# Maximum Recommended Spacing for Unbonded Single-Strand Tendons in One-Way PT Slabs Question Summary Determine the maximum spacing unbonded single-strand tend in a one-way post-tensioned (PT) slab based on **ACI 318-11 Chapter 18** and **PTI detailing criteria**. --- ## Step-by-Step Solution ### . Review Relevant Guidelines - **ACI 318-11 Chapter 18** provides general rules for post-tensioned slabs. - **PTI (Post-Tensioning Institute)** guidelines specify detailing criteria for tendons. ### 2. Recognize the options provided - **Option A:** "The spacing is not explicitly limited for one-way slabs." - **Option B:** "The larger of 5 ft and 8 times the slab thickness." - **Option C:** "4 times slab thickness." - **Option D:** "6 feet." --- ### 3. Analyze each option #### **Option A:** "Spacing is not explicitly limited for one-way slabs." - **Assessment:** According to ACI 318-11 and PTI, there **are** recommended maximum spacing limits to ensure proper post-tensioning force transfer, crack control, and ductility. - **Conclusion:** This statement is **incorrect** because limits do exist. --- #### **Option B:** "The larger of 5 ft and 8 times the slab thickness." - **Assessment:** This is a common rule of thumb in PT design. ACI 318-11 generally recommends that tendon spacing should not exceed the larger of: - 5 ft, or - 8 times the slab thickness \( (h) \). - **Rationale:** Ensures proper load transfer, minimizes crack widths, and provides ductility. - **Conclusion:** **This is the correct option** based on PTI and ACI 318-11. --- #### **Option C:** "4 times slab thickness." - **Assessment:** While sometimes used for other design considerations, ACI 318-11 and PTI typically specify a larger maximum spacing than 4h. - **Conclusion:** This option is **too conservative** and **not** aligned with standard guidelines. --- #### **Option D:** "6 feet." - **Assessment:** 6 ft is a fixed numerical limit but is not universally recommended as a maximum for all slab thicknesses. - **Conclusion:** Not a standard or universally applicable limit according to ACI 318-11. --- ## Final Answer ### **Correct option:** **B. The larger of 5 ft and 8 times the slab thickness.** --- ## Explanation Summary - ACI 318-11 and PTI criteria specify that the maximum tendon spacing should not exceed the larger of **5 ft** or **8 times the slab thickness**, ensuring effective load transfer and crack control. - Other options either do not align with these guidelines or are overly conservative or arbitrary. --- **Note:** Always verify with the latest codes and project specifications, as local amendments may vary.