S7C2-DESCENTE DE CHARGES 2

Load Descent Calculation Process
📌 The building plan dimensions are 12 meters by 5 meters, utilizing two structural bays for reference.
🏗️ Structural elements include square columns (30 cm sides) on bays 1 and 2, a 30 cm thick wall on bay 3, and 40 cm high beams (30 cm wide) spanning bays 1 and 2.
🧱 The floor slab is 30 cm thick, divided into two 6 m by 5 m sections, supported between bays 1 & 2 and bays 2 & 3. The entire structure is reinforced concrete with a unit weight ($\gamma$) of $25 \text{ kN/m}^3$.

Slab Load Analysis
📐 Load descent starts from the top: the floor slab, moving loads down through beams/walls to columns and foundations.
📈 The self-weight load per square meter ($p$) for the 30 cm thick slab is calculated as $\gamma \times \text{thickness}$, resulting in $p = 7.5 \text{ kN/m}^2$.
🔄 The slab load distributes to supports (beams/wall) based on tributary width (width of transfer, $d$). Each half-slab width is $3 \text{ m}$.
📉 For Beam Line 1, the resulting linear load ($p_1$) is $p \times d = 7.5 \text{ kN/m}^2 \times 3 \text{ m} = \mathbf{22.5 \text{ kN/m}}$.

Beam Load Calculation and Transfer to Columns
🏗️ For Beam Line 2, the tributary width doubles to $6 \text{ m}$ (two half-slabs), yielding a linear load ($p_2$) of $7.5 \text{ kN/m}^2 \times 6 \text{ m} = \mathbf{45 \text{ kN/m}}$.
➕ The total linear load on a beam must include its self-weight; for Beam Line 1 (30 cm x 40 cm cross-section), the self-weight is $\gamma \times \text{Section} = 3 \text{ kN/m}$ ($p_3$).
🎯 The total uniform linear load ($p_4$) on Beam Line 1 is $22.5 \text{ kN/m} + 3 \text{ kN/m} = \mathbf{25.5 \text{ kN/m}}$, used for flexural design.
⬇️ For symmetrical beams (5 m span), the concentrated load transferred to each column head ($P_{A1}$) is half the total load over the span: $25.5 \text{ kN/m} \times 2.5 \text{ m} = \mathbf{63.75 \text{ kN}}$.

Column Load Accumulation to Foundations
🪜 The load at the head of Column Line 1 ($63.75 \text{ kN}$) is augmented by the column's self-weight (2.3 m high, 30 cm x 30 cm section), which is $5.2 \text{ kN}$.
🛑 The total axial load at the foot of Column Line 1 is approximately $\mathbf{69 \text{ kN}}$, used for footing design.
📉 For Beam Line 2, the total uniform load is $45 \text{ kN/m} + 3 \text{ kN/m} = 48 \text{ kN/m}$ ($p_5$), resulting in a column head load ($P_{A2}$) of $48 \text{ kN/m} \times 2.5 \text{ m} = \mathbf{120 \text{ kN}}$.

Wall Load Accumulation to Foundations
🧱 The linear load at the top of Wall Line 3 ($22.5 \text{ kN/m}$) must include the wall's self-weight ($2.7 \text{ m}$ high, $30 \text{ cm}$ thick): $20.25 \text{ kN/m}$ ($p_6$).
📏 The final global linear load for the strip foundation is $22.5 \text{ kN/m} + 20.25 \text{ kN/m}$, rounded to $\mathbf{43 \text{ kN/m}}$, used for strip footing design.

Key Points & Insights
➡️ Load descent involves a hierarchical transfer: surface loads $\rightarrow$ line loads $\rightarrow$ point loads, ensuring all structural elements are properly sized.
➡️ Self-weight calculation is crucial; for a 30 cm slab, the self-weight adds $7.5 \text{ kN/m}^2$ to the dead load.
➡️ When calculating the total load on a beam, remember to add the beam's self-weight to the transmitted slab load to determine the final load for flexural design.
➡️ For multi-story structures, loads are cumulatively summed from upper floors down to the foundations at each level.

📸 Video summarized with SummaryTube.com on Nov 25, 2025, 22:32 UTC