of the framing substructure and a fair estimation for the in-plane stresses of the floor diaphragms.

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.

Safety vs. Economy in Performance-Based Design of Buildings: Inevitable Compromise or False Dilemma?

ABSTRACT The objective of the present paper is to investigate the influence of the design objective on the total cost of buildings. A series of reinforced concrete buildings are designed for various design objectives, and the construction cost is calculated. Additionally, the earthquake losses for three different earthquake scenarios are estimated. The total cost of the buildings is calculated as the sum of the construction cost plus the earthquake losses. The whole investigation demonstrates that designing for elastic response against the design earthquake is both the safest and the most economical in long-term option in the case of strong seismic excitations.

Effects of Local Site Conditions on Inelastic Dynamic Response of R/C Bridges

The purpose of this work is to study the effects of site conditions on the inelastic dynamic analysis of a reinforced concrete (R/C) bridge by simultaneously considering an analysis of the surrounding soil profile via the Boundary Element Method (BEM). The first step is to model seismic waves propagating through complex geological profiles and accounting for canyon topography, layering and material gradient effect by the BEM. Site-dependent acceleration time histories are then recovered along the valley in which the bridge is situated. Next, we focus on the dynamic behaviour of a R/C, seismically isolated non-curved bridge, which is modelled and subsequently analysed by the Finite Element Method (FEM). A series of non-linear dynamic time-history analyses are conducted for site dependent ground motions by considering non-uniform support motion of the bridge piers. All numerical simulations reveal the sensitivity of the ground motions and the ensuing response of the bridge to the presence of local soil conditions. It cannot establish a priori that these site effects have either a beneficial or a detrimental influence on the seismic response of the R/C bridge.

Parametric Study of Inelastic Seismic Response of Reinforced Concrete Frame Buildings

The objective of this paper is to investigate the influence of strength and stiffness distribution in-plan to the nonlinear seismic behaviour of reinforced concrete frame buildings. For this purpose, two 2-storey buildings, a two-way symmetric and a one-way symmetric with eccentricity relative to the y axis, are designed applying the Modal Response Spectrum Method of analysis according to Eurocode 8. Then, the calculated reinforcement of selected elements of the two structures is modified properly in order to generate seven building models with different strength distributions. Each model is subjected to seven strong ground motions acting in two orthogonal directions. The inelastic dynamic analysis is performed for three levels of seismic intensity corresponding to minor damages, moderate damages and severe damages. The structural response is evaluated by means of local Damage Indices for each element as well as of an Overall Structural Damage Index for the whole building. Useful conclusions concerning the nonlinear response are derived.

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.