STAAD.Pro 2007
INTERNATIONAL DESIGN CODES DAA037810-1/0001
A Bentley Solutions Center
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www.bentley.com/staad
Indian Codes
9-1
Concrete Design Per IS456
9A.1 Design Operations
STAAD has the capabilities of performing concrete design based
on limit state method of IS: 456 (2000).
9A.2 Section Types for Concrete Design
The following types of cross sections for concrete members can be
designed.
For Beams Prismatic (Rectangular & Square), T-Beams and
L-shapes
For Columns Prismatic (Rectangular, Square and Circular)
9A.3 Member Dimensions
Concrete members which will be designed by the program must
have certain section properties input under the MEMBER
PROPERTY command. The following example shows the required
input:
Section 9A
Concrete Design Per IS456
Section 9A9-2
UNIT MM
MEMBER PROPERTY
1 3 TO 7 9 PRISM YD 450. ZD 250.
11 13 PR YD 350.
14 TO 16 PRIS YD 400. ZD 750. YB 300. ZB 200.
will be done accordingly. In the above input, the first set of
members are rectangular (450 mm depth and 250mm width) and
the second set of members, with only depth and no width provided,
will be assumed to be circular with 350 mm diameter. The third set
numbers in the above example represen ts a T-shape with 750 mm
flange width, 200 width, 400 mm overall depth and 100 mm flange
depth (See section 6.20.2). The program will determine whether
the section is rectangular, flanged or circular and the beam or
column design
9A.4 Design Parameters
The program contains a number of parameters which are needed to
perform design as per IS:456(2000). Default parameter values
have been selected such that they are frequently used numbers for
conventional design requirements. These values may be changed to
suit the particular design being performed. Table 8A.1 of this
manual contains a complete list of the available parameters and
their default values. It is necessary to declare length and force
units as Millimeter and Newton before performing the concrete
design.
9A.5 Slenderness Effects and Analysis Consideration
Slenderness effects are extremely important in designing
compression members. The IS:456 code specifies two options by
which the slenderness effect can be accommodated (Clause 39.7).
Section 9A 9-3
One option is to perform an exact analysis which will take into
account the influence of axial loads and variable moment of inertia
on member stiffness and fixed end moments, the effect of
deflections on moment and forces and the effect of the duration of
loads. Another option is to approximately magnify design
moments.
STAAD has been written to allow the use of the first options. To
perform this type of analysis, use the command PDELTA
ANALYSIS instead of PERFORM ANALYSIS. The PDELTA
ANALYSIS will accommodate all requirements of the second-
order analysis described by IS:456, except for the effects of the
duration of the loads. It is felt that this effect may be safely
ignored because experts believe that the effects of the duration of
loads are negligible in a normal structural configuration.
Although ignoring load duration effects is somewhat of an
approximation, it must be realized that the approximate evaluation
of slenderness effects is also an approximate method. In this
method, additional moments are calculated based on empirical
formula and assumptions on sidesway
(Clause 39.7.1 and 39.7.1.1,IS: 456 - 2000).
Considering all these information, a PDELTA ANALYSIS, as
performed by STAAD may be used for the design of concrete
members. However the user must note, to take advantage of this
analysis, all the combinations of loading must be provided as
primary load cases and not as load combinations. This is due to the
fact that load combinations are just algebraic combinations of
forces and moments, whereas a primary load case is revised during
the P-delta analysis based on the deflections. Also note that the
proper factored loads (like 1.5 for dead load etc.) should be
provided by user. STAAD does not factor the loads automatically.
9A.6 Beam Design
Beams are designed for flexure, shear and torsion. If required the
effect the axial force may be taken into consideration. For all
Concrete Design Per IS456
Section 9A
9-4
these forces, all active beam loadings are prescanned to identify
the critical load cases at different sections of the beams. The total
number of sections considered is 13( e.g. 0.,.1,.2,.25,.3,.4,.5,.6,.7,.
75,.8,.9 and 1). All of these sections are scanned to determine the
design force envelopes.
Design for Flexure
Maximum sagging (creating tensile stress at the bottom face of the
beam) and hogging (creating tensile stress at the top face)
moments are calculated for all active load cases at each of the
above mentioned sections. Each of these sections is designed to
resist both of these critical sagging and hogging moments. Where
ever the rectangular section is inadequate as singly reinforced
section, doubly reinforced section is tried. However, presently the
flanged section is designed only as singly reinforced section under
sagging moment. It may also be noted all flanged sections are
automatically designed as rectangular section under hogging
moment as the flange of the beam is ineffective under hogging
moment. Flexural design of beams is performed in two passes. In
the first pass, effective depths of the sections are determined with
the assumption of single layer of assumed reinforcement and
reinforcement requirements are calculated. After the preliminary
design, reinforcing bars are chosen from the internal database in
single or multiple layers. The entire flexure design is per formed
again in a second pass taking into account of the changed effective
depths of sections calculated on the basis of reinforcement provide
after the preliminary design. Final provisions of flexural
reinforcements are made then. Efforts have been made to meet the
guideline for the curtailment of reinforcements as per IS:456-2000
(Clause 26.2.3). Although exact curtailment lengths are not
mentioned explicitly in the design output (finally which will be
more or less guided by the detailer taking into account of other
practical consideration), user has the choice of printing
reinforcements provided by STAAD at 11 equally spaced sections
from which the final detail drawing can be prepared.
Section 9A
9-5
Design for Shear
Shear reinforcement is calculated to resist both shear forces and
torsional moments. Shear design are performed at 11 equally
spaced sections (0.to 1.) for the maximum shear forces amongst
the active load cases and the associated torsional moments. Shear
capacity calculation at different sections with out the shear
reinforcement is based on the actual tensile reinforcement
provided by STAAD program. Two-legged stirrups are provided to
take care of the balance shear forces acting on these sections.
As per Clause 40.5 of IS:456-2000 shear strength of sections (< 2d
where d is the effective depth) close to support has been enhanced,
subjected to a maximum value of cmax.
Beam Design Output
The default design output of the beam contains flexural and shear
reinforcement provided at 5 equally spaced (0,.25,.5,.75 and 1.)
sections along the length of the beam. User has option to get a
more detail output. All beam design outputs are given in IS units.
An example of rectangular beam design output with the default
output option (TRACK 0.0) is presented below:
Concrete Design Per IS456
Section 9A
9-6
============================================================================ B E A M N O. 12 D E S I G N R E S U L T S M20 Fe415 (Main) Fe415 (Sec.) LENGTH: 4000.0 mm SIZE: 250.0 mm X 350.0 mm COVER: 30.0 mm DESIGN LOAD SUMMARY (KN MET) ---------------------------------------------------------------------------- SECTION |FLEXTURE (Maxm. Sagging/Hogging moments)| SHEAR (in mm) | P MZ MX Load Case | VY MX Load Case ---------------------------------------------------------------------------- 0.0 | 0.00 0.00 0.00 4 | 29.64 1.23 4
| 0.00 -25.68 1.23 4 | 400.0 | 0.00 0.00 0.00 4 | 27.97 1.23 4 | 0.00 -16.05 1.23 4 | 800.0 | 0.00 0.00 0.00 4 | 25.12 1.23 4 | 0.00 -7.17 1.23 4 | 1200.0 | 0.00 0.97 0.49 5 | 21.11 1.23 4
| 0.00 -0.14 1.32 6 | 1600.0 | 0.00 6.77 1.23 4 | 15.93 1.23 4 | 0.00 0.00 0.00 4 |
2000.0 | 0.00 11.06 1.23 4 | 9.59 1.23 4 | 0.00 0.00 0.00 4 | 2400.0 | 0.00 13.04 1.23 4 | 2.08 1.23 4
| 0.00 0.00 0.00 4 | 2800.0 | 0.00 12.45 1.23 4 | -5.43 1.23 4 | 0.00 0.00 0.00 4 | 3200.0 | 0.00 9.55 1.23 4 | -11.77 1.23 4 | 0.00 0.00 0.00 4 | 3600.0 | 0.00 4.73 1.23 4 | -16.95 1.23 4
| 0.00 0.00 0.00 4 | 4000.0 | 0.00 0.00 0.00 4 | -25.48 1.23 4 | 0.00 -17.36 1.23 4 | ----------------------------------------------------------------------------
SUMMARY OF REINF. AREA (Sq.mm) ---------------------------------------------------------------------------- SECTION 0.0 mm 1000.0 mm 2000.0 mm 3000.0 mm 4000.0 mm ----------------------------------------------------------------------------
TOP 259.04 161.29 0.00 0.00 176.31 REINF. (Sq. mm) (Sq. mm) (Sq. mm) (Sq. mm) (Sq. mm)
BOTTOM 0.00 160.78 160.78 160.78 0.00 REINF. (Sq. mm) (Sq. mm) (Sq. mm) (Sq. mm) (Sq. mm) ----------------------------------------------------------------------------
SUMMARY OF PROVIDED REINF. AREA
---------------------------------------------------------------------------- SECTION 0.0 mm 1000.0 mm 2000.0 mm 3000.0 mm 4000.0 mm ---------------------------------------------------------------------------- TOP 4-10 3-10 2-10 2-10 3-10 REINF. 1 layer(s) 1 layer(s) 1 layer(s) 1 layer(s) 1 layer(s)
BOTTOM 2-12 2-12 2-12 2-12 2-12 REINF. 1 layer(s) 1 layer(s) 1 layer(s) 1 layer(s) 1 layer(s)
SHEAR 2 legged 8 2 legged 8 2 legged 8 2 legged 8 2 legged 8 REINF. @ 100 mm c/c @ 100 mm c/c @ 100 mm c/c @ 100 mm c/c @ 100 mm c/c
----------------------------------------------------------------------------
============================================================================
Section 9A
9-7
9A.7 Column Design
Columns are designed for axial forces and biaxial moments at the
ends. All active load cases are tested to calculate reinforcement.
The loading which yield maximum reinforcement is called the
critical load. Column design is done for square, rectangular and
circular sections. By default, square and rectangular columns and
designed with reinforcement distributed on each side equally for
the sections under biaxial moments and with reinforcement
distributed equally in two faces for sections under uniaxial
moment. User may change the default arrangement of the
reinforcement with the help of the parameter RFACE (see Table
8A.1). Depending upon the member lengths, section dimensions
and effective length coefficients specified by the user STAAD
automatically determine the criterion (short or long) of the column
design. All major criteria for selecting longitudinal and transverse
reinforcement as stipulated by IS:456 have been taken care of in
the column design of STAAD. Default clear spacing between main
reinforcing bars is taken to be 25 mm while arrangement of
longitudinal bars.
Column Design Output
Default column design output (TRACK 0.0) contains the
reinforcement provided by STAAD and the capacity of the section.
With the option TRACK 1.0, the output contains intermediate
results such as the design forces, effective length coefficients,
additional moments etc. A special output TRACK 9.0 is introduced
to obtain the details of section capacity calculations. All design
output is given in SI units. An example of a long column design
(Ref.Example9 of SP:16, Design Aids For Reinforced Concrete to
IS:456-1978) output (with option TRACK 1.0) is given below.
Concrete Design Per IS456
Section 9A
9-8
============================================================================ C O L U M N N O. 1 D E S I G N R E S U L T S M20 Fe415 (Main) Fe415 (Sec.)
LENGTH: 3000.0 mm CROSS SECTION: 250.0 mm dia. COVER: 40.0 mm ** GUIDING LOAD CASE: 5 BRACED LONG COLUMN
DESIGN FORCES (KNS-MET) ----------------------- DESIGN AXIAL FORCE (Pu) : 62.0
About Z About Y INITIAL MOMENTS : 2.21 32.29
MOMENTS DUE TO MINIMUM ECC. : 1.24 1.24 SLENDERNESS RATIOS : 12.00 12.00 MOMENTS DUE TO SLENDERNESS EFFECT : 1.12 1.12 MOMENT REDUCTION FACTORS : 1.00 1.00 ADDITION MOMENTS (Maz and May) : 1.12 1.12
TOTAL DESIGN MOMENTS : 3.32 33.40 REQD. STEEL AREA : 1822.71 Sq.mm. MAIN REINFORCEMENT : Provide 17 - 12 dia. (3.92%, 1922.65 Sq.mm.) (Equally distributed)
TIE REINFORCEMENT : Provide 8 mm dia. rectangular ties @ 190 mm c/c SECTION CAPACITY (KNS-MET) --------------------------
Puz : 992.70 Muz1 : 36.87 Muy1 : 36.87
INTERACTION RATIO: 1.00 (as per Cl. 38.6, IS456)
============================================================================
Section 9A
9-9
Table 9A.1 Indian Concrete Design IS456 Parameters
Parameter Default Description Name Value
FYMAIN 415 N/mm2 Yield Stress for main reinforcing steel.
FYSEC 415 N/mm2 Yield Stress for secondary reinforcing steel.
FC 30 N/mm2 Concrete Yield Stress.
CLEAR 25 mm 40 mm
For beam members. For column members
MINMAIN 10 mm Minimum main reinforcement bar size.
MAXMAIN 60 mm Maximum main reinforcement bar size.
MINSEC 8 mm Minimum secondary reinforcement bar size.
MAXSEC 12 mm Maximum secondary reinforcement bar size.
BRACING 0.0 BEAM DESIGN
A value of 1.0 means the effect of axial force will be taken into account for beam design.
COLUMN DESIGN
A value of 1.0 means the column is unbraced about major axis.
A value of 2.0 means the column is unbraced about minor axis.
A value of 3.0 means the column is unbraced about both axis.
RATIO 4.0 Maximum percentage of longitudinal reinforcement in columns.
Concrete Design Per IS456
Section 9A
9-10
Table 9A.1 Indian Concrete Design IS456 Parameters
Parameter Default Description Name Value
RFACE 4.0 A value of 4.0 means longitudinal reinforcement in column is arranged equally along 4 faces.
A value of 2.0 invokes 2 faced distribution about major axis.
A value of 3.0 invokes 2 faced distribution about minor axis.
WIDTH ZD Width to be used for design. This value defaults to ZD as provided under MEMBER PROPERTIES.
DEPTH YD Total depth to be used for design. This value defaults to YD as provided under MEMBER PROPERTIES.
TRACK 0.0 BEAM DESIGN: For TRACK = 0.0, output consists of reinforcement details at START, MIDDLE and END. For TRACK = 1.0, critical moments are printed in addition to TRACK 0.0 output. For TRACK = 2.0, required steel for intermediate sections defined by NSECTION are printed in addition to TRACK 1.0 output.
COLUMN DESIGN:
With TRACK = 0.0, reinforcement details are printed. With TRACK = 1.0, column interaction analysis results are printed in addition to TRACK 0.0 output. With TRACK = 2.0, a schematic interaction diagram and intermediate interaction values are printed in addition to TRACK 1.0 output.
With TRACK = 9.0, the details of section capacity calculations are printed.
REINF 0.0 Tied column. A value of 1.0 will mean spiral reinforcement.
Section 9A
9-11
Table 9A.1 Indian Concrete Design IS456 Parameters
Parameter Default Description Name Value
ELZ 1.0 Ratio of effective length to actual length of column about major axis.
ELY 1.0 Ratio of effective length to actual length of column about minor axis.
ULY 1.0 Ratio of unsupported length to actual length of column about minor axis.
ULZ 1.0 Ratio of unsupported length to actual length of column about major axis.
TORSION 0.0 A value of 0.0 means torsion to be considered in beam design. A value of 1.0 means torsion to be neglected in beam design.
SPSMAIN 25 mm Minimum clear distance between main reinforcing bars in beam and column. For column centre to centre distance between main bars cannot exceed 300mm.
SFACE 0.0 Face of support location at start of beam. It is used to check against shear at the face of the support in beam design. The parameter can also be used to check against shear at any point from the start of the member.
EFACE 0.0 Face of support location at end of beam. The parameter can also be used to check against shear at any point from the end of the member. (Note: Both SFACE and EFACE are input as positive numbers).
Concrete Design Per IS456
Section 9A
9-12
Table 9A.1 Indian Concrete Design IS456 Parameters
Parameter Default Description Name Value
ENSH 0.0 Perform shear check against enhanced shear strength as per Cl. 40.5 of IS456:2000. ENSH = 1.0 means ordinary shear check to be performed ( no enhancement of shear strength at sections close to support) For ENSH = a positive value(say x ), shear strength will be enhanced up to a distance x from the start of the member. This is used only when a span of a beam is subdivided into two or more parts. (Refer note ) For ENSH = a negative value(say y), shear strength will be enhanced up to a distance y from the end of the member. This is used only when a span of a beam is subdivided into two or more parts.(Refer note) If default value (0.0) is used the program will calculate Length to Overall Depth ratio. If this ratio is greater than 2.5, shear strength will be enhanced at sections (
Section 9A
9-13
The span of the beam is subdivided four parts, each of length L
metre. The shear strength will be enhanced up to X metre from
both supports. The input should be the following:
Steps:
ENSH L MEMB 1 => Shear strength will be enhanced
throughout the length of the member 1,
positive sign indicates length
measured from start of the member
ENSH (X-L) MEMB 2 => Shear strength will be enhanced up to
a length (X-L) of the member 2, length
measured from the start of the member
ENSH L MEMB 4 => Shear strength will be enhanced
throughout the length of the member 4,
negative sign indicates length
measured from end of the member
ENSH (X-L) MEMB 3 => Shear strength will be enhanced up to
a length (X-L) of the member 3, length
measured from the end of the member
RENSH L MEMB 2 3 => Nearest support lies at a distance L
from both the members 2 and 3.
DESIGN BEAM 1 TO 4=> This will enhance the shear strength
up to length X from both ends of the
beam consisting of members 1 to 4 and
gives spacing accordingly.
Concrete Design Per IS456
Section 9A
9-14
At section = y1 from start of member 1 av = y1
At section = y2 from the start of member 2 av = y2+L
At section = y3 from the end of member 3 av = y3+L
At section = y4 from end of member 4 av = y4
where c, enhanced = 2dc/av
At section 0.0, av becomes zero. Thus enhanced shear strength will
become infinity. However for any section shear stress cannot
exceed c, max. Hence enhanced shear strength is limited to a
maximum value of c, max.
9A.8 Bar Combination
Initially the program selects only one bar to calculate the number
of bars required and area of steel provided at each section along
the length of the beam. Now, two bar diameters can be specified to
calculate a combination of each bar to be provided at each section.
The syntax for bar combination is given below.
START BAR COMBINATION
MD1 MEMB
MD2 MEMB
END BAR COMBINATION
Section 9A
9-15
MD2 bar diameter should be greater than MD1 bar diameter. The typical output for bar combination is shown below:
OUTPUT FOR BAR COMBINATION
--------------------------------------------------------------
| M A I N R E I N F O R C E M E N T |
--------------------------------------------------------------
SECTION | 0.0- 2166.7 | 2166.7- 6500.0 | 6500.0- 8666.7 |
| mm | mm | mm |
--------------------------------------------------------------
TOP | 6-20 + 1-25| 2-20 + 1-25 | 2-20 |
| in 2 layer(s)| in 1 layer(s) | in 1 layer(s) |
Ast Reqd| 2330.22 | 1029.90 | 582.55 |
Prov| 2376.79 | 1119.64 | 628.57 |
Ld (mm) | 940.2 | 940.2 | 940.2 |
--------------------------------------------------------------
BOTTOM | 4-20 | 2-20 | 2-20 |
|in 1 layer(s) | in 1 layer(s) | in 1 layer(s) |
Ast Reqd| 1165.11 | 582.55 | 582.55 |
Prov| 1257.14 | 628.57 | 628.57 |
Ld (mm) | 940.2 | 940.2 | 940.2 |
-------------------------------------------------------------
The beam length is divided into three parts, two at its ends and one at span. Ld gives the development length to be provided at the two ends of each section.
9A.9 Wall Design in accordance with IS 456-2000
Design of walls in accordance with IS 456-2000 is available in
STAAD.Pro.
Design is performed for in-plane shear, in-plane and out-of-plane
bending and out-of-plane shear. The wall has to be modeled using
STAADs Surface elements. The use of the Surface element
enables the designer to treat the entire wall as one entity. It greatly
simplifies the modeling of the wall and adds clarity to the analysis
and design output. The results are presented in the context of the
entire wall rather than individual finite elements thereby allowing
users to quickly locate required information.
Concrete Design Per IS456
Section 9A
9-16
The program reports shear wall design results for each load
case/combination for user specified number of sections given by
SURFACE DIVISION (default value is 10) command. The shear
wall is designed at these horizontal sections. The output includes
the required horizontal and vertical distributed reinforcing, the
concentrated (in-plane bending) edge reinforcing and the link
required for out-of-plane shear.
General format:
START SHEARWALL DESIGN
CODE INDIAN
FYMAIN f1
FC f2
HMIN f3
HMAX f4
VMIN f5
VMAX f6
EMIN f7
EMAX f8
LMIN f9 LMAX f10
CLEAR f11
TWOLAYERED f12
KSLENDER f13
DESIGN SHEARWALL LIST shearwall-list
END
Section 9A
9-17
The following table explains the parameters used in the shear wall
design. 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.
SHEAR WALL DESIGN PARAMETERS
Parameter Name Default
Value
Description
FYMAIN 415 Mpa Yield strength of steel, in current units.
FC 30 Mpa Compressive strength of concrete, in current units.
HMIN 8 Minimum size of horizontal reinforcing bars (range 6 mm 36 mm). If input is 6 (integer number) the program will assume 6 mm diameter bar.
HMAX 36 Maximum size of horizontal reinforcing bars (range 6 mm 36 mm). If input is 6 (integer number) the program will assume 6 mm diameter bar.
VMIN 8 Minimum size of vertical reinforcing bars (range 6mm 36mm). If input is 6 (integer number) the program will assume 6 mm diameter bar.
VMAX 36 Maximum size of vertical reinforcing bars (range 6mm 36mm). If input is 6 (integer number) the program will assume 6 mm diameter bar.
EMIN 8 Minimum size of vertical reinforcing bars located in edge zones (range 6mm 36mm). If input is 6 (integer number) the program will assume 6 mm diameter bar.
EMAX 36 Maximum size of vertical reinforcing bars located in edge zones (range 6mm 36mm). If input is 6 (integer number) the program will assume 6 mm diameter bar.
LMIN 6 Minimum size of links (range 6mm 16mm). If input is 6 (integer number) the program will assume 6 mm diameter bar.
Concrete Design Per IS456
Section 9A
9-18
SHEAR WALL DESIGN PARAMETERS
Parameter Name Default
Value
Description
LMAX 16 Maximum size of links (range 6mm 16mm). If input is 6 (integer number) the program will assume 6 mm diameter bar.
CLEAR 25 mm Clear concrete cover, in current units. TWOLAYERED 0 Reinforcement placement mode:
0 - single layer, each direction 1 - two layers, each direction
KSLENDER 1.0 Slenderness factor for finding effective height. Table 6
The following example illustrates the input for the definition of
shear wall and design of the wall.
Example
.
.
SET DIVISION 12
SURFACE INCIDENCES
2 5 37 34 SUR 1
19 16 65 68 SUR 2
11 15 186 165 SUR 3
10 6 138 159 SUR 4
.
.
.
SURFACE PROPERTY
1 TO 4 THI 18
SUPPORTS
1 7 14 20 PINNED
2 TO 5 GEN PIN
6 TO 10 GEN PIN
Section 9A
9-19
11 TO 15 GEN PIN
19 TO 16 GEN PIN
.
.
.
SURFACE CONSTANTS
E 2.17185e+007
POISSON 0.17
DENSITY 23.5616
ALPHA 1e-005
.
.
START SHEARWALL DES
CODE INDIAN
UNIT NEW MMS
FC 25
FYMAIN 415
TWO 1
VMIN 12
HMIN 12
EMIN 12
DESIGN SHEA LIST 1 TO 4
END
Notes
1. Command SET DIVISION 12 indicates that the surface boundary node-to-node segments will be subdivided into 12
fragments prior to finite element mesh generation.
2. Four surfaces are defined by the SURFACE INCIDENCES command.
3. The SUPPORTS command includes the new support generation routine. For instance, the line 2 TO 5 GEN PIN
assigns pinned supports to all nodes between nodes 2 and 5.
As the node-to-node distances were previously subdivided
by the SET DIVISION 12 command, there will be an
Concrete Design Per IS456
Section 9A
9-20
additional 11 nodes between nodes 2 and 5. As a result, all
13 nodes will be assigned pinned supports. Please note that
the additional 11 nodes are not individually accessible to the
user. They are created by the program to enable the finite
element mesh generation and to allow application of
boundary constraints.
4. Surface thickness and material constants are specified by the SURFACE PROPERTY and SURFACE CONSTANTS,
respectively.
5. The shear wall design commands are listed between lines START SHEARWALL DES and END. The CODE
command selects the design code that will be the basis for
the design. For Indian code the parameter is INDIAN. The
DESIGN SHEARWALL LIST command is followed by a
list of previously defined Surface elements intended as shear
walls and/or shear wall components.
Technical Overview
The program implements provisions of section 32 of IS 456-2000
and relevant provisions as referenced therein, for all active load
cases. The following steps are performed for each of the horizontal
sections of the wall.
Checking of slenderness limit
The slenderness checking is done as per clause no. 32.2.3. The
default effective height is the height of the wall. User can change
the effective height. The limit for slenderness is taken as 30.
Design for in-plane bending and vertical load (denoted by Mz
& Fy in the shear wall force output)
Walls when subjected to combined in-plane horizontal and vertical
forces produce in-plane bending in conjunction with vertical load.
According to clause no. 32.3.1, in-plane bending may be neglected
in case a horizontal cross section of the wall is always under
compression due combined effect of horizontal and vertical loads.
Otherwise, the section is checked for combined vertical load and
Section 9A
9-21
in-plane moment as column with axial load and uni-axial bending.
For this purpose, the depth is taken as 0.8 x horizontal length of
wall and breadth is the thickness of the wall. The reinforcement is
concentrated at both ends (edges) of the wall. The edge
reinforcement is assumed to be distributed over a len gth of 0.2
times horizontal length on each side. Minimum reinforcements are
according to clause no. 32.5.(a). Maximum 4% reinforcement is
allowed.
Design for in-plane shear (denoted by Fxy in the shear wall
force output)
By default, the program does not design only at the critical section
but at all the horizontal sections. By suitable use of the surface
division command, design at critical section as per clause no.
32.4.1 can be performed.
The design for in-plane shear is done as per clause no. 32.4. The
nominal shear stress is calculated as per clause no. 32.4.2 and it is
checked with the maximum allowable shear stress as per clause no.
32.4.2.1. The design shear strength of concrete is calculated as per
clause no. 32.4.3. Design of shear reinforcement is done as per
clause no. 32.4.4. Minimum reinforcements are as per clause no.
32.5.
Design for vertical load and out-of-plane vertical bending
(denoted by Fy and My respectively in the shear wall force
output)
Apart from the in-plane bending and horizontal shear force, the
wall is also subjected to out-of-plane bending in the vertical and
horizontal directions. The part of the wall which is not having
edge reinforcements (i.e. a zone of depth 0.6 x Length of the wall),
is designed again as column under axial load (i.e. vertical load)
and out-of-plane vertical bending. The minimum reinforcements
and maximum allowable spacings of reinforcements are as per
clause no. 32.5
Concrete Design Per IS456
Section 9A
9-22
Design for out-of-plane horizontal bending (denoted by Mx in
the shear wall force output)
The horizontal reinforcement which is already provided for in -
plane shear is checked against out-of-plane horizontal bending.
The wall is assumed as a slab for this purpose.
Design for out-of-plane shears (denoted by Qx and Qy in the
shear wall force output)
The out-of-plane shear arises from out-of-plane loading. The
nominal shear stresses are calculated as per clause no. 40.1.
Maximum allowable shear stresses are as per table 20. For shear
force in the vertical direction, shear strength of concrete section is
calculated as per section 4.1 of SP 16 : 1980 considering vertical
reinforcement as tension reinforcement. Similarly, for shear force
in the horizontal direction, shear strength of concrete section is
calculated considering horizontal reinforcement as tension
reinforcement. Shear reinforcements in the form of links are
computed as per the provisions of clause no. 40.4.
Shear Wall Design With Opening
The Surface element has been enhanced to allow design of shear
walls with rectangular openings. The automatic meshing algorithm
has been improved to allow variable divisions along wall and
opening(s) edges. Design and output are available for user selected
locations.
Description
Shear walls modeled in STAAD.Pro may include an unlimited
number of openings. Due to the presence of openings, the wall
may comprise up with different wall panels.
Section 9A
9-23
1. Shear wall set-up
Definition of a shear wall starts with a specification of the surface
element perimeter nodes, meshing divisions along node-to-node
segments, opening(s) corner coordinates, and meshing divisions of
four edges of the opening(s).
SURFACE INCIDENCE n1, ..., ni SURFACE s DIVISION sd1, ...,
sdj -
RECOPENING x1 y1 z1 x2 y2 z2 x3 y3 z3 x4 y4 z4 DIVISION
od1, ..., odk
where,
n1, ..., ni - node numbers on the perimeter of the shear wall,
s - surface ordinal number,
sd1, ..., sdj - number of divisions for each of the node-to-node distance on the surface perimeter,
x1 y1 z1 (...) - coordinates of the corners of the opening,
od1, ..., odk - divisions along edges of the opening.
Note:
If the sd1, ..., sdj or the od1, ..., odk list does not include all node-
to-node segments, or if any of the numbers listed equals zero, then
the corresponding division number is set to the default value (=10,
or as previously input by the SET DIVISION command).
Default locations for stress/force output, design, and design output
are set as follows:
SURFACE DIVISION X xd
SURFACE DIVISION Y yd
Concrete Design Per IS456
Section 9A
9-24
where,
xd - number of divisions along X axis,
yd - number of divisions along Y axis.
Note:
xd and yd represent default numbers of divisions for each edge of
the surface where output is requested. The output is provided for
sections located between division segments. For example, if the
number of divisions = 2, then the output will be produced for only
one section (at the center of the edge).
2. Stress/force output printing
Values of internal forces may be printed out for any user -defined
section of the wall. The general format of the command is as
follows:
PRINT SURFACE FORCE (ALONG ) (AT a) (BETWEEN d1, d2)
LIST s1, ...,si
where,
- local axis of the surface element (X or Y),
a - distance along the axis from start of the member to the full cross-section of the wall,
d1, d2 - coordinates in the direction orthogonal to ,
delineating a fragment of the full cross-section for
which the output is desired. **
s1, ...,si - list of surfaces for output generation
** The range currently is taken in terms of local axis. If the local
axis is directed away from the surface, the negative range is to be
entered.
Section 9A
9-25
Note:
If command ALONG is omitted, direction Y (default) is assumed.
If command AT is omitted, output is provided for all sections
along the specified (or default) edge. Number of sections will be
determined from the SURFACE DIVISION X or SURFACE
DIVISION Y input values. If the BETWEEN command is
omitted, the output is generated based on full cross-section width.
3. Definition of wall panels
Input syntax for panel definition is as follows:
START PANEL DEFINITION
SURFACE i PANEL j ptype x1 y1 z1 x2 y2 z2 x3 y3 z3 x4 y4 z4
END PANEL DEFINITION
where,
i - ordinal surface number,
j - ordinal panel number,
ptype - panel type, one of: WALL, COLUMN, BEAM
x1 y1 z1 (...) - coordinates of the corners of the panel,
4. Shear wall design
The program implements different provisions of design of walls as
per code BS 8110. General syntax of the design command is as
follows:
START SHEARWALL DESIGN
(...)
DESIGN SHEARWALL (AT c) LIST s
END SHEARWALL DESIGN
Concrete Design Per IS456
Section 9A
9-26
Note:
If the command AT is omitted, the design proceeds for all cross
sections of the wall or panels, as applicable, defined by the
SURFACE DIVISION X or SURFACE DIVISION Y input
values.
a. No panel definition.
Design is performed for the specified horizontal full cross-section,
located at a distance c from the origin of the local coordinates
system. If opening is found then reinforcement is provided along
sides of openings. The area of horizontal and vertical bars
provided along edges of openings is equal to that of the respective
interrupted bars.
b. Panels have been defined.
Only wall panel design is supported in Indian code.
9-27
Concrete Design Per IS13920
9A1.1 Design Operations
Earthquake motion often induces force large enough to cause
inelastic deformations in the structure. If the structure is brittle,
sudden failure could occur. But if the structure is made to behave
ductile, it will be able to sustain the earthquake effects better with
some deflection larger than the yield deflection by absorption of
energy. Therefore ductility is also required as an essential element
for safety from sudden collapse during severe shocks.
STAAD has the capabilities of performing concrete design as per
IS 13920. While designing it satisfies all provisions of IS 456
2000 and IS 13920 for beams and columns.
9A1.2 Section Types for Concrete Design
The following types of cross sections for concrete members can be
designed.
For Beams Prismatic (Rectangular & Square) & T-shape
For Columns Prismatic (Rectangular, Square and Circular)
Section 9A1
Concrete Design Per IS13920
Section 9A1
9-28
9A1.3 Design Parameters
The program contains a number of parameters that are needed to
perform design as per IS 13920. It accepts all parameters that are
needed to perform design as per IS:456. Over and above it has
some other parameters that are required only when designed is
performed as per IS:13920. Default parameter values have been
selected such that they are frequently used numbers for
conventional design requirements. These values may be changed to
suit the particular design being performed. Table 8A1.1 of this
manual contains a complete list of the available parameters and
their default values. It is necessary to declare length and force
units as Millimeter and Newton before performing the concrete
design.
9A1.4 Beam Design
Beams are designed for flexure, shear and torsion. If required the
effect of the axial force may be taken into consideration. For all
these forces, all active beam loadings are prescanned to identify
the critical load cases at different sections of the beams. The total
number of sections considered is 13. All of these sections are
scanned to determine the design force envelopes.
For design to be performed as per IS:13920 the width of the
member shall not be less than 200mm(Clause 6.1.3). Also the
member shall preferably have a width-to depth ratio of more than
0.3 (Clause 6.1.2).
The factored axial stress on the member should not exceed 0.1fck
(Clause 6.1.1) for all active load cases. If it exceeds allowable
axial stress no design will be performed.
Section 9A1
9-29
Design for Flexure
Design procedure is same as that for IS 456. However while
designing following criteria are satisfied as per IS-13920:
1. The minimum grade of concrete shall preferably be M20. (Clause 5.2)
2. Steel reinforcements of grade Fe415 or less only shall be used. (Clause 5.3)
3. The minimum tension steel ratio on any face, at any section, is given by
min = 0.24fck/fy (Clause 6.2.1b)
The maximum steel ratio on any face, at any section, is given by max = 0.025 (Clause 6.2.2)
4. The positive steel ratio at a joint face must be at least equal to half the negative steel at that face. (Clause 6.2.3)
5. The steel provided at each of the top and bottom face, at any section, shall at least be equal to one-fourth of the maximum
negative moment steel provided at the face of either joint. (Clause
6.2.4)
Design for Shear
The shear force to be resisted by vertical hoops is guided by the
Clause 6.3.3 of IS 13920:1993 revision. Elastic sagging and
hogging moments of resistance of the beam section at ends are
considered while calculating shear force. Plastic sagging and
hogging moments of resistance can also be considered for shear
design if PLASTIC parameter is mentioned in the input file. (Refer
Table 8A1.1)
Shear reinforcement is calculated to resist both shear forces and
torsional moments. Procedure is same as that of IS 456.
Concrete Design Per IS13920
Section 9A1
9-30
The following criteria are satisfied while performing design for
shear as per Cl. 6.3.5 of IS-13920:
The spacing of vertical hoops over a length of 2d at either end of
the beam shall not exceed
a) d/4
b) 8 times the diameter of the longitudinal bars
In no case this spacing is less than 100 mm.
The spacing calculated from above, if less than that calculated
from IS 456 consideration is provided.
Beam Design Output
The default design output of the beam contains flexural and shear
reinforcement provided at 5 equally spaced sections along the
length of the beam. User has option to get a more detail output. All
beam design outputs are given in IS units. An example of
rectangular beam design output with the default output option
(TRACK 1.0) is presented below:
Section 9A1
9-31 ============================================================================
B E A M N O. 11 D E S I G N R E S U L T S
M20 Fe415 (Main) Fe415 (Sec.)
LENGTH: 3500.0 mm SIZE: 250.0 mm X 350.0 mm COVER: 30.0 mm
DESIGN LOAD SUMMARY (KN MET)
----------------------------------------------------------------------------
SECTION |FLEXTURE (Maxm. Sagging/Hogging moments)| SHEAR
(in mm) | P MZ MX Load Case | VY MX Load Case
----------------------------------------------------------------------------
0.0 | 0.00 0.00 0.00 4 | 17.67 0.00 4
| 0.00 -2.74 0.00 5 |
291.7 | 0.00 1.15 0.00 5 | 16.26 0.00 4
| 0.00 0.00 0.00 4 |
583.3 | 0.00 4.61 0.00 5 | 13.97 0.00 4
| 0.00 0.00 0.00 4 |
875.0 | 0.00 7.44 0.00 5 | 10.78 0.00 4
| 0.00 0.00 0.00 4 |
1166.7 | 0.00 9.41 0.00 5 | 6.69 0.00 4
| 0.00 0.00 0.00 4 |
1458.3 | 0.00 10.33 0.00 5 | 1.10 0.00 5
| 0.00 0.00 0.00 4 |
1750.0 | 0.00 9.98 0.00 5 | -3.60 0.00 5
| 0.00 0.00 0.00 4 |
2041.7 | 0.00 8.23 0.00 5 | -10.02 0.00 4
| 0.00 0.00 0.00 4 |
2333.3 | 0.00 5.21 0.00 5 | -15.00 0.00 4
| 0.00 0.00 0.00 4 |
2625.0 | 0.00 1.14 0.00 5 | -19.08 0.00 4
| 0.00 0.00 0.00 4 |
2916.7 | 0.00 0.00 0.00 4 | -22.27 0.00 4
| 0.00 -3.79 0.00 5 |
3208.3 | 0.00 0.00 0.00 4 | -24.57 0.00 4
| 0.00 -9.35 0.00 5 |
3500.0 | 0.00 0.00 0.00 4 | -25.97 0.00 4
| 0.00 -15.34 0.00 5 |
*** DESIGN SHEAR FORCE AT SECTION 0.0 IS 68.60 KN.
- CLAUSE 6.3.3 OF IS-
13920
*** DESIGN SHEAR FORCE AT SECTION 3500.0 IS 75.24 KN.
- CLAUSE 6.3.3 OF IS-
13920
----------------------------------------------------------------------------
SUMMARY OF REINF. AREA (Sq.mm)
----------------------------------------------------------------------------
SECTION 0.0 mm 875.0 mm 1750.0 mm 2625.0 mm 3500.0 mm
----------------------------------------------------------------------------
TOP 226.30 0.00 0.00 0.00 226.30
REINF. (Sq. mm) (Sq. mm) (Sq. mm) (Sq. mm) (Sq. mm)
BOTTOM 0.00 203.02 203.02 203.02 0.00
REINF. (Sq. mm) (Sq. mm) (Sq. mm) (Sq. mm) (Sq. mm)
----------------------------------------------------------------------------
SUMMARY OF PROVIDED REINF. AREA
----------------------------------------------------------------------------
SECTION 0.0 mm 875.0 mm 1750.0 mm 2625.0 mm 3500.0 mm
----------------------------------------------------------------------------
TOP 3-10 2-10 2-10 2-10 3-10
REINF. 1 layer(s) 1 layer(s) 1 layer(s) 1 layer(s) 1 layer(s)
BOTTOM 2-12 2-12 2-12 2-12 2-12
REINF. 1 layer(s) 1 layer(s) 1 layer(s) 1 layer(s) 1 layer(s)
SHEAR 2 legged 8 2 legged 8 2 legged 8 2 legged 8 2 legged 8
REINF. @ 100 mm c/c @ 150 mm c/c @ 150 mm c/c @ 150 mm c/c @ 100 mm c/c
----------------------------------------------------------------------------
============================================================================
Concrete Design Per IS13920
Section 9A1
9-32
9A1.5 Column Design
Columns are designed for axial forces and biaxial moments per IS
456:2000. Columns are also designed for shear forces as per
Clause 7.3.4. All major criteria for selecting longitudinal and
transverse reinforcement as stipulated by IS:456 have been taken
care of in the column design of STAAD. However following
clauses have been satisfied to incorporate provisions of IS 13920:
1. The minimum grade of concrete shall preferably be M20. (Clause 5.2)
2. Steel reinforcements of grade Fe415 or less only shall be used. (Clause 5.3)
3. The minimum dimension of column member shall not be less than 200 mm. For columns having unsupported length
exceeding 4m, the shortest dimension of column shall not be
less than 300 mm. (Clause 7.1.2)
4. The ratio of the shortest cross-sectional dimension to the perpendicular dimension shall preferably be not less than 0.4.
(Clause 7.1.3)
5. The spacing of hoops shall not exceed half the least lateral dimension of the column, except where special confining
reinforcement is provided. (Clause 7.3.3)
6. Special confining reinforcement shall be provided over a length lo from each joint face, towards mid span, and on either
side of any section, where flexural yielding may occur. The
length lo shall not be less than a) larger lateral dimension of
the member at the section where yielding occurs, b) 1/6 of
clear span of the member, and c) 450 mm. (Clause 7.4.1)
7. The spacing of hoops used as special confining reinforcement shall not exceed of minimum member dimension but need
not be less than 75 mm nor more than 100 mm. (Clause 7.4.6)
Section 9A1
9-33
8. The area of cross-section of hoops provided are checked against the provisions for minimum area of cross-section of
the bar forming rectangular, circular or spiral hoops, to be
used as special confining reinforcement. (Clause 7.4.7 and
7.4.8)
Column Design Output
Default column design output (TRACK 0.0) contains the
reinforcement provided by STAAD and the capacity of the section.
With the option TRACK 1.0, the output contains intermediate
results such as the design forces, effective length coefficients,
additional moments etc. A special output TRACK 9.0 is introduced
to obtain the details of section capacity calculations. All design
output is given in SI units. An example of a column design output
(with option TRACK 1.0) is given below. ============================================================================
C O L U M N N O. 3 D E S I G N R E S U L T S
M20 Fe415 (Main) Fe415 (Sec.)
LENGTH: 3000.0 mm CROSS SECTION: 350.0 mm X 400.0 mm COVER: 40.0 mm
** GUIDING LOAD CASE: 5 END JOINT: 2 SHORT COLUMN
DESIGN FORCES (KNS-MET)
-----------------------
DESIGN AXIAL FORCE (Pu) : 226.7
About Z About Y
INITIAL MOMENTS : 0.64 146.28
MOMENTS DUE TO MINIMUM ECC. : 4.53 4.53
SLENDERNESS RATIOS : - -
MOMENTS DUE TO SLENDERNESS EFFECT : - -
MOMENT REDUCTION FACTORS : - -
ADDITION MOMENTS (Maz and May) : - -
TOTAL DESIGN MOMENTS : 4.53 146.28
** GUIDING LOAD CASE: 5
Along Z Along Y
DESIGN SHEAR FORCES : 43.31 76.08
REQD. STEEL AREA : 3313.56 Sq.mm.
MAIN REINFORCEMENT : Provide 12 - 20 dia. (2.69%, 3769.91 Sq.mm.)
(Equally distributed)
CONFINING REINFORCEMENT : Provide 10 mm dia. rectangular ties @ 85 mm c/c
over a length 500.0 mm from each joint face towards
midspan as per Cl. 7.4.6 of IS-13920.
TIE REINFORCEMENT : Provide 10 mm dia. rectangular ties @ 175 mm c/c
SECTION CAPACITY (KNS-MET)
--------------------------
Puz : 2261.52 Muz1 : 178.71 Muy1 : 150.75
INTERACTION RATIO: 1.00 (as per Cl. 39.6, IS456:2000)
============================================================================
********************END OF COLUMN DESIGN RESULTS********************
Concrete Design Per IS13920
Section 9A1
9-34
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 9A1.1 Indian Concrete Design IS13920 Parameters
Parameter
Name
Default Value Description
FYMAIN 415 N/mm2 Yield Stress for main reinforcing steel.
FYSEC 415 N/mm2 Yield Stress for secondary reinforcing steel.
FC 30 N/mm2 Concrete Yield Stress.
CLEAR 25 mm
40 mm
For beam members.
For column members
MINMAIN 10 mm Minimum main reinforcement bar size.
MAXMAIN 60 mm Maximum main reinforcement bar size.
MINSEC 8 mm Minimum secondary reinforcement bar size.
MAXSEC 12 mm Maximum secondary reinforcement bar size.
BRACING 0.0 BEAM DESIGN
A value of 1.0 means the effect of axial force will be taken into account for beam design.
COLUMN DESIGN
A value of 1.0 means the column is unbraced about major axis.
A value of 2.0 means the column is unbraced about minor axis.
A value of 3.0 means the column is unbraced about both axis.
RATIO 4.0 Maximum percentage of longitudinal reinforcement in columns.
RFACE 4.0 A value of 4.0 means longitudinal reinforcement in column is arranged equally along 4 faces.
A value of 2.0 invokes 2 faced distribution about major axis.
Section 9A1
9-35
Table 9A1.1 Indian Concrete Design IS13920 Parameters
Parameter
Name
Default Value Description
A value of 3.0 invokes 2 faced distribution about minor axis.
WIDTH ZD Width to be used for design. This value defaults to ZD as provided under MEMBER PROPERTIES.
DEPTH YD Total depth to be used for design. This value defaults to YD as provided under MEMBER PROPERTIES.
ELZ 1.0 Ratio of effective length to actual length of column about major axis.
ELY 1.0 Ratio of effective length to actual length of column about minor axis.
REINF 0.0 Tied column. A value of 1.0 will mean spiral reinforcement.
TORSION 0.0 A value of 0.0 means torsion to be considered in beam design.
A value of 1.0 means torsion to be neglected in beam design.
TRACK 0.0 BEAM DESIGN:
For TRACK = 0.0, output consists of reinforcement details at START, MIDDLE and END.
For TRACK = 1.0, critical moments are printed in addition to TRACK 0.0 output.
For TRACK = 2.0, required steel for intermediate sections defined by NSECTION are printed in addition to TRACK 1.0 output.
COLUMN DESIGN:
With TRACK = 0.0, reinforcement details are printed.
With TRACK = 1.0, column interaction analysis results are printed in addition to TRACK 0.0 output.
Concrete Design Per IS13920
Section 9A1
9-36
Table 9A1.1 Indian Concrete Design IS13920 Parameters
Parameter
Name
Default Value Description
With TRACK = 2.0, a schematic interaction diagram and intermediate interaction values are printed in addition to TRACK 1.0 output.
SPSMAIN 25 mm Minimum clear distance between main reinforcing bars in beam and column. For column centre to centre distance between main bars cannot exceed 300mm.
SFACE 0.0 Face of support location at start of beam. It is used to check against shear at the face of the support in beam design. The parameter can also be used to check against shear at any point from the start of the member.*
EFACE 0.0 Face of support location at end of beam. The parameter can also be used to check against shear at any point from the end of the member. (Note: Both SFACE and EFACE are input as positive numbers).*
ENSH 0.0 Perform shear check against enhanced shear strength as per Cl. 40.5 of IS456:2000.
ENSH = 1.0 means ordinary shear check to be performed ( no enhancement of shear strength at sections close to support)
For ENSH = a positive value(say x ), shear strength will be enhanced up to a distance x from the start of the member. This is used only when a span of a beam is subdivided into two or more parts. (Refer note after Table 8A.1 )
For ENSH = a negative value(say y), shear strength will be enhanced up to a distance y from the end of the member. This is used only when a span of a beam is subdivided into two or more parts.(Refer note after Table 8A.1)
If default value (0.0) is used the program will calculate Length to Overall Depth ratio. If this ratio is greater than 2.5, shear strength will be enhanced at sections (
Section 9A1
9-37
Table 9A1.1 Indian Concrete Design IS13920 Parameters
Parameter
Name
Default Value Description
be performed.
RENSH 0.0 Distance of the start or end point of the member from its nearest support. This parameter is used only when a span of a beam is subdivided into two or more parts. (Refer note after Table 8A.1)
EUDL None Equivalent u.d.l on span of the beam. This load value must be the unfactored load on span. During design the load value is multiplied by a factor 1.2. If no u.d.l is defined factored shear force due to gravity load on span will be taken as zero. No elastic or plastic moment will be calculated. Shear design will be performed based on analysis result.(Refer note)
GLD None Gravity load number to be considered for calculating equivalent u.d.l on span of the beam, in case no EUDL is mentioned in the input. This loadcase can be any static loadcase containing MEMBER LOAD on the beam which includes UNI, CON, LIN and TRAP member loading. CMOM member loading is considered only when it is specified in local direction. FLOOR LOAD is also considered.
The load can be primary or combination load. For combination load only load numbers included in load combination is considered. The load factors are ignored. Internally the unfactored load is multiplied by a factor 1.2 during design.
If both EUDL and GLD parameters are mentioned in the input mentioned EUDL will be considered in design
Note :
No dynamic (Response spectrum, 1893, Time History) and moving load cases are considered.
CMOM member loading in global direction is
Concrete Design Per IS13920
Section 9A1
9-38
Table 9A1.1 Indian Concrete Design IS13920 Parameters
Parameter
Name
Default Value Description
not considered.
UMOM member loading is not considered.
PLASTIC 0.0 Default value calculates elastic hogging and sagging moments of resistance of beam at its ends.
A value of 1.0 means plastic hogging and sagging moments of resistance of beam to be calculated at its ends.
IPLM 0.0 Default value calculates elastic/plastic hogging and sagging moments of resistance of beam at its ends.
A value of 1.0 means calculation of elastic/plastic hogging and sagging moments of resistance of beam to be ignored at start node of beam. This implies no support exists at start node.
A value of -1.0 means calculation of elastic/plastic hogging and sagging moments of resistance of beam to be considered at start node of beam. . This implies support exists at start node.
A value of 2.0 means calculation of elastic/plastic hogging and sagging moments of resistance of beam to be ignored at end node of beam. This implies no support exists at end node.
A value of -2.0 means calculation of elastic/plastic hogging and sagging moments of resistance of beam to be considered at end node of beam. . This implies support exists at end node. **
IMB 0.0 Default value calculates elastic/plastic hogging and sagging moments of resistance of beam at its ends.
A value of 1.0 means calculation of
Section 9A1
9-39
Table 9A1.1 Indian Concrete Design IS13920 Parameters
Parameter
Name
Default Value Description
elastic/plastic hogging and sagging moments of resistance of beam to be ignored at both ends of beam. This implies no support exist at either end of the member.
A value of -1.0 means calculation of elastic/plastic hogging and sagging moments of resistance of beam to be considered at both ends of beam. This implies support exist at both ends of the member.**
COMBINE 0.0 Default value means there will be no member combination.
A value of 1.0 means there will be no printout of sectional force and critical load for combined member in the output.
A value of 2.0 means there will be printout of sectional force for combined member in the output.
A value of 3.0 means there will be printout of both sectional force and critical load for combined member in the output. ***
HLINK Spacing of longitudinal bars measured to the
outer face
Longer dimension of the rectangular confining hoop measured to its outer face. It shall not exceed 300 mm as per Cl. 7.4.8. If hlink value as provided in the input file does not satisfy the clause the value will be internally assumed as the default one. This parameter is valid for rectangular column.
Bar combination has been introduced for detailing. Please refer section 8A1.6 for details.
* EFACE and SFACE command is not valid for member combination. ** IPLM and IMB commands are not valid for member combination. These commands are ignored for members forming physical member.
Concrete Design Per IS13920
Section 9A1
9-40
*** The purpose of COMBINE command is the following:
1. If a beam spanning between two supports is subdivided into many sub-beams this parameter will combine them into one member. It can also be used to combine members to form one continuous beam spanning over more than two supports.
2. When two or more members are combined during design plastic or elastic moments will be calculated at the column supports. At all the intermediate nodes (if any) this calculation will be ignored. Please note that the program only recognizes column at right angle to the beam. Inclined column support is ignored.
3. It will calculate sectional forces at 13 sections along the length of the combined member.
4. It will calculate critical loads (similar to that of Design Load Summary) for all active load cases during design. Beams will be combined only when DESIGN BEAM command is issued. The following lines should be satisfied during combination of members:
1. Members to be combined should have same sectional properties if any single span between two column supports of a continuous beam is subdivided into several members.
2. Members to be combined should have same constants (E, Poi ratio, alpha, density and beta angle)
3. Members to be combined should lie in one straight line. 4. Members to be combined should be continuous. 5. Vertical members (i.e. columns) cannot be combined. 6. Same member cannot be used more than once to form two different
combined members. 7. The maximum number of members that can be combined into one
member is 299.
Section 9A1
9-41
Note: Sectional forces and critical load for combined member output will only be available when all the members combined are successfully designed in both flexure and shear. ENSH and RENSH parameters will have to be provided (as and when necessary) even if physical member has been formed. The following lines show a standard example for design to be
performed in IS 13920.
STAAD SPACE
UNIT METER MTON
JOINT COORDINATES
..
MEMBER INCIDENCES
..
MEMBER PROPERTY INDIAN
..
CONSTANTS
.
SUPPORTS
.
DEFINE 1893 LOAD
ZONE 0.05 I 1 K 1 B 1
SELFWEIGHT
JOINT WEIGHT
.
LOAD 1 SEISMIC LOAD IN X DIR
1893 LOAD X 1
LOAD 2 SEISMIC LOAD IN Z DIR
1893 LOAD Z 1
LOAD 3 DL
MEMBER LOAD
UNI GY -5
LOAD 4 LL
Concrete Design Per IS13920
Section 9A1
9-42
MEMBER LOAD
. UNI GY -3
LOAD COMB 5 1.5(DL+LL)
3 1.5 4 1.5
LOAD COMB 6 1.2(DL+LL+SLX)
1 1.2 3 1.2 4 1.2
LOAD COMB 7 1.2(DL+LL-SLX)
1 1.2 3 1.2 4 -1.2
LOAD COMB 8 1.2(DL+LL+SLZ)
2 1.2 3 1.2 4 1.2
LOAD COMB 9 1.2(DL+LL-SLZ)
2 1.2 3 1.2 4 -1.2
PDELTA ANALYSIS
LOAD LIST 5 TO 9
START CONCRETE DESIGN
CODE IS13920
UNIT MMS NEWTON
FYMAIN 415 ALL
FC 20 ALL
MINMAIN 12 ALL
MAXMAIN 25 ALL
TRACK 2.0 ALL
*** Unfactored gravity load on members 110 to 112 is 8 t/m (DL+LL) i.e. 78.46 New/mm
EUDL 78.46 MEMB 110 TO 112
** Members to be combined into one physical member
COMBINE 3.0 MEMB 110 TO 112
*** Plastic moment considered
PLASTIC 1.0 MEMB 110 TO 112
DESIGN BEAM 110 TO 112
DESIGN COLUMN
END CONCRETE DESIGN
FINISH
Section 9A1
9-43
9A1.6 Bar Combination
Initially the program selects only one bar to calculate the number
of bars required and area of steel provided at each section along
the length of the beam. Now two bar diameters can be specified to
calculate a combination of each bar to be provided at each section.
The syntax for bar combination is given below.
START BAR COMBINATION MD1 MEMB MD2 MEMB END BAR COMBINATION
MD2 bar diameter should be greater than MD1 bar diameter. The
typical output for bar combination is shown below:
OUTPUT FOR BAR COMBINATION
----------------------------------------------------------------------------
| M A I N R E I N F O R C E M E N T |
----------------------------------------------------------------------------
SECTION | 0.0- 2166.7 | 2166.7- 6500.0 | 6500.0- 8666.7 |
| mm | mm | mm |
----------------------------------------------------------------------------
TOP | 6-20 + 1-25 | 2-20 + 1-25 | 2-20 |
| in 2 layer(s) | in 1 layer(s) | in 1 layer(s) |
Ast Reqd| 2330.22 | 1029.90 | 582.55 |
Prov| 2376.79 | 1119.64 | 628.57 |
Ld (mm) | 940.2 | 940.2 | 940.2 |
----------------------------------------------------------------------------
BOTTOM | 4-20 | 2-20 | 2-20 |
| in 1 layer(s) | in 1 layer(s) | in 1 layer(s) |
Ast Reqd| 1165.11 | 582.55 | 582.55 |
Prov| 1257.14 | 628.57 | 628.57 |
Ld (mm) | 940.2 | 940.2 | 940.2 |
----------------------------------------------------------------------------
The beam length is divided into three parts, two at its ends and one
at span. Ld gives the development length to be provided at the two
ends of each section.
Concrete Design Per IS13920
Section 9A1
9-44
Sample example showing calculation of design shear force as per
Clause 6.3.3
For Beam No. 1 and 2
Section Width b 250 mm
Depth D 500 mm
Characteristic Strength of Steel fy 415 N/sq. mm Characteristic Strength of Concrete fck 20 N/sq. mm Clear Cover 25 mm Bar Diameter 12 mm Effective Depth d 469 mm Eudl w 6.5 N/sq. mm Length L 4000 mm Ast_Top_A 339.29 sq. mm Ast_Bot_A 226.19 sq. mm Ast_Top_B 226.19 sq. mm Ast_Bot_B 339.29 sq. mm
Section 9A1
9-45
Steps
Calculation of Simple Shear
Simple shear from gravity load on span =
Va = Vb = 1.2 * w * L / 2 = 15600N
Calculation of Moment Of Resistances Based On Area Of Steel Provided
Sagging Moment Of Resistance of End A Mu, as =
0.87 * fy * Ast_Bot_A * d * ( 1 - Ast_Bot_A * fy / b * d * fck)
= 36768130.05 N
Hogging Moment Of Resistance of End A Micah =
0.87 * fy * Ast_Top_A * d * ( 1 - Ast_Top_A * fy / b * d * fck)
= 54003057.45 N
Sagging Moment Of Resistance of End A Mu, bs =
0.87 * fy * Ast_Bot_B * d * ( 1 - Ast_Bot_B * fy / b * d * fck)
= 54003057.45 N
Hogging Moment Of Resistance of End A Mob =
0.87 * fy * Ast_Top_B * d * ( 1 - Ast_Top_B* fy / b * d * fck)
= 36768130.05 N
Calculation of Shear Force Due To Formation Of Plastic Hinge At Both Ends Of The Beam Plus The Factored Gravity Load On Span
FIG1: SWAY TO RIGHT
Vur,a = Va - 1.4 [ ( Mu,as + Mu,bh ) / L ] = -10137.69104 N Vur,b = Va + 1.4 [ ( Mu,as + Mu,bh ) / L ] = 41337.69104 N
Concrete Design Per IS13920
Section 9A1
9-46
FIG2: SWAY TO LEFT
Vul,a = Va + 1.4 [ ( Mu,ah + Mu,bs ) / L ] = 53402.14022 N
Vul,b = Va - 1.4 [ ( Mu,ah + Mu,bs ) / L ] = - 22202.14022 N Design Shear Force Shear Force From Analysis At End A , Va,anl = 11.56 N Design Shear Force At End A, Vu,a = Max ( Va,anl, Vur,a, Vul,a) = 53402.14022 N
Shear Force From Analysis At End B , Vb,anl = -6.44 N Design Shear Force At End B, Vu,b = Max ( Vb,anl, Vur,b, Vul,b) = 41337.69104 N
For Beam No. 3
Section Width b 300 mm
Depth D 450 mm
Characteristic Strength of Steel fy 415 N/sq. mm
Characteristic Strength of Concrete fck 20 N/sq. mm
Clear Cover 25 mm
Bar Diameter 12 mm
Effective Depth d 419 mm
Eudl w 6.5 N/sq. mm
Length L 3000 mm
Ast_Top_A 226.19 sq. mm
Ast_Bot_A 339.29 sq. mm
Ast_Top_B 452.39 sq. mm
Ast_Bot_B 226.19 sq. mm
Section 9A1
9-47
Calculation of Simple Shear
Simple shear from gravity load on span =
Va = Vb = 1.2 * w * L / 2 = 11700N
Calculation of Moment Of Resistances Based On Area Of Steel Provided
Sagging Moment Of Resistance of End A Mu,as =
0.87 * fy * Ast_Bot_A * d * ( 1 - Ast_Bot_A * fy / b * d * fck)
= 48452983 N
Hogging Moment Of Resistance of End A Mu,ah =
0.87 * fy * Ast_Top_A * d * ( 1 - Ast_Top_A * fy / b * d * fck)
= 32940364.5 N
Sagging Moment Of Resistance of End A Mu,bs =
0.87 * fy * Ast_Bot_B * d * ( 1 - Ast_Bot_B * fy / b * d * fck)
= 32940364.5 N
Hogging Moment Of Resistance of End A Mu,bh =
0.87 * fy * Ast_Top_B * d * ( 1 - Ast_Top_B* fy / b * d * fck)
= 63326721.3 N
Calculation of Shear Force Due To Formation Of Plastic Hinge At Both
Ends Of The Beam Plus The Factored Gravity Load On Span
FIG1: SWAY TO RIGHT
Vur,a = Va - 1.4 [ ( Mu,as + Mu,bh ) / L ] = -40463.862 N Vur,b = Va + 1.4 [ ( Mu,as + Mu,bh ) / L ] = 63863.862 N
Concrete Design Per IS13920
Section 9A1
9-48
Vul,a = Va + 1.4 [ ( Mu,ah + Mu,bs ) / L ] = 42444.3402 N
Vul,b = Va - 1.4 [ ( Mu,ah + Mu,bs ) / L ] = -15144.34 N Design Shear Force Shear Force From Analysis At End A , Va,anl = -10.31 N Design Shear Force At End A, Vu,a = Max ( Va,anl, Vur,a, Vul,a) = 42444.3402 N
Shear Force From Analysis At End B , Vb,anl = -23.81 N Design Shear Force At End B, Vu,b = Max ( Vb,anl, Vur,b, Vul,b) = 63863.862 N
9-49
Steel Design Per IS800
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.
Section 9B
Steel Design Per IS800
Section 9B
9-50
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 fy
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 0.6fy nor the
permissible stress ac calculated based on the following formula:
(Clause: 5.1.1)
f f
nccf
nyf
0 6.
[( ) ( ) ]
where,
ac = Permissible stress in axial compression, 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 105 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
Section 9B
9-52
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
fy = 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)
6.2.3) :(Clause
])f y(n
)f cb(n
[
1/n
f yf cb0.66bc
where,
fy = Yield stress of steel, in Mpa
n = A factor assumed as 1.4.
fcb = Elastic critical stress in bending, calculated by the
following formula:
f k X k Yc
c [ ]
Section 9B
9-53
where,
X YIT
r DMP
yr 1
1
20 1 Y =
26.5x10
( / )
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
c1 ,c2 = 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
Section 9B
9-54
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 stabil ity 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
Section 9B
9-56
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
Section 9B
9-58
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