Well-conceived shelter construction practices are vital to protect hay supplies from Oklahoma’s often devastating weather, where wind gusts of 50 to 60 miles per hour are not uncommon.
“Producers often talk about the weather, but proper construction of hay shelters is one area where they can actually do something about it,” said Carol Jones, Oklahoma State University biosystems and agricultural engineer.
Most critical wind forces are uplifting forces which tend to pull the roof off the frame and poles out of the ground. Jones said the direction of the force, upward, is the opposite of what many people expect.
“If we’re looking at a partially filled building with the wind blowing in the open side, the force could exceed 20 pounds per square foot uplift,” she said. “For a 40-foot by 80-foot building, this is equivalent to 32 tons of force pushing upward.”
Jones said the roof must be tied down all the way to the ground to resist this upward force during high winds.
Roof frames and trusses or rafters should be fastened to supporting members with tie-downs such as storm clips, framing anchors and straps. Producers also should fasten support members and beams or girders to framing poles via bolts or pole barn nails.
“Knee braces can be added to increase the strength and stiffness of these joints,” Jones said. “If constructing a new shelter, poles should be anchored in concrete rather than using tamped earth anchorages.”
Concrete anchorages are many times stronger than tamped earth in resisting uplift, and full, reinforced anchorages can increase the pole’s lateral stiffness in resisting racking of the frame.
Jones said the additional cost is minimal for building a new shelter or reinforcing an existing one.
“Hay supplies are a key part of most livestock operations’ profitability,” she said. “It’s not worth risking a reduction in hay quality when it can be protected so easily.”