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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.

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SEISMIC BUILDING CODE OF PAKISTAN

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  1. SEISMIC BUILDING CODE OF PAKISTAN NED UNIVERSITY OF ENGINEERING & TECHNOLOGY

  2. CHAPTER 3 SITE CONSIDERATIONS

  3. 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

  4. CHAPTER 4 SOILS AND FOUNDATIONS

  5. 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

  6. 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)

  7. 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

  8. 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).

  9. CHAPTER 5 STRUCTURAL DESIGN REQUIREMENTS

  10. 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

  11. 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:

  12. TABLE 5-A – UNIFORM AND CONCENTRATED LOADS

  13. 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)

  14. 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.

  15. 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).

  16. Division II – Snow Loads

  17. 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)

  18. Division III – Wind Design • Table 5-G • Table 5-H • Table 5-K • Table 5-F

  19. 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.

  20. 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.

  21. 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.

  22. 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

  23. 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

  24. Table 5-Q & R – Seismic Coefficient Ca & Cv PREV

  25. Table 5-K – Occupancy Category PREV

  26. 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

  27. Table 5-N – Structural Systems PREV

  28. 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: (5.30-15) • 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

  29. 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.

  30. Vertical Structural Irregularities

  31. Plan Structural Irregularities

  32. 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.

  33. 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)

  34. 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:

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