2structural modeling.pdf

7/28/2019 2structural modeling.pdf

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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 structure with loads applied in any plane, isthe 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 anyhorizontal load, it must be analyzed as a SPACE structure. Specification of the correct structure type

reduces the number of equations to be solved during the analysis. The degrees of freedom associated

with frame elements of different types of structures is illustrated in Figure

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:


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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 elements and the term ELEMENTwill 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.

Global Coordinate System

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

1. 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 directions. Thetranslational degrees of freedom are denoted by u1, u2, u3 and the rotational degrees of

freedom are denoted by u4, u5 & u6.

2. 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 (angle in

degrees). The Z coordinate is identical to the Z coordinate of the cartesian system and itspositive direction is determined by the right hand rule.

3. Reverse Cylindrical Coordinate System: This is a cylindrical type coordinate system (Fig.

1.4) where the R- plane corresponds to the X-Z plane of the cartesian system. The righthand rule is followed to determine the positive direction of the Y axis.


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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

PHDVXUHGLQWKHIROORZLQJVSHFLILHGZD\7KLVDQJOHZLOOEHGHILQHGDVWKHEHWDDQJOH)RURIIVHWmembers 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 Y-axis, as in the case of a column in a structure, the beta

angle is the angle through which the local z-axis 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.


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Command Formats

Free-Format Input

All input to STAAD is in free-format style. Input data items should be separated by blank

spaces (not commas) from the other input data items. Quotation marks are neverneeded to separate any alphabetic words such as data, commands or titles. Limit a data

item to 24 characters.

Commenting Input

For documentation of a STAAD data file, the facility to provide comments is available.

Comments can be included by providing an asterisk (*) mark as the first non-blank

character in any line. The line with the comment is "echoed" in the output file but not

processed by the program.

Example

JOINT LOAD

* THE FOLLOWING IS AN EQUIPMENT LOAD

2 3 7 FY 35.0

Meaning of Underlining in the Manual:

Exact command formats are described in the latter part of this section. Many words in

the commands and data may be abbreviated. The full word intended is given in the

command description with the portion actually required (the abbreviation) underlined.

For example, if the word MEMBER is used in a command, only the portion MEMB need

be input. It is clearer for others reading the output if the entire word is used, but an

experienced user may desire to use the abbreviations.

d) Meaning of Braces and Parenthesis:

In some command formats, braces enclose a number of choices, which are arranged

vertically. One and only one of the choices can be selected. However, several of thelisted choices may be selected if an asterisk (*) mark is located outside the braces.


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Description

The UNIT command can be specified any number of times during an analysis. All data is assumed

to be in the most recent unit specification preceding that data. Also, the input unit for angles is

always degrees. However, the output unit for joint rotations (in joint displacement) is radians.

For all output, the units are clearly specified by the program.

UNIT KIP FT

UNIT INCHUNIT METER KNS

UNIT CM MTON

Input/Output Width Specification

Purpose

These commands may be used to specify the width(s) of the lines of output file(s).

For OUTPUT WIDTH,

i1 = 72 or 118 depending on narrow or wide output.

Description

The user may specify the required input/output width, as required, using this command. For

INPUT width, 79 is always used. The program can create output using two different output

widths - 72 (default) and 118. The 72-character width may be used for display on most CRTs and

(}]v]vP }v }]_ ]X dZ -character width may be used for printing on

ov_]X


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Notes

This is a customization facility that may be used to improve the presentation quality of the run

documents.

Separator Command

Purpose

This command may be used to specify the desired separator character that can be used to

separate multiple lines of data on a single line of input.

General format:

SEPARATOR a1

Description

The semicolon (;) is the default character which functions as the separator for multiple line data

on one line. However, this separator character can be changed by the SEPARATOR command to

any character a1, other than the comma or asterisk.

Notes

Comma (,) or asterisk (*) may not be used as a separator character.

Ignore Specifications

Purpose

This command allows the user to provide member lists in a convenient way without triggering

error messages pertaining to non-existent member numbers.

General format:

IGNORE LIST

Description

IGNORE LIST may be used if the user wants the program to ignore any nonexistent member thatmay be included in a member list specification. For example, for the sake of simplicity, a list of

members may be specified as MEMB 3 TO 40 where members 10 and 11 do not exist. An error

message can be avoided in this situation by providing the IGNORE LIST command anywhere in

the beginning of input. A warning message, however, will appear for each nonexistent members


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The command JOINT COORDINATES CYLINDRICAL specifies a Cylindrical Coordinate System (see

Figure 1.3). Join(]v]vPZU}v}}]vX

JOINT COORDINATES CYLINDRICAL REVERSE specifies a Reverse Cylindrical Coordinate system

(see Figure 1.4). Joints are defined us]vPZUv}}}]v

JTORIG causes the program to use a different origin than (0, 0, 0) for all of the joints entered

with this JOINT COORDINATES command. It is useful in instances such as when the center of

cylinder is not at (0, 0, 0) but at a different point in space. The JTORIG command should be

entered on a separate command line. Basically after the joint coordinates are entered or

generated, then the xOrigin, yOrigin, and zOrigin values are added to the coordinates. For

example a cylinder could be generated about the Y axis then moved by this command to its

proper place. To create multiple offset structural parts, enter additional JOINT COORDINATES

commands, each one followed by its JTORIG command. An example showing the use of this

command is provided later in this section.

The multiple JOINT COORDINATES command concept allows UNIT changes and PERFORM

ROTATION commands in between, such that these commands would apply to a selected portion

of the joints. However, the PERFORM ROTATION command applies to all prior defined joints, not

just those in the previous JOINT COORDINATE command.

NOREDUCE BAND causes the program to execute without performing a bandwidth reduction.

Example

JOINT COORDINATES NOREDUCE BAND

dZZWd}uuvZ]}o]v}(]v}Zv[ number of times with

specified coordinate increments. The REPEAT ALL command functions similar to the REPEAT

command except that it repeats all previously specified input back to the most recent REPEAT

ALL command, or all joint data if no previous REPEAT ALL command has been given. Note: Use

ZWd>>_}]}v}(}](vX~tZv]vPZZWd

and REPEAT ALL commands, joint numbering must be consecutive and should begin with 1.)

* i1 = The joint number for which the coordinates are provided. Any integer number

within the limit (see section 5.2 for limit) is permitted.

x1, y

1and z

1AyUz ~ZU}(}o]v]o}ZUz }(}o]v]o}}]v}(

the joint.

For PLANE analyses z1 is an optional data item when defining input for individual joints. z1 is

always required for joint generation. The following are used only if joints are to be generated.

* i2 = The second joint number to which the joint coordinates are generated.


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WORKED OUT EXAMPLES

Example 1 A simple beam with two joints

Example 2 A simple beam with three joints

or

Example 3 A Plane frame with 4 joints equally spaced in

both x axes and y axes

or


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Examples 4 A Plane frame with 9 joints unequally spaced in both axes

Example 5 A Space frame with 27 joints unequally

spaced in x, y& z axes

Member Incidences Specification

Purpose

This set of commands is used to specify MEMBERs by defining connectivity between JOINTs.

REPEAT and REPEAT ALL commands are available to facilitate generation of repetitive patterns.

The member/element incidences must be defined such that the model developed represents

one single structure only, not two or more separate structures. STAAD is capable of detecting

multiple structures automatically.

General format:


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Description

dZZWd}uuvZ]}o]v}(]v}Zv[vu}(]u]Z

specified member and joint increments. The REPEAT ALL command functions similar to the

REPEAT command except that it repeats all previously specified input back to the most recent

REPEAT ALL command or to the beginning of the specification if no previous REPEAT ALL

command has been issued. (When using REPEAT and REPEAT ALL commands, member

numbering must be consecutive).

i1 = Member number for which incidences are provided. Any integer number

(maximum six digits) is permitted.

i2 = Start joint number.

i3 =End joint number.

Note:

Use ZWd>>_U }}(uuZ]oo](}}v[v}

back to the last REPEAT ALL.

The following data are used for member generation only:

i4 = Second member number to which members will be generated.

i5 = Member number increment for generation.

i6 = Joint number increment which will be added to the incident joints. (i5 and i6

will default to 1 if left out.)

n = Number of times repeat is to be carried out.

mi = Member number increment

ji = Joint number increment

Example

MEMBER INCIDENCES

1 1 2

2 5 7 5

7 11 13 13 2 3

In this example, member 1 goes from joint 1 to 2. Member 2 is connected between joints 5 and

7. Member numbers from 3 to 5 will be generated with a member number increment of 1 and a


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Structural modeling 2.23

This example creates the 510 members of a ten story 3 X 4-bay structure (this is a continuation of the

example started in Section 5.12). The first input line creates the twenty columns of the first floor:

1 1 21 ; 2 2 22 ; 3 3 23 ; ... ; 19 19 39 ; 20 20 40

The two commands (21 21 22 23 and REPEAT 4 3 4) create 15 members which are the second floor

"floor" beams running, for example, in the east-west direction:

21 21 22; 22 22 23; 23 23 24

24 25 26; 25 26 27; 26 27 28

... ... ...

33 37 38; 34 38 39; 35 39 40

The next two commands (36 21 25 39 and REPEAT 3 4 4) function similar to the previous two

commands, but here create the 16 second floor "floor" beams running in the north-south direction:

36 21 25; 37 22 26; 38 23 27; 39 24 28

40 25 29; 41 26 30; 42 27 31; 43 28 32

... ... ... ...

48 33 37; 49 34 38; 50 35 39; 51 36 40

The preceding commands have created a single floor unit of both beams and columns, a total of 51

members. The REPEAT ALL now repeats this unit nine times, generating 459 new members and finishing the

ten story structure. The member number is incremented by 51 (the number of members in a repeating

unit) and the joint number is incremented by 20, (the number of joints on one floor).

Re definition of Joint and Member Numbers

Purpose

This command may be used to redefine JOINT and MEMBER numbers. Original JOINT and MEMBER

numbers are substituted by new numbers.

General Format:


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1.24 STAAD.Pro

Description

Joint and member numbers can be redefined in STAAD through the use of the SUBSTITUTE command.

After a new set of numbers is assigned, input and output values will be in accordance with the new

numbering scheme. The user can design numbering schemes that will result in simple input specification

as well as easy interpretation of results. For example, all joints in first floor of a building may berenumbered as 101, 102 ...., all second floor joints may be renumbered as 201, 202 ....., etc.

Example

UNIT METER

SUBST JOINT YR 9.99 10.0 START 101

SUBST COLUMN START 901

Joints with Y coordinates ranging from 9.99 to 10 meters will have a new number starting from 101.

Columns will be renumbered starting with the new number 901.

Note

Meaningful re-specification of JOINT and MEMBER numbers may significantly improve ease of

interpretation of results. This command may be in between incidence commands

MEMBER INCIDENCE

SUBSTITUTE

ELEMENT INCIDENCE

Listing of entities (Members / Elements / Joints, etc.) by Specification of GROUPS

This command allows the user to specify a group of entities such as joints, members, plate & solid

elements and save the information using a 'group-name'. The 'group-name' may be subsequently used

in the input file instead of a member/element/joint list to specify other attributes. This very useful

feature allows avoiding of multiple specifications of the same member/joint list. Following is the general

format required for the GROUP command.

General format:

START GROUP DEFINITION

(GEOMETRY) _(group-name) member/element/solid-list

...... (default)


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GEOMETRY

_TAGC 101 TO 135

END

MEMBER PROPERTIES

_TAGB TA LD L40304

_TAGC TA ST W12X26

To view the group formed go to select/group name/select the group _TAGA the members 40 to 50 are

highlighted as given above

Rotation of Structure Geometry

Purpose

This command may be used to rotate the currently defined joint coordinates (and the attached

members/elements) about the global axes.

General format

where, d1,d2, d3 are the rotations (in degrees) about the X, Y and Z global axes respectively. This

command may be entered after the Joint Coordinates or between two Joint Coordinate commands or

after all Member/Element Incidences are specified. This command can be used to rotate the structure

geometry (defined prior to this command) by any desired angle about any global axis.

The rotated configuration is used for analysis and design. While specifying this command, the sense of

the rotation should conform to the right hand rule.

Description

This command can be used to rotate the geometric shape through any desired angle about any global

axis. The rotated configuration can be used for analysis and design.

Example

PERFORM ROTATION X 20 Z -15


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e) The INACTIVE MEMBER command should not be used if the MEMBER TENSION/COMPRESSION

command is used.

f) The INACTIVated members may be restored for further nd set of load processes (such as an analysis

or design for a 2cases) by using the CHANGE command.

g) The DELETE MEMBER command should be used to delete elements too. Specify the command as

DELETE MEMBER j where j is the element number of the element you wish to delete. In the example

shown below, 29 to 34 and 43 are element numbers.

h) Loads that have been defined on members declared as INACTIVE members will not be considered in

the analysis.This applies to SELFWEIGHT, MEMBER LOADS, PRESTRESS and POSTSTRESS LOADS,

TEMPERATURE LOADs, etc.

i) The DELETE JOINT command must be specified before all incidence commands such as MEMBER

INCIDENCE, ELEMENT INCIDENCE, etc.

Example

INACTIVE MEMBERS 5 7 TO 10

DELETE MEMBERS 29 TO 34 43

Documents

2structural modeling.pdf