Enhancing Thinking Skills in Science Context Lesson 6 Critical Thinking in Engineering Process

Introduction to the different types of bridges beam bridge suspension bridge arch bridge

Why are there different types of bridges? The major difference between the three types of bridges is the distance that they can cover in a single span. Span is the difference between two supports. Each of the different types of bridges holds weight in different ways.

Beam Bridge A beam bridge is basically a rigid horizontal structure that rest on two supports, one located at each end of the bridge as shown in Figure (a). A simple beam bridge is flat across and supported by two ends.

What happens to the bridge when a load is put on the bridge? When the load pushes down on the beam the top edge is pushed together or compressed, while the bottom of the beam is stretched or is under tension.

What factor(s) should you consider when you build a beam bridge? The beam must be strong enough so that it can support its own weight together with the added weight of the traffic crossing it.

Arch Bridge An arch bridge is composed of a curved structure with abutments on each end.

What happens to the bridge when a load is put on the bridge? The weight of the load is carried outward along the curve of the arch to the abutments at each end of the arch. The abutments also keep the end of the bridge from spreading outward.

What factor(s) should you consider when you build an arch bridge? The arch bridge is always under compression because the weight of the deck is pushed outward along the curve of the arch towards the abutments. The rise in the form of the curved arch causes the vertical load to have a horizontal thrust.

Suspension Bridge The suspension bridge literally suspends the roadbed from huge cables, which extends from one end of the bridge to the other. The cables are attached to two tall towers and are secured at each end by anchorages.

What happens to the bridge when a load is put on the bridge? The cable carries the weight on a suspended bridge to the anchorages that are imbedded in solid rock or massive concrete blocks. The cables are spread over a large area in order to evenly distribute the load inside the anchorages to prevent the cables from breaking free.

What factor(s) should you consider when you build a suspension bridge? The anchorages help to stabilise the bridge. Therefore, the tower must be embedded to the earth firmly. In such a way, the cables transfer the forces to the towers which carry the forces directly into the earth where they are firmly imbedded.

Scenario The class is divided into groups of 4 or 5. You are required to design and build a bridge made of drinking straws. The bridge will cross a gap of 50cm. The width of the bridge must not be less than 20cm. The total mass of the bridge must not exceed 50 g. The strength of the bridges would be tested by hanging loads from the middle of the bridges.

Activity 1 Draft a design

Activity 1 Now, you have 10 minutes to discuss with your group members to design the bridge. Draft the steps you come across. Also, sketch a picture of the bridge you intend to build.

Activity 2 Introduction to the steps suggested by Isidro-Cloudas and Cassis, Glenn in engineering process

Activity 2 The steps involved in Engineering Process are written on 6 cardboards. You are required to design a bridge. Arrange the cardboards in correct order. Try to answer the following questions.

Activity 2 Question: What is the sequence of Engineering Process to design the bridge?

Activity 2 Answer: Identify the Problem  Determine the Constraints Brainstorm the preliminary design and choose the best design Analysis of Design  Design Refinement  Implementation Plan

Activity 2 Question: What is/are the task(s) performed in each step of Engineering Process?

Activity 2 Answer Identify the Problem  Before you start, the problem or task that is going to be undertaken must be known.

Activity 2 Answer Determine the Constraints Constraints are the limitations that must be considered before you begin designing your bridge.

Activity 2 Answer Brainstorm the preliminary design and choose the best design Once both the problem(s) or task have been determined and the constraints have been identified, the group needs to think of as many ways as possible to solve the problem. Even though all of the ideas may not be good ones, they may inspire another idea that may lead to a solution to the problem(s). Once all reasonable ideas are listed and the sketches are drawn, the group should choose the best two or three ideas for further development. The rough sketches should be converted to scaled or measured drawings.

Activity 2 Answer Analysis of Design  The designs are studied based on their merit in relationship to strength, cost, market appeal, and manufacturability. A decision should be made at this point on which design to use or rather to begin a new design.

Activity 2 Answer Design Refinement  Each design team should attempt to rectify the problems by making improvements in the design.

Activity 2 Answer Implementation Plan Once the final design has been approved, it must be translated from an idea on paper to the real thing.

Activity 3 Redesign the bridge

Activity 3 According to steps of Engineering Process, draw a completed design of the bridge you intend to build. THREE spatial views of the bridge should be included. You may consider the materials provided and the following rubrics to draw the diagram:

Activity 3 Materials provided 80 drinking straws, 1 sticky tape, 10 paper clips, 1 pair of scissors, 1 roll of strings, some A4 papers.

Activity 3 Points can be earned by the following rules. The drawing is neat and legible. The three spatial views are labelled. The bridge span is at least 30 cm long. The roadbed is at least 5 cm wide. The distance between the bridge supports is at least 10 cm apart.

Activity 3 Question: Compare the steps you drafted with the Engineering Process. Discuss among yourselves which steps you need to reconsider.

Activity 3 Question: What are the constraints when you build a bridge?

Activity 3 Answers: Weight, length and width of the bridge, materials and other requirements of the bridge itself.

Bridge Building Contest Activity 4 Bridge Building Contest

Activity 4 Build a bridge according to your completed design. You may change your design if there is a serious problem in your design. You may refer to the rubrics to build the bridge. The strength of the bridges would be tested by hanging loads from the middle of the bridges until it begins to buckle.

Activity 4 At the end of this activity, you are going to evaluate the designs of different groups and choose  a. the most cost-effective design (materials used vs strength) b. the strongest bridge design

Activity 4 Points can be earned by the following rules. The team adhered to the design. The model is neatly done. The model is built with materials supplied. The bridge span is at least 30 cm long. The roadbed is at least 5 cm wide. The distance between the bridge supports is at least 10 cm apart.

Professional’s judgment Activity 5 Professional’s judgment

Activity 5 An expert or professional is invited to give you comments so that you know which aspects of the bridge design need improvements.