1. **Problem Statement:** Design the critical slab panel using the ACI moment-coefficient method according to BNBC 2020 loading requirements with material properties $f'_{c} = 4$ ksi and $f_{y} = 60$ ksi. 2. **Step 1: Determine Design Loads** - Identify the dead load, live load, and any other applicable loads from BNBC 2020. - Calculate the factored load $w_u = 1.2D + 1.6L$ (typical LRFD load combination). 3. **Step 2: Calculate Panel Dimensions and Support Conditions** - Define the slab panel dimensions (length $L_x$, width $L_y$). - Determine support conditions (simply supported, continuous, etc.) to select moment coefficients. 4. **Step 3: Calculate Moments Using ACI Moment-Coefficient Method** - Use ACI moment coefficients $m_x$ and $m_y$ based on panel aspect ratio and support conditions. - Calculate factored moments: $$M_x = m_x \times w_u \times L_x^2$$ $$M_y = m_y \times w_u \times L_x^2$$ 5. **Step 4: Determine Required Reinforcement** - Calculate nominal moment capacity $M_n = \frac{M_u}{\phi}$ where $\phi$ is the strength reduction factor (typically 0.9). - Use concrete and steel properties to find required steel area $A_s$: $$A_s = \frac{M_n}{\phi \times f_y \times d}$$ where $d$ is effective depth. 6. **Step 5: Check Minimum and Maximum Reinforcement** - Verify $A_s$ meets minimum and maximum reinforcement limits per ACI and BNBC. 7. **Step 6: Detail Reinforcement** - Provide bar size, spacing, and layout to satisfy $A_s$. **Final Answer:** The critical slab panel design requires moments $M_x$ and $M_y$ calculated from the ACI moment coefficients and factored loads, with reinforcement area $A_s$ designed using $f'_{c} = 4$ ksi and $f_{y} = 60$ ksi according to the steps above.