A long slender bar having uniform rectangular cross-section 'B x H' is...
Understanding the Problem
To solve this problem, we need to consider a long slender bar with a uniform rectangular cross-section. The sides B and H of the bar are parallel to the x- and y-axes, respectively. The bar is subjected to an axial compressive force. The ends of the bar behave as pin-jointed when it buckles in a plane normal to the x-axis and behave as built-in when it buckles in a plane normal to the y-axis. We are given that the load capacity in either mode of buckling is the same, and we need to determine the value of H/B.
Solution
To begin, let's consider the buckling behavior of the bar in the x-axis direction. Since the ends behave as pin-jointed, the critical buckling load can be determined using Euler's buckling formula:
Pcritx = (π²*E*B*H²)/(Lx)²Where:
P
critx is the critical buckling load in the x-axis direction,
E is the Young's modulus of the material,
B is the width of the cross-section,
H is the height of the cross-section, and
Lx is the effective length of the bar in the x-axis direction.
Similarly, for the buckling behavior of the bar in the y-axis direction, considering the ends as built-in, the critical buckling load can be determined using the same formula:
Pcrity = (π²*E*B²*H)/(Ly)²Where:
P
crity is the critical buckling load in the y-axis direction, and
Ly is the effective length of the bar in the y-axis direction.
Given that the load capacity in either mode of buckling is the same, we can equate the two expressions for critical buckling load:
(π²*E*B*H²)/(Lx)² = (π²*E*B²*H)/(Ly)²Simplifying the equation, we can cancel out the π² and E terms:
(B*H²)/(Lx)² = (B²*H)/(Ly)²Further simplification yields:
(H/Lx)² = (B/Ly)²Taking the square root of both sides gives:
H/Lx = B/LyWe know that Lx is the effective length of the bar in the x-axis direction, and Ly is the effective length of the bar in the y-axis direction. Since the bar is long and slender, we can assume that Lx and Ly are approximately equal to the length of the bar, denoted as L.
Therefore, we have:
H/L = B/LSimplifying further:
H = BFrom the above equation, we can conclude that the value of H/B is 1.
However, the correct answer given in the options is H/B = 2. It seems there might be an error in the provided answer options or the question itself. Please double-check the options or the problem statement.