Tall Building Architectures

Federal Judicial Academy Phase-II, Islamabad Chapter-9

9.1 Introduction

This theory aims to provide guidance and minimum standards for the designers of tall buildings in seismically active regions anywhere in the world.

A tall building is defined here in as a building of sufficient height for the period of the first translational mode of vibration to exceed 4 seconds or for its height to exceed 50m.

However, this can also be used to assess the performance of medium-rise buildings where this is needed. 9.2 Earthquake

Earthquake is a shaking of the ground caused by the sudden breaking and shifting of large sections of Earth’s rocky outer shell. Earthquakes are among the most powerful events on earth, and their results can be terrifying.

A severe

Base isolators act as shock absorbers. A moat allows the building to sway.

FIG 9.1

Engineers have developed a number of ways to build earthquake-resistant structures. Their techniques range from extremely simple to fairly complex. For small- to medium-sized buildings, the simpler reinforcement techniques include bolting buildings to their foundations

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and providing support walls called shear walls. Shear walls, made of reinforced concrete

(concrete with steel rods or bars embedded in it), help strengthen the structure and help resist rocking forces. Shear walls in the center of a building, often around an elevator shaft or stairwell, form what is called a shear core. Walls may also be reinforced with diagonal steel beams in a technique called cross-bracing.

Builders also protect medium-sized buildings with devices that act like shock absorbers between the building and its foundation. These devices, called base isolators, are usually bearings made of alternate layers of steel and an elastic material, such as synthetic rubber. Base isolators absorb some of the sideways motion that would otherwise damage a

The goal is to determine the causes of the damage and to recommend changes in steel moment-resisting frame design and construction to ensure ductile behavior of the joints.

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FIG 9.6

The selection of the type of lateral-force-resisting elements to use in a building is often based on economics. A single type of resisting element is commonly used in most building types,

9.8.3 Dynamic Analysis

Dynamic analysis shall be performed to obtain the design seismic forces, and its distribution to different levels along the height of the building and to the various lateral loads resisting elements for the following buildings

1. Regular building

Those greater than 120ft in height in area where PGA>0.24g, and those greater than 120ft in height in area where PGA0.24g, and those greater than

120ft in height in areas where PGA< 2 km 5 km > 5 km

A 1.5 1.2 1.0

B 1.3 1.0 1.0

C 1.0 1.0 1.0

Near source factor Nv

Table 9.3

Seismic

Source Type

Closest Distance To Known Seismic

Source

< 2 km 5 km 10 km > 10 km

A 2.0 1.6 1.2 1.0

B 1.6 1.2 1.0 1.0

C 1.0 1.0 1.0