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By LUTHER JEREMY
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Get instant insights and key takeaways from this YouTube video by LUTHER JEREMY.
Slab Classification and Design Method
📌 Slab type classification is determined by the ratio of the longest span () to the shortest span (): if , it is a one-way slab; if , it is a two-way slab.
📐 The design approach used for this slab calculation is the strip method (per meter strip).
🏗️ It is assumed that the slab and beams are cast monolithically, resulting in fixed (jepit) support conditions on all edges for elastic analysis.
Moment Coefficient Calculation (Two-Way Slab)
🔍 For a two-way slab with fixed supports on all sides, the moment coefficients ($C$) from PBI 1971 tables are used to find internal forces () based on span ratios.
💡 The required moments are calculated using the general formula (where is the factored load and $L$ is the span length):
(The division by 1000 converts the result to for a design strip of ).
🏠 Dead loads (SDL) include self-weight (concrete density ) plus finishes (e.g., tiles, ceiling), and live loads are based on the building function (e.g., for residential).
📉 The factored load combination used is , which resulted in in the example.
Flexural Reinforcement Design (Field Area - Y-Direction)
📏 Design is performed for a wide strip () with slab thickness and concrete cover of .
📏 The minimum spacing for longitudinal reinforcement must not exceed $2h$ (i.e., ). The assumed spacing was using bars.
⚙️ The required tensile reinforcement area () is determined by calculating the number of bars needed () multiplied by the area of one bar. The required was .
⚖️ The minimum reinforcement area () is governed by the yield strength (); for , is calculated using a specific PBI formula (resulting in in the example). The design must satisfy .
Shear Design
⚙️ Shear forces ($V$) are exported from ETABS, requiring the stiffness modifiers for the slab elements to be set to 0.25 for all , etc.
💥 The load combination for shear analysis uses serviceability factors: $1.0 D + 1.0 L$ (not factored loads).
✔️ The calculated shear capacity provided by the concrete () must be greater than the required factored shear force (). In the example, the capacity was significantly higher than the demand, requiring zero shear reinforcement () as is typical for slabs.
Deflection Check (Serviceability Limit State)
📊 Deflection () must be checked using service loads (1.0 D + 1.0 L, unfactored) applied to both spans ( and ).
⚠️ For conservatism, the compression reinforcement area should be assumed as zero () when calculating the effective moment of inertia ().
📏 The instantaneous deflection check involves comparing the calculated deflection to the allowable limit (e.g., $L/360$). The example showed very small deflections ( instantaneous deflection under dead load) indicating good stiffness.
Key Points & Insights
➡️ Assume Monolithic Construction: Assume the slab and beams are cast together to justify using fixed (jepit) support conditions for the design calculations, which influences moment coefficients.
➡️ Determine Slab Type Early: Quickly calculate to classify the slab as one-way or two-way, dictating the subsequent design tables and approaches used.
➡️ Reinforcement Placement Visualization: In two-way slabs, understand that reinforcement laid along the spans (e.g., ) runs perpendicular to the longer direction, and the calculated number of bars ($N$) is along the direction (e.g., ).
➡️ Shear Stiffness Modification: Before exporting shear forces from structural analysis software (ETABS), modify the slab stiffness coefficients to 0.25 as per code requirements for accurate shear calculation transfer.
📸 Video summarized with SummaryTube.com on Nov 20, 2025, 11:57 UTC
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Full video URL: youtube.com/watch?v=JdPeBZPRh2c
Duration: 40:55
Get instant insights and key takeaways from this YouTube video by LUTHER JEREMY.
Slab Classification and Design Method
📌 Slab type classification is determined by the ratio of the longest span () to the shortest span (): if , it is a one-way slab; if , it is a two-way slab.
📐 The design approach used for this slab calculation is the strip method (per meter strip).
🏗️ It is assumed that the slab and beams are cast monolithically, resulting in fixed (jepit) support conditions on all edges for elastic analysis.
Moment Coefficient Calculation (Two-Way Slab)
🔍 For a two-way slab with fixed supports on all sides, the moment coefficients ($C$) from PBI 1971 tables are used to find internal forces () based on span ratios.
💡 The required moments are calculated using the general formula (where is the factored load and $L$ is the span length):
(The division by 1000 converts the result to for a design strip of ).
🏠 Dead loads (SDL) include self-weight (concrete density ) plus finishes (e.g., tiles, ceiling), and live loads are based on the building function (e.g., for residential).
📉 The factored load combination used is , which resulted in in the example.
Flexural Reinforcement Design (Field Area - Y-Direction)
📏 Design is performed for a wide strip () with slab thickness and concrete cover of .
📏 The minimum spacing for longitudinal reinforcement must not exceed $2h$ (i.e., ). The assumed spacing was using bars.
⚙️ The required tensile reinforcement area () is determined by calculating the number of bars needed () multiplied by the area of one bar. The required was .
⚖️ The minimum reinforcement area () is governed by the yield strength (); for , is calculated using a specific PBI formula (resulting in in the example). The design must satisfy .
Shear Design
⚙️ Shear forces ($V$) are exported from ETABS, requiring the stiffness modifiers for the slab elements to be set to 0.25 for all , etc.
💥 The load combination for shear analysis uses serviceability factors: $1.0 D + 1.0 L$ (not factored loads).
✔️ The calculated shear capacity provided by the concrete () must be greater than the required factored shear force (). In the example, the capacity was significantly higher than the demand, requiring zero shear reinforcement () as is typical for slabs.
Deflection Check (Serviceability Limit State)
📊 Deflection () must be checked using service loads (1.0 D + 1.0 L, unfactored) applied to both spans ( and ).
⚠️ For conservatism, the compression reinforcement area should be assumed as zero () when calculating the effective moment of inertia ().
📏 The instantaneous deflection check involves comparing the calculated deflection to the allowable limit (e.g., $L/360$). The example showed very small deflections ( instantaneous deflection under dead load) indicating good stiffness.
Key Points & Insights
➡️ Assume Monolithic Construction: Assume the slab and beams are cast together to justify using fixed (jepit) support conditions for the design calculations, which influences moment coefficients.
➡️ Determine Slab Type Early: Quickly calculate to classify the slab as one-way or two-way, dictating the subsequent design tables and approaches used.
➡️ Reinforcement Placement Visualization: In two-way slabs, understand that reinforcement laid along the spans (e.g., ) runs perpendicular to the longer direction, and the calculated number of bars ($N$) is along the direction (e.g., ).
➡️ Shear Stiffness Modification: Before exporting shear forces from structural analysis software (ETABS), modify the slab stiffness coefficients to 0.25 as per code requirements for accurate shear calculation transfer.
📸 Video summarized with SummaryTube.com on Nov 20, 2025, 11:57 UTC
Find relevant products on Amazon related to this video
As an Amazon Associate, we earn from qualifying purchases

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