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The image on the right shows a pedestrian bridge in Newport, Wales - Leaving Cert DCG - Question B-1 - 2021
Question B-1
The image on the right shows a pedestrian bridge in Newport, Wales. It is based on a parabola. Fig. B-1 shows the elevation, plan and end view of a model of the bri... show full transcript
Worked Solution & Example Answer:The image on the right shows a pedestrian bridge in Newport, Wales - Leaving Cert DCG - Question B-1 - 2021
Step 1
Draw the given elevation and end view of the bridge.
Answer
To draw the elevation and end view, begin by establishing the required rectangular outline for the supports and the curve ABC.
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Elevation Outline: Start with a rectangle that spans the entire width of the bridge (20 m to 190 m). The vertex of the curve ABC at point B should be 70 m above the base. Locate points immediately above at intervals (e.g., X: 0, 20, 40, etc.) to plot the parabola.
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End View: Project the vertical line downwards from points A and C. The ends of the bridge supports should be marked at the appropriate distances, considering the total width of the bridge and maintaining the vertical height of 70 m at the apex (B).
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Connect the points: Outline the shape of the parabolic curve ABC, ensuring it's a smooth curve connecting points from the elevation.
Step 2
Project the given plan.
Answer
For projecting the given plan:
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Projection Points: Draw horizontal projections from the established curve ABC in elevation to the corresponding points in the plan.
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Mirror to Lower Curve: You can utilize symmetry here since the curve ABC is parabolic—mirror the upper parts to form the lower curve.
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Draw Curves: At intervals, draw curves representing the tension cables that form part of the bridge structure.
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Support Structures: From the elevations and projections, indicate the bridge's tension cables and cross members accurately on the projected plan.
Step 3
Determine the true shape of the curve ABC.
Answer
To determine the true shape of the curve ABC:
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Rabatement: Begin with a rabatement of ABC in the end view, which allows for a clearer understanding of how the curve appears when viewed from a distance perpendicular to the vertex.
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Projecting Points: From the stroked elevation of curve ABC, create vertical projections to determine corresponding points along the true shape.
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Draw the True Shape: Connect these newly established points to construct an accurate representation of the parabolic curve that is true in shape, ensuring the smoothness of the curve is maintained throughout.