Preparatory Course (task NA 3.6) Basics of experimental testing and theoretical background

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1 Preparatory Course (task NA 3.6) Basics of experimental testing and theoretical background Module 4 TEST SYSTEM Part 1 SHAKING TABLE TECHNOLOGY ACTUATORS PUMPS PERFORMANCES Dr. J.C. QUEVAL, CEA/Saclay 10/03/2010 1

2 2 The principal methods are: - Quasi-static loading test method, - Shaking table testing method, - Effective force method, - Pseudo-dynamic testing method, - Real time pseudo-dynamic testing method, - Real time dynamic hybrid testing method, - Centrifuge tests 10/03/2010 2

3 3 : m5x5a Quasi-static loading test method The test specimen is subjected to slowly changing prescribed forces or deformations by means of hydraulic actuators. Effective force method (EFT) The method consists to apply dynamic forces to a test specimen that is anchored rigidly to an immobile ground and to perform real-time earthquake simulation : m4x4a : m3x3a : m2x2a : m1x1a 10/03/2010 3

4 4 Pseudo-dynamic testing method (PDT) That method consists to apply slowly varying forces to a structural model. The motions and deformations observed in the test specimens are used to infer the inertial forces that the model would have been exposed to during the actual earthquake. The method uses substructure techniques. Real time pseudo-dynamic testing method This method is the same as the pseudodynamic test except that it is conducted in the real time. This method introduces problem in control, such as delay caused by numerical simulation and actuators. Fi F2 F1 10/03/2010 4

The inertial effects and structure assembly issues are well represented but the

5 5 Shaking table testing method The test structures may be subjected to actual earthquake acceleration records to investigate dynamic effects. The inertial effects and structure assembly issues are well represented but the size of the structures are limited or scaled by the size and capacity of the shake table. 10/03/2010 5

6 6 Real time dynamic hybrid testing method That method allows to combine shaking table tests and real time substructure techniques. For large structure, which cannot be test on shaking table, a part of the structure is represented by a mockup tested on the shaking table and the other part of the structure is modeled and theirs effects are applied by additional actuators using substructure techniques. Fi Centrifuges For soil tests and soilstructure interaction, tests can be performed on reduced scale mockup with centrifuges. 10/03/2010 6

7 Electro dynamic shakers Some large shakers allow providing

The addition of a slip table extends the capabilities.

for vibration control from 5 to 2500 Hz Up to ± 25 mm for

7 7 Electro dynamic shakers Some large shakers allow providing static load support up to 5000 kg. The addition of a slip table extends the capabilities. The biggest performances are about: Useful frequency range for vibration control from 5 to 2500 Hz Up to ± 25 mm for displacement available Maximum vibration force rating: 160 kn. Excitation mono axial only 10/03/2010 7

8 8 Advantages Large frequency range of excitation and specially at very high frequency (up to 2000 Hz), Low distortion. Disadvantages Very low stroke (1 or 2 inches), Does not run at very low frequency (under 2 or 5 Hz), Important volume or size, Very expensive, Limited forces, Limited static load compensation. 10/03/2010 8

9 9 Hydraulic actuators Advantages Long stroke (200 mm and over), Important force or power, Multi axial excitations are possible, Low volume or size, Limited cost. Disadvantages Frequency range limited to 100 Hz or 300 Hz, Important distortion Low velocity. For seismic tests, all laboratories use hydraulic actuators because it is necessary to have important stroke, important forces at low frequency (lower than 35 Hz). 10/03/2010 9

10 10 10/03/

11 11 Components of a shaking table - the plate, - actuator (s), - servo valves, - accumulators, - hydraulic pumps, - piping system, - cooling system, - controllers and associated sensors. 10/03/

12 Hydraulic pumps Heat exchang e Huile/ea u Water warm/cold Power Accumulat or Pressure actuator Power Accumulat or Return actuator HSM Accumulat or actuator Return line actuator Accumulator

12 12 Hydraulic pumps Heat exchang e Huile/ea u Water warm/cold Power Accumulat or Pressure actuator Power Accumulat or Return actuator HSM Accumulat or actuator Return line actuator Accumulator Pressure line to actuator Oil pilote return line Plate Additionn al Software Accelerometer Accelerometer Pressure Command Servovalv e Driv e Controller Cooling system LVDT Servo LVDT Act 10/03/

13 13 - a cylinder with hydrostatic bearings [Servotest] or special bearings with very low friction coefficient [MTS], - a piston, - two swivels (one at each extremity), - one or several servo valves, - a LVDT transducer in the piston, - a small LVDT in the servo valve, A - a pressure sensor, - some time a load cell. several types of linear actuator: - Single-acting (A) - Double- acting, single rod (B), - Double-acting, double-rod (C). B C 10/03/

14 14 10/03/

15 SEISMIC ENGINEERING RESEARCH INFRASTRUCTURES FOR EUROPEAN SYNERGIES 15 10/03/

16 16 Return pilot Pressure pilote Command Servovalve The servo valve is the heart of the system. It is a kind of hydraulic amplificator which gives oil to the actuator as function of a low level signal Pressure Actuator Return Actuator Return pilot Command Pressure pilote Return Actuator Pressure 10/03/2010Actuator 16

17 17 *The voice coil servo valve 10/03/

18 18 The Flapper nozzle valves servo valve 10/03/

19 19 Working Parts Operating Principle Pilot or First Stage Power or Second Stage Transformation: electric signal (low power) in hydraulic force (high power) 10/03/

20 20 Operating Principle Pilot Stage Hydraulic Amplifier Armature and Flapper are rigidly joined and supported by a thin wall Flexure tube. Fluid continuously flows from the supply pressure P through both inlet orifices, through the nozzle flapper chamber then to return R. The rocking motion of the armature/flapper throttle flows through one nozzle or the other. This diverts flow to A or B or builds up pressure if A or B are blocked. 10/03/

21 Operating Principle Power Stage valve spool 4 way Spool slides within the Bushing or Sleeve. The bushing contains holes that connect to supply pressure P and return R.

21 21 Operating Principle Power Stage valve spool 4 way Spool slides within the Bushing or Sleeve. The bushing contains holes that connect to supply pressure P and return R. At Null, the spool is centred in the bushing; spool lands cover P and R openings. Spool motion to either side of null allows fluid to flow from P to one of the control port and from other control port R. 10/03/

22 22 Operating Principle Power Stage valve spool Bushing Spool 10/03/

23 Operating Principle Torque motor & Spool operation The electrical current in the torque motor coils creates magnetic forces on the ends of the armature.

23 23 Operating Principle Torque motor & Spool operation The electrical current in the torque motor coils creates magnetic forces on the ends of the armature. The armature and flapper assembly rotates about the flexure tube support. The Flapper closes-off one of the nozzles and diverts the flow to the spool end. The spool then moves to open P to control port C2 and opens C1 to R The spool pushes the Ball end of the Feed Back Spring, thus creating a restoring Torque on the Armature/Flapper. 10/03/

24 Operating Principle Torque motor & Spool operation As the feedback torque becomes equal to the torque from the magnetic forces, the armature/flapper moves back to the centre position.

24 24 Operating Principle Torque motor & Spool operation As the feedback torque becomes equal to the torque from the magnetic forces, the armature/flapper moves back to the centre position. The spool stops at the position where the feedback spring torque equals the torque due to the input current. Therefore the spool position is proportional to the input current. With the constant pressure, Flow to load is proportional to spool position. 10/03/

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34 34 10/03/

35 35 The plate By the past, some plates were built in reinforced concrete 10/03/

36 The plate The majority of the plates is made in steel. To increase the performance in acceleration, a solution is reducing the mass of the plate.

36 36 The plate The majority of the plates is made in steel. To increase the performance in acceleration, a solution is reducing the mass of the plate. For this reason, some plates have been made in aluminum alloy (for example AZALEE shaking table). The advantage is to decrease the mass, by this solution is more expensive, and the plates are more brittle and there are some problems for welding. The AZALEE shaking table has a 6 m x 6 m plate made in AG7 (aluminum alloy). The plate weights about 24 tons. 10/03/

37 SEISMIC ENGINEERING RESEARCH INFRASTRUCTURES FOR EUROPEAN SYNERGIES 37 To have a good control of the table and to not overload the mockup fixed to the plate, the natural frequencies of the plate must be over the frequency range of the time history. 10/03/

38 Mode 1 Mode 2 Mode 3 Mode 4 Mode 5 Mode 6 Test results

1 Hz CAST3M free-free 82,4 Hz 100 Hz 120 Hz - - - SAP -

5 Hz Mode 1 Mode 2 Mode 3 Mode 4 Mode 5 Mode 6 SAP plate

38 38 Mode 1 Mode 2 Mode 3 Mode 4 Mode 5 Mode 6 Test results free-free 80.5 Hz 95.7 Hz Hz Hz Hz Hz CAST3M free-free 82,4 Hz 100 Hz 120 Hz SAP - free-free 80 Hz 95 Hz 117 Hz Hz Hz Hz Mode 1 Mode 2 Mode 3 Mode 4 Mode 5 Mode 6 SAP plate fixed 54.3 Hz 54.3 Hz 65.7 Hz 73.5 Hz 73.5 Hz 99 Hz 10/03/

39 Hz 33,7 Hz 20 Hz Abaque pour les modes de flexion de la maquette 21,4 Hz 16 Hz Hz 10,6 Hz Chute de fréquence (% ) ,6 Hz 14,4 Hz SMART sur plaque rigide 10,6 Hz 11,1 Hz 7,3 Hz 10,6 Hz Camus Ox et Oy 6,8 Hz 5,3 Hz 8,02 Hz SMART sur plaque rigide 10,6 Hz 5,3 Hz 5,3 Hz 5 Hz 2,56 Hz 5,3 Hz 2,64 Hz Ecoleader 3,73 Hz 0 1,44 Hz Moment en pied de structure (t.m) = masse modale x hauteur du centre de masse modale 8 Hz 5,3 Hz 5 Hz 3 Hz Fréquence de la m aquette encastrée au sol 10/03/

40 Accumulators The aims of these accumulators are: to increase the performances of the actuator (distortion and velocity) accumulator pressurized at 125

40 40 Accumulators The aims of these accumulators are: to increase the performances of the actuator (distortion and velocity) accumulator pressurized at 125 bars, to decrease hydraulic shocks in the piping (return line, accumulators pressurized at 3 bars). Discharge of the accumulator Accumulator Charging 10/03/

The accumulators are pressurized when the pumps starts and they give

41 41 Some others accumulators can be placed directly on the hydraulic line to increase the power or the global flow of the testing facility. The accumulators are pressurized when the pumps starts and they give flow for a short duration when the testing facility needs oil. 10/03/

42 42 Bladder accumulators consist of a pressure vessel and an internal elastomeric bladder that contains the gas. The bladder is charged through a gas valve at the top of the accumulator, while a poppet valve at the bottom prevents the bladder from being ejected with the outflowing fluid. The poppet valve is sized so that maximum volumetric flow (typically to 15 liter/sec, but up to 140 liter/sec for high-flow designs) cannot be exceeded. The bladder can be replaced, usually through the fluid end of the vessel. To operate, the bladder is charged with nitrogen to a pressure specified by the manufacturer according to the operating conditions. When system pressure exceeds gas-precharge pressure of the accumulator, the poppet valve opens and hydraulic fluid enters the accumulator. The change in gas volume in the bladder between minimum and maximum operating pressure determines the useful fluid capacity. Piston accumulators have an outer cylinder tube, end caps, a piston element, and sealing system. The cylinder holds fluid pressure and guides the piston, which forms the separating element between gas and fluid. Charging the gas side forces the piston against the end cover at the fluid end. As system pressure exceeds the minimum operating level for the accumulator, the piston moves and compresses gas in the cylinder. Each type of separated, hydropneumatic accumulator has advantages, but bladder designs are generally considered the most versatile. For shock and pulsation, for example, bladder models are ideal. Piston units are not recommended because they are too slow to react to shock waves. 10/03/

43 43 Oil pressure in a bladder accumulator ( or Floating piston accumulator) 10/03/

44 44 Open view of accumulators (hydro-pneumatic) bladder accumulator 10/03/

45 45 Open view of Floating piston accumulator 10/03/

46 46 Hydraulic power system The principal parts of a hydraulic power system are: a motor, a pump, a pressure regulator, a tank, a filtration system, an oil cooler. 10/03/

47 47 Several types of pump: Gear pumps - Vane pumps - Radial-piston pumps - Axial-piston swash-plate pump Output : Pressurrized oil Gear pumps Oil Input 10/03/

48 48 Several types of pump: Gear pumps - Vane pumps - Radial-piston pumps - Axial-piston swash-plate pump Vane pumps 10/03/

49 49 Radial-piston pumps 10/03/

50 50 Radial-piston pumps 10/03/

51 51 Radial-piston pumps 10/03/

52 52 Axial-piston swash-plate pump 10/03/

53 53 Axial-piston swash-plate pump 10/03/

54 54 Axial-piston swash-plate pump 10/03/

55 55 Axial-piston swash-plate pump 10/03/

56 56 Variation of the output pressure/flow 10/03/

57 57 piston cylinder block Suction kidney Pressure kidney valve plate 10/03/

58 58 11 cm³ trapped volume 0.3 cm³ compression volume compression starts angle cm³ trapped volume 0.3 cm³ compression volume compression ends angle 12 standard pump 0.3 cm³ 11 angle 1.22 ms l/min ~21% of 69 l/min 10/03/

59 59 Pressure 400 bar Time ms Standard l/min 60 Flow Rotation 10/03/

60 60 piston cylinder block suction kidney valve plate pressure kidney Precompression volume 10/03/

61 61 11 cm³ trapped volume 0.3 cm³ compression volume compression starts 11 cm³ trapped volume 0.3 cm³ compression volume compression ends chamber refill starts angle cm³ trapped volume 0.3 cm³ compression volume chamber refill ends angle 12 angle 35 PVplus 0.3 cm³ 23 angle 2.56 ms 7.04 l/min 10% of 69 l/min 10/03/

62 62 10/03/

63 63 10/03/

64 64 Pressure ripple reduction 10/03/

65 65 Precom- pression volume 10/03/

66 66 Pump Housing Optimization reduces pump nois - absolute reduction in noise emission - frequency shift to better sound Precompression Volume Reduces Flow and Pressure Pulsation by 40-60% - no extra cost: additional casting core is offset by material saving - minor effect on pump noise - major effect on system noise 10/03/

67 67 Several type of regulation Bypass regulated constant pressure hydraulic power supply Stroke regulated constant pressure hydraulic power supply Constant pressure hydraulic power supply with servo load 10/03/

68 The oil Generally these oils are used: Shell TELLUS 46 or Mobil DTE 25 - Class of pollution ISO The ISO class of the oil is characterized by a code with 2 numbers relative to the number of

68 68 The oil Generally these oils are used: Shell TELLUS 46 or Mobil DTE 25 - Class of pollution ISO The ISO class of the oil is characterized by a code with 2 numbers relative to the number of particles with diameter > 5 microns/milli-liter and with diameter > 15 microns /milli-liter Example: Required Class ISO 13/9 13 = 400 to 800 particles size 5 microns 9 = 250 to 500 particles size 15 microns Limit Class: ISO15/11 - Bulk modulus (Compressibility) = à kg/cm² - Flash Point (temperature) = 236 C - Viscosity at 40 C = 46 mm²/s 10/03/

69 SEISMIC ENGINEERING RESEARCH INFRASTRUCTURES FOR EUROPEAN SYNERGIES 69 10/03/

3. DESCRIPTION OF SHAKING TABLE SYSTEM COMPONENTS

17 3. DESCRIPTION OF SHAKING TABLE SYSTEM COMPONENTS 3.1. INTRODUCTION The earthquake simulator is a system that consists of several components which must be designed to effectively work together. Each