What does weight (mass) irregularity signify in a building structure?

Weight (mass) irregularity in a building structure signifies a situation where the effective mass of any storey is significantly higher than that of an adjacent storey, typically defined as being more than 150% of the adjacent storey. This condition can lead to uneven distribution of forces during events such as seismic activity, making the structure more susceptible to failure.

In building design, maintaining a uniform mass distribution is crucial for structural integrity. When one storey has more mass than another, it can result in an imbalance that affects the overall dynamic response of the building. The increased mass can lead to greater forces acting on the lower storeys during dynamic loads, which is a key consideration in seismic or lateral load analysis.

This concept is vital for architects and engineers when designing buildings, especially in earthquake-prone areas. Ensuring that mass irregularities are minimized can help in achieving a structure that behaves predictably under various loads, thereby enhancing safety and performance.

While other options suggest various conditions of mass irregularity, they do not appropriately describe the critical implications of significant mass disparity as indicated in the correct choice.