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Earthquake Damage, Northern Iran, June 20, 1990 |
| A magnitude 7.7 earthquake occurred in the Gilan Province between the towns of Rudbar and Manjil in northern Iran on Thursday, June 21, 1990 (June 20 at 21:00 GMT). The event, the largest ever to be recorded in that part of the Caspian Sea region, may have been composed of two or more closely-spaced earthquakes occurring in rapid succession. These quakes, exceptionally close to the surface for this region, were also unusually destructive. This slide set depicts damage resulting from intensive ground motion and soil liquefaction. It shows damage to buildings of various types, including unreinforced masonry, steel structures, and concrete buildings. |
Building Damaged by Ground Failure, Iran | |
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Building Damage, Liquefaction Wall crack caused when soils liquefied and building settled during the earthquake. Soils liquefy when ground water near the surface is forced between the grains of sand during an earthquake. The sandy soil behaves like a very thick liquid. Structures then settle or tip in the liquefied soil or are ripped apart as the ground spreads laterally or flows. Photo Credit: M. Mehrain, Dames and Moore. |
Differential Settlement, Liquefaction, Iran | |
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Building Damage, Liquefaction Large differential settlement due to liquefaction. The building to the left sank relative to the small (lighter) attached structure. The structures probably do not share a joined foundation. Much evidence of liquefaction was identified in the towns of Astaneh Ashrafieh, Lushan, and Noosher. These villages are located on soft sediments near the shore of the Caspian Sea. The foundations of structures were affected by the spreading or weakening of the liquefied soils, causing extensive structural damage. Photo Credit: M. Mehrain, Dames and Moore |
Destruction of Unreinforced Masonry Buildings, Iran | |
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Building Damage, Unreinforced Masonry Destruction of buildings in the epicentral region near Manjil. The majority of the smaller residential and commercial buildings in the areas of highest impact were of unreinforced masonry bearing wall construction. This included the towns of Rudbar, Manjil, and Lushan where many of the buildings collapsed or were damaged beyond repair. The brittle masonry materials used in these structures perform poorly under conditions of strong seismic loading. The heavy weight of the masonry floors and roofs also contributed significantly to the failure of these buildings. Photo Credit: M. Mehrain, Dames and Moore |
Collapse of Unreinforced Masonry Buildings, Iran | |
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Building Damage, Unreinforced Masonry C\Widespread collapse of unreinforced masonry buildings in a mountain village near Manjil. In the villages construction was mainly of irregularly-shaped lava blocks set in dried mud, or of sun-dried mud bricks with similar "cement." The roofs in these villages were of thick layers of dried mud spread upon reeds laid across closely spaced horizontal poles -- a construction practice that was highly vulnerable to earthquake damage. Photo Credit: M. Mehrain, Dames and Moore |
Roof Collapse, Iran | |
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Building Damage, Unreinforced Masonry Roof collapse in an unreinforced masonry bearing-wall structure near Manjil. The roof was a brick-infilled steel beam system without adequate support for its weight. Roofs, ceilings, and floors constructed with this commonly used "jack arch system" contributed to building failures and to the unusually high death toll. As many as half the buildings completed in the early 1970s in Iran had jack arches. In the jack arch system, steel beams or a reinforced concrete joist system spanned the distance between the main girders across the length of the building. An arch made of small bricks connected the beams. Each arch had a rise of only about ten centimeters. The "valleys" of this wave-like surface were filled with mortar. The completed ceiling, roof, or floor was thick and heavy. Frequently the steel support beams were not tied together properly or were left untied. When the beams shook, the arches fell creating a "domino effect" that caused other floors to fail. The floors also failed at the hinges where they met the supporting columns and collapsed to the ground. As many as half the buildings completed in the early 1970s in Iran had such jack arches. Photo credit: M. Mehrain, Dames and Moore |
Parapet and Roof Collapse, Iran | |
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Building Damage, Unreinforced Masonry Parapet and partial roof collapse of Rasht City Hall. In the towns, building collapse resulted primarily from the rupture of poorly welded connections in steel frames, and from the heavy weight of ceiling and roof masonry. Photo credit: M. Mehrain, Dames and Moore |
X-Cracking in Shear Walls, Iran | |
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Building Damage, Unreinforced Masonry Typical major damage to buildings with many unreinforced shear walls. Note "X-cracking." Unreinforced hollow or solid brick masonry infill, extensively used in Iranian buildings, performed poorly during this earthquake. In Rasht, sixty kilometers from the epicenter, the buildings incurred widespread damage due to such unreinforced masonry sheer walls. However, two thick solid unreinforced masonry walls were placed at the opposite ends of some mid-rise buildings in Rasht. These walls acted as shear-resisting elements and appeared to have improved the overall performance of the buildings. Photo Credit: M. Mehrain, Dames and Moore |
Structural Damage to Walls, Iran | |
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Building Damage, Unreinforced Masonry The presence of a reinforced concrete bond beam (a concrete beam poured on the top of walls) prevented a roof collapse in this building. This construction practice was generally effective in reducing the total collapse of structures. Photo Credit: M. Mehrain, Dames and Moore |
Damage to Unnreinforced Masonry Infill Walls, Iran | |
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Steel Structures Typical damage to hollow-clay, unreinforced masonry infill walls which are common in buildings throughout Iran. The unreinforced masonry is usually not structural but is attached outside the load-bearing structure. This masonry tends to fall away from the wood or steel superstructure during earthquakes. These buildings had to be evacuated even though they did not fail structurally. Photo Credit: M. Mehrain, Dames and Moore |
Damage to Building with Reinforced Infill Walls, Iran | |
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Steel Structures Masonry infill walls in Manjil that were constructed with light steel reinforcement. Steel sections had been installed in the plane of the wall reducing the possibility of wall buckling. Photo Credit: M. Mehrain, Dames and Moore |
Damage Due to Inadequate Cross-Bracing, Iran | |
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Steel Structures Damaged four-story steel structure with inadequate bracing on one side. The braces failed at their connections during the shaking. The braces were later repaired and the building was restored. Photo Credit: M. Mehrain, Dames and Moore |
Tilt of 8-story Steel Structure, Iran | |
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Steel Structures Tilt from the perpendicular of an eight-story steel structure that was under construction at the time of the earthquake. There were insufficient moment frames in the direction in which the tilt occurred. The damage to the building resulted from inadequate design and detailing and deficiency in workmanship. Photo Credit: M. Mehrain, Dames and Moore |
Damage to Building with Rod Bracing, Iran | |
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Steel Structures Although the rod bracing ruptured in this light steel industrial building in Ganjeh, 30 km from the epicenter, there was no structural damage. Only two per cent of the buildings in the area were fabricated with steel frames or reinforced concrete. Had these types of construction been extensively used, the damage and death toll would have been lowered considerably. Photo Credit: M. Mehrain, Dames and Moore |
Concrete Frame Construction, Iran | |
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Building Damage, Concrete Buildings Typical Iranian concrete frame construction with brick infill. As in past earthquakes, nonductile concrete-frame buildings performed poorly, and unreinforced masonry infill construction was most vulnerable to earthquake damage. Photo Credit: M. Mehrain, Dames and Moore |
Collapse of Mid-Rise Concrete Building, Iran | |
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Building Damage, Concrete Buildings Collapse of a mid-rise concrete building and damage to the adjacent building. The two adjacent five-story concrete-frame buildings were both under construction at the time of the earthquake. The structure on the right collapsed completely damaging the corner column of the structure to the left. Photo Credit: M. Mehrain, Dames and Moore |
Total Failure of Mid-Rise Concrete Building, Iran | |
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Building Damage, Concrete Buildings Total failure of a mid-rise concrete building in Rasht. The building had plain (undeformed) bars for reinforcement. In the City of Rasht, far-field, long-period ground motion appeared to cause the partial or total collapse of many such mid-rise buildings. Photo Credit: M. Mehrain, Dames and Moore |
Damage to Elevated Concrete Water Tank, Iran | |
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Other Structural Damage Concrete elevated water tank, empty at the time of the earthquake, shows only tension cracks at the base of its shaft. Elevated water tanks sway like inverted pendulums during earthquake shaking. When the tanks are filled with sloshing water, the shafts supporting the tanks generally fails. In general, such elevated concrete water tanks sustained damage in this earthquake. Photo Credit: M. Mehrain, Dames and Moore |
Collapse of Concrete Water Tank, Iran | |
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Other Structural Damage This elevated concrete water tank, two-thirds full at the time of the earthquake, collapsed. The tank was 46 m high and had a volume of 1,500 m3. The structure had a reinforced concrete shaft and a prestressed concrete tank and had served the City of Rasht for 20 years. Fortunately the tank collapsed away from an adjacent building. Photo Credit: M. Mehrain, Dames and Moore |
Pier Displacement of Concrete Bridge, Iran | |
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Other Structural Damage Large lateral pier displacement of undamaged concrete bridge. Although the lateral displacement at the ground level was about 25.4 cm there was no observable damage either to the columns or girders of this bridge. In general bridges performed relatively well in the 1990 Iranian earthquake. Photo Credit: M. Mehrain, Dames and Moore |
Sefidrud Dam, Iran | |
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Other Structural Damage Relatively undamaged Sefidrud Dam located within one km of the fault. The buttress dam has a height of 106 m, a length of 425 m, and a base width of 100 m. The dam was reportedly designed for a static lateral force coefficient of 0.25. The reservoir was almost full at the time of the earthquake and experienced very intense ground motion (0.60g). Horizontal and diagonal cracks occurred at the top of some buttresses, but the dam remained stable. However, a massive rockfall near the dam caused the collapse of the guard house and the death of the guard. Photo Credit: M. Mehrain, Dames and Moore |