Summarized Design Calculations – Pressure Break Tank Adam Swierczek
EWB Guatemala Project 12/6/10
Objective: Determine whether the provided architectural drawings are sufficient for a Pressure Break Tank (PBT) design.
Allowable tension in concrete based on AASHTO recommendations
Side Panel Design
From Roark, Formulas for Stress and Strain 5th Edition, Table 26, Case 9d – One edge free, other three edges supported. Distributed load varies linearly along the length of the side panel.
The stress, s, on the side panel is significantly less than the allowable tensile stress, therefore no reinforcement is needed. Also, since the PBT will be placed below grade, there is a lack of large temperature differences, meaning no shrinkage and temperature steel is needed.
Bottom Design
From Roark, Formulas for Stress and Strain 4th Edition, Table X, Case 36 –all four edges supported. Distributed load is uniform over the entire bottom of the PBT.
The stress, s, on the bottom is significantly less than the allowable tensile stress, therefore no reinforcement is needed. Also, since the PBT will be placed below grade, there is a lack of large temperature differences, meaning no shrinkage and temperature steel is needed.
Lid Design
Deflections
Minimum Thickness of Lid – ACI 318-08 Table 9.5(a) – simply supported, one-way slab
The designed lid thickness is sufficient for deflection requirements.
Flexure
From Roark, Formulas for Stress and Strain 4th Edition, Table X, Case 36 –all four edges supported. Distributed load is uniform over the entire bottom of the PBT.
The stress, s, on the lid is significantly less than the allowable tensile stress, therefore no reinforcement is needed. However, since the lid will be placed above grade, shrinkage and temperature steel should be used.
Shear
Shear capacity, φVn, is computed using equation 22-9 from ACI 318-08.
The maximum stress seen by the lid is 202lb, while the shear capacity is 1034.1lb. This means that the lid design is more than sufficient for shear requirements. The design checks allow for the PBT to be constructed without the use of structural reinforcement. In addition, all design checks were satisfied by the design depicted in the architectural plans.
Weir Strength Design
Stress Design:
From Roark, Formulas for Stress and Strain 5th Edition, Table 26, Case 10d – One edge free, other three edges supported. Distributed load varies linearly along the length of the side panel.
The minimum thickness needed for stress purposes of the weir is 0.32in.
Compressive Design:
A slender column is defined by ACI 318-08 Section 10.10.1 as having a ratio of . Solve for the thickness, t.
Assuming a factor of safety of 1.75, t = 4.72” = 12cm
Recommended reinforcement of a column is around 1% of the total area of the column.
Compressive strength of the weir is as follows:
These calculations show that if the weir is 12cm thick, it can withstand significantly more compressive force than one adult could provide. In addition to compressive reinforcement, transverse reinforcement of #4 bars should be placed every 6 in.
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