RICERCA ITALIANA     

Innovative technologies and materials for seismic retrofit of existing structures

Università degli Studi "G. d'Annunzio" Chieti-Pescara

Abstract

The main goal of the proposed research is to assess and enhance methodologies and materials for the design, testing and modeling of the seismic strengthening of existing structures. Both reinforced concrete (RC) (mainly frames, shear wall and bridges) and masonry structures (mainly historical and traditional structures and bridges) will be considered. The main strengthening technique studied will be the application of Fiber Reinforced Polymers (FRP), but other methods, such as the application of external prestressing, will also be considered. The design methods will refer to current and emerging design guidelines in Italy, the European Union and North America. Available design equations will be evaluated and eventually improved. The different research units of the proposed project will use a number of structural elements to be strengthened starting from different levels of damage. The research units will also use state of the art techniques for frame and finite element modeling. The research activities will develop along two interconnected phases: 1) experimental tests on structural members to be loaded in the lab and in situ under monotonic and cyclic loads; b) numerical modeling of structural members and frames under both static and dynamic loads. The proposed project is the continuation of a previously funded two-year research (Cofin 2002). The original research scope is extended here to seismic design and masonry structures.

The EXPERIMENTAL phase focuses >>>

Principal Investigator

Enrico SPACONE Università degli Studi "G. d'Annunzio" CHIETI-PESCARA

Research Objectives

The main objective of the proposed research is the advancement of the state-of-the-art in the field of seismic retrofitting of existing RC and masonry structures. The research will develop along two interconnected, parallel phases. The objectives of the two phases are described hereafter.

EXPERIMENTAL PROGRAM: The experimental program will focus on a series of tests on structural members, as built and strengthened, whose aim is a better understanding of the damage and failure mechanisms under monotonic and cyclic loads. Both RC and masonry specimens will be considered.

As for reinforced concrete, the Brescia, Firenze and Rome 3 units can rely on structural members (beams, columns, joints, shear walls) that have already been tested in the lab or that have been extracted from buildings to be demolished. Such members represent a unique opportunity to study structures designed according to dated safety criteria and in need of retrofitting/strengthening in order to satisfy the modern seismic design criteria. Brescia, Firenze, Rome 1 and Rome 3 will deal with the problem of shear strengthening of RC members with insufficient transverse reinforcement. Brescia will retest an already tested and damaged full scale, five-story structural wall. The aim of the new cyclic tests is the assessment of wall strengthening through external prestressing. The Firenze, Rome 1 and Rome 3 units will join forces in studying the shear strengthening with FRPs of RC beams >>>

First Results

POINT 1: A preliminary numerical study will allow to assess the effectiveness of the new repair and to study the optimal position of the external cables and their pre-tension. Extremely useful and important results will derive from the cyclic tests on the repaired wall and from the comparison of the response of the repaired and original wall.

POINT 2: The tests on the beams will allow to identify the stress distributions in the FRP sheets across the crack, with the aim of 1) expressing them analytically, b) obtaining a design equation expressing the dependence by the crack geometry and by the placing of the FRP sheet/tissue. Regarding the tests on the columns, the effectiveness of the interventions with FRP with respect to the traditional interventions will be evaluated. For what concerns the study of the frames with and without infill the obtained information will be utilized for a) the validation of the FRP reinforcements in case of large contact stresses transferred by the infill and/or by the dissipative bracings, b) the evaluation of the reliability of the results obtainable through nonlinear analysis methods.

POINT 3: Following the experimental tests, it is expected to assemble a comprehensive data base to characterise and quantify, through appropriate design rules, 1) the reduction of the confinement effect when strengthening reinforced columns having rectangular cross-section, 2) the cyclic behaviour of confined structural members.
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Timescale

24 months

National and international background

The assessment of existing RC and masonry structures under static and dynamic loads is a topic of great research and practical interest. Such interest stems on one side from the different levels of degradation shown by the existing infrastructure, and on the other from the fact that many existing structures do not satisfy the safety criteria of the current seismic design philosophies. Recent studies conducted in Canada estimate that the investments necessary worldwide to rehabilitate the existing infrastructure are around a thousand billion dollars (ISIS Canada 2000).

Recent earthquakes have underlined the seismic vulnerability of existing structures and infrastructures, as shown, for instance, by the catastrophic collapses of buildings, bridges and highway structures (Comartin et al. 1995, Hall 1995). Even when human casualties are low, the economic impact can be extremely heavy, as the Northridge earthquake in the US has demonstrated in 1995. This earthquake caused few victims, but the highest economic losses in history due to an earthquake. Few months ago the catastrophic earthquake that destroyed Bam in Iran has once again shown the seismic vulnerability of monumental structures, which are even more difficult to retrofit. Older buildings are of particular interest in Italy because of the presence of several important historical buildings made of load bearing cooked brick, stone and raw earth masonry. For such buildings it is necessary to investigate >>>