Desain Pelat Satu Arah SNI 2847-2019

Summary

The video explains the design of a one-way reinforced-concrete slab using SNI 2847:2019, then demonstrates the process with a classroom-floor example.

1. What a slab does

A slab provides a flat horizontal floor surface and transfers building loads to beams or other supports, then to columns, foundations, and the ground. It also helps tie the building frame together. Slabs and beams are commonly cast together as a monolithic structure, and slabs are generally thin relative to their span.

2. Loads to include

The presenter distinguishes between:

• Dead load: The weight of permanent building components, such as the slab, walls, floor finishes, ceilings, and other fixed materials.
• Live load: Loads from building use and occupants. The applicable live load depends on the room’s function; the video uses a classroom as an example.

For the sample classroom floor, the video estimates the dead load from the slab and finishes at about 3.65 kN/m² and cites a classroom live load of 1.92 kN/m². It then reports an ultimate load of 11.48 kN/m² for the design example. These input loads do not appear to reconcile with the reported ultimate-load value, so the load calculation should be checked against the original video and applicable code before use.

3. How to identify a one-way slab

A slab supported on two opposite sides is treated as one-way. A slab supported on all four sides can also be treated as one-way if the ratio of its longer span to shorter span is greater than 2.

In a one-way slab, bending and deflection occur mainly across the shorter span, so the main reinforcement runs in that direction. A four-sided slab with a span ratio below 2 is generally treated as a two-way slab, with reinforcement in both directions.

The video also illustrates how a slab’s load is shared by supporting beams. Equal spans produce a more even distribution. For unequal spans with a ratio below 2, the distribution is described as triangular on the short-span beams and trapezoidal on the long-span beams. As the span difference increases, the distribution approaches a one-way pattern.

4. Preliminary thickness, cover, and reinforcement rules

For normal-weight concrete and the assumed reinforcement grade, the video gives these preliminary minimum-thickness ratios based on support condition:

• Simply supported: span divided by 20
• One end continuous: span divided by 24
• Both ends continuous: span divided by 28
• Cantilever: span divided by 10

Other material strengths or conditions may require an adjustment under the code. Deflection limits depend on the floor’s situation; the presenter cites span/180 for one case and directs viewers to select the applicable limit in SNI.

The example uses a concrete cover of about 25 mm where the slab is exposed to weather or ground, and 20 mm where it is not. For the reinforcement case discussed, the video uses a minimum steel ratio of 0.002 of the slab cross-sectional area. It also limits bar spacing to the lesser of three times the slab thickness or 450 mm.

5. Approximate moment method

The presenter says approximate moment coefficients from the code can be used only when specified conditions are met. These include a prismatic member, uniformly distributed loading, live load no greater than three times dead load, a continuous slab with at least two spans, and adjacent-span lengths that do not differ by more than about 20%.

The coefficients depend on the location being checked—for example, a span end, an interior support, or the middle of a span—and are multiplied by the factored load and the square of the span length to estimate design moments.

6. Worked one-way-slab example

The example slab measures 2 m × 5 m, so the longer-to-shorter span ratio is 2.5 and the slab is treated as one-way. The assumed slab thickness is 120 mm, with concrete strength of 25 MPa and reinforcement yield strength of 400 MPa.

1. Check the slab thickness. With one end continuous, the video uses (L/24). For a 2 m span, the calculated minimum is about 83 mm; the proposed 120 mm thickness passes this check.

2. Calculate design moments. Using the example’s reported ultimate load of 11.48 kN/m² and its approximate moment coefficients, the presenter obtains a negative support moment of about 5.1 kN·m and a positive span moment of about 3.28 kN·m.

3. Calculate the effective depth and required steel. For a 120 mm slab thickness and the assumed cover and bar size, the effective depth is taken as about 95 mm. The presenter uses force equilibrium between the tensile force in the reinforcement and the concrete compression block to calculate the steel area needed for the support moment.

4. Apply the minimum-reinforcement requirement. The calculated steel area is less than the minimum required area, which the example gives as 240 mm² per metre. Therefore, minimum reinforcement controls.

5. Select reinforcement and check spacing. Using 10 mm bars, the presenter selects D10 at 300 mm spacing. This satisfies the stated spacing limits of 450 mm and three times the slab thickness.

6. Check moment capacity. With D10 bars at 300 mm, the provided steel area is about 262 mm² per metre. The example calculates a design moment capacity greater than the reported support moment, so the reinforcement is accepted for that check.

7. Detail the slab reinforcement. The presenter uses the same D10-at-300-mm arrangement in the span and for the secondary or distribution reinforcement, because the calculated span moment is smaller and the minimum-steel requirement governs.

Speakers and sources featured

The speaker is the video’s presenter/host. The subtitles do not state a personal name; the channel is identified in the metadata as Jafar Iskandar.

Sources cited by the presenter include:

• SNI 2847:2019 — reinforced-concrete design provisions
• SNI 1727 — dead- and live-load definitions and examples; the subtitles refer to editions inconsistently
• PPRG 1987 — examples of building-component dead loads