📚 Year 7 CIE Engineering: Case Study Practical Exercise | 七年级 CIE 工程：案例分析实战演练
Welcome to a hands-on case study in Year 7 CIE Engineering. In this practical exercise you will design, build and test a simple paper bridge. The challenge is to create a structure that can span a 20 cm gap and support a mass of 500 g using only a limited set of materials. By working through each stage of the engineering design process you will experience what real engineers do every day – from understanding a problem to evaluating a final prototype.
欢迎参加七年级 CIE 工程实践案例分析。在这个实践练习中，你将设计、建造并测试一座简易纸桥。挑战在于仅用有限材料制作一个可以跨越 20 厘米间隙并支撑 500 克质量的桥梁。通过经历工程设计过程的每个阶段，你将体验真实工程师的日常工作——从理解问题到评估最终原型。
1. Case Study Introduction | 案例介绍
Our case study centres on an everyday situation: you need a small bridge to carry a load across a gap, such as between two tables. The bridge must be made from just two sheets of A4 paper and a small amount of PVA glue. No other materials, such as tape, paper clips or cardboard, are allowed. This limitation forces you to think creatively about how paper can be folded, rolled and joined to gain strength.
我们的案例围绕一个常见场景：你需要一座小桥来承载重物跨越间隙，例如两张桌子之间。桥只能由两张 A4 纸和少量白胶制成。不允许使用其他材料，如胶带、回形针或卡纸。这一限制迫使你创造性地思考如何通过折叠、卷曲和连接让纸张获得强度。
The main goal is to support a 500 g mass without the bridge collapsing or bending more than 5 cm. You will follow the engineering cycle: define the problem, research ideas, design a solution, build a prototype, test it, and then improve it. This case study is a perfect introduction to real-world engineering skills.
主要目标是支撑 500 克的质量，且桥梁不坍塌或弯曲超过 5 厘米。你将遵循工程循环：定义问题、研究构思、设计解决方案、搭建原型、测试并改进。这一案例是入门真实工程技能的绝佳方式。
2. Understanding the Design Brief | 理解设计任务书
Before you touch any materials you must fully understand the design brief. The brief clearly states the performance requirements, constraints and success criteria. For our paper bridge the key requirements are: span a gap of exactly 20 cm, carry a load of at least 500 g placed at the centre, deflect no more than 5 cm, and be built only from two sheets of A4 paper (80 g/m²) and PVA glue.
在接触任何材料之前，你必须彻底理解设计任务书。任务书清楚地写明了性能要求、限制条件与成功标准。对于我们的纸桥，关键要求是：恰好跨越 20 厘米的间隙，在中心放置至少 500 克的载荷，挠度不超过 5 厘米，并且只能由两张 A4 纸（80 g/m²）和白胶建造。
Constraints are just as important as requirements. You are not allowed to laminate the paper, use reinforcements like drinking straws, or pre-stress the structure with tape. The bridge must be free-standing and simply rest on the two surfaces. These rules simulate the real-world constraints engineers face, such as cost, weight and material availability.
限制条件与要求同样重要。你不得将纸塑封，不得使用吸管等加强物，也不得用胶带预加应力。桥必须自立，仅搭放在两个支撑面上。这些规则模拟了工程师面对的现实约束，比如成本、重量和材料可获得性。
3. Research and Brainstorming | 研究与头脑风暴
Research helps you discover how real bridges manage forces. Learn about three common bridge types: beam bridges (simple flat deck), truss bridges (triangular frames) and arch bridges (curved shape that pushes down and out). Paper has very low tensile strength when flat, but it becomes stiffer when folded into shapes like tubes or triangles.
研究帮助你了解真实桥梁如何应对力的作用。学习三种常见桥型：梁桥（简单的平板桥面）、桁架桥（三角形构架）和拱桥（向下外推的曲线形状）。纸张平放时抗拉强度极低，但折叠成管状或三角形后就会变得刚硬。
With your team, brainstorm at least five different ideas. Sketch quick thumbnail drawings to capture how the paper might be folded, rolled into tubes, or layered. Remember, a truss made of small paper triangles can spread a load efficiently. Write down every idea, even if it seems impossible at first – wild ideas often lead to clever solutions.
与你的团队一起，头脑风暴至少五种不同的想法。快速绘制缩略草图，捕捉纸张如何折叠、卷成管状或层叠。记住，由小纸三角构成的桁架可以有效分散载荷。记下每个想法，哪怕起初看似不可能——大胆的想法常常催生巧妙的方案。
4. Developing Design Specifications | 制定设计规格
Design specifications are a detailed list of what your bridge must achieve and how you will measure success. Translate the brief into measurable targets. For example, target a span of exactly 20 cm with a tolerance of ±2 mm, support a central mass of 500 g for at least 10 seconds, and limit the downward deflection to less than 5 cm.
设计规格是一份详细的清单，列出你的桥梁必须达成什么以及如何衡量成功。将任务书转化为可测量的指标。例如，跨度精确为 20 厘米，公差 ±2 毫米；在中心支撑 500 克质量至少 10 秒；向下挠度小于 5 厘米。
Include aesthetic and practical targets too. The bridge should have a neat appearance and use no more than 10 g of liquid glue to keep the mass low. Write your specifications as a numbered list in your design journal. This document will guide your decision-making and help you evaluate later.
还要包括美观和实用目标。桥梁外观应整洁，液体胶水用量不超过 10 克以保持自重较轻。将规格以编号列表形式记入你的设计日志。这份文件将指引你的决策并帮助后期评估。
5. Sketching and Selecting the Best Idea | 草图绘制与方案选择
Now it is time to draw your designs properly. Use a pencil and ruler to create isometric or orthographic sketches of your favourite two ideas. Annotate each drawing with labels showing the main structural features, such as ‘top chord’, ‘web truss’ or ‘rolled tube supports’. Indicate dimensions and where glue will be applied.
现在该认真绘制你的设计了。用铅笔和尺子为你最中意的两个方案绘制等轴测图或正投影图。为每张图加上标注，指出主要结构特征，比如“上弦杆”、“腹杆桁架”或“卷管支撑”。标明尺寸和施胶位置。
Then evaluate each idea against your specifications using a decision matrix. Score each concept on span accuracy, strength, mass, ease of construction and aesthetics from 1 (poor) to 5 (excellent). Choose the design with the highest total score. This systematic selection mirrors how engineers choose the best concept.
然后用决策矩阵对照规格评估每个方案。从跨度精度、强度、自重、施工难易和美观方面给每个概念评分，1 分（差）到 5 分（优秀）。选择总分最高的设计。这种系统化选择反映了工程师筛选最佳概念的方式。
6. Materials and Tools Planning | 材料与工具规划
You have only two A4 sheets of paper and PVA glue. Plan how you will cut, fold and join the paper to minimise waste. Lightly mark cutting lines with a pencil before you cut. You can fold the paper while dry to create sharp creases, then apply a thin layer of glue along the edges to secure the shape.
你只有两张 A4 纸与白胶。规划如何切割、折叠和连接纸张以尽量减少浪费。切割前用铅笔轻画切割线。可以先干折纸张做出清晰折痕，然后沿边缘涂一薄层胶水固定造型。
Tools needed are a ruler, a craft knife (if allowed), scissors, a cutting mat, a glue spreader (or a scrap piece of paper) and a small brush for precise glue application. Clamps or paperclips may be used temporarily to hold joints while the glue dries, but the final bridge must contain no metal parts.
所需工具包括尺子、美工刀（如果允许）、剪刀、切割垫、涂胶器（或一小片废纸）以及用于精细涂胶的小刷子。可用夹子或回形针在胶水干燥时暂时固定接头，但最终桥梁不得包含金属部件。
7. Building the Prototype | 制作原型
Begin construction by forming your main structural members. For a truss bridge, roll paper tightly into tubes of about 5 mm diameter to act as chord members, then fold strips into a zigzag pattern for the webs. Use a tiny amount of glue at each joint and press firmly for 30 seconds. Work on a flat surface to keep alignment straight.
开始制作主体结构构件。对于桁架桥，将纸紧卷成直径约 5 毫米的管子作为弦杆，再将纸条折叠成锯齿状作为腹杆。每个连接处用极少量的胶水并压紧 30 秒。在平整表面上操作以保持直线对准。
Assemble the two side trusses first and let them dry completely. Then join the sides with cross-bracing paper strips to prevent the bridge from twisting. Finally, add a flat deck on top if your design includes one. Handle the fragile paper structure gently, as too much pressure can tear wet joints.
先组装两侧桁架并彻底晾干。然后连接两侧，添加纸制横向支撑以防止桥梁扭曲。最后，如果设计中包含桥面，则在顶部铺上平板。轻拿轻放脆弱的纸质结构，因为过多的压力会撕裂未干的胶接点。
8. Testing the Bridge | 测试桥梁
Set up a testing station by placing two tables or blocks exactly 20 cm apart. Position your bridge so it rests on the edges without being glued to them. Use a string and a small cup or plastic bag to hang the load from the bridge’s centre. Slowly add mass (e.g., coins, weights) until either 500 g is reached or failure occurs.
搭建一个测试站点，将两张桌子或木块精确间隔 20 厘米放置。将桥放在边缘上，无需把它们粘在一起。用绳子和小杯子或塑料袋从桥中心悬挂载荷。逐次缓慢增加质量（例如硬币、砝码），直至达到 500 克或发生破坏。
Measure the deflection at the centre with a ruler as you add each 100 g increment. Record the mass at which the first visible crack appears or the bridge touches the floor. Safety reminder: wear safety goggles, and keep feet clear of falling weights.
每增加 100 克就用直尺测量中心挠度。记录首次出现可见裂缝或桥触地时的质量。安全提醒：佩戴护目镜，双脚远离可能落下的重物。
9. Recording and Analysing Data | 记录与分析数据
Organise your test data in a clear table. Record the load applied and the corresponding deflection. A sample table is shown below:
将测试数据整理在一个清晰的表格中。记录施加的载荷与对应挠度。示范表格如下：
| Load (g) | Deflection (cm) | Observation |
|---|---|---|
| 0 | 0.0 | Bridge resting |
| 100 | 0.8 | Slight bend |
| 200 | 2.1 | Creaking sound |
| 300 | 3.5 | Noticeable twisting |
| 400 | 4.7 | Joint cracking |
| 500 | Failed at 4.9 | Centre truss snapped |
Plot a graph of deflection against load. A steepening curve suggests buckling or rapid weakening. Analyse which part of your bridge failed first and why. Did a joint come unstuck, did a tube flatten, or did the whole structure twist? This tells you where the stress was highest.
绘制挠度-载荷图。曲线变陡表明出现了屈曲或快速弱化。分析桥的哪一部分最先失效以及原因。是接头脱胶，管道压扁，还是整体扭曲？这告诉你应力集中在何处。
10. Identifying Weak Points and Improving | 找出弱点并改进
From your test data, identify the weak points. Perhaps the bottom chord was under tension and tore, or the truss diagonals buckled under compression. Record these observations. Discuss with your team how the design could be altered to make the bridge stronger without using extra material.
根据测试数据，找出薄弱环节。可能是下弦杆受拉撕裂，或者斜腹杆受压屈曲。记录这些观察结果。与团队讨论如何在不增加材料的情况下修改设计以使桥梁更坚固。
Possible improvements include: doubling the number of truss elements, changing a triangular pattern to a Warren truss, increasing the depth of the beam, or using a different folding technique to create stiffened edges. Pick one or two changes and plan a second prototype if time allows. This iterative improvement is at the heart of engineering.
可能的改进包括：将桁架构件数量加倍、将三角形样式改为 Warren 桁架、增加梁的高度，或采用不同的折叠技术来形成加劲边缘。选择一两个改动，如果时间允许则规划第二个原型。这种迭代改进正是工程学的核心。
11. Final Evaluation against Specifications | 对照规格的最终评估
After testing your improved bridge, go back to your original specifications. Did the bridge meet the span requirement? Did it hold the full 500 g without exceeding the deflection limit? Was it constructed from only the allowed materials? Answer each specification with a pass or fail, and provide a brief explanation.
在测试了改进后的桥梁之后，回到你最初的规格。桥是否满足了跨度要求？它是否在不超出挠度限制的情况下支撑了 500 克？它是否仅用允许的材料建成？逐一回答每项规格，用通过或未通过记录，并给出简要解释。
Reflect on the design process. What worked well? What would you do differently next time? Perhaps you realised that pre-bending the paper softened it, or that using less glue sped up drying. Write a short evaluation paragraph explaining what you learned about structural behaviour, teamwork and time management.
反思设计过程。哪些方面做得好？下次你会采取什么不同做法？也许你发现预折纸会使其变软，或者少用胶水能加快干燥。写一段简短的评估，说明你在结构行为、团队协作和时间管理方面学到了什么。
12. Conclusion: Engineering Design Process | 结论：工程设计过程
This case study has taken you through the full engineering design cycle: define, research, design, build, test, evaluate and improve. You have seen how constraints force creativity and how testing exposes weaknesses. By documenting your decisions and learning from failure, you are already thinking like an engineer.
本次案例分析带你经历了完整的工程设计循环：定义、研究、设计、建造、测试、评估和改进。你已经看到约束如何激发创造力，测试如何暴露弱点。通过记录决策并从失败中学习，你已经开始像工程师一样思考。
Keep these skills in mind for future projects. The able to identify a problem, generate ideas, plan methodically and test rigorously will help you in all STEM subjects. Remember, the best bridges are often the simplest ones – and the journey of making them is just as important as the final result.
将这些技能牢记于心，用于未来的项目。能够识别问题、产生创意、有条理地规划和严格测试，将在所有 STEM 学科中助你一臂之力。记住，最好的桥梁往往是最简单的——而制作它们的过程与最终结果同等重要。
Published by TutorHao | Engineering Revision Series | aleveler.com
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