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SE 110.22 Forces in an Overdeterminate Truss
Education / GUNT Hamburg / Engineering Mechanics and Machine Elements / Statics /

Overdeterminate trusses are employed where overdimensioning is purposely required because safety must be maintained in the event of failure of an element, such as in aircraft construction. With additionally inserted bars a statically determinate truss becomes internally statically indeterminate. In this case the truss is termed statically overdeterminate. 
  The SE 110.22 experimental set-up permits investigation and comparison of statically determinate and statically indeterminate trusses. Using the bars and node discs, a statically determinate, single plane truss is first constructed. On installation of a surplus bar the truss becomes overdeterminate. By way of a load application device, straight or inclined forces are applied to the truss, thereby simulating various load cases. The occurring tensile and compressive forces in the bars are recorded by means of strain gauges. 
  Computerised evaluation is provided by measurement amplifier FL 151. The software is used to manage the measurement data and provide graphical representation of the bar forces. The software features a comprehensive help function.

  The various elements of the experiment are clearly laid-out and housed securely in a storage system. The complete experimental set-up is arranged in the frame SE 112.

  The well-structured instructional material sets out the fundamentals and provides a step-by-step guide through the experiments.


Learning Objectives / Experiments

- Measurement of the bar forces in a statically  determinate and statically overdeterminate, single  plane truss

- Distribution of forces in the single plane truss

  dependent on the use of a surplus bar
- Dependency of the bar forces on the external  force

  * magnitude, direction, point of application
- Comparison of measurement results with  mathematical methods

  * method of joints
  * Ritter’s method of sections


- Basic principle: measurement of forces using  strain gauges


[1] Investigation of bar forces in statically overdeterminate trusses
[2] Surplus bar, longitudinally adjustable
[3] Straight and inclined loading possible
[4] Strain gauge to measure force on each bar
[5] Measurement amplifier FL 151 required
[6] Software to evaluate measurement data
[7] Storage system to house the components

[8] Experimental set-up in frame SE 112


Technical Data

Bars: 8
- 5 bars, fixed 300mm
- 2 bars, fixed 424mm
- 1 bar, adjustable 400...450mm
- angle between bars: 30°, 45°, 60°, 90°
- maximum bar force: 500N
- strain gauge on each bar
- height of truss max. 270mm
- length of truss max. 500mm
Load application device

 -500...+500N, graduations: 10N
Dial gauge: measurement range: 0...20mm


Dimensions and Weight
Weight: approx. 10 kg
Scope of Delivery
1 set of bars
5 node discs
1 load application device
1 set of cables
1 software CD
1 storage system
1 set of instructional material
Order Details

022.11022  SE 110.22  Forces in an Overdeterminate Truss