Revista Română de Materiale / Romanian Journal of Materials 2015, 45 (3), 255 – 261 255

DISIPAREA DE ENERGIE – UN INDICATOR AL DEGRADĂRILOR STRUCTURALE POTENŢIALE LA STRUCTURILE DIN ZIDĂRIE

ENERGY DISSIPATION - AN INDICATOR OF POTENTIAL STRUCTURAL DAMAGES FOR MASONRY STRUCTURES

NICOLAE DANIEL STOICA∗ , MIRCEA BARNAURE Universitatea Tehnică de Construcţii Bucureşti, Bd. Lacul Tei 122-124, 020396, Bucureşti, România

For existing buildings masonry, numerical simulation

of the seismic behaviour is difficult, involving complex nonlinear models. Testing large-scale models on shaking tables involves important costs and time. Still, the main purpose of testing or simulations is often to identify structural vulnerabilities probable failure modes so that the correct strengthening solution can be chosen. A simplified method for the assessment of the potential structural degradation pattern for simple masonry buildings is proposed. This method is based on energy dissipation and can be easily implemented by practicing engineers. Four case studies are performed using linear numerical models. The results are compared with observations on buildings tested on shaking tables.

Pentru clădirile existente din zidărie, simularea

numerică a comportării la acţiunea seismică este dificilă, implicând modele neliniare complexe. Testarea pe platforma seismică pe modele la scară mare implică timp şi costuri ridicate. De multe ori, scopul simulărilor este de a identifica vulnerabilităţile structurii şi modurile probabile de cedare astfel încât să se poată alege soluţiile corecte în vederea consolidării. Este propusă o metodă simplificată de stabilire a degradărilor structurale potenţiale pentru clădiri din zidărie simplă, pe baza disipării de energie, care să poată fi uşor implementată de inginerii practicieni. Sunt realizate patru studii de caz, utilizând modele numerice liniare. Rezultatele sunt comparate cu observaţiile din cadrul testelor pe platforma seismică pentru clădirile analizate.

Keywords: d. Masonry, d. Construction, c. Mechanical properties, b. Fracture, b. Modelling 1. Introduction

Although masonry as a building material has been used for thousands of years, its structural behaviour, in particular under seismic loading, is not yet sufficiently well known. For current design of new buildings, practicing engineers use the principles and the formulas indicated in the in-force national and European regulations [1, 2]. By design, it is ensured that, in case of a seismic event, the building is not damaged or if post-elastic deformations occur, they follow certain controlled failure mechanisms, while fragile failure patterns are avoided. As regulations also include formulas for determining the properties of the materials, the current design of buildings masonry can be achieved using linear numerical models.

For the analysis of existing buildings, numerical modelling is difficult, as the structural behaviour of masonry structures submitted to earthquake loads is influenced by many parameters [3]. The diversity of bricks and mortars used, the jointing details, the presence of reinforcement or confining elements lead to numerical modelling involving complicated tools [4] that are generally hard to implement by practicing engineers for current structural design.

For this reason, laboratory testing is often used, preferably using full-scale models. Costs are significant and the models cannot be no matter how large, but they depend on the height of the laboratories, the surface of the shaking table and the weight it can carry.

The main purpose of structural analysis is often to unravel the likely failure modes so that appropriate strengthening solutions can be chosen. A simplified method allowing a preliminary analysis with reduced modelling costs and time is very useful for practicing engineers.

The possibility of using, for existing unreinforced masonry buildings, simplified linear numerical models is analysed. The ETABS 2013 software is used. Four case studies are performed, on models of buildings previously tested on shaking tables. The degradation of the structures is assessed based on the amount of energy dissipated. The results are compared to observations during the tests on the shaking table.

2. Assessing structural degradations based on

dissipated energy In the last years, several solutions regarding

the numerical modelling of the behaviour of

∗ Autor corespondent/Corresponding author, E-mail: stoica@utcb.ro

256

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N.D. Stoica, M. Barnaure / Disiparea de energie – un indicator al degradărilor structurale potenţiale la structurile din zidărie 261

areas with a low probability for failure are infinitely rigid lead to results similar to those obtained on the complete model.

This simple method is based on linear models that closely resemble those employed in designing new masonry structures. If such an approach is followed by practicing structural engineers, they can obtain a qualitative estimate of the likely structural failure modes of unreinforced masonry buildings. In essence, solutions aimed at dealing with the structural retrofit may be selected even without having to resort to complex numerical models or to perform shake table earthquake simulations.

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