Answer:
Treating a connection as fully rigid assumes that the joint can transfer large bending moments without any relative rotation between connected members. While this approach reduces the bending stress in the beam itself, it can lead to an uneconomical design. The joint must be oversized to accommodate the high moment, leading to increased material costs and potentially more complex fabrication. Moreover, this rigid connection may not reflect the actual behavior of the structure under real loading conditions, which could result in overdesigning the joint and thus failing to achieve cost-efficient material use. Instead, considering more realistic connection stiffness could optimize both the joint and overall structure design.
