Flat slab buildings for commercial, office, and residential use are built in many countries. Yet, their performance under seismic and gravity actions is still not very well understood. Many studies have been carried out in North America and Asia, but European research is lagging behind and Eurocode 8 does not fully cover the design of buildings with flat slab frames used as primary seismic elements.
The SlabSTRESS Transnational Access project at the ELSA Reaction Wall of the Joint Research Centre studied the response of flat slab reinforced concrete buildings under earthquake and gravity loads. The objective of the project was twofold: to study the ultimate capacity and failure modes of flat slab structures with different layouts of reinforcement and to verify the effectiveness of steel studs for the repair of damaged slab-column connections.
The test specimen was a full-scale two-storey flat slab structure with plan dimensions 9×14 m. Punching shear reinforcement was placed only in the slab of the second storey. In addition, uniformly distributed horizontal reinforcement was placed in half of the slab at each floor, while, in the other half, the same amount of horizontal reinforcement was mostly concentrated close to the columns.
The testing programme included two pseudodynamic tests (hybrid simulation of the physical specimen and numerical shear walls) with input corresponding to the Serviceability and Ultimate Limit States and three quasi-static tests under imposed cyclic displacement with increasing amplitude (three slab-column joints were strengthened after the first cyclic test).
The project provided new knowledge on the response of flat-slab structures with different detailing rules that could not be captured in previous tests on column-slab sub-assemblies. The results will help calibrate models, verify the Eurocode and Model Code models for punching shear, and develop new rules for the deformation-based design and detailing of flat-slab structures subjected to earthquake and gravity loads, as well as to improve the design of flat-slab frames as primary seismic structures.
The results of the project are being exploited by the 14 users of the SlabSTRESS project and by 19 research groups from 13 countries, who participate in an ongoing blind prediction competition.
More information: www.slabstress.org, www.researchgate.net/project/SlabSTRESS
All experimental and documentation data will be made available through the SERIES Data Access Portal after the completion of the blind prediction competition.
SERA work package |
WP 9 / TA 2 |
Authors |
I. Lanese, A. Pavese |
Keywords |
Full-scale silo, seismic isolation, dynamic testing, shake table testing. |
The transnational access (TA) framework of the SERA project gave European and worldwide researchers the opportunity to target an extremely wide range of crucial aspects in earthquake engineering and seismology fields, trough the access to the largest collection of high-class European Research Infrastructures. The EUCENTRE experience, in addition to the coordination of the TA framework, resulted in relevant contributions to earthquake engineering fields in which experimental data on full-scale structures and non-structural components is very limited.
EUCENTRE TA activities encompass real time dynamic testing of innovative optimized variable-friction seismic isolation devices, silo structures and industrial facilities with respect to early warning and protection from dangerous leakage and both structural and non-structural damage.
In Figure 1, a real full-scale silo tested on the EUCENTRE shake table is pictured. The structural design of steel flat-bottom ground-supported silos containing granular material represents a challenging issue. They differ from many other civil structures since the weight of the silo structure is sensibly lower than the one of the ensiled particulate material and, in case of earthquake ground motion, the particle-structure interaction plays a fundamental role on the global dynamic response. The complex mechanism through which the ensiled material interacts with the silo wall has been studied since the XIX century. Nonetheless, several issues are still to be addressed regarding “grain-silo systems” and structural failures still occur, with potential loss and spread of huge amount of the ensiled content. To this end, an extensive experimental campaign with several parametric shake table test runs has been carried out. A wide spectrum of related aspects has been targeted, such as the dynamic characterization (frequency, damping ratio, amplification, etc.) of such complex silo-grain system, the experimental assessment of the static pressure (during and at the end of the filling phase), and the seismic dynamic over-pressures exerted by the ensiled material on the silo wall. Furthermore, the assessment of the benefits obtained introducing a seismic isolation system based on curved surface sliders at the base of the silo has been carried out.
In order to fully exploit the potential of this testing campaign, a fruitful collaboration between EUCENTRE and worldwide researchers as well as a deeply analyzed specific selection of a variety of shake table input signals were successfully carried out within the testing campaign preliminary phases.
Journal and conference publications are currently either under review or in preparation.
The SERA Deliverable D9.1 submitted on M24 of the project include detailed information on the above described experimental activity.
All data will be included in the SERA database.
SERA work package |
WP 10 / TA 3 |
Authors |
M. D’Aniello, R. Landolfo, L. Di Sarno, A. Le Maoult, G. Rastiello |
Keywords |
Steel moment resisting frames, Detachable Joints, ductile claddings, Near Fault earthquake, Seismic design |
The FUTURE testing campaign aims to qualify the behavior of steel moment frames equipped with different types of replaceable beam-to-column joints, as well as to investigate the influence of energy-efficient ductile non-structural claddings under near-fault (NF) seismic scenarios. Therefore, a 50-ton scale 2:3 model was designed and manufactured.
The experimental mock-up is a two-story one-bay steel frame (5 m x 5 m) that has been sub-structured from a reference steel building that is a typical example of archetype for multi-story office building of the standard EU practice. It has been designed to detach and to replace easily all components that will experience plastic deformation. In particular, three types of beam-to-column joints are examined, namely reduced beam section (RBS), haunched (H) and extended stiffened (ES) sections.
The mock-up is ready and some preliminary tests have already been conducted for signal testing (empty shake table). However, the experimental campaign has not started yet, as due to the unpredictable on-going COVID-19 crisis which is currently affecting all Europe, especially Italy and France, the mock-up could not be delivered to CEA site (still blocked in Italy).
All experimental data are freely available at http://ged_laboweb.sylos.com/GED_LaboWEB and on the European database at http://www.dap.series.upatras.gr/
SERA work package |
WP 10 / TA 3 |
Authors |
M. Fragiadakis, L. Di Sarno, A. Saetta, M.G. Castellano, I. Rocca, S. Diamantopoulos, V. Crozet, I. Politopoulos, T. Chaudat, S. Vasic, I.E. Bal, E. Smyrou, I. Psycharis, T.C. Hutchinson, L. Berto |
Keywords |
Earthquake Engineering, museum contents, statues rocking, shake table tests |
In the framework of SEREME project, an extensive experimental campaign on the seismic response of museum artefacts, with emphasis on statues and busts, was performed using AZALEE shake table of CEA in Saclay, France. The objective of this experimental campaign was to give insight on the seismic behaviour of statues and busts as well as to evaluate the effectiveness of two different mitigation methods used to improve the seismic behaviour of these artefacts. A total of five couples of real scale marble artefacts were tested, three busts installed on marble pedestals and two statues. Seven different testing arrangements were considered during this experimental campaign and a total of 281 seismic tests were performed. Regarding the employed mitigation techniques, two different isolators types were used. First, a local isolation method, based on SMA wires, was used in order to enhance the seismic behaviour of a single artefacts. Then, three pendulum isolators were employed in order to isolate a floor on which a group of artefacts (2 or 3 artefacts) was installed. In order to give a direct evaluation of the isolators effectiveness, for each test configuration, a couple of two similar artefacts were tested together in an isolated and a non-isolated arrangement. Furthermore, to evaluate the influence of the frequency content of the excitation as well as the directionality of the seismic excitation, 12 different waveforms were applied to the shake table (7 uni-directional motions, 3 bi-directional motions and 2 tri-directional motions). Regarding the instrumentation, the artefacts motions were recorded using both accelerometers, gyroscopic and displacement sensors.
The achievement of this experimental campaign are:
All experimental data are freely available at http://ged_laboweb.sylos.com/GED_LaboWEB and on the European database at http://www.dap.series.upatras.gr/
SERA work package |
WP 11 / TA 4 |
Authors |
P.X. Candeias., A.A. Correia , A. Campos Costa, C. Calderini , N. Bianchini, M. Rossi , N. Mendes, P.B. Lourenço, P. Casadei |
Keywords |
Earthquake Engineering, shaking table, masonry structures, cross vaults, retrofitting |
This report introduces one of the H2020 SERA project transnational access experimental activities, involving 3D shaking table tests on masonry cross vaults. Widely spread among monumental masonry buildings (mainly in churches and palaces), masonry cross vaults are some of the most vulnerable horizontal structural elements. Acting as a ceiling and a structural horizontal diaphragm with significant mass, vaults’ mechanical behaviour affects the overall seismic response of buildings, in terms of strength, stiffness, and ductility. Moreover, their local damage and collapse may produce significant losses in terms of cultural assets and casualties.
The full experimental campaign consisted of three different testing phases and specimens: a 1:5 reduced scale cross vault made of 3D-printed blocks assembled with dry joints, a 1:1 scale model of a brick unreinforced masonry cross vault and a 1:1 scale model of a brick masonry cross vault reinforced with the TRM technique, covering the lack of knowledge in this field. The overall research project included the initial design of the test specimens, their construction, the preparation of the test setup, the shaking table tests and the analysis and post-processing of results.
The main focus of the research was the study of the shear failure along with the shell of the vault itself, which very often occurs during earthquakes in monumental buildings. From the experimental and numerical studies performed, it was possible to observe a systematic location of the hinges in concordance with Heyman’s theory. The shear failure was obtained by designing specific boundary conditions, showing, as expected, the main concentrations of damage along the rib of the vault. The capacity of the structure under dynamic loading is higher than the capacity obtained from previously performed quasi-static tests.
The expected outcomes have been satisfied, namely: evaluation of the maximum acceleration applicable to cross vaults, evaluation of the diaphragm stiffness and ultimate displacement capacity of cross vaults, identification of the damage mechanisms, evaluation of the role of the seismic input on the dynamic response of these vaults, comparison between static and dynamic tests and evaluation of the influence of the test type.
In conclusion, by improving the knowledge and the modelling/analyses approaches of vaulted masonry structures, this research contributes to a better safety assessment of heritage buildings and to a better design of strengthening interventions, thus contributing to an improvement of the safety and preservation policies of heritage buildings in the EU.
The test results are disseminated to the wider scientific community through the open access experimental database of the SERA project.
SERA work package |
WP 11 / TA 4 |
Authors |
AA. Correia., P.X. Candeias., A. Campos Costa., S. Pampanin, J. Ciurlanti., S. Bianchi, D. Perrone, M. Palmieri, D. Grant, G. Granello, A. Palermo, A. Filiatrault |
Keywords |
Earthquake Engineering, shaking table, performance-based design, self-centering, dissipaters |
This report introduces one of the H2020 SERA project transnational access experimental activities, involving 3D shaking table tests of a two-storey 1:2 scaled fully prefabricated dry-assembled building. It contains two-bay timber-concrete low-damage seismic frames, post-tensioned rocking dissipative timber seismic walls and comprising different low-damage or high-performance non-structural components (fiber-reinforced gypsum and masonry partitions/glass and GFRC facades). The project aimed to promote a research effort within the European environment for the development of an integrated low-damage building system.
The high socio-economic impact of moderate-to-strong earthquakes and the increased public awareness of seismic risk have facilitated the acceptance and implementation of damage-control technologies, whose development is nowadays demanded. Performance-based design criteria and objectives need a shift towards a low-damage design approach and technical solutions for engineers and stakeholders to control the performance/damage of the entire building system, including superstructure, foundation systems and non-structural elements. Moreover, this new design philosophy should be considered to define an ultimate “earthquake-proof” building system.
The full experimental campaign consisted of three different testing phases and specimen configurations, i.e. skeleton building, skeleton building with internal gypsum partitions, and building with an integrated system made of an internal masonry wall and exterior envelopes. The overall research project included the initial design of the test building and its structural and non-structural detailing, the construction of the specimen, the preparation of the test setup, the shaking table test and the analysis and post-processing of results.
Concerning the global performance, the specimen behaved as expected with demand parameters coherent with the ones calculated during the design process. Regarding the non-structural components, the in-plane behaviour confirmed the good response of these components due to the introduced non-structural detailing. The out-of-plane accelerations allowed to define the relative amplification factors which were estimated within a range of 2-3 for all non-structural systems when compared to the building levels, apart from the masonry infills where the amplification is found to be around 2.
The dynamic shaking table tests confirmed the seismic performance of the low-damage skeleton for timber-concrete structures. Furthermore, it proved the high potential for implementing an integrated low-damage or high-performance structural/non-structural building solution for the next generation of buildings. On the other hand, the observed (low) damage conditions will suggest improvements to the system detailing to be applied and studied in future research.
The test results are disseminated to the wider scientific community through the open access experimental database of the SERA project.
SERA work package |
WP 11 / TA 4 |
Authors |
A.A. Correia, P.X. Candeias, F.L. Ribeiro, I. Tomić, A. Penna, M. DeJong, C. Butenweg, I. Senaldi, G. Guerrini, D. Malomo, K. Beyer |
Keywords |
Earthquake Engineering, shaking table, unreinforced masonry, adjacent structures, dynamic interaction |
Historical city centres throughout Europe have developed and densified during long periods. The densification caused the historical centres to be characterized by masonry building aggregates. In building aggregates, facades of adjacent buildings often share a structural wall. Furthermore, the connection between the older and the newer units is often made through weakly interlocking stones or by a dry joint. Since the densification was often a process spanning throughout long periods, it is not uncommon for adjacent units to be constructed of different materials, to have different distributions of openings and different floor and roof heights. However, advances in the development of analysis methods for such aggregates have been impeded by the lack of experimental data.
This report thus introduces one of the H2020 SERA project transnational access experimental activities, involving 3D shaking table tests of a half-scale stone masonry aggregate. It consists of two building units with a common wall and different floor heights. The walls are constructed as double-leaf stone masonry without interlocking between the leaves, except at corners and openings. The overall research project included the initial design of the building aggregate, the construction of the specimen, the preparation of the test setup, the shaking table test and the analysis and post-processing of results. It contributes significantly to the collection and dissemination of experimental data on the interaction of building units in order to understand better the phenomena involved in their dynamic behaviour.
To ensure that the results can be compared with previous test campaigns, the construction material was reproduced the one used for previous shaking table tests, as much as possible. Nevertheless, the research project includes a complete set of material characterization tests, including a large number of tests on mortar samples and wallettes tested in simple and diagonal compression.
The experimental data produced is also valuable to calibrate adequately the substantial number of complex non-linear models and modelling approaches required to capture the buildings' response. There were numerous participants from academic and professional teams in the blind prediction competition organised within the project, which confirms the interest of the research carried out.
The test results are disseminated to the wider scientific community through the open access experimental database of the SERA project.
The scope of the ARISTA project (project team: Cyprus University of Technology, Ecole Centrale de Nantes, DENCO Structural Engineering) was to experimentally study the seismic behaviour of a 1:1.5 scaled three-storey two-bay RC frame with smooth bar reinforcement. The frame was designed using gravity loads only and lacked any seismic design or detailing. The experiment in one of the few worldwide, in which a specimen with smooth bar reinforcement and size (i.e., number of storeys and full scale) was tested. It provided invaluable information for design guidelines and code rules.
The ARCO project (project team: University of Liege, Liege, University of Lisbon, Aarhus University) focused on the effect of axial restraint on the seismic behaviour of short coupling beams. This effect is generated by the interaction between the coupling beam and the adjacent shear walls. As the beam cracks under loading, it tends to extend in the longitudinal direction and pushes upon the walls. Because of the large stiffness of the walls, compression force develops in the beam, which limits the opening of the cracks. As a consequence of this effect, beams are characterised by a shear-dominated response, being susceptible to brittle shear failures. The only test variable was the level of axial restraint. A fourth beam was tested under a large inelastic pulse in one direction followed by a push to failure in the opposite direction. This unconventional cyclic loading scenario can be associated with a near-fault pulse-type ground motion.
The project HitFrames (project team: University Liverpool, University of Naples Federico II, University of Ljubljana, University College London, University of Toronto and FIP Industriale) investigated effective methods for the seismic assessment and retrofitting of existing non-compliant steel frames. Recent earthquakes in the Mediterranean region demonstrated that present steel, multi-storey, residential, framed buildings are designed primarily for gravity loads, exhibiting low energy absorption and inadequate dissipation capacity under seismic loadings. The low lateral stiffness and strength of the steel framed structures and the slender masonry infills induce significant lateral drifts, buckling and/or fractures to structural steel members. Additionally, the current provisions for the seismic performance assessment of existing steel structures are scarce and they do not account for the presence of the infills.
SERA work package |
WP 13 / TA 6 |
Authors |
G. Fiorentino, C. Cengiz, F. De Luca, M. Dietz, L. Dihoru, D. Lavorato, D. Karamitros, B. Briseghella, T. Isakovic, Ch. Vrettos, A. Topa Gomes, A. Sextos, G. Mylonakis and C. Nuti |
Keywords |
Seismic Soil-Structure Interaction, Integral Bridges, Shaking Table, backfill/pile isolation, Eurocode 8. |
Integral Abutment Bridges (IABs) are characterised by the absence of bearing supports and expansion joints between the deck and the abutments/piers, thus reducing construction and maintenance costs. IABs are characterised by a complex Soil-Structure Interaction (SSI) with respect to conventional bridges; therefore, the static and dynamic effects of the SSI should be considered in the design. Despite the large number of IABs worldwide and related numerical studies, few experimental tests were performed, and codes lack related seismic prescriptions, including Eurocodes.
Project SERENA aimed at conducting experimental shaking table tests on a scaled bridge model inserted into the large “shear stack” soil container of the EQUALS – BLADE Laboratory of the University of Bristol. The novelties of the project are the following:
The bridge model was scaled to match the dimensions of the soil container on the shaking table. In doing so, attention was paid to the development of appropriate scaling laws that will allow extending the results obtained with the scaled model to real scale IABs. The results in terms of accelerations allow recognising some patterns in the seismic response of the model and the soil. In the backfill, it was found that the inclusion of layers of PU foam increases the accelerations in the soil while, on the other, its presence reduces the accelerations of the bridge, which are smaller than in the surrounding soil. After the tests, settlements in the configurations with compressible inclusion layers behind the abutment wall were larger. This result indicates the necessity of a careful design of approaching slabs. The pile disconnection is promising as well. Scaling laws here developed will permit to analyse real backward bridges. The results can be used as a first step towards developing engineering provisions for IABs which are absent from existing regulations such as Eurocode 1998.2 (Bridges). Further experimental and numerical analyses can be proposed based on this research such as the validation of scaling methodologies, use of different backfill soil, different geometries of backfill soil or the development of behaviour factor for IABS.
Data used in the publications are available in full within each publication. Data access can be granted through the SERA project data portal. Data upload onto Celestina software is ongoing
SERA work package |
WP 13 / TA 6 |
Authors |
F. Vassiliou, M. Broccardo, C. Cengiz, M. Dietz, L. Dihoru, S. Gunay, K. Mosalam, G. Mylonakis, A. Sextos, B. Stojadinovic |
Keywords |
Rocking structures, seismic excitation, model verification, response modification, earthquake engineering |
The 3D rocking oscillator model is useful because it describes the seismic behavior of unanchored equipment and because unrestrained rocking has been suggested as a seismic response modification technique. A major critique against rocking systems has been that their responses are not only hard to predict by existing numerical models, but that the response is inherently unpredictable. Therefore, in the context of earthquake engineering, the objective of this study is to answer two important questions: Is wobbling motion inherently unpredictable? If not, are existing models good enough to predict the response?
To this end, an experimental campaign has been designed to obtain observations of wobbling motion to be compared with those gained from numerical simulations. Two sets of models were studied: “Free Rocking” representing unanchored equipment; and “Wobbling Frame” representing a design approach that can be used for the rocking isolation of bridges or buildings. To constrain the uncertainty in the excitation, a stochastic model was used to generate synthetic ground motion ensembles that match the physical characteristics of recorded ground motions. Each ensemble contained 100 excitations. One ensemble was used to study the Free Rocking specimens and two ensembles were used to study the Wobbling Frame.
Numerical simulation of the tests on the Free Rocking specimens is currently being performed. The response of the Wobbling Frame was the subject of an international blind prediction contest. The contestants had to predict the Cumulative Distribution Functions (CDF) of the maxima of the responses. Thirteen teams using FEM, DEM and Rigid Dynamics models responded. Notably, the same model predicted the CDF of the response for one ground motion family well, while it performed poorly on the other (Fig. 1). This finding shows that there is space for improvement in modelling of wobbling structures. Interestingly, both FEM and DEM can overestimate or underestimate the response depending on the input parameters used.
Moreover, the best models used zero Rayleigh damping and only relied on friction between the contact surfaces to dissipate energy, showing that damping models should be physics-based. An analytical dynamics model that prevents sliding and twisting was found to consistently overestimate the response of this structure because it did not model sliding. A more involved investigation on the modelling parameters that optimize the prediction of the Wobbling Frame is the subject of current research.
Data upload onto Celestina software is ongoing.
Blind prediction contest data is available at: https://peer.berkeley.edu/news-and-events/2019-blind-prediction-contest
SERA work package |
WP 13 / TA 6 |
Authors |
Di Michele, E. Spacone, G. Camata, G. Brando, A. Sextos, A. Crew, G. Mylonakis, M. Dietz, L. Dihoru, H. Varum, G. Manolis and P. Casadei |
Keywords |
Earthquake engineering, three-leaf masonry walls, effects of vertical ground motion component, masonry wall reinforcement |
The main scope of the RE-Bond (REsponse of as-Built and strengthened three-leaf masONry walls by Dynamic tests) project was to investigate the effects of the vertical ground motion component on the response of three-leaf walls, representative of buildings found in historical canters in Central Italy.
Squat rectangular and T-walls were tested on the shake table as-built and after reinforcement with composite cross ties. The selection of the recorded ground motion signal focused on near fault records with an important vertical component. The walls were designed to represent walls at the top level of a masonry building with low axial load. Also, the walls were designed to fail in shear. The tested specimens showed indeed shear failure with clearly visible diagonal cracks. The wall strength decreased due to the presence of the vertical ground motion component with respect to the test with the horizontal component only. The cross ties improved the behaviour of the walls by increasing their strength. Reinforcement of the masonry walls was applied by the Italian Kerakoll group): GeoSteel connectors with mortar injections were added on the entire thickness of the longitudinal wall and diagonal steel connectors with mortar injections were added between the two orthogonal walls in T-walls. Reinforcement increased the seismic capacity by 20 % thanks to the presence of the connectors. Extensive numerical modelling of the tested walls accompanied the test. The test results are currently being interpreted.
Publications and openly accessible deliverables are in preparation.
Data upload onto Celestina software is ongoing.
SERA Workpackage |
WP 13 / TA 6 |
Authors |
A. Kazantzi, A. Elkady, Matt Dietz, L. Dihoru, R. De Risi, D. Vamvatsikos, D. Lignos, E. Miranda and G. Mylonakis |
Keywords |
Nonstructural component, steel fuses, peak floor acceleration, peak component acceleration, component ductility |
Community-critical buildings often face lengthy functionality disruptions due to non-structural damage triggered by even low- or moderate-intensity earthquakes. The problem lies in the dynamics of narrowband excitations appearing at the floors (and ceilings) of buildings and the corresponding resonant response of many rigidly-connected components, introducing component accelerations that can exceed by several orders of magnitude the (already amplified) peak floor response. In contrast, as was recently proven through analytical studies undertaken by members of this research team, a controlled yielding anchor could offer a reliable detuning effect that only requires a minor ductility of 1.5-2.0 to achieve substantial reductions in acceleration demands.
NSFUSE experimental project offered an actual verification of the concept at hand, by means of a series of one-dimensional earthquake simulation tests realized at the Bristol University shake table facility. The test specimen tested on the shake table was a Single-Degree-of-Freedom (SDOF) carriage-like configuration, that was able to move on two rollers supports. The test specimen was attached to its one end to two “fuse” plates, essentially acting as cantilevers to provide resistance to the sliding of the carriage. For targeting different vibration periods, the carriage was loaded with different masses, whereas by modifying the geometry of the steel fuses different stiffness and component ductility levels were attained. The shake table tests were conducted using narrow-band floor acceleration input signals that were recorded in instrumented buildings in California (USA) during three different earthquake events.
The NSFUSE experimental campaign provided concrete evidence for the benefits of designing the non-structural components (or their anchors) to respond in-elastically during earthquakes that are sufficiently strong to induce damages in such elements. In fact, it was showcased that:
All in all, the NSFUSE project offered ample evidence for the fuse concept and therefore to soon find its way in prospective design codes.
Data upload onto Celestina software is ongoing.
SERA work package |
WP 13 / TA 6 |
Authors |
D. Foti, S. Silvestri, S. Ivorra, D. Theodossopoulos, S. Baraccani, V. Vacca, R. White, M. Dietz, G. Mylonakis |
Keywords |
Groin vault, shaking table test, 3D printed blocks, frequencies, SEBESMOVA3D |
A huge number of shaking table tests was performed on a scaled groin vault model made of 3D printed plastic blocks filled with mortar.
The vault was built according to two support conditions (on four fixed supports and two fixed supports and two one-way moveable carriages equipped with lateral springs) as well as different boundary conditions along the four lateral arches (wooden panels, Plexiglas panels, cut Plexiglas panels and no panels) to account for different confinement levels.
Random signals were systematically carried out to get the dynamic properties of the vault model. Harmonic inputs with different frequencies ranging between 1 Hz and 50 Hz were imposed in one horizontal direction with increasing amplitude, up to collapse.
The presence of a gum layer in-between two following blocks has a strong influence on the global behaviour. Furthermore, it seems to govern the dynamic response of the vaulted structure, especially for high-acceleration and low-frequency harmonic inputs. The results of the experimental campaign revealed a strongly non-linear behaviour.
The most important results can be summarised as follows:
Data upload onto Celestina software is ongoing.
SERA work package |
WP 13 / TA 6 |
Authors |
A.L. Simonelli, M. Fragiadakis, A. Gajo, A.M. Kaynia, J. de Novais Bastos, G. Anoyatis, L. Di Sarno, A. Penna, D. Aliperti, I. Taflampas, S. Diamantopoulos, F.G. Esfahani, P. Kowalczyk, M. Dall'Acqua, F. Fossi, E. Marotti, F. Zotti, R. De Risi, D. Karamitros, M. Dietz, C. Taylor, G. Mylonakis |
Keywords |
Earthquake engineering, Seismic hazard, Site effects, Near-fault effects, Modal identification. |
The investigation of vertical ground motions, near-fault effects, and the ensuing soil-structure interaction is still scarce; therefore, the SHATTENFEE project aimed at investigating near-fault response of soil. To do so, the vertical dynamic behaviour of a typical soil deposit, with and without the presence of a foundation pile, has been explored experimentally by using the 6-degree-of-freedom shaking table of the University of Bristol.
A newly designed test rig, which comprises a 3.2 m high and 0.9 m diameter PERSPEX® cylinder, was utilised to experimentally analyse the vertical wave propagation of homogeneous soil in a 1:10 scaled model. For scaling the time by using frequency similitude between the prototype and the model, two values (3 and 7) were considered. A total of 209 tests were carried out during the experiments. Different types of dynamic functions and seismic records were used as input motion at the base of the cylindrical model. To perform the dynamic identification of the system, vertical noise functions and sweep functions (sinusoidal waveforms) were utilised. To assess the seismic response of the scaled model, natural records were also applied. Three near-fault vertical accelerograms were selected from the Italian Strong Motion Network (RAN database): L’Aquila 2009 (AQK station), Mirandola 2012 (MRN station) and Centro Italia 2016 (AMT station, near Amatrice).
The SHATTENFEE has investigated the vertical dynamic behaviour, in free-field conditions, of Leighton Buzzard Sand-B to estimate:
The dynamic response of the homogeneous soil is studied by analysing and comparing the acceleration time-histories recorded at different levels of the soil column; thus, the amplification function is computed which, in turn, provides the natural frequency of the soil model. When a vertical noise function with an amplitude of 0.05 g was considered, a value of 46.5 Hz was determined for the soil column.
Accurate measurements of Vp were also performed during the experiments, allowing the evaluation of the soil stiffness and frequency variation with the level of excitation (soil nonlinearity in compression). The measurement of the Vp allowed the validation of the theoretical formula for the vertical period Tv (Tv=4H/Vp).
Finally, the accelerometric data recorded at the base (along the soil columns) and the soil surface (analysed both in the time and in the frequency domain) revealed that the vertical amplification is significant confirming the results obtained from the predictions of the numerical simulations.
List all publications or openly accessible deliverables relevant to your main results.
Data upload onto Celestina software is ongoing.
SERA work package |
WP 13 / TA 6 |
Authors |
T. L. Karavasilis, G. Brando, A. Pagliaroli, S. Bhattacharya, A. Benavent-Climent, P. Kloukinas, G. Camata, M. Mariotti, M. Dietz, D. Karamitros, G. Mylonakis |
Keywords |
Soil-Structure Interaction, Steel Structures, Ductility Demand, Shaking table Tests, Earthquake Engineering |
The SSI-STEEL project (Soil-Structures Interaction effects for STEEL structures) deals with an experimental campaign to be carried out, through shaking table tests, on different steel structural systems to achieve a better knowledge about the SSI effects on their dynamic linear and nonlinear responses. In particular, three structural types are investigated, those are: i) a Concentrically Braced Frame (CBF), ii) a Moment Resisting Frame (MRF) – also considering the presence of a beam reduced end sections – and iii) dual steel frame (DSF) with a new brace-type damper made of a shape memory alloy material.
Few similar experimental studies concerning SSI effects on steel frames are currently present in literature. They are often focused on Single-Degree-of-Freedom (SDOF) systems made of a column with a mass atop or, when more complex structures are considered, only investigate specific aspects influencing the structural response of steel structures, such as the deformation in the elastic field.
On the other hand, there are non-experimental studies that compare the SSI influence on the responses of different steel structural types designed according to the same criteria, as well as that also consider nonlinear phenomena such as buckling and yielding. These are the aspects that the project aims to investigate with the goal to lead the current knowledge to a larger extent and to propose modification factors, to be expressed as a function of the soil-to-structure relative stiffness, to be included in the current design formulations that are of interest for technicians. Therefore, the proposed research represents a significant breakthrough in the field of structural/geotechnics engineering, with evident returns in terms of Code/Provisions updates and meaningful design tools that will be used by engineers in the future.
Currently, the prototypes to be tested have been designed, manufactured and shipped to the University of Bristol (UBRI). Also, the most suitable accelerograms have been selected based on numerical analyses carried out in ABAQUS, FLAC and MIDAS software. Although ten (10) laboratory days have already been provided by the host, the shaking table tests have not been carried out yet, as UBRI and the earthquake lab closed following the escalation of the COVID-19 pandemic in the UK. The pandemic also restricted the visiting researchers who could not travel to Bristol. The tests will be carried out later, after the restrictions are lifted.
The following publications have been scheduled:
Data upload onto Celestina software is ongoing.
Transnational access under the scope of the SERA project offered a combined and integrated collaboration between IZIIS and other respectable institutions from six different countries: Slovenia, Ireland, England, Greece, Turkey, and Poland. Directly involved in three different projects were the following user groups:
It is important to note that very fruitful and close cooperation was established through exchange of knowledge and experience among the institutions and industrial companies involved in the research projects. Two PhD students from IZIIS worked in partnership for their doctoral thesis using the results from the experimental testing of the models. Outcomes will be publicized through publication in international scientific and engineering journals with an excellent track record by the primary means of ensuring that the project results will reach an audience as wide as possible in a durable way. Additionally, presence at the upcoming conferences is confirmed among the participants.
All these activities will ensure the availability of a key resource for upcoming researchers that can continue the research projects using the available sources as a base in the future work.
All data including results, pictures and other information will be available on Data Access Portal.
This project used the Turner Beam Centrifuge and Servo-Hydraulic shaker at the University of Cambridge to investigate the behaviour of anchored sheet pile retaining walls in the sand under earthquake loading. Tests on walls with a variety of geometries were carried out in plane strain conditions, at a centrifugal acceleration of 60 g, preparing the models within a homogeneous dry medium-dense layer (DR = 50 %) of fine-grained siliceous Hostun sand. Both the retaining wall and the anchor plate were modelled using aluminium alloy plates with a bending stiffness at prototype scale similar to that of an AZ28 steel sheet pile profile, while the tiebacks were modelled using four steel cables hinged at both ends. Displacement profiles within the backfill sand were measured using PIV photogrammetry techniques in order to illustrate the failure mechanisms mobilised during dynamic loading.
Table 1 reports, for each test, the critical acceleration and the expected failure mechanism according to the theoretical model proposed by Caputo et al. (2018), adopting two values for the soil peak friction angle, estimated using the empirical formula proposed by Bolton (1979). In the first two tests (AF02 and AF03), a local failure of the anchor system was expected, while a global failure mechanism was predicted for the last two tests (AF04 and AF05).
From the analysis of the experimental data, it was possible to compute the evolution, during the applied earthquakes, of the internal forces in the structural members (axial force in the tieback and bending moment distribution in the wall) and the displacements of the anchor plate and the main wall. Moreover, from a preliminary analysis of the experimental results, it was possible to highlight the role played by the critical acceleration on the maximum internal forces and the maximum displacements experienced by the system during the applied earthquake.
Figure 1 shows the contours of shear strains computed during the strongest earthquake applied in test AF05 (earthquake EQ3). The shear strains mainly develop along a failure surface going from the bottom of the anchor wall to the toe of the retaining wall, suggesting a global failure mechanism of the whole anchor-soil-wall system. As shown in Figure 1, this observation is entirely consistent with the theoretical log-spiral failure surface proposed by Caputo et al. (2018).
Different projects were proposed and diverse tests were performed at the EuroProteas structure in Euroseistest: validation of 3D wave propagation models, calculation of foundation impedance functions, definition of design spectra considering soil-foundation-structure interaction, evaluation of 3d complex site effects, evaluation of the impact of structural rocking, foundation rocking isolation methods, investigation of rubber-soil mixtures as innovative isolation material, guidelines for metabarriers of seismic material, and investigation of scour effects.
All recorded data from the tests in EuroProteas and Euroseistest will be made available through the dedicated SERA-TA data portal (www.dap.series.upatras.gr).
Until now, six of planned eight TA projects at NORSAR have been finalized. The six users visiting NORSAR for these projects are all early career scientists either working on their PhDs (3) or with recently finalized PhDs (3). All finalized projects focused on different aspects of array-data analysis. Four visitors came with their own data, observed with different arrays in different environments:
The two other projects were about:
During the about one month long stays at NORSAR, all TA users became familiar with different aspects of seismic array-data processing: the influence of array geometry and instrumentation, the resolution of array specific measurements (backazimuth and slowness), different beamforming techniques, the influence of frequency contents on signal processing results, the separation of seismic signals from noise with arrays, and the importance of including the entire wavefield (vertical and horizontal components) in the analysis.
All users continue the analysis at their home institutions after the research visits. Most of the analysis was performed with NORSAR’s array processing software package, which the TA users could freely copy for later usage at their home institutions.
(Status December 2019)
All TA users had free access to NORSAR’s database during their visits and these data are openly accessible via the Norwegian EIDA node (http://eida.geo.uib.no/fdsnws/dataselect/1/).
D2.17 Final compilation of technical reports
*This version of the technical reports has to be accepted by the European Commission.