The equipment in the L.E.D.A. Research Centre’s Structures Laboratory allows for effective cooperation between professors, students and technicians, with the possibility of developing new studies and research aimed at preparing degree theses, Master’s theses and PhD theses, as well as drafting scientific publications, also in collaboration with other Italian and foreign universities and research bodies.
In addition to the activities within the University, given the high seismicity that characterises our area, the studies carried out at the Structures Laboratory can make a significant contribution to the scientific development of our nation in the field of seismic risk mitigation.
It is well known that one of the fundamental problems in seismic risk mitigation is the identification of risk conditions and interventions to minimise their impact, such as the construction of new buildings with anti-seismic criteria and the reduction of seismic vulnerability of existing buildings.
Over time, this research has led to a considerable evolution in the criteria for the design and construction of artefacts.
However, the real “test” of the goodness of the new numerical calculation methods and implementation only occurs in the presence of an earthquake.
Since it is not possible to wait for real seismic events to have a clearer understanding of structural behaviour in the presence of an earthquake, it becomes essential to carry out simulations and obtain answers by testing appropriate models even on a large scale.
In this context, the presence of the Laboratory of Structures of the L.E.D.A. research centre becomes a strategic element of extraordinary importance because, thanks to the high technological level instrumentation with which it is equipped, it will make it possible to understand the phenomena related to the response of structures to earthquakes.
The Structures Workshop is divided into the three sections presented below.
The most important section of the L.E.D.A. Centre’s Structures Laboratory is the “Full Scale Components and Structures” section due to the presence of an impressive research infrastructure, consisting of a Strong Floor – Reaction Wall contrast system, equipped with a series of servo-hydraulic actuators complete with the hydraulic power unit and control system.
The reaction wall is the second-highest wall in Europe and the sixth-highest globally.
The choice of the construction system and the functional scheme of the contrasting structure resulted from the critical analysis of similar existing laboratories.
In particular, the ELSA (European Laboratory for Structural Assessment) laboratory of the JRC (Joint Research Centre), one of the most important laboratories in the world equipped with large reaction facilities for pseudo-dynamic tests, was considered as a reference point in the design phase of the L.E.D.A. centre’s contrast system.
The equipment available in the Materials Section of the Laboratory offers great potential in the field of experimentation for the qualification of construction materials, making it possible to analyse all the phases of their production process, from design to preliminary tests to be carried out also at the production plants.
In the “Materials” section, it will also be possible to carry out tests on innovative materials, using a Rexroth 2000 kN servo-hydraulic actuator operating with both force and displacement in addition to the equipment listed above control.
This section of the Laboratory deals with the planning and executing destructive and non-destructive in-situ investigations of materials and structures.
It is possible to work on existing structures and infrastructures, carrying out the necessary diagnostic investigations for a correct geometric and mechanical characterisation of the structures to identify all those parameters essential for assessing their safety.
It is also possible to work in new construction, performing, for example, all qualification operations for concrete mixing plants, site acceptance checks, and all structural investigations and checks for the static testing of newly built buildings.
The following are among the tests that can be performed using the equipment available in the “In-situ tests” section.
The Structures Laboratory of the L.E.D.A. research centre is under the responsibility of Prof. Marinella Fossetti, associate professor in the scientific-disciplinary field ICAR/09 Construction Technique.
The main lines of research of the Structures Laboratory of the L.E.D.A. research centre are in the field of seismic risk mitigation of the existing building stock and the field of anti-seismic design of newly built structures and infrastructures according to innovative technologies and criteria, with the possibility of performing combinations of complex numerical analyses and advanced experimental investigations even on full-scale samples.
The main lines of research can be grouped into the following thematic areas:
Theoretical studies.
Development of advanced numerical models, mainly through the finite element method; analytical formulations of specific problems; writing functional algorithms with appropriate programming languages; design of calculation tools for solving specific structural analyses.
Numerical procedures and analytical formulations can be validated by comparing different theoretical methods or by comparing them with results obtained from experimental tests.
Experimental studies in the pseudo-static field.
Execution of experimental tests on materials, structural elements and full-scale structures, applying load or displacement histories in a monotonic and cyclic range to simulate actions, including seismic actions or distortions and displacements greater than those of normal operation.
Since the tests are conducted in a pseudo-static field, the response of the material or structure can be accurately observed and measured even at later stages after the maximum strength has been reached.
Experimental studies in the pseudo-dynamic field.
Performing experimental tests on full-scale components and structures.
As is well known, hybrid experimental-numerical test methods allow the dynamic response of a structure subject to seismic actions to be obtained without vibrating table tests.
The research consists of optimising test set-ups for the execution of tests at the L.E.D.A. Laboratory, with particular reference to the development of continuous pseudo-dynamic tests and hybrid tests with substructure.
L.E.D.A.’s Strong Floor – Reaction Wall contrast system results from a design based on a critical analysis of similar existing laboratories.
In particular, the ELSA (European Laboratory for Structural Assessment) laboratory at the JRC (Joint Research Centre), one of the world’s most important laboratories with large reaction facilities for pseudo-dynamic tests, was considered a reference point.
L.E.D.A.’s Strong Floor – Reaction Wall contrast system results from a design based on a critical analysis of similar existing laboratories.
In particular, the ELSA (European Laboratory for Structural Assessment) laboratory at the JRC (Joint Research Centre), one of the world’s most important laboratories with large reaction facilities for pseudo-dynamic tests, was considered a reference point.
The reaction wall is 14 m high and is the second-highest wall in Europe and the sixth-highest globally.
The Reaction Wall has a caisson construction system with a horizontal rectangular section measuring about 14.00 4.00 m from the floor level of the Laboratory. It is developed in height on four decks with an intermediate floor level of about 3.50 m. To ensure that the wall can be inspected and to facilitate the assembly and disassembly of the devices to be attached to the wall, as well as the passage and housing of the plant engineering system, there are openings along the rear longitudinal section of the wall that are 1.00 m wide and about 1.90 m high, and square openings along the front longitudinal section with a side of 0.25 m. In addition, further openings have been appropriately prepared inside the reaction wall, in the transversal partitions and in the floor slabs.
The Strong Floor was also built using a caisson construction system.
The height of the caisson is 5.00 m and is characterised by a base plate and a floor plate with a thickness of 1.00 m. In plan, the Strong Floor has dimensions of approximately 34.00 14.00 m (including the cross-section of the wall). It is divided into two portions concerning the Reaction Wall: the front portion with dimensions of 20.00 14.00 m and the rear portion with dimensions of 10.00 [1] 14.00 m. The Reaction Wall and the Strong Floor are post-tensioned through a prestressing reinforcement system consisting of Dywidag bars and strands.
The outer baffles of the Reaction Wall and the top plate of the Strong Floor are provided with Ø 65 mm holes, spaced 1.00 m apart, to ensure anchorage of the test set-up through assembly and disassembly of plates and anchor bolts.
Hydraulic power station
The Bosch Rexroth, hydraulic power unit is shared by the Experimental Dynamics Laboratory and the Structures Laboratory.
It consists of a high-capacity reservoir, several main motor-pump units to serve the high dynamics, a motor-pump unit for pseudo-dynamic tests, several recirculation, filtration and heat exchange units, a water cooling circuit system, an electrical cabinet containing the PLC (Programmable Logic Controller) to manage the power station itself, pipes (rigid and flexible) and manifolds for distribution and sectioning, and several storage units.
The figure shows the motor-pump unit of the hydraulic power station serving the pseudo-dynamics tests
The servo-actuators serving the contrast system are made by Bosch Rexroth and exploit various technologies available to drastically reduce first breakaway friction (also known as stick-slip).
The servo-actuators feature a double rod design, a “backlash-free” ball joint on both ends of the cylinder, a load cell (located between the rod and ball joint) sized for a force at maximum pressure, a built-in digital position sensor with micrometre resolution, an external optical scale to measure actual displacement and to close the control loop, and a high-performance servo valve with a capacity of 30 litres per minute for the 500 kN cylinder and 60 litres per minute for the 1000 kN cylinder.
Servo-valves allow operation in the dynamic range up to frequencies of 100 Hz and also enable fatigue tests to be carried out.
In addition, there is a high-flow servo valve with a capacity of 300 litres per minute, which allows fatigue tests to be carried out at higher frequencies.
Servo actuator calibration bench
A special bench is available for calibrating hybrid servo actuators:
In the calibration bench, the force measured by the load cell is compared with the force measured by the servo actuators’ pressure transducers to derive the correlation.
The servo-actuators are managed by the hydraulic control unit interfaced with the user via a PC connected to the RT3-S control system produced by Trio Sistemi e Misure.
The RT3 controller allows the complete management of the test equipment, from setting the optimal configuration parameters to performing tests and measuring and recording the acquired data, which can then be exported.
The Structures Laboratory of the L.E.D.A. research centre is equipped with high-tech instrumentation with internationally unique features that make it possible to carry out experimental investigations even on full-scale structures.
Some of the equipment in the Structures Laboratory for each of the sections already shown in the presentation section of the Laboratory is shown below.
Some of the equipment in the Structures Laboratory for each of the sections already shown in the presentation section of the Laboratory is shown below.
Trio control system RT3–S
The RT3 controller consists of an embedded system managed by a software application developed in the Labview environment, which operates in real-time and interfaces via an Ethernet network link with a PC running Windows XP.
Electronic modules are integrated into the RT3 system to condition the transducers, drive the servo-valves and manage the hydraulic equipment according to the specific characteristics of the end application.
Displacement acquisition can take place using laser sensors and analogue position transducers.
For both, the acquisition system is provided by power cables that connect the transducers to the control system, with which data can be acquired by setting a predefined sampling rate.
The transmission of signals from the measuring sensors to the central unit is digital.
In this way, it is possible to guarantee the total absence of interference in data transmission and, therefore, the absence of errors in the measurement of experimentally measured quantities.
Acquisition of displacements
Luchsinger laser sensors of the optoNCDT 1302 series with 200 mm measuring range, max. linearity 40 µm, max. resolution 4 µm, 750 Hz measuring speed and scalable analogue output.
Balluff Micropulse BTL7-A/E501-M analogue position transducer, measuring range 0 to 500 mm.
Some of the equipment in the “Materials” section
One of the most significant pieces of equipment in the “Materials” section of the Laboratory is the 2000kN Rexroth actuator, which allows a series of static tests on structural components (beams, walls, columns, nodes, etc.) to qualify traditional and innovative technological solutions.
The actuator is a servo-hydraulic system that operates with force and displacement control. It features a maximum stroke of 10 cm and a joint that allows the correct load distribution on the specimen.
The actuator is attached to a contrasting frame, as shown in the following figure.
Rexroth 2000 kN actuator for structural component testing
set-up
Hydraulic unit
Hydraulic unit
Servo-hydraulic actuator
Servo-hydraulic actuator
Inspection system
Inspection system
The servo-hydraulic actuator drive system is provided by a hydraulic power unit consisting of: an oil tank with a capacity of 100 litres, block complete with servo valve, pressure regulating valve, μ 6 delivery filter, external gear pump with a capacity of 16 litres/min – operating pressure 250 bar, air heat exchanger, 10 kW electric motor, electric control panel including PLC programmed to the functions of the hydraulic actuators.
The servo-actuator is interfaced with the user via a PC connected to a control system equipped with RT3 software produced by TRIO Sistemi e Misure Srl, similar to that used in the “Components and full-scale structures” section of the same Laboratory.
The displacement acquisition system is also similar to that used in the Laboratory section described above.
There is also an additional acquisition system consisting of digital comparators with a resolution of 0.001 mm (ABSOLUTE Digimatic ID-S, model S43- 7908″) that send data via a wireless system consisting of a U-WAVE-T emitter and U-WAVE-R receiver.
3000 kN press, motorised with Servotronic
The machine enables tests to be carried out to determine the compressive strength of cubic and cylindrical specimens and determine the compressive secant modulus of elasticity.
It consists of a four-column frame, load plates and a hydraulic system.
The machine comes complete with a servo-driven control unit to make the test fully automatic in all its phases of acquisition, display, data processing, including adjusting the load gradient and software for printing the results.
Leveling grinding machine
Used for flattening and grinding cubic and cylindrical specimens of concrete, bricks, natural stone, etc. It consists of a steel structure supporting the abrasive head, the coolant collection and decantation tank with an electric pump and the splash protection casing.
The specimens are fixed employing appropriate brackets, which ensure the coupling and locking.
The descent of the sanding head is automatic, with adjustment for a minimum feed of 0.05 mm.
Tank for curing concrete specimens
The curing tank is used for curing specimens in an air-conditioned chamber with constant humidity and temperature.
The tank consists of a sheet steel structure subjected to anti-corrosion treatment employing total hot-dip galvanisation.
Complete with a grid at the base, it is equipped with a thermoregulator with an immersion heating element.
Vibrating table 800 x 400 mm
Used to compact concrete specimens in the Laboratory.
The table is made of a sturdy steel plate, equipped with an electric vibrator with 3000 vibrations/minute.
The vibrating intensity can be adjusted by acting on the eccentric masses.
The table has fixing brackets, a control panel and a footswitch.
Matching plan
Test bench for checking the flatness of concrete, brick and natural stone specimens, etc. The bench consists of a 632x400x73 mm block of black granite, with a lapped surface that guarantees high precision and gives excellent results in the sliding of cylindrical specimens.
The top has an accuracy of 00 according to DIN 876 and is made of granite, guarantees dimensional stability over time, thermal stability, hardness, wear-resistance and oxidation resistance.
The top rests on feet supported by a steel frame.
The feet are height-adjustable so that the top itself can be levelled.
100 litre vertical axis mixer
Used to prepare the mortar and concrete mixes.
As the mixer has a vertical axis, it incorporates less air during the mixing phase, takes less time and ensures perfect homogeneity even for mixtures with a low percentage of water concerning the cement used.
Frame for hydrostatic weighing
Used to determine the specific gravity of hardened concrete, aggregates and solid materials in general.
It consists of a jumper support frame with a hooked tie-rod, a movable platform on which a vertically adjustable tank rests employing a crank for weighing both in water and in air, a stainless steel basket and an electronic scale with a lower hook.
Automatic computerised tropicalized Vicat apparatus
The device determines the start and end-setting time of a hydraulic binder.
Manufactured with anti-corrosion and tropicalised components for use in humidity and temperature controlled environments as the Standards require.
It automatically performs the entire test, ensuring results of absolute precision and repeatability.
Le Chatelier moulds and trays
Le Chatelier moulds are used to determine cement specimens’ stability (expansion) in both cold and boiling water.
The Le Chatelier tray is used to heat Le Chatelier moulds immersed in water to boiling point.
The inner chamber is made of stainless steel and can accommodate up to 12 Le Chatelier moulds in the basket.
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