9-49

Steel Design Per IS800

Section 9B
9B.1 Design Operations

STAAD contains a broad set of facilities for designing structural

members as individual components of an analyzed structure. The
member design facilities provide the user with the ability to carry
out a number of different design operations. These facilities may
be used selectively in accordance with the requirements of the
design problem. The operations to perform a design are:

 Specify the members and the load cases to be considered in the

design.
 Specify whether to perform code checking or member
selection.
 Specify design parameter values, if different from the default
values.
 Specify whether to perform member selection by optimization.

These operations may be repeated by the user any number of times

depending upon the design requirements. The entire ISI steel
section table is supported. Section 8B.13 describes the
specification of steel sections.
 Steel Design Per IS800
9-50 Section 9B

9B.2 General Comments

This section presents some general statements regarding the

implementation of Indian Standard code of practice (IS:800 -1984)
for structural steel design in STAAD. The design philosophy and
procedural logistics for member selection and code checking are
based upon the principles of allowable stress design. Two major
failure modes are recognized: failure by overstressing, and failure
by stability considerations. The flowing sections describe the
salient features of the allowable stresses being calculated an d the
stability criteria being used. Members are proportioned to resist
the design loads without exceeding the allowable stresses and the
most economic section is selected on the basis of least weight
criteria. The code checking part of the program checks stability
and strength requirements and reports the critical loading
condition and the governing code criteria. It is generally assumed
that the user will take care of the detailing requirements like
provision of stiffeners and check the local effects such as flange
buckling and web crippling.

9B.3 Allowable Stresses

The member design and code checking in STAAD are based upon
the allowable stress design method as per IS:800 (1984). It is a
method for proportioning structural members using design loads
and forces, allowable stresses, and design limitations for the
appropriate material under service conditions. It would not be
possible to describe every aspect of IS:800 in this manual. This
section, however, will discuss the salient features of the allowable
stresses specified by IS:800 and implemented in STAAD.
Appropriate sections of IS:800 will be referenced during the
discussion of various types of allowable stresses.
 Section 9B 9-51

9B.3.1 Axial Stress

Tensile Stress

The allowable tensile stress, as calculated in STAAD as per IS:800

is described below.

The permissible stress in axial tension,  at in MPa on the net

effective area of the sections shall not exceed

 at = 0.6 f y

where,

fy = minimum yield stress of steel in Mpa

Compressive Stress

Allowable compressive stress on the gross section of axially

loaded compression members shall not exceed 0.6f y nor the
permissible stress  ac calculated based on the following formula:
(Clause: 5.1.1)

f f
  0.6
[(f cc)n (f y)n]

where,

 ac = Permissible stress in axial compr ession, in Mpa

fy = Yield stress of steel, in Mpa
fcc = Elastic critical stress in compression = 2 E/ 2
E = Modulus of elasticity of steel, 2 X 10 5 Mpa
=l/r = Slenderness ratio of the member, ratio of the effective
length to appropriate radius of gyration
n = A factor assumed as 1.4.
 Steel Design Per IS800
9-52 Section 9B

9B.3.2 Bending Stress

The allowable bending stress in a member subjected to bending is

calculated based on the following formula: (Clause: 6.2.1)

 bt or  bc = 0.66 fy

where,

 bt = Bending stress in tension

 bc = Bending stress in compression
f y = Yield stress of steel, in MPa

For an I-beam or channel with equal flanges bent about the axis of
maximum strength (z-z axis), the maximum bending compressive
stress on the extreme fibre calculated on the effective section shall
not exceed the values of maximum permissible bending compressive
stress. The maximum permissible bending compressive stress shall be
obtained by the following formula: (Clause: 6.2.2)

f cb  f y
σbc  0.66 (Clause : 6.2.3)
1/n
n n
[(f cb)  (f y) ]

where,

f y = Yield stress of steel, in Mpa

n = A factor assumed as 1.4.
fcb = Elastic critical stress in bending, calculated by the
following formula:

c
f  k [ X  k Y]
c
 Section 9B 9-53
where,

1 IT 26.5x10
X  Y 1 MP Y=
20 r D (1/ r y)

k1 = a coefficient to allow for reduction in thickness or

breadth of flanges between points of effective lateral
restraint and depends on , the ratio of the total area of
both flanges at the point of least bending moment to the
corresponding area at the point of greatest bending
moment between such points of restraint.

k2 = a coefficient to allow for the inequality of flanges, and

depends on , the ratio of the moment of inertia of the
compression flange alone to that of the sum of the moment
of the flanges each calculated about its own axis parallel to
the y-yaxis of the girder, at the point of maximum bending
moment.

1 = effective length of compression flange

ry = radius of gyration of the section about its axis of

minimum strength (y-y axis)

T = mean thickness of the compression flange, is equal to the

area of horizontal portion of flange divided by width.

D = overall depth of beam

c 1 ,c 2 = respectively the lesser and greater distances from the

section neutral axis to the extreme fibres.

9B.3.3 Shear Stress

Allowable shear stress calculations are based on Section 6.4 of IS:800 .

For shear on the web, the gross section taken into consideration consist
of the product of the total depth and the web thickness. For shear
parallel to the flanges, the gross section is taken as 2/3 times the total
flange area.
 Steel Design Per IS800
9-54 Section 9B

9B.3.4 Combined Stress

Members subjected to both axial and bending stresses are

proportioned accordingly to section 7 of IS:800. All members
subject to bending and axial compression are required to satisfy
the equation of Section 7.1.1.(a) for intermediate points, and
equation of Section 7.1.1.(b) for support points.

For combined axial tension and bending the equation of Section

7.1.2. is required to be satisfied.

Cm coefficients are calculated according to the specifications of

Section 7.1.3. information regarding occurrence of sidesway can
be provided through the use of parameters SSY and SSZ. In the
absence of any user provided information, sidesway will be
assumed.

9B.4 Design Parameters

In STAAD implementation of IS:800, the user is allowed complete

control of the design process through the use of design parameters.
Available design parameters to be used in conjunction with IS:800
are listed in Table 7B.1 of this section along with their default
values and applicable restrictions. Users should note that when the
TRACK parameter is set to 1.0 and use in conjunction with this
code, allowable bending stresses in compression (FCY & FCZ),
tension (FTY & FTZ), and allowable shear stress (FV) will be
printed out in Member Selection and Code Check output in Mpa.
When TRACK is set to 2.0, detailed design output will be
provided.

9B.5 Stability Requirements

Slenderness ratios are calculated for all members and checked

against the appropriate maximum values. Section 3.7 of IS:800
 Section 9B 9-55
summarizes the maximum slenderness ratios for different types of
members. In STAAD implementation of IS:800, appropriate
maximum slenderness ratio can be provided for each member. If
no maximum slenderness ratio is provided, compression members
will be checked against a maximum value of 180 and tension
members will be checked against a maximum value of 400.

9B.6 Truss Members

As mentioned earlier, a truss member is capable of carrying only

axial forces. So in design no time is wasted in calculating bending
or shear stresses, thus reducing design time considerably.
Therefore, if there is any truss member in an analysis (like bracing
or strut, etc.), it is wise to declare it as a truss member rather than
as a regular frame member with both ends pinned.

9B.7 Deflection Check

This facility allows the user to consider deflection as a criteria in

the CODE CHECK and MEMBER SELECTION processes. The
deflection check may be controlled using three parameters which
are described in Table 7B.1. Note that deflection is used in
addition to other strength and stability related criteria. The local
deflection calculation is based on the latest analysis results.

9B.8 Code Checking

The purpose of code checking is to verify whether the specified

section is capable of satisfying applicable design code
requirements. The code checking is based on the IS:800 (1984)
requirements. Forces and moments at specified sections of the
members are utilized for the code checking calculations. Sections
may be specified using the BEAM parameter or the SECTION
command. If no sections are specified, the code checking is based
on forces and moments at the member ends.
 Steel Design Per IS800
9-56 Section 9B

The code checking output labels the members as PASSed or

FAILed. In addition, the critical condition (applicable IS:800
clause no.), governing load case, location (distance from the start)
and magnitudes of the governing forces and moments are also
printed out.

9B.9 Member Selection

STAAD is capable of performing design operations on specified

members. Once an analysis has been performed, the program can
select the most economical section, that is, the lightest section,
which satisfies the applicable code requirements. The section
selected will be of the same type (I-Section, Channel etc.) as
originally specified by the user. Member selection may be
performed with all types of steel sections listed in Section 7B.13
and user provided tables. Selection of members, whose properties
are originally provided from user specified table, will be limited to
sections in the user provided table. Member selection can not be
performed on members whose cross sectional properties are
specified as PRISMATIC.

The process of MEMBER SELECTION may be controlled using

the parameters listed in Table 8B.1. It may be noted that the
parameters DMAX and DMIN may be used to specify member
depth constraints for selection. If PROFILE parameter is provided,
the search for the lightest section is restricted to that profile. Up to
three (3) profiles may be provided for any member with a section
being selected from each one.

9B.10 Member Selection By Optimization

Steel section selection of the entire structure may be optimized.

The optimization method utilizes a state-of-the -art numerical
technique which requires automatic multiple analysis. The user
may start without a specifically designated section. However, the
section profile type (BEAM, COLUMN, CHANNEL, ANGLE etc.)
must be specified using the ASSIGN command (see Chapter 6).
 Section 9B 9-57
The optimization is based on member stiffness contributions and
corresponding force distributions. An optimum member size is
determined through successive analysis/design iterations. This
method requires substantial computer time and hence should be
used with caution.

9B.11 Tabulated Results of Steel Design

For code checking or member selection, the program produces the

result in a tabulated fashion. The items in the output table are
explained as follows:

a) MEMBER refers to the member number for which the design

is performed

b) TABLE refers to the INDIAN steel section name which has

been checked against the steel code or has been selected.

c) RESULT prints whether the member has PASSED or FAILed.

If the RESULT is FAIL, there will be an asterisk (*) mark in
front of the member number.

d) CRITICAL COND refers to the section of the IS:800 code

which governs the design.

e) RATIO prints the ratio of the actual stresses to allowable

stresses for the critical condition. Normally a value of 1.0 or
less will mean the member has passed.

f) LOADING provides the load case number which governs the

design.

g) FX, MY and MZ provide the axial force, moment in local y-

axis and moment in local z-axis respectively. Although
STAAD does consider all the member forces and moments
(except torsion) to perform design, only FX,MY and MZ are
printed since they are the ones which are of interest , in most
cases.
 Steel Design Per IS800
9-58 Section 9B

h) LOCATION specifies the actual distance from the start of the

member to the section where design forces govern.

i) If the parameter TRACK is set to 1.0, the program will block

out part of the table and will print allowable bending stress es
in compression (FCY & FCZ) and tension (FTY & FTZ),
allowable axial stress in compression (FA), and allowable
shear stress (FV). When the parameter TRACK is set to 2.0
for all members parameter code values are as shown in Fig
8B.1.
STAAD.Pro CODE CHECKING - (ISA )
***********************

|---------------------------------------------------------------------------|
| Y PROPERTIES |
|************* | IN CM UNIT |
| * |=============================| ===|=== ------------ |
|MEMBER 7 * | | | AX = 72.4 |
| * | ST ISLB400 | | --Z AY = 32.0 |
|DESIGN CODE * | | | AZ = 27.5 |
| IS-800 * =============================== ===|=== SY = 86.8 |
| * SZ = 965.3 |
| * |<---LENGTH (ME= 3.00 --->| RY = 3.1 |
|************* RZ = 16.3 |
| |
| 104.6( KN-METR) |
|PARAMETER |L1 STRESSES |
|IN NEWT MM | IN NEWT MM|
|--------------- + -------------|
| KL/R-Y= 95.4 | FA = 84.8 |
| KL/R-Z= 18.4 + fa = 1.6 |
| UNL = 3000.0 | FCZ = 116.6 |
| C = 400.0 + FTZ = 165.0 |
| CMY = 0.85 | FCY = 165.0 |
| CMZ = 0.85 + FTY = 165.0 |
| FYLD = 249.9 | L3 fbz = 108.4 |
| NSF = 0.9 +---+---+---+---+---+---+---+---+---+---| fby = 0.0 |
| DFF = 325.0 92.7 FV = 100.0 |
| dff = 4383.0 ABSOLUTE MZ ENVELOPE |
| (WITH LOAD NO.) |
| |
| MAX FORCE/ MOMENT SUMMARY ( KN-METR) |
| ------------------------- |
| |
| AXIAL SHEAR-Y SHEAR-Z MOMENT-Y MOMENT-Z |
| |
| VALUE -23.7 61.3 0.0 0.0 104.6 |
| LOCATION 0.0 0.0 0.0 0.0 0.0 |
| LOADING 3 1 0 0 1 |
| |
|***************************************************************************|
|* *|
|* DESIGN SUMMARY ( KN-METR) *|
|* -------------- *|
|* *|
|* RESULT/ CRITICAL COND/ RATIO/ LOADING/ *|
| FX MY MZ LOCATION |
| ====================================================== |
| PASS IS-7.1.2 0.667 1 |
| 9.62 T 0.0 -104.6 0.00 |
| |
| DEFLECTION * PASS |
| RATIO: 0.074 LOADING: 3 LOCATION: 0.67 |
|* *|
|***************************************************************************|
 Section 9B 9-59

9B.12 Indian Steel Table

This is an important feature of the program since the program will

read section properties of a steel member directly from the latest
ISI steel tables (as published in ISI-800). These properties are
stored in memory corresponding to the section designation (e.g.
ISMB250, etc.). If called for, the properties are also used for
member design. Since the shear areas are built in to these tables,
shear deformation is always considered for these members.

Almost all ISI steel tables are available for input. A complete
listing of the sections available in the built -in steel section library
may be obtained using the tools of the graphical user interface.

Following are the descriptions of all the types of sections

available:

Rolled Steel Beams (ISJB, ISLB, ISMB and ISHB).

All rolled steel beam sections are available the way they are
designated in the ISI handbook., e.g. ISJB225, ISWB400, etc.

20 TO 30 TA ST ISLB325

NOTE:
In case of two identical beams, the heavier beam is designated
with an „A” on the end., e.g. ISHB400 A, etc.

1 TO 5 TA ST ISHB400A
 Steel Design Per IS800
9-60 Section 9B

Rolled Steel Channels (ISJC, ISLC and ISMC)

All these shapes are available as listed in ISI section handbook.

Designation of the channels are per the scheme used by ISI.

10 TO 20 BY 2 TA ST ISMC125
12 TA ST ISLC300

Double Channels

Back to back double channels, with or without spacing between

them, are available. The letter D in front of the section name will
specify a double channel, e.g. D ISJC125, D ISMC75 etc.

21 22 24 TA D ISLC225

Rolled Steel Angles

Both rolled steel equal angles and unequal angles are available for
use in the STAAD implementation of ISI steel tables. The
following example with explanations will be helpful in
understanding the input procedure:

ISA 150 X 75 X 8

Angle symbol Thickness in mm

Long leg length in mm Short leg length in mm

At present there is no standard way to define the local y and z axes

for an angle section. The standard section has local axis system as
illustrated in Fig.2.4 of this manual. The standard angle is
specified as:

51 52 53 TA ST ISA60X60X6
 Section 9B 9-61
This specification has the local z-axis ( i.e., the minor axis
corresponding to the V-V axis specified in the steel tables. Many
engineers are familiar with a convention used by some other
programs in which the local y-axis is the minor axis. STAAD
provides for this convention by accepting the command:

54 55 56 TA RA ISA50X30X6 (RA denotes reverse angle)

Double Angles

Short leg back to back or long leg back to back double angles can
be specified by inputting the word SD or LD, respectively, in front
of the angle size. In case of an equal angle either LD or SD will
serve the purpose. For example,

14 TO 20 TA LD ISA50X30X5 SP 1.5
23 27 TA SD ISA75X50X6

Rolled Tees (ISHT, ISST, ISLT and ISJT)

All the rolled tee sections are available for input as they are
specified in the ISI handbook. Following example illustrates the
designated method.

1 2 5 8 TA ST ISNT100
67 68 TA ST ISST250

Pipes (Circular Hollow Sections)

To designate circular hollow sections from ISI tables, use PIP

followed by the numerical value of diameter and thickness of the
section in mm omitting the decimal section of the value provi ded
for diameter. Following example will illustrate the designation.
 Steel Design Per IS800
9-62 Section 9B

10 15 TA ST PIP 213.2
(Specifies a 213 mm dia. pipe with 3.2 mm wall thickness)

Circular pipe sections can also be specified by providing the

outside and inside diameters of the section. For example,

1 TO 9 TA ST PIPE OD 25.0ID 20.0

(specifies a pipe with outside dia. of 25 and inside dia. of 20
in current length units)

Only code checking and no member selection will be performed if

this type of specification is used.

Tubes (Rectangular or Square Hollow Sections)

Designation of tubes from the ISI steel table is illustrated below.

TUB 400 200 12.5

Tube Symbol Thickness in mm

Height in mm Width in mm

Example:

15 TO 25 TA ST TUB 160808

Tubes, like pipes, can also be input by their dimensions (Height,

Width and Thickness) and not by any table designations.

6 TA ST TUBE DT 8.0 WT 6.0 TH 0.5 is a tube that has a height

of 8, a width of 6, and a wall thickness of 0.5.
 Section 9B 9-63
Note that only code checking and no member selection is
performed for TUBE sections specified this way.

Plate And Angle Girders (With Flange Plates)

All plate and angle grinders (with flange plates) are available as
listed in ISI section handbook. The following example with
explanations will be helpful in understanding the input procedure.

I 1000 12 A 400 12

A F
B E
C D

A Plate and angle girder symbol.

B Web plate width in mm.
C Web plate thickness in mm.
D Flange angle (Flange angle key below):
E Flange plate width in mm.
F Flange plate thickness in mm.

SYMBOL ANGLE(A X B X t)(all in mm)

A 150X150X18
B 200X100X15
C 200X150X18
E 200X200X18
 Steel Design Per IS800
9-64 Section 9B

SINGLE JOIST WITH CHANNELS AND PLATES ON THE

FLANGES TO BE USED AS GIRDERS

All single joist with channel and plates on the flanges to be used
as girders are available as listed in ISI section handbook. The
following example with explanations will be helpful in
understanding the input procedure.

IW 450 350 X 10 20

A E
B D
C

A Joist Designation: IW450=ISWB450

B Top flange channel designation:

350=ISMC350

C Constant (always X).

D Top flange plate thickness in mm.

NOTE: D is 0 for no plate.

E Bottom flange plate thickness in mm.

NOTE:

The heavier ISWB600 has been omitted, since the lighter

ISWB600 is more efficient.
 Section 9B 9-65
Note: Once a parameter is specified, its value stays at that
specified number till it is specified again. This is the way STAAD
works for all codes.

Table 9B.1 Indian Steel Design - IS : 800 Parameters

Parameter Default Value Description

Name
KY 1.0 K value in local y-axis. Usually, this is minor axis.
KZ 1.0 K value in local z-axis. Usually, this is major axis.
Length in local y-axis to calculate slenderness
LY Member Length
ratio.
LZ Member Length Same as above except in local z-axis (major).
250 MPA
FYLD Yield strength of steel.
(36.25 KSI)
NSF 1.0 Net section factor for tension members.
Unsupported length for calculating allowable
UNL Member Length
bending stress.
Same as above provided as a fraction of actual
UNF 1.0
member length.
0.0 = Sidesway in local y-axis.
SSY 0.0
1.0 = No sidesway
SSZ 0.0 Same as above except in local z-axis.
0.85 for
CMY sidesway and
Cm value in local y & z axes
CMZ calculated for no
sidesway
180 (Comp. Allowable Kl/r for slenderness calculations for
MAIN compression members.
Memb.)
400 (Tension Allowable Kl/r for slenderness calculations for
TMAIN tension members.
Memb)
0.0 = Suppress critical member stresses
1.0 = Print all critical member stresses
2.0 = Print expanded output. If there is
deflection check it will also print the
TRACK 0.0
governing load case number for deflection
check whenever critical condition for
design is not DEFLECTION.
(see fig.8B.1)
 Steel Design Per IS800
9-66 Section 9B

Table 9B.1 Indian Steel Design - IS : 800 Parameters

Parameter Default Value Description

Name
DMAX 100.0 cm. Maximum allowable depth.
DMIN 0.0 cm. Minimum allowable depth.
Permissible ratio of the actual to allowable
RATIO 1.0
stresses.
0.0 = design only for end moments and those at
locations specified by the SECTION
command.
BEAM 3.0 1.0 = calculate section forces at twelfth points
along the beam, design at each
intermediate location and report the critical
location where ratio is maximum.
Search for the lightest section for the profile
PROFILE -
mentioned.
None
"Deflection Length" / Maxm. allowable local
DFF (Mandatory for
deflection
deflection check)
Start Joint Joint No. denoting starting point for calculation of
DJ1
of member "Deflection Length" (See Note 1)
End Joint of Joint No. denoting end point for calculation of
DJ2
member "Deflection Length" (See Note 1)

NOTES:

1) "Deflection Length" is defined as the length that is used for

calculation of local deflections within a member. It may be
noted that for most cases the "Deflection Length" will be equal
to the length of the member. However, in some situations, the
"Deflection Length" may be different. For example, refer to
the figure below where a beam has been modeled using four
joints and three members. Note that the "Deflection Length"
for all three members will be equal to the total length of the
beam in this case. The parameters DJ1 and DJ2 should be used
to model this situation. Also the straight line joining DJ1 and
DJ2 is used as the reference line from which local deflections
are measured. Thus, for all three members here, DJ1 should be
"1" and DJ2 should be "4".
 Section 9B 9-67

1 2 3 4 EXAMPLE : PARAMETERS
1 2 3
D DFF 300. ALL
DJ1 1 ALL
D = Maximum local deflection for members DJ2 4 ALL
1 2 and 3.

2) If DJ1 and DJ2 are not used, "Deflection Length" will default
to the member length and local deflections will be measured
from original member line.

3) The above parameters may be used in conjunction with other

available parameters for steel design.

9B.13 Column With Lacings And Battens

For columns with large loads it is desirable to build rolled sections

at a distance and inter-connect them. The joining of element
sections is done by two ways:

a) Lacing and b) Batten

Double channel sections (back-to-back and face-to-face) can be

joined either by lacing or by batten plates having rivetted or
welded connection.

Table 8B.2 gives the parameters that are required for Lacing or
batten design. These parameters will have to be provided in unit
NEW MMS along with parameters defined in Table 9B.1.
 Steel Design Per IS800
9-68 Section 9B

Note: Once a parameter is specified, its value stays at that

specified number till it is specified again. This is the way
STAAD works for all codes.

Table 9B.2 Indian Concrete Design IS800 Parameters

Parameter Default Value Description

Name
CTYPE 1 Type of joining
CTYPE = 1 implies single lacing with rivetted
connection
CTYPE = 2 implies double lacing with rivetted
connection
CTYPE = 3 implies single lacing with welded
connection
CTYPE = 4 implies double lacing with welded
connection
CTYPE = 5 implies batten with rivetted
connection
CTYPE = 6 implies batten with welded
connection
THETA 50 degree Angle of inclination of lacing bars. It should lie
between 40 degree and 70 degree.
DBL 20 mm Nominal diameter of rivet
FVB 100 N/mm2 Allowable shear stress in rivet

FYB 300 N/mm2 Allowable bearing stress in rivet

WMIN 6 mm Minimum thickness of weld
2
WSTR 108 N/mm Allowable welding stress
EDIST 32 mm (Rivetted Edge Distance
Connection)
25 mm (Welded
Connection)
 Section 9B 9-69

Table 9B.2 Indian Concrete Design IS800 Parameters

Parameter Default Value Description

Name
DCFR 0.0 0.0 implies double channel back-to-back.
1.0 Implies double channel face-to-face.
This parameter is used when member
properties are defined through user provided
table using GENERAL option.

COG 0.0 mm Centre of gravity of the channel. This

parameter is used when member properties
are defined through user provided table using
GENERAL option.

SPA 0.0 mm Spacing between double channels. This

parameter is used when member properties
are defined through user provided table using
GENERAL option.