Bentley 2006 User Manual

STAAD.Pro 2006

TECHNICAL REFERENCE MANUAL

Part Number: DAA036990-1/0001

A Bentley Solutions Center

www.reiworld.com
www.bentley.com/staad

STAAD.Pro 2006 is a suite of proprietary computer programs

of Research Engineers, a Bentley Solutions Center. Although
every effort has been made to ensure the correctness of these
programs, REI will not accept responsibility for any mistake,
error or misrepresentation in or as a result of the usage of
these programs.

RELEASE 2006

© 2006 Bentley Systems, Incorporated. All Rights Reserved.

Published March, 2006

About STAAD.Pro

STAAD.Pro is a general purpose structural analysis and design program with
applications primarily in the building industry - commercial buildings, bridges and
highway structures, industrial structures, chemical plant structures, dams, retaining
walls, turbine foundations, culverts and other embedded structures, etc. The program
hence consists of the following facilities to enable this task.

1. Graphical model generation utilities as well as text editor based commands for

creating the mathematical model. Beam and column members are represented using
lines. Walls, slabs and panel type entities are represented using triangular and
quadrilateral finite elements. Solid blocks are represented using brick elements.
These utilities allow the user to create the geometry, assign properties, orient cross
sections as desired, assign materials like steel, concrete, timber, aluminum, specify
supports, apply loads explicitly as well as have the program generate loads, design
parameters etc.

2. Analysis engines for performing linear elastic and pdelta analysis, finite element

analysis, frequency extraction, and dynamic response (spectrum, time history,
steady state, etc.).

3. Design engines for code checking and optimization of steel, aluminum and timber

members. Reinforcement calculations for concrete beams, columns, slabs and shear
walls. Design of shear and moment connections for steel members.

4. Result viewing, result verification and report generation tools for examining

displacement diagrams, bending moment and shear force diagrams, beam, plate and
solid stress contours, etc.

5. Peripheral tools for activities like import and export of data from and to other

widely accepted formats, links with other popular softwares for niche areas like
reinforced and prestressed concrete slab design, footing design, steel connection
design, etc.

6. A library of exposed functions called OpenSTAAD which allows users to access

STAAD.Pro’s internal functions and routines as well as its graphical commands to
tap into STAAD’s database and link input and output data to third-party software
written using languages like C, C++, VB, VBA, FORTRAN, Java, Delphi, etc.
Thus, OpenSTAAD allows users to link in-house or third-party applications with
STAAD.Pro.

About the STAAD.Pro Documentation

The documentation for STAAD.Pro consists of a set of manuals as described below.
These manuals are normally provided only in the electronic format, with perhaps some
exceptions such as the Getting Started Manual which may be supplied as a printed book
to first time and new-version buyers.

All the manuals can be accessed from the Help facilities of STAAD.Pro. Users who
wish to obtain a printed copy of the books may contact Research Engineers. REI also
supplies the manuals in the PDF format at no cost for those who wish to print them on
their own. See the back cover of this book for addresses and phone numbers.

Getting Started and Tutorials : This manual contains information on the contents of
the STAAD.Pro package, computer system requirements, installation process, copy
protection issues and a description on how to run the programs in the package.
Tutorials that provide detailed and step-by-step explanation on using the programs are
also provided.

Examples Manual

This book offers examples of various problems that can be solved using the STAAD
engine. The examples represent various structural analyses and design problems
commonly encountered by structural engineers.

Graphical Environment

This document contains a detailed description of the Graphical User Interface (GUI) of
STAAD.Pro. The topics covered include model generation, structural analysis and
design, result verification, and report generation.

Technical Reference Manual

This manual deals with the theory behind the engineering calculations made by the
STAAD engine. It also includes an explanation of the commands available in the
STAAD command file.

International Design Codes

This document contains information on the various Concrete, Steel, and Aluminum
design codes, of several countries, that are implemented in STAAD.

The documentation for the STAAD.Pro Extension component(s) is available separately.

Table of Contents

STAAD.PRO Technical Reference Manual

Section 1 General Description 1 -

1.1 Introduction 1 - 1

1.2 Input Generation 2

1.3 Types of Structures 2

1.4 Unit Systems 3

1.5 Structure Geometry and Coordinate Systems 4

1.5.1 Global Coordinate System 4

1.5.2 Local Coordinate System 7

1.5.3 Relationship Between Global & Local Coordinates 11

1.6 Finite Element Information 18

1.6.1 Plate/Shell Element 18

1.6.2 Solid Element 31

1.6.3 Surface Element 35

1.7 Member Properties 37

1.7.1 Prismatic Properties 39

1.7.2 Built-In Steel Section Library 41

1.7.3 User Provided Steel Table 42

1.7.4 Tapered Sections 42

1.7.5 Assign Command 42

1.7.6 Steel Joist and Joist Girders 43

1.7.7 Composite Beams and Composite Decks 47

1.7.8 Curved Members 48

1.8 Member/Element Release 48

1.9 Truss/Tension/Compression - Only Members 49

1.10 Tension/Compression - Only Springs 49

1.11 Cable Members 50

1.11.1 Linearized Cable Members 50

1.11.2 Non Linear Cable & Truss Members 53

1.12 Member Offsets 54

1.13 Material Constants 55

1.14 Supports 56

1.15 Master/Slave Joints 57

1.16 Loads 57

1.16.1 Joint Load 57

1.16.2 Member Load 58

1.16.3 Area Load / Oneway Load / Floor Load 60

1.16.4 Fixed End Member Load 62

1.16.5 Prestress and Poststress Member Load 62

1.16.6 Temperature/Strain Load 1 - 65

1.16.7 Support Displacement Load 1 - 65

1.16.8 Loading on Elements 65

1.17 Load Generator 67

1.17.1 Moving Load Generator 67

1.17.2 Seismic Load Generator based on UBC, IBC and other
codes 68

1.17.3 Wind Load Generator 69

1.18 Analysis Facilities 70

1.18.1 Stiffness Analysis 70

1.18.2 Second Order Analysis 75

1.18.2.1 P-Delta Analysis 75

1.18.2.2 Imperfection Analysis 77

1.18.2.3 Non Linear Analysis 77

1.18.2.4 Multi-Linear Analysis 77

1.18.2.5 Tension / Compression Only Analysis 78

1.18.2.6 Nonlinear Cable/Truss Analysis 78

1.18.3 Dynamic Analysis 81

1.18.3.1 Solution of the Eigenproblem 81

1.18.3.2 Mass Modeling 81

1.18.3.3 Damping Modeling 83

1.18.3.4 Response Spectrum Analysis 83

1.18.3.5 Response Time History Analysis 84

1.18.3.6 Steady State and Harmonic Response 86

1.19 Member End Forces 88

1.19.1 Secondary Analysis 93

1.19.2 Member Forces at Intermediate Sections 93

1.19.3 Member Displacements at Intermediate Sections 93

1.19.4 Member Stresses at Specified Sections 94

1.19.5 Force Envelopes 94

1.20 Multiple Analyses 95

1.21 Steel/Concrete/Timber Design 96

1.22 Footing Design 96

1.23 Printing Facilities 96

1.24 Plotting Facilities 97

1.25 Miscellaneous Facilities 97

1.26 Post Processing Facilities 1 - 98

Section 2 American Steel Design 2 -

2.1 Design Operations 2 - 1

2.2 Member Properties 2

2.2.1 Built - in Steel Section Library 2

2.3 Allowables per AISC Code 7

2.3.1 Tension Stress 7

2.3.2 Shear Stress 7

2.3.3 Stress Due To Compression 7

2.3.4 Bending Stress 7

2.3.5 Combined Compression and Bending 9

2.3.6 Singly Symmetric Sections 2 - 9

2.3.7 Torsion per Publication T114 2 - 9

2.3.8 Design of Web Tapered Sections 11

2.3.9 Slender compression elements 11

2.4 Design Parameters 11

2.5 Code Checking 18

2.6 Member Selection 19

2.6.1 Member Selection by Optimization 20

2.6.2 Deflection Check With Steel Design 20

2.7 Truss Members 20

2.8 Unsymmetric Sections 21

2.9 Composite Beam Design as per AISC-ASD 21

2.10 Plate Girders 23

2.11 Tabulated Results of Steel Design 23

2.12 Weld Design 26

2.13 Steel Design per AASHTO Specifications 29

2.14 Steel Design per AISC/LRFD Specification 56

2.14.1 General Comments 56

2.14.2 LRFD Fundamentals 57

2.14.3 Analysis Requirements 58

2.14.4 Section Classification 59

2.14.5 Axial Tension 59

2.14.6 Axial Compression 60

2.14.7 Flexural Design Strength 61

2.14.8 Combined Axial Force And Bending 61

2.14.9 Design for Shear 61

2.14.10 Design Parameters 62

2.14.11 Code Checking and Member Selection 64

2.14.12 Tabulated Results of Steel Design 65

2.14.13 Composite Beam Design per the American LRFD

3rd edition code 66

2.15 Design per American Cold Formed Steel Code 73

2.16 Castellated Beams 2 - 82

Section 3 American Concrete Design 3 -

3.1 Design Operations 3 - 1

3.2 Section Types for Concrete Design 2

3.3 Member Dimensions 2

3.4 Design Parameters 3

3.5 Slenderness Effects and Analysis Consideration 6

3.6 Beam Design 7

3.6.1 Design for Flexure 7

3.6.2 Design for Shear 8

3.6.3 Design for Anchorage 8

3.6.4 Description of Output for Beam Design 9

3.6.5 Cracked Moment of Inertia – ACI Beam Design 12

3.7 Column Design 13

3.8 Designing elements, shear walls, slabs 18

3.8.1 Element Design 3 - 18

3.8.2 Shear Wall Design 3 - 20

3.8.3 Slabs and RC Designer 28

3.8.4 Design of I-shaped beams per ACI-318 3 - 35

Section 4 Timber Design 4 -

4.1 Timber Design 4 - 1

4.2 Design Operations 13

4.3 Input Specification 16

4.4 Code Checking 17

4.5 Orientation of Lamination 18

4.6 Member Selection 4 - 18

Section 5 Commands and Input Instructions 5 -

5.1 Command Language Conventions 5 - 2

5.1.1 Elements of The Commands 3

5.1.2 Command Formats 5

5.1.3 Listing of Members by Specification of Global Ranges 8

5.2 Problem Initiation And Title 10

5.3 Unit Specification 12

5.4 Input/Output Width Specification 14

5.5 Set Command Specification 15

5.6 Separator Command 19

5.7 Page New Command 20

5.8 Page Length/Eject Command 21

5.9 Ignore Specifications 22

5.10 No Design Specification 23

5.11 Joint Coordinates Specification 24

5.12 Member Incidences Specification 29

5.13 Elements and Surfaces 33

5.13.1 Plate and Shell Element Incidence Specification 34

5.13.2 Solid Element Incidences Specification 36

5.13.3 Surface Entities Specification 38

5.14 Element Mesh Generation 42

5.15 Redefinition of Joint and Member Numbers 48

5.16 Listing of entities by Specification of GROUPS 50

5.17 Rotation of Structure Geometry 53

5.18 Inactive/Delete Specification 54

5.19 User Steel Table Specification 56

5.20 Member Property Specification 65

5.20.1 Specifying Properties from Steel Tables 69

5.20.2 Prismatic Property Specification 73

5.20.2.1 Prismatic Tapered Tube Property Specification 75

5.20.3 Tapered Member Specification 77

5.20.4 Property Specification from User Provided Table 78

5.20.5 Assign Profile Specification 79

5.20.6 Examples of Member Property Specification 80

5.20.7 Composite Decks 5 - 82

5.20.8 Curved Member Specification 5 - 86

5.20.9 Applying Fireproofing on members

5.21 Element/Surface Property Specification 103

5.21.1 Element Property Specification 104

5.21.2 Surface Property Specification 105

5.22 Member/Element Releases 106

5.22.1 Member Release Specification 107

5.22.2 Element Release Specification 110

5.22.3 Element Ignore Stiffness 112

5.23 Member Truss/Cable/Tension/Compression Specification 113

5.23.1 Member Truss Specification 114

5.23.2 Member Cable Specification 116

5.23.3 Member Tension/Compression Specification 118

5.24 Element Plane Stress and Inplane Rotation Specification 123

5.25 Member Offset Specification 125

5.26 Specifying and Assigning Material Constants 127

5.26.1 The Define Material Command 129

5.26.2 Specifying CONSTANTS for members, plate elements
and solid elements 131

5.26.3 Surface Constants Specification 138

5.26.4 Modal Damping Information 140

5.26.5 Composite Damping for Springs 143

5.26.6 Member Imperfection Information 144

5.27 Support Specifications 145

5.27.1 Global Support Specification 146

5.27.2 Inclined Support Specification 150

5.27.3 Automatic Spring Support Generator for Foundations 153

5.27.4 Multi-linear Spring Support Specification 158

5.27.5 Spring Tension/Compression Specification 161

5.28 Master/Slave Specification 166

5.29 Draw Specifications 169

5.30 Miscellaneous Settings for Dynamic Analysis 170

5.30.1 Cut-Off Frequency, Mode Shapes or Time 171

5.30.2 Mode Selection 173

5.31 Definition of Load Systems 175

5.31.1 Definition of Moving Load System 176

5.31.2 Definitions for Static Force Procedures for Seismic
Analysis 181

5.31.2.1 UBC 1997 Load Definition 182

5.31.2.2 UBC 1994 or 1985 Load Definition 187

5.31.2.3 Colombian Seismic Load 192

5.31.2.4 Japanese Seismic Load 195

5.31.2.5 Definition of Lateral Seismic Load per IS:1893 198

5.31.2.6 IBC 2000/2003 Load Definition 201

5.31.2.7 CFE (Comision Federal De Electricidad)

Seismic Load 208

5.31.2.8 NTC (Normas Técnicas Complementarias)

Seismic Load 212

5.31.2.9 RPA (Algerian) Seismic Load 5 - 217

98

5.31.2.10 Canadian (NRC 1995) Seismic Load 5 - 221

5.31.3 Definition of Wind Load 234

5.31.4 Definition of Time History Load 238

5.31.5 Definition of Snow Load 244

5.32 Loading Specifications 245

5.32.1 Joint Load Specification 247

5.32.2 Member Load Specification 248

5.32.3 Element Load Specifications 251

5.32.3.1 Element Load Specification - Plates 252

5.32.3.2 Element Load Specification - Solids 256

5.32.3.3 Element Load Specification - Joints 258

5.32.3.4 Surface Loads Specification 261

5.32.4 Area Load/One Way Load/Floor Load Specification 264

5.32.5 Prestress Load Specification 278

5.32.6 Temperature Load Specification 285

5.32.7 Fixed-End Load Specification 287

5.32.8 Support Joint Displacement Specification 288

5.32.9 Selfweight Load Specification 291

5.32.10 Dynamic Loading Specification 292

5.32.10.1 Response Spectrum Specification 293

5.32.10.1.1 Response Spectrum Specification in
Conjunction with the Indian IS: 1893
(Part 1)-2002 Code for Dynamic Analysis 299

5.32.10.1.2 Response Spectrum Specification per
Eurocode 8 304

5.32.10.2 Application of Time Varying Load for Response

History Analysis 310

5.32.11 Repeat Load Specification 313

5.32.12 Generation of Loads 316

5.32.13 Generation of Snow Loads 330

5.33 Rayleigh Frequency Calculation 331

5.34 Modal Calculation Command 333

5.35 Load Combination Specification 334

5.36 Calculation of Problem Statistics 339

5.37 Analysis Specification 340

5.37.1 Steady State & Harmonic Analysis 346

5.37.1.1 Purpose 347

5.37.1.2 Define Harmonic Output Frequencies 350

5.37.1.3 Define Load Case Number 351

5.37.1.4 Steady Ground Motion Loading 352

5.37.1.5 Steady Force Loading 354

5.37.1.6 Harmonic Ground Motion Loading 357

5.37.1.7 Harmonic Force Loading 360

5.37.1.8 Print Steady State/Harmonic Results 364

5.37.1.9 Last Line of Steady State/Harmonic Analysis 367

5.38 Change Specification 368

5.39 Load List Specification 371

5.40 Section Specification 373

5.41 Print Specifications (includes CG and Story Drift) 5 - 375

5.42 Stress/Force output printing for Surface Entities 5 - 382

5.43 Print Section Displacement 384

5.44 Print Force Envelope Specification 386

5.45 Post Analysis Printer Plot Specifications 388

5.46 Size Specification 389

5.47 Steel and Aluminum

5.47.1 Parameter Specifications 392

5.47.2 Code Checking Specification 395

5.47.3 Member Selection Specification 396

5.47.4 Member Selection by Optimization 398

5.47.5 Weld Selection Specification 399

5.48 Group Specification 400

5.49 Steel Take Off Specification 403

5.50 Timber Design Specifications 404

5.50.1 Timber Design Parameter Specifications 405

5.50.2 Code Checking Specification 406

5.50.3 Member Selection Specification 407

5.51 Concrete Design Specifications 408

5.51.1 Design Initiation 409

5.51.2 Concrete Design-Parameter Specification 410

5.51.3 Concrete Design Command 412

5.51.4 Concrete Take Off Command 413

5.51.5 Concrete Design Terminator 414

5.52 Footing Design Specifications 415

5.52.1 Design Initiation 418

5.52.2 Footing Design Parameter Specification 419

5.52.3 Footing Design Command 420

5.52.4 Footing Design Terminator 422

5.53 Shear Wall Design 423

5.53.1 Definition of Wall Panels for Shear Wall Design 425

5.53.2 Shear Wall Design Initiation 426

5.54 End Run Specification 5 - 428

Design Specifications 391

Index

General Description

Section

1.1 Introduction

The STAAD.Pro 2006 Graphical User Interface (GUI) is normally used

to create all input specifications and all output reports and displays (See
the Graphical Environment manual). These structural modeling and
analysis input specifications are stored in a text file with extension
“.STD”. When the GUI does a File Open to start a session with an existing
model, it gets all of its information from the STD file. A user may
edit/create this STD file and have the GUI and the analysis engine both
reflect the changes.

The STD file is processed by the STAAD analysis “engine” to produce
results that are stored in several files with extensions such as ANL, BMD,
TMH, etc. The ANL text file contains the printable output as created by
the specifications in this manual. The other files contain the results
(displacements, member/element forces, mode shapes, section
forces/moments/displacements, etc.) that are used by the GUI in post
processing mode.

This section of the manual contains a general description of the analysis
and design facilities available in the STAAD engine. Specific information
on steel, concrete, and timber design is available in Sections 2, 3, and 4 of
this manual, respectively. Detailed STAAD engine STD file command
formats and other specific user information is presented in Section 5.

The objective of this section is to familiarize the user with the basic
principles involved in the implementation of the various analysis/design
facilities offered by the STAAD engine. As a general rule, the sequence in

1

1-1

General Description

F

Section 1

1-2

which the facilities are discussed follows the recommended sequence of
their usage in the STD input file.

1.2 Input Generation

The GUI (or user) communicates with the STAAD analysis engine through
the STD input file. That input file is a text file consisting of a series of
commands which are executed sequentially. The commands contain either
instructions or data pertaining to analysis and/or design. The elements and
conventions of the STAAD command language are described in Section 5
of this manual.

The STAAD input file can be created through a text editor or the GUI
Modeling facility. In general, any text editor may be utilized to edit/create
the STD input file. The GUI Modeling facility creates the input file
through an interactive menu-driven graphics oriented procedure.

1.3 Types of Structures

A STRUCTURE can be defined as an assemblage of elements. STAAD is
capable of analyzing and designing structures consisting of both frame,
plate/shell and solid elements. Almost any type of structure can be
analyzed by STAAD.

A SPACE structure, which is a three dimensional framed

or input,

see section

5.2

structure with loads applied in any plane, is the most general.

A PLANE structure is bound by a global X-Y coordinate

system with loads in the same plane.

A TRUSS structure consists of truss members which can

have only axial member forces and no bending in the members.

A FLOOR structure is a two or three dimensional

structure having no horizontal (global X or Z) movement of the
structure [FX, FZ & MY are restrained at every joint]. The floor
framing (in global X-Z plane) of a building is an ideal example of
a FLOOR structure. Columns can also be modeled with the floor in
a FLOOR structure as long as the structure has no horizontal
loading. If there is any horizontal load, it must be analyzed as a
SPACE structure.

Section 1

F

Specification of the correct structure type reduces the number
of equations to be solved during the analysis. This results in a
faster and more economic solution for the user. The degrees of
freedom associated with frame elements of different types of
structures is illustrated in Figure 1.1.

Structure Types

1-3

Figure 1.1

1.4 Unit Systems

or input,

see section

5.3

The user is allowed to input data and request output in almost all
commonly used engineering unit systems including MKS, SI and
FPS. In the input file, the user may change units as many times as
required. Mix and match between length and force units from
different unit systems is also allowed. The input-unit for angles (or
rotations) is degrees. However, in JOINT DISPLACEMENT
output, the rotations are provided in radians. For all output, the
units are clearly specified by the program.

General Description

F

Section 1

1-4

1.5 Structure Geometry and Coordinate Systems

A structure is an assembly of individual components such as
beams, columns, slabs, plates etc.. In STAAD, frame elements and
plate elements may be used to model the structural components.
Typically, modeling of the structure geometry consists of two
steps:

A. Identification and description of joints or nodes.

B. Modeling of members or elements through specification of

connectivity (incidences) between joints.

In general, the term MEMBER will be used to refer to frame

or input,

see sections

5.11 to 5.17

elements and the term ELEMENT will be used to refer to
plate/shell and solid elements. Connectivity for MEMBERs may be
provided through the MEMBER INCIDENCE command while
connectivity for ELEMENTs may be provided through the
ELEMENT INCIDENCE command.

STAAD uses two types of coordinate systems to define the
structure geometry and loading patterns. The GLOBAL coordinate
system is an arbitrary coordinate system in space which is utilized
to specify the overall geometry & loading pattern of the structure.
A LOCAL coordinate system is associated with each member (or
element) and is utilized in MEMBER END FORCE output or local
load specification.

1.5.1 Global Coordinate System

The following coordinate systems are available for specification of
the structure geometry.

A. Conventional Cartesian Coordinate System: This coordinate

system (Fig. 1.2) is a rectangular coordinate system (X, Y, Z)
which follows the orthogonal right hand rule. This coordinate
system may be used to define the joint locations and loading

Section 1

directions. The translational degrees of freedom are denoted by

, u2, u3 and the rotational degrees of freedom are denoted by u4,

u

1

& u6.

u

5

B. Cylindrical Coordinate System: In this coordinate system, (Fig.

1.3) the X and Y coordinates of the conventional cartesian system
are replaced by R (radius) and Ø (angle in degrees). The Z
coordinate is identical to the Z coordinate of the cartesian system
and its positive direction is determined by the right hand rule.

C. Reverse Cylindrical Coordinate System: This is a cylindrical type

coordinate system (Fig. 1.4) where the R- Ø plane corresponds to
the X-Z plane of the cartesian system. The right hand rule is
followed to determine the positive direction of the Y axis.

1-5

Figure 1.2 : Cartesian (Rectangular) Coordinate System

General Description
Section 1

1-6

Figure 1.3 : Cylindrical Coordinate System

Figure 1.4 : Reverse Cylindrical Coordinate System

Section 1

1.5.2 Local Coordinate System

A local coordinate system is associated with each member. Each
axis of the local orthogonal coordinate system is also based on the
right hand rule. Fig. 1.5 shows a beam member with start joint 'i'
and end joint 'j'. The positive direction of the local x-axis is
determined by joining 'i' to 'j' and projecting it in the same
direction. The right hand rule may be applied to obtain the positive
directions of the local y and z axes. The local y and z-axes
coincide with the axes of the two principal moments of inertia. The
local coordinate system is always rectangular.

A wide range of cross-sectional shapes may be specified for
analysis. These include rolled steel shapes, user specified
prismatic shapes etc.. Fig. 1.6 shows local axis system(s) for these
shapes.

1-7

General Description
Section 1

1-8

Figure 1.5a

Figure 1.5b

Section 1

1-9

Figure 1.6a - Local axis system for various cross sections

when global Y axis is vertical.

NOTE: The local x-axis of the above sections is going into the paper

1-10

General Description
Section 1

Figure 1.6b - Local axis system for various cross sections

when global Z axis is vertical (SET Z UP is specified).

Section 1

F

1.5.3 Relationship Between Global & Local
Coordinates

Since the input for member loads can be provided in the local and
global coordinate system and the output for member-end-forces is
printed in the local coordinate system, it is important to know the
relationship between the local and global coordinate systems. This
relationship is defined by an angle measured in the following
specified way. This angle will be defined as the beta (β) angle.
For offset members the beta angle/reference point specifications
are based on the offset position of the local axis, not the joint
positions.

Beta Angle

When the local x-axis is parallel to the global Vertical axis, as in

or input,

see section

5.26

the case of a column in a structure, the beta angle is the angle
through which the local z-axis (or local Y for SET Z UP) has been
rotated about the local x-axis from a position of being parallel and
in the same positive direction of the global Z-axis (global Y axis
for SET Z UP).

When the local x-axis is not parallel to the global Vertical axis,
the beta angle is the angle through which the local coordinate
system has been rotated about the local x-axis from a position of
having the local z-axis (or local Y for SET Z UP) parallel to the
global X-Z plane (or global X-Y plane for SET Z UP)and the local
y-axis (or local z for SET Z UP) in the same positive direction as
the global vertical axis. Figure 1.7 details the positions for beta
equals 0 degrees or 90 degrees. When providing member loads in
the local member axis, it is helpful to refer to this figure for a
quick determination of the local axis system.

1-11

1-12

General Description
Section 1

Reference Point

An alternative to providing the member orientation is to input the
coordinates (or a joint number) which will be a reference point
located in the member x-y plane (x-z plane for SET Z UP) but not
on the axis of the member. From the location of the reference
point, the program automatically calculates the orientation of the
member x-y plane (x-z plane for SET Z UP).

Y

x

x

y

z

y

z

x

x

y

x

Z

z

y

z

z

x

y

z

y

x

x

y

y

x

x

z

z

y

z

y

z

z

y

y

z

x

X

x

Relationship between Global and Local axes

Figure 1.7

Section 1

1-13

Figure 1.8

1-14

General Description
Section 1

Figure 1.9

Section 1

1-15

Figure 1.10

1-16

General Description
Section 1

Figure 1.11

Section 1

1-17

Figure 1.12

General Description

F

1-18

Section 1

1.6 Finite Element Information

or input, see

sections 5.11, 5.13,

5.14, 5.21, 5.24, and

5.32.3

STAAD is equipped with a plate/shell finite element, solid finite
element and an entity called the surface element. The features of
each is explained below.

1.6.1 Plate/Shell Element

The Plate/Shell finite element is based on the hybrid element
formulation. The element can be 3-noded (triangular) or 4-noded
(quadrilateral). If all the four nodes of a quadrilateral element do
not lie on one plane, it is advisable to model them as triangular
elements. The thickness of the element may be different from one
node to another.

“Surface structures” such as walls, slabs, plates and shells may be
modeled using finite elements. For convenience in generation of a
finer mesh of plate/shell elements within a large area, a MESH
GENERATION facility is available. The facility is described in
detail in Section 5.14.

The user may also use the element for PLANE STRESS action
only (i.e. membrane/in-plane stiffness only). The ELEMENT
PLANE STRESS command should be used for this purpose.