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PROBLEM A.2
Determine ycg, which marks the location of the centroid, and then calculate the moments of inertia Ix' and Iy' for beam T.
00:00 Identifying the Centroid Location of Each Rectangle
✅ The first thing to do to calculate the ycg is to divide the cross section into rectangles and locate their centroid (ycg') in relation to the x axis.
02:10 Calculation of the Centroid of the Cross Section
✅ After identifying the location of the centroid of each rectangle, we have to calculate their areas to calculate the ycg of the section. In possession of all the data, it is now easy, just replace the values of the centroids and areas of the rectangles in the ycg formula.
ycg = Σycg'.A'/ΣA
04:15 The Moment of Inertia Formula
✅ To determine the moment of inertia in relation to the main axes, the following formula must be applied:
I = 'I' + A.d², where:
I' = moment of inertia of the rectangle (b.h^3/12) in relation to its centroid.
A = area of the rectangle.
d = distance between the centroid of the cross section and the centroid of the rectangle.
05:09 Calculation of the Moment of Inertia with Respect to the x-axis'
✅ Since we know which formula to apply, now just replace the values in the moment of inertia formula.
NOTE: remember that the base "b" of the rectangle analyzed is the one whose dimension is parallel to the x' axis, since we are calculating the moment of inertia in relation to this axis.
07:37 Calculation of the Moment of Inertia with Respect to the y' axis
✅ Note that to calculate the moment of inertia in relation to the y' axis, the formula A.d² does not apply, since the distance d = 0, since the y' axis passes through the centroid of each rectangle.
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📚 Source: Mechanics of Materials 7th Ed. (R.C. Hibbeler)
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