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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.

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.

This article attempts to define pinching of two structural joints, reinforced concrete (RC) and wood ones. In particular, the research outlines differences and analogies between pinching of an RC portal and a Light Timber Frame (LTF) wall. This is done by focusing on the concavity of pinching in their response under repeated cycles, which produces differences in the energy dissipation. The response of the two structural archetypes under pseudo-static and dynamic simulations is analysed using the Atan hysteresis model modification. The truncated incremental dynamic analysis (TIDA) of the two systems modelled as single-degree-of-freedom (SDOF) oscillators yielded the fragility curves, approximated by a lognormal cumulative distribution (CDF). The stability of RC under repeated cycles reveals its significant resilience compared to LTF structures. The examination of the fragility functions supports a discussion about the relation between the pinching concavity and the notion of structural resilience by introducing a robustness index ranging from 0 to 1. Ultimately, a parametric analysis of a fictitious structural system derived from the timber one by varying the concavity of the pinching path leads to the estimation of the robustness index as a function of the pinching concavity.

A generalized cyclic steel model characterized by isotropic and kinematic hardening, inelastic buckling in compression and corrosion of rebars in reinforced concrete (RC) structures is presented. This model has been implemented in in-house fiber code CYRUS-M developed in MATLAB, to perform seismic analysis of RC sections. The model is particularly accurate with respect to experimental cyclic behavior of rebars with buckling in compression when the strain does not exceed 1.5 %. 12 configurations of RC cross-sections were selected as case studies for 3 geometries and different steel configurations, assumed representative of RC columns or bridge piers (in a suitable scale). Each section was subjected to two groups of cyclic curvature histories representative of severe seismic loads, not far from collapse. Different axial loads and corrosion percentages (no corrosion, moderate or high) have been selected to perform cyclic parametric analyses. The results of the comparison among RC sections with uncorroded and corroded rebars have been discussed. Numerical results show that the maximum compressive strain is always smaller than 1.5 %, therefore the proposed steel model is a valid tool for structural assessment. Corrosion reduces the section capacity in terms of strength and energy dissipation and hysteretic damping.

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.

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 reports on a collaborative activity developed as part of the DPC-ReLUIS Research Project, year 2017. It aims at comparing the results obtained by considering alternative options in the definition of the nonlinear FEM model employed in pushover analyses for seismic assessment of existing RC frames. Specifically, the RC frame structure of the De Gasperi-Battaglia school building located in Norcia, Italy, is considered as a relevant case-study. This structure has been designed in the ‘60s of the past century according to the seismic code of the time and, hence, without taking into account the principles of Capacity Design. Although the building was actually retrofitted before the 2016 Central Italian earthquake, in this paper its original configuration has been considered. The nonlinear behaviour of the frame structure has been modelled by both following alternative approaches and employing different analysis codes. Therefore, this paper proposes an overview about how different the simulation output can be as a result of different modelling and analysis choices. In doing that, the work can be relevant to practitioners, as they may be warned about the consequences of those choices in terms of seismic vulnerability evaluation.

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.

High-Performance Fibre-Reinforced Cementitious Composites (HPFRCC) is a class of materials studied extensively for applications in structural rehabilitation of existing structures and in design of new structures. These materials have high mechanical strength, pseudo-strain-hardening behaviour and low porosity due to a highly dense microstructure of the cementitious matrix. Furthermore, they guarantee great durability by adding microfibres in the proper ratio, which limits the crack opening. This paper deals with the mechanical properties assessment of HPFRCC mixtures designed with locally available materials. Different HPFRCC mix designs were considered with a very compact cementitious matrix reinforced with two different types of microfibres: high-density polyethylene fibres and hooked stainless steel fibres considering 1% or 2% of the volume contents. The influence of the fibre contents on the compressive and tensile strengths, the strain-hardening performance and the fracture energy are discussed.

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.

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.

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 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.

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.

The seismic signals, recorded at different surface points during the propagation of the seismic waves through soil, show differences due to the soil-wave interaction. The seismic design actions should be evaluated properly in case of distant foundation points as these differences can be great. In this paper, asynchronous seismic signals are generated at surface starting from a few well-known recordings for the same seismic event. The EW accelerometric components of the main shock recorded at two recording stations (AQA, AQV) near L'Aquila city (Italy) on 4-06-2009 are the generation inputs. The seismic wave propagates along the direction between AQA and AQV. These signals are representative of a possible asynchronous excitation applied on a bridge. Five arrays of asynchronous accelerograms are generated at the foundations of the bridge to perform statistical elaboration of the results. Different bridge positions are supposed along the propagation direction of the wave to evaluate the spatial variability of the generated signals. The generated signals at AQA and AQV stations are compared with the available recordings at the same points (generation inputs) in term of power spectra, acceleration and displacement response spectra. Finally, the most detrimental soil distortions for the bridge deck are calculated for some bridge positions.

"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."

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.

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.

The effects of infill panels on the response of r.c. frames subjected to seismic action are widely recognized. Numerous experimental investigations were effected and several analytical models were developed on this subject. This work, which is part of a larger project dealing with specific materials and structures commonly used in Italy, discusses experimental tests on masonry and samples of bare and infilled portals. The experimental activity includes tests on elemental materials, and 12 wall samples. Finally, three one-bay one-story reinforced concrete frames, designed according to the outdated Italian technical code D.M. 1996 without seismic details, were tested (bare and infilled) under constant vertical and cyclic lateral load. The first cracks observed on the framed walls occurred at a drift of about 0.3%, reaching its maximum capacity at a drift of 0.5% while retaining its capacity up to a drift of 0.6%. Infill contributed to both the stiffness and strength of the bare reinforced concrete frame at small drifts thus improving overall system behavior. In addition to the experimental activities, previously mentioned, the recalibration of a model proposed by Comberscue (1996) was evaluated. The accuracy of an OpenSees non linear fiber based model of the prototype tested, including a strut element was verified through a comparison with the final experimental results. This work has been partially supported by research grant DPC-ReLUIS 2014.

"The research presented in this paper deals with the seismic protection of existing frame structures by means of passive energy dissipation. An iterative displacement-based procedure, based on capacity spectrum, to design dissipative bracings for seismic retrofitting of frame structures is described and some applications are discussed. 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."

Existing reinforced concrete frame buildings with non-ductile detailing suffered severe damage and caused loss of life during earthquakes. Different rehabilitation systems have been developed to upgrade the seismic performance of this kind of structures. The research discussed in this paper, carried out under the partial financial support of “convenzione Dipartimento di Protezione Civile- Consorzio RELUIS, signed 11/07/2005 (repertorio n. 540), research line 2, deals with the seismic protection of frame structures, in particular for the application presented buckling restrained steel braces (BRB) have been selected. A displacement-based procedure to design dissipative bracing for the seismic protection of frame structures is proposed and some applications are discussed. A two- fold performance objective is considered to protect the structure against the collapse and the non- structural damage by limiting global displacements and interstorey drifts. As an example, some r.c. frame buildings, designed according to the non-seismic Italian Code, have been analyzed also considering the infills and retrofitted with BRB via the proposed procedure. In order to assess the effectiveness of the proposed rehabilitation design procedure non linear static and dynamic time- history analyses have been performed. Concluding the necessity of performing dynamic analysis, instead of non linear static analysis, on structures with dissipative bracing systems has been discussed.