Knowledge of structures CMT 6-5
Achievement standard 1.24 AS 91061
A structure refers to framework that is used to support a load(s). A framework is comprised of structural members that are assembled using pin or fixed joints. The integrity of a framework is reliant on the strength, weight, material and profile of its structural members; the combination and means of joining structural members; and the safety factors applied to the structure.
Knowledge within this component includes understanding of how pin jointed structural members transfer forces when a framework is subjected to gravitational loads; how safety factors are applied to ensure a frameworks integrity; and calculating using vector diagrams the magnitude, direction and type of force acting on pin jointed structural members in a framework.
Learning Objective: CMT 6-5
Students will:
- Demonstrate understandings of basic structures
Indicators
Students can:
- explain what is meant by tension, compression, shear and torsion
- explain the safety factors applied to a framework
- explain how structural members and pin joints transfer forces in a framework
- discuss how the integrity of a framework is established.
Progression
Prior to level 6 students should be developing an understanding of range of simple strucutres and techniques used when constructing them. Relevant health and safety and codes of practice should also be a focus of the teaching and learning programme.
At level 6 students investigate basic structures limited to pin jointed columns and beams. They learn what is meant by tension, compression, shear and torsion; identify types of structural members and joints; how safety factors are applied in the design of these basic structures; how structural members and pin joints transfer forces; and how the integrity of a structure is established.
The Teacher Guidance section provides information that supports teachers scaffolding of learning from levels 1-8 of the curriculum. This allows for differentiation of a programme of learning.
The deliberate use of provide, guide, and support in this section signals that as students' capacity for self-management increases, teachers progressively reduce the level of scaffolding provided.
- Provide – the teacher should take full responsibility for introducing and explicitly teaching new knowledge, skills or practices.
- Guide – the students have a level of understanding and competency on which they can draw but the teacher remains primarily responsible for continuing to develop these.
- Support – the students take primary responsibility for their own learning, drawing on all their previous experiences to consolidate and extend their understanding. The teacher is supportive rather than directive.
- The Teacher Guidance also uses the term ensure to indicate when the teacher plays a monitoring role to check that conditions critical for learning are present.
Teacher Guidance
To support students to understanding basic structures at level 6, teachers could:
- Ensure students are aware that frameworks are designed to withstand loads of a greater
capacity than they are placed under.
- Provide opportunity for students to understand the causes and effects of internal forces
within frameworks. That is, the relationship between tension, compression, bending, shear and torsion in structural framework members, and how material selection (i.e. composition, profile) is used to address this (eg, round pipe rather than solid round is used when members subjected to a compressive force).
- Provide opportunity for students to understand how "safety factor" is applied across different framework structure contexts (eg, bridges, cranes, trusses)
- Provide opportunity for students to understand the structural members that form a framework (eg, Posts, beams, struts, ties) and how they are joined (eg, fixed, pin joint, moving) across different framework structure contexts.
- Provide opportunity for students to understand how pin jointed structural members in a framework transfer forces due to gravity load to ensure the frameworks integrity is maintained.
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Contexts for teaching and learning
This learning objective is a knowledge objective and hence there is no requirement for students to actually construct the structure(s) they are studying. However within a programme of work it would possible to tie the knowledge related to this learning objective with a project where students are actually designing and/or constructing an outcome that involves a structural framework. Knowledge of structures could be covered before students design and make their own technological outcome that includes a structure of some description.
It would be beneficial if during the teaching and learning students look at a range of structures even if they are only going to study one example in detail for assessment. Students should be provided with the opportunity to explore a range of structures to identify where, how and why pin joints are used, and to fully understand how these structures derive their structural integrity. Examples of suitable strucutres include such things as bridges, climbing frames and other playground equipment, gazebos, scaffolding or ladders, roofing trusses, or a furniture item.
Before beginning assessment, the students will gather and analyse the data they need in order to demonstrate comprehensive understanding. They may do this as a separate investigation or they may do it as part of another project. For example, the task of creating a presentation focusing on a particular could be in preparation for, or reflection on, a project in which they design and/or construct that structure. They may also be part of a group investigation as part of their learning but the assessment task is an individual piece of work. Other possible contexts could include the construction of:
- a piece of furniture such as a coffee table, a stool, or a shelving unit
- a step ladder or a climbing frame
- a support frame or brackets.
As part of this teaching and learning, students should learn abut the following concepts
Structures and their components- To develop their understandings, students need to explore a range of basic pin jointed column and beam structures. This could include scaffolding, ladders and some types of furniture, bridges and playground equipment.
Loads- Students must develop an understanding of the difference between internal loads and external loads acting on structural members when they investigate safety factors. For example a ladder that is leaning against a wall and being in a state of equilibrium as opposed to someone climbing the ladder and applying load to the rungs
Forces-Teachers should support and scaffold student learning so that they clearly understand the concepts of tension, compression, shear and torsion in pin jointed columns and beams.
Joints- Students should develop their knowledge of the types of joints found in structural members, for example mortise and tenon joints commonly found in chair construction; bolted joints and welded joints commonly found in playground equipment. This can be done through a range of class activities, deconstruction or construction of simple structures as part of a wider teaching and learning programme
This will then enable them to demonstrate their understanding of:
- what is meant by the terms: forces, structural members, and safety factor as they relate to structural frameworks;
- the different types of structural members and joining methods used in structural frameworks;
- how different structural components transfer forces, resist loads, and contribute to ensuring the integrity of frameworks.
Students need to understand the importance of diagrams in this topic. The use of annotated diagrams will support them in demonstrating understanding of structural frameworks. For example generating a diagram to show members and types of joints.
It is also important that the context of structures is engaging for students by looking at real examples of structural frameworks. These could be from a historical and/or contemporary perspective, and could include local, national, or international examples. For example students could look at iconic bridges from around the world, or research scaffolding in different countries (an Internet search of scaffolding in the third world will yield fascinating results!). Alternatively they may focus their study on a well-known local structure, school environments and simple furniture structures and playground equipment.
The topic can be further enriched with visiting speakers (eg a futureintech ambassador who is a structural engineer) or a visit to a local structure of interest.
When exploring the concept of the integrity of a structural framework an interesting angle can be to look at well-known cases where the structure has failed. An Internet search of bridge failure or similar would be a possible starter to then go on and explore structural integrity.
The focus at this level is static loads, however when exploring safety factors the concept of loading is introduced so within the learning programme students could explore such things as how wind and earthquake loads are different in different parts of the country. Without being a requirement as such at this level students could be introduced to the building code and various NZ standards.
Literacy considerations
Teachers need to ensure students understand the specialist language related to structures.
- Structures for this achievement standard are limited to pin-jointed columns and beams. Examples of structures may include but are not limited to – furniture, ladders, scaffolding, and bridges.
- Forces for this achievement standard are limited to – tension, compression, shear and torsion.
- Loads for this achievement standard are limited to static point loads.
- Safety factors for this achievement standard are limited to considerations of the internal loads acting on structural members.
- The integrity of a structure is reliant on but is not limited to – the strength, weight, material and profile of structural members; the combination and means of joining structural members; and safety factors applied to the structure.
Teachers will need to support students to develop an understanding of all these terms. Merely providing a list of definitions will not be sufficient.
In addition students must understand the academic language necessary to prepare evidence to demonstrate their understanding. Students need to understand words such as describe, explain, and discuss. Teachers need to give students strategies to understand what is expected for these different words – for example what does it mean to explain integrity of the structure, or discuss how safety factors have been applied?
The following definitions will assist students in their understanding of the requirements:
- To identify is to state an idea.
- To describe is a statement that gives details about the outcome or idea.
- To explain is to describe in detail with reasons – often including the how and why.
- To discuss requires an explanation that is comprehensive, detailed, and broad and show evidence of some complexity in thinking. It may be a reasoned argument presenting a particular point of view, or a comparison and contrast between two ideas or concepts; or it may be a detailed reasoning and relationship between several complex ideas that are either in a relationship or they may be compared and contrasted.
Resources to support teaching and learning
Other useful websites include:
Useful texts include:
- Advanced Level Technical Drawing. E. Jackson ISBN 0 582 32328 2
- Technical and Professional Drawing Book 2. Robin Sinclair and Terry Guy ISBN 456 01450 0
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Assessment for qualifications
The following achievement standard(s) could assess learning outcomes from this learning objective:
- AS91061 Construction and Mechanical Technologies 1.24: Demonstrate understanding of basic concepts related to structures
To be successful students will need to demonstrate their understanding of the following
- the specific structure that is the focus, for example, a mini gazebo, ladder, some furniture items , shelving
- what is meant by tension, compression, torsion, and shear and explain the impact that each has on structural members (using diagrams or other illustrations to support your explanation)
- the types of structural members and joints used in structures and explain how these structural members and joints transfer the forces of tension, compression, torsion, and shear, using illustrations and examples that relate to their focus structure(s)
- how these types of structural members resist static point loads
- the purpose and function of safety factors that relate to internal static point loads acting on structural members, specifically explaining why designers need to plan for structural capacity beyond the expected load (in their focus structure and at least one other structure)
- how the integrity of their focus structure would be established, explaining why specific materials (material types and their profiles) and assembly techniques would be used and why specific safety factors would be calculated
- compare and contrast the usefulness of different tests and other ways of addressing issues that relate to:
- The strength, weight, material type, and profile of the structural members
- The combination of all the structural members and the means by which they are joined
- Safety factors that apply to the structure
Key messages from the standard
Key terms
- Structures for this achievement standard are limited to pin jointed columns and beams. Examples of structures may include but are not limited to – furniture, ladders, scaffolding and bridges. (Explanatory Note 3)
- Forces for this achievement standard are limited to – tension, compression, shear and torsion. (Explanatory Note 4)
- Loads for this achievement standard are limited to static point loads. (Explanatory Note 5)
- Safety factors for this achievement standardare limited to considerations of the internal loads acting on structural members. (Explanatory Note 6)
When explaining safety factors applied to a structure students should consider the implications of static load and how structural members and pin joints transfer forces in a structure
For excellence students need to discuss how safety factors have been applied to ensure the integrity of a structure. Explanatory note 7 clarifies the concept of integrity of a structure
The integrity of a structure is reliant on but is not limited to – the strength, weight, material and profile of structural members; the combination and means of joining structural members; and safety factors applied to the structure.
Evidence for this standard may be generated as students make outcomes with strong structural integrity requirements or may be generated by stand-alone activities. So the evidence could be embedded in a student’s portfolio associated with a practical project, or could be produced as a separate report or presentation related to a separate research investigation or other stand-alone activity. Refer to the conditions of assessment for further details.
For the most up to date information, teachers should be referring to the latest version of the standards, conditions of assessment and assessment resources on TKI and the moderators reports, clarifications documents and student exemplars on the NZQA website. See links below.
Resources to support student achievement
Assessment resources:
Annotated Exemplars
Last updated August 16, 2019
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