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STAAD BASICS
- NOTES ON THE EFFECTIVE USE OF STAAD-PRO REL 3.1 -

- FOR STRUCTURAL ANALYSIS -

By R. P. Clarke

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TABLE OF CONTENTS

1.0

SKELETAL STRUCTURES – STATIC LOADS 1.1 SIGN CONVENTION 1.2 FUNDAMENTAL COMMANDS 1.3 EXAMPLE

3 5 6

2.0

CONTINUUM STRUCTURES – STATIC LOADS 2.1 2.2 2.3 SIGN CONVENTION FUNDAMENTALCOMMANDS EXAMPLE

9 9 11 11

3.0

SKELETAL STRUCTURES - DYNAMIC LOADS 3.1 3.2 FUNDAMENTAL COMMANDS EXAMPLE

14 14 15

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STAAD BASICS

The following is a description of fundamental considerations for the effective use of STAAD-PRO Release 3.1 for the analysis of structures. It must be mentioned however that since STAAD is a computer program, blind faith should notbe placed in STAAD or any other engineering program. This is due to the following factors. (1): The results are only as good as the modeling of the structure in terms of load effects representation, effective structural systems, the connection behavior, and the material idealizations. (2): The procedures used in programs are not transparent to the user. (3): Computer programs usually have bugs.(4): Dependence on software can reduce the engineer's intuition of the actual behavior of the structure. It is therefore strongly recommended that until at least one year's experience of continually using STAAD is obtained, and for important structures, parallel hand calculations for the analysis and design of the structure be done as well. For section 1.0 it is presumed that the reader understandsStructural Theory and the Stiffness Matrix Method of Structural Analysis. For section 2.0 it is presumed that the reader understands the fundamentals of Plate Theory, and the Finite Element Method based on the stiffness formulation. For section 3.0 it is presumed that the reader understands Structural Dynamic Analysis by the Lumped Mass Time History Method. 1.0 SKELETAL STRUCTURES – STATIC LOADS1.1 SIGN CONVENTION

It is vital to understand the STAAD coordinate system in order to properly use STAAD. This is needed to ensure that the input data is as intended, and for the interpretation of the analysis results. Coordinate Systems: Since STAAD uses the Matrix Displacement Method of structural analysis, there are 2 Cartesian coordinate systems - the local and the global. The geometry ofthe structure as a whole is defined by the nodes at the ends of the various structural members, and each node has a unique number. Each member also has a unique number and the topology of the member is defined relative to the node numbers at its ends. This establishes the "MEMBER INCIDENCES" table. The location of each node is defined relative to a global coordinate system. By default, the origin ofthe global coordinate system is at node number 1.

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The location of points or sections within each structural member is defined relative to the local coordinate system with the origin at the left end node of the member viewed horizontally. Each member has its own local coordinate system.

A. FORCES AT A SECTION OF A MEMBER This applies to the sign of the quantityin the STAAD member stress diagram such as the bending moment diagram. POSITIVE FORCE AT THE SECTION NEGATIVE FORCE AT THE SECTION Bending: Mz Axial: Fx Shear: Fy

B. FORCES ACTING ON A MEMBER'S END In STAAD this is called the "MEMBER END FORCES"

POSITIVE FORCE ON THE MEMBER NEGATIVE FORCE ON THE MEMBER

Bending: Mz Axial: Fx Shear: Fy Torsion: Mx

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1.2FUNDAMENTAL ANALYSIS COMMANDS

Regardless of the structure being analysed, the following are fundamental steps and STAAD command keywords shown in the brackets: 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. Define whether the problem is 2D or 3D (STAAD PLANE or SPACE) Define the length and force units (UNITS) Define the nodes and their locations (JOINT COORDINATES) Define the member and their nodes...