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How to increase allowable bending moment ? 1.Increase truss dimensions = most effective 2.Increase diameter main chords 3.Increase wall thickness main.

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Presentation on theme: "How to increase allowable bending moment ? 1.Increase truss dimensions = most effective 2.Increase diameter main chords 3.Increase wall thickness main."— Presentation transcript:

1 How to increase allowable bending moment ? 1.Increase truss dimensions = most effective 2.Increase diameter main chords 3.Increase wall thickness main chord

2 Bending moment caused by Wind force Loading force Wind force

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4 Wind loading on a canopy or projection screen Fh= 1,3 x wind Pressure * Wind surface Fmembrane tension = Fh / 0,8

5 Beaufort number Wind speed / wind pressure Land conditions km/hm/skN/m^ Calm. Smoke rises vertically ,001Wind motion visible in smoke ,007Wind felt on exposed skin. Leaves rustle ,02Leaves and smaller twigs in constant motion ,04Dust and loose paper raised. Small branches begin to move ,07Smaller trees sway ,12Large branches in motion. Whistling heard in overhead wires. Umbrella use becomes difficult ,18Whole trees in motion. Effort needed to walk against the wind ,27Twigs broken from trees. Cars veer on road ,37Light structure damage ,50Trees uprooted. Considerable structural damage ,67Widespread structural damage. 12>117>32.70,85Massive and widespread damage to structures.

6 Transversal force ( Also known as shear force )

7 Example’s of situations when transversal forces will be determine the maximum loading: 1.A heavy load on a short span. 2.A heavy load near to the suspension point. 3.Truss constructions underneath a stage floor.

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9 How to increase allowable transversal force ? 1.Increase the diameter of the brace 2.Increase the wall thickness of the brace 3.Increase wall thickness of the main chord

10 NORMAL FORCE

11 Examples of situations when a normal force occurs: Towers Columns Rafter trusses in a MPT or ST roof

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14 How to increase the normal force? 1.Increase tube diameter 2.Increase wall thickness of tubes

15 TORSION FORCE

16 Examples of situations when torsion will occur: Equipment on a boom arm Equipment which are all positioned on one tube of a truss

17 How to increase the normal force? 1.Increase the amount of cross braces inside the truss. 2.Use a bigger truss.

18 Deflection The elastic movement of a structure under load Deformation by self weight and pay load > the truss starts to bend/deflect

19 How to minimise deflection ? 1.Increase truss dimensions = most effective 2.Use stiffer material e.g. steel 3.PRE-camber the truss

20 Example of PRE-camber the truss

21 When is deflection important ? 1.When rigging a fixed LED screen. 2.Personal feeling > a floor which deflects a lot “feels” unsafe

22 Suspending load from a truss system. Heavy loading should always be attached near or to or at the nodepoints Small loadings up to 100 Kg can be attached anywhere on the truss.

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24 Possible mistakes of a Truss.  Parallel running braces  Miss nodding

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26 Miss Nodding

27 Analising loading of truss structures. The type of structure determines the allowable loading. Loading tables are only valid for simply supported spans. Other types of constructions or structures have to be calculated in a structural report.

28 Simply supported span: Truss on two hoists, truss on two towers

29 Continious span: Truss on three or more hoists, truss on three or more towers

30 Span: Free span is the total length between 2 suspension points Loading capacity: The ability of the truss to withstand a load within its tolerances

31 Reaction force on suspension points

32 Situation 1: Spann of 20m loaded with 2000 Kg UDL ( including selfweight of the truss.) The spann is suspended on 2 chainhoist. Eache suspention point will be loaded by 1000 Kg, a 1 ton motor can be used.

33 Situation 2: Spann of 20m loaded with 2000 Kg UDL ( including selfweight of the truss.) the spann is suspended on 3 chainhoist. The 2 outer suspension poins will be loaded with 380 Kg, and the middle suspention point will be loaded with 1240 Kg, the middle motor now needs to be a 2 ton chain hoist.

34 Know your load: Know the suspended loads from your Truss Know the reaction forces on the suspension points Make upfront a rigging plot of the loading setup

35 Know your load: Know the suspended loads from your Truss Know the reaction forces on the suspension points Make upfront a rigging plot of the loading setup

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38 Text underneath the loading table

39 TRUSS STANDARDS Design standards DIN 4113 German standard VPLT SR 1.0 German “Code of practice” BS 8118 British standard BS / BS British standard for design, manufacture and use Euro-code 9 European standard (not enforced yet)

40 TRUSS STANDARDS Standards for temporary structures Design standards DIN 4112 German standard BS Temporary Demountable structures British “code of practice “ EN European standard for temporary demountable structures

41 TECHNICAL TRAINING Questions?


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