土木工程外文翻译2-建筑结构(编辑修改稿)

土木工程外文翻译2-建筑结构(编辑修改稿)内容摘要：

r nonstructural damage。 damage to gypsum board interior walls appeared to be significantly less severe. Chimney damage ranging from cracking to twisting and collapse was observed throughout the epicentral area. Such damage was observed in as many as 30% to 40% of the homes in the older areas of Watsonville. Chimney damage in Santa Cruz was less frequent and was primarily limited to older, unreinforced chimneys. Severe structural damage to homes observed could mainly be attributed to failure of unbraced cripple walls and lack of sill anchorage. These cripple walls are short wood stud framing present between the foundation and first floor of the building. Because they are not sheathed with plaster, as are walls in the living area, they are substantially weaker and a mon location for failures. Such damage was mainly observed in pre1940s homes with horizontal wood sheathing. These homes moved laterally from several inches to a foot, until the cripple walls became unstable and collapsed. Damage to utility lines due to this motion was frequent. In Watsonville, cripple wall failures were observed in approximately 10% to 20% of the pre1940s residences throughout the area, with many blocks suffering close to 100% failures. In Santa Cruz, damage appeared to occur mainly in the area of poorer soils. Nearly all of the homes on Pacific Avenue south of the Pacific Garden Mall had cripple wall failures Severe damage was also apparent on Myrtle Street, near the wastewater treatment plant at Neary Lagoon. On one block, five of twentyfive homes had cripple wall failures. On this street, correlation of damage with quality of maintenance and general preearthquake condition was evident. Apparently, older homes that had been restored architecturally often also had structural upgrades. The table on the following page shows none of the homes with good preearthquake condition to be severely damaged, while only one poor condition home was in the light damage category. In one Watsonville block, only one house did not fall from its foundations. It had just been seismically upgraded and had a new foundation without cripples. Its interior also had no damage, not even sheetrock cracking. San Francisco Marina District The most severely damaged area in San Francisco was the Marina district. The soils in this area consist mainly of soft, saturated sands and silts, some of which are naturally occurring, but most of which were filledin for the PanamaPacific Exposition circa 1915. Most of the buildings in the Marina district are apartment buildings and singlefamily houses of woodframe construction, two to five stories high, built in the 1920s. Most of these buildings are constructed with parking garages at the first story. A large percentage of the buildings in the Marina district suffered damage. Although plaster and stucco cracking was evident in all buildings in the Marina district, the most severe damage was observed in midrise (four to fivestory) apartment buildings. Several of these buildings collapsed pletely and many more were damaged beyond repair. Failure of these buildings was due to two main effects. First, the mass and stiffness of the buildings may have produced fundamental periods of vibration close to the predominant period of vibration that was amplified by the soft soils in the area. Second, it appeared that nearly all of the collapsed and partially collapsed buildings had the same configuration: these buildings all had numerous garage door openings at the first level, resulting in a lack of story shear strength or a soft story. Many of the severely damaged buildings were located on corners, and hence had two of their four exterior walls perforated with garage door openings. Some of these corner buildings also exhibited twisting behavior, which further worsened their performance. Seismic settlement and liquefaction caused severe cracking and buckling of streets and sidewalks in the Marina district. Soil failures did not appear to be a direct cause of building collapses。 however, they undoubtedly contributed to the overall problem Seismicity and Geology The epicenter of the Richter magnitude earthquake was located about 10 miles northeast of Santa Cruz along a segment of the San Andreas Fault, near Loma Prieta in the Santa Cruz Mountains. The focal depth has been placed at 11 miles. This is unusually deep, as typical California earthquake focal depths are 4 to 6 miles. A magnitude aftershock occurred approximately minutes after the main shock, and thousands of aftershocks have been recorded since. In the week following the earthquake, a total of 300 of these have been magnitude or greater and 20 have been greater than . The aftershock zone stretches across 25 miles from just north of Los Gatos near Highway 17, to south of Watsonville near Highway 101. This zone corresponds with the areas of greatest damage. The zone ranges from about 2 to 11 miles in depth and is believed to be the length of rupture associated with the main shock. Surface Effects Surface displacements with offsets of up to 3 or 4 feet along a zone about 20 miles long would normally be expected to acpany an earthquake of this magnitude. Instead many cracks have been found over several discontinuous and indistinct zones. There are several possible explanations for this lack of clear surface expression. The earthquake was unusually deep, making it difficult for the bedrock rupture to propagate to the ground surface. The bination of rugged topography, thick soil, and forest cover could also make surface breaks less distinct. The State Commission report of the 1906 earthquake described very similar surface rupture characteristics along the Santa Cruz Mountains portion of the San Andreas Fault. Historical Seismicity The San Andreas Fault trends no。