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Chapter 1: Buildings

B: AN INTRODUCTION TO STRUCTURAL CONCEPTS IN EARTHQUAKE MITIGATION DESIGN

PART 2: TECHNICAL COMMENTARY, Part 2

 

THE FOLLOWING IS A DESCRIPTION OF BUILDING DESIGN IRREGULARITIES THAT CAN LEAD TO INCREASED DAMAGE IN EARTHQUAKES

2.4.1.1.1 In-Plane Discontinuity Irregularity: An in-plane discontinuity irregularity shall be considered to exist in any primary element of the lateral-force-resisting system whenever a lateral-force-resisting element is present in one story, but does not continue, or is offset within the plane of the element, in the story immediately below. Figure 2-1 depicts such a condition.

2.4.1.1.2 Out-of-Plane Discontinuity Irregularity: An out-of-plane discontinuity irregularity shall be considered to exist in any primary element of the lateral-force-resisting system when an element in one story is offset out-of-plane relative to that element in an adjacent story, as depicted in Figure 2-2.

2.4.1.1.3 Severe Weak Story Irregularity: A severe weak story irregularity shall be considered to exist in any direction of the building if the ratio of the average shear DCR of any story to that of an adjacent story in the same direction exceeds 125%. For buildings with flexible diaphragms, each line of framing shall be independently evaluated. 

2.4.1.1.4 Severe Torsional Strength Irregularity: A severe torsional strength irregularity shall be considered to exist in any story if the diaphragm above the story under consideration is not flexible and, for a given direction, the ratio of the critical element DCRs for primary elements on one side of the center of resistance of a story, to those on the other side of the center of resistance of the story, exceeds 1.5.

Proceed to RISK ASSESSMENT


Figure 2-1 In-Plane Discontinuity in Lateral System 

Figure 2-2 Typical Building with Out-of-Plane Offset Irregularity


 

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