Structural Design |
Structural Design
Structural design considerations
The philosophy of limit state design is used for storage tanks, which should be designed to safely support the imposed loads, but allowing for the properties of plastic. The concept of limit state design is to consider the probability distributions of all parameters (applied loads and material strength and stiffness) to provide better control over risk than traditional design methods.
The two most common limit states to be considered are:
1. Ultimate limit state - the structure should not become unstable or collapse under working loads or foreseeable overload.
2. Serviceability limit state of deflection - deflections of the units and the surrounding ground should be at acceptable levels (for example to prevent surface deformation).
Further advice can be found in CIRIA document C680, Structural design of modular geocellular drainage tanks. S Wilson: 2008.
Waterloc250 has been extensively tested to verify the following structural performance figures.
Structural performance figures
| Property | Vertical loading on top face | Lateral loading on side face |
|---|---|---|
| Short term characteristic compressive strength | 350kN/mē | 82kN/mē |
| Short term load to cause 1mm deflection | 47kN/mē | 7.1kN/mē |
Construction plant
A minimum of 300mm cover must be applied before mechanical compaction can take place. Abnormal construction traffic must be prevented from crossing the tank and in particular cranes and other similar plant should not be located over the tank unless a specific site assessment has been undertaken. Once surfacing is complete, heavy construction traffic should be prevented from passing over the installation unless the design specifically allows for this.
