Contoh Perhitungan Analisa Balok Lentur dengan Tekuk Lokal | SNI 1729-2015 Struktur Baja Lightboard

Summary

This video tutorial provides a detailed explanation on how to calculate the strength of beams, particularly focusing on local buckling in structural profiles. It covers the assessment of local buckling potential in WF (Wide Flange) profiles and how variations in yield stress can influence structural integrity. The video includes practical examples, calculations, and a comparison between welded profiles and manufactured profiles. The importance of checking the slenderness ratios and the effects of local buckling on beam strength are explored, with insights into how to adjust for these factors in engineering designs.

Takeaways

• 😀 The video focuses on calculating the strength of beams with local buckling, particularly using the example of a WF profile.
• 😀 Local buckling is checked by comparing the slenderness ratios of the flanges and web of a WF profile, where specific thresholds are provided.
• 😀 For WF profiles, the slenderness ratio (λ) values are essential in determining if local buckling will occur, with certain values indicating potential plastic or elastic buckling zones.
• 😀 The strength of a beam can reach its plastic limit (MP3) if local buckling does not occur, as demonstrated in the example calculations.
• 😀 If the yield stress (Fb) is changed (e.g., from 240 MPa to 410 MPa), local buckling can still be avoided for standard market-provided profiles.
• 😀 A calculation example shows that increasing the yield stress leads to a very slight reduction in beam strength, indicating that local buckling only slightly affects the strength.
• 😀 Local buckling is more commonly observed in built-up profiles (i.e., welded from plates) compared to factory-manufactured profiles.
• 😀 The modulus of elasticity and the section modulus are crucial parameters in calculating the nominal strength of beams subjected to local buckling.
• 😀 For non-factory profiles (welded profiles), local buckling may lead to a significant reduction in strength, as shown in the detailed calculation for a built-up profile.
• 😀 The video highlights the importance of understanding local buckling's impact on beam strength and provides clear formulas for calculating the nominal moment of a beam with or without buckling.

Q & A

What is the main topic discussed in the video?

The main topic discussed in the video is how to calculate the strength of beams, particularly focusing on the impact of local buckling and its effect on various beam profiles, including WF profiles and welded profiles.

What is local buckling, and why is it important to consider in beam design?

Local buckling refers to the failure mode where parts of a beam, typically the web or flanges, buckle under stress due to high slenderness ratios. It is important to consider because it reduces the nominal strength of the beam, affecting its overall structural integrity.

How do you check for local buckling in a beam?

To check for local buckling, you need to calculate the slenderness ratios between the wing (sayap) and body (badan) thicknesses. If these ratios exceed specific critical values, local buckling is likely to occur, and strength reduction must be accounted for.

What are the critical values used to assess local buckling in WF profiles?

For WF profiles, the critical slenderness ratios are calculated as follows: for the wing (sayap), the ratio should be less than a value determined by the formula 0.38 times the square root of the modulus of elasticity divided by the yield stress (Fb). For the body (badan), this value is calculated using 3.7 times the square root of the modulus of elasticity divided by the yield stress (Fb).

What happens if a beam enters the 'plastic' zone due to local buckling?

If a beam enters the 'plastic' zone due to local buckling, its strength can reach the maximum plastic moment (MP3), which is the theoretical maximum strength. However, this value may be reduced depending on how much the beam experiences local buckling.

What is the significance of the material yield stress (Fb) in the calculations?

The material yield stress (Fb) is a critical parameter in the calculations because it influences the slenderness ratio, which in turn determines whether local buckling occurs. A higher Fb reduces the likelihood of local buckling and allows for a higher nominal strength.

How does local buckling affect the nominal strength of a beam?

Local buckling typically causes a reduction in the beam's nominal strength. In the example discussed, local buckling caused a reduction of approximately 1-2% in the plastic moment, depending on the severity of the buckling and the profile used.

What are the differences between factory-produced WF profiles and welded profiles regarding local buckling?

Factory-produced WF profiles are generally less prone to local buckling because they are designed and tested to prevent such issues. In contrast, welded profiles are more susceptible to local buckling due to their construction, which may lead to structural weaknesses at the joints.

How is the nominal strength of a welded profile affected by local buckling?

For welded profiles, local buckling can significantly reduce the nominal strength. In the example discussed, the strength was reduced by around 12% due to local buckling, as opposed to a minor reduction in factory-produced profiles.

What should be done if a beam profile shows signs of local buckling?

If a beam profile shows signs of local buckling, the nominal strength must be reduced according to the degree of buckling. This reduction is calculated using specific formulas and adjustments based on the profile's material properties and the extent of local buckling.