Seismic building code of pakistan
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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.

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Seismic building code of pakistan



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
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
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
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
    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:

    Division i general design requirements1
    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 (5.12-1)

    • 1.2 D + 1.6 L + 0.5 (Lr or S) (5.12-2)

    • 1.2 D + 1.6 (Lror S) + (f1L or 0.8 W) (5.12-3)

    • 1.2 D + 1.3 W + f1L + 0.5 (Lr or S) (5.12-4)

    • 1.2 D + 1.0 E + (f1L + f2S) (5.12-5)

    • 0.9 D ± (1.0 E or 1.3 W) (5.12-6)

  • Division i general design requirements2
    Division I – General Design Requirements

    • The allowable design combinations being;

      • D (5.12-7)

      • D + L + (Lrr or S) (5.12-8)

      • D + (W or E / 1.4) (5.12-9)

      • 0.9 D ± E / 1.4 (5.12-10)

      • D + 0.75 [L+ (Lror S) + (W or E / 1.4)] (5.12-11)

  • 5.12.4 provides load combinations for special seismic conditions;

    • 1.2 D + f1 L+ 1.0 Em (5.12-17)

    • 0.9 D ± 1.0 Em (5.12-18)

  • 5.13Limits 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
    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: (5.14-1)

    • Rs = S/40-1/2

  • Where:

    • 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 iii wind design
    Division III – Wind Design

    • 5.20 defines the wind pressure on a surface as:

      P = CeCqqsIw(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 design1
    Division III – Wind Design

    • Table 5-G

    • Table 5-H

    • Table 5-K

    • Table 5-F

    Division iv earthquake design
    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 beingexceeded 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
    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 selection1
    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
    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

    (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 structure period – Structure Period

    • Structure Period:The fundamental time period T shall be determined from equation 5.30-8 or from equation 5.30-9

    Method A


    Method B



    5 30 1 1 seismic dead load – 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.


    Distribution of lateral forces
    Distribution of Lateral forces

    • 5.30.5 – Vertical distribution of force:

    Where Ftis the concentrated force at the top: Ft = 0.07 TV

    • There fore the force at a level x is:


    • 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
    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 ∆Mshall 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.

  • 5 31 dynamic analysis
    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 Caand 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
    Division V – Soil Profile Types

    • The basic soil profile types are the same as defined in section 4.4

    • - Average shear wave velocity may be computed as:


    Division v soil profile types1
    Division V – Soil Profile Types

    • - Average Field Penetration resistance may be computed as:

    • - Average Un-drained Shear Strength may be computed as: