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Highlights • Drift in CBFs designed to EC8 is dependent on mean ground motion period. • Increased drifts when ratio of mean period to fundamental structural period is low. • In these cases numerically calculated drifts can exceed values predicted by codes. • Regression models developed to peak predict global and inter-storey drift in CBFs. Abstract The influence of mean ground motion period, T m , on the inelastic drift response of steel Concentrically Braced Frame (CBF) structures designed to Eurocode 8 is investigated. Incremental dynamic analysis is performed for a set of case study frames with varying structural characteristics at four different seismic intensity levels. From the results of these analyses, regression models for predicting both global and inter-storey drift are developed. It is shown that that both global and inter-storey drift tend to increase nonlinearly as the ratio of fundamental structural period to mean ground motion period, T 1 / T m , decreases below unity. The rate of this increase is dependent on the ground motion intensity, represented by the EC8 behaviour factor q. The first mode participation factor, relative storey stiffness and column-to brace stiffness are also shown to influence inter-storey drift response. The values of drift predicted by the developed regression models are compared to values predicted by design codes as well as other predictive models developed in previous studies. It is observed that design codes can under predict drift at lower T 1 / T m values. [ABSTRACT FROM AUTHOR]

In Europe, computation of displacement demand for seismic assessment of existing buildings is essentially based on a simplified formulation of the N2 method as prescribed by Eurocode 8 (EC8). However, a lack of accuracy of the N2 method in certain conditions has been pointed out by several studies. This paper addresses the assessment of effectiveness of the N2 method in seismic displacement demand determination in non-linear domain. The objective of this work is to investigate the accuracy of the N2 method through comparison with displacement demands computed using non-linear time-history analysis (NLTHA). Results show that the original N2 method may lead to overestimation or underestimation of displacement demand predictions. This may affect results of mechanical model-based assessment of seismic vulnerability at an urban scale. Hence, the second part of this paper addresses an improvement of the N2 method formula by empirical evaluation of NLTHA results based on EC8 ground-classes. This task is formulated as a mathematical programming problem in which coefficients are obtained by minimizing the overall discrepancy between NLTHA and modified formula results. Various settings of the mathematical programming problem have been solved using a global optimization metaheuristic. An extensive comparison between the original N2 method formulation and optimized formulae highlights benefits of the strategy. [ABSTRACT FROM AUTHOR]

A cloud method for generating percentile engineering demand parameter versus intensity measure (EDP-IM) curves of a structure subjected to a set of synthetic ground motions is presented. To this end, an ensemble of synthetic ground motions based on available real ones is generated. This is done by using attenuation relationships, duration and suitable Gutenberg-Richter relations attributed to the considered seismic hazard at a given site by estimating a suitable distribution of magnitude and site to source distance. The study aims to clarify the significance of the duration and frequency content on the seismic performance of structures, which were not considered in developing percentile incremental dynamic analysis (IDA) curves. The collapse probabilities of two steel moment-resisting frames with different ductility levels generated by IDA and the proposed cloud method are compared at different intensity levels. When compared with conventional IDA, the suggested cloud analysis (SCA) methodology with the same run number of dynamic analyses was able to develop response hazard curves that were more consistent with site-specific seismic hazards. Eliminating the need to find many real records by generating synthetic records consistent with site-specific seismic hazards from a few available recorded ground motions is another advantage of using this scheme over the IDA method.. [ABSTRACT FROM AUTHOR]

In this paper, seven real earthquake records are scaled according to Eurocode 8 design acceleration spectrum by using SESCAP (Selection and Scaling Program). SESCAP is a scaling program based on time domain scaling method and developed by using MATLAB, GUI software. Real and scaled earthquake records are used for linear time history analyses of a six-storied reinforced concrete building modeled as spatial by SAP2000. Eurocode 8 allows the use of real earthquake records for linear and nonlinear time history analyses of structures. In the case of using three earthquake records in linear and nonlinear time history analyses, maximum results of structural responses are used for design of structures. If at least seven time history analyses are performed, the mean responses of the structures are taken into account rather than the maximum results. For the selection of maximum results of structural response from thirty five groups are created by calculating combination of threes of seven real and scaled earthquake records, and another group including all of the seven real and scaled earthquake records are created for selection of mean. Relative floor displacements along X axis of the building are preferred as structural response of the building in this study. It is seen that differences between mean value and maximum value of the relative floor displacements along X axis of the building induced by seven and three scaled earthquake records respectively are less than ones obtained from real earthquake records. [ABSTRACT FROM AUTHOR]

Highlights • The impact of the target spectrum on the acceleration causing collapse is investigated. • The impact of the number of ground motions on structural response is investigated. • Several MDOF and SDOF models are considered in the study. • A minimum of 15 ground motions should be used for time-history analysis. • The CS offers 1.2–2.3 times larger accelerations causing collapse than the UHS. Abstract The impact of the type of target response spectrum and the number of ground motions on the response of buildings is investigated. The parametric study involves the selection of ground motions based on the Eurocode 8 spectrum, a conditional spectrum using the official seismotectonic model of Slovenia, a uniform hazard spectrum based on the seismotectonic model of the SHARE project, and the corresponding conditional spectrum. In addition to the variation of the target response spectrum, the number of selected ground motions was varied from 7 to 60. Selected sets of ground motions were used to investigate the seismic response of eight reinforced concrete buildings with fundamental vibration periods from 0.15 s to 1.76 s. The aim of the study was to analyse the variation of target displacements obtained by a pushover-based method, i.e. the median displacement corresponding to a seismic intensity with a return period of 475 or 2475 years, and the median spectral acceleration causing collapse, which was estimated by incremental dynamic analysis. It was found that the target spectrum and the number of ground motions have a limited impact on the target displacement, especially if it corresponds to seismic intensities with a return period of 475 years. Additionally, the impact of the number of ground motions on the median spectral acceleration causing collapse is much lower than the impact of the target response spectrum. When the conditional spectrum was used as the target spectrum for ground motion selection instead of the design response spectrum prescribed by Eurocode 8, the resulting median spectral acceleration causing collapse increased by a factor of between 1.2 and 2.3. [ABSTRACT FROM AUTHOR]

Highlights • The details of the project of a 6-storey CLT building are presented. • The design for gravity and seismic loads is discussed in detail. • A recently developed proposal of revision of the timber chapter within the Eurocode 8 on seismic design is applied. • The design of the anchoring connections to the concrete foundation for multi-storey timber buildings is discussed. • Some details are also given regarding construction issues and fire design. Abstract This paper presents the design and construction of a six-storey residential cross-laminated timber (CLT) building in Florence, Italy. The different phases of the design process are described in detail, together with the production, transportation and on-site construction. Special emphasis is given to the seismic design, where a recently developed proposal for the revision of the Eurocode 8 has been applied, demonstrating its feasibility. Some design and construction issues are also addressed, including the connection of hold-down anchors to the concrete foundation. This connection represents the weakest link of the traditional commercial connectors used for CLT buildings, especially concerning the seismic design. [ABSTRACT FROM AUTHOR]

The damping reduction factor (DRF) is used in earthquake engineering in order to estimate the seismic response of buildings with high damping ratio from the one which has damping ratio equal to 5%. Many expressions were given to this factor as a function of different parameters in literature. The concern of these formulations is to find a simple and a reliable formulation, which presents a challenge. This is the major reason to look for a new simple method to estimate the DRF values with a good approximation. The primary objective of this work is to develop a new method to estimate the DRF using Artificial Neural Networks (ANN). This method is developed for the seismic Eurocode 8 (EC8). In a first step, seeking for sets of ground motions records that gives as average the best approximation of the target spectra of EC 8. Afterward, those records are used to estimates the exact response spectra and the DRF values in function of damping ratio ξ and period (T) through a time History Analysis. In a second step, those results are used as neural networks database to predict the DRF in function of ξ and T. The proposed approach is original and the associated results are interesting and promising. [ABSTRACT FROM AUTHOR]

This paper focuses on the assessment of the behaviour of Concrete Filled Steel Tube (CFST) columns with square/rectangular cross-section, made with Rubberized Concrete (RuC), under flexural loading. The study aims to evaluate the differences between this type of composite members and typical CFST members made with standard concrete (StdC), namely in terms of the influence of the rubber aggregate replacement ratio on member strength, ductility, and energy dissipation capacity. The experimental campaign comprised the testing of 16 square members, 12 RuCFST and 4 StdCFST, and 4 rectangular RuCFSTs. A number of parameters were investigated, namely the cross-section slenderness (i.e., the width-to-thickness ratio of the steel tube), the aggregate replacement ratio (i.e., the percentage of sand aggregate of the concrete mixture that is substituted by rubber particles), axial load level and lateral loading type. The test results are compared with the member capacities obtained with the application of Eurocode 4. The results show a minimal influence of the type of concrete infill on the monotonic and cyclic behaviour of the members and also allow concluding that the European code is conservative in predicting the capacity of the specimens. Furthermore, the results obtained demonstrate that the cross-section slenderness has an important role on the behaviour of these members. Nonetheless, the requirements pertaining this parameter that are currently defined in Eurocodes 4 and 8 can be relaxed. [ABSTRACT FROM AUTHOR]

According to EN 1998-1, chevron concentrically braced frames (C-CBFs) are expected to provide limited ductility due to the interactions between the braces and intercepted beam. As a consequence, EN 1998-1 recommends values of the behaviour factor (namely q = 2 and q = 2.5 in ductility class medium and high, respectively) lower than that (i.e. q = 4) given for other concentric bracing configurations, e.g. both cross and single diagonal CBFs. The research activity presented in this paper is addressed to revise the design rules and requirements of EN 1998-1 for C-CBFs in order to improve the ductility and the dissipative capacity of this structural system. The study is organized in two parts: in the first part design rules recently presented in literature are assessed, while in the second part new design criteria are proposed and validated against the results obtained from incremental dynamic analyses carried out on 2D frames extracted from low, medium and high rise buildings. [ABSTRACT FROM AUTHOR]

Timber buildings in earthquake prone regions must be designed to withstand the seismic actions. The N2 method, already employed in the Eurocode 8 to check the seismic resistance of a building employing its capacity curve, uses inelastic spectra calculated on the basis of the system ductility. Such a procedure was extensively used for the design of steel and reinforced concrete structures. Timber structures, however, have a different and more complex hysteretic behaviour characterized by significant pinching, strength degradation and softening. Consequently, the current version of the N2 proposed spectrum may be inadequate for the design of timber systems. This paper investigates the accuracy of the N2 spectrum for timber structures by calculating the ‘rigorous’ inelastic spectra for natural seismic records selected to match, with their average, a chosen design elastic spectrum. A purposely developed software has been used to obtain the inelastic spectra for a Single Degree of Freedom (SDOF) system characterized by a slip-type hysteretic relationship with pinching typical of timber structures. Two different sets of records have been considered: the former is consistent, on average, with a given design spectrum from Eurocode 8, the latter is taken from a strong motion database by selecting the records having soil class A and PGA within a chosen range. Non-linear dynamic analyses have been carried out by varying the level of ductility and the natural vibration period of the SDOF systems. The effects of hardening or softening of the system behaviour have also been analysed. Two analysis procedures have been used with the aim to have a further confirmation of the achieved results. The comparisons between the rigorous and the approximated N2 spectrum demonstrate that, in general, the N2 method always give fairly good results in estimating the inelastic spectra even for timber structures. [ABSTRACT FROM AUTHOR]

One issue of major importance regarding the application of seismic assessment guidelines is that of the deformation capacity limits prescribed for the various limit states. In the case of existing steel structures, Part 3 of Eurocode 8 (EC8-3) defines the limits in terms of plastic rotations, which are only applicable to cases where normalized axial load levels are lower than 0.3 and to cross-section classes of type 1 and 2. These limits resemble the ones defined in ASCE 41, suggesting a direct reproduction from the latter document despite their derivation on the basis of typical American profiles. Hence, this paper aims at evaluating the deformation capacity of European steel members and to answer the question of how adequate are the current EC8-3 limits. Based on detailed FE models, the influence of member imperfections, axial load and real ground motion records is assessed. Fracture due to ultra-low cycle fatigue is taken into account and general expressions for predicting the rotation capacity of a wide number of European cross-section profiles are proposed. [ABSTRACT FROM AUTHOR]

Chevron concentrically braced frames are one of the most cost-effective solutions for seismic resistant steel buildings. Therefore, this system is widely used in Europe and North America. Both European and North American codes adopt capacity design rules aiming at enforcing the dissipative behaviour into the braces and at preventing the damage in the remaining structural members. However, in order to achieve this purpose, European and North American codes recommend some different requirements and detailing rules, which substantially influence the overall performance and energy dissipation capacity. The research presented in this paper is addressed (i) to verify the effectiveness of the design requirements prescribed by Eurocode 8 (EC8) compared to North American codes (i.e. both AISC 341 and CSA-S16), (ii) to identify the criticisms of EC8 needing revision and upgrading. In order to achieve these objectives, a comprehensive parametric numerical study based on nonlinear dynamic analyses is carried out. 2D frames extracted from low, medium and high-rise buildings are analysed and the main structural parameters affecting the performance against lateral loads are described and discussed. The critical review of the examined standards and the discussion of numerical results highlight that the design rules given by North American codes are more effective than those recommended by the current version of EC8. In particular, EC8-compliant frames show the poorest energy dissipation capacity with tension bracing members almost in elastic range and severe demand on those in compression. On the contrary, both CSA- and AISC-compliant cases exhibit satisfactory energy dissipation capacity. [ABSTRACT FROM AUTHOR]

The paper validates Ω* method proposed by some of the authors in previous papers for design of X-Concentric Braced Frames (X-CBFs). This method was obtained relaxing some of the requirements of the method provided by the European seismic code (Eurocode 8, EC8). Therefore, Ω* method is conceptually similar to that of EC8, which makes it easy to be incorporated into EC8 and to be embraced by the European structural designers. The paper analyses the seismic performance of a set of X-CBFs designed both according to EC8 and Ω* methods. Several buildings characterised by different numbers of storeys, numbers of bracings in plan and by different bay spans are considered. Non-linear dynamic analyses have been carried out by the computer code CLAP to evaluate the seismic performance of the analysed buildings. The results of the numerical analyses show that the Ω* method: (i) reduces the unnecessary global overstrength which typically is found in structures designed in accordance to EC8 design rules; (ii) leads to an optimized structural design; (iii) ensures a local and global ductility of braces under cyclic actions comparable to EC8 design solutions; (iv) has a greater “flexibility” in the design process. [ABSTRACT FROM AUTHOR]

Water towers are widely used in our society as one of water distribution facilities within water network systems. In the event of a severe earthquake, however, a single plastic hinge that occurs in a water tower could cause its total collapse before nonlinear resources of the rest of the tower remains fully utilised. This research presents an innovative technique for the assembly of a water tower using the slits in its reinforced concrete shaft for the purpose of mitigating the seismic response. Slit shafts were designed to have four slits at 90° intervals along the full height of the shafts. The shaft parts were connected to each other at the bottom, top and every five meters with coupling beams. The slit width was used as a variable in this study which varied between 50 mm and 2000 mm. The nonlinear seismic performance of the proposed slit towers was analysed by means of a finite element approach with respect to soil types defined in Eurocode 8 and seismic behaviour were compared to the solid water tower. A detailed observation of the compression and tension stress distributions with respect to the slit width was performed. The obtained analytical results revealed that slit width in the reinforced concrete tower affect the failure mode and stiffness of a water tower significantly. With an appropriate design, the conversion of a solid water tower into a slit tower can significantly increase its ductility under seismic action without significantly compromising its bearing capacity. The results showed that contours of tension and compression stress intensity in shafts, which could lead to a failure of water towers, highly depended on the slit width. In the solid water tower, the stress concentration dominated at the base of the shaft, however in the narrow slit water towers the stresses were equally distributed along the height of the shafts. Also, the stresses were mostly concentrated at the top of the shafts in the wide slit water towers. Conclusively, the results provided useful information regarding the compression stress distribution along the slit shafts in the water towers which can be used in obtaining an optimum slit shaft design for different soil types. [ABSTRACT FROM AUTHOR]

Several research studies have proved the beneficial effects resulting from the presence of moment resisting frames and braced frames in dual structural systems. Nonetheless, Eurocode 8 provides design rules only for dual systems with moment resisting frames and concentrically braced frames and thus ignores that moment resisting frames may beneficially combine with other types of braced frames. In this paper, a design procedure for dual systems with moment resisting frames and eccentrically braced frames is proposed based on the current design provisions of Eurocode 8 for dual structures with moment resisting frames and concentrically braced frames. To evaluate the effectiveness of the proposed procedure, the seismic response of the designed systems is evaluated through incremental nonlinear dynamic analysis. The buildings considered are founded on hard or soft soil and are characterised by different values of the link length and number of storeys. [ABSTRACT FROM AUTHOR]

Timber constructions have been widely suggested to be seismically resistant based on post-disaster reconnaissance studies. This observation has, however, remained to a large extent anecdotal due to the lack of experimental work supporting it, especially for certain timber architectural forms, including traditional timber frame ' hımış' structures. To fill this gap, the authors carried out an extensive full-scale testing scheme using frames of various geometrical configurations, tested under reverse-cyclic lateral loading with/without infill (brick and adobe) or cladding ( bağdadi and şamdolma) (Aktas et al. in Earthq Spectra 30(4):1711-1732, 2014a, b). The tests concluded that hımış frames had high energy dissipation capabilities due mostly to nailed connections. Infill/cladding significantly helped improve stiffness and lateral load strength of the frames, and timber type did not seem to make a remarkable impact on the overall behaviour. The current paper, on the other hand, uses test data to calculate capacity/demand ratios based on capacity spectrum method and Eurocode 8 to elaborate more on the performance of ' hımış' structures under seismic loading. The obtained results are discussed to draw important conclusions with regards to how frame geometry and infill/cladding techniques affect the overall performance. [ABSTRACT FROM AUTHOR]

This article focuses on the likelihood of the weak storey behaviour and the weak storey collapse of diagonally concentrically braced frames designed according to Eurocode 8 provisions. The emphasis is primarily put on the nature and development of the weak storey behaviour in order to designate the effects that shall be taken into account in an effective design procedure. In a second stage, the focus is on developing supplementary conditions to Eurocode 8 based on plastic analysis that can enhance the designs by preventing the occurrence of weak storeys. [ABSTRACT FROM AUTHOR]

Previous research showed that steel moment-resisting frames (MRFs) with viscous dampers may experience column plastic hinges under strong earthquakes and highlighted the need to further assess the efficiency of capacity design rules. To partially address this need, three alternatives of a prototype building having five, 10 and 20 stories are designed according to Eurocode 8 using either steel MRFs or steel MRFs with dampers. Incremental dynamic analysis (IDA) is conducted for all MRFs and their collapse resistance and plastic mechanism is evaluated. The results show that steel MRFs with dampers are prone to column plastic hinging in comparison to steel MRFs. The steel MRFs with dampers are then iteratively re-designed with stricter capacity design rules to achieve a plastic mechanism that is approximately similar to that of steel MRFs. The performance of these re-designed steel MRFs with dampers indicates, that overall, enforcement of stricter capacity design rules for columns is not justified neither from a collapse resistance or a reparability perspective. [ABSTRACT FROM AUTHOR]

Nonstructural components (NSCs) should be subjected to a careful and rational seismic design, in order to reduce the economic loss and to avoid threats to the life safety, as well as what concerns structural elements. The design of NSCs is based on the evaluation of the maximum inertia force, which is related to the floor spectral accelerations. The question arises as to whether Eurocode 8 is able to predict actual floor response spectral accelerations occurring in structures designed according to Eurocode 8. A parametric study is conducted on five RC frame structures in order to evaluate the floor response spectra. The structures, designed according to Eurocode 8, are subjected to a set of earthquakes, compatible with the design response spectrum. Time-history analyses are performed both on elastic and inelastic models of the considered structures. Eurocode formulation for the evaluation of the seismic demand on NSCs does not well fit the numerical results. Some comments on the target spectrum provided by AC 156 for the seismic qualification of NSC are also included. [ABSTRACT FROM AUTHOR]

This paper proposes a new fuzzy logic controller, which is designed for seismic protection of base-isolated structures utilizing piezoelectric friction damper against near-fault earthquakes for different ground sites. According to the elastic design spectrum that Eurocode 8 recommends, one 5% damped elastic design spectrum for Chi-Chi earthquake is proposed to generate artificial earthquakes of different ground sites. The proposed controller employs a hierarchic fuzzy control algorithm, in which a supervisory fuzzy controller governs a sublevel fuzzy controller by altering its input normalization factors according to current level of ground motion. In order to simultaneously reduce the base displacement and superstructure responses of the base-isolated structure during seismic excitations, genetic algorithm is employed to optimize the supervisory fuzzy controller and the preload of piezoelectric friction damper. The efficiency of the proposed controller is also compared with passive controller and a linear quadratic Gauss optimal controller. Numerical results show that the proposed fuzzy logic controller has favorable performance in mitigating the responses of the base-isolated structure. [ABSTRACT FROM AUTHOR]

The seismic behavior of flat-bottom silos containing grain-like material still presents strong uncertainties and current design codes tend to provide too conservative formulations for the estimation of the seismic actions. Over the years, some researchers focused on the dynamic behavior of such silos mainly through numerical investigations. Analytical formulations for the evaluation of the pressures exerted by the ensiled grain on the silo wall under seismic excitation were developed by Younan and Veletsos (J Struct Eng ASCE 124(1):62-70 ) and, more recently, by Silvestri et al. (Bull Earthq Eng 10(5):1535-1560 ). Experimental shaking-table tests were performed on silo specimens (Silvestri et al. EESD , submitted), which showed good agreement with the Silvestri's analytical formulations, even if some theoretical limits of validity were not satisfied. This has encouraged a complete revision and refinements of the theoretical framework, which is the object of this paper. In detail, the static and the dynamic actions exchanged between different grain portions and between the grain and the silo wall are idealised in a more physically consistent way. The analytical developments are carried out by means of simple free-body dynamic equilibrium equations. The refinements yield to a significant extension of the theoretical limits of validity and to a new set of analytical formulas for the wall pressures and for the wall shear and bending moment. A comparison of the analytical formulas with (i) the consolidated Janssen (Zeitschrift des vereines deutcher Ingenieure 39:1045-1049 ) and Koenen (Centralblatt der Bauverwaltung 16:446-449 ) theory for static design of silos and (ii) with the Eurocode 8 provisions for seismic design of silos and with the experimental results is also performed in order to (i) check the updated theoretical model in static conditions and (ii) verify the reliability of the different formulations in accelerated conditions, respectively. The refined theory confirms that the portion of ensiled material that interacts with the silo wall is significantly smaller than the effective mass suggested by Eurocode 8. [ABSTRACT FROM AUTHOR]

This paper presents the results of a series of shake-table tests on a half-scale, four-storey building with reinforced concrete and unreinforced masonry walls. Due to the lack of reference tests, the seismic behaviour of such mixed structures is poorly understood. The test unit was subjected to several runs of increasing intensity yielding performance states between minor damage and near collapse. Before the test, the expected peak table accelerations leading to different limit states were estimated using the capacity spectrum method, and the predicted values corresponded rather well to actual sustained accelerations. Next to these analyses, the paper describes the test unit, instrumentation and input motion, and comments on the response of the mixed structure in terms of damage evolution and global response quantities, such as force-displacement response and drift and acceleration profiles. The raw and post-processed data sets are made publically available, and all relevant information with regard to data organisation and post-processing procedure is described in an appendix to this paper. The test serves therefore as a benchmark for the validation of numerical models of such mixed structures. The project aims at providing a foundation for the development of seismic design and assessment methods of mixed structures, which are currently not covered by structural codes, including Eurocode 8. [ABSTRACT FROM AUTHOR]

The seismic assessment of existing buildings is an essential issue of seismic engineering. This work is focused on the evaluation of the seismic performance of existing RC buildings according to the current Italian Technical Code, which almost coincides with the European Eurocode 8. Alternative types of analyses, all consistent to the Code provisions, have been performed with reference to a case-study, that is a real RC hospital building. An accurate knowledge of the building has been achieved, as a result of a collaboration between the University of Florence and the Regional Government. Both elastic and inelastic modeling, as well as static and dynamic ones, have been adopted in the analysis. The global response-with special attention to torsional effects-and the seismic performance of each single member have been found with all the performed analyses. The comparison among the analyses has been performed in terms of both global and local response parameters, and the reliability of each analysis has been pointed out. [ABSTRACT FROM AUTHOR]

A ground motion with a PGA of 0.39 g, above the 475-year design earthquake specified in the Greek seismic code and the National Annex to Eurocode 8, was recorded about 100 m from the municipal theatre of Argostoli, the capital of the Ionian island of Kefalonia. The building, the largest in volume in the town, was designed and constructed to the 1959 seismic code for lateral loads (about 30 % of those specified today). Suffering also from severe reinforcement corrosion and poor concrete quality, it provided the ground to apply for the first time (in 2005) Part 3 of Eurocode 8 for seismic assessment and retrofitting. The assessment based on nonlinear dynamic analysis showed that the buidling was deficient even under ground motions with PGA less than 0.05 g. Alongside the need to tackle corrosion, the design of the retrofitting had to face several constraints and requirements: minimal disruption of the facility's operation, accessibility to the foundation only along the building perimeter, no change to the façade and minimal intervention to the other lateral sides. A very cost-effective retrofitting was designed, employing: (a) one-sided RC or fibre-reinforced polymer (FRP) overlays and two new walls at the perimeter, (b) connection of the two structurally independent and torsionally imbalanced units of the building in a single structure, and (c) one-sided FRP jacketing of selected interior elements. Less than 7 years after the works were completed, the building went unscathed through a Magnitude 6.1 earthquake. Serious damage was limited to four nonstructural masonry infill panels at the penthouse, which, according to the retrofit design, could be sacrificed, so as to protect vulnerable structural elements that could not be retrofitted in the first place. Nonlinear dynamic analyses of the response of the retrofitted building to the recorded ground motions are in agreement with the observed performance. They show also that, had the as-built facility not been retrofitted, it might have collapsed in the earthquake. [ABSTRACT FROM AUTHOR]

The objections raised by researchers to the design provisions reported in Eurocode 8 make the efficient seismic performance of the eccentrically braced structures designed according to this code unlikely. Given the rationality and the number of the objections, this paper aims to summarize the criticism of researchers and report the opinion of the Authors. The objections raised to the design procedure of eccentrically braced structures regard aspects common to the design of steel structures and aspects specifically related to the design of eccentrically braced structures. The significance of these objections is also shown by means of exemplary cases. [ABSTRACT FROM AUTHOR]

In this paper, the Theory of Plastic Mechanism Control (TPMC) is applied to the seismic design of dual systems composed by moment-resisting frames and Chevron braced frames. The application of TPMC is aimed at the design of dual systems able to guarantee, under seismic horizontal forces, the development of a collapse mechanism of global type. This design goal is of primary importance in seismic design of structures, because partial failure modes and soft-storey mechanisms have to be absolutely prevented due to the worsening of the energy dissipation capacity of structures and the resulting increase of the probability of failure during severe ground motions. With reference to the examined structural typology, diagonal and beam sections are assumed to be known quantities, because they are, respectively, designed to withstand the whole seismic actions and to withstand vertical loads and the net downward force resulting from the unbalanced axial forces acting in the diagonals. Conversely column sections are designed to assure the yielding of all the beam ends of moment-frames and the yielding and the buckling of tensile and compressed diagonals of the V-Braced part, respectively. In this work, a detailed designed example dealing with the application of TPMC to moment framechevron brace dual systems is provided with reference to an eight storey scheme and the design procedure is validated by means of non-linear static analyses aimed to check the actual pattern of yielding. The results of push-over analyses are compared with those obtained for the dual system designed according to Eurocode 8 provisions. [ABSTRACT FROM AUTHOR]

The Theory of Plastic Mechanism Control (TPMC) has been recently extended to the case of Eccentrically Braced Frames (EBFs) with inverted Y-scheme, i.e., EBFs with vertical links. In this paper a further validation of the design procedure, based on TPMC, is provided by means of Incremental Dynamic Analyses (IDA) pointing out the fulfilment of the design goal, i.e., the development of a pattern of yielding consistent with the collapse mechanism of global type where all the links are yielded and all the beams are yielded at their ends while all the columns and the diagonal braces remain in elastic range with the only exception of the base sections of first storey columns. In particular, a study case is designed according to both TPMC and Eurocode 8 provisions and the corresponding seismic performances are investigated by both push-over and IDA analyses. The results show the different performances obtained in terms of pattern of yielding, maximum interstorey drift, link plastic rotation demand and sharing of the seismic base shear between the momentresisting part and the bracing part of the structural system. The seismic performance improvement obtained by means of TPMC, compared to Eurocode 8 provisions, is pointed out. [ABSTRACT FROM AUTHOR]

This paper presents average numerical results of 2128 nonlinear dynamic finite element (FE) analyses of lightweight acceleration-sensitive non-structural components (NSCs) attached to the floors of one-bay three-storey reinforced concrete (RC) primary structures (P-structures) with different eccentricity ratios. The investigated parameters include the NSC to P-structure vibration period ratio, peak ground acceleration, P-structure eccentricity ratio, and NSC damping ratio. Appropriate constitutive relationships were used to model the behaviour of the RC P-structures. The NSCs were modelled as vertical cantilevers fixed at their bases with masses on the free ends and varying lengths so as to match the vibration periods of the P-structures. Full dynamic interaction was considered between the NSCs and P-structures. A set of seven natural bi-directional ground motions were used to evaluate the seismic response of the NSCs. The numerical results show that the acceleration response of the NSCs depends on the investigated parameters. The accelerations of the NSCs attached to the flexible sides of the P-structures increased with the increase in peak ground acceleration and P-structure eccentricity ratio but decreased with the increase in NSC damping ratio. Comparison between the FE results and Eurocode 8 (EC8) predictions suggests that, under tuned conditions, EC8 provisions underestimate the seismic response of the NSCs mounted on the flexible sides of the plan-irregular RC P-structures. [ABSTRACT FROM AUTHOR]

A significant number of existing reinforced concrete building structures were designed and built before 1970, prior to the enforcement of modern seismic design codes. The response of these structures when subjected to cyclic loads, such as that induced by earthquakes, is strongly influenced by the bond properties between the reinforcing bars and the surrounding concrete. This paper describes the results of a testing campaign composed of seven unidirectional cyclic tests and one monotonic test performed on full-scale columns built with plain bars, without adequate reinforcement detailing for seismic demands. An additional unidirectional cyclic test was carried out on a specimen with deformed bars for reference. The influence of bond properties, a cold joint at the base, lapping of longitudinal reinforcing bars, amount of reinforcing steel, cross-section dimensions and imposed loading history (monotonic or cyclic) is discussed. Finally, a correction coefficient to the expressions of EC8-3 for the calculation of ultimate rotation capacity of columns with plain reinforcing bars is proposed. [ABSTRACT FROM AUTHOR]

Some model building codes stipulate that the design displacement of a building can be computed using the elastic static analysis results multiplied by the deflection amplification factor, Cd. This approach for estimating the design displacement is essential and appealing in structural engineering practice when nonlinear response history analysis (NRHA) is not required. Furthermore, building codes stipulate the consideration of accidental torsion effects using accidental eccentricity, whether the buildings are symmetric-plan, or asymmetric-plan. In some model building codes, the accidental eccentricity is further amplified by the torsional amplification factor Ax in order to minimize the discrepancy between statically and dynamically estimated responses. Therefore, this warrants exploration of the reliability of statically estimated design displacements in accordance with the building code requirements. This study uses the discrepancy curves as a way of assessing the reliability of the design displacement estimates resulting from the factors Cd and Ax. The discrepancy curves show the exceedance probabilities of the differences between the statically estimated design displacements and NRHA results. The discrepancy curves of 3-story, 9-story, and 20-story example buildings are investigated in this study. The example buildings are steel special moment frames with frequency ratios equal to 0.7, 1.0, 1.3, and 1.6, as well as existing eccentricity ratios ranging from 0% to 30%. [ABSTRACT FROM AUTHOR]

Modern codes for earthquake resistant building design require consideration of the so-called accidental design eccentricity, to account for torsional response caused by several factors not explicitly considered in design. This provision requires that the mass centres in the building floor be moved a certain percentage of the building's dimension (usually 5%) along both the x and y axes and in both positive and negative directions. If one considers also the spatial combinations of the two component motion in a dynamic analysis of the building, the number of required analyses and combinations increases substantially, causing a corresponding work load increase for practicing structural engineers. Another shortcoming of this code provision is that its introduction has been based primarily on elastic results from investigations of oversimplified, hence questionable, one story building models. This problem is addressed in the present paper using four groups of eccentric braced steel buildings, designed in accordance with Eurocodes 3 (steel) and 8 (earthquake design), with and without accidental eccentricities considered. The results indicate that although accidental design eccentricities can lead to somewhat reduced inelastic response demands, the benefit is not significant from a practical point of view. This leads to suggestions that accidental design eccentricities should probably be abolished or perhaps replaced by a simpler and more effective design provision, at least for torsionally stiff buildings that constitute the vast majority of buildings encountered in practice. [ABSTRACT FROM AUTHOR]

This paper evaluates the effectiveness of three nonlinear static methods for the prediction of the dynamic response of in-plan irregular buildings. The methods considered are the method suggested in Eurocode 8, a method previously proposed by some of the authors and based on corrective eccentricities and a new method in which two pushover analyses are considered, one with lateral forces applied to the centres of mass of the floors and the other with only translational response. The numerical analyses are carried out on a set of refined models of reinforced concrete framed buildings. The response predicted by the nonlinear static analyses is compared to that provided by nonlinear dynamic analyses. The effectiveness of the nonlinear static methods is evaluated in terms of absolute and interstorey displacements. [ABSTRACT FROM AUTHOR]

Deep mining may induce quakes reaching magnitude m L of 4.5 to 5.5 and leading to surface ground motion with Modified Mercalli intensities up to VIII. Such strong ground motions may cause serious damages in civil infrastructure in the vicinity of mines. However any adaptation of a classic seismic code in design faces an impending problem of differences in spectral content and duration between the surface records of the rockbursts and natural earthquakes, as well as in their different risk definitions. This paper presents a system to define design seismic load based on forecasted surface horizontal particle velocity from the rockbursts expected during the planned mining activities. Such forecasts are routinely prepared by the geophysical mine services. Respective seismic load may then be applied in the design of buildings and other structures to mitigate the rockburst induced seismic effects on them. For this purpose the European seismic code, Eurocode 8, is adapted. [ABSTRACT FROM AUTHOR]

Ljubljana is one of three regions with the highest seismic hazard in Slovenia. In addition soft sediments in the Ljubljana basin have a strong influence on seismic ground motion. We used macroseismic data to investigate the influence of local geological structure on earthquake intensities in greater Ljubljana area. We determined intensities for eleven earthquakes according to ground classification based on Eurocode 8 standard (EC8). The results showed a systematic increase in observed seismic intensities, determined according to European Macroseismic Scale (EMS-98), as the seismogeological characteristics of the ground deteriorated. Only one ground type (D) showed slightly lower intensities than expected. This may be due to some unrevealed geological and other factors, or because of very limited macroseismic data available for this particular ground type. [ABSTRACT FROM AUTHOR]

Dealing with steel moment resisting frames (MRFs), the latest version of Eurocode 8 allows us to dissipate the seismic input energy in connections provided that their characteristics under cyclic loads are certified by means of experimental testing. Within the beam-to-column joint typologies to be used in seismic resistant steel frames, the double split tee joint (DST) represents an interesting solution due to its easy fabrication and repair after a destructive seismic event. Nevertheless, the cyclic behavior of this joint typology is usually characterized by pinching and strength degradation phenomena due to the plastic engagement of the rectangular T-stubs which compromises the use of DST joints as dissipative elements. Within this framework, in this paper, in order to improve the hysteretic behavior of this connection typology, a new type of dissipative DST joint is presented. In particular, the proposed dissipative T-stub is designed substituting the rectangular T-stubs with the so-called X-shaped T-stubs, whose flange plates are cut into an hourglass shape similar to that of ADAS dampers. In particular, in the paper, a model that is able to predict the resistance of the proposed X-shaped T-stubs accounting for moment–shear interaction is developed and rules for designing the optimum shape of dissipative DST joints are proposed. Finally, the results of an experimental activity on real scale joints are presented aiming to verify the reliability of the proposed design approach and to compare the cyclic behavior of classical and X-shaped DST joints evidencing the benefits provided by the proposed dissipative joint. [ABSTRACT FROM AUTHOR]

In seismic design of steel structures, the "dual-steel" concept concerns the combined use of High Strength Steel (HSS) in non-dissipative members and Mild Carbon Steel (MCS) in dissipative zones, in order to control the global frame behavior into a ductile overall failure mode. In this paper, a comprehensive parametric study devoted to investigate the seismic design and performance of Eurocode 8 compliant dual-steel Moment-Resisting Frames (MRF) is presented and discussed. The overall seismic performance has been analysed through static and dynamic nonlinear analyses against three limit states: damage limitation (DL), severe damage (SL) and near collapse (NC). The investigated parameters cover both geometric and mechanical variables, as the type columns, span length, number of storeys and spectral shape. The analyses showed that the use of HSS in Eurocode 8 compliant MRFs is effective to provide overall ductile mechanism, but it may lead to inefficient and uneconomical structures characterized by limited plastic demand due to the large design overstrength. The comparison between dual steel MRFs with those entirely made of MCS showed that: i) in order to fulfil the codified drift requirements and to limit the stability coefficients, the same shapes for members should be used for both structures in the most of cases; ii) a similar performance can be recognized in both dual steel and single grade steel structures under both damage limitation and significant damage limit state; and iii) dual steel frames guarantee a better control of plastic mechanism than single grade steel frames at near collapse limit state. [ABSTRACT FROM AUTHOR]

The present paper describes the effectiveness of design provisions of Eurocode 8, 2004 and IS 456 regarding the regular and irregular structures. To achieve this purpose, fifteen storey two-dimensional plane frames, three in number, were designed as per EC 8 provisions (medium and high ductility class) and IS 456 provisions for 27 different ground motions normalized to EC 8 design spectrum intensity for PGA = 0.35 g (design earthquake) and for PGA = 0.70 g (collapse prevention earthquake). The first frame (A) is a regular frame without setbacks and the other two frames (B and C) contain different configurations of setbacks in the upper storey. Firstly, these frames were designed in accordance with EC 8 and IS 456 to obtain optimum cross-sections of the structural members. Secondly, the seismic performance of the designed frames was evaluated based on both local and global criteria by inelastic static pushover and inelastic time-history analysis. Finally, EC 8 and IS 456 designed frames were compared regarding the seismic response, analysis methods and economy. Based on the observations, some important conclusions were drawn. [ABSTRACT FROM AUTHOR]

The main objective of this article is to propose a simplified methodology to assess the expected seismic damage in reinforced concrete buildings from a probabilistic point of view by using Monte Carlo simulation. In order to do so, the seismic behaviour of the building was studied by using random capacity obtained by considering the mechanical properties of the materials as random variables. From the capacity curves, the damage states and fragility curves can be obtained, and curves describing the expected seismic damage to the structure as a function of a seismic hazard characteristic can be developed. The latter can be calculated using the capacity spectrum and the demand spectrum according to the methodology proposed by the Risk-UE project. In order to define the seismic demand as a random variable, a set of real accelerograms were obtained from European and Spanish databases in such a way that the mean of their elastic response spectra was similar to an elastic response spectrum selected from Eurocode 8. In order to combine the uncertainties associated with the seismic action and the mechanical properties of materials, two procedures are considered to obtain functions relating the peak ground acceleration to the maximum spectral displacements. The first method is based on a series of non-linear dynamic analyses, while the second is based on the well-known ATC-40 procedure called equal displacement approximation. After applying both procedures, the probability density functions of the maximum displacement at the roof of the building are gathered and compared. The expected structural damage is finally obtained by replacing the spectral displacement calculated using ATC-40 and the incremental dynamic procedure. In the damage functions, the results obtained from incremental static and dynamic analyses are compared and discussed from a probabilistic point of view. [ABSTRACT FROM AUTHOR]

Time history analyses have been preferred commonly in earthquake engineering area to determine earthquake performances of structures in recent years. Advances in computer technology and structural analysis have led to common usage of time history analyses. Eurocode 8 allows the use of real earthquake records as an input for linear and nonlinear time history analyses of structures. However, real earthquake records with the desired characteristics sometimes may not be found, for example depending on soil classes, in this case artificial and synthetic earthquake records can be used for seismic analyses rather than real records. Selected earthquake records should be scaled to a code design spectrum to reduce record to record variability in structural responses of considered structures. So, scaling of earthquake records is one of the most important procedures of time history analyses. In this paper, four real earthquake records are scaled to Eurocode 8 design spectrums by using SESCAP (Selection and Scaling Program) based on time domain scaling method and developed by using MATLAB, GUI software, and then scaled and real earthquake records are used for linear time history analyses of a six-storied building. This building is modeled as spatial by SAP2000 software. The objectives of this study are to put basic procedures and criteria of selecting and scaling earthquake records in a nutshell, and to compare the effects of scaled earthquake records on structural response with the effects of real earthquake records on structural response in terms of record to record variability of structural response. Seismic analysis results of building show that record to record variability of structural response caused by scaled earthquake records are fewer than ones caused by real earthquake records [ABSTRACT FROM AUTHOR]

This paper investigates the seismic response of lightweight acceleration-sensitive non-structural components (NSCs) mounted on irregular reinforced concrete (RC) primary structures (P-structures) using non-linear dynamic finite element (FE) analysis. The aim of this paper is to study the influence of NSC to P-structure vibration period ratio, peak ground acceleration, NSC to P-structure height ratio, and P-structure torsional behaviour on the seismic response of the NSCs. Representative constitutive models were used to simulate the behaviour of the RC P-structures. The NSCs were modelled as vertical cantilevers fixed at their bases with masses on the free ends and varying lengths so as to match the frequencies of the P-structures. Full dynamic interaction is considered between the NSCs and P-structures. A set of 21 natural and artificial earthquake records were used to evaluate the seismic response of the NSCs. The numerical results indicate that the behaviour of the NSCs is significantly influenced by the investigated parameters. Comparison between the FE results and Eurocode (EC8) predictions suggests that EC8 underestimates the response of NSCs mounted on the flexible sides of irregular RC P-structures when the fundamental periods and heights of the NSCs match those of the P-structures. The perceived cause of this discrepancy is that EC8 does not take into account the amplification in the dynamic response of NSCs induced by the torsional behaviour of RC P-structures. [ABSTRACT FROM AUTHOR]