Measurement Acquisition of Soil-Structure Impedance Function
ERIES-MAS-SIF
Dataset Description
Full-scale in situ forced vibration experimental campaign aimed at measuring seismic impedance functions (IF) of a shallow, rigid reinforced concrete foundation mockup at the EuroSeistest experimental site, Thessaloniki, Greece, conducted as part of the ERIES Transnational Access programme. The experiment is designed to characterize the 6×6 impedance matrix of the soil-foundation interface through the application of monotonic, mono-frequential sinusoidal inertial forces using unbalanced motor shakers anchored to the foundation, under the assumption of rigid body mechanics. Three loading configurations are applied in sequence — vertical, horizontal, and rocking — across a frequency range of 1 to 20 Hz in 1 Hz steps. The dataset is intended as reference experimental data for the validation of numerical models and methods for quantifying and assessing soil-structure interaction under dynamic loads, with particular relevance to the seismic safety assessment of nuclear facilities on shallow foundations.
Specimens
1. Strong footing
1
Reinforced concrete foundation mockup with stiffened peripheral walls, designed to replicate in situ the configuration of a shallow, rigid foundation representative of nuclear building foundations at 1/10 scale relative to full-size structures. The foundation slab has a square cross-section of 3.00 × 3.00 m and a thickness of 0.40 m. To ensure sufficient rigidity and satisfy the rigid body assumption underlying the impedance function measurement protocol, the slab is stiffened by a peripheral wall 0.40 m thick and 0.60 m high, whose outer face is located 0.40 m from the edge of the top surface of the slab. The mockup therefore has an overall plan footprint of 3.00 × 3.00 m and a total height of 1.00 m from the base of the slab to the top of the stiffening walls. The structure has two planes of geometric and loading symmetry. The mockup is cast in concrete class C30/40 with high-adherence steel reinforcement (fyk = 500 MPa), designed in accordance with Eurocodes NF EN 1990, NF EN 1991 and NF EN 1992 with Greek national annexes and the soil characteristics of the EuroSeistest site. Eight unbalanced motor shakers are anchored symmetrically at the top of the stiffening walls, positioned to apply resultant inertial forces in the vertical, horizontal, and rocking directions by adjustment of the initial position of the unbalanced masses. The mockup is placed directly on the soil surface (shallow foundation), with careful treatment of the slab-soil interface to ensure optimum contact. The approximate total weight of the mockup is 178 kN.
1. Strong shaking
The testing programme consists of forced vibration tests using unbalanced motor (UM) shakers anchored to the stiffening walls of the foundation mockup. The shakers generate sinusoidal inertial forces by rotating unbalanced masses at constant angular velocity; the direction of the resultant force — vertical, horizontal, or rocking — is controlled by adjusting the balance position of the unbalanced masses on each side of the mockup symmetrically. The impedance function at a given frequency is measured during steady-state dynamic equilibrium, i.e. when the unbalanced motors rotate at constant angular velocity, such that the inertial force has a sinusoidal amplitude at the target pulsation. The frequency range covered is 1 to 20 Hz in steps of 1 Hz, with adapted step protocols at frequencies below 5 Hz where heavier unbalances are required due to the quadratic dependence of inertial force on frequency. Each frequency is held until steady-state conditions are reached. Tests are carried out at three amplitude levels in sequence — low, medium, and high — to cover both the quasi-linear and moderately nonlinear response domains. All forced vibration tests are preceded by an ambient noise recording.
Ambient noise — test type: ambient noise recording; shakers: conducted prior to all forced vibration tests.
Task 3.1/low amplitude — test type: forced vibration; loading directions: vertical, horizontal, rocking; frequency range: 1–20 Hz; frequency step: 1 Hz (with adapted protocol below 5 Hz); amplitude level: low (quasi-linear domain)
Task 3.2/medium amplitude — test type: forced vibration; loading directions: vertical, horizontal, rocking; frequency range: 1–20 Hz; frequency step: 1 Hz (with adapted protocol below 5 Hz); amplitude level: medium
Task 3.3/high amplitude — test type: forced vibration; loading directions: vertical, horizontal, rocking; frequency range: 1–20 Hz; frequency step: 1 Hz (with adapted protocol below 5 Hz); amplitude level: high (moderately nonlinear domain)
Note on shaker capacity constraints: for a safety factor SF ≥ 3 corresponding to quasi-linear operating conditions, the sum of inertial force amplitudes generated by the unbalanced motors must remain below 60 kN for vertical loading, 20 kN for horizontal loading, and 50 kN for rocking loading. Expected average foundation displacement during quasi-linear tests is approximately 0.1 mm, increasing for higher amplitude tests.
Instrumentation
The instrumentation follows the same sensor suite deployed in prior ERIES experimental campaigns at the EuroSeistest site and comprises triaxial accelerometers for structural response, triaxial broadband seismometers for free-field soil response, and laser displacement sensors for foundation kinematics. Specific instrument models, location IDs, sampling frequencies, and recording directions are consistent with those established for the EuroSeistest site instrumentation framework and will be confirmed and detailed in the instrumentation drawings to be deposited alongside the dataset.
ETNA2 triaxial accelerometer (Kinemetrics) — measured quantity: acceleration; units: m/s²; deployed on the foundation slab; recording directions: north-south, east-west, vertical; synchronized to GPS time reference; data formats: raw (.sac), converted, and synchronized.
CMG-40 triaxial broadband seismometer (Guralp Systems) — measured quantity: velocity; units: m/s; deployed on the soil surface at varying distances from the foundation mockup along both the east-west and north-south directions to capture the spatial distribution of ground motion; synchronized to GPS time reference; data formats: synchronized.
Waycon laser displacement sensor — measured quantity: displacement; units: mm; deployed to monitor vertical and horizontal movements of the foundation slab; data formats: raw (.xy) and converted.
Additional instrumentation specific to the impedance function measurement protocol: pressure sensors or synchronization units monitoring the shaker instruction signals, used to establish the amplitude and phase relationship between the applied inertial force and the recorded foundation motion, which is the primary quantity from which the impedance matrix is derived.
Data formats planned: raw, converted (engineering units), and synchronized (for ETNA2 and CMG-40 only). File naming convention will follow the standard EuroSeistest scheme: date (YYYYMMDD), test identifier, location ID, recording direction, unit type, and processing stage.
Project Metadata
Rights
Creative Commons Attribution 4.0 International.
CC BY 4.0
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