Seismic Behaviour and Design of Irregular and Complex Civil Structures V

This chapter presents recent developments in rocking self-centering systems for seismic resistance. These systems have shown great potential for damage-free seismic applications, leading to extensive research to investigate their behavior and develop design tools. However, most available methods for designing these systems focus on two-dimensional regular structures, limiting their applicability to real-world problems. We present recently developed methods for the analysis and design of these systems, applicable to irregular buildings. Efficient numerical methods for dynamic nonlinear time history analysis are discussed, specialized for self-centering systems to reduce computational burden. These methods are used to develop efficient gradient-based optimization procedures for automatic design. The optimization problems are formulated to minimize the construction cost, subject to performance constraints that match design code requirements for general irregular structures. The problem is formulated in a continuous form, enabling efficient solutions using gradient-based optimization algorithms. The results of the designed structures show attractive solutions, especially for irregular buildings, which cannot be achieved using currently available methods for these systems.

Although existing masonry buildings do not generally exhibit a high vertical irregularity, they can be affected by a relevant plan irregularity. In this manuscript simplified and numerical studies are adopted to investigate the plan irregularity of a sample of 143 residential masonry layouts. Initially the structures are divided according to building typologies; then, a simplified methodology to evaluate the plan irregularity is used to classify the structures. The results of the simplified procedure, expressed in terms of scores or percentages of irregularity are compared with the outcomes of nonlinear static analysis executed over case studies representative of wider building classes. The work shows that the evaluation of the eccentric ratio between mass and stiffness barycentre may lead to proper plan irregularity scoring coherent with the numerical results, while geometrical classifications on the architectural shape omitting the contribution of resistant area can overestimate the irregularity effect.

Structural engineers may use rules from nowadays seismic design codes in order to decide if a structure is torsional sensitive or not. For example, such rules from the Romanian and the European Seismic Design Code deal with measures like the torsional ratio, the radius of gyration or displacements of the floor edges. If torsional sensitivity cannot be avoided, it implies limited structural nonlinear behavior, a 3D model and at least modal analysis as structural investigation method. This paper verifies the compliance of results computed by applying different torsional sensitivity rules and investigates the influence of the plan layout on the torsional behavior of the analyzed structures. Single-story structures were analyzed, considering that they model accurate enough the behavior of multi-story vertical monotone structures. The aim of the paper is to give some insight into the practical applicability of seismic design code rules for torsional sensitivity. 18 different single-story structural layouts established from 6 structural types by changing the position of the structural walls were analyzed. Torsional flexible, torsional stiff layouts and central core structures were investigated. The influence of frames as lateral resisting elements throughout the structural layout was neglected. Static linear analysis was performed for unidirectional seismic input. Effects of static as well as of accidental eccentricity were considered. Floor edge displacements, torsional Eigen period, torsional ratio and radius of gyration were computed. In a second step dynamic nonlinear analysis was performed in order to check if trends observed from static linear analysis change.

Most current seismic codes take account of the effect of uncertainty in the in-plan distribution of mass introducing an accidental eccentricity, which is generally equal to 5% of the length of the deck of the building. The same codes, instead, do not account for the uncertainty in the distribution of mass along the height of the building. This paper verifies whether the in-elevation irregularity promoted by the uncertainty in the distribution of mass can be neglected with specific regard to steel concentrically braced frames in the chevron configuration. To this end, two 8-story concentrically braced frames are first designed assuming a distribution of mass that is constant along the height. Multiple stripe analyses are then carried out on numerical models with either uncertain or median properties of loads and mass. The performances of the structures are determined in terms of mean annual frequency of exceedance of Damage Limitation, Significant Damage and Near Collapse limit states. Further, attention is focused on the heightwise distribution of drifts and local response parameters achieved for prefixed values of the selected intensity measure.

Structural irregularity in elevation may compromise the seismic response of buildings. Hence, to obtain a seismic performance of irregular buildings not lower than that of their regular counterpart, most seismic codes require that a reduced behaviour factor should be used for their design. These provisions appear to be not well supported by the literature. Indeed, most of the studies were devoted to judging the effectiveness of nonlinear static methods of analysis in evaluating the seismic response of regular and irregular structures. Only a few studies have focused on the detrimental impact that the irregularity in elevation may have on the seismic response of code-conforming seismic-resistant building structures. This paper analyses RC frames with different types and levels of irregularity in the distribution of stiffness along the height. Their seismic response is evaluated by nonlinear dynamic analysis. The seismic performance of the irregular frames is compared with that of the regular one. The results obtained show that the capacity design criteria given in Eurocode 8 make the storey collapse mechanism unlikely to occur also for frames with irregular distribution of stiffness. This leads to a suitable seismic performance even if the unreduced behaviour factor is used for their design.

Earthquakes threaten buildings, causing humanitarian and economic crises. Conventional earthquake resistance designs allow structural damage to absorb earthquake energy ignoring financial losses that persist from building damage. The Base Isolation System has been developed to promote damage-free seismic protection. When applicable, Base Isolation System ensure operational facilities during earthquakes with no visible deformations. This is done by limiting seismic energy flow using flexible isolators that shift the structure's period away from dominant seismic periods. Acceleration decreases, and relative displacement increases but is concentrated at the base level. Multi-Floor Isolation (MFI) aims to reduce isolation level drift and costs, making it feasible for medium- to high-rise structures. However, efficient MFI design is unpredictable and depends on many factors, including the locations of the isolation levels and dampers, their properties, and the structural elements’ stiffness. Therefore, a formulation of an optimization problem is needed. Current optimization methodologies for MFI structures are limited and computationally demanding. This research proposes an efficient gradient-based optimization approach for enhancing the seismic response of a new irregular 2D shear frame design containing MFI and dampers. The developed methodology optimizes the vertical distribution of the isolation layers and dampers and their properties. Results of an irregular sixteen-story concrete shear frame are shown.

The nonlinear response of an irregular base-isolated building depends on the angle of seismic incidence (ASI). The variation in the structural response caused by the ASI depends on whether the horizontal ground motion set considered as the seismic input has a notable directivity effect. In a previous study by the author, the ratio of the equivalent velocities of the cumulative energy input along the major and minor axes (REI) was considered to select ground motion sets with a notable directivity effect. A question of interest concerns the relationship between the ratio REI and the variation in the structural response parameters. In this study, nonlinear time-history analyses of two five-story irregular base-isolated building models are performed using 15 long-period pulse-like ground motion records considering various ASIs. Then, the relationships between the ratio REI and the variation in the peak and cumulative response parameters are investigated. The main findings of this study are that (i) the variation in the response parameter generally becomes larger when the ratio REI is close to zero and (ii) the variation in the total input energy resulting from ASI is negligibly small and independent of the ratio REI.

Building performance is a critical factor in resilience planning for post-crisis recovery, such as after an earthquake. Residual deformations and drifts from large earthquakes can compromise a building's functionality and serviceability. Retrofitting these structures is often impractical or extremely challenging, demanding considerable time and financial investment. An effective strategy to improve seismic performance involves systems that prevent damage to primary building components, like structural systems designed to rock. This study examines asymmetric rocking models for steel and concrete buildings using nonlinear time history analysis. The utility of rocking behavior in asymmetric steel braced frames to manage seismic torsional response is evaluated using seven earthquake records. It also explores the enhancement of structural response through the adjustment of tendon prestress levels, yielding encouraging outcomes. The innovative system is then applied to concrete shear wall buildings. The results show that this system enables the asymmetric structure to stay mostly within the immediate occupancy performance level. Post-tensioned cables lead to a reduction in structural deformation by more than 70%. The introduction of a repairable shear wall with rocking motion makes the first vibration mode more dominant, showing marked differences between the torsional and the first two transverse modes.

Registered evidence demonstrates that the edges of symmetric-plan buildings will experience dissimilar displacements when subjected to ground motions. This unexpected increase in the building response is mainly due to the presence of rotational excitations at the building base and the irregular distribution of mass, stiffness or strength of the building. Accidental torsion was a topic of much research in the 90’s; however, many questions are still unsolved due to the intrinsic uncertainty of the phenomenon. Building codes approaches for considering accidental torsion have not been extensively tested and may lead to distinct results. To address these issues, this study comprehensively examines the accidental torsion of symmetric plan buildings using recorded information from real buildings. Empirical relationships between the percentage increase in displacements (PID) due to accidental torsion and the coupled frequencies ratios from 76 U.S. buildings are obtained and compared against similar relationships results from previous studies. From this comparison, it is clear that the proposed relationships follow the same trend of the literature, but they have the advantage of using coupled frequency ratios and data from 76 buildings. In a future research, code requirements will be verified using correlations obtained from advanced statistical models.

During the 2012 Emilia earthquake, several precast RC industrial buildings were damaged or collapsed due to a strong rotational response triggered by the presence of a single or few eccentric walls within the regular mesh of columns. The objective of this work is to analyse the torsional effects induced by an eccentric wall in one-storey frame structures, and to provide formulas for a quick estimation of the displacement of the flexible side. Starting from the typical structural scheme of industrial one-storey structures consisting of a regular grid of uniformly spaced columns, a stiff lateral shear wall has been added to make the structure asymmetric. A response parameter (displacement amplification factor), defined as the ratio between the translational displacement of the irregular structure over the translational displacement of the corresponding equivalent regular structure without the added wall/s, is introduced to evaluate the torsional response of the system. An analytical formula is derived by means of a linear static analysis. The results indicate that the presence of a shear wall, albeit significantly stiffer than the columns (or even infinitely rigid) with respect to lateral action, does not always lead to a reduction of the seismic displacement demand in the columns.

Displacement-based design methods (DBDM) have been extensively studied and developed to become applicable design tools for different types of structures. For ultimate limit states where non-linear behaviour is expected, most of these methods assume that the nonlinear maximum response of a structure can be approximated through a single-degree-of-freedom (SDOF) reference system associated with its fundamental mode. For this reason, most of these methods have been studied extensively in planar frames and buildings with moderate torsional effects. This paper presents a modification of the DBDM proposed by López and Ayala [1] to be applied in the design of 3D in-plan asymmetric buildings by means of spectral decomposition. This approach would allow an improvement in design of buildings where torsional effects are significant.

This paper presents the seismic response of a 4-storey office building subjected to uniaxial and biaxial seismic excitations. The building located in Montreal, QC, has a square floor plan and the steel braced frames are displaced in two distinct configurations that lead to a regular and an irregular (torsionally sensitive) building. As per the code requirements, the former and the latter are designed for 5% and 10% accidental eccentricity, respectively. From incremental dynamic analysis applied on the 3D model using OpenSees resulted that the 5% accidental eccentricity is adequate for regular building design. Meanwhile, both regular and irregular buildings satisfy the collapse safety criterion under uniaxial and biaxial seismic excitations. Although both buildings yield similar responses under uniaxial excitations, the irregular building exhibited lower collapse margin ratio under biaxial excitation, which indicates inconsistency in design regulation and further research is required.

Modal response spectrum may give unconservative results for highly torsionally stiff in-plan asymmetric buildings such as those composed of shear walls. Previous studies carried out by the authors suggest that the estimation of seismic response may be improved by means of the so-called additional mass eccentricity artifice. This consists of performing modal response spectrum analysis of a modified elastic model where the centre of mass is displaced a distance termed additional mass eccentricity. This paper presents equations for the calculation of additional mass eccentricities that may be used for assessment and design of in-plan irregular shear wall buildings located at soft soil sites of Mexico City.

Existing steel structures are characterised by a wide variability in terms of structural conception and adopted constructional details. Moreover, older steel buildings are often irregular in plan and in elevation. These structures are usually non-conforming with normative provisions currently in force. Such unconformity can possibly lead to severe structural shortages. An existing six-storey steel building located in Naples is investigated as a case study. The selected building features both concentrically braced frames (CBF) along the transversal direction and moment-resisting frames (MRF) in the longitudinal direction, in which non-conforming beam-to-column joints were adopted. Multiple on-site surveys carried out by the Authors allowed the complete characterization of the structure. The global behaviour of the investigated structure was inspected by means of finite element simulations. Non-linear analyses showed that the case study has a poor seismic performance in both directions. Hence, a seismic strengthening intervention was designed and numerically checked. The efficiency of the proposed solution is presented by comparing the global response in both ante- and post-opera configurations.

Damage to primary structural members reduces story stiffness and, in severe cases, changes the mode shape of frames, introducing structural irregularity that is a critical factor for damage assessment. This paper presents an investigation to clarify the changes in vertical stiffness distribution caused by damage and examine the effectiveness of a rapid repair process. The study used the test data of a full-scale shaking table test of a four-story steel frame representing a hospital facility with a weak-base/strong-column design conducted in 2020. The relationship between the damage states of the structure and the structural characteristics including natural frequency, mode shapes, and stiffness was evaluated by system identification. Using a numerical model of the specimen, a widely-used repair method that rapidly reverts the column base's overall stiffness was proven effective through the subsequent analyses.

This paper presents an innovative optimization strategy for enhancing the seismic retrofitting of inelastic Moment Resisting Frames (MRFs) equipped with nonlinear Fluid Viscous Dampers (FVDs) and Negative Stiffness Devices (NSDs), with a particular focus on irregular structures. The primary objective of this approach is to minimize a cost-related function that encompasses expenses linked to the supplemental FVDs and NSDs. The method concurrently optimizes the mechanical traits and spatial arrangement of both FVDs and NSDs, efficiently utilizing differentiable functions for a gradient-based optimization technique. Adhering to computational efficiency, gradients are determined through adjoint sensitivity analysis. The structural response assessment employs Nonlinear Time History Analysis (NTHA), accommodating the nonlinearity of MRF elements, FVDs, and NSDs. The PEER framework is adopted to introduce a performance constraint using loss estimation analysis. A practical case study underscores the efficacy of this methodology, highlighting its capacity to minimize costs while considering seismic performance and nonlinear behavior. This optimization approach stands as a powerful tool for seismic retrofitting, capitalizing on the combined advantages of FVDs and NSDs for irregular structures, while offering computational efficiency for real-world implementation.

This study investigates the seismic response of Reinforced Concrete (RC) framed buildings designed for gravity loads only, as very common in the Italian residential building stock before 1970. In particular, starting from the same building configuration (both in plan and elevation), the attention is mainly focused on the evaluation of the role of staircases on the global seismic behaviour, considering three possible cases: neglecting the presence of staircases, with the staircase substructure realised with cantilevered steps from knee beams, and with the staircase substructure realised with cantilevered steps from RC walls. The seismic response is investigated by nonlinear pushover analysis, and the results obtained from two different modelling approaches are discussed and compared. Even though staircases are considered as secondary structural elements and often calculated separately from the main structure, they can be elements of potential damage in buildings. The results obtained, although preliminary, highlight the non-negligible effect of the staircase typology on the seismic response, in terms of period of vibration, lateral stiffness, maximum base shear and ductility. Moreover, the presence of stairs can also give raise to torsional effects.

Despite the high seismicity that characterizes many areas of the world, structures currently in use are not necessarily able to sustain seismic forces and need to be upgraded to prevent economic and human losses. Hence, this paper proposes the addition of an external 3D steel exoskeleton, named e-EXOS, to existing RC buildings as a technique to mitigate their vertical irregularities and improve the seismic response of the RC frame structures. The effectiveness of the e-EXOS system is tested on a case study RC framed building, designed without seismic provisions. Two sizes of the e-EXOS truss are considered, to investigate if and how much this affects the structural response. The seismic response of the RC frame, with and without e-EXOS, is determined by incremental nonlinear dynamic analysis and the performance is assessed in terms of mean annual frequency of exceedance of the SD and NC limit states.

Nonlinear Time History Analyses (NTHAs) are considered the most precise and realistic analytical methods available. However, due to their simplicity, reduced computational demands, and fewer output data requirements, Pushover (PO) analyses are frequently favoured in design practices. According to European and Italian seismic standards, the seismic demand derived from Pushover (PO) analyses must be calculated using the “original” N2 method. Initially designed for planar frames with responses dominated by the fundamental mode of vibration, the N2 method is now also applied to 3D structural analyses. The building is analysed along the two reference axes, and the results are then combined using established rules. This study assesses the accuracy and effectiveness of the original N2 method and the combination rules in predicting seismic demands in Pushover (PO) analyses. Additionally, this paper evaluates the “extended” N2 method (N2ext) in order to address the limitations of the original method. To achieve this, a series of case-study buildings, typical of older Italian RC structures, are analysed. The seismic demands from these nonlinear static analyses are calculated for three levels of seismic hazard and then compared with the results from Nonlinear Time History Analyses (NTHAs), which serve as the benchmark.

Vertical extension of existing buildings is a sustainable and fascinating strategy for urban densification in contemporary cities, allowing for accommodating the growing demand for usable spaces with no land take. An innovative approach has been recently suggested by the authors to rise the building height while reducing the seismic demand on the existing structure: it consists of vertical addition equipped with seismic isolation at its base, realised on the roof of the existing structure, thus configuring as an Intermediate Isolation System (IIS) working as a nonconventional tuned mass damper. In this paper, the possibility of regularizing, as well as reducing, the dynamic response of the existing structure through an appropriate design of the isolation system is examined. For this purpose, an existing masonry building, with eccentricity between the stiffness and mass centroids, is selected and analysed as a case study. Several solutions for the isolation system, both in terms of period and distribution of isolators shear stiffnesses, are considered. Analysis results are discussed and design implications are suggested.

The paper presents a study on the dynamic monitoring of a complex building in the port area of Bari, Southern Italy. The building consists of two mixed structures (masonry-reinforced concrete) at different heights, connected by a reinforced concrete spiral staircase. The aim of the study was to assess the structural behaviour of the building during excavation activities in the port, which lasted for about 3 months and were performed by a dredger. An experimental program was conducted, recording accelerations from biaxial and triaxial accelerometers at strategic points in the building. The experimental results were used for operational modal analysis to identify the main frequencies of the structure. After, a model updating procedure was carried out using structural analysis software. The main object of numerical updating consisted in finding some unknown parameters: (a) the mechanical properties of the masonry panels; (b) the mechanical properties of the reinforced concrete members; (c) the boundary conditions and the constraint degrees that characterize the numerical model. All the steps performed to fit the experimental and numerical results are reported in the paper, showing original and interesting results that are discussed in a broader view, especially when referring to structural health monitoring of complex structures.

In this paper, a suspended super high-rise building system is proposed, in which the core tube is used as the load-bearing and lateral force-resisting member of each suspension substructure. There are several suspension substructures distributed along the height. The suspension substructures swing in the earthquake, and the phase of each substructure will be different, which artificially forms a “snake dance” mechanism, thus avoiding excessive overturning moment. The dynamics of the suspended super high-rise building is first formulated for both core tube and suspended substructures. A semi-active control algorithm based on a set of fuzzy rules is introduced. The effectiveness is tested by the numerical MR device model built in MATLAB, while the model for the suspended super high-rise building system is created in OpenSEES. The collaborative simulation between MATLAB and OpenSEES is used to simulate the semi-active control on the suspended super high-rise building system. According to the result, the phases of suspended substructures are different, and the overturning moment and the displacement of the suspended substructures decrease significantly compared with the uncontrolled case.

The friction pendulum system/bearing (FPS/FPB) is a novel isolation device in building engineering. It has a more prominent vertical bearing capacity, more significant horizontal displacement, and uncoupled mechanical properties in various directions compared to traditional laminated rubber bearings. However, the FPS cannot resist any tension in the vertical direction as its components are contacted by vertical compression. The applications in high-rise buildings, particularly those with large height-to-width ratios, are severely limited by the overturning moment. To promote the use of buildings isolated by FPS, a 12-story frame-shear wall structure with a height-to-width ratio of 2.7 was designed and isolated by FPS. A corresponding scaled model was constructed, and shaking table tests were conducted. The study found that the 12-story frame-shear wall structure was elastic under service level earthquakes, repairable under maximum considered earthquakes and even very rare earthquakes (with an annual exceedance probability of 10–4) of intensity IX. The floor response of the superstructure was significantly reduced. The seismic isolation performance improved with increased earthquake intensity after the FPS completely slid.

Masonry buildings present plan or vertical irregularity generally caused by structural modifications suffered over time. Most recent earthquakes highlighted how structural irregularity strongly affects the vulnerability and the seismic response of masonry buildings. In the context of historical city centres, vertical irregularity due to sudden variations in mass, stiffness and strength on walls along the building height, was investigated. In the center of Florence the vertical irregularity is often due to changes made over time for functional needs or for an economic return. Large portions of masonry walls on the ground floor were removed to allow a new distribution of the interior spaces and the scheme of the openings at the different floors of the building due to the internal renovation of the flats, the partial rooftop addition, usually for an economical return, as common in densely populated urban areas. In this paper, a simplified numerical procedure is proposed to evaluate the influence of vertical irregularity on the seismic response of masonry walls along the building height. This simplified procedure can be useful for both academic research and professional activity.

This paper describes the experimental and numerical study of the main building of the Early Childhood Protection Association (APPI - Associação Protetora da Primeira Infância) in Lisbon. The case study pertains to a mixed timber and brick masonry structure featuring an original design dating back to the 20th century. Steel frames were incorporated as part of rehabilitation carried out in 2014. This study intends to: (i) use laser scanning for the on-site data geometric acquisition and develop an H-BIM (Heritage-Building Information Modelling), a comprehensive tool that provides access to various entities responsible for the management and conservation of the building, (ii) identify dynamic characteristics through in-situ environmental vibration tests; (iii) calibrate and validate the numerical model developed for nonlinear static analyses and seismic response simulation; (iv) study the seismic capacity of the building in its current condition, proposing adequate strategies for modelling this type of buildings through an equivalent frame modelling approach and identifying main vulnerabilities. The building was originally regular and then, after rehabilitation, transformed into a non-regular structural configuration in the plan. The developed work highlights the importance of sequence and constructive details for accurate numerical modelling.

Masonry buildings in historical sites are difficult to analyse as independent structures since they typically have common walls with adjacent structural units. Whenever seismic forces interact with these categories of building compounds, their behaviour differs from that of individual buildings considered as independent structures. The research examines in detail a simplified methodology for analysing the vulnerability of masonry building aggregates presenting a case study in Castelpoto, a municipality of Benevento (Italy). The investigated structure is an existing masonry building compound with a non-regular configuration consisting of seven structural units, SUs. Specifically, three SUs are placed in the head position, two cells are in the corner position and the other two cells are enclosed between two adjacent SUs. The vertical structure has an irregular stone texture, while the horizontal structural components are made up of wooden floors and, in some cases, steel beams and masonry arches. The numerical analysis evaluates first, a multiscale procedure to investigate the vulnerability of the whole aggregate and, then, the interaction of the individual SUs in the seismic conditions to more effectively predict the seismic behaviour of the investigated clustered structural units. Finally, structural retrofitting interventions are proposed to improve the expected performance level of the building under consideration, as well as its seismic dissipative capacity.

Prestressed concrete segmental bridges, constructed by cantilevering with medium to large span lengths during the 1950s to 1970s and still in service, are now reaching the end of their nominal service life and were designed according to outdated Technical Codes. Therefore, the seismic assessment of these bridges must take into account the roles of piers, bearings, and drop-in spans, which are susceptible to beam pounding. The paper focuses on the seismic vulnerability assessment of bridges with a first approach through using response spectrum analysis; afterwards, the efficiency of various non-linear static analysis procedures is compared with the results from non-linear response history analysis, demonstrating that bearings play a crucial role in evaluating seismic vulnerability to longitudinal motion, especially for the segmental framed scheme with drop-in spans.

This work presents a complex analysis conducted on a viaduct located in Sicily, south of Italy, with different FEMs both linear and non-linear. The numerical investigation concerns the complexity of both the structural scheme and the effects of seismic actions on the response behaviour of the viaduct. The FE model has been constructed based on the original draws, while the mechanical characteristics of the materials have been estimated by means of an extensive in-situ testing campaign comprising concrete coring and sclerometer tests. The expanded joints have been modelled using link elements having a linear behaviour. The springs of the link have a stiffness calibrated by the instructions provided in the original draws and/or considering dimensions and materials of expanded joints of a similar viaduct, which has been demolished few years ago. Linear and non-linear analyses have been carried out to investigate the influences of the seismic action on the global response behaviour of the viaduct, especially studying how the variation of the axial force along the piers, due to seismic signals characterized by a significant vertical component, influences the load bearing capacity of both single elements and overall behaviour of viaduct.

The soil-structure interaction is commonly overlooked in seismic analyses of buildings. However, its omission may lead to an overestimation of seismic performance, especially in the context of complex heritage buildings of significant importance. This study focuses on the seismic performance of the Mosque-Cathedral of Cordoba (Spain), a UNESCO World Heritage Site representing the evolution of Islamic Architecture in the Iberian Peninsula since the VIII century. The building is situated in an earthquake-prone area in the southern Iberian Peninsula, constructed over soft alluvial soil. This research introduces a novel aspect by considering soil-structure interaction in the seismic analysis, particularly focusing on the Abd al-Rahman I sector, the most aged portion of the structure. A finite element model has been developed and calibrated using in situ testing. Nonlinear static analyses were conducted to assess the soil-structure interaction effects on the seismic performance of this sector. The findings reveal potential severe damage to certain parts of the building. It is noteworthy that the presence of alluvial strata amplifies the seismic action, and the results demonstrate a notable worsening when accounting for soil-structure interaction effects.

The dynamic behaviour assessment of buildings is usually carried out involving several simplifications, such us omitting the soil-structure interaction (SSI) effects. However, several studies have concluded that the SSI can worsen the behaviour of tall buildings over soft soils. Hence, in this work, the SSI effects have been considered to assess the dynamic behaviour of a case study tall reinforced concrete (RC) building. To do so, time-domain incremental dynamic analyses have been carried out. A 3D model of the building has been developed in the OpenSees framework. Nonlinear springs have been used to simulate the soil-pile interaction. The case study building is located in Seville (Spain). It was constructed prior to the Spanish seismic codes and it is located on alluvial soil. The results of the complete SSI model have been compared with the numerical analyses of the fixed-base hypothesis. Numerical results showed that this case-study will not comply with the seismic safety requirements. Static analyses demonstrated that the damage can be worsened by up to 12%, if the SSI is considered. Dynamic analyses revealed that, at the lower storeys, there is a risk of severe damage and of the collapse of the columns, which is increased up to a 22%, if the SSI is considered.

The soil structure interaction is usually omitted in the seismic analyses of ancient historical buildings, considering the fixed base condition. However, usually, these buildings present a poor foundation, and they are over soft strata, making the assumption of the fixed base condition unrealistic. This paper aims to assess the seismic behaviour of the well-known Giralda tower (Seville, Spain) considering the soil-structure interaction (SSI). It was built with unreinforced brick masonry walls in the XII century. A 3D nonlinear numerical model based on the finite element method has been developed, considering the foundation and the soil. Nonlinear static and dynamic analyses have been carried out in the OpenSees framework. The SSI has been simulated through the direct method. The interaction with the Cathedral has been borne in mind. The results have shown that, if the soil structure interaction is considered, the peak strength is similar to the fixed base model, but the displacement is approximately doubled. This leads to an increase of the damage expected.

The Geotechnical Seismic Isolation (GSI) is a new solution to mitigate the earthquake effects on superstructures. It consists in improving the mechanical properties of the foundation soil to reduce the seismic energy that reach the foundations. The use of gravel-rubber mixtures (GRMs) is an affordable GSI solution because of their excellent dynamic properties and eco-sustainability. The present paper shows the main results of a numerical investigation on the performance of a GRM layer underneath the foundations of a typical reinforced-concrete Italian building, located in Fleri (Catania, Italy), severely damaged during the 2018 Catania earthquake. The hypothesized GRM layer was characterized by a rubber content equal to 30% per weight. Both the soil-structure system with and without the GRM were modelled. To do so, a 2D FEM approach was used. An equivalent visco-elastic behaviour material for the soil and the GRM was adopted. A visco-inelastic behaviour material for the structure was employed. By comparing the two 2D FEM models (with and without the GRM), it was possible to evaluate the suitability of the GRM as seismic isolation of the structure. Interesting reductions of the spectral ordinates were achieved equal to about 25% and 40% at the foundation level and at the roof of the structure, respectively.

The close arrangement of buildings in urban areas causes the interaction effect of the vicinity to profoundly affect the response of structures. Furthermore, previous earthquakes have revealed that the soil type of the construction site would be very impressive on the seismic response of structures. With this approach, the effects of structure-soil-structure interaction and the seismic performance of structures in a group have been widely taken into account. By considering different embedment depths for the foundation, the main purpose of the present study is to investigate and compare the interaction effects of adjacent structures on seismic responses within different construction sites. Applying the Direct Method as well as defining a suitable boundary environment, the superstructure involved two 6- and 12-story concrete moment resisting frames in two different cases of deploying the foundation on the ground surface or in a depth equal to 30% of the structural height within the profiles containing soil types II and III. The modeling procedure has been conducted three-dimensionally using OpenSees platform. Investigating the acceleration, lateral displacement and shear force responses of the adjacent structures showed that the vicinity and interaction effects on the dynamic responses are dependent on the soil type as well as the embedment depth of the foundation. So that the reduction of the embedment depth within a continuum of soil type II increased the maximum acceleration and story shear force responses for the 12-story frame by 59% and 25%, respectively.

The buildings located near or on top of the railway systems are generally affected by the rail-induced vibration. Vertical vibration isolation is an effective measure to reduce the influence of rail transit vibration. However, the vertical isolated structures are prone to overturning moment which can result in rocking of the superstructure under earthquake. To resolve this issue, three-dimensional (3D) vibration isolation which involves a system that combines both the vertical vibration isolation and horizontal seismic isolation is proposed. This study carried out a shaking table test to compare the rocking behaviour of a vertical isolated structure and a 3D isolated structure. The testing structure was a three-story steel frame structure, with an aspect ratio of 3.3, and the vibration isolation bearings were installed under the column bases. Test results demonstrated that the rocking amplitude of the vertical isolated structure was about 2 times of the non-isolated conventional structure. While the horizontal accelerations and rocking amplitudes of the 3D vibration isolated structure were about 70% smaller than the structure with only vertical vibration isolation. This study verified the effectiveness and necessity of 3D vibration isolation in the rail-induced vibration control.

Seismic isolation technology is an effective means to improve the seismic performance of buildings and important equipment. However, the seismic isolation of tall flexible electrical equipment remains challenging due to the strict requirements of a large tensile capacity and self-centering ability. In this study, a modular metal seismic isolation bearing (MMSIB) is proposed. The MMSIB is composed of steel plates, linear guides and sliders, springs, and friction dampers. The linear guide rails are used to restrict the direction of movement and prevent the overturning of the MMSIB, and the springs are used to adjust the horizontal stiffness of the MMSIB and provide self-centering ability through pre-tension. The friction dampers are used to control horizontal deformations of the MMSIB with adjustable energy dissipation ability. The effectiveness of the MMSIB is verified via a shaking table test of a 110 kV current transformer (CT). The results show that the MMSIB exhibits excellent isolation performance. The acceleration response at the top of the CT is found to be reduced to 7.32%-32.57% of that of the non-isolated specimen. The MMSIB can provide sufficient anti-overturning ability that satisfies the requirement of the inter-layer seismic isolation of electrical equipment with supports. The MMSIB has good self-centering ability with limited residual deformation that is less than the reference value.

There is a scarcity of research on underground storage tanks, and their seismic behaviour remains inadequately understood. To investigate the seismic response of an underground liquefied natural gas storage tank, a shaking table test was carried out under different excitation directions and spectral characteristics of input waves for various liquid level states of the underground liquefied natural gas storage tank model designed according to a reduced scale of 1/60. The acceleration of the tank, and the dynamic soil pressure, and the hydrodynamic pressure were evaluated through the test. Results mainly show that as the amplitude of the input waves increase, the liquid-structure coupling effect makes the liquid act as a strong damping force, thereby mitigating the vibrations of the tank to some extent. The soil pressure from the bottom to the top first decreased sharply and then increased steadily under each case. The storage liquid was initially manifested as a large fluctuation, and then appeared to be a periodic fluctuation gradually. The long period ground motion has a serious impact on the liquid stored in the underground tank, which will bring significant nonlinear dynamic water pressure impact to the inner tank wall.

RC frame structure is a commonly used structural system in China, in which the frame joint connects the beams and columns and is the key part of force transmission. Various damage patterns have been inspected in past studies, which are caused by the coupled effect of beams, columns and joints in the damage developing. In order to realize the performance-based design targets of RC frame structures, it is necessary to accurately identify the seismic damage pattern of an RC frame structure, which is also a prerequisite to suggest the repair procedure effectively. According to the test data of 147 RC beam-column joint assemblies collected from 68 Chinese literatures, it is found that the final failure modes of RC beam-column joint assemblies can be classified into bending failure (B), bending shear failure (BJ) and shear failure (J). The failure mode is determined by various mechanical and geometric properties, and damage development processes. In this study, the characteristic crack pattern is employed to classify damage states (DS), and further to establish the fragility curves of RC beam-column joint assemblies with B, BJ and J failure modes, respectively. The displacement angle was taken as the engineering demand parameter (EDP). It is found that obvious differences were observed in the damage phenomena of different types of joint assemblies, which are closely related to the bearing capacity characteristic points. According to the database and determination of damage status, the seismic damage of RC frame structures can be easily assessed in the field reconnaissance, and subsequent repair and reinforcement method could be correctly suggested.