System modeling and analysis considerations

This chapter helps the analyst decide how to model the structural system as a whole. It aims for modeling accuracy that is sufficient for design and addresses evaluation of diaphragm stiffness. The chapter discusses modeling details such as the choice of elements to use for modeling structural components and the specification of element properties. It should be noted that choices in discretization of the structure and modeling of structural components affect computed deformations, and thus the acceptability of a given design is a function not only of the modeling choices, but also of the modeling basis assumed when the acceptance criteria values were established. Modeling of diaphragm flexibility requires use of a three-dimensional model. Unrealistically large damping forces can arise when conventional damping models are used in models of structures undergoing significant softening during nonlinear response.