Building Code of Pakistan

KEY ASPECTS OF BUILDING CODE OF PAKISTAN
SEISMIC PROVISIONS-2007

ABSTRACT:

Building Code of Pakistan, Seismic Provision 2007, serves two purposes. First is to define the earthquake level for each tehsil of the country, which buildings have to be designed. Secondly, it provides codified procedures and guidelines for planning, design, analysis and detail of building structures.. The topics covered include site considerations, soil and foundations, general structural design requirements, reinforced concrete buildings, structural steel buildings, masonry buildings, architectural elements and mechanical & electrical systems. Effective implementation of this code can lead to significant improvement in the seismic safety of buildings in the country. The paper presents overview of the key aspects of the code.

INTRODUCTION:

A seismic building code provides a rational, uniform and methodical basis for providing optimally economical way of ensuring earthquake resistant design of buildings. Earthquake hazard varies in different parts of the country. This has to be realistically defined. Intensive studies have been carried out to the evaluate the geology of Pakistan and to identify possible sources of earthquakes. Based on an evaluation of these data, a seismic zoning map of Pakistan has been prepared. This has also been presented in a tabular form, where each tehsil of the country has been listed together with its seismic zone. Detailed codified procedures are then given for design of different types of buildings structures.

CONTENTS

The main chapters of the code are as follows:

• Scope
• Seismic Hazard
• Site Consideration
• Soils Foundations
• Structural Design Requirements
• Structural Tests and Inspection
• Structural Concrete
• Structural Steel
• Masonry
• Architectural Elements
• Mechanical and Electrical Systems

1-SCOPE:

The code applies to buildings and building like structures. Other Civil Structures, Like bridges, dam, tunnels, harbors, pipelines, transmission lines, power plants and various special structures are covered by this Code.

2-SEISMIC HAZARD:

Pakistan is divided into five seismic zones on the basis of ground motion that has a 10% probability of exceedance in 50 years. The zones are based on peak ground acceleration ranges summaries in plate #13 of the appendix to this paper.
A few sites/towns of Pakistan are situated in the lowest seismic zone i.e. Zone-1 About ten tehsils of the country are in seismic zone-4 Rest of the area being in Zones 2 and 3.
Seismic Zoning map of Pakistan, individual provinces and tables listing Seismic Zones of Tehsils of Pakistan are given in plate #14 to Plate #29.

3-SITE CONSIDERATIONS:

A brief over-review on “Site Considerations” introduces the structural designer to the hazards associated with fault rupture, liquefaction and potential landslides.
The code does not allow major construction with in 200 meters on either side an active fault. Specially designed single storey buildings are, however, allowed.

4-SOILS AND FOUNDATIONS:

The type of soils over which a building is situated plays an important role in its seismic response. Earthquake of similar intensities may cause different levels of damage depending upon the type of soil on a specific site.
For the purpose of evaluation of the seismic force on a structure, the code classifies the soils into six categories from Sa to Sf on the basis of shear wave velocity. At present the classification follows well-established international codes and is listed in plate # 42.
In addition to soil classification, the code addresses special requirements for foundations constructed in seismic zones 3 & 4.

5-STRUCTURAL DESIGN REQUIREMENTS:

An exhaustive chapter of the code titled “ Structural Design Requirements” deals with the loads and load combinations to be dealt with in the analysis and design of structures. Although code targets the seismic provisions only, it was considered appropriate to mention in some details the dead, live, wind snow and other non-seismic loads also. This has facilitated to incorporate the ways in which seismic efforts are to be combined with other loads.

6- STRUCTURAL CONCRETE:

At present most of the medium-rise to high-rise construction comprises structural concrete with an increasing use of compressive strengths much higher than traditionally used strength of 2500 to 3000 psi. The code, though does not covers explicity, the general design of concrete members, seismic requirements for reinforcement, lap locations, minimum member dimensions and confinement of concrete by stirrups and ties. The minimum requirements for concrete and reinforcement strengths are also prescribed.

7- STRUCTURAL STEEL:

The structural steel construction in Pakistan has traditionally been more or less limited to the industrial facilities and some other non-building structures. It is much less common than the reinforced concrete construction. However, keeping in view large potential of structural steel in future construction, it has been given an extensive treatment in the code. The code covers loads, materials, connections and various structural systems with particular reference to seismic design. Composite construction comprising reinforced concrete and structural steel is also covered in detail.

8-MASONARY:

Masonry is the most common type of construction for low rise construction not only in Pakistan but other parts of the world also. Due to its extensive use a large area scale countrywide research is required to formulate Pakistan specific code clauses. This of course is a long-term process and shall prove a fertile field of research scholars in coming years. For the time being some internationally accepted standards are incorporated in the code providing a great degree of flexibility to the designer based on materials available, quality of construction expected and skills of the designer himself. The designer may choose from working stress design, strength design and empirical design method. All three-design procedures give due to consideration to seismic safety as per level of expected ground acceleration.

9-ARCHITECTURAL ELEMENTS:

The chapter 10 of the code focuses on the seismic provisions for architectural components of structures. To start off, computational procedure for the design lateral seismic force for the architectural components has been stated along with a mention about its application and mode of transfer to the main structural system.
The importance of consideration of the interrelationship between the architectural and structural system has been highlighted with regard to the structures response so that a progressive failure can be avoided.
The chapter discusses the provisions for different architectural components for suspended ceilings have been stated. A special mention has been given to account for the overturning effects of equipments attached to these floors. On the other hand, floors, which comply with certain requirements of connections, anchorage, bracing systems, stringers etc, shall be designed as special access floors.
The including part of the chapter includes provisions for partitions. A table having values for seismic co-efficient and performance criteria factors (these two shall be used for computation of seismic force) corresponding to various architectural components has been provided.

10-MECHANICAL AND ELECTRICAL SYSTEMS:

The concluding chapter 11 of the code consists of special seismic provisions for mechanical and electrical components of the building.
The chapter emphasizes the need for the designers to take structural dynamics into consideration while analyzing the support mechanism and attachments for the mechanical and electrical components. Computational procedure of design seismic lateral force is mentioned along with its application , mode of transfer and the fundamental period of vibration of the mechanical and electrical components. The interrelationship of systems or components and their effect on each other shall be considered so that failure of such components does not cause the failure of the main design structural system. Provision shall be also made to eliminate seismic impact for impact-prone equipment.
A table having values for seismic coefficient and performance criteria factors (these two shall be used for computation of seismic force) corresponding to various mechanical and electrical components, has been provided.

11-CONCLUSION:

Building code of Pakistan (Seismic provision 2007) is a first step to a never-ending journey. The rapid advances of technology require periodic updating of building codes even in developed countries. This is much more required in our case. The instant adaptation of code is the prime requirement but we should look forward to the next step right from today till we achieve a truly country specific code based on local research supplemented by international provinces.

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Building Code of PAkistan