4.3. SR 08-03-2015 - Laserfiche WebLink

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City of Elk River Jackson Street Water Tower Condition Assessment July 1,2015 CDG Project#15010.00 latticed bars on the inside edges. Put together, these pieces form a square leg that rises to the tank in three sections. Each section is connected with four steel splice plates, two of which are bolted and riveted inside the legs, and two that are bolted on the legs' exterior surfaces. Two issues were observed, both located on the legs, which will need further maintenance beyond the obvious painting. First, the base of each leg is filled with concrete that promotes the drainage of water out of the leg assembly. It appears that water naturally flows to the sides of this concrete and along the edge of the inside of the legs,which has resulted in some deterioration and loss of cross sectional area of the steel. The thickness of the steel channels is important, as this is what transfers the load of the water tower to the foundation. At this time, the condition of the steel is behind the concrete is unknown. It would be important to investigate the condition of the steel behind the concrete further during the painting project by removing a portion of the concrete infill and inspecting the steel. If the corrosion is worse than what is observed presently, some remedial action may need to be done to strengthen the base, such as the addition of steel plates to replace the loss of cross sectional area due to corrosion. If it is determined that additional steel needs to be added, a sample of the steel should be taken and tested to determine its physical properties. Steel produced during the time of the construction of this water tower did not have the same physical properties of modern day steel, and may not be able to be welded. This testing information will inform the design of the connection of any additional steel members, if needed. The second potential concern involves the steel splice plates connecting the leg sections. Some of the plates are bowing as result of rust jacking,which occurs when the backside of the metal rusts and expands, causing the front of the panel to move outward. This appears to be happening exclusively on the eight plates on the outside perimeter of the Tower,which is not surprising since the slope of these surfaces allows water to travel down the legs and flow behind the connection plates. Since these plates hold the legs together, they are integral to the structural integrity of the Tower. If the plates continue to corrode, the connection between each section will weaken and the structural capacity of the legs will diminish. Paint is chipping on the Water Towers legs, tie rods, and horizontal girders; the surface of much of the exposed steel is covered in rust. A significant amount of lichen is also growing on some of these surfaces. The condition of the underside of the tank and its surrounding walkway platform was observed to be similar to that of the legs, tie rods, and girders, with a significant amount of weathered paint and rust. The sides of the tank appeared to be in good condition relative to the rest of the Tower, but the roof and cap are weathered with rust stains present from seams in the roof panels. Considering that the Water Tower structure is no longer supporting the weight of water in a full tank, maintenance and periodic observation will be all that is required, and no major structural modifications will be necessary. Some minor modifications may be necessary as identified above. 2s CC COLLABORATIVE DesignGroup,;nc.