For the beam shown below, and using the answers for the reactions at A and B from questions 1 and 2:

Sketch the shear force diagram and use this to answer the following question;

What is the magnitude in kN and sign of the shear force just to the right hand side of support A, expressing the result to one decimal place

Question

For the beam shown below, and using the answers for the reactions at A and B from questions 1 and 2:

Sketch the shear force diagram and use this to answer the following question;

What is the magnitude in kN and sign of the shear force just to the right hand side of support A, expressing the result to one decimal place

BlackTom AI · Accepted Answer

To approach this question, we first identify the goal: determine the shear force just to the right of support A, from the shear force diagram (SFD) corresponding to the given beam, and express the value to one decimal place in kN with its sign.

Key concept: the shear force immediately to the right of a support equals the reaction at that support minus any downward loads that occur between the support and the point where you evaluate the shear. In many beam problems with simple supports and loads, the shear just to the right of A is essentially equal to the reaction at A minus any immediate downward load at A (if any) or minus any load introduced immediately to the right of A before the first cut drawn for the SFD.

Step-by-step reasoning for evaluating the value (in general, since the exact loads and reaction values from questions 1 and 2 aren’t provided here):
- Step 1: Sketch the beam with supports A and B and plot all external loads (point loads, distributed loads) along the span, as given in the diagram.
- Step 2: Note the reaction at A, typically denoted RA, which would have been obtained in questions 1 or 2. The sign convention commonly used is that upward reactions are positive for shear, and downward loads create negative jumps in the SFD.
- Step 3: Draw the shear force diagram starting at the left end, applying RA at A upward as you pass A, then stepping down by any applied loads as you move to the right, and finally applying RB at B if you draw the entire span. The value just to the right of A will be RA minus any immediate downward load at A (or simply RA if no load is applied exactly at A).
- Step 4: Read the shear value immediately to the right of A from the SFD. This value is the shear force at that section, with its sign indicating whether the beam section tends to cut the right-hand segment in a particular sense (positive above the beam convention or negative, depending on the adopted sign convention).
- Step 5: Convert this value to the requested one-decimal place precision and express the sign explicitly (e.g., +20.5 kN or −20.5 kN).

Why an answer like 20.5 kN might be correct (in-context reasoning):
- If RA is 20.5 kN and there is no downward load applied immediately to the right of A, the shear to the right of A would be +20.5 kN (assuming the chosen positive sign convention is upward or to the left depending on the diagram’s convention). In that case, the magnitude would be 20.5 kN with a positive sign.
- If there is a downward load immediately after A of, say, 5 kN, then the shear just to the right of A would be RA − 5 kN, which would yield a different magnitude and possibly a different sign.

Important caveats about this specific item:
- The prompt references questions 1 and 2 for the reactions at A and B. Without the numeric values of RA (and any immediate loads near A) or the exact loading diagram, you cannot independently verify the 20.5 kN figure from first principles here.
- The absence of answer options in the provided data means we cannot evaluate alternative choices or confirm partial credit reasoning for multiple options.

In summary, to validate the given numeric value, you would: (a) confirm RA from questions 1/2, (b) examine the immediate region to the right of A for any downward load, (c) read the SFD value just to the right of A, and (d) report the magnitude to one decimal place with the appropriate sign. The key is that the sign reflects the chosen convention and whether the net shear at that location tends to cause the right-hand segment to slide up or down relative to the left-hand segment.

STRCTENG 302 Steel Quiz No 1: Basic Knowledge Mechanics and Structural Steel Review

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