SEISMIC DESIGN STEPS.pptx

SEISMIC DESIGN STEPS
Prof. Samirsinh P Parmar
Mail: spp.cl@ddu.ac.in
Asst. Prof. Dept. of Civil Engg.
Dharmsinh Desai University, Nadiad,
Gujarat , Bharatvarsh.

Content of the presentation:
A. Planning stage
• Geometry
• Other Considerations
B. Design Stage
• Structure engineering
• Captive columns
• Soft story
SPP-DoCL, DDU, Nadiad, Gujarat, Bharat. 2

ABSTRACT
This article discusses some basic principles of seismic design, where the main goal
is ensuring safety for occupants. There are three important requirements before
starting a seismic design:
• Step 1: Determine the potential seismic forces and all major hazards to which an
area is vulnerable, and develop a design that accounts for all of them.
• Step 2: Performance based requirements must be established, based on the risks
posed by natural hazards on the buildings and its occupants.
• Step 3: Understand that earthquakes are dynamic, and every building responds
differently. Therefore, teams must work together and communicate all the terms
and methods used in the seismic design.

STEPS IN SEISMIC DESIGN:
A.PLANNING STAGE:
1. Plan the building and structures in a symmetrical way both in plan (horizontal
axis) and elevation. (vertical axis).
2. Avoid open ground (Soft storey) which is used for car parking.
3. Avoid weak storey and provide strong diaphragm. That is thinner slabs and flat
slabs are to be avoided.
4. Provide openings for doors and windows at a distance of min 0.6 m from the
column edges. Follow the IS code 4326 –page 11-for more details for masonry
structures.
5. Do not add appendages like water tanks and swimming pools etc which will
create a vast difference of Cm and Cr. (Center of Mass & Center of rigidity)

6. Conduct soil test and investigate the soil nature
to avoid soil liquefactions.
7. Follow the IS codal and NBC provisions while in Planning stage which will aid
more safer structures.
8. Select good materials-concrete ingredients, brick, steel etc. Specially steel having an
elongation of above 14% and yield strength of 415N/mm^2.
9. The yield stress shall not be greater than 415N/mm^2. Steel having an yield strength
500 N/mm^2 may be used provided the % of elongation is above 14%. Make sure
before approving it by means of lab. test results.
10. Provide plinth beam at ground level , lintel and roof band (masonry structures).
11. Do not lower the beams in RCC frames at lintel level to have financial savings
since the load path will not be there.
A.PLANNING STAGE:

The location and physical properties of the site are the primary influences the entire
design process.
The following questions can serve as a checklist to identify seismic design
objectives:
1) Where is the location of the nearest fault?
2) Are there unconsolidated natural or man-made fills present?
3) Is there a potential for landslide or liquefaction on or near the site?
4) Are there vulnerable transportation, communication, and utilities connections?
5) Are there any hazardous materials on the site to be protected?
6) Is there potential for battering by adjacent buildings?
7) Is there exposure to potential flood from tsunami, seiche, or dam failure?
A.PLANNING STAGE:

Establish Seismic Design Objectives
A performance-based approach to establishing seismic design objectives is
recommended. This determines a level of predictable building behavior by
responding to the maximum considered earthquake. A threat/vulnerability
assessment and risk analysis can be used to define the level of performance
desired for the building project.
Some suggested seismic design performance goals are:
• Conform to local building codes providing "Life Safety," meaning that the
building may collapse eventually but not during the earthquake.
• Design for repairable structural damage, required evacuation of the building,
and acceptable loss of business for stipulated number of days.

Some suggested seismic design performance goals are:
• Design for repairable nonstructural damage, partial or full evacuation, and
acceptable loss of business for stipulated number of days due to repair.
• Design for repairable structural damage, no evacuation required, and
• No structural damage, repairable nonstructural damage, no evacuation, and
• No structural or nonstructural damage, and no loss of business caused by
either (excluding damage to tenants' own equipment such as file cabinets,
bookshelves, furniture, office equipment etc. if not properly anchored).
Establish Seismic Design Objectives

Select/Design Appropriate Structural Systems
Seismic design objectives can greatly influence the selection of the most appropriate structural
system and related building systems for the project. Some construction type options, and
corresponding seismic properties, are:
• Wood or timber frame (good energy absorption, light weight, framing connections are critical).
• Reinforced masonry walls (good energy absorption if walls and floors are well integrated;
proportion of spandrels and piers are critical to avoid cracking)
• Reinforced concrete walls (good energy absorption if walls and floors well integrated;
proportion of spandrels and piers are critical to avoid cracking)
• Steel frame with masonry fill-in walls (good energy absorption if bay sizes are small and
building plan is uniform)
• Steel frame, braced (extensive bracing, detailing, and proportions are important)
• Steel frame, moment-resisting (good energy absorption, connections are critical)
• Steel frame, eccentrically braced (excellent energy absorption, connections are critical)
• Pre-cast concrete frame (poor performer without special energy absorbing connections)

• Structural and architectural detailing and construction quality control
is very important to ensure ductility and natural damping and to keep
damages to a limited and repairable range.
• The prospect of structural and nonstructural damage is not likely to be
eliminated without the prudent use of energy-dissipating devices.
• The cost of adding energy-dissipating devices is in the range of 1–2%
of the total structural cost.
• This is not a large number, particularly when related to the life-cycle
cost of the building.
• Within a 30–50 year life cycle the cost is negligible
Select/Design Appropriate Structural Systems

B.DESIGN STAGE: Structural analysis:
• The structural designer should address the influence of masonry infill walls in the lateral force
behavior of the structure, either by taking them into account in the design process
or
• By a separation gap from the column. If a separation gap is provided, then appropriate measures
should be taken to warrant the out-of-plane stability of the masonry when subjected to lateral forces
from wind or earthquake. The gap min 20 mm to 50mm or but comply with calculation.
1. Avoid weak column and strong beam design.
2. Provide thick slab which will help as a rigid diaphragm. Avoid thin slab and flat
3. slab construction.
4. Provide cross walls which will stiffen the structures in a symmetric manner.
5. Provide shear walls in a symmetrical fashion. It should be in outer boundary to have large lever arm
to resist the EQ forces.

6. FOR CANTILEVERS IT IS DESIGNED FOR GRVITY ANFD OTHER LOADS AS
USUAL FOR THE TOP BARS AND THICKNESS BUT DESIGNED IN ADDITION
TO THAT AS PER THE IS CODE 1893-2002 CLAUSE 7.12.2.2 which states:
All horizontal projections like corniced and balconies shall be designed and
checked for stability for five times the design coefficient specified in 6.4.5(that is
=10/3 Ah). .{Vb=AhW}
For design example wide page 335 of ADVANCED R.C. DESIGN BY P.C. VARGHESE.
Ductility is defined as the ability of a structure to undergo inelastic deformations beyond the
initial yield deformation with NO DECREASE IN THE LOAD RESISTANCE.
B.DESIGN STAGE: Structural analysis:

Building Configuration:
• This term defines a building's size and shape, and structural and nonstructural elements.
Building configuration determines the way seismic forces are distributed within the
structure, their relative magnitude, and problematic design concerns.
• Regular Configuration buildings have Shear Walls or Moment-Resistant Frames or
Braced Frames and generally have:
• Low Height to Base Ratios
• Equal Floor Heights
• Symmetrical Plans
• Uniform Sections and Elevations
• Maximum Torsional Resistance
• Short Spans and Redundancy
• Direct Load Paths
• Irregular Configuration buildings are those that differ from the "Regular" definition and
have problematic stress concentrations and torsion.

GEOMETRY:(ref: page 624 to 628 of earthquake Design concept-by Dr.C.V.R.Murthy)
• Building need to be proportioned reasonably to avoid unduly long, tall or wide dimensions which
are known to result in poor seismic performance during an earthquake. Thus urban by-laws tend to
control the overall geometry of the buildings with respect to the plot size. These are helpful in
controlling problems like blockade of roads or collapsing on adjacent buildings in an unfortunate
situation of a building collapse during an earthquake.
• Height/plot width <1.3 as per clause 6.6 NBC(1983)(part III) for plot size and clause 9.4.1 for
height.
• Ex: plot area 10.0x18.0m-Max.permissible height= 1.3x10=13.0m
• Length to width ratio<1.66 Clause 6.6 NBC & 8.2.1 for side open space.
• Ex: helps in ensuring rigid diaphragm action.
• Plot area 12mx20m
-deduct standard setbacks.
-Remaining maximum coverage area:6.0mx15.5m.
-Maximum possible plan size: 6mx9.6m.

LENGTH OF BUILDING:
• Shall not be more than 150m.
• Clear height of 6m at every 30m intervals at ground level for a passage of 7.5m width.
Thermal consideration requires expansion joints after every 45m.
These joints become seismic joints in buildings locates in seismic zones.
In such situations, the 150m specified is not relevant.
30m
150m (max)
6m
7.5m

OTHER CONSIDERATIONS:
• IS 1893 Provisions.
-Improve shape and subsequently behavior of
building during earthquake shaking.
Design provisions may not exist to explicitly limit the height of buildings.
But, it is desirable to ensure that
- Buildings are not made too long.
- Building height gives a regular (desired)
slenderness ratio.

HOW TO INCREASE THE DUCTILITY :
CAN BE INCREASED IN A SECTION BY:
• Decrease the percentage of tension steel (pt).
• Increase the percentage compression steel (pc).
• Decrease in the tensile strength of steel. (Fy=415N/mm^2).
• Increase in the compressive strength of concrete.-Min M20 to M30 and above.
• Increase in the compression flange area in flanged beams (T and L beams) and
• Increase in the transverse (Shear) reinforcement.

opening
opening opening
masonry masonry
masonry
c
o
l
u
m
n
c
o
l
u
m
n
Beam
Solution:
1. Add ties at closer spacing. Preferably spiral ties.
2. Provide masonry walls on either side equal to twice the opening sizes by reducing the openings.
3. The best solution is to avoid the opening so that no captive column is created.
CAPTIVE COLUMNS:
Captive column

masonry masonry
masonry
c
o
l
u
m
n
c
o
l
u
m
n
Beam
CAPTIVE COLUMNS: SOLUTIONS.
OPENING
OPENING OPENING
L
L
L L
L
1 1
a
2

SOFT STOREY:
This case is usually by providing car park at the ground floor.
In this case try to provide masonry walls as possible as to provide stiffness to columns.
If not possible design the columns and beams in soft storey for moments and shears by 2.5 times from
the analysis results. Clause 7.10.3a –IS 1893(part1)-2002

b) Besides the columns designed and detailed for the calculated storey shears and
moments, shear walls placed symmetrically in both directions of the buildings as far
as away from the center of the buildings as feasible; to be designed exclusively for
1.5 times the lateral storey shear forces calculated as before. (clause 7.10.3.b)
In another solution is to provide (cross bracings (in elevation) without hindrance to
vehicular movements.
L,T, + SHAPE COLUMNS CAN BE USED BUT DESING IS A STILLA MATTER .

• SOME BASIC BRACING TYPES:
DIAGONAL BRACING X- BRACING V- BRACING
K- BRACING
INVERTED V- BRACING SPP-DoCL, DDU, Nadiad, Gujarat, Bharat. 25

DETAILING:
1) GOOD DETAILING IS AS IMPORTANT AS DESIGN AND PLANNING.
2) FOLLOW THE DUCTILE DETAILING AS PER IS CODE 13920-1993. ANCHORAGE AND
OVERLAPPING ARE TO BE AS PER THE CODE.
3) IS CODE 4326-1993-EARTHQUAKE RESISTANT DESIGN AND CONSTRUCTION OF
BUILDNGS-IS TO BE FOLLOWED.

RELEVANT CODES AND STANDARDS
• Federal Emergency Management Agency (FEMA)
• International Code Council (ICC)
• National Earthquake Hazards Reduction Program (NEHRP)
• Standards of Seismic Safety for Existing Federally Owned and Leased
Buildings

CONSTRUCTION STAGE:
1. Good planning and design will not alone aid in resisting seismic forces but good
workmanship and construction practice will add more strength for resisting the seismic
forces.
2. Select good materials . Follow the mix design as obtained by the lab.
3. Provide the covers as per codal provisions. Do not use the aggregates, marble pieces
and other means except the mortar cover blocks.
4. Follow the design details as furnished by the structural engineer and do not make any
deviations.
5. Compact the concrete by means of needle vibrator.
6. Cure the concrete for at least a minimum period.
7. Experienced supervisor should be employed to have good quality control at site.

Seismic Design Strategies And Devices
• Diaphragms: Floors and roofs can be used as rigid horizontal planes, or diaphragms, to
transfer lateral forces to vertical resisting elements such as walls or frames.
• Shear Walls: Strategically located stiffened walls are shear walls and are capable of
transferring lateral forces from floors and roofs to the foundation.
• Braced Frames: Vertical frames that transfer lateral loads from floors and roofs to
foundations. Like shear walls, Braced Frames are designed to take lateral loads but are used
where shear walls are impractical.
• Moment-Resistant Frames: Column/beam joints in moment-resistant frames are designed to
take both shear and bending thereby eliminating the space limitations of solid shear walls or
braced frames. The column/beam joints are carefully designed to be stiff yet to allow some
deformation for energy dissipation taking advantage of the ductility of steel (reinforced
concrete can be designed as a Moment-Resistant Frame as well).

Seismic Devices
Concentric Braced Frame
Eccentric Braced Frame, with link
beams

Earthquake Resistant Building

• Energy-Dissipating Devices: Making the building structure more resistive
will increase shaking which may damage the contents or the function of the
building.
• Energy-Dissipating Devices are used to minimize shaking.
• Energy will dissipate if ductile materials deform in a controlled way.
• An example is Eccentric Bracing whereby the controlled deformation of
framing members dissipates energy.
• However, this will not eliminate or reduce damage to building contents.
• A more direct solution is the use of energy dissipating devices that function
like shock absorbers in a moving car.
• The period of the building will be lengthened and the building will "ride
out" the shaking within a tolerable range.
Seismic Devices: Energy-Dissipating Devices

Moment Resistance Frame

• Base Isolation: This seismic design strategy involves separating the building from the
foundation and acts to absorb shock. As the ground moves, the building moves at a slower
pace because the isolators dissipate a large part of the shock.
• The building must be designed to act as a unit, or "rigid box", of appropriate height (to
avoid overturning) and have flexible utility connections to accommodate movement at its
base.
• Base Isolation is easiest to incorporate in the design of new construction.
• Existing buildings may require alterations to be made more rigid to move as a unit with
foundations separated from the superstructure to insert the Base Isolators.
• Additional space (a "moat") must be provided for horizontal displacement (the whole
building will move back and forth a whole foot or more).
• Base Isolation retrofit is a costly operation that is most commonly appropriate in high
asset value facilities and may require partial or the full removal of building occupants
during installation.
Seismic Devices: Energy-Dissipating Devices

There are many types of dampers used to mitigate seismic effects, including:
• Hysteric dampers utilize the deformation of metal parts
• Visco-elastic dampers stretch an elastomer in combination with metal parts
• Frictive dampers use metal or other surfaces in friction
• Viscous dampers compress a fluid in a piston-like device
• Hybrid dampers utilize the combination of elastomeric and metal or other parts
Seismic Devices: Dampers

Supplemental energy
dissipation devices

Refer for further information:
• http://www.ce.memphis.edu/7119/Notes2/ASCE003c12_p119-142.pdf
• http://structurespro.info/wp-content/uploads/2020/03/Lecture-4-a-
Code-based-Seismic-Design-of-Structures.pdf

SEISMIC DESIGN STEPS.pptx

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