What type of elements are prone to buckling under compression?

The correct answer is long elements, as they are particularly susceptible to buckling under compression due to their geometry. Buckling occurs when a structural member is subjected to critical loads that exceed its ability to withstand compressive forces, leading to a sudden lateral deflection.

In long elements, the slenderness ratio plays a significant role in their stability. As these elements have greater length compared to their cross-sectional dimensions, even a small compressive load can result in significant deflection and potential failure. This behavior is governed by Euler's buckling theory, which indicates that the critical load at which buckling occurs decreases as the length of the member increases relative to its cross-sectional area.

Conversely, thick or short elements tend to be more stable under compressive loads because they have a larger cross-sectional area capable of distributing stress more evenly. Short elements are often capable of carrying greater loads without buckling as they do not have significant lengths to develop lateral deflections. Therefore, long elements are the most likely to experience buckling when subjected to compressive forces, making them the correct choice in this context.