Refer to the exhibit by clicking on the EXHIBIT button above.

The required minimum wood protection thickness is 1.75 inches , making option B correct. AWC Technical Report No. 10 establishes a thermal-separation methodology for protecting steel connectors and fasteners with sacrificial wood cover. Because the question specifies that the wood cover itself must provide the entire 60-minute fire-protection period, the protection thickness must be calculated using the thermal-separation provisions rather than relying on residual fire resistance from the connector or steel plate.

TR10 applies a reduction to the protection contribution of the base wood layer. Its connection examples use the relationship in Section 4.4.1.3, with the required thermal protection time divided by 0.85. For a 60-minute requirement, back-calculating the prescribed nonlinear wood charring equation gives approximately 1.71 inches of required wood thickness. The practical minimum corresponding to the available choices is therefore 1.75 inches.

The principle is critical for special inspection: steel connection components have high thermal conductivity and must remain below the temperature limits assumed by the connection fire design. The inspector must verify actual wood-cover thickness, fastening, continuity, and any gaps before concealment.

References/Topics: AWC Technical Report No. 10, Sections 4.4.1.3 and 4.5; connection thermal separation; wood protection of steel connectors. TR10 demonstrates the same calculation methodology for wood-covered steel connections.

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