NED UNIVERSITY OF ENGINEERING & TECHNOLOGY

SEISMIC BUILDING CODE OF PAKISTAN

CHAPTER 3

SITE CONSIDERATIONS

Site ConsiderationsChapter 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 hazardLiquefactionLandslide and Slope instabilitySensitive clays

CHAPTER 4

SOILS AND FOUNDATIONS

Soils and FoundationsChapter 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 Profiles4.5 – Requirements for Foundation4.6 – Seismic Soil Pressures and Soil Retaining

Structures

4.4 – Soil ProfilesSoil 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 FoundationFoundation 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, 4Superstructure-to-Foundation ConnectionPiles, Caps and CaissonsFoundation Tie BeamsWall Foundations of Masonry and Timber BuildingsFootings on or adjacent to Slopes

4.6 – Seismic Soil Pressures and Soil Retaining StructuresThis 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 CoefficientsDynamic Active and Passive Soil PressuresDynamic 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 RequirementsChapter 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 RequirementsThis 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:

USE OR OCCUPANCYUNIFORM

LOAD1

 

CONCENTRATED LOAD

Category Description kN/m2 psf kN lbs

1. Access floor system

Office use 2.4 50 9.0 2,0022

Computer use 4.8 100 9.0 2,0002

2. Armories   7.2 150 0 0

3. Assembly areas3 and auditoriums and balconies therewith

Fixed seating areas 2.4 50 0 0Movable seating and other areas

4.8 100 0 0

Stage areas and enclosed platforms

6.0 125 0 0

4. Cornices and marquees   2.9 604 0 05. Exit facilities5   4.8 100 0 06

6. Garages

General storage and/or repair

4.8 100   7

Private or pleasure-type motor vehicle storage

2.4 50   7

7. HospitalsWards and rooms 1.9 40 4.5 1,00

02

8. Libraries

Reading rooms 2.9 60 4.5 1,0002

Stack room 6.0 125 6.7 1,5002

9. Manufacturing

Light 3.6 75 9.0 2,0002

Heavy 6.0 125 13.5

3,0002

10. Offices  2.4 50 9.0 2,00

02

11. Printing plants

Press rooms 7.2 150 11.2

2,5002

Composing and linotype rooms

4.8 100 9.0 2,0002

12. Residential8

Basic floor area 1.9 40 0 06

Exterior balconies 2.9 604 0 0Decks 1.9 404 0 0Storage 1.9 40 0 0

13. Restrooms9          14. Reviewing stands, grandstands, bleachers, and folding

and telescoping seating 

4.8 100 0 0

15. Roof decks

Same as area served or for the type of occupancy accommodated

       

16. SchoolsClassrooms 1.9 40 4.5 1,00

02

17. Sidewalks and driveways Public access 12.0 250   7

18. StorageLight 6.0 125    Heavy 12.0 250    

19. Stores  4.8 100 13.

53,0002

20. Pedestrian bridges and walkways   4.8 100    

TABLE 5-A – UNIFORM AND CONCENTRATED LOADS

Division I – General Design RequirementsSection 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 (Lr or 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 RequirementsThe allowable design combinations being;

D (5.12-7)D + L + (Lr r 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+ (Lr or 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)

5.13 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/40-0.024For FPS: (5.14-1)

Rs = S/40-1/2Where:

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 SelectionThe 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 systemsBearing 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 SelectionSection 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 ProcedureDesign Base Shear – (Equation 5.30-4)

(Design Base Shear)

(The total Seismic Dead Load) (Section 5.30.1.1)

(Importance factor, depending on the use of the building)(Table 5-K)

(Seismic Coefficient, depending on seismic zone and soil profile type)(Table 5-R)

(Elastic fundamental Time Period of the structure) To be calculated as stated in Section 5.30.2.2

(Response modification factor, representing Over Strength and global ductility capacity of lateral force-resisting systems)(Table 5-N)

≤ ≤

NEXT

5.30.2.2 – Structure Period5.30.2.2 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 LoadSeismic 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 forces5.30.5 – Vertical distribution of force:

Where Ft is the concentrated force at the top: Ft = 0.07 TVThere 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 LimitationsThe 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 Analysis5.31.2-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 TypesThe basic soil profile types are the same as defined

in section 4.45.36.2.1 - Average shear wave velocity may be

computed as:

(5.36-1)

Division V – Soil Profile Types5.36.2.2 - Average Field Penetration

resistance may be computed as:

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