In previous editions of the ACI code the factor Lambda (λ) was limited to specific values for “lightweight concrete” and “sand lightweight concrete”. In the 2008 edition you may now use a more specific value for your particular concrete mix.
So now, rather than determining this value automatically based on input concrete density, there is an input for this factor in the Materials spreadsheet. The Lambda factor affects concrete shear strength and required bar development lengths.
Also new in the 2008 ACI code is a requirement to perform P-Delta analysis (instead of the moment magnification procedure). In order to get code checks in RISA-3D you are now required to turn on P-Delta through the Load Combinations spreadsheet.
There is an option in the Preferences settings of the program (available through the Tools menu) to disable this requirement.