Final answer:
Performance problems with Unreinforced Masonry Bearing Walls and Flexible Diaphragms include wall cracking or collapse under lateral loads, due to low shear strength and the excessive deformation of flexible diaphragms, leading to added stress and potential failure.
Step-by-step explanation:
Unreinforced Masonry Bearing Walls with a Flexible Diaphragm can have several performance problems, especially under seismic loads or heavy wind loads. These walls are typically constructed of materials like brick or concrete, which have small shear moduli, indicating that they are weak in resisting shear stresses. A flexible diaphragm, such as a wooden floor or roof, can exacerbate these issues because it does not provide the necessary lateral support to the walls. During an earthquake or strong winds, the lack of shear strength can result in the walls cracking or even collapsing due to their inability to withstand lateral forces. Additionally, the flexible diaphragm can deform significantly, leading to a phenomenon known as diaphragm drift, which further increases the stresses on the unsupported masonry walls. Modern construction techniques have mitigated these problems by using steel and steel-reinforced concrete, which have much higher capacities for dealing with shear stresses.
Beth's comments are concerned with the support necessary for stone vaulting, emphasizing the need for strong walls and piers but the concept is similar in that, without adequate reinforcement, any structure under heavy load or dynamic stress may suffer from performance issues.