Experimental Research in Earthquake Engineering

The George E. Brown, Jr. Network for Earthquake Engineering Simulation (NEES) is a network of 14 advanced laboratories (https://nees.org/sites-mainpage/laboratories) connected by a state-of-the-art cyberinfrastructure that fosters collaboration in research and education (https://nees.org/). In its ninth-year of operations, over 400 multi-year, multi-investigator projects have been completed or are in progress in NEES, yielding many advances in earthquake engineering and a wealth of valuable experimental data. The NEES platform for collaboration, NEEShub, provides convenient access to the NEES central data repository (Project Warehouse) and hosts a range of tools for data visualization, analysis, computational simulation, education, collaboration and hosts a rich set of resources aimed at disseminating new earthquake engineering knowledge to the profession as well as educating the next generation of researchers and practitioners. In this paper, brief descriptions of some of the many research, outreach, information technology, and educational accomplishments of NEES are given.

With the invention of the Semantic Web, computing paradigm is experiencing a shift from databases to Knowledge Bases (KB), in which ontologies play a major role in enabling reasoning power that can make implicit facts explicit to produce better results for users. In addition, KB‐based systems provide mechanism to manage information and semantics thereof that can make systems semantically interoperable and as such can exchange and share data between them. To overcome the interoperability issues and to exploit the benefits offered by the state of the art technologies, we moved to the KB-based system. Essentially, we have developed an earthquake engineering ontology using a faceted approach with a focus on research project management and experiments. Following the validation of the ontology by a domain expert, it was published in the knowledge representation language RDF and integrated to the generic ontology WordNet. The experimental data coming from, inter alia, cyclic and pseudo-dynamic tests were also published in RDF. We used Jena, OWLIM and Sesame tools for publishing, storage and management, respectively. Finally, after integrating the tools, ontologies and data, we developed a system to evaluate the effectiveness of the approach and in fact we found quite convincing and satisfactory results.

The European scientific community is currently highly fragmented, with each laboratory holding experimental data, stored in some cases in a non-structured way. As a consequence, dissemination and use of experimental results outside the laboratory where they are produced can be problematic. This leads to wasteful duplication of tests and ultimately limits the impact of earthquake engineering research on practice, innovation and earthquake risk mitigation. One part of the SERIES Networking Activities aims at facilitating the exchange of data and data communication among research infrastructures in Europe by providing access to data through a distributed database. The scope was not to build a central database where local databases would either migrate or merge, but instead to provide centralised access to database nodes that are distributed over a network and are able to dialog with a central portal in a uniform manner. To this end, database nodes use Web Services to cast their data into a uniform standard format. The paper concentrates on the architecture and the implementation of the Distributed Database.

At the beginning of the project, the access and exchange of data within the European scientific community was highly fragmented and the diffusion of information among laboratories was not sufficient. The outcome of an inquiry performed among partner laboratories at the beginning of SERIES showed that data storage in an unstructured way was the common approach in most of the cases. Naturally, access to and elaboration of the data was restricted only to the local users, a fact leading to a very low impact of the results on practice because of their limited dissemination and the difficulties in collaboration among researchers. SERIES (Networking Activity NA1) aimed, among others, at overcoming this state by establishing a culture of preservation of data in a structured way and by facilitating data exchange and collaboration with the broader research community. A structured database in which data are stored according to a commonly agreed Exchange Data Format has been implemented at the SERIES laboratory sites; tools for the management and automatic data import have been developed to facilitate data supply from participating laboratories. The data stored in the local databases are then made publically accessible to external users by means of a Data Access Portal, hosted in the University of Patras. The elements of the so-called SERIES virtual database are here described.

The work presented herin was presented at the Concluding Workshop of the European funded Project (SERIES) jointly organized with US-NEES on “Earthquake Engineering Research Infrastructures” in Ispra held on May 28–30, 2013. The paper is intended for use by Research Testing Facilities, Certification and Accreditation Bodies, and Standardization Institutions as a reference document about the qualification of large research facilities acting in the field of the seismic engineering. The paper illustrates the demand of qualification for the large research testing facilities in Europe and how the EC funded SERIES Project responded by producing a Common Protocol for the qualification.

This chapter reports three recent developments aimed towards faster computations and more accurate execution of real-time hybrid simulations (RTHS). The first of these developments is a standalone RTHS system which can accommodate integration time steps as small as 1 ms. The fast execution feature eliminates the approximations that would be introduced by the application of a predictor-corrector smoothing technique and increases the applicability range of explicit integration methods. The second development is the use of an efficient equation solver in RTHS which reduces computation time. This efficient solver, which decreases the computation time by factorizing the Jacobian of the system of linear algebraic equations only once at the beginning of the simulation, is especially beneficial in RTHS which involves analytical substructures with large number of degrees of freedom (DOF). The third development is a novel use of a three-variable control (TVC) for RTHS on a shaking table configuration. Although the TVC, which employs velocity and acceleration control in addition to the typical displacement control, is commonly used in conventional shaking table tests, this development is the first application of TVC in RTHS.

The assessment of the seismic performance of an old concrete bridge was conceived within the RETRO Transnational Activity funded by the SERIES research project. The installation of isolation devices -one per column- for each pier portal frame interposed between the cap beam and the deck was proposed as seismic retrofit, fully complying with Eurocode 8 requirements. A comprehensive set of hybrid simulations was conceived to simulate the dynamic response of the existing 400 m span Rio Torto Viaduct, both in the isolated and the non-isolated cases. In order to support the pseudo-dynamic test design, a refined fiber based FE model of the bridge was implemented in the well-known OpenSEES software; time history analyses highlighted appreciable nonlinearities in the dynamic response of the system under the Serviceability Limit State (SLS). As a consequence, a Numerical Substructure (NS) capable of reproducing such nonlinear behaviour was deemed necessary. Nonetheless, implementation issues relevant to the typical solving time dictated by the controller time step, made the use of complex fiber based FE models not suitable for testing purposes. In this perspective, the paper presents the design of a suitable NS, which is based on a rational and nonlinear reduction of the aforementioned OpenSEES Reference Model (RM). Moreover, in order to impose a consistent degradation of physical and numerical piers, a testing procedure based on recursive identification and model updating sessions is proposed. The numerical tools and simulations developed in the project are presented and discussed.

One of the tasks within the FP7-SERIES project was the creation of a European Platform for Geographically Distributed Tests. This platform was envisioned to be able to deal with different protocols and algorithms so that its users and facilities would not be restricted to one specific protocol. The platform should also prove the possibility of performing geographically continuous distributed tests since up to now such tests were stop and go. However, through the use of an efficient substructure algorithm, continuous tests can be performed using standard network connections. With that in mind, several activities were performed at the University of Kassel that involved major earthquake engineering facilities around the world. With each partner, continuous time-scaled hybrid simulation tests with a non-linear substructure were performed exploring the available protocols. In addition, preliminary tests using Large Numerical models and a Linux cluster were also performed in order to assess the extensibility of the platform to more complex and larger models.

The deficiency of seismic design standards for piping systems, their components and support structures necessitates experimental investigations of such structures under earthquake loading to extract valuable information for the amendments/development of relevant design guidelines. This paper describes an experimental test campaign carried out at the University of Trento, Italy, on a full-scale piping system in order to evaluate its seismic performance. In particular, a typical industrial piping system containing several critical components, such as elbows, a bolted flange joint and a Tee joint, was tested under different levels of earthquake loading corresponding to serviceability and ultimate limit states suggested by performance-based earthquake engineering standards. Hybrid Simulations with Dynamic Substructuring (HSDS) in both pseudo- and real-time were adopted to conduct seismic tests. Experimental results displayed a favorable performance of the piping system and its components; they remained below their yield limits without any leakage even for the Collapse Limit State. As a result, the proposed model reduction techniques were fully justified.

Distributed hybrid testing offers a promising approach to use resources from geographically separate laboratories in a highly efficient way, to perform more complex, larger-scale tests than are possible in most individual laboratories. The method involves splitting a structure into a set of substructures (some tested physically, some modelled numerically) located in different laboratories. Simulation of the full structural response involves simultaneous testing of the substructures with feedback of data between them, requiring fast communication through computer networks. To handle systems involving rate dependence, there is a desire for test speed to approach real time. In addition to the increased difficulty of tracing errors caused by the distributed environment, organizing and planning distributed experiments creates much more complexity than in single-laboratory hybrid tests. This points to the importance of a platform to support the testing activities. This platform has been achieved by means of a specification called Celestina, created at the University of Oxford. Celestina provides a framework for conducting the experiment workflow. It provides a specification for the services to be implemented under three main headings of networking, test definition and experiment execution, and supports to data exchange during a test. It does not force any particular implementation, which can be independently developed and implemented under this framework, nor does it restrict the actual method of data exchange. In this article we discuss the design and conception of the specification as well as one implementation that has been validated through a series of substructured “numerical experiments” in partnership with the University of Kassel.

The experimental investigation of soil-structure interaction (SSI) phenomena is typically performed on a shaking table with a model foundation-structure system embedded in a soil container. As the size and power of the shaking table limits the size of the specimen, only small scale models can be tested using this method. Novel structural testing methods to overcome such restrictions have been developed. The substructuring test methodology requires only an unpredictable subcomponent of the test system to be present in the laboratory, the remainder being confined to a linked numerical model that runs simultaneously. This chapter considers two potential applications of substructuring to shaking table SSI studies. In the first, the soil-foundation system is modeled numerically, the superstructure physically. The second is the inverse problem with the superstructure modeled numerically, the soil-foundation system physically. Tests and simulations are used to reveal that the prevalent substructuring controllers can not compensate for the dynamics of shaking tables. In response, a new model-based control strategy called Full-State Compensation via Simulation (FSCS) is developed that offers an improved performance. With the shaking table dynamics adequately compensated, substructuring test results are shown to align with the results from an entirely physical SSI test, verifying substructuring test methods for shaking table SSI applications.

This Chapter proposes a framework for the control of shaking tables on the basis of adaptive signal processing and parameter estimation methods. The applied methodology bypasses any analytical modeling scheme and treats the table as a black–box mechanical system, the output of which must replicate a predefined time–series of diverse spectral characteristics. A central feature of the proposed scheme is the operation in acceleration mode that allows a wider response spectrum to be actually implemented to the specimen. Control is achieved by realizing a two–stage procedure, at which (i) the dynamics of the shaking table are identified, including any transfer delay, and (ii) an inverse controller is adaptively estimated and placed in series before the table’s controller, aiming at filtering the reference acceleration in a way that cancels the table dynamics. Both stages, which can can be applied either on–line, or off–line, must be conducted with the specimen installed on the table. For its practical evaluation, the method is successfully applied to shaking table waveform replication tests under the installation of an approximately linear specimen of sufficiently high mass (comparable to the mass of the table) and complex geometry.

RETRO’ project aims at studying the seismic behaviour of existing reinforced concrete (RC) bridges and the effectiveness of retrofitting systems based on seismic isolation of the deck of the viaduct. The research program focuses on a typical non-compliant bridge system for earthquake loading, designed for gravity loads only. The prototype structure is the Rio Torto bridge system, which is located in a region of medium seismic hazard in Italy. The seismic vulnerability of the as-built framed pier bridge is first assessed. A typical seismic isolation system, employing slide spherical bearings, is then designed as a passive control retrofitting measure. The present chapter discusses the non-linear response of the Rio-Torto viaduct in the “as-built” and “isolated” configurations. The seismic performance assessment is carried out by utilizing refined non-linear structural models implemented in an advanced and reliable computer platform. The earthquake behaviour of refined models used for the sample structure accounts for non-linear phenomena of the viaduct, e.g. strain penetration of plain bars, shear deformation of transverse beams, flexural deformations in columns and beams. The finite element models are calibrated on the basis of experimental tests results. The assessment of the seismic response system is investigated in terms of local and global response parameters. In addition, the effectiveness of the isolation systems used as a retrofitting system is also investigated numerically. The outcomes of the comprehensive nonlinear analyses are used to simulate the seismic response of the viaduct in the as-built and isolated configurations during Pseudo-dynamic testing, which is illustrated in a companion chapter.

The RETRO project aims at studying the seismic behaviour of existing reinforced concrete (RC) bridges and the effectiveness of innovative retrofitting systems. A typical as-built RC highway viaduct, designed primarily for gravity loads, has been analysed experimentally. The objective of the laboratory test program is twofold: (1) improve the knowledge of the non-linear behaviour of RC framed piers without seismic detailing and (2) assess the effectiveness of seismic isolation systems as a structural mitigation measure. Two large scale framed piers with two and three levels were re-designed and tested using the PsD method with hybrid (analytical and experimental) simulation. Two test configurations were considered: (1) the as-built bridge layout and (2) the viaduct retrofitted by means of Friction Pendulm (FP) isolators. The seismic performance evaluation was carried out at two limit states, i.e. at serviceability and ultimate limit states. The experimental tests stressed the high structural vulnerability of the viaduct, confirmed by the extensive shear damage in the transverse beams and the fix-end rotation effects generated by the bond slip of plain steel bars in the columns embedded in the foundation. The effectiveness of the isolation system with FP devices was also demonstrated. Nevertheless, the friction of the FP devices is a critical response parameter which may vary significantly because of the pressure due to vertical loads, strong motion velocity and temperature. The reliable evaluation of the friction parameter is of paramount importance to prevent the onset of damage within the framed piers.

In the scope of the transnational access activities of the European research project SERIES, the Laboratório Nacional de Engenharia Civil (LNEC) has provided access to its 3D shaking table to the international construction company Wienerberger AG and to a group of European experts, in order to perform full-scale seismic tests on an industrial solution for buildings using a modern unreinforced thermal insulation clay block masonry structure. Such solution represents a very common construction method in Central Europe and, although there are cyclic shear test results available, its effective dynamic response under seismic events still requires experimental validation. For this purpose, two full-scale mock-ups with different geometries were tested on the 3D shaking table using a series of seismic records with increasing intensity. This paper focuses on the most relevant experimental results regarding the structural response of the specimens, e.g., the dynamic response evolution, the collapse mechanism identified and the maximum drift values measured. The paper closes with the main conclusions drawn and with proposals for future developments.

Eurocode 8 imposes the use of reinforced solutions in order to ensure that the in-plane and out-of-plane damage of masonry infill walls due to seismic actions complies with given performance level requirements. Nevertheless, Eurocode 8 does not provide design rules or methodologies for the detailing of such reinforcement. An experimental programme was thus defined for assessing the response of innovative solutions for non-load bearing masonry enclosures using LNEC’s triaxial shake table. Two reinforcement solutions were tested on single leaf clay brick infill walls: (i) horizontal reinforcement in the bedding planes of the masonry units and (ii) reinforced mortar coating. Furthermore, a testing device for masonry infill panels was specifically conceived for this project. A detailed description of the methods used is given and the experimental results are partially presented and interpreted on the basis of the structural response and its evolution with damage.

According to current standards, the use of unreinforced masonry is only recommended in regions of low to moderate seismicity as a resisting system to carry earthquake-induced horizontal forces. This requirement is however felt as rather conservative and leading to uneconomical constructive solutions, in particular for low seismic regions. Moreover, the seismic analysis of masonry structures has to be performed along two main perpendicular directions, usually neglecting the contribution of wall elements perpendicular to the seismic action. Horizontal elements (spandrel, etc.) are also commonly disregarded. In such a context, the present contribution provides an overview of experimental results obtained from shake table tests on unreinforced masonry frames carried out in the EQUALS Laboratory of Bristol University in order to assess, and possibly enhance, current design rules. The study is focused on the contribution of walls perpendicular to the seismic action and on the influence of the frame effect induced by the coupling of the walls through horizontal reinforced concrete elements, such as lintels and floor slabs. Another point of interest of the study is the influence of the gravity loading situation, comparing a floor slab supported by the shear walls as well as by the perpendicular elements, with a floor slab supported by the perpendicular walls only. Tests are performed on walls constructed with units and construction methods typical of the North-Western European region.

With the introduction of higher seismic design forces in the Swiss loading standard of 2003 most unreinforced masonry (URM) buildings fail to satisfy the seismic design check. For this reason, in new construction projects, a number of URM walls are nowadays replaced by reinforced concrete (RC) walls. The lateral bracing system of the resulting structure consists therefore of URM walls and some RC walls which are coupled by RC slabs and masonry spandrels. The same situation characterises a number of seismically retrofitted URM building across Europe in which RC walls are added to the original structure to improve its seismic behaviour. Within the framework of the FP7-SERIES project, a four-storey RC-URM wall structure was tested on the shake table at the EUCENTRE TREES Laboratory (Laboratory for Training and Research in Earthquake Engineering and Engineering Seismology) in Pavia (Italy). The test was conducted at half-scale and is part of a larger research initiative on mixed RC-URM wall systems initiated at EPFL (École Polytechnique Fédérale de Lausanne, Switzerland). The key objective of the testing campaign was to gain insight into the dynamic behaviour of mixed RC-URM wall structures and to provide input for the definition of a performance-based design approach of such mixed structural system. Multiple shaking at increasing intensity was used to test the dynamic behaviour of the examined building. During the final shaking several of the URM walls lost their axial load bearing capacity, however, the structure did not collapse as it was subjected to uni-directional loading only and the axial load was transferred to the RC walls and the URM walls that were loaded out-of-plane. Random noise vibration tests were performed to monitor the elongation of the natural periods induced by the damage progression. The paper presents details on the structural system and the selected ground motion, the test set-up and the instrumentation. Additionally, initial results of the shake table test are presented with a first interpretation of the observed structural behaviour.

A challenging prototype building having irregularly placed shear walls in plan has been designed and tested on the AZALEE shaking table at the TAMARIS laboratory in CEA/Saclay. The research project, called ENISTAT, was funded by the SERIES project via Transnational Access to the CEA/Saclay facility in France. The project has three main objectives: (1) Study the behaviour of the mock-up under increasing bi-directional horizontal synthetic earthquake records; (2) Attempt to evaluate the experimental results using modern experimental techniques for data acquisition; (3) Implement & monitor the performance of a new structural element that allows for wall-slab connection to reduce thermal energy losses. Rutherma elements were used only at the second floor level as a connection member between the shear walls and the slab. After initial low level tests, seismic tests having PGA’s of 0.1, 0.2, 0.4, 0.6 and 0.8 g were applied consecutively. During the first three tests, i.e. up to 0.4 g, no significant damage was observed in the structural members except minor hairline cracks on the spandrel beams. At the 0.6 g test, more cracks in beams were observed without any major crack in walls. During the 0.8 g test, separation of the shear wall member from the foundation was observed on the flexible side. No damage on the Rutherma breakers was observed.

The BRACED project investigated the ultimate behaviour of concentrically braced frames (CBFs). The research programme was designed to validate empirical models for the ductility capacity of hollow section bracing members and recent proposals for the improved detailing of gusset plate connections, to identify active yield mechanisms and failure modes in different brace member/connection configurations, and to provide essential data on the earthquake response of European CBFs. The central element of the integrated experimental and numerical research programme is a series of shake table experiments on full-scale model single-storey CBFs designed to Eurocode 8 (CEN EN 1998-1:2004, Eurocode 8: Design of structures for earthquake resistance—Part 1: General rules, seismic actions and rules for buildings. European committee for standardization, 2004). Twelve separate experiments were performed on the Azalee seismic testing facility at CEA Saclay. The properties of the brace members and gusset plate connections were varied between experiments to examine a range of feasible properties and to investigate the influence of conventional and improved design details on frame response. Each experiment examined the response of the test frame and brace-gusset plate specimens to table excitations scaled to produce elastic response, brace buckling/yielding and brace fracture. These experiments were supported by complementary quasi-static cyclic tests and correlative numerical simulations using pushover and time-history analysis using the OpenSees seismic analysis software. The outputs of the research programme represent a unique set of data on the ultimate earthquake response of CBFs with realistic brace members and connections. The principal experimental outcomes include measurements of elastic frame stiffness and its evolution with brace damage, measurements of the displacement ductility capacity of the brace specimens; an evaluation of the influence of brace connection configuration and gusset plate detailing on frame stiffness, damping and ductility; and observations on the contributions of brace and connection yielding to overall inelastic deformation of CBFs.

This paper presents the work developed to design a shaking-table test at the EUCENTRE Lab, for the evaluation of the maximum capacity of a 3-storey building subjected to earthquake loading. The structural system of the building is composed of cast-in-situ sandwich squat reinforced concrete walls using polystyrene as a support for the concrete. The purpose of this test is to verify the dynamic behavior of this structural typology under earthquake acceleration. Previous to the shakeing-table tests carried out at the EUCENTRE Lab, extensive analytical and numerical research was developed on a set of models of the building under seismic input. Also, experimental tests were performed on single r.c. panels subjected to pseudo-static cyclic loading. The structural specimen was a structural system composed of cast-in-situ squat sandwich concrete walls characterized by 5.50 × 4.10 m in plan and 8.25 m in height. The input for the simulation was the Montenegro earthquake of April 1979. The construction of this building was developed outside the laboratory; it was lifted and pulled inside using hydraulic jacks and a roller system. A bracing system was developed to assure the integrity of the structure during the transportation process. This chapter presents some preliminary results of the shaking-table tests.

This paper describes the experimental procedures and presents preliminary results of the international project entitled “High- Performance Composite-Reinforced Earthquake Resistant Buildings with Self-Aligning Capabilities”. The goal of the project was to increase our understanding of the seismic performance of woodlaminated frames with locally reinforced members. Two sets of experiments were performed. First, a full-scale one-story frame with relatively rigid connections was tested on a shaking table, Kasal et al. (J Perform Constr Fac, 2013). To achieve a stiff connection, hardwood blocks and self-tapping screws 120–250 mm long were used to facilitate the connection between beams and columns. Next, a scaled three-story frame was tested. Highly stressed regions of beams and columns of the second frame were reinforced with glass fiber (GF) sheets to mitigate potential brittle failure in anticipated weak zones. Frictional connections between beams and columns permitted a control of the magnitude of dissipated energy in the system. The connections were expected to behave stiffly under small excitations, dissipate energy through friction during moderate seismic excitation, and degrade at higher seismic loads. While the friction can be relatively well predicted, the degradation of the connection cannot, due to the uncertainty in properties of wood.

Structural connections are a major feature for the seismic performance of precast concrete shear walls. A joint connecting beam (JCB) is proposed as an alternative to the widely used technologies of mechanic sleeve and sleeve-mortar splicing connections to connect the reinforcement of precast concrete shear walls. The JCB is composed of staggered splicing rectangular steel loops protruding from the wall panel, an assembly of longitudinal steel bars and stirrups, and casted concrete. This paper describes the horizontal cyclic loading tests performed on six slender precast concrete shear walls with the JCB subjected to constant axial loading and located at different heights along the wall; the performance of the specimens is compared with that of a monolithic shear wall. The collapse of the test specimen, the top lateral loading-displacement hysteretic curve, lateral load capacity, deformation, energy dissipation, stiffness degradation and reinforcement strain were analyzed. The test results show that the shear bearing capacity of precast concrete shear walls with a JCB is slightly smaller than that of a monolithic shear wall; the failure mode, stiffness degradation and energy dissipation capacity of the precast shear wall specimen are similar to those of the monolithic shear wall specimen, with a superior ductility factor. The results indicate that the concept and detailing of the joint connecting beam is feasible and applicable to precast concrete shear wall structures. The proposed system has the advantages of no welding, no costly mechanic sleeves and speeds up the construction progress of precast concrete structure. Recommendations on structural design are proposed for further application in the field.

In the framework of the SAFECAST Project, a full-scale three-storey precast building was subjected to a series of pseudodynamic (PsD) tests in the European Laboratory for Structural Assessment (ELSA). The mock-up was constructed in such a way that four different structural configurations could be investigated experimentally. Therefore, the behaviour of various parameters like the types of mechanical connections (traditional as well as innovative) and the presence or absence of shear walls along with the framed structure were investigated. The first PsD tests were conducted on a dual frame-wall precast system, where two precast shear wall units were connected to the mock up. The first test structure sustained the maximum earthquake for which it was designed with small horizontal deformations. In the second layout, the shear walls were disconnected from the structure, to test the building in its most typical configuration, namely with hinged beam-column connections by means of dowel bars (shear connectors). This configuration was quite flexible and suffered large deformations under the design level earthquake. An innovative connection system, embedded in the precast elements, was then activated to create emulative beamcolumn connections in the last two structural configurations. In particular, in the third layout the connectors were restrained only at the top floor, whereas in the fourth layout the connection system was activated in all beam-column joints. The PsD test results showed that, when activated at all the floors, the proposed connection system is quite effective as a means of implementing dry precast (quasi) emulative moment-resisting frames.

As part of the SERIES project, a number of physical model tests were conducted in the Laboratory of Soil Mechanics, National Technical University of Athens, to investigate fault rupture propagation through sand and its interaction with caisson foundations. Both normal and reverse faulting was simulated parametrically by varying the position of the caisson relative to the emerging fault rupture. The displacements and rotation of the foundation, as well as the deformation of the soil mass were recorded through image analysis and laser scanning of the ground surface. In the first case, high-resolution digital cameras were utilized to capture images of the deformed soil, which were then processed through image analysis. In the latter case, a novel technique was developed and applied through a custom system, designed and constructed inhouse. After each displacement increment the ground surface was scanned with 8 laser displacement transducers, travelling along the specimen at constant speed, producing a digital relief of the deformed surface. The caisson is shown to act as a kinematic constraint, substantially altering the rupture path. Its horizontal and vertical movement and rotation are a function of its position relative to the fault rupture. Depending on the latter, a variety of interaction mechanisms develop, such as bifurcation of the rupture path and diffusion of plastic deformation.

In numerical simulation of soil media, the problem of wave propagation is of a great importance. Proposed in this paper is a new formulation of infinite elements which can be used in numerical simulation of wave propagation problems in infinite domains. In numerical simulation of wave propagation, the finite elements are used to model the near field, whereas the infinite elements are used to represent the behaviour of the far field. Formulations and various implementation aspects of the proposed infinite elements are illustrated. The accuracy and efficiency of the proposed approach is considered by comparing the obtained results with analytical and other numerical results. For better explanation, a couple of examples were analyzed such as one dimensional wave propagation problems arising from the Heaviside step function and impulse functions. In order to get a more complete insight, two dimensional wave propagations in soil medium were considered and the results are presented accordingly. Finally, a soil layer subjected to seismic excitation was analysed. The new infinite element was developed using the User Programmable Features of the ANSYS software, which enables creating new elements within the robust ANSYS core algorithm. The main advantage of the proposed infinite elements is that they can be used directly within a finite framework with minor modifications such as the Jacobian matrix and added absorbing properties. The performed analysis using the infinite elements shows very promising results and provides a good tool for simulation of boundary conditions.

This paper reports the outcomes of a series of shaking table tests performed at the EQUALS lab of Bristol University in the framework of the project entitled “ASESGRAM”, carried out within the Transnational Access Activities of the SERIES Project. The experimental test campaign was devoted to the evaluation of the effective behaviour of flat-bottom silos filled with grain under dynamic excitation, and to the experimental verification of the results obtained in previous analytical research work by the authors (Silvestri et al., Bull Earthq Eng 10:1535–1560, 2012). This analytical counterpart starts from the basic assumptions of Eurocode 8 (EN 1998–4, Eurocode 8. Design of structures for earthquake resistance, Part 4: silos, tanks and pipelines, CEN, 2006) excluding the calculation of horizontal shear forces among consecutive grains. This difference leads to a new physically-based evaluation of the effective mass of the grain, which horizontally pushes on the silo walls. The analyses are developed by simulating the earthquake ground motion with time constant vertical and horizontal accelerations and are carried out by means of simple dynamic equilibrium equations that take into consideration the specific mutual actions developed in the ensiled grain. The findings indicate that in case of squat silos (characterized by low, but usual, height/diameter slenderness ratios), the portion of the grain mass that interacts with the silo walls turns out to be noticeably lower than the total mass of the grain in the silo and the effective mass adopted by Eurocode 8 (EN 1998–4, Eurocode 8. Design of structures for earthquake resistance, Part 4: silos, tanks and pipelines, CEN, 2006). Different series of tests have been performed with different heights of the ensiled material to simulate a more or less squat silo. In the tests, the ensiled material consisted of Ballotini Glass. In this paper, the silo specimen and the test instrumentation are described, and the test program and the results are presented. Strong qualitative indications are obtained, which basically confirm that the wall-grain friction coefficient plays an important role in the actions at the base of the silo walls.

This chapter aims at identifying, describing and quantifying multi-building interactions and site-city effects through experimental, theoretical and numerical crossed-analysis. Multiple Structure-Soil-Structure interactions are investigated through an idealized experimental model of a city on a soft layer the properties of which are simple enough to be reproduced in numerical and theoretical models. The experimental set-up is designed to provide a good matching between the fundamental frequencies of the city and of the layer. Experimental results show (i) drastic changes in the layer’s response with two low amplitude resonance peaks favorable to longer coda and beatings and (ii) unconventional depolarization effects. The resulting data is compared with the theoretical city-impedance model derived by homogenization methods (Boutin and Roussillon, Bull Seismol Soc Am 94(1):251–268, 2004) and with a 2D hybrid BEM-FEM numerical model (Padrón et al., Cálculo de estructuras de barras incluyendo efectos dinámicos de interacción suelo-estructura. Master thesis, Universidad de Las Palmas de G.C., Spain. http://hdl.handle.net/10553/10472, 2004). The specific features of multiple interactions are successfully reproduced by both models providing a qualitative and quantitative agreement with experimental results and with one another.

Seismic safety of underground facilities such as pipelines, culverts, subways and tunnels becomes an essential requirement for sustained economic and social development. Many engineers earlier thought that the underground structures had been inherently safe against earthquakes, but then, especially after the failure of some underground facilities during 1995 Kobe, Japan, 1999 Kocaeli, Turkey and 1999 Chi Chi, Taiwan earthquakes the safety evaluation of underground structures has become a major concern of the engineers. This research aims to investigate the dynamic response of box shaped underground structures buried in dry sand. For this purpose, a series of centrifuge tests were carried out under harmonic sinusoidal motions by considering the nonlinear behavior of both structure and surrounding soil. Hence, response of model ground and deformation of the buried models were examined with special reference to the dynamic soil structure interaction. A specific variable considered in this study is the rigidity of buried box structures. Three different models with varying rigidities were used in the tests. Different deformations schemes of the sidewalls were analyzed under harmonic motions. Results of the centrifuge experiments were evaluated and compared to the predictions obtained from closed-form solutions recommended in the literature.

A series of dynamic centrifuge tests on rectangular tunnel models embedded in dry and saturated sands is presented. The tests were carried out at the geotechnical centrifuge facility of IFSTTAR in Nantes, France, within the Transnational Access action DRESBUS II funded by the SERIES research project. The experimental program focused on salient parameters controlling the dynamic response of the soil-tunnel system such as soil-to-tunnel relative flexibility, soil-tunnel interface characteristics, soil saturation and characteristics of the input motion. Among the innovative features of the experimental set up were sand pluvation, models saturation and tunnels waterproofing techniques. A dense monitoring scheme was implemented, including accelerometers, displacement sensors, pore pressure sensors and specially designed extensometers for measuring side-wall deformations and diagonal distortion of the tunnel. A preliminary interpretation of the experimental data revealed the effect of the above parameters on the racking deformation modes of the tunnel sections.

The Chapter summarizes representative experimental results from dynamic centrifuge tests that were performed on square model-tunnels embedded in dry sand. Two model-tunnels were used, a rigid and a flexible one, with the latter model collapsing during the test. The tests were carried out at the geotechnical centrifuge facility of the University of Cambridge, within the Transnational Access action of the SERIES Research Project (TA Project: TUNNELSEIS). The experimental data is presented in terms of acceleration in the soil and on the tunnel, earth pressures on the side walls of the tunnel and internal forces of the tunnel lining. The collapse mechanism of the flexible tunnel is presented and discussed based on the recorded response. The goal of this program is two fold: to better understand the seismic behaviour of this type of structures, and to use the high quality data to validate the numerical models, which should be used for the design of rectangular embedded structures. The interpretation of the results reveals (i) “rocking” response of the tunnels in addition to racking, (ii) existence of residual values on the earth pressures on the side walls and on the internal forces after shaking, affected significantly by the flexibility of the tunnels, and (iii) modification of the induced shear wave field from the presence of the shallow tunnel, which in turn is affecting its seismic response. These issues are not well understood and often are not considered by simplified seismic analysis methods.

The seismic performance of a square footing, resting on a liquefiable sand layer, with a non-liquefiable clay crust, is examined herein, with the aid of three centrifuge experiments. Emphasis is given on the seismic settlements of the foundation, while it is for the first time attempted to measure its (degraded) post-shaking bearing capacity, with the aid of a hydraulic piston, specially programmed to push the footing to failure, immediately after the end of shaking and before the dissipation of excess pore pressures. Aimed to examine the effect of clay crust thickness H on foundation performance, the experiments were performed for H = 2/3B, B and 5/3B, with B being the width of the footing. Following a brief presentation of the testing configuration, soil properties and excitation characteristics, the experimental results are presented and evaluated through comparison with relevant numerical and analytical predictions. Thus, the beneficial effect of the clay crust thickness H is quantitatively substantiated and the existence of a “critical clay crust thickness”, beyond which subsoil liquefaction does not deter foundation performance, is experimentally verified.

This paper describes the experimental work carried out under ‘PROPWALL’, a research project on the seismic performance of embedded walls in saturated sand carried out by Transnational Access to the Turner Beam Centrifuge of the University of Cambridge. The experimental equipment, the model preparation and the monitoring devices are described in detail. The results are presented in terms of accelerations, wall deflections, bending moments and excess pore pressures, as monitored by means of the devices installed on the walls and within the soil mass.

The SERIES project “Experimental and Numerical Investigations of Nonlinearity in soils using Advanced Laboratory-Scaled models” (ENINALS) was focused on the centrifuge modeling of seismically-induced strains vs. stratigraphic features and it was applied to the heterogeneous alluvia of the Tiber River in the Rome historical centre. Four soil samples, representing two homogeneous soil columns (only clay and only sand respectively) and two heterogeneous soil columns (including a clay level between two sand ones) were tested in the IFSTTAR centrifuge. The applied dynamic input represents the maximum expected seismic action in Rome and it was reproduced at the centrifuge shaking device following three approaches: (i) a natural time history, (ii) an equivalent sinusoidal signal, and (iii) a multifrequential equivalent signal derived by the recently proposed LEMA_DES approach. The here reported preliminary results: (i) demonstrate the reliability of a “cut and install” procedure for realizing the saturated multilayer samples; (ii) give new insights on the reliability of multifrequencial dynamic equivalent signals for scale-reduced analogical modeling.

A review of the commonly used viscous model for damping is presented as well as of expressions recently developed for the expected value of the first mode damping ratio of soil-structure systems. The statistical expressions show that the parameter that is best correlated with damping in steel and concrete buildings is building height while in wood and masonry structures it is the spectral acceleration at the fundamental period. The paper illustrates that the high variance with which damping ratios are typically identified (compared to frequencies) is the result of low Fisher information in the (relatively short) seismic response transients.

At IZIIS, within the framework of the SERIES project, two types of wireless sensors have been developed. The first one, the MIMRACS (Micro Integrated Measuring Recording and Communication System) sensor, presents an intelligent self-controlled high integrated GPS/GPRS/WEB based micro processing digital 3D measurement device, with the possibility of power independence suitable for measuring, storing and transferring data at the exact time of their appearance. The MIMRACS has 3 MEMS Model 3028 piezoresistive accelerometers, one for each orthogonal axis, a microprocessor, a 24-bit A/D converter, programmable amplifiers, a programmable trigger, an inclinometer, a gyroscope, GPS/GPRS/GSM modules, Flash memory, USB communication and power supply. The other one, SAWARS (Standalone Wireless Acceleration Recording System), is developed on a similar platform as the MIMRACS, with the difference that it is more compact and lighter, with one Model 3028 piezoresistive accelerometer and a Zigbee module and protocol for wireless communication. Both sensors are suitable for laboratory testing (shake table testing), full scale measurements (ambient and force vibration) and seismic and health monitoring of structures. The MIMRACS sensor may also be used as a standalone seismic station as part of a network for monitoring and recording strong motion data. MIMRACS sensors have been tested in laboratory conditions by shake table—standalone testing and testing on models, while recorded signals are compared to traditional wired accelerometers. The comparison results show very good correlation. In this paper, both wireless sensors are presented in detail, including their hardware and software, as well as a comparison of results from various experimental tests.