ERIES-ALL4wALL

2023 - 2025

Seismic Eng.

João Pacheco de Almeida

Ryan Hoult

António A. Correia

Paulo Candeias

Gwendal Cumunel

Yunhyeok Han

+9 more

GEM Taxonomy string

2023 - 2025

Seismic Eng.

GEM Taxonomy string

Shake-table Tests on Two 40-ton Reinforced Concrete U-shaped Walls with Uniaxial and Bidirectional-Torsional Response

ERIES-ALL4wALL

RC STRUCTURES

Dataset Description

This dataset is a collection of data from the experimental campaign investigating the dynamic and torsional performance of reinforced concrete (RC) U-shaped walls. The experimental program was conducted at the National Laboratory for Civil Engineering (LNEC) in Lisbon, Portugal. Two half-scale RC U-shaped core wall specimens were tested on a bidirectional large shake table. The dataset includes: conventional data (i.e., potentiometers, LVDTs, accelerometers), virtual target tracking, motion capture with OptiTrack system, and Distributed Fibre Optic Sensors (DFOS). This dataset is published in conjunction with a Data Paper in Earthquake Spectra titled, "Shake-table Tests on Two 40-ton Reinforced Concrete U-shaped Walls with Uniaxial and Bidirectional-torsional Response".

The ERIES-ALL4wALL project involves shake-table testing of two slender U-shaped walls, designated as UWS1 and UWS2. These walls are subjected to increasing-intensity input motions that induce, in an alternating manner, unidirectional flexure without torsion along the wall weak axis, and bidirectional flexure with torsion. The tests herein described are the first to assess the torsional nonlinear dynamic response of U-shaped walls. The project concurrently focuses on determining (UWS1) and minimizing (UWS2) residual displacements.

In addition to studying the interaction of torsion and bi-directional flexure in the dynamic response of RC U-shaped core walls, and to investigate, under realistic excitation conditions, a new technology that has the potential to minimize post-earthquake residual displacements, namely the adoption of iron-based shape memory alloy (FeSMA) rebars, the ERIES-ALL4wALL project had the two following objectives: (i) develop and calibrate numerical models for the walls’ response, which was also needed to estimate the behavior of the units prior to the tests; (ii) apply innovative instrumentation techniques, including distributed fiber optic sensing (DFOS), camera-based vibration measurements, and a motion capture system.

FeSMA

Structural wall

Shake-table testing

Specimens

1. UWS1

The two half-scale U-shaped wall units, denoted UWS1 and UWS2, are identical in geometry. The walls have a thickness (tw) of 100 mm, with web and flange lengths (Lw and Lf) of 1300 mm and 1050 mm, respectively. These wall units share the same cross-sectional dimensions as previously tested quasi-static wall units but vary with respect to their reinforcement detailing. Differing from previous quasi-static units, these units for dynamic tests have two 100 mm thick intermediate slabs spaced 1.5 m apart. They intend to partially represent the effect of story slabs in the wall response, namely regarding warping and distortion. Each slab measures 1900 mm x 1620 mm and is hollow inside the core wall. The slabs were reinforced with two layers of mesh of 6 mm diameter, with a square spacing of 100 mm. The foundation block, measuring 2.1 m x 2.1 m, was fastened to the shake table floor using sixteen M30 threaded bars evenly spaced at 500 mm orthogonal intervals. A top collar (obtained by considerably increasing the wall thickness at the head) was employed to support the top masses, which is expected to only partially restrain warping. The dimensions of the top collar include a depth of 500 mm. The wall height, measured from the foundation top to the wall collar and approximately the center of the imposed mass blocks, is 4.54 m and 5.1 m.

The design of the test units followed a similar approach to others. Rather than strictly adhering to a specific code, the design prioritized high ductility using capacity design principles deemed reasonable. However, certain aspects, such as longitudinal reinforcement placement, aligned with international building standards for high ductility—e.g., Ductility Class Medium (DCM) or High (DCH) according to Eurocodes 2 and 8. The wall units were designed with boundary elements containing a higher concentration of longitudinal and transverse reinforcement to ensure the development of high compressive strains in these regions, necessary for a ductile wall response.

The two test units differed in the material used to vertically reinforce these boundary elements: UWS1 was reinforced with 12 mm (Φ12) conventional steel according to Eurocode 8.

1. UWS1 Shake-table test

The wall units were tested on the large 3D shake table at the National Laboratory for Civil Engineering (LNEC) in Lisbon, Portugal. The maximum capacities of the horizontal actuators are 700 kN in the west-east (WE) direction and 500 kN in the north-south (NS) direction, with these cardinal directions represented in the attached figures. The positive axis conventions are defined as north to south and west to east. The shake table can achieve maximum displacements and velocities of ±200 mm and ±700 mm/s, respectively, in either direction. The table has a maximum payload capacity of approximately 40 tons.

To generate the required lateral inertial forces and reach the flexural capacity of the scaled wall units, several mass blocks were used. These included 1.13-ton and 0.59-ton blocks, which were connected to the collar (head) of the wall. These mass blocks have a cross-section of 840 mm × 840 mm, with thicknesses of 250 mm for the 1.13-ton blocks (red blocks) and 130 mm for the 0.59-ton blocks (yellow blocks). A total of 16 (arranged in a 4 x 4 grid) 1.13-ton mass blocks were placed on the collar of the wall unit, along with 12 (arranged in a 4 x 3 grid) 0.59-ton mass blocks. This setup results in a total mass of about 25.16 tons above the collar. Including the mass of the wall unit’s collar, which is approximately 3.27 tons, the total mass at the top of the wall is 28.43 tons.

Assuming that the materials are the same for the full-scale prototype and for these half-scale models, the scale factors using the Cauchy-Froude similitude laws were derived. These similitude laws and the corresponding scaling factor/s were applied to the ground motions applied to the test specimens, which essentially shifts the spectral acceleration response.

The 2016 Central Italy earthquake event of moment magnitude Mw 6.5 was the largest of the three main events that occurred on 30 October 2016. The normal faulting event ruptured a 15 km-long section of the fault at a shallow depth of 3‒7 km (Cheloni et al., 2017; Stewart et al., 2018). The seismometer station MZ04 was one of many that captured the event of October 30. The MZ04 recording station (Luzi et al., 2020) was located at a close Joyner-Boore distance (Rjb) of 6.4 km, with an epicentral distance of 23 km. The station is situated on site class C (CEN, 2004b) with an estimated shear wave velocity in the upper 30 m (VS30) measured of 355 m/s. The corresponding spectra were used as target motions for these tests, adjusted using a time-step (dt) correction from 0.005 s to 0.0035 s, following the laws of similitude. Specifically, the ground motions were time-scaled by a factor of λ^(-1/2) (where λ is the geometric scaling factor), resampled to 200 Hz (dt = 0.005s), and cropped to a 30-second duration, with a 40 Hz low-pass filter applied. The peak ground acceleration (PGA) in the north-south (NS) and west-east (WE) directions is approximately 0.64 g and 0.81 g, respectively.

The dynamic tests of units UWS1 and UWS2 included nine different levels of ground (input) motion (GM0 – GM8), each corresponding to a different amplitude and combination of the horizontal west-east (HNN record in the MZ04 station) and north-south (HNE record in the MZ04 station) components. The HNN ground motions were applied in the WE direction of the shake table, and the HNE ground motions were applied in the NS direction. As previously defined, the positive direction of the ground motion corresponds to the positive direction of the shake table.

For consistency with the shake table cardinal directions and conventions, the HNN and HNE directions have been renamed WE and NS, respectively. The first input motion, GM0, and all odd-numbered input motions (e.g. GM1, GM3, etc.), are unidirectional in the WE direction only. The other input motion levels are bidirectional and are intended to induce bidirectional flexural and torsional demands.

Instrumentation

Conventional Instrumentation

Throughout testing, the behavior of the walls was monitored using conventional instrumentation. Linear variable differential transformers (LVDTs) measured the vertical elongation of the wall edges and the wall base with a gauge length of 70 mm. LVDTs also measured any uplift of the foundation edges. Wire potentiometers (also referred to as string pots) were used to measure the global in-plane horizontal displacements at the collar (head) of the wall and the shear deformation of the lower region of the wall. Additionally, an optical measurement system was used to measure the in-plane displacements at the collar and base of the wall. Accelerometers were installed at the base (on the foundation), the intermediate slabs, and the collar of the wall to measure the in-plane and vertical accelerations. For the sake of brevity, the precise locations of these instruments, along with their corresponding names and numbers, are not included here but can be found in the dataset.

Virtual Targets and DIC

The motion of the Web and Flange Two was recorded during both experimental campaigns (UWS1 and UWS2) using a network of cameras synchronized by an external electronic trigger.

Two different surface texturing and camera systems were applied to the structure to facilitate optical measurements. The first texturing involved a grid of 168 (UWS1) and 201 (UWS2) black spray-painted circles and crosses, each approximately 5 cm in diameter. Such virtual sensor targets were painted on specific locations of the wall units — such as the base, slabs, collar, and second and third levels — to capture the global dynamic behavior of the RC U-shaped walls, including modal identification and maximum amplitudes. Discrete target detection and tracking through digital image correlation enabled the determination of each target's spatial position at every frame, recorded at a frequency of 100 Hz. Additionally, the use of cruciform (cross-shaped) virtual sensors theoretically allowed for the measurement of not only translational motions, as provided by the circular targets, but also of local rotations at the sensor locations.

Three Basler digital cameras — two acA1300-200um models and one acA1440-220um model — were used to record the upper regions of the walls above the ground floor. To enable three-dimensional (3-D) reconstruction of the vibratory field based on stereovision principles, the cameras were strategically positioned. Specifically, one camera captured the exterior surface of the Web, another focused on the exterior surface of Flange Two, and the third camera recorded both surfaces, ensuring comprehensive coverage.

The second surface texturing involved the application of a speckle pattern to the ground floor surfaces of the Web and Flange Two, designed to enable high-resolution measurements of displacement and strain fields, as well as the evolution of crack patterns. This speckle pattern was created using a stamp roller to produce a random distribution of black dots, each approximately 2.5 mm in diameter.

To capture data, three-dimensional digital image correlation (DIC) systems were employed. Each system consisted of two pairs of video cameras, with one pair monitoring the Web and the other pair focusing on Flange Two. Specifically, two Vieworks VC-12MX-M-180 cameras (designated as V1 and V2) recorded the motion of the Web, while two JAI SP-12000M-CXP4 cameras (designated as JA1 and JA2) captured the motion of Flange Two. The DIC system recorded at a frequency of 100 Hz and 50 Hz for units UWS1 and UWS2, respectively. Detailed information regarding the camera equipment and settings can be found in the documentation accompanying the dataset.

Motion Capture

The OptiTrack motion capture system used in the tests consists of ten cameras: four OptiTrack PrimeX 22 cameras (2.2 MP resolution, 2048 × 1088) and six OptiTrack Prime 17W cameras (1.7 MP resolution, 1664 × 1088). The cameras were strategically positioned around the test specimens, primarily towards the northwest, to capture multiple viewpoints (both in height and orientation) of the exterior surfaces of the north flange (or Flange Two) and web. All cameras operated at a frame rate of 100 Hz with an exposure time of 8 ms. Motive software (version 3.0.3) was used to track the three-dimensional displacements of 90 reflective markers (19 mm in diameter) affixed to the wall’s exterior surface.

Lo Feudo et al. (2025) shows a detailed comparison between the 3D optical tracking of the painted targets, motion capture markers, and conventional instrumentation employed in this study.

Distributed Fiber-Optic Strain Sensing

State-of-the-art high-definition fiber-optic sensing was employed to measure strains in selected reinforcing bars for UWS1. This instrumentation technique has been successfully applied in previous quasi-static testing of RC U-shaped core walls using the same methodology. Strain data was collected using the LUNA ODiSI 6104 Series optical distributed sensor interrogator, a four-channel system from DIMIONE Systems. The DFOS provided high-spatial-resolution measurements (5.2 mm) with an accuracy of more than 30 με. Data was recorded at a frequency of 16.67 Hz during the testing of unit UWS1.

Three longitudinal rebars in the north flange of wall unit UWS1 were selected for bonding DFOS to the reinforcing steel to derive strain profiles along the height of the wall. A small groove (1 mm wide and 1 mm deep) was cut along the longitudinal ribs of each rebar, a widely adopted practice in previous research to securely attach DFOS to steel reinforcement and to minimize the risk of premature fiber failure. The sensing fiber used was a polyimide-coated fiber. Following preliminary performance tests, a general-purpose adhesive (“Loctite 401,” based on cyanoacrylate technology) was applied to bond the fiber within the groove, a method that has been successfully implemented in previous studies. Additionally, an epoxy coating (“ESK-50”) was applied over the glued fiber to provide an extra layer of protection between the fiber and the surrounding concrete.

Unlike previous quasi-static tests where this instrumentation technique was successfully employed, the dynamic nature of the tests reported here resulted in significant data loss from the LUNA system during recording. Despite these challenges, some strain data was captured, especially during the initial input motion levels, albeit sporadically. As a result, the authors have chosen to publish the raw DFOS data in its current form, recognizing its potential value for future research.

2. UWS2

As described above, the walls of UWS2 have a thickness (tw) of 100 mm, with web and flange lengths (Lw and Lf) of 1300 mm and 1050 mm, respectively. The wall height, measured from the foundation top to the wall collar and approximately the center of the imposed mass blocks, is 4.54 m and 5.1 m.

In contrast to UWS1, UWS2 was reinforced with Φ10.7 iron-based shape memory alloys (FeSMA). The FeSMA material was selected to reduce the residual displacements of the wall. Additionally, the units differed in the amount of vertical rebars in the boundary elements, commonly expressed in terms of reinforcement ratio (ρwv), which is the ratio of the area of the lumped longitudinal rebars to the area of concrete in the boundary regions. For example, the flange boundary ends of UWS1, detailed with 6 × 12 mm steel rebars, have a ρwv of approximately 2.3 %, whereas the 7 × 10.7 mm FeSMA rebars (with an effective area of 89.9 mm²) in UWS2 result in a ρwv of 2.1 %. The 4 × 12 mm steel rebars at each web-flange intersection of UWS1 was replaced by 5 × 10.7 mm FeSMA rebars in UWS2. The specific amount of longitudinal reinforcement in each wall was chosen to achieve similar strengths, as predicted from sectional analyses.

The FeSMA rebars extend from the foundation to a lap-splicing region above the first slab. Within the ground-story height (i.e., below the first-story slab), they were shrink-wrapped to promote unbonded behavior with the concrete. Only the rebar ends, i.e. along the foundation and the lap-splice region, remained effectively anchored (i.e. bonded), preventing the strain recovery resulting from the heating process; instead, the shape memory effect induced by heating results in recovery stress and the prestressing of the wall.