Definite methods for the three-dimensional structural analysis of space frames are methods with a great number of unknowns, developed by the application of displacement method to multistory structures. These programs can solve every kind of orthogonal or non-orthogonal general purposed structural systems. The SAP series developed by Wilson (1970. 1980. 1992) and ideCAD STRUCTURAL IDS (1998) are programs using definite methods.

IdeCAD^® STRUCTURAL IDS is a real 3D analysis program going to solution using the same definite methods used by the programs mentioned above. In this program, the story planes are assumed infinitely rigid in themselves. All the displacements and rotations of the joints in the same story are dependent to each other. However, the user can make the displacements of any joint independent of the story.

The structure has a single bearing system and this system is a space frame. The frame elements are columns, beams, shear walls and panels. The panels are the vertical shear walls located between two columns. The elements can be in any location and angle in the space. There may be any kind of steps and intermediate stories. Shortly, every kind of structures that can be modeled by space bars and vertical shear walls and panels can be definitely solved by ideCAD^® STRUCTURAL IDS 3-dimensionally. The process of the 3D analysis method used by the ideCAD^® STRUCTURAL IDS program is summarized below.

The nodes of the structure defined in space are the column-beam or beam joints in the stories. Every joint has six displacement components. If the opposite is not defined by the user, the lateral displacements X and Y and the rotation around Z of all the joints are common. The other three components are the vertical displacement in vertical Z axis and the rotations around X and Y axes. In intermediate stories with no rigid diaphragms all six displacements are appointed independent of each other.

 The stiffness matrices of bar and panel elements are formed in their own local axes. The stiffness matrices of columns and beams are in 12x12 dimensions. On the other hand, the stiffness matrices of panels are in 6x6 dimensions.

The element stiffness matrices are converted to structure global stiffness by means of direction cosines. This operation is made by means of special bar transformation matrices, considering the dependence to joints.

The global stiffness matrix of the structure is formed.

The global stiffness matrix and the load vector of the structure is solved by means of a special Gauss Elimination Method and the story displacements are found from the global coordinates.

The displacements are calculated at element coordinates.

12 end forces are found for every bar.

The end forces of columns and beams are Tx, Ty, Nz, Mx, My, Mz

The end forces of panel elements are N, T, M

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