Element Library

The analysis engine supports a variety of 1 and 2-dimensional finite elements typically used in the modeling of bridge structures. The 1-dimensional element is always linear elastic while the 2-dimensional element may be either linear elastic or be assigned material properties that vary with time. All elements may be placed into and removed from the system at any solution interval. Once an element is removed from the system it cannot be returned. All elements can either be plane or space type elements. Plane frame elements lie in the global X-Y plane and are formed identically as their space frame counter-parts.

Setting	Description
1-Dimensional Element	The 1-dimensional element has either 1 or 2 defining nodes and is used to model supports or the connection between adjacent structural elements.
Space Frame Element	The space frame element is a two-node linear bending element: a third node is associated with it, referred to as the K-node, in order to give direction to the local 2-2 and 3-3 axes. The 1-axis is oriented along the axis of the element. The element has twelve degrees-of-freedom (DOF): three translational and three rotational at each node point. Shear deformations are considered if a shear area is specified in either the 2 or 3 direction. The shear modulus is computed using the following equation: (0.5 * E) / (1+v), where v is the Poisson's Ratio. The plane frame element is identical to the space frame element accept that it has six DOF and it is constrained to the global X-Y plane, with positive "Y" being vertically upward.
Element Stiffness Matrix	The element stiffness matrix is developed by computing the initial-end flexibility coefficient matrix, inverting to obtain the initial end stiffness matrix and then using equilibrium equations to obtain the remaining stiffness coefficients. This method of computing the element stiffness matrix permits section properties to change along the length of the element since the end flexibility coefficients are computed using a summation procedure over the length of the element.
Non-Prismatic	Section properties will almost always change within a span element when those components are non-prismatic. Non-prismatic spans are modeled as a series of prismatic segments. The number of prismatic segments and their lengths are determined by the user and are independent of the number of intermediate node points on each span. Therefore, node points will not usually coincide with changes in section properties and thus the need for the flexibility approach for the element stiffness matrix.
Element Load Vectors	The element load vectors are computed using a similar approach to the element stiffness matrix. Initial end displacements are obtained due to loads over each prismatic segment, and then transformed into initial end using the element stiffness matrix. Terminal end forces are obtained using equilibrium equations.