Mid-Continent Earthquakes And Their Effect On Concrete Structures Essa

Mid-Continent Earthquakes and Their Effect on Concrete Structures Disasters come in many shapes, sizes, and forms yet all are detrimental to people and structures of all types. The most terrifying of all disasters are natural disasters, the force of nature is rivaled by no man made disaster. One of the natural disasters that has terrorized as well as fascinated humans through out history is the earthquake. Most earthquakes are associated with areas such as Southern California or China, but the most detrimental aspect of disaster is the element of suprise. In this case areas such as Central North America and North Turkey have been visited by the violent shock of a mid-continent earthquake. These earthquakes are violent and cause mass amounts of structural damage and total destruction of many structures. Concrete being a very brittle material is affected greatly during an earthquake but through technology many advancements have been made to compensate for the damaging effects caused by an earthquake. This paper will discuss mid-continent earthquakes of the past, their effect on concrete structures, problems effecting concrete structures, and alternative materials and solutions to bypass those problems during future earthquakes. Mid-Continent Earthquakes A series of earthquakes occurred between December 1811 and February 1812 in the New Madrid Seismic Zone which is in the Mississippi River Valley. These earthquakes may have been caused by a series of buried faults and anomalous rock formations that formed 500 million years ago when tectonic forces tried and failed to split North America in two. This structure known as the Reelfoot Rift is the zone of weakness that could account for the earthquakes during this period (Reducing Losses 1995). This series of earthquakes was characterized by ground warping, fissuring, severe landslides, and caving stream banks. An area of over 600,000 square kilometers was damaged during the 1811-1812 period of earthquakes (USGS 2000). During the earthquakes ground shaking occurred as the land moved up and down and caused trees to bend, chimneys to fall, and log cabins to be thrown to the ground. Liquefaction was also a problem during the mid-continent earthquakes where the shaking transformed water saturated soil or sediment into a thick quicksand like slurry (Reducing Losses 1995). Sand bars and points of islands in the Miss. River gave way while some whole islands disappeared. This period of earthquakes was also characterized by deformation which is either elastic or inelastic. Both types of deformation were apparent during the earthquakes. When the rocks snapped back after movement during the elastic deformation large cracks in the ground were opened up. Inelastic deformation occurred when land was uplifted while other parts sunk and remained in that position. This uplift of the ground and the waves moving during the ground shaking gave the appearance that the Miss. River was flowing North. A very recent mid-continent earthquake occurred in Turkey called the Izmit Earthquake. The rupture appeared to be about 110 km in length and occurred during August of 1999. This earthquake occurred along a strike slip fault where there were recorded offsets of 1.2m to 4.9m (USGS 1999). There was a mass destruction of buildings and as a result about 300,000 people were killed or injured (USGS 1999) while many were left homeless in campsites where diseases were rampant. Ground shaking was tremendous as a result of the 7.5 Richter scale rated earthquake where many buildings were flattened. Deformation was evident in the Izmut Bay where the fault leaves the eastern side of the bay and slumps along the crack formed scarps (USGS 1999). Sag ponds were a result of the liquefaction that occurred along the strike slip fault. This earthquake was devastating to the residents of northern Turkey but a lot of valuable information was extracted in order to prevent that magnitude of disaster in the future. Effects and Problems of Earthquakes on Concrete Structures Earthquakes are very detrimental to concrete structures which are very brittle and struggle and often lose to the violent shaking of the earth and the many ramifications that are brought about by the shaking. Damage to the structures are caused by the materials inertia and resistance to movement that causes the concrete to fail and ultimately the collapse of the building. Ground acceleration is the key aspect from an engineering point of