Transcript d seismic building code of pakistan

SEISMIC BUILDING CODE OF
PAKISTAN
NED UNIVERSITY OF ENGINEERING &
TECHNOLOGY
CHAPTER 3
SITE CONSIDERATIONS
Site Considerations
 Chapter 3 highlights different types of soil hazards that can damage
a structure, in case of an earthquake.
 In conjunction some outlines are provided in order to select a site
as to avoid maximum damage from these hazards.
 These hazards are listed as ;




Fault rupture hazard
Liquefaction
Landslide and Slope instability
Sensitive clays
CHAPTER 4
SOILS AND FOUNDATIONS
Soils and Foundations
 Chapter 4 emphasizes on the component where the SSI (Soil-
Structure-Interaction) takes place.
 Sections 4.1 – 4.3 define the different terminologies and
terms used in the Chapter.
 However, the core information is divided into the rest of the
sections which forms the backbone of the chapter.
 4.4 – Soil Profiles
 4.5 – Requirements for Foundation
 4.6 – Seismic Soil Pressures and Soil Retaining Structures
4.4 – Soil Profiles
 Soil profile development procedures are identified here.
 Vs Method (Average shear wave velocity method)
 N Method (Average field penetration resistance method)
 Su Method (Average undrained shear strength method)
4.5 - Requirements for Foundation
 Foundation requirements in different conditions are presented
here, as to make certain that the underlying soil does not impose
significant damage on the superstructure.
 Rules given in this Chapter for foundations are applicable to the
foundations of reinforced concrete, structural steel, timber and
masonry buildings.
 Some of the topics discussed are:






Foundation Construction in Areas in Seismic Zones 2, 3, 4
Superstructure-to-Foundation Connection
Piles, Caps and Caissons
Foundation Tie Beams
Wall Foundations of Masonry and Timber Buildings
Footings on or adjacent to Slopes
4.6 – Seismic Soil Pressures and Soil
Retaining Structures
 This section presents different soil pressure coefficients (and
distribution) at rest and incase of an earthquake, on retaining
structures for design and analysis purposes. Such as:
 Total Active and Passive Pressure Coefficients
 Dynamic Active and Passive Soil Pressures
 Dynamic Soil Pressures in Layered Soils
 In addition to soil pressure, stability requirements for
retaining walls are also provided. Such as:
 Factor of safety against sliding (F.S. = 1.1)
 Factor of safety against over-turning (F.S. = 1.3)
 Reduction factor to convert the dynamic internal forces applicable for section
design of RCC (RZA = 1.5) and Steel sheet piles (RZA = 2.5).
CHAPTER 5
STRUCTURAL DESIGN REQUIREMENTS
Structural Design Requirements
 Chapter 5 is divided into five sub divisions
 Division I – General Design Requirements
 Division II – Snow Loads
 Division III – Wind Design
 Division IV – Earthquake Design
 Division V – Soil Profile Types
Division I – General Design
Requirements
 This division provides the general design requirements applicable




to all structures.
Sections 5.1 to 5.4 present a general description of the
terminologies used in the division.
Section 5.5 presents the requirements to achieve a stable
structure, discussing issues such as; complete load path,
overturning, distribution of horizontal shear force, anchorage, etc.
Section 5.6 defines the partition loads on buildings and access
floor system as 21 psf & 10.5 psf, respectively.
Section 5.7 defines the live loads and their distribution on the
floors according to different occupancies, enlisted in Table 5-A.
 Along side it also discusses the cases for live load reduction as given
by the following equation:
TABLE 5-A – UNIFORM AND CONCENTRATED LOADS
USE OR OCCUPANCY
Category
1. Access floor system
Description
Office use
Computer use
2. Armories
3. Assembly areas3 and auditoriums and balconies therewith
Fixed seating areas
Movable seating and other areas
Stage areas and enclosed platforms
4. Cornices and marquees
5. Exit facilities5
6. Garages
7. Hospitals
8. Libraries
9. Manufacturing
General storage and/or repair
Private or pleasure-type motor
vehicle storage
Wards and rooms
Reading rooms
Stack room
Light
Heavy
10. Offices
11. Printing plants
12. Residential8
Press rooms
Composing and linotype rooms
Basic floor area
Exterior balconies
Decks
Storage
UNIFORM
LOAD1
CONCENTR
ATED LOAD
kN/m2
psf
kN
lbs
2.4
4.8
7.2
2.4
4.8
6.0
50
100
150
50
100
125
9.0
9.0
0
0
0
0
2,0022
2,0002
0
0
0
0
2.9
4.8
4.8
2.4
604
100
100
50
0
0
0
06
1.9
2.9
6.0
3.6
6.0
2.4
7.2
4.8
1.9
2.9
1.9
1.9
40
60
125
75
125
50
150
100
40
604
404
40
4.5
4.5
6.7
9.0
13.5
9.0
11.2
9.0
0
0
0
0
1,0002
1,0002
1,5002
2,0002
3,0002
2,0002
2,5002
2,0002
06
0
0
0
4.8
100
0
0
1.9
12.0
6.0
12.0
4.8
4.8
40
250
125
250
100
100
4.5
1,0002
7
7
13. Restrooms9
14. Reviewing stands, grandstands, bleachers, and folding and telescoping seating
15. Roof decks
16. Schools
17. Sidewalks and driveways
18. Storage
19. Stores
20. Pedestrian bridges and walkways
Same as area served or for the type
of occupancy accommodated
Classrooms
Public access
Light
Heavy
7
13.5
3,0002
Division I – General Design
Requirements
 Section 5.11 (Other Minimum Loads) provides description of other
loads and some other guidelines, such as;





Impact loads
Interior wall loads
Retaining walls
Water accumulation
Heliport and heli-stop landings
 5.12 – Load Combinations; load combinations for ultimate and
allowable conditions are provided. The major design combinations
being:






1.4 D
1.2 D + 1.6 L + 0.5 (Lr or S)
1.2 D + 1.6 (Lr or S) + (f1L or 0.8W)
1.2 D + 1.3W + f1L + 0.5 (Lr or S)
1.2 D + 1.0 E + (f1L + f2S)
0.9 D ± (1.0 E or 1.3W)
(5.12-1)
(5.12-2)
(5.12-3)
(5.12-4)
(5.12-5)
(5.12-6)
Division I – General Design
Requirements
 The allowable design combinations being;
 D
 D + L + (Lr or S)
r
 D + (W or E / 1.4)
 0.9 D ± E / 1.4
 D + 0.75 [L+ (Lr or S) + (W or E / 1.4)]
(5.12-7)
(5.12-8)
(5.12-9)
(5.12-10)
(5.12-11)
 5.12.4 provides load combinations for special seismic conditions;
 1.2 D + f1 L+ 1.0 Em
 0.9 D ± 1.0 Em
(5.12-17)
(5.12-18)
 5.13 Limits the deflection of structural members, which shall not
exceed the values set forth in Table 5-D, based on the factors set
forth in Table 5-E.
Division II – Snow Loads
 UBC-97 is referred for calculating the minimum design load:
 Pf = Ce I Pg
(40-1-1)
 Where:
 Ce = snow exposure factor (see Table A-16-A).
 I = importance factor (see Table A-16-B).
 Pg =basic ground snow load, psf (N/m2) – (For 50-year mean recurrence interval
maps)
 Snow loads in excess of 1.0 kN/m2 (20.88 psf) may be reduced for each
degree of pitch over 20 degrees by Rs as determined by the formula:
 Rs = S/40-0.024
 For FPS:
 Rs = S/40-1/2
 Where:
(5.14-1)
 Rs = snow load reduction in kilo-Newton per square meter (lb/ft2) per degree of pitch over 20
degrees.
 S = total snow load in kilo-Newton per square meter (lb/ft2).
Division II – Snow Loads
Division III – Wind Design
 5.20 defines the wind pressure on a surface as:
P = Ce Cq qs Iw
(5.20-1)
 Where
 Ce = combined height, exposure and gust factor coefficient as given in Table 5-G.
 Cq = pressure coefficient for the structure or portion of structure under consideration as given in Table
5-H.
 Iw = importance factor as set forth in Table 5-K.
 P = design wind pressure.
 qs = wind stagnation pressure at the standard height of 10 meters (33 feet) as set forth in Table 5-F.
 Unless detailed wind data is available;
 All the structures inland shall be designed to resist a wind velocity of not less
than 144 km per hour (90 mph) at a height of 10 meters (33 ft)
 All the structures along the coast shall be designed to resist a wind velocity of
not less than 180 km per hour (109 mph) at a height of 10 meters (33 ft).
 5.21: The primary frames or load-resisting system of every structure shall be
designed for the pressures calculated using Formula (5.20-1) and the pressure
coefficient, Cq, of either Method 1 (Normal Force Method) or Method 2 (Projected Area
Method)
Division III – Wind Design
 Table 5-G
 Table 5-H
 Table 5-K
 Table 5-F
Division IV – Earthquake Design
 Sections 5.26 to 5.28 provide some basic definitions and
notations used in the chapter. Some of them being:
 Design Basis Ground Motion is that ground motion that has a 10 percent
chance of being exceeded in 50 years as determined by a site-specific
hazard analysis or may be determined from a hazard map.
 Design Response Spectrum is an elastic response spectrum for 5 percent
equivalent viscous damping used to represent the dynamic effects of the
Design Basis Ground Motion for the design of structures in accordance
with Sections 5.30 and 5.31.
 Soft Storey is one in which the lateral stiffness is less than 70 percent of the
stiffness of the storey above.
 Weak Storey is one in which the storey strength is less than 80 percent of
the storey above.
5.29 – Criteria Selection
 The procedures and the limitations for the design of structures are
described here considering seismic zoning, site characteristics,
occupancy, configuration, structural system and height.
 5.29.6 - Structural systems
 Bearing wall system. A structural system without a complete vertical load-
carrying space frame.
 Building frame system. A structural system with an essentially complete space
frame providing support for gravity loads. Resistance to lateral load is
provided by shear walls or braced frames.
 Moment-resisting frame system. A structural system with an essentially complete
space frame providing support for gravity loads. Moment-resisting frames
provide resistance to lateral load primarily by flexural action of members.
 Dual system. Resistance to lateral load is provided by shear walls or braced
frames and moment resisting frames (SMRF, IMRF, MMRWF or steel
OMRF). The moment-resisting frames shall be designed to independently
resist at least 25 percent of the design base shear.
5.29 – Criteria Selection
 Section 5.29.8 provides the criteria to choose the procedure of
lateral force analysis.
 Simplified Static :
 Buildings of any occupancy (including single-family dwellings) not more than
three storeys in height excluding basements that use light-frame construction.
And other buildings not more than two storeys in height excluding
basements.
 Static:
 All structures, regular or irregular, in Seismic Zone 1 and in Occupancy
Categories 4 and 5 in Seismic Zone 2.
 Regular structures under 73.0 meters (240 feet) in height with lateral force
resistance provided by systems listed in Table 5-N. And irregular structures
not more than five storeys or 20 meters (65 feet) in height.
 Structures having a flexible upper portion supported on a rigid lower portion
where both portions of the structure considered separately can be classified as
being regular.
 Dynamic:
 The dynamic lateral-force procedure of Section 5.31 shall be used for all
other structures.
5.30.2 – Static Force Procedure
 Design Base Shear – (Equation 5.30-4)
(Seismic Coefficient, depending
on seismic zone and soil profile
type)(Table 5-R)
(Importance factor,
depending on the use of the
building)(Table 5-K)
≤
(The total Seismic
Dead Load)
(Section 5.30.1.1)
≤
(Design Base Shear)
(Response modification
factor, representing Over
Strength and global ductility
capacity of lateral force-resisting
systems)(Table 5-N)
(Elastic fundamental Time
Period of the structure) To be
calculated as stated in Section
5.30.2.2
NEXT
5.30.2.2 – Structure Period
 5.30.2.2 Structure Period:The fundamental time period T shall
be determined from equation 5.30-8 or from equation 5.30-9
Method A
(5.30-8)
Method B
(5.30-9)
PREV
Table 5-Q & R – Seismic Coefficient Ca & Cv
PREV
Table 5-K – Occupancy Category
PREV
5.30.1.1 – Seismic Dead Load
Seismic dead load, W, is the total dead load and applicable portions of
other loads listed below.
 1. In storage and warehouse occupancies, a minimum of 25
percent of the floor live load shall be applicable.
 2. Where a partition load is used in the floor design, a load of not
less than 0.48 kN/m2 (10 psf) shall be included.
 3. Design snow loads of 1.44 kN/m2 (30 psf) or less need not be
included. Where design snow loads exceed 1.44 kN/m2 (30 psf),
the design snow load shall be included, but may be reduced up to
75 percent where consideration of siting, configuration and load
duration warrant when approved by the building official.
 4. Total weight of permanent equipment shall be included.
PREV
Table 5-N – Structural Systems
PREV
Distribution of Lateral forces
 5.30.5 –Vertical distribution of force:
Where Ft is the concentrated force at
the top: Ft = 0.07 TV
 There fore the force at a level x is:
(5.30-15)
 5.30.6 – Horizontal distribution of force:
 The design storey shear, Vx, shall be distributed to the various
elements of the vertical lateral-force-resisting system in
proportion to their rigidities
5.30.9-Drift and 5.30.10-Drift Limitations
 The maximum inelastic drift is to be calculated by:
∆M = 0.7 R ∆S
(5.30-17)
 Where ∆S is the drift computed from the elastic analysis
of the frame, using load combinations in section 5.12
 Calculated storey drift using ∆M shall not exceed 0.025 times
the storey height for structures having a fundamental period
of less than 0.7 second. For structures having a fundamental
period of 0.7 second or greater, the calculated storey drift
shall not exceed 0.020 times the storey height.
Vertical Structural Irregularities
Plan Structural Irregularities
5.31 – Dynamic Analysis
 5.31.2-Ground Motions: The ground motion representation
shall be one
 having a 10-percent probability of being exceeded in 50 years,
 shall not be reduced by the quantity R
 and may be one of the following:
 An elastic design response spectrum constructed using the values of Ca
and Cv consistent with the specific site.
 A site-specific elastic design response spectrum based on the geologic,
tectonic, seismologic and soil characteristics associated with the specific
site. (for a damping ratio of 0.05)
 Ground motion time histories developed for the specific site shall be
representative of actual earthquake motions.
 The vertical component of ground motion may be defined by scaling
corresponding horizontal accelerations by a factor of two-thirds.
Division V – Soil Profile Types
 The basic soil profile types are the same as defined in section
4.4
 5.36.2.1 - Average shear wave velocity may be computed as:
(5.36-1)
Division V – Soil Profile Types
 5.36.2.2 - Average Field Penetration resistance may be computed
as:
 5.36.2.3 - Average Un-drained Shear Strength may be computed
as: