Research Underway to Build
a Better Salt Storage Shed
A research project is underway to construct a salt storage shed in Newmarket, NH. This storage shed differs from others in size, shape, and the materials used to complete it.
The shed is being constructed under the direction of Professor Charles Goodspeed, Civil Engineering University of New Hampshire (UNH) and in cooperation with David Walker, the Public Works Director in Newmarket. The project is being completed by UNH Civil Engineering Students. The purpose of the study is to test various new materials and techniques and is funded by the Federal Highway Administration, New Hampshire Department of Transportation, and Shimizu Corporation of Tokyo, Japan. Materials for the roof have been donated by US Decking.
The shed is built on an unusually small plot of land. It is nestled between the road and a ledge, which was partially removed to build it. The shed measures only 60 feet across but the design allows for 500 cubic yards of materials to be stored inside. The shed is built on an octagonal foundation. The outside walls will be backfilled.
The floor and walls are constructed of concrete reinforced with Fiber Reinforced Plastic (FRP) grids. The roof is constructed of steel corrugated sheets pre-stressed into a hyperbolic parabolid (hypar) shape. Essentially, a hypar roof is saddleshaped.
FRP was used for reinforcement instead of steel reinforcement because the chloride ions from salt are water soluble and penetrate concrete which eventually rusts steel reinforcement. Rusted steel expands and forces concrete to crack and spall. Composed of carbon and glass fibers, FRP is a non-corrosive material. It was used in a 2-dimensional grid and comes in 4’ x 12’ sheets. The average grid spacing is 4 inches.
The walls are six feet high and 12 inches thick. They are reinforced to flex both inward and outward. Two supports are attached to each wall section to resist lateral loads. The supports are 12” x 16” and the same height as the walls. Four 4’x4’ columns were cast each with six 3/4” x 18” long anchor blots to connect the roof system to the walls. Concrete strengths of 4000 psi were used to construct the walls and 5000 psi in the slab.
The hypar roof materials are economical although the roof is labor intensive to fabricate. Another significant advantage to the hypar roof is that it allows for a high peak (32’) providing room for a front end loader and dump truck to maneuver inside. The entrance to the shed is 13’6” high and 20’ wide.
To construct the hypar roof four panels were fabricated from corrugated steel sheets. Each panel consists of two sheets laid with the corrugations perpendicular to each other. The panels were prestressed by laying the sheets between two telephone poles, with opposite corners pointing out towards the poles. The other corners were secured to the ground using anchor bolts. A cable was run from the top of one pole, beneath the two sheets, through a pulley and to the top of other pole. The cable was then continued to another ground anchor 62 feet away from the pole. A come-along was placed between the ground anchor and the cable. Tension was applied to the cable using the come-along until the sheets are deformed into the desired shape.
To retain the hypar shape approximately 5000 screws were inserted into each panel. The panels were joined along the ridge using steel plates, and the panels were attached to the supports using the six 3/4” x 18” anchor bolts.
The design of the shed allows a municipality to build a structure that will withstand the damaging effects of salt on concrete and be economical to construct.