Footing Design

Beam Design Cost Analysis

Riverton City Steel Framed Structure

We used AutoDesk Revit to model the structure. We also created approximate models of the salters to get an idea of how they would look in the structure.

Modeling

Riverton City Public Works moved to a new location and requested the design for the relocation of a steel framed structure to store their snow-plow salters during the summer months. While the structure would be rebuilt as before, it was requested that (4) additional beams (referred to as salter beams) be added to support (4) 3.1 kip snow plow salters. Considering the additional weight of the salters, it was also required that the footings be re-designed to support the new loads and that the existing beams and columns be analyzed to verify that they could support the new weight. The purpose of the structure is to allow the snow plow trucks to back into the structure with the new steel beams in place and still be able to easily load the salters on the truck.

Plans

After demands for the critical beams and columns were calculated by hand and verified by StruCalc, the footings for the new structure were designed. The square footing design can be seen in the detail below. The footings were also designed for the possibility that the snow plow truck drives over the top of the footing.

We decided early on that we would choose a W8-shape beam to support the salters since this shape would fit nicely inside the flanges of the girder, making for easier construction. Our final recommendation for beam size is a W8X21. This beam’s capacity meets all of the demands, as seen in the table below.

The shape of the salter beams was decided after consulting Michael Hunsaker at PDM Steel. Here we learned which shapes were most common and therefore cheapest. W-shapes proved to be the cheapest at $0.38 per pound, while HSS started around $0.50 per pound. Table 4, provided below, shows the overall cost of new materials and labor. By our estimates, the project may cost less than $2000.

Chris BickFooting DesignBeam DesignCost AnalysisPlans

Daniel PaceFooting DesignBeam DesignOptions AnalysisCost Analysis

Reed CrosbyGraduate Mentor

Leah O’NeillWeld DesignSeismic DesignCost AnalysisModelingPoster

The Task

IncrediBuilders Engineering

Limiting States Demand Capacity

Yielding [kip-ft] 23.6 76.5

Lateral Torsional Buckling [kip-ft] 23.6 25.4

Shear [kip] 2.70 62.1Deflection [in] <0.82 0.67

Material Size Length/Volume Quantity Total Cost ($)Weld for salter beam 3/16" 6" 16 68.16Weld for baseplate 1/4" sufficient 6 20.00W8x21 W8x21 15' 4 781.38Rebar #4 30" 36 122.40Concrete 36"x36"x30" 22.5 ft3 6 450.00Anchor Bolts 1/2" 7" 24 40.32Labor - - - 230.00

Grand Total $1712.26

To connect the salter beams to the girders, Riverton City Public Works requested a weld connection. Since the salter beams fit nicely within the flanges of the girders, we have specified two 6” long web-to-web 3/16” fillet welds for each salter-girder connection. The demands were less than 3 kips and the weld provides a 50 kip capacity. If desired, welds only 2” long will still exceed the demands by 14 kips.

Using AutoCAD, we created plans for the structure so that construction of the footings and the addition of the salter beams could go as smoothly as possible.

Options AnalysisTo design the most cost-efficient structure, we needed to explore several options. Several options were easy to rule out due to cost of material, including using HSS pipes in place of W-shape for the salter beams.

A second option was to flip the two bays so the original girders could also act as the salter beams. This would cut out the cost of the salter beams altogether and only require slightly larger footings. However, since the roofing was installed in one direction, the tin and channels were already designed to fit that direction. Changing this would call for new tin and channels, and could cost more than adding four beams to hold the salters.

Seismic DesignAt the request of Riverton City Public Works, we considered seismic design. However, laterally bracing the structure would require cross bracing through the bays, which would render them useless or impractical (as seen below). Our official recommendation is that seismic design not be pursued.

Weld Design

The Design

The demands on the existing columns and girders were recalculated and the capacities exceed the demands. No additional members are needed.

The final steel framed structure is designed to support (4) snow plow salters, two in each bay. Each salter will be supported by two W8X21 beams, with a total of (4) beams. These added beams will fit snugly within the flanges of the existing W12X40 girders, which will allow each beam and girder to be welded web-to-web with two 6” long 3/16” fillet welds. Each footing has been designed to withstand a demand of 16.2 kips. The square footing dimensions are 3 ft2 and 30 inches deep, to meet permafrost depth requirements.