What Is a Drag Strut vs. a Chord in Diaphragm Design?
Chords resist the diaphragm's bending (the tension/compression at the boundaries — the beam's flanges); drag struts (collectors) deliver the shear to the vertical elements (the axial — the interior; the load path). The chord: the moment's; the drag strut: the shear's delivery. The design: the chord's (the M/d), the strut's (the Fpx), and the connections' (the capacity). The diaphragm's — the two members distinguished.
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The chord
The bending (the diaphragm's — the deep beam; the moment's — the M/d; the boundaries' — the tension/compression), the steel (the continuous — the rebar's; the splices'), and the wood (the rim's — the blocking; the SDPWS).
The drag strut
The shear's delivery (the diaphragm's — the collected; the strut's — the axial; the wall's — the dragged), the discontinuity (the offset — the spanning), and the overstrength (the Omega — the discontinuous's).
Design together
The analysis (the diaphragm's — the beam; the forces'), the detailing (the connections' — the capacity; the combined — the chord-strut's), and the example (the concrete — the thickened; the steel — the beams'). The chord is the boundary — the strut is the path.
The bottom line
Chords resist diaphragm bending (M/d at boundaries); drag struts deliver shear to vertical elements (Fpx axial, Omega0 at discontinuities) — design and detail both per ASCE 7 12.10.
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