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Bridge Design Improvement Worksheet

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Bridge Design Improvement Worksheet

A local council needs a lightweight bridge for a model footpath. Review the design evidence, plan a safe improvement, then explain how you would test it. Use the case study below; no previous build or feedback sheet is needed.

Design brief and test results

The bridge must span a 30 cm gap, support a small load at its centre and use no more than 20 craft sticks. A team made a model from craft sticks and PVA glue. During testing, the centre sagged and one side joint separated. The model held 600 g before failing. The team has time for one redesign and one retest. Their goal is to hold at least 900 g without using extra sticks.

Test

What happened

Centre-load test

Joint inspection

Design limit

A. Diagnose and improve

Answer using evidence from the brief and test results. Give reasons, not just a list of changes.

1.Which two problems should the team prioritise in its redesign? Choose the best answer.

The bridge is too colourful and uses too many different shapes.
The deck sags under a central load, and a side joint separates.
The gap is too short, and the test load is too light.
The bridge is too heavy and too wide.

2.Suggest one change to reduce the deck sag while staying within the 20-stick limit. Explain how your change could help spread or carry the load.

3.The team plans to add more glue to the separated joint. Give one reason this might not solve the problem, and one improvement to the joint design or assembly.

4.The team has 20 sticks and must not exceed that limit. State one way to make room for reinforcement without increasing the total number of sticks.

B. Work safely and test fairly

Imagine you are constructing the redesigned model in a supervised technology workshop. Follow the school workshop rules and the instructions for each tool and material.

5.A craft stick needs trimming with a craft knife. What is the safest response?

Cut quickly towards your hand so the stick cannot move.
Use the knife only if the teacher has authorised it; work on a cutting mat, keep hands clear, cut away from yourself, and follow the demonstrated method.
Hold the stick in the air and ask a partner to steady it.
Use any tool available without checking whether it is suitable.

6.PVA glue gets on a student's skin, and a blob spills onto the bench. Describe two safe actions the student should take, including who should be told.

7.True or false: Before testing, clear the area beneath and around the bridge, place the load gently at the centre, and keep faces and fingers away from the structure.

TrueFalse

8.Write a fair retest plan. Include what must stay the same, how the load should be added, and what evidence to record.

C. Communicate your redesign

Make your idea clear enough that another student could understand what you changed and why.

9.Draw a labelled side view of your improved bridge across the 30 cm gap. Show at least one change intended to reduce sag or strengthen the weak joint. Label the deck, supports and your improvement.

10.Complete the design decision: “I changed ___ because the test showed ___. I will know the change helped if ___.” Use the case-study evidence and name one measurable success sign.