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Cross masonry vaults are common structural elements in historical buildings. They are largely diffused in all European countries, including those characterized by higher levels of seismicity. Although they have been constructed for centuries, they represent some of the most vulnerable elements of traditional architecture, especially with reference to horizontal loads. The understanding of their structural behaviour under seismic loading is a crucial aspect for the accurate assessment of the safety of historical buildings. In the present work, the seismic response of cross masonry vaults is analysed through the Finite Element Method (FEM) and static non-linear analyses considering the effect of different brick patterns and boundary conditions. A simplified micro-modelling approach is adopted for the generation of the FEM models and two different brick arrangements are considered, i.e., radial bricks and diagonal bricks, which are the most widespread in European cross vaults. Two different boundary conditions are assumed in order to simulate a vault with and without lateral confinement. Static non-linear analyses are performed by monotonically incrementing a lateral acceleration until collapse. Results are analysed in terms of maximum load factor, stiffness, ductility, crack pattern and damage mechanisms. The analysis of the results shows that not only boundary conditions, but also the brick pattern strongly influences the vault seismic response both in terms of stiffness and ductility as well as in terms of global capacity.

Many factors affect the earthquake vulnerability of reinforced concrete (RC) structures, constituting a large part of the existing building stock. Short column in RC structures is one of the reasons for earthquake damage. Significant damages may occur due to brittle fractures in structural elements when the shear resistances are exceeded under the effect of high shear stress in short columns formed due to architectural and topographic reasons. This study created structural models for three situations: the hill slope effect, band-type window and mezzanine floor, which may cause short column formation. The structural analyses by SAP2000 were compared with the reference building model with no short columns. Structural analyses were performed separately according to strength-based and deformation-based design approaches in the updated Türkiye Building Earthquake Code (TBEC-2018). Short column formation; the effects on soft-storey irregularity, the relative storey drifts, column shear force, plastic rotation in columns, roof displacement, base shear force and column damage levels were investigated. As a result of the analysis, it was determined that the relative drifts from the first floor of the building decreased significantly due to the band-type window and slope effect, which caused the second storey to fall into the soft-storey status. In addition, short-column formation caused a significant increase in both plastic rotation demand and shear force in short columns.

The seismic behaviour of precast reinforced concrete industrial structures has been extensively investigated in recent decades, especially after the damage caused by recent earthquakes. The interaction of the roof’s horizontal diaphragm with the structural and non-structural elements can influence the seismic behaviour of these buildings. Thus, the present study aims to investigate this interaction, through nonlinear static and dynamic analyses using a simplified macro element to simulate the behaviour of cladding panels and an equivalent truss approach to simulate the roof in-plane stiffness. The analyses were performed on several structural models considering the current European single-storey precast reinforce concrete industrial building stock, with or without cladding wall panels, and with rigid or flexible diaphragm roof. Despite the uncertainties associated with the ability of common roof systems to ensure a rigid diaphragm, the analyses allowed the establishment of a correlation between the buildings generic properties and the roof horizontal stiffness required to approach a rigid diaphragm effect. In general, the results show that the consideration of a rigid diaphragm in numerical models may tend to produce a more realistic seismic behaviour of the overall structure. Furthermore, the contribution of facade cladding wall panels significantly influences the seismic behaviour of the building, especially for high-rise buildings. published

This work presents the simulations of the non-linear dynamic response of a three-dimensional finite-discrete element model. The model simulates a half-scale masonry building aggregate tested on a shake table by other Authors. The aggregate is made of two un-connected building units having different heights and slightly different wall thicknesses. The floors are made of timber beams and boards. The modelling approach accounts jointly for in-plane and out-of-plane responses, which can be expected given the high flexibility of the floors, and for the separation between the two building units. The simulations are related both to the blind predictions, according to a scheduled testing sequence, and to the post-dictions according to the actual testing sequence and some model calibrations. The prediction model overestimates displacements, underestimates base shear and fairly predicts the damage pattern of comparable experimental runs. The use of the recorded shake table motion improves the accuracy of the post-diction simulations, while still delivering beam unseating. A higher Young’s modulus of the blocks improves markedly the predictions. The strengthening intervention with steel angles connecting floors to walls is only approximately modelled and does not improve the outcomes of the simulations. In summary, the adopted modelling approach is capable of accounting for the pounding between the two building units, predicting the most significant damage as well as estimating approximate average of peak values of base shear and displacements, while individual time histories are less accurately estimated.

Precast reinforced concrete panels are commonly used as wall claddings in precast buildings. The cladding panels are generally evaluated as non-structural members and are joined to structural systems via mechanical, welding, and bolted dry connections. Several failures were observed in the last seismic events in Southern Europe, which demonstrate the deficiencies of the cladding connections in terms of strength and ductility. A comprehensive research activity named SAFECLADDING was conducted in Europe to provide knowledge for proper seismic design of precast structures with cladding panels. In this context, energy dissipative steel cushions were developed and evaluated through the extensive experimental and numerical studies. Steel cushions can provide robust interaction of the structural system with the cladding panels. This paper numerically evaluates the effects of cladding panels with steel cushions on the global seismic behaviour of the buildings. An existing representative industrial building is selected to perform intensive nonlinear dynamic analyses. Analyses performed on the bare and hybrid systems showed that the hybrid system has high performance in terms of story drifts, internal forces, and deformations with respect to the bare system. The overall drifts in longitudinal and transversal directions of the building are reduced by about 78 and 54%, respectively. Average residual drifts of cladding panels and steel cushions indicated that the applied steel cushion placement scheme has a promising re-centring capability during seismic action. The research presented herein was accomplished via the valuable experimental and numerical data derived FP7 project, "SAFECLADDING: Improved Fastening Systems of Cladding Wall Panels of Precast Buildings in Seismic Zones" research for SME associations, grant agreement number 314122, coordinated by Mr. Alessio Rimoldi from BIBM, Belgium. The financial support provided by the Commission of the European Communities through SAFECLADDING and other project partners are greatly acknowledged. The study was conducted at the Structural and Earthquake Engineering Laboratory (STEELab) of Istanbul Technical University. Support for the laboratory staff and graduate students is gratefully acknowledged. Publisher's Version

Shear walls have high strength and stiffness, which could be used at the same time to resist large horizontal loads and weight loads, making them pretty beneficial in several structural engineering applications. The shear walls could be included with openings, such as doors and windows, for relevant functional requirements. In the current study, a building of G + 13 stories with RC shear walls with and without openings has been investigated using ETABS Software. The seismic analysis is carried out for the determination of parameters like shear forces, drift, base shear, and story displacement for numerous models. The regular and staggered openings of the shear wall have been considered variables in the models. The dynamic analysis is carried out with the help of ETABS software. It has been observed that shear walls without openings models perform better than other models, and this is in agreement with the previous studies published in this area. This investigation also shows that the seismic behaviour of the shear wall with regular openings provides a close result to the shear wall with staggered openings. At the roof, the displacement of the model with regular openings was 38.99 mm and approximately 39.163 mm for the model with staggered openings. However, the model without a shear wall experienced a displacement of about 56 mm at the roof. Generally, it can be concluded that the openings have a substantial effect on the seismic behaviour of the shear wall, and that should be taken into consideration during the construction design. However, the type of opening (regular or staggered) has a slight effect on the behaviour of shear walls.

The Algerian seismic code assumes that the beam-column joints in monolithic reinforced concrete (RC) buildings are fully rigid. However, many experiments have proven the existence of relative rotations in these connections, and then the presence of relative transfer of bending moment. The present work aims to investigate the effect of beam-column joints modelling on the global seismic behaviour of reinforced concrete (RC) moment-resisting frames buildings, designed according to the Algerian seismic code recommendations. To consider the nonlinear deformation of the connections, an analytical model developed recently is used. This model includes two important deformation mechanisms; the first one covers the slippage of the continuous reinforcement within the column, whereas the second involves slippage caused by creating bending cracks at the extremities of the beams. Three multi-storey RC frames with different setback geometry, including a reference frame, are studied considering the connections as rigid/deformable. The nonlinear static procedure or pushover analysis is used to perform a nonlinear analysis of the studied structures and the results in terms of capacity curve, target displacement, storey drift, storey stiffness and the response reduction factor are presented. The results show the necessity of considering the beam-column connection flexibility when modelling this type of building.

In this work, a general method for the design of concentric braced steel frames (CBF) with active tension diagonal bracings, applicable to single- and multi-storey structures, is presented. The method is based on the use of an elastic modal analysis with a response spectrum, which is carried out using an appropriate modified elastic stiffness of diagonal bracings. The reliability of the proposed method is validated through the analysis of significant case studies, making a series of numerical comparisons carrying out time-history non-linear dynamic analysis.

Recent research on the mechanical characterisation of Steel Reinforced Grout (SRG) has highlighted its excellent performance as strengthening solutions for masonry structures. Using SRG with limited fabric density ensures a good textile-matrix interlocking, preventing at the same time the failure due to slippage or debonding from the substrate. This paper presents an experimental investigation on the use of SRG as in-plane strengthening solution for shear masonry walls composed of handmade solid clay brick and hydraulic lime mortar. Cyclic shear compression tests were carried out on walls strengthened with SRG comprising low density steel sheets (LDS). The SRG was applied on both faces of the walls with a strip configuration, using one and two layers of LDS. The experimental programme aimed to study the influence of the number of textile layers on the in-plane response of strengthened masonry walls in terms of failure mechanism, load-bearing capacity, energy dissipation, and ductility. The authors gratefully acknowledge the financial support from the Ministry of Economy and Competitiveness, Spain and from the Ministry of Science, Innovation and Universities of the Spanish Government, as well as that of the ERDF (European Regional Development Fund) through the project SEVERUS (Multilevel evaluation of seismic vulnerability and risk mitigation of masonry buildings in resilient historical urban centres, Ref. num. RTI2018-099589-B-I00). The reinforcement systems and construction of the specimens for the experimental programme have been funded by Kerakoll Spa through the RTD project “Seismic Strengthening of Masonry Walls” (Ref. num. A-01278). The authors wish to thank Paolo Casadei, José Luis Sanchez and José Dobón from Kerakoll Spa for their involvement and support. The support from Secretaria d’Universitats i Investigació de la Generalitat de Catalunya, Spain through a predoctoral grant awarded to the first author is also gratefully acknowledged. Peer Reviewed Objectius de Desenvolupament Sostenible::11 - Ciutats i Comunitats Sostenibles Objectius de Desenvolupament Sostenible::9 - Indústria, Innovació i Infraestructura::9.1 - Desenvolupar infraestructures fiables, sostenibles, resilients i de qualitat, incloent infraestructures regionals i transfrontereres, per tal de donar suport al desenvolupament econòmic i al benestar humà, amb especial atenció a l’accés assequible i equitatiu per a totes les persones Objectius de Desenvolupament Sostenible::9 - Indústria, Innovació i Infraestructura Objectius de Desenvolupament Sostenible::11 - Ciutats i Comunitats Sostenibles::11.4 - Redoblar els esforços per a protegir i salvaguardar el patrimoni cultural i natural del món Objectius de Desenvolupament Sostenible::13 - Acció per al Clima Objectius de Desenvolupament Sostenible::13 - Acció per al Clima::13.1 - Enfortir la resiliència i la capacitat d’adaptació als riscos relacionats amb el clima i els desastres naturals a tots els països

Residential masonry buildings represent a large stock among highly vulnerable structures in medium–high seismic hazard areas, often built without any anti-seismic provisions. Their rehabilitation and/or strengthening according to optimised intervention strategies is topical and may contribute to revaluating zones characterized by depopulation phenomena. In this paper, a terraced building struck by the 2016 Central Italy earthquake is analysed through a frame by macro element (FME) model. The building is composed of six two-storey units made of stone and clay block masonry walls and semi-rigid diaphragms. The numerical model was calibrated based on the damage pattern caused by the earthquake and then used to carry out parametric analyses on the strengthened conditions by simulating both one unit and the entire terrace. The effects of interventions applied to either vertical or horizontal components, both singularly and in combination, were analysed in terms of nonlinear static analyses, and quantified by a performance factor, according to the upgraded seismic code in Italy. Kinematic analyses also completed the assessment of the building. Results compared the capacity of interventions in attaining the targets defined for improvement at both local and overall levels.

In recent past, the authors developed an innovative modular system for low rise building made by structural sandwich panels. This system was conceived with the focus on the rationalization of the construction process and on the thermal efficiency of the building. Thus, the precast panels comprise two outer Steel Fibre Reinforced Self-Compacting Concrete (SFRSCC) layers, a thermal insulation material and Glass Fibre Reinforced Polymer (GFRP) connectors. Studies previously made by the authors have proved the viability of the proposed solution when subjected to flexural loads (out-of-plane loads). However, the in-plane biaxial cyclic behaviour of these type of panels has not yet been assessed. Therefore, to investigate the response of these panels to loading conditions that can occur in a seismic event, an experimental program was carried out. This program was composed of almost real-scale panels (2.0 m by 2.0 m), with and without openings, which were subjected to a constant vertical load representative of the load transferred by the slab to the panel, while horizontal reversed cyclic loading was imposed to the top of the panel. The in-plane cyclic behaviour of the panels was evaluated in terms of strength, stiffness, ductility and energy dissipation. The results have shown that the tested prototypes were able to withstand high values of lateral loads, namely 212 kN and 155 kN in the prototypes without and with opening, respectively., The first author acknowledges the financial support provided by FAPDF. The second author acknowledges the financial support provided through the project ICoSyTec (POCI-01-0145-FEDER-027990) financed by Fundação para a Ciência e Tecnologia (FCT) and co-funded by FEDER through Operational Competitiveness and Internationalization Programme (POCI).

International audience; In this paper, an experimental study aiming at understanding the seismic behaviour of dry stone retaining walls is presented. Harmonic shaking table tests have been carried out on scaled-down dry-joint retaining walls involving parallelepiped bricks. It is found that a thicker wall is more resistant and that a given retaining wall is less sensitive to higher frequencies. For those higher frequencies, the walls accept larger displacements before collapsing. The displacements start to occur from a given threshold, which depends on the wall geometry but not on the frequency of the base motion. The typical toppling failure is observed for slender wall and/or low frequency inputs. For less slender walls or higher frequency inputs, walls experience local sliding failures until the complete collapse of the system. The acceleration at failure reported during the dynamic tests have been compared to the corresponding pseudo-static resistance, enabling a conservative estimate of the seismic behaviour coefficient for pseudo-static analysis of this class of retaining walls. This novel experimental dataset is aimed to serve as a validating framework for future numerical or analytical tools in the field.

Concrete-filled steel tube (CFST) columns have been widely used in the construction industry because of their excellent compression capacity and torsion resistance. Regarding traditional CFST columns, the H-CFST column with an additional H-section steel member embedded in the core concrete provides improved fire and compression resistance. In this study, the seismic performance of nine H-CFST columns under cyclic torsional and compression–cyclic torsional loads was experimentally analysed. In the experiments, the failure mode, torque versus torsional angle hysteresis, torque versus torsional angle skeleton, torsional stiffness degradation, and energy dissipation capacity were determined. The hysteretic curves of the H-CFST columns under torsion were relatively plump in shape and exhibited no ‘pinching’ phenomenon, and the torsional stiffness of the H-CFST columns under unloading and reverse loading was approximately equal to the initial torsional stiffness. In addition, the applied compression had remarkable effects on the torsional capacity, torsional ductility, torsional stiffness, and hysteretic loop energy dissipation of the H-CFST columns. The shear capacities of the steel and concrete under normal stress or combined normal and shear stress were determined based on the latest theories and test results. Moreover, design method for the determination of the torsional capacity of H-CFST columns under compressive torsion is proposed based on the test results, and the theoretical contribution ratio of the H-section steel, steel tube, and concrete in the H-CFST columns to the torsional capacity was determined.

International audience; Rammed earth (RE) is a construction material which is manufactured by compacting the soil within a formwork, in superimposed layers. RE is attracting scientific studies because of its sustainable properties : a very low embodied energy and an advantageous living comfort due to a particular benefic hygro-thermal behaviour. Numerous studies have been conducted to investigate RE material and RE structures, however, a lack of knowledge on the seismic performance of RE buildings is noticed. This paper presents an advanced numerical study to investigate the in-plane seismic behaviour of RE walls. First, a numerical model of an in-situ RE wall was constructed by using discrete element modelling (DEM). The relevancy of the numerical model was verified by comparing dynamic properties of the model with that measured on the in-situ wall. Then, a real earthquake excitation was applied to the model, in order to evaluate the seismic performance of the RE wall studied. This is the first time, to our knowledge, that a dynamic discrete explicite analysis was performed for a RE wall. The excitation was scaled at different amplitudes to assess the damages following different earthquake intensities. The results showed that for seismic excitations lower than 2.3 m/s2, RE walls studied had satisfying in-plane earthquake performance.

This paper proposes a new type of composite shear wall with concrete-filled steel tubular frames and artificial vertical slits. The seismic behaviour of this new shear wall is studied by using a cyclic loading test. The failure mode, load-carrying capacity, ductility, stiffness degradation, hysteresis behaviour and energy dissipating capacity shown in the course of the test are studied. And this paper proposes the calculation formula of normal section bearing capacity. The main research results are as follows. Firstly, the failure mode of this new shear wall is the flexural failure. Secondly, compared with the ordinary reinforced concrete shear wall with slits, the new shear walls with concrete-filled steel tubular frames and slits show a better performance in load-carrying capacity, ductility, stiffness degradation and energy dissipating capacity.

Despite the use of rammed earth became marginal in the second half of the past century, Portugal still holds an important built heritage. Recently, a growing use of rammed earth has been observed in modern constructions, but it is putting aside the roots of traditional rammed earth construction. The seismic behaviour of rammed earth buildings is still insufficiently comprehended, constituting a matter of great concern, since most of the traditional dwellings are built on regions with important seismic hazard. Moreover, the complex architecture of modern rammed earth buildings is expected to make their seismic behaviour even more fragile. This paper intends to provide a better comprehension on the seismic behaviour of rammed earth constructions from Portugal. For this purpose, twenty traditional dwellings were evaluated on the basis of a simplified approach, while a modern construction was investigated by means of destructive and non-destructive testing approaches. The main findings of these approaches are discussed in detail, but it can be highlighted that the architectural features of traditional rammed earth buildings benefit their seismic behaviour, while the complex architecture of modern rammed earth buildings demands using advanced engineering tools for their seismic assessment., This work was partly financed by FEDER funds through the Competitivity Factors Operational Programme - COMPETE and by national funds through FCT Foundation for Science and Technology within the scope of projects POCI-01-0145-FEDER-007633 and POCI-01-0145-FEDER-016737 (PTDC/ECM-EST/2777/2014). The support from grant SFRH/BPD/97082/2013 is also acknowledged. The authors wish also to express gratitude to Eng. Sergio Morgado and Mr. Francisco Seixas for providing access to the house of Forjales and conditions to perform the destructive and non-destructive tests., info:eu-repo/semantics/publishedVersion

The performance of heavy-timber structures in earthquakes depends strongly on the inelastic behavior of the mechanical connections. Nevertheless, the nonlinear behavior of timber structures is only considered in the design phase indirectly through the use of an R-factor or a q-factor, which reduces the seismic elastic response spectrum. To improve the estimation of this, the seismic performance of a three-story building designed with ring-doweled moment resisting connections is analyzed here. Connections and members were designed to fulfill the seismic detailing requirements present in Eurocode 5 and Eurocode 8 for high ductility class structures. The performance of the structure is evaluated through a probabilistic approach, which accounts for uncertainties in mechanical properties of members and connections. Nonlinear static analyses and multi-record incremental dynamic analyses were performed to characterize the q-factor and develop fragility curves for different damage levels. The results indicate that the detailing requirements of Eurocode 5 and Eurocode 8 are sufficient to achieve the required performance, even though they also indicate that these requirements may be optimized to achieve more cost-effective connections and members. From the obtained fragility curves, it was verified that neglecting modeling uncertainties may lead to overestimation of the collapse capacity., This work had financial support of the Portuguese Science Foundation (FCT), through PhD grant PD/BD/113679/2015 included in InfraRisk-PhD program., info:eu-repo/semantics/publishedVersion

Reinforced masonry walls are commonly used as a primary lateral load resisting system in buildings in regions of moderate or high seismicity. Mortarless reinforced masonry (MLRM) walls are constructed using concrete masonry units placed without mortar and then interconnected by concrete grout. The absence of mortar can overcome several issues during the construction of conventional reinforced masonry walls. Previous research mainly focused on mortarless systems using three-dimensional interlocking blocks without vertical reinforcement. In this study, a total of six MLRM walls were constructed and tested under cyclic loadings to investigate their seismic behaviour. Experimental parameters included axial load ratio, shear span ratio, and vertical reinforcement ratio of the walls. Test results showed that the MLRM walls exhibited high stiffness, good deformation capacity, and reasonable energy dissipation capacity. The response of all six walls under cyclic loadings was controlled by 3–4 cracks formed at bed joints between the concrete masonry units, and their failure was dominated by flexure with the occurrence of slight shear sliding. The load-displacement envelope, strength, and energy dissipation of all tested MLRM walls are discussed.

Because soluble salt in saline soil dissolves with water, utility tunnels built in saline soil foundation are more likely to damage due to by groundwater and earthquake. In this study, new cementitious composite materials were developed by using slag, building gypsum, quicklime, and magnesia. The unconfined compressive strengths of the saline soil solidified by new cementitious composite materials and cement are investigated, and the optimum proportion of the different components of the new cementitious composite materials is determined. We found from microscopic characteristics of the saline soil solidified by the new cementitious composite materials and cement that the new materials could better absorb chloride ions. Finally, the new cementitious composite materials were applied to saline soil foundation reinforcement of a utility tunnel. By using the finite element method (FEM) and shaking table tests, it can be seen that the displacement, acceleration and extent of damage of the utility tunnel after saline soil foundation reinforcement using new cementitious composite materials significantly decreased; therefore, the new cementitious composite materials can improve the seismic behaviour of the utility tunnel and shows potential future engineering application value.

Limit analysis is a computationally efficient tool to assess the resistance and the failure mode of structures but does not provide any information on the displacement capacity, which is one of the concepts which most affects the seismic safety. Therefore, since many researchers did not consider limit analysis as a possible tool for the seismic assessment of structures, its widespread employment has been prevented. In this paper this common belief is questioned and the authors show that limit analysis can be useful in the evaluation of the seismic performance of frame structures. In particular, to overcome the limitation on the possibility to evaluate the displacements of a structure based on a limit analysis approach, an approximated capacity curve is reconstructed. The latter is based on a limit analysis strategy, which takes into account the second order effects, and evaluates the displacement capacity considering a post-peak softening branch and a threshold on the allowed plastic rotations. Then, based on this simplified capacity curve, an equivalent single degree of freedom system is defined in order to assess the seismic performance of frame structures. The proposed simplified strategy is implemented in a dedicated software and the obtained results are validated with well-established approaches based on nonlinear static analyses, showing the reliability and the computational efficiency of this methodology, 27 pages, 9 figures, 5 tables

The adoption of a constructive system in seismic area is related to the clarity and direct applicability of the reference technical code. The use of Cold-Formed Steel (CFS) products for structural applications in seismic area has not been properly contextualized in the current European technical standard. In order to bridge this gap, many national and international companies are promoting experimental activities with the main aim of investigating and interpreting the seismic behaviour of these systems. In this framework, an important collaboration between the University of Naples “Federico II” and the Lamieredil S.p.A. company started in the last years. In particular, the research activity involves the experimental characterization of the seismic response of strap-braced CFS walls by means of monotonic and cyclic tests on full-scale prototypes. Furthermore, in order to evaluate the influence of the main structural components on the global response, the experimental campaign is completed with tests on materials and main connection systems.

This paper presents an innovative and sustainable timber constructive system that could be used as an alternative to traditional emergency housing facilities. The system proposed in this study is composed of prefabricated modular elements that are characterized by limited weight and simple assembly procedures, which represent strategic advantages when it comes facing a strong environmental disaster (e.g. an earthquake). The complete dismantling of structural elements and foundations is granted thanks to specific details and an innovative connection system called X-Mini, capable of replacing traditional anchoring devices (i.e. hold downs and angle brackets) by resisting both shear and tension loads. This constructive system, denoted as Hybrid Timber Frame (HTF), takes advantage of the strong prefabrication, reduced weight of light-frame timber systems, and of the excellent strength properties of the Cross Laminated Timber (CLT) panels. Specifically, the solid-timber members typically used in the structural elements of light-frame systems are replaced by CLT linear elements. The results of experimental tests and numerical simulations are critically presented and discussed, giving a detailed insight into the performance of the HTF under seismic conditions.

The creation of new openings in masonry walls is a frequent intervention in existing buildings. Depending on their size and position, these interventions may cause a significant decrease of the wall’s original in-plane strength and stiffness, thus compromising the building seismic resistance. Therefore, in masonry buildings, strengthening techniques may be required to (i) restore as much as possible the loss of stiffness and strength, (ii) be reversible and (iii) respect the compatibility between materials, particularly in the case of historical buildings. In an attempt to comply with these requirements, engineering practitioners often introduce very stiff steel profiles forming a ring-frame inside the opening for fully restoring the stiffness and resistance without substantially increasing the building's weight. However, the effectiveness of this technique is typically quantified using linear elastic analysis and a simple sum of the flexural and shear stiffness of the masonry panels and the steel ring-frame. The present work aims to improve the knowledge and better understanding of the effectiveness of this traditional steel ring-frame technique, through experimental and numerical methods. The experimental program was designed to provide a full assessment of the effects of introducing a new door opening in brick masonry walls, from the cutting process to the application of in-plane cyclic lateral deformations. The steel ring-frame was designed using numerical tools and consisted of four profiles welded together and tied to the surrounding masonry wall by means of steel dowels dry-driven into calibrated holes of the brick. Results show that the steel ring-frame system restores the original solid wall’s in-plane strength and ductility, but not the lateral stiffness, despite the use of large steel profiles., MIUR -Ministero dell’Istruzione, dell’Università e della Ricerca(undefined)

The results of a preliminary experimental study carried out to evaluate the seismic behaviour of a bracing system, designed to reduce the seismic vulnerabilities in lightweight steel (LWS) suspended ceilings, are presented in the current paper. The experimental investigation involved 12 cyclic tests on the bracing system carried out according to FEMA 461 loading protocol. A special test set-up for a universal testing machine was designed to test the system under two different directions of the horizontal seismic action, which could cause one or two braces of the bracing system to act as an element under tension. Test results were analysed in terms of strength, stiffness and damage phenomena. The study also demonstrates that a preliminary evaluation of the experimental cyclic response of a bracing system for LWS suspended ceilings under horizontal seismic actions can be performed by using a universal testing machine. Two case studies were developed in order to give preliminary information about the evaluation of the maximum ceiling area that a single bracing system can cover. The two case studies are residential reinforced concrete six-storey buildings located in two different geographical locations in Italy: Naples and L'Aquila, which are characterized by medium-high (0.17 g) and high (0.26 g) intensity of seismic loads, respectively. Based on the assumption of a weight for the ceilings in the range from 50 to 150 N/m2, a ceiling area ranging from 5.5 to 32 m2 was defined as the maximum area that a bracing system can cover.

Building systems fabricated with cold-formed steel (CFS) profiles and members made of wood, gypsum, or other materials allow solving a range of issues arising in common constructional elements thanks to their advantages, such as lightness, strength, durability, physical stability, sustainability, and cost-effectiveness. As a result of this inherent competitiveness of CFS based buildings, their use has been gradually increasing in recent years both in the field of structural systems as non-structural architectural components and, above all, in the area of earthquake resistant buildings, where lightness play a key role. After a general introduction, the paper gives an overview of the current codification and ongoing research on CFS non-structural architectural and structural systems. Finally, the main conclusions are summarised, and possible future developments are outlined.

This paper deals with the experimental determination of ductility of ultra-high-performance fiber-reinforced concrete (UHPFRC) columns with longitudinal passive reinforcement, tested under combined axial and alternate flexural load. The influence of axial load has been studied, as well as the presence or not of a reduced shear reinforcement. One companion column made of ordinary concrete and with a high shear reinforcement ratio has also been tested for comparison. The ductility has been assessed with energy dissipation and ductility coefficient calculations. In addition, the maximum bending moment has been compared with theoretical calculation, using the material characteristics determined from characterization tests. The paper concludes that UHPFRC columns with a longitudinal reinforcement which have not been specifically designed for seismic resistance do display a ductility coefficient higher than 2 and a noticeable ability to protect the rebars from buckling, but have a rather high decrease of bending moment under the succession of series of alternate flexural load cycles.; Cet article traite de la détermination expérimentale de la ductilité de poteaux en béton fibré à ultra-hautes performances (BFUP) armés de quelques aciers longitudinaux, testés sous sollicitations axiales et transversales alternées. L'influence de différents paramètres tels que l'intensité de la charge axiale ou bien la présence d'aciers transversaux a été examinée. Un poteau témoin réalisé en béton ordinaire, et fortement armé transversalement, a également été testé pour servir de référence. La ductilité a été estimée à travers l'énergie dissipée et à travers le calcul de coefficients de ductilité. Le moment maximal atteint a été comparé avec le moment théorique calculé à partir des lois de comportement des différents matériaux. L'article conclut que les poteaux BFUP armés longitudinalement, non dimensionnés pour développer une résistance au séisme, ont un coefficient de ductilité supérieur à 2 et montrent une bonne aptitude à protéger les aciers des phénomènes de flambement. Ils montrent toutefois une décroissance assez rapide du moment résistant sous la succession des cycles de flexion.

Lightweight steel framed systems (LWS) are innovative construction systems whose application has been steadily increasing over the years thanks to the huge benefits in terms of structural and environmental efficiency. Typical LWS products are usually combined with gypsum, wood and cement-based panels and can be used to build both structural and non-structural systems. After a brief description of the most common LWS constructional systems, this paper provides a state-of-the-art review of their behaviour under seismic actions. In particular, the main past and ongoing research works on lightweight steel framed structural and non-structural systems are briefly summarized and a critical comparison among seismic codes available in North America, Europe and Oceania is presented. Finally, an overview of studies carried out at the University of Naples “Federico II”, Italy, on this topic is presented together with the shaking table tests carried out recently on both LWS structural and non-structural architectural systems.

The mechanical coupling of timber products to the masonry walls of unreinforced masonry (URM) buildings is generating considerable interest in terms of seismic vulnerability mitigation. An extensive experimental investigation on timber panel to masonry wall connections realised with screw anchor fasteners is presented. A total of 64 shear tests under monotonic, cyclic and semi-cyclic loading conditions were performed on site in a historic URM building. The examined parameters were: masonry type, timber panel product and material, load-to-grain direction, fastener geometry and steel grade. The outcomes of the campaign are then reported and discussed focusing on the strength and stiffness properties and on the dissipation capacity and residual strength of the connection under cyclic load. Moreover, a log-normal distribution fitting is proposed for the maximum load and slip modulus measurements of all the cyclic test configurations analysed. Finally, the principal experimental observations are listed along with recommendations for future work or use in practice.

The seismic behaviour of masonry structures is, as well-known, strongly influenced by axial stresses. During a seismic event, variations in axial loading cause in fact a change, that can be substantial, in the response in the lateral resistance capacity of masonry panels. Moreover, the axial stress can be modified by the vertical component of the seismic input during an event, which can amplify the strength variations, in particular if there is a near-fault excitation. In general, such vertical component is neglected in a traditional design. In this work, the influence of the vertical component of a seismic event is evaluated by measuring the lateral resistance of masonry piers. Such influence is estimated through a cyclic phenomenological model which calculates in an analytical way the lateral strength of a masonry panel on the base of the actual axial loading, reached step-by-step during a non-linear analysis. This model is used to simulate the cyclic behaviour of an unreinforced masonry facade made of 3 piers, having the same section for 2 floors and connected by rigid spandrels. The wall, representative of a typical masonry facade, is subjected to a series of earthquake records, with and without the vertical component of the seismic input. The differences in the responses are quantified through the use of seismic reduction factors, in such a way to satisfy the checking of the piers adopting the current design codes.

Seven infilled reinforced concrete (RC) frames strengthening with profiled steel sheet bracing are researched on the effect of axial compression ratio (0.3~0.9). Hysteretic curves, envelope curves, stiffness degradation curves, ductility and energy dissipation capacity are analysed in the finite element. The results show that profiled steel sheet bracing plays a good role in reinforcing infilled RC frames and the hysteretic curves express plump relatively. With the increase of axial compression ratio, the bearing capacity is improved significantly. The axial compression ratio has little effect on the lateral stiffness of the structure, and the initial stiffness increases slightly with the increase of axial compression ratio. The structure has good ductility when the axial compression ratio is less than 0.6. The ductility is declined with the increase of axial compression ratio. As the displacement increases, the energy dissipation capacity of the specimens increases. However, the energy dissipation capacity is reduced as the increase of axial compression ratio.

Acknowledgments: The first, third and fourth author would like to acknowledge the support financially support by: Project POCI-01-0145-FEDER007457 – CONSTRUCT – Institute of R&D In Structures and Construction funded by FEDER funds through COMPETE2020 – Programa Operacional Competitividadee Internacionalização (POCI) – and by national funds through FCT – Fundaca~o para a Cieˆncia e a Tecnologia, Portugal; namely through there search project P0CI-01-0145-FEDER-016898 – ASPASSI – Safety Evaluation and Retrofitting of Infill masonry enclosure Walls for Seismic demands. In addition, the second author would like to acknowledge the financial support to the research Unit RISCO (FCT/UID/ ECI/04450/2013) also funded by FEDER – Portugal funds through COMPETE2020 – Programa Operacional Competitividadee Interna cionalização (POCI) – and by national funds through FCT – Fundaca~o para a Cieˆncia e a Tecnologia of Portugal. The authors also acknowledge the constructive comments and suggestions given by the anonymous reviewers which improved the quality of the manuscript. The primary objective of this manuscript is to present a systematic review of experimental studies regarding infill masonry walls out-of-plane (OOP) behaviour. An extended database was built containing information from each experimental campaign and specimen tested. Parameters such as geometric dimensions, material and mechanical properties, test setups and loading protocols and test results were collected. A systematic review methodology s conducted with the aim of filter the more relevant work in this field. For the analysis of each parameter in the infill wall OOP performance, three different groups were defined: as built specimens, specimens with previous in-plane damage and retrofitted specimens. Comparisons were drawn between the specimens of each group to assess the impact of those parameters on the panel response. Empirical relationships were proposed to predict the infill panels OOP capacity according to the aspect ratio, panel slenderness, percentage of masonry units’ voids, masonry properties and previous in-plane drift. The results demonstrated that previous damage caused by in-plane tests that reached a maximum drift until 1.25% can reduce about 70% the OOP capacity of the panel, changing the failure mode of the panel that can result in fragile collapses. It was also observed that the parallel flexural strength parallel to the horizontal bed joints can increase the panel OOP maximum strength until 5 times. info:eu-repo/semantics/publishedVersion

In-plane seismic behaviour of concrete sandwich panel-infilled steel frame (CSP-ISF) was experimentally and numerically investigated. Four large-scale, single bay and single story steel frame specimens were tested under reversed cyclic lateral loading. Three infilled frames with different aspect ratios along with one bare frame were considered. It was found that addition of sandwich panels leads to considerable increase in the lateral stiffness and strength, ductility, energy dissipation capacity as well as equivalent viscous damping ratio of the steel frames. Furthermore, the maximum shear capacity of CSP-ISF specimens was validated by analytical approaches which showed good agreement with experimental results. Based on the present experiments, structural performance levels required for Performance-based Analysis are also proposed for concrete sandwich panel used as infill walls. Finally, a numerical model is presented to analyze the nonlinear behaviour of CSP-ISFs., This study was supported by the grants from Rasht Municipality (Grant No. 221/9351/ALF)., info:eu-repo/semantics/publishedVersion

This study evaluates the use of a composite material composed of multiaxial hybrid glass-fibers and polypropylene fabric coated in a hydraulic lime-based mortar (referred to as textile-rein...

Over the last years, the seismic behaviour of infilled reinforced concrete (RC) structures has been the focus of innumerable experimental and numerical studies. A big effort is being made by the scientific community to increase the knowledge regarding the seismic performance of these types of structures and to improve the numerical modelling capabilities to predict their expected behaviour accurately. In 2015, a blind prediction contest was organized by the Faculty of Civil Engineering, University of Osijek, with the main goal of inviting the technical and scientific community to predict the nonlinear seismic behaviour of a 1:2.5 scaled 3D building structure. A three-storey infilled RC structure was subjected to a sequence of ten incremental earthquakes in a shake table test. The blind numerical simulations were carried out by different international teams invited by the organizational committee. The teams knew only the specimen geometry, reinforcement detailing, material properties, and ground motions recorded during the testing. In this context and, in the light of the authors’ success in the contest, the present paper mainly aims at presenting several issues regarding the numerical modelling strategies adopted (and related difficulties) which proved to yield good results while also providing some insight regarding key problems in numerical simulations of infilled RC structures under seismic actions. The main numerical results obtained by all of the participating teams will be presented and compared with the experimental ones. Discussion concerning the reasons behind the mismatching of some results will be presented. Finally, a parametric study was carried out with the aim of assessing the influence of some modelling issues and parameters on the structural global response, in particular when affected by some variations. info:eu-repo/semantics/publishedVersion

A finite-element modeling approach has been used in this study to predict the nonlinear behavior and failure patterns of rectangular reinforced concrete structural walls. Efficiency of the ...

Recent earthquakes exposed the poor performance of precast RC structures, imposing damage on both structural and non-structural elements. The concentration of damage at the beam-to-column connections highlights the vulnerability of these systems and the need to understand and improve its seismic performance. The numerical simulation of connection systems in efficient software packages has been addressed in the past by several authors. However, these models fail in describing the different mechanisms independently and, therefore, are difficult to apply to generic connection solutions. Once identified the main lateral load resisting mechanisms involved, a new numerical model is proposed accounting for friction, dowel behaviour and the contribution of the neoprene components. The proposed model was validated against different experimental tests and a parametric study was performed to understand the contribution of the different components, especially in what concerns to the maximum horizontal strength and hysteretic energy dissipation. info:eu-repo/semantics/publishedVersion

An existing reinforced concrete building with moment-resisting frames can be vulnerable during an earthquake owing to its deficient columns. The present paper reports a study on the enhancement of flexural strength and behaviour of columns, by concrete jacketing. First, the performance of the interface of additional concrete cast against the prepared surface of existing concrete was studied. Tests were then conducted on reference (without strengthening) and jacketed column specimens, to study the enhancement of strength of a retrofitted column section under the interaction of axial load and bending moment. Subsequently, interior beam�column�slab sub-assemblage specimens were tested under simultaneous vertical and lateral loading. It was observed that the selected jacketing scheme was effective in enhancing the flexural strength, as well as in retaining the ductility and energy dissipation in the behaviour. The moment�curvature behaviour of a retrofitted column section was predicted based on the layered analysis. The information was fed in the lateral load against drift analysis of a computational model of a retrofitted sub-assemblage specimen, using an incremental non-linear technique. The paper presents the method of analysis and guidelines for retrofitting of columns for seismic forces. � 2014, Thomas Telford Services Ltd. All rights reserved.

Many surviving ancient monuments are freestanding stone masonry structures, which appear to be vulnerable to horizontal dynamic loads such as earthquakes. However, such structures have stood for thousands of years despite numerous historic earthquakes. This study proposes a scaled-down dynamic centrifuge modelling test to study how these masonry structures resist seismic loading. The test is proposed for seismic risk assessments to evaluate risk of damage from a future seismic event. The seismic behaviour of a 3-storey, freestanding stone block structure has been modelled and tested within a centrifuge. Models were made at 3 different scales and dynamic tests were conducted using different centrifugal acceleration fields so that the behaviours could be transformed to an equivalent full-scale prototype and compared. Data from 2 earthquakes and a sweeping signal were used to simulate the effects of earthquake ground motion within the centrifuge. The acceleration and frequency responses at each storey height of the model were recorded in different centrifugal acceleration fields. Similar behaviours appeared when the results of the small-scale models were transformed to a full-size prototype scale. This confirms that the seismic behaviour of stone masonry structures can be predicted using scaled-down models.

Termoizolacija postavljena ispod temeljne ploče građevine ili ispod trakastog temelja sprečava pojavu toplinskog mosta na kontaktu između građevine i temeljnog tla te smanjuje potrošnju energije kod modernih pasivnih i niskoenergetskih kuća. U ovom se radu analizira seizmičko ponašanje građevina raznih visina i tlocrtnih katnih dimenzija, za razne uvjete tla i za razne vrste termoizolacijskih slojeva. Rezultati pojednostavljenih seizmičkih analiza pokazuju da se potencijalno negativni utjecaji postavljanja izolacije ispod temeljne ploče mogu očekivati samo kod građevina koje se sastoje od više od dva ili tri kata., Thermal insulation under the building foundation plate or under the strip foundations prevents the thermal bridge on the contact between the building and supporting terrain and reduces the energy consumption in modern passive and low energy houses. In the paper the seismic behaviour of buildings with different heights, floor plan dimensions, on different soil conditions and on different thermal insulation layers have been analysed. The results of simplified seismic analyses have shown, that the potentially negative influences of inserting the insulation under the foundation plate could be expected only for buildings with more than two or three storeys.

The number of structures protected by seismic isolation is increasing all over the world, for both new structures and retrofits. New technologies had been first used for strategic and relevant structures, for which a higher level of safety is required, while the additional cost, which their use could determine, cut down the application to residential buildings. In this paper, an overview of the historical use of the isolation concepts and a selected list of the main applications of seismic isolation in the world are presented, with particular focus on the application in Italy. The suitability of seismic isolation for the protection of structures against earthquakes has already been demonstrated during strong earthquakes, when base-isolated buildings reported no damage. Obviously, structural health monitoring systems would give suitable information about the actual behaviour of base-isolated structures, also during low magnitude earthquakes. The experimental data obtained during the recent seismic sequence in Italy pointed out the importance of studying in deep the effective behaviour also in these cases. © 2017, Springer-Verlag Berlin Heidelberg.

The paper discusses the seismic design of multi-storey buildings made from cross-laminated timber panels (‘crosslam’). The use of seismic analysis methods such as the modal response spectrum and the non-linear static (push-over) analysis is discussed at length, including issues such as the modelling of crosslam walls and connections, the evaluation of the connection stiffness, and the schematization of floor panels. It was found that it is crucial to account for the flexibility of the connections (hold-downs and angle brackets) between upper and lower walls, since otherwise the vibration periods of the building would be underestimated. The basics of capacity design to ensure the attainment of ductile mechanisms in crosslam timber structures under seismic actions are presented. The ductile failure mechanism is characterized by plasticization of connectors (hold-downs, angle brackets and screws) between adjacent wall panels and between panels and foundations. The crosslam panels and the connections between adjacent floor panels must be designed for the overstrength of the connectors to ensure that they remain elastic during the earthquake and the ductile failure mechanism is attained. Based on the results of preliminary quasi-static cyclic tests, a value of 1.3 was found for the overstrength factors of hold-downs and angle brackets. A case study multi-storey crosslam massive wooden building was then analysed using the non-linear push-over analysis as implemented in the N2 method recommended by the Eurocode 8. The building was modelled using shell elements and non-linear links to schematize the hold-downs and angle brackets. The building ductility, calculated from the bilinear curve equivalent to the actual non-linear push-over curve, was then investigated. Such a quantity, defined as the ratio of the displacement at the near collapse state and the maximum elastic displacement of the top floor, was found to rise from 1.7 to 2.5 when ductile instead of brittle hold-downs and angle brackets are used. Furthermore, the maximum peak ground acceleration the building can resist raised from 0.2 g to 0.4 g , demonstrating the importance of using ductile connectors in seismic design.

In the current Japanese bridge design code, the seismic load of only one direction (1-dimension, 1-d) is considered. However, in fact, an actual seismic load has three components for N-S (north-south), E-W (east-west) and U-D (up-down) directions. The current paper presents a series of numerical results of steel box columns, which are used as piers of viaduct, under 3-d seismic load with 3 components. Two types of ground motion patterns of the main shock and the maximum aftershock measured in the Chuetsu Earthquake in 2004 are used as the seismic load. The results indicate that the severer deformation arises in the columns under 2-d (N-S and E-W components) or 3-d seismic load than the 1-d load by the main shock. However, under the aftershock, which contains ground motion of higher frequency, 1-d load gives larger displacement., Article, THIN-WALLED STRUCTURES. 49(5):544-553 (2011)

The recent seismic events demonstrated that the high vulnerability of existing RC structures is often related to the joint subassemblies shear failure which may lead to the collapse of the entire structural system. However, most of the available computer programs do not properly account for this aspect. This paper deals with the numerical seismic assessment of RC structural systems designed without proper seismic details in the joint panel and the benefits of the FRP local strengthening. A new modelling strategy has been developed to account for the joint nonlinear behaviour and the fiber reinforced polymer (FRP) strengthening in the finite element method (FEM). Several case studies were selected for the model validation. At the subassembly level, the model predictions were compared with recent experimental tests on full-scale beam-column joints with and without FRP strengthening. At the structure level, a case study building damaged in the joints during the L'Aquila earthquake and then retrofitted with FRP systems was analyzed. The predicted structural performances and structural damages were compared with observational data. Furthermore, the benefits of the joint FRP strengthening on the global seismic performances were numerically assessed. © 2016 Elsevier Ltd.

Stone masonry is one of the oldest and most worldwide used building techniques. Nevertheless, the structural response of masonry structures is complex and the effective knowledge about their mechanical behaviour is still limited. This fact is particularly notorious when dealing with the description of their out-of-plane behaviour under horizontal loadings, as is the case of the earthquake action. In this context, this paper describes an experimental program, conducted in laboratory environment, aiming at characterizing the out-of-plane behaviour of traditional unreinforced stone masonry walls. In the scope of this campaign, six full-scale sacco stone masonry specimens were fully characterised regarding their most important mechanic, geometric and dynamic features and were tested resorting to two different loading techniques under three distinct vertical pre-compression states; three of the specimens were subjected to an out-of-plane surface load by means of a system of airbags and the remaining were subjected to an out-of-plane horizontal line-load at the top. From the experiments it was possible to observe that both test setups were able to globally mobilize the out-of-plane response of the walls, which presented substantial displacement capacity, with ratios of ultimate displacement to the wall thickness ranging between 26 and 45 %, as well as good energy dissipation capacity. Finally, very interesting results were also obtained from a simple analytical model used herein to compute a set of experimental-based ratios, namely between the maximum stability displacement and the wall thickness for which a mean value of about 60 % was found.

The paper presents a theoretical and experimental study on the slenderness of the diagonal members of concentrically X braced steel frames. According to Eurocode 8 and Italian Standard, the non-dimensional slenderness of the diagonal members should be lower than an upper limit, in order to provide sufficient hysteretic energy dissipation, and greater than a lower limit, to avoid overloading the columns in the pre-buckling stage. This seismic design provision requires the realistic evaluation of the diagonal member slenderness. A reduced scale test bench was designed to study X braced steel frames with different geometrical characteristics of diagonal members and with restraints as similar as possible to the theoretical ones. The results confirm the theoretical prediction of the effective length factor of the diagonal members which exhibited good hysteretic behaviour with large inelastic deformation capacity under cyclic loading. The low values of the effective length factor suggest the use of plates to realise the diagonal member instead of the classical angles as shown in the design example.

The cyclic behaviour of reinforced concrete columns has been object of many experimental studies in the last years, mostly focused on the unidirectional loading of columns under constant axial load conditions. In this research work, the existing test on reinforced concrete (RC) columns under biaxial load has been reviewed, underlying their main findings. In general, the experimental results show that the RC columns' response is highly dependent on the loading pattern, and the biaxial loading induces a decrease in the maximum strength and anticipates each damage state. Thus, in columns where demands are expected with large moments in both directions, specific detailing should be provided in their critical regions in order to improve the columns' performance and avoid premature failure.

In recent years, the seismic behaviour of structural systems composed of squat concrete walls has been the object of a renewed interest. This paper presents the results obtained in a large experimental campaign carried out as a joint effort between the University of Bologna and the Eucentre labs in Pavia. This effort aims at the assessment of the seismic performances of cellular structures composed of cast in situ sandwich squat concrete walls. In order to shed light upon the seismic behaviour (stiffness, strength, ductility, energy-dissipation) of such structures, a number of tests were performed upon two dimensional (3.0 m by 3.0 m) cast in situ sandwich squat concrete walls (with and without openings). In the experimental tests a number of horizontal in-plane loading cycles were imposed to the specimens, while the vertical load was kept constant. The results obtained have shown that the tested elements are characterized by: (i) high values of the maximum horizontal load applied to the structural systems (higher than the applied vertical load); (ii) residual bearing capacity with respect to the vertical loads, also when large lateral deformations are imposed; and (iii) high ductility.

Damage observed in existing structures after recent earthquake events pointed out the key importance of beam-to-column joints in influencing the global response of reinforced concrete structures. In the last two decades several theoretical and empirical models have been proposed for evaluating shear strength of beam-to-column joints. The present paper reports an overview of the models currently available in the scientific literature for evaluating shear capacity of exterior beam-to-column joints. The present study is the first step of a wide analysis aimed at assessing such models and improving them. Moreover, the uncertainties deriving by applying the mentioned models will be also quantified therein, by means of well-established procedures for probabilistic seismic analysis of structures. The final results of that study are reported within a companion paper.

This paper aims at presenting the results of two experimental tests concerning the cyclic behaviour of a dissipative column-to-foundation connection for precast concrete elements. The tested joints are characterized by the use of high strength threaded steel bars partially un-bonded in grouted sleeves and by steel support elements which allow an easy assemblage and centering of the column. The two specimens differ in bar number and bar diameter of the un-bonded high-strength bars adopted to restore the flexural continuity. The experimental results are compared to the response of a pocket foundation joint and they show a good performance of the joint in term of resistance, ductility, cycle stability and energy dissipation. The specimen damage is localized at the column base thus allowing a simple retrofitting after a seismic event.

The influence of structural overstrength on the seismic behaviour of steel structures and on the assessment of the q-factor has been studied by means of a suitable procedure, based on the selection of a significant set of homogeneous historical earthquakes and on the statistical analysis of the dynamic inelastic response of the structure to these accelerograms. Six schemes of steel frames, proportioned according to different design criteria and therefore with different amounts and distribution of overstrength, have been analysed. Three values of the behaviour factor have been considered for each one. The large number of results, obtained by more than 4800 dynamic analyses, has been elaborated in a statistical way, providing damage level indexes which express the probability of yielding and collapse and the plastic level reached, both for the single section and the whole frame. Interesting conclusions have been obtained. In particular, the effectiveness of the capacity design criteria in reducing the probability of collapse of frames has been highlighted. Similar good results have been obtained even when the same overstrength is given to all columns, without any particular attention to its distribution, while the increment of the beam resistance was not favourable in any case. Moreover, a very large improvement in safety has been obtained with just a little increase in the column strength over that supplied by the application of the capacity design criterion. The global behaviour appears thus connected to a new parameter herein defined and named ''effective behaviour factor'', which takes into account the mean overstrength bath of beams and columns. Copyright (C) 1996 Elsevier Science Ltd.