Georgios Tsionis

Seismic fragility of RC framed and wall-frame buildings designed to the EN-Eurocodes

Fragility curves are constructed for a portfolio of prototype regular RC frame and wall-frame buildings designed and detailed to EC2 and EC8. The aim is to use EC8’s own seismic performance assessment methods and criteria for existing buildings to evaluate how EC8 achieves its performance goals for new RC buildings. The overall conclusion is that these goals are met in a very consistent and uniform way across all types of buildings considered and their geometric or design parameters, except for RC walls of Ductility Class Medium, which may fail early in shear despite their design against it according to EC8. In fact, these walls do not perform much better than those of braced systems designed to EC2 alone. Therefore, wall shear seems to be an aspect in EC8 worth looking at again. Another finding is that the slenderness limits and the lateral bracing requirements of EC2 for 2nd-order effects under factored gravity loads place severe restrictions on the size of columns and walls, which, although ignored in ordinary seismic design practice, materially impact the outcome of the design and, to a smaller extent, the seismic fragilities of the building’s members. Mixing in the same building columns with significantly different stiffness most often penalizes the more flexible ones and not the stiff, despite their smaller deformation capacities. Another finding is that the reduction in fragility from higher design peak ground accelerations is disproportionately low. Even buildings designed for gravity loads only, but in full accordance to EC2, possess substantial seismic resistance.

Capacity design and seismic performance of multi-storey precast structures

ABSTRACT The seismic design of multi-storey precast structures is at present not covered by specific provisions of the European seismic codes. To fill such gap, capacity design criteria for multi-storey precast concrete frames with hinged beams are presented. Based on the same approach prescribed by the codes for monolithic cast-in-place frames, a distribution of floor forces and a value of behaviour factor are assumed to perform a static linear analysis of the structure. A parametric study aimed to validate the design method is carried out by varying, within the range of practical interest, the main design parameters such as the number of storeys, the mass-over-stiffness ratios and the stiffness characteristics of the columns. The results of dynamic modal analyses and non linear static analyses show that the proposed method can safely be applied to ordinary multi-storey concrete precast frames characterized by structural regularity and limited flexibility.

Numerical Analysis of RC Bridge Piers with Rectangular Hollow Cross-section Retrofitted with FRP Jackets

The research presented in this article deals with the seismic retrofit of bridge piers with rectangular hollow cross-section using fiber-reinforced polymer (FRP) jackets. A two-level numerical approach that combines finite element method (FEM) analyses and fiber modeling is proposed. The FEM is used to study the effect of FRP jackets on the properties of concrete. The analyses show that the existing empirical laws for FRP-confined concrete are not suitable for piers with hollow cross-section, as the effect of confinement is not uniform within the cross-section and the stress–strain curves show softening after peak strength. Fiber modeling is used to study the global behavior of reinforced concrete piers with rectangular hollow cross-section wrapped with FRP jackets. To account for confinement, the properties of the concrete fibers are modified according to the results of the FEM analyses. The proposed method is validated against experimental results and used for an extensive parametric study. It is found that the effectiveness of jacketing is conditioned by the axial load, longitudinal reinforcement, and jacket dimensions. An empirical design equation is formulated on the basis of the numerical analyses.

Fragility Functions of Road and Railway Bridges

This Chapter presents a literature review of seismic fragility functions for reinforced concrete road and railway bridges. It first covers the main issues in fragility analysis, such as the systems for classification of bridges, methods for deriving fragility functions, intensity measures, damage states and damage measures. A section is dedicated to the way the uncertainties regarding the seismic action, geometry, material properties and modelling are treated in existing studies. The Chapter deals also with the recent developments that examine special issues which were not addressed in the first generation of fragility curves. They refer to damaged and retrofitted bridges, the effects of corrosion, skew, spatial variability of the seismic action and liquefaction. Finally, a method for fast fragility analysis of regular bridges is presented. The method applies to bridges with continuous deck monolithically connected to the piers or supported on elastomeric bearings and with free or constrained transverse translation at the abutments.

Seismic Fragility of RC Buildings Designed to Eurocodes 2 and 8

Fragility curves are constructed for prototype regular RC frame and wall-frame buildings designed and detailed per EC 2 and EC 8. The aim is to evaluate how the Eurocodes achieve their seismic performance goals for RC buildings designed to them. These goals seem to be met in a consistent and uniform way across all types of buildings considered and their geometric or design parameters, except for concrete walls of Ductility Class Medium, which may fail early in shear despite their design against it per EC 8. In fact they do not perform much better than those in braced systems per EC 2 alone.