4Wind loading on a canopy or projection screen Fh= 1,3 x wind Pressure * Wind surface Fmembrane tension = Fh / 0,8
5Wind speed / wind pressure Beaufort numberWind speed / wind pressureLand conditionskm/hm/skN/m^20-0.2Calm. Smoke rises vertically.11-60,001Wind motion visible in smoke.27-110,007Wind felt on exposed skin. Leaves rustle.312-190,02Leaves and smaller twigs in constant motion.420-290,04Dust and loose paper raised. Small branches begin to move.530-390,07Smaller trees sway.640-500,12Large branches in motion. Whistling heard in overhead wires. Umbrella use becomes difficult.751-620,18Whole trees in motion. Effort needed to walk against the wind.863-750,27Twigs broken from trees. Cars veer on road.976-870,37Light structure damage.1088-1020,50Trees uprooted. Considerable structural damage.110,67Widespread structural damage.12>117>32.70,85Massive and widespread damage to structures.
7Example’s of situations when transversal forces will be determine the maximum loading: A heavy load on a short span.A heavy load near to the suspension point.Truss constructions underneath a stage floor.
27Analising 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.
28Simply supported span: Truss on two hoists,truss on two towers
29Continious span:Truss on three or more hoists,truss on three or more towers
30Span:Free span is the total length between 2 suspension pointsLoading capacity:The ability of the truss to withstand a load within its tolerances
32Situation 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.
33Situation 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.
34Know your load: Know the suspended loads from your Truss Know the reaction forces on the suspension pointsMake upfront a rigging plot of the loading setup
35Know your load: Know the suspended loads from your Truss Know the reaction forces on the suspension pointsMake upfront a rigging plot of the loading setup
39TRUSS STANDARDS Design standards DIN 4113 German standard VPLT SR 1.0 German “Code of practice”BS British standardBS / BS British standard for design, manufacture and useEuro-code 9 European standard (not enforced yet)
40TRUSS STANDARDS Standards for temporary structures Design standards DIN German standardBS Temporary Demountable structures British “code of practice “EN European standard for temporary demountable structures