The CRSI Design Guide for Reinforced Concrete Diaphragms is a great resource that provides explanatory materials, including stiffness modeling and analysis. Also included are worked out design examples to illustrate the proper application of the code requirements. It is based on ACI 318-14.
Your question references the ACI318-05 edition. In the 2014 edition of ACI 318, a new chapter devoted to the design and detailing of reinforced concrete diaphragm was included for the first time.