商业结构 Commercial Structures

商业结构
Loma Prieta地震和它的余震导致了一系列商业结构的大面积顺坏损坏.正如这个量级的典型地震一样,有一大批地理范围受到了影响.被波及的地区包括8个郡,从南部的Monterey和San Benito,到北部的San Francisco, Alameda, 和 Contra Costa .总共有大约3000平方英里面积的建筑结构遭受到了破坏.
尽管地震带来的破坏面积很广,但是这些破坏很零散.据估计,最接近震中的地区,包括Hollister, Los Gatos, Santa Cruz, 和 Watsonville 经历了最集中的破坏.再远一点,仅仅是那些地基建在松软的土质上的质量非常差的建筑物遭到了严重的破坏,这些土质在地震的运动中中被破坏和坍塌.这和1985年的墨西哥地震产生的影响是相似的.
地震的影响是具有很强的方向性的.大多数破坏发生在从西北向东南方向延伸的狭窄地段,大约与San Andreas Fault平行.因此沿着 San Francisco 湾的许多地区逃脱了这场截难.
不稳固的石质建筑物
正如在过去的California 地震中所发现的那样,最集中和严重的建筑物结构破坏发生在不稳固的石质建筑物结构中.不稳固的石质建筑物结构包括木头框架的屋顶和地板,这些屋顶和地板是由很厚的不稳固的墙砖支撑的,这种结构在California一直流行到30年代,那时抗震材料在建筑上的应用阻止了它进一步的发展.因此,不稳固的石质建筑物结构通常在 California 的老城区中的集中商业地段被发现. (毕业设计 )

Commercial Structures

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    The Loma Prieta Earthquake and its subsequent aftershocks resulted in widespread damage to a variety of commercial structures. A large geographical area was affected, as is typical for an earthquake of this magnitude. The affected area encompasses eight counties, from Monterey and San Benito in the south to San Francisco, Alameda, and Contra Costa in the north. In total, building structures experienced damage over an area of approximately 3,000 square miles.
    Although damage was widespread, it was also quite sporadic. As would be expected, areas closest to the epicenter including Hollister, Los Gatos, Santa Cruz, and Watsonville experienced the most concentrated damage. Farther away, heavy damage was generally limited to buildings of very poor construction founded on soft soils that failed or amplified the earthquake ground motions. This is similar to the effects noted in the 1985 Mexico City Earthquake.
Earthquake effects also tended to be highly directional. Most damage occurred within a narrow band that extends northwest to southeast, approximately paralleling the San Andreas Fault. Thus many communities along the margins of San Francisco Bay escaped serious damage.

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                        Unreinforced Masonry Buildings

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As has been observed in past California earthquakes, the most concentrated and severe damage to building structures occurred in unreinforced masonry (URM) bearing-wall buildings. URM buildings, constructed of wood-frame roof and floor systems supported by thick unreinforced brick walls, were commonly constructed throughout California until the 1930s, when the adoption of building codes with seismic-resistive provisions prevented their further development. As a result, URM buildings are typically found in the central business districts of older California cities
    Failures of URM buildings result from inadequate anchorage of the masonry walls to roof and floor diaphragms, as well as the limited strength and ductility of the basic building materials and poor construction workmanship. Deterioration of the sand-lime mortar and wood framing due to weather exposure frequently contributes to poor performance. California has recently enacted legislation (SB 547) requiring cities to identify URM buildings and develop plans to reduce the risk they present.

Damage to URM buildings in the Loma Prieta Earthquake ranged from dramatic collapses near the epicenter to fallen parapets in Martinez, more than 70 miles away. Life-threatening collapses also occurred in Hollister, Los Gatos, Oakland, and the San Francisco financial district. The roofs and floors in many buildings with collapsed walls seemingly defied gravity by continuing to stand after losing their load-bearing support. Generally, buildings with through-wall anchorage to floor and roof framing performed better than buildings without this feature.

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