# Maximum Recommended Spacing for Unbonded Single-Strand Tendons in One-Way PT Sl ## Background In post-ted (PT) slab systems, spacing of tendons is critical for structural performance and safety. While ACI 318-11 and PTI detailing guidelines provide specific criteria, some spacing limits are not explicitly stated for one-way. ## Relevant Guidelines - **ACI 318-11 Chapter 18**: Focuses on post-tensioning, including tendon spacing and detailing. - **PTI (Post-Tensioning Institute) Detailing Criteria**: Provides practical limits for tendon spacing to prevent issues like tendon congestion and ensure proper force transfer. ## Key Point *The spacing of unbonded tendons in one-way slabs is generally governed by practical considerations rather than strict limits, but certain minimum and maximum spacing recommendations are used.* --- ## Recommended Spacing Criteria ### 1. **According to ACI 318-11 and PTI:** - **No explicit maximum spacing limit** for unbonded tendons in one-way slabs. - **However**, a common practical limit is based on slab thickness, **to ensure effective force transfer and control of crack widths**. ### 2. **Common Practice and Guidelines:** - The **larger of**: - **5 ft**, or - **8 times the slab thickness**, is often used as a maximum spacing criterion for unbonded tendons. - **Alternative options**: - 4 times the slab thickness - 6 ft (a fixed value) --- ## Final Answer **The maximum recommended spacing for unbonded single-strand tendons in a one-way PT slab system, based on ACI 318-11 and PTI criteria, is:** ### **The larger of 5 ft and 8 times the slab thickness.** --- ## Summary Table | Criterion | Description | |---|---| | Max spacing | **Larger of 5 ft and 8 times slab thickness** | | Other options | 4 times slab thickness, 6 ft (less common/practical) | --- ## Conclusion - **In practice**, designers typically use the larger of **5 ft** or **8 times the slab thickness** as the maximum tendon spacing. - **This ensures proper force transfer and crack control** in one-way PT slabs. **Final note:** Always verify with the latest codes and project-specific requirements.