## Step-by-Step Solution **Question Recap** > What is the size factor, \( K_{zb} \), for a No.2 Grade 38×235 joist in bending? --- ### **Step 1: Identify the Size of the Lumber** - The dimensions given are **38 mm × 235 mm** (metric units). - In North American lumber sizes, **38 mm × 235 mm** is the metric equivalent of a nominal **2 × 10** joist (actual: 1.5 in × 9.25 in ≈ 38 mm × 235 mm). --- ### **Step 2: Understand the Size Factor (\(K_{zb}\))** - The size factor \( K_{zb} \) (sometimes just \( C_{F} \) in NDS terminology) is used to adjust the allowable bending strength of sawn lumber based on its size. - The **NDS (National Design Specification)** for Wood Construction provides these values. --- ### **Step 3: Find the Size Factor for 2×10 Joist** - For **No.2 Grade** and joists with a thickness of 2 inches (38 mm) and depth > 8 inches (203 mm), the NDS provides standard values. - **From NDS Supplement Table 4A (2021, and similar previous years):** - For a 2-inch thickness and depth 10-inch (i.e., 2×10), \( K_{zb} = 1. \). --- ### **Step 4: Final Answer** \[ \boxed{K_{zb} = 1.} \] --- ### **Explanation** - The size factor for bending (\( K_{zb} \) or \( C_{F} \)) is **1.** for a No.2 Grade 38×235 (2×10) joist, because the adjustment is only required for depths less than or equal to 8 inches (203 mm); for 2×10 and larger, the factor is 1.. --- ## **Summary Table** | Joist Size | NDS Size Factor (\(K_{zb}\)) | |-----------------|:---------------------------:| | 2×4, 2×6, 2×8 | > 1. | | 2×10, 2×12 | 1. | --- ## **Final Answer** \[ \boxed{K_{zb} = 1.} \] for a No.2 Grade 38×235 joist in bending.