Structural Components and Systems

For The Seismic Retrofit of Tilt-up Buildings

Modified Mercalli Scale

MODIFIED MERCALLI SCALE
MMI Observed Effects of Earthquake
I Not felt except by very few under especially favorable conditions.
II Felt only by a few persons at rest, especially by those on upper floors of buildings
III Felt quite noticeably by persons indoors, especially by those on upper floors of buildings. Hanging objects may swing slightly. Vibrations similar to those caused by the passing of a light truck. Vehicles at rest may rock slightly. May not be recognzed as an earthquake.
IV Felt indoors by many, outdoors by few. Hanging objects swing. Some awakened from sleep. Windows, dishes, and doors rattle. Glasses clink. Crockery clashes. Timber framed buildings may make creaking, cracking, or popping noises. Vibrations similar to those caused by the passing of a heavy truck. Jolt may feel like a heavy vehicle or object hitting the building. Vehicles at rest rock noticeably.
V Felt by most everyone. Most awakened from sleep. Liquids disturbed, some spilled. Small unstable objects displaced or upset. Some dishes and windows may be broken. Doors swing, close, open. Shutters, pictures move. Pendulum clocks may stop, start, or change rate.
VI Felt by all. Many frightened, some run outdoors. Persons walk unsteadily. Windows, dishes, and glassware broken. Knickknacks, books, etc., fall off shelves. Pictures fall off walls. Furniture moved or overturned. Small bells ring (church, school). Trees and bushes may be visibly shaken, or heard to rustle. Weak plaster cracked, damaged, or fallen. Slight damage to Type D masonry structures.
VII Difficult to stand. Noticed by drivers of moving vehicles. Hanging objects quiver. Furniture broken. Fall of plaster, loose bricks, stones, tiles, cornices, unbraced parapets, and architectural ornamentation. Weak chimneys broken at roof line. Damage negligible in buildings of good seismic design and construction. Damage slight to moderate in well-built ordinary structures. Damage considerable in poorly built structures. Moderate damage to Type D masonry structures, including cracks. Some cracks in Type C masonry structures. Waves on ponds; water turbid with mud. Small slides and caving in along sand or gravel banks. Large bells ring. Concrete irrigation ditches damaged.
VIII Steering of moving vehicles affected. Twisted, damaged, and/or fallen chimneys, factory stacks, towers, elevated tanks, monuments, and freestanding walls of stucco or masonry construction. Damage slight in specially designed structures. Damage considerable in ordinary buildings, with some partial collapses. Damage great in poorly built structures. Collapse of inadequately secured tilt-up wall panels. Unbolted frame houses shifted on their foundations. Type C masonry structures heavily damaged, with some partial collapse. Some damage to Type B masonry structures. No damage to Type A masonry structures. Branches broken from trees. Decayed piling broken off. Changes in flow or temperature of springs and wells. Cracks in wet ground and on steep slopes.
IX General panic. Damage considerable in specially designed structures. Well designed frame structures racked and no longer plumb. Damage great in substantial buildings, with some partial collapses. Unbolted frame houses shifted off of their foundations. Type D masonry structures destroyed. Type C masonry structures heavily damaged, sometimes with complete collapse. Type B masonry structures seriously damaged. Serious damage to reservoirs. Underground pipes broken. Conspicuous cracks in the ground. In alluvial areas sand and mud ejected, earthquake fountains, sand craters.
X Most masonry and frame structures destroyed with their foundations. Some well-built wooden structures and bridges destroyed. Serious damage to dams, dikes, embankments. Large landslides. Water thrown on banks of canals, rivers, lakes, etc. Sand and mud shifted horizontally on beaches and flat land. Rails bent slightly.
XI Few structures remain standing. Bridges destroyed. Rails bent greatly. Underground pipelines completely out of service.
XII Nearly total catastrophic destruction. Large rock masses displaced. Lines of sight and level distorted. Objects thrown into the air.

Masonry Building Types:

  • Type A - Good workmanship, mortar and design. Reinforced, especially laterally, and bound together by using steel, concrete, et cetera; designed to resist lateral forces.
  • Type B - Good workmanship and mortar; reinforced, but not designed in detail to resist lateral forces.
  • Type C - Ordinary workmanship and mortar; no extreme weaknesses like failing to tie in at corners, but neither reinforced nor designed against horizontal forces.
  • Type D - Weak materials, such as adobe; poor mortar; low standards of workmanship; weak horizontally.