3. lengkung FC

Summary

This video explains the design and planning process for horizontal curves in road engineering, specifically focusing on full-circle (FC) curves. It covers key concepts such as determining the point of intersection (PI), calculating the curve's radius, and avoiding dangerous locations like steep terrains and river areas. The video also discusses the importance of the design speed, selecting the correct radius to ensure safety, and the absence of transition curves in FC designs. Additionally, it outlines the use of STA points, the calculation of relative slopes, and the creation of a superelevation diagram to ensure smooth transitions on curved roads.

Takeaways

• 😀 Full circle curves are used in road design for large radii where a direct path isn't possible due to natural obstacles like forests or rivers.
• 😀 A point of intersection (PI) is determined where the straight path between two points (A and B) intersects, but it should avoid steep slopes, inclines, or river areas to prevent safety issues.
• 😀 Full circle curves do not require a transition or spiral curve; they go directly from the straight path into the curve.
• 😀 TC (Circle Hand) refers to the straight segment transitioning directly into the curve, while CT (Curve to Hand) is the opposite transition from curve back to straight.
• 😀 The radius of the curve (RC) must be greater than the minimum radius (R) to avoid steep, dangerous turns.
• 😀 Design speed (V) plays a crucial role in determining the appropriate curve radius (RC) using a standard table like the Bina Marga table for highway construction.
• 😀 Key formulas are provided for calculating different parts of the curve, such as TC (scale arm), EC (curve location), and the length of the circular arc (LC).
• 😀 STA (station points) are calculated based on the distances from known points (e.g., from A to PI, from TC to CT, and from CT to B), which helps in accurate placement of curve elements.
• 😀 Relative slope (the magnitude of the slope due to elevation differences) is essential for determining the safety and comfort of vehicles on curved roads.
• 😀 The superelevation diagram is used to calculate how the road will transition from normal elevation to maximum superelevation to ensure smooth navigation through curves.

Q & A

What is a full circle curve (FC curve) in road engineering?

A full circle curve (FC curve) is a type of bend that consists of a part of a circle and is typically used for large radii. It is designed to avoid fractures and is especially useful when a direct road path between two points is not feasible due to environmental obstacles like protected forests or nature reserves.

Why can't a road between city A and city B be built as a straight line?

A straight line between city A and city B cannot be built because there are areas that cannot be passed through, such as protected forest areas or nature reserves. Therefore, the road must be diverted, requiring a bend or curve in the road design.

What is the significance of the point of intersection (PI) in road curve design?

The point of intersection (PI) is crucial in determining where the curve should begin. It is important to avoid placing the PI on steep slopes, river areas, or incline zones, as these locations pose risks to road safety, requiring the construction of additional structures like bridges.

What is the role of a transition curve in a full circle curve?

In a full circle curve, there is no transition curve. This means that vehicles move directly from a straight path into a curve without any gradual change in direction, which can increase the sharpness of the turn. Full circle curves are generally designed for large radii to accommodate this design.

How is the radius (RC) for a full circle curve determined?

The radius (RC) for a full circle curve is determined based on the design speed (V) of the road. The minimum radius must not be used, as a curve with a minimum radius would be too steep and dangerous. Instead, a larger radius is selected, typically using guidelines like the Bina Marga table to ensure the curve is safe and comfortable for vehicles.

What is the significance of the EC value in determining a curve?

The EC value is used to determine the location of the curve along the road. It helps identify the specific section where the curve starts, and from EC to AL, the length of the circular arc is calculated, which defines the curve's geometry.

What factors should be considered when calculating the STA (Station) points in road curve design?

When calculating the STA points, the distances from point A to PI, from PI to TC, and from TC to CT should be taken into account. These distances help define the positions of various points along the curve, ensuring accurate and consistent measurements for road construction.

How does the relative slope affect the design of a full circle curve?

The relative slope is determined based on the planned road speed and the difference in elevation along the transition curve. It is important to calculate the slope to ensure the road is safe and comfortable for vehicles, even though a transition curve doesn't exist in a full circle curve. This slope can be adjusted using a table based on the planned speed.

What is the role of the superelevation diagram in curve design?

The superelevation diagram is used to plot how the elevation of the road changes from normal to maximum superelevation. This diagram is essential in ensuring that the road provides the necessary banking (superelevation) for vehicles to safely navigate the curve without losing traction, especially in high-speed situations.

What is the main reason for using a full circle curve instead of a simple bend with a transition curve?

A full circle curve is used when a sharp bend with no transition curve is necessary, often due to space constraints or design requirements. It allows for a consistent curve but requires careful planning to ensure the radius is large enough to avoid safety issues related to steep turns.