1. DESIGN AND DETAILING FOR EARTHQUAKE LOADS
IS 800: SECTION 12
DESIGN AND DETAILING FOR EARTHQUAKE LOADS

2. Steel Buildings with no damage after Kobe earthquake

3. ADVANTAGES OF USING STEEL FOR EARTHQUAKE RESISTANCE
Neither Corrosion nor Cost can be a factor against Steel Structures
Steel …
is Ductile and gives robust structures
can withstand reversal of stresses
can dissipate considerable energy under cyclic loading
is produced with quality control and suits Capacity Design
gives light and flexible structures – reduction in seismic load
can be easily retrofitted, repaired and rehabilitated with speed

4. SECTION 12 DESIGN AND DETAILING FOR EARTHQUAKE LOADS
CONTENTS
General
Load and Load Combinations
Response Reduction Factors
Connections, Joints and Fasteners
Columns and column splice
Story drift
Ordinary Concentric Braced Frames (OCBF)
Special Concentric Braced Frames (SCBF)
Eccentrically Braced Frames (EBF)
12.10 Ordinary Moment Frames (OMF)
12.11 Special Moment Frames (SMF)

5. SECTION 12 DESIGN AND DETAILING FOR EARTHQUAKE LOADS
12.1 Scope: Design and Detailing for earthquake resisting frames only
12.2 Load and Load Combinations
Earthquake Loads as per IS 1893 – 2002 except for R-factors
load combinations for limit state design
1.5 (DL+ LL)
1.2 (DL + LL + EL)
0.9 DL EL
Special requirements to avoid instabilities like
buckling & over-turning
a) 1.2 DL +0.5 LL EL
b) 0.9 DL EL
(Conti….)

6. SI.No Lateral Load Resisting System R 1 Braced frame systems:
SECTION DESIGN AND DETAILING FOR EARTHQUAKE LOADS Response Reduction Factors
SI.No Lateral Load Resisting System R
Braced frame systems:
a)Ordinary Concentrically Braced Frames (OCBF)
b) Special Concentrically Braced Frame (SCBF)
c) Eccentrically Braced Frame (EBF)
Moment Frame System:
a)   Ordinary moment frame (OMF)
b)   Special moment frame (SMF)
(Conti….)

7. CONNECTIONS, JOINTS AND FASTENERS
All bolts used in frames resisting earthquake loads shall be fully tensioned, High Strength Friction Grip (HSFG) bolts, in standard holes.
All welds used in frame resisting earthquake loads shall be complete penetration butt welds, except in column splice
Bolted joints shall not be designed to share load in combination with welds on the same faying surface
The black bolts or fillet welds may be used
in frames not intended to resist earthquake
loads provided they can tolerate the deformation.

8. BEAM-TO-COLUMN CONNECTIONS
(a) Simple – transfer only shear at nominal eccentricity
Used in non-sway frames with bracings etc.
Used in frames upto 5 storeys
(b) Semi-rigid – model actual behaviour but make analysis
difficult (linear springs or Adv.Analysis). However lead
to economy in member designs.
(c) Rigid – transfer significant end-moments undergoing
negligible deformations. Used in sway frames for
stability and contribute in resisting lateral loads and
help control sway.

9. BEAM-TO-COLUMN CONNECTIONS
Rigid beam-to-column connections a) Short end plate
b) Extended end plate c) Haunched
column web
stiffeners
diagonal
stiffener
web plate
(a)
(b)
(c)

10. When Pr/Pc is greater than 0.4…..
12.5 COLUMNS
Column strength
When Pr/Pc is greater than 0.4…..
Pr is required compressive strength of the member
Pc is actual compressive strength of the member
…… the required axial compressive in the absence of moment to be determined from load combinations
a) 1.2 DL +0.5 LL EL
b) 0.9 DL EL
The required strength determined in above need not exceed
1.2 times the connecting beam or brace nominal strength
the resistance of the foundation to uplift.
Actual load on column during severe earthquake could be higher due to
system over-strength, frame action, strain hardening & vertical motion

11. COLUMN SPLICE
Partial-joint penetration groove welds, provided in columns splice, shall be designed for 200% of the required strength.
Pmin =0.6 fyAf
STORY DRIFT
The Design Story Drift and story drift limits shall be confirm to IS:

12. SEISMIC BEHAVIOUR OF FRAMES
Sway frames and non-say frames
Braced and un-braced frames
Concentrically Braced Frames (CBF)
Eccentrically Braced Frames (EBF)
(a)Diagonal
bracing
(b)Cross or
X-bracing
(c )Chevron
(d)Eccentric
Link Beams
Bracing systems in Steel Frames

13. GENERAL COMMENTS ON FRAME CLASSIFICATION
Structural steel frames classified as ordinary and special depending upon their design ductility levels
High seismic zones and important frames, relying more on ductility and use of higher response reduction factors would be beneficial from economic and safety consideration
Ordinary frames not permitted in seismic zones IV and V
Also in Zone III for structures with I > 1.0

14. 12.7 ORDINARY CONCENTRICALLY BRACED FRAMES (OCBF)
Frame Configuration
Provisions only for diagonal and X- bracing
V and inverted-V to be designed as per specialist literature
K-braced frames not permitted
Bracing Members
Slenderness of bracing member < 120
P(required) < 0.8 P(design)
Bracing cross-section not slender (b/t < 15.7 )
Bracing slopes in both directions
Tensile braces carry 30-70% of load
Built-up braces: local slenderness < 0.4 Overall slenderness
Connection strength to withstand 1.2Agfy, force under additional load combinations and maximum possible force
Check for tension rupture, block shear and gusset local buckling
Connection to withstand 1.2 Mp of brace section

15. 12.8 SPECIAL CONCENTRICALLY BRACED FRAMES (SCBF)
Frame Configuration
Provisions only for diagonal and X- bracing
V and inverted-V to be designed as per specialist literature
K-braced frames not permitted
Bracing Members
Slenderness of bracing member < 160
P(required) < 1.0 P(actual)
Bracing cross-section plastic (b/t < 9.4 )
Bracing slopes in both directions
Tensile braces carry 30-70% of load
Built-up braces: local slenderness < 0.4 Overall slenderness
Connection as in OCBF
Columns should have plastic cross-sections
Splices to resist shear and 0.5Mp of smaller section
12.9 Eccentrically Braced Frames (EBF) as per specialist literature

16. 12.10 ORDINARY MOMENT FRAMES (OMF)
Rigid or Semi-rigid moment Connections permitted.
Rigid moment connection to withstand 1.2Mp of beam or the maximum moment that can be delivered, whichever is less.
Semi-rigid connections to withstand 0.5Mp of beam, or the maximum moment that can be delivered, whichever is less .
The design moment shall be achieved within a rotation of 0.01 rad.
The stiffness and strength of semi-rigid connection shall be accounted for in the analysis and design, and the overall stability of the frame ensured
Both Rigid and Semi-Rigid connection, to withstand a shear resulting from the load combination 1.5DL+1.5LL plus the shear corresponding to the design moment defined above (respectively).
In Rigid fully welded connections, continuity plates (stiffener plates) of thickness equal to or greater than the thickness of the beam flange shall be provided and welded to the column flanges and web.

17. 12.11 SPECIAL MOMENT FRAMES (SMF)
Beam-to-column joints and connections
Rigid connections only, to withstand a moment of 1.2Mp of beam.
In case of a reduced beam section, 0.8Mp of unreduced section.
The connection to withstand a shear from the load combination 1.2DL+ 0.5LL plus the shear from the application of 1.2 Mp in the opposite sense, at each end of the beam. The shear strength need not exceed the value corresponding to additional load combinations.

18. BUCKLING OF WEB PLATES IN SHEAR
cr
Shear buckling of a plate

19. Beam-to-column joints and connections (SMF)
In column strong axis connections, the panel zone shall be checked for shear buckling at the design shear defined above. Doubler plates or diagonal stiffener may be used to strengthen the web against shear buckling.
The individual thickness of the column webs and doubler plates, shall exceed (dp+bp)/90.
Continuity plates (stiffener plates) shall be provided in all strong axis welded connections except in end plate connection dp bp
Continuity
plate

20. SPECIAL MOMENT FRAMES (SMF)
Beam and column limitation
Beam and column sections shall be plastic or compact. At potential plastic hinge locations, they shall be necessarily plastic.
The section selected for beams and columns shall satisfy the following relation
 Mpc > 1.2  Mpb
Lateral support to the column at both top and bottom beam flange levels shall be provided so as to resist at least 2% of the beam flange strength, except for the case described below.
A Plane frame with support in the direction perpendicular to its plane, shall be checked for buckling, also under the additional load combination.

21. Dept. of Civil Engineering Email: sr.satishkumar@gmail.com
12.12 Column Bases
Fixed column bases and anchor bolts to withstand a moment of 1.2 times Mp of column section
All bases to withstand full shear under all load combinations or 1.2 times shear capacity of column section whichever is higher
Dr. S. R. Satish Kumar
Dept. of Civil Engineering
IIT Madras
THANK YOU