Edoardo Cosenza

Damage indices and damage measures

This article reviews the ground motion parameters than can be assumed as structural and non-structural damage measures. Measures of seismic damage potential based on ground motion records are first described, followed by a discussion of the damage measures relating to simple (linear) and more complex (non-linear) structural responses. The second section reviews the measures of damage phenomena which govern structural degradation and/or collapse, including experimental results and analytical models. The relationship between earthquake characteristics and type and level of damage on the seismic response of structures is examined, and data from different well-known destructive earthquakes are given.

Development length of FRP straight rebars

Abstract In recent years, some attempts have been performed to extend general design rules reported in the codes for steel reinforced concrete to Fiber Reinforced Polymer (FRP) materials; this is the case of relationships adopted in the evaluation of the development length clearly derived by extension of the formulations used for steel rebars. However, such relationships seem to be inappropriate for FRP reinforcing bars: in fact, experimental test results have shown that bond behaviour of FRP bars is different from that observed in case of deformed steel ones. As a consequence, a new procedure for the evaluation of development length based on an analytical approach is needed in order to directly account for the actual bond-slip constitutive law as obtained by experimental tests on different types of FRP reinforcing bars. An analytical solution of the problem of a FRP rebar embedded in a concrete block and pulled-out by means of a tensile force applied on the free end is presented herein. Such solution leads to an exact evaluation of the development length when splitting failure is prevented. Finally, based on the analytical approach, a limit state design procedure is suggested to evaluate the development length.

Local buckling curves for the design of FRP profiles

Local buckling in FRP profiles is analyzed. Some experimental results in compression and bending, where local buckling of the flanges in compression occurred, are described and the critical stresses are summarized. A numerical model by the finite element method (FEM) is introduced and validated by comparison of the numerical results with the experimental ones. This finite element model is applied for a wide parametric analysis in order to individuate a buckling curve for the local buckling of the flange. An analytical expression of the buckling curve is developed, taking into consideration the orthotropy of the material, in which the restraint action of the web on the flange is explicitly introduced as a function of the geometrical and mechanical data of the section sub-components. The reliability of the proposed curve as a design tool is confirmed by comparison with the experimental results.

Integrated seismic early warning and structural health monitoring of critical civil infrastructures in seismically prone areas

A large part of Europe is exposed to medium/high seismic risk. Throughout the past decades serious structural damage and collapse have occurred in different countries. Examples of structures at risk are existing infrastructure and public buildings. Efficient seismic protection is especially required in these structures. In fact, an earthquake can lead to a high number of injury or death since these structures are often crowded. On the other hand, strategic structures have to be fully operational to manage the aftershock emergencies. This article deals with some results of a research focused on the development of optimized structural health monitoring (SHM) technologies and data processing techniques for critical structures in seismically prone areas. Specific solutions are proposed to take advantage of seismic early warning systems (SEWSs), which are becoming very popular and effective worldwide. The most relevant aspects of seismic early warning (SEW) and SHM systems are herein reviewed and the main issues related to their integration are discussed in order to properly design the final system. Attention is mainly focused on dynamic behavior in operational conditions and on earthquake effects. Hardware and software solutions adopted for the characterization and monitoring of the dynamic response of a sample building are illustrated pointing out the capability of the same architecture to host data and information provided by SEW applications. Finally, datasets in operational conditions are used to evaluate the fundamental modal parameters of the structure by output-only techniques, whose potentialities and limitations in the presence of weakly and heavily nonstationary signals have been also assessed. In particular, they have been applied, respectively, to the records collected during crowded football matches hosted at the stadium located nearby the sample building and during the recent L’Aquila earthquake mainshock.

A MULTILEVEL APPROACH TO THE CAPACITY ASSESSMENT OF EXISTING RC BUILDINGS

In the present paper a rational mechanical based approach for the seismic capacity assessment of classes of buildings is presented and capacity curves in terms of ultimate strength and deformation capacities are derived. The proposed procedure allows the main parameters (morphologic and geometric configuration, mechanical properties etc.) to be chosen and their relative influence on the capacity of RC buildings to be evaluated. This evaluation is helpful, since it permits, in the framework of vulnerability assessment at a regional or sub-regional scale, to have a measure of the error that is related to the amount of the information available. Consequently, depending on the relative influence of parameters on response, and also considering the different type of parameters and related availability (by public databases for low order parameters, or by field survey for high order ones), a multilevel building class specification in function of input variables is proposed.

NON-LINEAR ANALYSIS OF COMPOSITE BEAMS UNDER POSITIVE BENDING

Abstract The structural behaviour of steel–concrete composite beams depends on the interaction between the steel beam and the concrete slab. Therefore, the connection largely influences the global behaviour of the beam and its modelling is a key issue in the analysis of these structures. An effective model requires the introduction of an explicit relationship between slip and interaction force given by each connector, which is strongly non-linear. In this paper, a numerical procedure that allows a reliable analysis of the structural behaviour of composite beams subjected to sagging moment due to short term loads, both in serviceability and ultimate state, is proposed.

Multi-Criteria Decision Making for Seismic Retrofitting of RC Structures

The upgrading of existing structures that are not adequate to withstand seismic demand is a widely adopted and effective approach aimed at risk reduction. Nowadays, many are feasible retrofit strategies, employing traditional and/or innovative materials, and several options are available to professionals. Each one has different performances in respect to some criteria, i.e., technical and/or economical, by which each alternative can be evaluated. The selection of the most suitable retrofit strategy for a particular structure may be not straightforward since, in many applications, there is no alternative which clearly emerges among others as the best one according to the whole of the criteria considered. Multi-Criteria Decision Making (MCDM) methods are decision-support procedures used in many fields allowing the evaluation and comparison of a set of alternatives when many evaluation criteria are involved. Ranking the alternative solutions leads to the identification of the optimal solution, which better performs in respect to all relevant goals. This article discusses how such methodological framework may be applied to the seismic retrofit of sub-standard structures. The procedure is presented via an application to an under-designed reinforced concrete (RC) building. Four different seismic upgrading alternative strategies, reflecting common as well as innovative retrofit approaches, are designed to get the required performance level and compared by using the TOPSIS – MCDM method.

Ductility of composite beams under negative bending: an equivalence index for reinforcing steel classification

Abstract Reinforcing steel actually available on the European market is generally characterised by a good strength, but also by reduced ductility; on the other hand European codes concerning concrete and composite structures point out the importance of using reinforcing steel with sufficient ductility. In this paper, the influence of the properties of reinforcing steel on the rotational capacity of composite beams under negative bending is theoretically analysed using a refined model, validated with experimental tests. An equivalence criterion for the classification of reinforcing steel is also introduced. Plastic rotation that can be sustained by composite beams at failure is assumed as the main parameter to define the equivalent structural performance. To this end, the results of a wide parametric analysis are discussed. The comparison with similar analyses made for concrete structures shows that one classification for reinforcing steel seems to be not reliable for both types of structures.

SEISMIC ASSESSMENT OF GRAVITY LOAD DESIGNED R.C. FRAMES: CRITICAL ISSUES IN STRUCTURAL MODELLING

Reinforced concrete frames designed according to early seismic provisions or, sometimes, without any seismic provision, have usually low strength and, in most cases, show limited ductility. Very often details are poor and, consequently, the critical zones do not behave in a ductile way, showing brittle mechanisms of failure. Because of these problems, the assessment of existing reinforced concrete (RC) structures requires a refined procedure. A summary of models that permit the analysis of the non-linear behaviour of RC structures is discussed. An innovative numerical model is presented wich takes into account the most important mechanical phenomena affecting the non-linear behaviour of the RC frames. In conclusion, the influence of different strength and deformation sources on the global behaviour of existing buildings is studied and the needed capabilities of the numerical models are underlined.

EXPERIMENTAL BEHAVIOUR AND NUMERICAL MODELLING OF SMOOTH STEEL BARS UNDER COMPRESSION

Many existing reinforced concrete buildings located in seismic regions are characterised by internal steel reinforcement made of smooth bars and stirrups with inadequate spacing. These bars could be subjected to significant compression and eventually buckle. This paper deals with a comprehensive experimental campaign investigating the compressive behaviour of smooth bars for different values of the ratio L/D, L being the restraints distance and D the bar diameter. The stress-strain relationship is then modelled ranging from an elastic-plastic behaviour identical to that in tension (L/D=5) to the elastic buckling behaviour (L/D>20). The comparison between the experimental results and the outcomes of the model confirms the accuracy of the proposed stress-strain relationship.