An international FRP manufacturer requested the design of two deep wetwells with cascade shelves. The purpose of the FRP wetwells were for transmitting falling water from grade down to as much as 72 meters (240 ft) below grade. For over more than two years Clark Engineers has assisted in the pre-design and design of these wetwells. The design encompassed construction and long term operation as well as upset conditions such as flood and earthquakes. The design had to be competitive economically to compete with the more traditional concrete wetwell.

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.

Each wetwell had a large vent opening near the top. Due to the large opening size a FEA was performed using Solidworks Simulation to design the opening compensation ring.

Finite Element Analysis of a Large [Cascade Wetwell] with Internal Shelves and Wall

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.

Example Model Views

Model Isometric View