The collapse zone distance for URM walls scales with building height according to which rule?

The collapse zone distance for URM walls scales with building height according to which rule?

• A. Three times the height
• B. Twice the height
• C. Independent of height
• D. Four times the height

Answer: (A)

The key idea is that the collapse zone around unreinforced masonry walls grows with the wall height. For URM walls, safety guidelines use a conservative rule: set the collapse distance at three times the wall height. This 3× height multiplier reflects that taller walls have longer debris paths when they fail, so a distance proportional to height provides a safer buffer for people and nearby structures. Why this works: URM walls can collapse rapidly and in a sweeping pattern, and taller walls can project debris farther. A multiplier of three offers a practical, conservative separation that scales with the size of the wall, rather than a fixed distance. Why the other options don’t fit: doubling the height would under-protect taller walls; quadrupling the height is more conservative than the standard practice and isn’t the common rule; making the distance independent of height ignores how debris travel increases with wall size.

The key idea is that the collapse zone around unreinforced masonry walls grows with the wall height. For URM walls, safety guidelines use a conservative rule: set the collapse distance at three times the wall height. This 3× height multiplier reflects that taller walls have longer debris paths when they fail, so a distance proportional to height provides a safer buffer for people and nearby structures.

Why this works: URM walls can collapse rapidly and in a sweeping pattern, and taller walls can project debris farther. A multiplier of three offers a practical, conservative separation that scales with the size of the wall, rather than a fixed distance.

Why the other options don’t fit: doubling the height would under-protect taller walls; quadrupling the height is more conservative than the standard practice and isn’t the common rule; making the distance independent of height ignores how debris travel increases with wall size.