Fall 2002Biernbaum, MSU HRT 221, pg 13Functional Features and Design Criteria(Meeting 6)Ref: AEN 12Strength and Integrity (see Greenhouse Engineering)The are many different forces acting on the greenhouse structure. An attempt has been madeby the National Greenhouse Manufacturers Association to standardize the terminology andthe requirements for commercially built greenhouses. (See http://www.ngma.com)- dead load: weight of the structure + heat and ventilating equipment + long term crops- live load: due to building use such as workers on the roof or short term crops minimum design - 15 lbs per square foot of floor- snow load: weather information, type of snowminimum design at 15 lbs per square foot of floorgutter connected greenhouses may have problem- wind load: the structure must resist both lateral forces and lifting forces which developmust resist 80 mph wind16-20 lbs per square foot- foundation: must be designed to take vertical load as well as horizontal and lifting forcesdue to windbase of the foundation below the frost lineStructural influence on light transmission- orientation as discussed previously- roof slope influences light transmission35omost satisfactory26 to 28 degrees common (6 - 12 slope)(<26odecreases condensation runoff and snow removal)- minimize structural members to minimize shading, also minimize overheadequipment for heating, electricity, irrigation, etc. which may shade the cropStructural influence on climate control- roof slope on condensation and snow removal- pad to fan distance for evaporative cooling- adequate passive ventilation- heating efficiencysurface area to floor areainfiltration rateStructural limitations to access and working heightWorking height has increased over the years from heights as low as 8 feet to heightsof 10 to 12 feet in Dutch designs and newer construction. It is not unusual to seeeven 14 foot tall gutters at times. May need access for vehicles to remove the crop.
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