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The seismic resilience of structures and infrastructures is affected by damage accumulation phenomena, mainly related to the type of hysteresis. Specifically, pinching drives the cyclic response of several building materials, such as reinforced concrete and masonry. Structural systems affected by pinching phenomena are prone to exhibit a dramatic increment of their displacement response after multiple cycles (e.g. repeated earthquakes). The authors estimate a reinforced concrete pier's response using truncated incremental dynamic analysis by concatenating three earthquake scenarios. The authors adopted a Bouc–Wen class hysteresis model to simulate the reinforced concrete pier's cyclic response, matching its experimental cyclic response. The current analysis proved that ductility and resistance primarily drive the seismic response after a single earthquake. However, the performance after multiple earthquakes strongly depends on the pinching, degradation and drift accumulation, which are generally neglected in standard design practices.

This study presents the results of a refined numerical investigation meant at understanding the time-dependent cyclic behavior of reinforced concrete (RC) bridge columns under chlorides-induced corrosion. The chloride ingress in the cross-section of the bridge column is simulated, taking into account the effects of temperature, humidity, aging, and corrosion-induced cover cracking. Once the partial differential equations governing such multiphysics problem are solved through the finite-element method, the loss of reinforcement steel bars cross-section is calculated based on the estimated corrosion current density. The nonlinear cyclic response of the RC bridge column under corrosion is, thus, determined by discretizing its cross-sections into several unidirectional fibers. In particular, the nonlinear modeling of the corroded longitudinal rebars exploits a novel proposal for the estimation of the ultimate strain in tension and also accounts for buckling under compression. A parametric numerical study is finally conducted for a real case study to unfold the role of corrosion pattern and buckling mode of the longitudinal rebars on the time variation of capacity and ductility of RC bridge columns.

Failures of structures are often tragic events, however represent an opportunity to improve the understanding of phenomena. In this paper, after the review of Bridge collapses, on August 14, 2018, the history of Polcevera Bridge is presented, starting from aging considerations done by its designer Riccardo Morandi in 1981, analyzing the outcomes of inspections in the years from mid ‘80s with references to Italian Regulations on inspections, the interventions done during bridge life, and finally some considerations on its collapse. The case is certainly a reference for reinforced concrete bridges built just after the 2nd world war in a highly corrosion-prone environment due to nearby sea and industrial as well as chloride pollution. Large reference is done to data included into the Report of the Commission of Italian Ministry of Infrastructures for the failure of Polcevera Bridge. Monitoring for assessment of performance decay due to corrosion is discussed with reference to the meaningful example considered.

Reinforced concrete (RC) bridge piers damaged after a strong earthquake are repaired. The damaged concrete and the steel reinforcement parts are replaced by rebar segments connected to the existing rebar parts by welding connections and by a self-compacting concrete jacket respectively. A modest transverse steel reinforcement, not sufficient to improve the seismic pier capacity, is used to simplifies the concrete cast in modest volumes. After the repair, a carbon fiber reinforced polymer (Carbon FRP) reinforcement is applied to enhance the pier ductility and the shear strength. Three RC circular columns, representative of piers, were repaired and reinforced by the proposed strategy to be tested in lab applying a deformation history due to a strong earthquake. The piers were able to sustain very strong seismic demand and therefore the proposed repair and retrofitting interventions are effective. The strain distribution of the Carbon FRP reinforcement was measured and discussed to increase the very modest database presented in the literature.

In recent years, many research activities were undertaken to develop a reliable and practical analysis procedure to identify the safety level of existing structure. There are many literatures available on the seismic evaluation procedures of buildings using nonlinear static analysis (pushover) instead of performing, as in the well known incremental dynamic analysis (IDA), complex non-linear dynamic analysis (RHA). Conversely, only a few studies are available in literature regarding seismic evaluation of existing bridges, although bridges are strategic infrastructures in every country. The aim of this work is to carry out a seismic evaluation case study for an existing RC bridge, with reinforcement affected by corrosion, using nonlinear static (pushover) analysis. The work starts from an efficient pushover proposal named Incremental Modal Pushover Analysis (IMPA). This procedure has been developed for higher modes sensitive structures; bridge are commonly characterized by a very high participating mass ratio for the higher modes and therefore the application of IMPA to bridges appears as a promising procedure. The procedure, together with some results of the application on one case study, are presented herein.

The expansion joints in the multi-span simply supported bridge can be eliminated by using the link slab. The ultra-high performance concrete (UHPC) with high tensile strength and crack resistance is an effective material for the link slab. However, the cast-in-situ UHPC link slab need to be cured with steam curing. Therefore, the construction processes are complicated and the construction quality is difficult to guarantee. In this paper, the prefabricated UHPC link slab which can be assembled on site to simply the construction process, accelerate the construction speed and reduce the labor cost was proposed. Finite element models of the prefabricated and cast-in-situ UHPC link slabs under bending were built by using ABAQUS. The ultimate bearing capacity of the prefabricated link slab was nearly the same of the cast in situ and the crack resistance slightly lower. Finally, the influence of the bolt (used to connect the prefabricated link slab) number and the distance from the bolt to the edge of the link slab on the crack resistance and ultimate bearing capacity of the prefabricated link slab were obtained.

During the last years, several mechanics-based macromodels have been proposed to assess the cyclic response of infilled RC frames. However, the uncertainties behind the assumptions on damage and failure mechanisms compromise the reliability of such approaches. For this reason, this paper proposes a new data-driven hysteresis model for the cyclic response of infilled RC frames. The infill panel is schematized as a single-degree-of-freedom element, whose constitutive law is given by the proposed hysteresis model. The model combines a degrading Bouc-Wen element with a slip-lock element, which is introduced specifically to reproduce the pinching effect due to crack openings in the masonry panel. The parameters governing the model have clear physical meanings and are calibrated on the basis of an experimental data set of cyclic responses of single-story single-bay RC infilled frames. The calibrations are carried out by means of a genetic algorithm-based optimization. Analytical correlation laws linking the model parameters with geometric and mechanical properties of the RC infilled frame are proposed and validated by blind validation tests. Results show adequate accuracy of the model in reproducing the cyclic response of infilled frames characterized by significantly different geometrical and mechanical features. The model is defined by a smooth analytical hysteresis law, with great advantages regarding numerical stability and computational effort. This makes it suitable for dynamic and stochastic simulations.

The function of bridges would be significantly influenced by the damage of piers during the earthquake, which would affect the rescue and reconstruction after the earthquake. Therefore, it is of great significance to carry out the comparative study on the seismic design and check of piers by the Chinese and European codes. The results show that the seismic design concepts of piers in the Chinese and European codes are the same. The behaviour factor and the seismic importance factor are used to reduce the seismic action in the European code and the Chinese code, respectively. For the check of shear capacity, the contributions of stirrups and concrete are separately considered in the European code, while they are simultaneously considered in the Chinese code. The steel weight of the pier designing by using Chinese codes is lower than that using European codes. The requirement on the minimum transverse reinforcement ratio in the European code is higher than that in the Chinese code.

An efficient yet accurate procedure has been developed for the seismic assessment of reinforced concrete bridges subject to chloride-induced corrosion. Specifically, the procedure involves using an incremental modal pushover analysis to assess corroded bridges as an alternative and less computationally demanding approach to non-linear dynamic analysis. A multi-physics finite-element analysis is performed to evaluate the effects of chloride-induced corrosion on bridge columns. In doing so, chloride ingress in concrete is numerically simulated as a discussion process by considering the effects of temperature, humidity, corrosion-induced cover cracking and concrete aging. The estimated chloride concentration is then employed to evaluate the corrosion current density, from which the effects of corrosion on reinforcement, cracked cover concrete, confinement and plastic hinge length can be determined for subsequent non-linear static analysis. A case study of a typical bridge structures is presented. The proposed procedure can be used to assess the seismic performance of irregular reinforced concrete bridges exposed to severe corrosive environments.

Near-fault ground motions can cause severe damage to civil structures, including bridges. Safety assessment of these structures for near fault ground motion is usually performed through Non-Linear Dynamic Analyses, while faster methods are often used. IMPAb (Incremental Modal Pushover Analysis for Bridges) permits to investigate the seismic response of a bridge by considering the effects of higher modes, which are often relevant for bridges. In this work, IMPAb is applied to a bridge case study considering near-fault pulse-like ground motion records. The records were analyzed and selected from the European Strong Motion Database and the pulse parameters were evaluated. In the paper results from standard pushover procedures and IMPAb are compared with nonlinear Response-History Analysis (NRHA), considering also the vertical component of the motion, as benchmark solutions and incremental dynamic analysis (IDA). Results from the case study demonstrate that the vertical seismic action has a minor influence on the structural response of the bridge. Therefore IMPAb, which can be applied considering vertical motion, remains very effective conserving the original formulation of the procedure, and can be considered a well performing procedure also for near-fault events.

A large number of bridges are designed and built without considering seismic actions and, differently from buildings, there are currently no comprehensive guidelines to evaluate existing bridges without performing, as in the well known incremental dynamic analysis (IDA), complex non linear dynamic analyses (RHA). Bridges are structurally very different from building but, at the same time, are sensitive to higher modes as well as many multi-storey buildings that inspired innovative pushover procedures such as the well known modal pushover analysis (MPA). In the present study the incremental modal pushover analysis (IMPA), a pushover based approach already proposed and applied on buildings by the same authors, is revised and proposed for bridges (IMPAβ). IMPAβ accounts for the effects of higher modes in order to accurately estimate the seismic response of bridges; the effect of higher modes is considered by introducing a suitable number of modes to ensure the participation of a predefined total effective modal mass. The efficiency of the proposed method is demonstrated by conducting a study on two bridges, one regular and one irregular, and the IDA analysis is employed as reference solution. Numerical results indicate good accuracy of the proposed method in assessing the seismic response and a very good accuracy if compared to other available pushover procedures available in the literature.

This paper deals with the design of an innovative school building under construction in the historical center of Ariano Irpino (Italy). The building has been designed to be integrated into the historical Town, with very peculiar and innovative structural aspects. The very characteristic heritage location, with small access roads and typical historical buildings, and the site topography, at the top of the hill characterized by sloping sides and high retaining structures, with high seismic hazard, strongly influenced the structural and architectonical solution. In order to deal with the site complexity, and realize a sustainable building, the designers developed an innovative solution: the substructure is a reinforced concrete (r.c.) volume on three sides underground, the superstructure is composed by a couple of timber buildings. Between the base and the timber buildings a base isolation system is placed (which results above the third floor of the complex). The use of cast onsite concrete offer an optimal solution for the basement, with the multiple function of soil retaining system, foundation and location for several fundamental functions (gym, conference hall and restaurants), whereas the use of timber frames and cross-laminated timber (CLT) elements, for the buildings in elevations, allows to obtain a low energy consumption and eco-sustainability, not requiring big construction machines, notwithstanding the use of prefabrication. In this paper the architectural and structural solutions are presented discussing functionality, safety and sustainability issues.

This paper presents a smooth hysteresis model for reinforced concrete (RC) structural elements based on the differential equation of the Bouc–Wen model. Stiffness degradation and strength degradation are defined by introducing a damage index that includes both dissipated energy and maximum displacement. The pinching effect acts directly on the stiffness of the system and is controlled by an activation energy. The degrading functions are connected to the actual processes with which the damage occurs, thereby giving each parameter a physical meaning. The simple formulation of the model allows a straightforward identification of the best-fitting parameters and an easy interpretation of the results. Applications to the cyclic behaviour of RC structural elements demonstrate that the model is well capable of describing complex hysteretic behaviours involving degradation and pinching effects.

In the present study, the incremental modal pushover analysis (IMPA), a pushover-based approach already proposed and applied to buildings by the same authors, was revised and proposed for bridges (IMPA&beta, ). Pushover analysis considers the effects of higher modes on the structural response. Bridges are structurally very different from multi-story buildings, where multimodal pushover (MPA) has been developed and is currently used. In bridges, consideration for higher modes is often necessary: The responses of some structural elements of the bridge (e.g., piers) influence the overall bridge response. Therefore, the failure of these elements can determine the failure of the whole structure, even if they give a small contribution total base shear. Incremental dynamic analysis (IDA) requires input accelerograms for high intensities, which are rare in the databases, while scaling of generated accelerograms with a simple increment of the scaling acceleration is not appropriate. This fact renders IDA, which is by its nature time-consuming, not straightforward. On the contrary, the change of input spectrum required by IMPA is simple. IMPA&beta, also utilizes a simple complementary method coupled to MPA, to obtain bounds at very high seismic intensities. Finally, the two incremental methods based on static nonlinear and dynamic nonlinear analyses are compared.

The stock of existing buildings across most of the European earthquake-prone countries has been built before the enforcement of modern seismic design codes. In order to assure uniform levels of safety and reduce the social and economic impact of medium to high earthquakes costly seismic intervention plans have been proposed. But their application, in order to define which building should primarily be retrofitted, requires adequate vulnerability assessment methodologies, able to model the effective non-linear response and to identify the relevant failure modes of the structure. In the case of reinforced concrete (RC) buildings, due to the lack of application of capacity design principles and the aging effects due to exposition to an aggressive environment, existing structures can exhibit premature failures with a reduction of available strength and ductility. In the last couple of decades some state-of-the-art simplified models aiming at capturing the complex interaction between shear and flexural damage mechanisms as well as behavior of rebar corrosion have been proposed in specialized literature and, in some cases, implemented in regulatory building codes and guidelines. The present paper presents how those phenomena that have a significant impact in reducing the element capacity in term of strength and energy dissipation can be implemented in the assessment of the structures.

Link slab is proposed to eliminate deck joints for multi-span simply supported girder bridge. However, the conventional reinforced concrete (RC) link slab tends to produce cracks that cause leakage and deterioration. In order to improve the crack resistance of RC link slab, ultra-high performance concrete (UHPC) link slab is proposed. Based on the test results of UHPC link slab under monotonic tensile loading, the validity and accuracy of the finite element model (FEM) built by ABAQUS was verified. The parametric analyses based on the verified FEM were carried out to study the influence of different parameters on the tension behaviors of UHPC link slab. The results indicate that with an increase in rubber sheet length or reinforcement ratio, the maximum concrete stress at top fiber decreased by 13.8% and 17.9%, respectively. The tension stiffness is mainly influenced by the rubber sheet length and link slab thickness.

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.

Twenty years have passed from the most recent studies about the dynamic behavior of the leaning Tower of Pisa. Significant changes have occurred in the meantime, the most important ones concerning the soil-structure interaction. From 1999 to 2001, the foundation of the monument was consolidated through under-excavation, and the "Catino" at the basement was rigidly connected to the foundation. Moreover, in light of the recent advances in the field of earthquake engineering, past studies about the Tower must be revised. Therefore, the present research aims at providing new data and results about the structural response of the Tower under earthquake. As regards the experimental assessment of the Tower, the dynamic response of the structure recorded during some earthquakes has been analyzed in the time- and frequency-domain. An Array 2D test has been performed in the Square of Miracles to identify a soil profile suitable for site response analyses, thus allowing the definition of the free-field seismic inputs at the base of the Tower. On the other hand, a synthetic evaluation of the seismic input in terms of response spectra has been done by means of a hybrid approach that combines Probabilistic and Deterministic Seismic Hazard Assessment methods. Furthermore, natural accelerograms have been selected and scaled properly. A finite element model that takes into account the inclination of the structure has been elaborated, and it has been updated taking into account the available experimental results. Finally, current numerical and experimental efforts for enhancing the seismic characterization of the Tower have been illustrated.

This paper focuses on the pulse-like near-fault ground motion, developing a probabilistic seismic demand model to estimate the seismic response of regular continuous bridges. A three-span bridge with continuous deck is taken as the basic case to establish 25 representative samples by changing the geometrical parameters and modeled with OpenSees software. The ground motions of both near fault and far fault are selected from PEER NGA strong ground motion database. The seismic response of the bridge is evaluated using the drift ratio at the top of the pier. A series of nonlinear dynamic time history analysis is carried out to compare the damage obtained with near-fault and far-fault ground motions for three different site conditions. Subsequently, a sensitivity analysis is performed on the design parameters according to the orthogonal experimental design methodology. After selecting the Housner intensity as the most suitable intensity measure and drift ratio as the engineering demand parameter, the probabilistic seismic demand model is established for the near-fault earthquake on the site II condition which is classified by Chinese design code. The results show that the near-fault earthquake can lead to more serious damage with respect to regular bridges and that the probabilistic seismic demand model allows for a quick evaluation of the seismic behavior of regular continuous bridges under pulse-like near-fault earthquake.

Performance-based seismic design can generate predictable structure damage result with given seismic hazard. However, there are multiple sources of uncertainties in the seismic design process that can affect desired performance predictability. This paper mainly focuses on the effects of near-fault pulse-like ground motions and the uncertainties in bridge modeling on the seismic demands of regular continuous highway bridges. By modeling a regular continuous bridge with OpenSees software, a series of nonlinear dynamic time-history analysis of the bridge at three different site conditions under near-fault pulse-like ground motions are carried out. The relationships between different Intensity Measure (IM) parameters and the Engineering Demand Parameter (EDP) are discussed. After selecting the peak ground acceleration as the most correlated IM parameter and the drift ratio of the bridge column as the EDP parameter, a probabilistic seismic demand model is developed for near-fault earthquake ground motions for 3 different site conditions. On this basis, the uncertainty analysis is conducted with the key sources of uncertainty during the finite element modeling. All the results are quantified by the “swing” base on the specific distribution range of each uncertainty parameter both in near-fault and far-fault cases. All the ground motions are selected from PEER database, while the bridge case study is a typical regular highway bridge designed in accordance with the Chinese Guidelines for Seismic Design of Highway Bridges. The results show that PGA is a proper IM parameter for setting up a linear probabilistic seismic demand model; damping ratio, pier diameter and concrete strength are the main uncertainty parameters during bridge modeling, which should be considered both in near-fault and far-fault ground motion cases.

On 21st August 2017, an earthquake ( $$M_{L}\,3.6$$ ; $$M_{W}\,3.9$$ ; $$M_{d}\,4.0$$ ) struck the municipality of Casamicciola Terme on the island of Ischia, Italy. It was a peculiar earthquake: low magnitude, very superficial (focus depth of about 1.7 km), centered in a high population density area. Despite the island was historically struck by destructive earthquakes during the last centuries, buildings vulnerability in the area was high. Many masonry buildings (main structural typology in Casamicciola Terme and on the island) collapsed or were severely damaged, occasionally exposing the original, dating back to end of nineteenth century, wooden frame that is one of the first examples of code designed anti-seismic structures in Italy. In this study, preliminary data and field observations of the 21st August 2017 Ischia earthquake are given. First, data from the permanent seismic network are used to assess seismic input characteristics and compare them to the known seismic hazard. Building vulnerability is then analyzed via the results of field observations carried out soon after the seismic event, thus providing significant information about quality of materials, construction techniques, structural performance and interpretation of possible damage mechanisms.

The most recent studies about the seismic behavior of the leaning Tower of Pisa that consider the soil-foundation-structure interaction date back to twenty years ago. From 1999 to 2001, the foundation of the monument was consolidated by means of under-excavation and the "Catino" at the basement was rigidly connected to the foundation. Meanwhile, significant progresses have been made in the field of earthquake engineering. Therefore, the need exists to assess the dynamic behavior of the Tower in light of the novelties occurred in the past decades. In the present study, the mechanical characteristics of the foundation have been calibrated comparing the outcomes of the experimental dynamic monitoring with the results of the finite element analysis performed on a simple but effective model. The scenario earthquakes for return periods equal to 130 years and 500 years are also presented.

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.

Existing reinforced concrete frame buildings designed for vertical load only could suffer severe damage during earthquakes. In recent years, many research activities have been paid to develop reliable and practical analysis procedure to identify the safety level of existing structures. The research discussed in this paper deals with proposal of an efficient incremental procedure to estimate seismic capacity of irregular structures performing few pushover analysis (one for every relevant modal shape) and applying a series of Modal Pushover Analysis (MPA). This approach, similar to the Incremental Dynamic Analysis (IDA), replaces the Nonlinear Response History Analyses (NL_RHA) by simple pushover analyses. In this work, this idea, named IMPA (Incremental Modal Pushover Analysis), is proposed for a 3D complex building and this application is described and discussed.

Due to the superior mechanical properties and durability, the ultra-high performance concrete (UHPC) has been widely used for the design of various types of structures, while research on its performance has been rapidly growing in the last five years. While the application of UHPC in bridge engineering is limited due to its higher cost, relatively little is known about the mechanical behavior of UHPC in different bridge components. In order to inform future research needs, this paper provides a comprehensive review of the properties of UHPC and its application in bridge engineering. Applications in various bridge components, such as the piers, girders, decks, and link slabs used for jointless bridges have been summarized. This review also discusses future research on optimized UHPC mix designs considering economic cost and its applications in both jointed and jointless bridges.

Near-fault events can cause severe damage to civil structures, including bridges. Many studies have demonstrated that the seismic assessment is not straightforward. Usually, dealing with near-fault ground motion, the structural analysis is performed using Nonlinear Response-History Analysis (NRHA) but in the last years, many authors have tested existing pushover-based procedures originally developed and validated using far-field events. Between those procedures, the Incremental Modal Pushover Analysis (IMPAb) is a pushover-based procedure specifically developed for bridges that, in this work, was applied to a case study considering near-fault pulse-like ground motion records. The records were analyzed and selected from the European Strong Motion Database. In the paper the results obtained with IMPAb together with other standard pushover procedures, are compared with NRHA and incremental dynamic analyses, the vertical component of the motion has been also considered. Results obtained with the bridge case study demonstrate that the vertical seismic action has a minor influence on the structural response and that IMPAb is confirmed as a very effective pushover-based method that can be applied also for near-fault events.

This paper discusses the seismic behavior of reinforced concrete (RC) bridge structures, focusing on the shear&ndash, flexure interaction phenomena. The assessment of reinforced concrete bridges under seismic action needs the ability to model the effective non-linear response in order to identify the relevant failure modes of the structure. Existing RC bridges have been conceived according to old engineering practices and codes, lacking the implementation of capacity design principles, and therefore can exhibit premature shear failures with a reduction of available strength and ductility. In particular, recent studies have shown that the shear strength can decrease with the increase of flexural damage after the development of plastic hinges and, in some cases, this can cause unexpected shear failures in the plastic branch with a consequent reduction of ductility. The aim of the research is to implement those phenomena in a finite-element analysis. The proposed model consists of a flexure fiber element coupled with a shear and a rotational slip spring. The model has been implemented in the OpenSEES framework and calibrated against experimental data, showing a good ability to capture the overall response.

A new strategy that repairs severely damaged reinforced concrete (RC) columns after an earthquake is proposed as a simpler and quicker solution with respect to the strategies currently available in the literature. The external concrete parts are removed from the column surface along the whole plastic hinge region to uncover the steel reinforcement. The transverse steel is cut away, and each longitudinal rebar is locally substituted by steel rebar segments connected by welding connections to the original undamaged rebar pieces outside the intervention zone. The new rebar segments have a reduced diameter achieved by turning to ensure plastic deformation only in the plastic hinge, protecting the original rebar and the welding connections. The connection is specifically designed to be effective and simple, and is directly realized on column reinforcement. Finally, the removed concrete is restored by a jacket built with high-performance concrete with steel or polymer fibers. The use of concrete with high volume fraction of polymer fibers to repair the column is investigated for the first time in this paper. This concrete was characterized by compression and flexural tests in the laboratory and its mechanical characteristics were compared with those of the concrete with steel fibers, which are being increasingly used in construction. The repair strategy was applied to two RC columns (1:6 scaled bridge piers), tested by asymmetric cyclic tests. The results show that the column strength, stiffness, and ductility were restored, and the energy dissipation capacity improved. The experimental evidence was investigated by fiber models in OpenSees.

This paper presents a numerical study to evaluate the behavior of reinforced concrete (RC) columns with circular section repaired and retrofitted by high-performance fiber-reinforced cement composites (HPFRCC) jackets and external carbon fiber-reinforced polymer (CFRP) wrapping. The column damage is due to degradation of concrete and steel rebars for effect of the corrosion. Different HPFRCC mix designs were considered to repair the column assuming different fiber types (polyethylene, stainless steel) and volume contents (1% or 2%). These HPFRCC concretes were developed and tested experimentally at the lab of the University of Roma Tre (Salvador Filho et al. in Mechanical properties of HPFRCC reinforced with different types and volumes of fibres [1]). The numerical analyses were conducted by means of fiber models using the software OpenSees (OpenSees structural software [computer software]. Pacific Earthquake Engineering Research Center, University of California, Berkeley, CA, [2]) applying a vertical load and a displacement history (section rotation). The analyzed sections represent the undamaged section, the section damaged for effect of rebar corrosion, and the repaired and retrofitted sections. The first numerical results about the section strength capacities for each type of repair material are discussed.

This study deals with the assessment of the shear strength characteristic value (V rck ) limited by the concrete strut crushing for existing reinforced concrete (RC) beams on the base of the available material data. A procedure to determine V rck is presented and applied to two existing RC beams extracted from an old structure built in the early 1900s. This procedure requires: (i) an analytical or numerical model for the beam shear strength, (ii) mean and standard deviation values for each uncertain basic variable and (iii) a proper formulation for the tolerance factor depending on amount of data, assumed fractile and given confidence level. The shear strength model adopted in this study is the one proposed by the Italian Code NTC 2008 for beams with transversal steel reinforcement. Several non-destructive tests (namely, rebound and sonic tests) and destructive tests on concrete were performed, and the experimental outcomes showed a great variability of the compressive strength along the same beam, as usual for many old concretes. For that reason, V rck values for each beam were calculated assuming different knowledge levels about the concrete compressive strength. Each level of knowledge is defined taking into account a different combination of available data about the compressive strength carried out from destructive tests. A comparison among the V rck values obtained for each knowledge level is shown to draw useful considerations about the beam shear strength assessment based on materials test data.

Recently, as a result of seismic events occurrences in Italy, building safety has become a topic of considerable interest. Most of existing reinforced concrete frame buildings designed for vertical loads only and without construction details, which guarantee ductility and dissipative capacity. Then it is necessary to develop a reliable and practical analysis procedure for professional use.

The dynamic response of long structures (e.g., bridges) is sensitive to the spatial variability of strong ground motion (asynchronous motion). Ground motion differences increase from point to point with increasing foundation distance. This latter is due to two physical phenomena: soil-wave interaction, that causes the loss of coherence and local amplification; wave traveling with finite velocity, that causes signals time lag. This ground motion variability produces a different structural demand compared to the synchronous one, which is the only one considered by designers in the majority of cases. A few codes consider this type of actions, therefore further research efforts are necessary. In this study, asynchronous ground motions are generated by means of a new generation procedure implemented in the software GAS 2.0 using as input the simultaneous strong motion records from the April 6th, 2009, L'Aquila (Italy) at the seismic stations AQA and AQV, located in the Aterno River valley. These records are used to calibrate the generation model and to produce sets of asynchronous earthquake sampling. The asynchronous earthquake sets are applied on a typical highway reinforced concrete bridge to study its dynamic response considering two different configurations: non-isolated with traditional supports and isolated bridge with lead rubber bearings. The bridge is placed in two positions along the wave propagation direction: a position near one recording station and a position between the two stations to consider local soil effects. The response parameters investigated are the maximum relative displacements of soil and deck. The results show that there is an important variation of relative displacement along the direction of wave propagation due to asynchronous motion with effects that designer should consider for the structural details design of isolated and non-isolated bridges. Keywords: Asynchronous motion, Bridges, Seismic response, Earthquake spatial variability

The shear strength of reinforced concrete beams extracted from existing buildings often reveals insufficient transversal steel reinforcement, mainly due to design or construction defects or increased design load requirements. FRP wrapping is one of the best solutions to improve beam shear strength as the retrofitting intervention is fast and the cost is modest. Design codes provide clear indication about the retrofitting design of simply supported beams, while the case of a beam with negative moments at the end is not considered, although this is in the case of a beam in a framed structure. One of the main uncertainties lies in the effectiveness of the FRP U sheet anchorage behavior in the area of negative bending moments with cracked concrete. This may limit the shear strength of the retrofitted beam. In this study, two beams extracted from an existing building constructed in the 1930s in Rome and retrofitted by carbon fiber-reinforced polymer (C-FRP) U strips placed at beam ends, where also negative bending moments were present, and have been evaluated with experimental tests at the laboratory of the Department of Architecture of Roma Tre University. Beam steel and concrete characteristics were evaluated by means of different tests. The experimental results are discussed considering the final results in terms of maximum shear resistance in the presence of negative bending moments. Load deflections at different points along the beam, shear-C-FRP deformation along the reinforcement strips and the damage state for different load levels, are presented. The importance of avoiding possible fragile mechanisms in the sections retrofitted with FRP is clearly shown.

This research studies the seismic behavior of repaired and seismically upgraded reinforced concrete bridges that were severely damaged after an earthquake. These bridges were designed according to the previous Italian Code (1986) which did not include capacity design rules and proper construction details. Pseudo-dynamic tests were performed on these bridges by means of in-house test apparatus. Seismic actions similar to those used for undamaged bridges were applied. A repaired and retrofitted specimen in a 1:6 scale of the most stressed pier was tested physically in the lab while the rest of the bridge was simulated numerically. The scale factors of the pier specimens guarantee a global similitude to resisting shear and moment, confinement, buckling of longitudinal rebars and anchorage behaviour. The specimens were repaired through use of epoxy adhesive, stainless steel rebar parts, self-compacting concrete and strengthened with C-FRP wrapping. Finally the seismic behavior of the repaired and retrofitted bridge was compared to that of an Italian built bridge and to a bridge designed according to Eurocode 8 for the seismic design of bridges, both tested in previous researches. Conclusions on the overall behaviour were positive and recommendations for the improvement of some repair and retrofitting techniques are illustrated for future application and investigation.

The seismic actions used to design long structures, as bridges, should be attentively evaluated, since, due to seismic wave propagation through soil, at distant foundation points signals are different. Signal frequency content varies from point to point for at least two reasons: soil-wave interaction; wave traveling time from one point to the other. Asynchronous seismic waves produce distortions at the bridge foundations which are usually not considered in design practice. In this paper, the responses of two RC bridges, one with deck supported by traditional bearing and one by Lead Rubber Bearings (isolators), subjected to asynchronous or synchronous signals were studied. These signals were generated at the surface starting from the EW components of the main shock recorded at two recording stations (AQA, AQV) near L'Aquila city (Italy) on 4-06-2009. The soil distortions which produce maximum stresses on deck or on piers were evaluated for the two bridges (non-isolated and isolated) in case of synchronous and non-synchronous excitations. The first results are discussed to understand the effects of asynchronous excitation on the responses of the two bridges.

The seismic behavior of Chinese RC (Reinforced Concrete) bridge piers with insufficient seismic details, severely damaged after an earthquake and then repaired and retrofitted by rapid interventions is investigated. The proposed interventions are applied on the damaged steel rebar and concrete parts in plastic hinge zone to guarantee the proper plastic dissipation of the seismic energy and the necessary shear strength and ductility improvements. New longitudinal shaped rebars and concrete jackets are used to substitute the pier damaged parts. Two repair and retrofitting procedures are presented and applied on 1:6 scaled pier specimens designed on the base of Chinese codes [1]-[3]: the first one uses an self-compacting concrete to build the concrete jacket and carbon Fiber Reinforced Polymer (CFRP) wrapping to assure the seismic improvements; the second one uses an ultra-high performance fiber reinforced concrete (UHPFRC) with steel fiber to build the concrete jacket and to assure the seismic upgrading allowing time and cost saving. The results of the first experimental tests on 1:6 scaled pier specimens repaired and retrofitting by the two procedures, are compared and discussed.

Ground motions in proximity to the causative fault of an earthquake are significantly affected in many cases by forward-directivity effects. The resulting seismic action on bridge is characterized by an important pulse type motion that is not considered in many international structural designed codes. In this paper, the effects of near-fault ground motions applied on regular highway bridges with design parameters selected by a sampling method, are discussed and compared with the ones of the same bridges subjected to far-fault earthquakes. Time history analyses were performed on fiber element bridge models by means of OpenSees considering seven near-fault earthquake input records with significant velocity pulse selected worldwide from the PEER database considering the same site conditions, and the El-centro earthquake record as ordinary far-field earthquake. The results are analyzed in term of top pier drift ratio, pier slenderness ratio, PGA and earthquake intensity parameters.

The Emilia, May–July 2012, earthquake hit a highly industrialized area, where some tens thousands industrial buldings, mainly single storey precast structures, are located. Due to the likelihood of strong after shocks and the high vulnerability of these structures, the authorities first asked for a generalized seismic retrofit after the strong shakings of May 20th. In order to accelerate community recovery, this requirement was later loosened, leaving out the buildings which had undergone a strong enough shaking without any damage; the strong enough shaking was defined with reference to the ultimate limit state design earthquake. To the authors’ knowledge, it is the first time that the information on the earthquake intensity and structural damage is used for such a large scale post earthquake simplified safety assessment. In short, the earthquake was used as large experimental test. This paper shows the details of the models and computations made to identify the industrial buildings which have been considered earthquake tested and therefore not compelled to mandatory seismic retrofit. Since earthquake indirect (e.g. due to economic halt) costs may be as large the direct ones, or even larger, it is believed that this method may considerably lower the earthquake total costs and speed up the social and economic recovery of a community.

"Existing reinforced concrete frame buildings with non-ductile detailing could suffer severe damage and caused loss of life during earthquakes. In recent years many research activities have been paid to develop innovative and more reliable structural control devices and different rehabilitation systems have been studied to upgrade the seismic performance of this kind of structures. The research discussed in this paper deals with the seismic protection of frame structures by means of passive energy dissipation. A displacement-based procedure to design dissipative bracing for the seismic protection of frame structures is proposed and some applications are discussed. The procedure, based on the displacement based design and using the capacity spectrum method, aims to be used as a professional tool as it does not require sophisticated dynamic nonlinear analyses but only common non linear static analyses. Two performance objective have been considered developing the procedure: to protect the structure against structural damage or collapse and avoid non-structural damage, this is done limiting global displacements and interstorey drifts. In the paper the argument is discussed and compared to other different existing approaches. After the presentation the procedure is applied to case studies. The applications are: two 2D r.c. frames, one infilled and one bare, and finally a real application on an existing 3D."

Realistic assessment of network structural safety requires modelling of a reasonably large part of the network itself. Although this statement may appear too demanding, both for modelling and computing reasons, there are clear motivations and technological possibilities to do complex network analyses. In this paper, the safety analyses of three infrastructures that have been shaken by an earthquake are described, modelled and computed: the electric power, water and road systems. For each network, results extracted from real networks, some of which have been studied in the past by the authors, are presented and discussed. No inter-network analysis is carried out, although it is recognised that this would be the most complete approach. The common parts in the procedure to model and analyse each network, via Monte Carlo simulations, are detailed at the beginning of the paper, thus showing the many common points that show up in any network analysis.

The research presented in this paper deals with the seismic retrofitting of existing frame structures by means of passive energy dissipation. An iterative displacement based pro cedure, based on capacity spectrum is described and some applications are discussed. The general procedure has also been discussed referring to the case of existing steel concentric braced frame structures (CBF). The procedure can be used with any typology of dissipative device and for different performance targets. In this work the procedure has been applied, with both traditional pushover (load profile proportional to first mode) and multimodal pushover, to an existing r.c. frame building. In the application presented the buckling restrained braces have been used in order to prevent damages to both the structure and non structural elements. The use of multimodal pushover proves to be more effective than pushover based on single mode in case of medium rise r.c. frame building (higher than 30 metres) but, once this building is retrofitted, and therefore regularized, with a bracing system, the difference between using monomodal or multimodal pushover becomes not significant.

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.

In this paper a rapid repair and retrofitting technique for reinforced concrete (rc) Chinese bridges damaged by a strong earthquake, is proposed and tested. This intervention is an upgrade of the one tested with very good results during a previous experimental research on bridges designed according to the old Italian code without proper seismic details. The improvement of the repair operation consists in the use of dissipation systems to substitute the damaged rebar parts at pier base guaranteeing the correct plastic distribution in plastic hinge only. Dissipation systems with different configurations were considered to optimize the intervention. The repaired and retrofitted Italian bridge already studied in the previous research, was designed according to Chinese codes but with insufficient transversal steel reinforcement. Some pier specimens (scale 1:6) of the most stressed pier of this bridge, with and without dissipation systems, were built. A C- FRP wrapping was applied to increase the insufficient shear strength and the ductility in plastic hinge. Cyclic tests were carried out on the scaled specimens at Fuzhou University lab (China) to evaluate the effectiveness of the proposed technique.

In recent years, many research activities were undertaken to develop a reliable and practical analysis procedure to identify the safety level of existing structures: Incremental Dynamic Analysis (IDA) is considered to be one of the most accurate methods to estimate the seismic demand and capacity of structures. However, the executions of many complex and computationally heavy nonlinear response history analyses (NL_RHA) are required. This paper deals with the proposal of an efficient Incremental Modal Pushover Analysis (IMPA) to obtain capacity curves by replacing the nonlinear response history analysis of the IDA procedure with Modal Pushover Analysis (MPA). In this work, the MPA is extended and applied to three-dimensional asymmetric structures and finally it is used in order to obtain a “multimodal” capacity curve: therefore MPA method is used to evaluate both displacements, as in the standard method, and base shear (this is a novelty). According to this approach the proposed procedure (IMPA) is defined and applied to estimate the structure’s seismic response and capacity for given seismic actions. This new procedure is finalized to obtain a capacity curve, as commonly done performing pushover, but it accounts also higher modes effects. Finally IMPA is applied to an existing irregular framed building and compared with NL_RHA.