Davide Lavorato

Damage patterns in the town of Amatrice after August 24th 2016 Central Italy earthquakes

The impact of the two seismic events of August 24th 2016 on the municipality of Amatrice was highly destructive. There were 298 victims, 386 injured, about 5000 homeless, and the historical center of the town suffered a great number of partial and total collapses. The 260 strong motion records obtained for the first event were analyzed and plotted in a shakemap, comparing them with the macroseismic damage surveys made in 305 localities. On the basis of an inspection survey made in September 2016, a map of the damage patterns of the buildings in the historical center was elaborated according to the EMS 98 classification. The damage level resulted very high with more than 60% of the inspected buildings showing partial or total collapse. The elevated level of destruction was mainly caused by the high vulnerability of the masonry buildings, mostly due to specific vulnerability factors such as the poor quality of masonry, the lack of connections between walls and the poor connection between external walls and floors.

Experimental program for pseudodynamic tests on repaired and retrofitted bridge piers

ABSTRACT This research aims to study the seismic performance of existing r.c. bridge piers specimens heavily damaged after previous pseudodynamic tests and actually repaired and upgraded by using self compacting concrete, stainless steel rebars and CFRP wrapping. Pier specimens are representative of tall and squat circular r.c. piers designed according to Eurocode 8 or Italian Code before 1986. The study comprehends preliminary tests carried out on self compacting concrete and stainless steel bars, as well as on going pseudodynamic tests in order to evaluate the effectiveness of adopted repairing and upgrading techniques to increase both ductility and shear strength.

Generation of Non-synchronous Earthquake Signals

In this chapter, we describe two procedures to generate earthquake asynchronous signals at different space points for the same seismic event. The foundations of long structures, such as bridges, are placed at distant space points. The earthquake signals at these points have different characteristics and their correct evaluation is important to define design actions. However, design codes around the world do not consider this complex type of action in a consistent manner. The point-to-point signal variation is due both to time lag, since the seismic waves move through the soils with a finite velocity among distant points, and to a change of the signal frequency contents. This depends on physical complex soil-wave interaction phenomena during wave propagation (reflection, refraction, filtering, amplification, etc.). In this chapter, two different generation procedures (PR1 and PR2) to determine the non-synchronous actions at different surface points are shown. Both procedures have been implemented in MATLAB. PR1 generates asynchronous signals at the soil surface. It starts from recorded signals at a few surface points for the same seismic event. PR2 produces asynchronous surface signals by amplifying the bedrock signals obtained by a bedrock propagation process. The inputs for the bedrock propagation are obtained via deconvolution of the recorded surface signals. These latter are also the inputs of the PR1 procedure. Detailed knowledge of soil characteristics is required (soil layers, shear wave velocity profiles, soil density, nonlinear materials shear moduli and damping curves), which relies on in situ tests. Deconvolution and amplification processes are performed by Equivalent-Linear Earthquake Site Response (1D soil model, SHAKE91 (Schnabel et al. 1972) and EERA (Bardet et al. 2000)). PR1 and PR2 are then applied to an example case. Asynchronous surface signals are generated at eight foundation points of a bridge placed in the Aterno Valley near the city of L’Aquila in Italy, where recordings are available at different recording stations (AQA and AQV) for the same earthquake. The EW component of the strong main shock of 4-6-2009 in L’Aquila is selected as input for the two procedures. Finally, the comparison between the signals resulting by PR1 and PR2 and the input signals recorded at the same points is discussed in term of effects on the structures (acceleration response spectrum) and characteristics of the generated signals (Fourier amplitude spectra, coherences for each frequency) to evaluate the differences between the two procedures and between the procedures and the actually recorded signals.

Degrading bouc-wen model parameters identification under cyclic load

The purpose of this article is to describe the Bouc–Wen model of hysteresis for structural engineering which is used to describe a wide range of nonlinear hysteretic systems, as a consequence of its capability to produce a variety of hysteretic patterns. This article focuses on the application of the Bouc–Wen model to predict the hysteretic behaviour of reinforced concrete bridge piers. The purpose is to identify the optimal values of the parameters so that the output of the model matches as well as possible the experimental data. Two repaired, retrofitted and reinforced concrete bridge pier specimens (in a 1:6 scale of a real bridge pier) are tested in a laboratory and used for experiments in this article. An identification of Bouc–Wen models parameters is performed using the force–displacement experimental data obtained after cyclic loading tests on these two specimens. The original model involves many parameters and complex pinching and degrading functions. This makes the identification solution unmanageable and with numerical problems. Furthermore, from a computational point of view, the identification takes too much time. The novelty of this work is the proposal of a simplification of the model allowed by simpler pinching and degrading functions and the reduction of the number of parameters. The latter innovation is effective in reducing computational efforts and is performed after a deep study of the mechanical effects of each parameter on the pier response. This simplified model is implemented in a MATLAB code and the numerical results are well fit to the experimental results and are reliable in terms of manageability, stability, and computational time.

Behavior of the Leaning Tower of Pisa: Analysis of Experimental Data from Structural Dynamic Monitoring

Understanding the structural behavior of heritage buildings is usually a very complicated task because they typically present complex deterioration and damage patterns which cannot be fully evaluated by means of visual inspections. Moreover, the reliability of such constructions largely depends on different materials, structural components and details, the health of which is often unknown or affected by great uncertainties. In this regard, the experimental dynamic testing of heritage buildings and monuments subjected to ambient vibrations has become a valuable tool for their assessment because of the minimum interference with the structure. Traffic-induced vibrations are not always a feasible dynamic load for monumental buildings due to their very low intensity or owing to existing restrictions to road and rail traffic. On the other hand, the analysis of the experimental response under earthquakes can lead to more relevant information about the dynamic behavior of historic constructions, provided that the structure is equipped with a permanent sensor network. Within this framework, the present work illustrates preliminary results carried out from time and frequency domain analyses performed on the experimental dynamic response of the leaning tower of Pisa using seismic records. The main dynamic features of the monument have been identified, and then examined taking into account the seismic input and the soil-foundation-structure interaction.

Rapid Repair Technique to Improve Plastic Dissipation of Existing Chinese RC Bridges

A rapid repair and retrofitting technique for reinforced concrete (rc) Chinese existing bridges damaged by a strong earthquake, is proposed and tested. These bridges were designed according to Chinese codes [1] [2] [3] but with insufficient transversal steel reinforcement. The damaged rebar and concrete parts were replaced by new bar systems and concrete cast respectively. Finally, a C-FRP wrapping was applied to increase the insufficient shear strength and to guarantee the necessary ductility in plastic hinge. This repair technique is an upgrade of the one tested with very good results during a previous experimental research [4] on bridge designed according to old Italian code [5] without proper seismic details. A new bar system assures that plastic dissipation is distributed in plastic hinge only. Some pier specimens (in scale 1:6) were built with and without the new bar systems. These specimens were tested by cyclic tests at Fuzhou University lab (China) to evaluate the effectiveness of the intervention.

Parameter identification of degrading and pinched hysteretic systems using a modified Bouc–Wen model

Abstract The Bouc–Wen (BW) model is a successful differential equations model used to describe a wide range of nonlinear hysteretic systems. However, it is unable to describe force degradation, stiffness degradation and pinching effects. Therefore, Baber and Noori proposed a generalisation, developing the Bouc–Wen–Baber–Noori (BWBN) model. Nevertheless, it is composed of many parameters and complex pinching and degrading functions. Thus, it is necessary to develop a simpler and reliable model to be used for practical applications. In this paper, a modified BW model is proposed. It involves a more direct physical meaning of each parameter and allows achieving a substantial reduction of computational effort and numerical deficiencies. This is obtained through simpler pinching and degrading functions that entail a decrease of the number of parameters. The result is a straightforward model, capable of predicting the behaviour of degrading and pinched hysteretic systems. An application of the proposed scheme to a real case is also presented, in which reinforced concrete bridge piers that were physically tested in the laboratory are considered. The force–displacement data are used to perform the identification process of the model parameters via a Genetic Algorithm. The numerical results are accurate since they coincide with the experimental ones.

Modified Monti-Nuti Model for Different Types of Reinforcing Bars Including Inelastic Buckling

The material model for reinforcing bar takes a very important role in the seismic analysis of reinforced concrete structures. The seismic performance of the structural elements such as column will be overestimated if the inelastic buckling is not incorporated in the material model. The Monti-Nuti Model could consider the buckling effect properly. The critical slenderness and anisotropy were discussed which has an important effect on the seismic behaviors of the reinforcement. Then this paper proposed a modified Monti-Nuti Model for different types of reinforcing bars, such as carbon steel reinforcement and stainless steel reinforcement including inelastic buckling. Subsequently, the implementation of the modified Mont-Nuti Model in OpenSees was introduced. Through validating with the experimental curves, the numerical curves generated by the modified model verified its capability.

Cyclic Behaviors of Steel Braces in Concentrically Braced Frames

In this paper, a new model named as “brace01” for steel brace is presented on the basis of experimental data on different types of steel struts. This model shows a peasant capability in the structural analysis of Concentrically Braced Frames. A brace is idealized as a pin-ended member with a plastic hinge located at its midspan. This expression of the model is proposed by combining the mechanical properties and the phenomenological characters. The model for steel brace is implemented in an effective way in OpenSees. The calibration of the material model is done by comparing the numerical curves generated by the numerical model with the experimental curves of pin-ended steel braces. The new model is proved applicable to practical Concentrically Braced Frame.