Theory of Structure - Questions

posted Jul 23, 2019, 8:37 AM by jeffery jim   [ updated Jul 24, 2019, 9:41 AM ]
Most of the time, some of the basics or fundamentals in regard to theory of structure will be tested and gauged in both objective and subjective paper. 

For objective paper, most of the questions require you to demonstrate understanding and solve simple equations and key concepts. As for key concept, it is always about the likely shape of a diagram or a graph correspond to the question. Usually objective paper requires an efficiency of answering each question in 2.5 minutes. Hence, all possible questions are those questions which require around 5 minutes without proper training or skill.

The following paper is the subjective paper. If theory structure is one of the main questions, it evolves around a few other sub-questions, typically around 3 to 4 sub-questions which are part of the questions or decision which requires interpretation or justification. The time required to finish this question is around 30 to 40 minutes with great efficiency and the list of possible questions shall be questions which require around 30 minutes for the main question and around 10 minutes per sub-question without great efficiency. If you need time to refer to books or any other reference, it is safe to project the possible questions require you around 1 hour to complete.

So let us go through the possible questions based on typical chapters in theory of structure reference book. In this case, we only discuss determinate structures since this is the core to manual calculation where structure is required to stay in equilibrium. For determinate structure, vectorial sum of forces is assumed as zero and the sum of moments reaction is also zero. A structure which is indeterminate means the overall static equilibrium equations are not sufficient in determining internal forces and reactions.

Determinate Structures

Principal of Statics
This is the main chapter which requires you to demonstrate your basic understanding about type of forces and value of each forces in different planar or axis which may be related to loads and actions in BS EN 1991. Apart from that, you are required to understand some moment diagrams and the concept of triangle of forces, the free body diagram and principle of superposition. This chapter is contribute mostly to the objective questions and possible independent part or sub-question for subjective questions.

Statically determinate pin-jointed frames
This is among the favorite to pop out in both objective (simple symmetrical truss) and subjective (relatively simple but non-symmetrical truss) paper where a simple truss requires determination of forces at certain node(s). In this case, it is important to understand the sign convention before starting the analysis. One good tip for candidates is to get familiar with basic truss system so that it would be easy to assign the direction of internal (tensile & compressive) force. There are several methods of analysis which are quite common such as; method of resolution at the nodes, method of sections, method of force coefficients, and method of substitution of members.

Elements in flexure
This particular chapter can be considered as the core to most objective and subjective questions. It involved fundamentals in sketching applied loading, load intensity diagram, shear force diagram, and bending moment diagram. Candidates need to understand the relationship of these diagram and how these are calculated or generated involving beams and rigid frames. 

Elastic deformation
After candidate manage to generate all the above-mentioned diagrams, in certain sub-questions, candidate is required to sketch the deformation or deflection of simple beam or rigid frame using Macaulay's method, virtual work (unit-load) method, conjugate beam method. Pin-jointed frame is one of the classic question in subjective paper, therefore candidate should well-versed with this particular types of frame and continuous exercise make you familiarized with steps and will expedite your calculation.

Influence lines
Another alternative to possible subjective question with less sub-questions is the influence line which involves some movements of load(s) throughout the structure such as bridge and cranes and the determination of the maximum design force in the members. This method involves trial and error during positioning of load(s). The only way to stay sharp and expedite your calculation would be the familiarization of shapes and diagrams for various type of structural beam or frames. At times, sub-questions will require you to only sketch the shape without specifying the value (in case of independent and non-calculation sub-questions). Apart from that, you have to be good in dissecting isometric structure and convert it into simplified frame with proper type of support(s).

Space frames
Instead of limiting the structure calculation in 2 axes, there is high possibility, subjective questions and its sub-questions may require you to do analysis involving structure in 3 dimension. Candidate should be good in trigonometry.


Indeterminate Structures

Static Indeterminacy

Virtual work methods

Indeterminate pin-jointed frames

Conjugate beam methods

Influence lines

Elastic Center and column analogy methods

Moment distribution methods

Model analysis

Plastic analysis and design

Elastic Instability

Elastic-plastic analysis
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