Diaphragms With Intermediate Offsets - The Analysis of Irregular Shaped Structures - page 161

CHAPTER 4
Diaphragms With
Intermediate Offsets

4.1 Introduction

Structures with horizontal offsets (notches) located at the interior of the diaphragm
span are fairly common. These offsets cause a reduction in the depth of the diaphragm,
which creates a discontinuity in the diaphragm chords or struts. These offsets some-
times occur at several locations along a chord or on opposite sides of the diaphragm.
Unlike a single end notch, a transfer diaphragm must be installed on each side of the
offset to receive the disrupted chord forces and dissipate them into the diaphragm, as
shown in Fig. 4.1. The analysis methods used in Chap. 3 provide all the tools necessary
to analyze these types of diaphragms. As demonstrated in Chap. 3, the complexity of
the analysis in the longitudinal direction is influenced by the configuration of the shear
wall layout.

4.2 Intermediate Offset, Transverse Loading

The problem associated with diaphragms having an intermediate notch, when loaded
in the transverse direction, is the offset of the diaphragm chord. The reduced depth of
the diaphragm at the offset increases the chord force and the deflection of the diaphragm
at that location. The disrupted chord force at the reduced section can be very large and
can present some difficulty in transferring the force into the main body of the dia-
phragm.

Example 4.1: Intermediate Notch, Offset to the Left of Centerline, Analysis in the
Transverse Direction
The diaphragm shown in Fig. 4.1 has a length of 150 ft and a depth of 50 ft, with a 20 ft
wide by 10 ft deep offset which occurs between grid lines 2 and 3. The offset (notch)
causes a disruption in the diaphragm chord at grid lines 2C and 3C. A 200 plf load is
applied uniformly along the entire length of the diaphragm in the transverse direction.
The depth of the diaphragm between grid lines A and B is 40 ft. The offset chord is
extended into transfer diaphragms TD1 and TD2 by two longitudinal collectors which
are located between grid lines 1 and 2 and between grid lines 3 and 4, respectively. The
collectors extend the entire depth of the transfer diaphragms. The transfer diaphragm

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