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1、STRUCTURAL MODELINGANDEXPERIMENTALTECHNIQUESLecturer: Wenhui HEChapter 8 Loading System Static Structural Testing2Static Loading Systems3Spherical joint test of the West TowerSteel space truss test4Test of components: Beams (bending)Columns (axial)Beam-columns (both)Devices (connectors etc)Test of s

2、tructures: Single loadsMultiple loadsStructural testing (static means slow loading, acceleration effect not considered)5Purpose of testing: Determine strength limitsDetermine flexibility/rigidity of structureTest set-up: Define and construct modelsImplement proper boundary conditions(Instrument mode

3、l and references)Implement loadingStructural testing (static means slow loading, acceleration effect not considered)6Static time is not a factor (infinitely slow)Quasi-static very slowly applied loading in one direction (monotonic)Quasi-static - reversed cyclic loadingDynamic (random) loading shake

4、table excitationsQuestion #1: What types of loading need to be applied?7Component Testing : 1 beams (bending, shear, etc)2 columns (axial, bending, shear, P-, creep, etc)3 special devices (dampers, isolators, etc)Subassembly Testing : 1 beam-column-slab-joint cruciform2 parts of framesLoading Condit

5、ions:1 single loads, i.e. axial load for column buckling2 multiple loads, i.e. P- effect, axial and shear loads3 base loads, i.e. earthquake simulationsStructural testing8Purpose of Testing: 1 determine strength limits (crack, yield, ultimate, etc)2 determine flexibility/stiffness of structures3 ver

6、ify analytical tools4 verify failure theories Experimental Setup Process: 1 design and construct model2 implement proper boundary conditions3 instrument model4 implement loading and reaction load requirementsStructural testing9i.e. Typical loadcell : It is desired to put a constant moment over the l

7、oad cellTry Example setup: Calibrate bending moment load cells10i.e. Typical loadcell : Now we can calibrate loadcells! Set gain (signal amplification) such that the output voltage corresponds to the applied moment.Example setup: Calibrate bending moment load cells11Single point loads: -Vertical and

8、 lateral.Loading Arrangements12Distributed loads: Loading Arrangements13Distributed loads: Loading Arrangements14Distributed loads: Loading Arrangements15Calibrated weights with a balance Pressure transducer F P * A-Area of piston = constant) i.e. Load Measuring Devices163) Mechanical transducer P (

9、K = constant)Load Measuring Devices4) Stress-strain based transducer171) Actuator: This is an open loop system that controls the linear or rotary motion of a load in response to an input command.Servo controlled devices for loading(Usually operates based on a command without precise knowledge of the

10、 magnitude of the load. Load may vary up to 10% ; Open loop)18Hydraulic Servomotors (actuators) convert hydraulic power into mechanicalmotion. produce a closed loops ystem.Servo controlled devices for loadingTransducers - provide feedbackServomotor - high level energy converter such as an electrical

11、 or hydraulic motor.Modulator - provides a conversion of low power input command (for the servoactuator) or the error signal(for the servosystem) to a high power output that operates the servomotor19Servo-system: Here feedback is used with a servoactuator to produce a closed loops ystem.Servo contro

12、lled devices for loadingTypes - Linear motion/Rotary motionRequirements - Low fluid leakage/Low friction/Seals are critical.Servo controlled Devices for Loading.20Servocontrol can be done using any mechanical variable.Displacement (displacement control)Force (force control)Strain Differential Pressu

13、re(Velocity)(Acceleration) (etc)Servo controlled devices for loading21Actuator needs to haveServovalve (which converts electrical signal into differential pressure)Pressure (at constant flow) from a power supplyTotal actuator capacity is (A area of piston): Sufficient oil flowAccumulation (reservoir

14、)Servo controlled devices for loading22Hydraulic Servomotors (actuators)Servo controlled devices for loading23Constant value loadingLow rate loading (ramp)LoadDisplacementSaw-tooth loadingLoadDisplacemenReference loads24Lateral and vertical.Biaxial (or triaxial)Static Loadings for Structural Testing

15、25Need to identify yielding limit.Need to plan inelastic loadingNeed to stop test upon collapse1 Choose force control for elastic range2 Load up to 3/4 of calculated yielding force3 Determine stiffness (slope) in elastic range4 Calculate approximately the yielding displacement (by extrapolation)Load

16、 History for Case Study: Loading near collapse with cyclic static loading.26Need to identify yielding limit.Need to plan inelastic loadingNeed to stop test upon collapse5 Switch to displacement control and develop cycles in terms of displacements (can be constant rate, with T1 T2, or constant time,

17、with T1= T2)6 Increase cycles as desired (two of each alternating with two low cycles in between).Load History for Case Study: Loading near collapse with cyclic static loading.275 Switch to displacement control and develop cycles in terms of displacements (can be constant rate, with T1 T2, or constant time, with T1= T2)6 Increase cycles as desired (two of each alt