The purpose of the FRP wetwell was for transmitting falling water from grade to 64 meters below grade. The wetwell was vertical so shelves were designed so that the water would cascade and dissipate energy. Also, an internal dividing wall was designed.
The ribbed shell wall, shelves, and dividing wall were modeled using the Finite Element Analysis (FEA) program Femap / NX Nastran. The model is shown below. A shell section of 9000 mm length was used so that whole-number spacings of shelves and ribs were modeled.
To increase stiffness, the shelves and dividing wall were designed as foam-core sandwich panels. This was achieved with Femap using a laminate property type. The laminate property allows for specifying layers of different thicknesses and material properties as well as viewing results for each layer. Additionally, bond strength between the layers was checked.