Damage‐based design with no repairs for multiple events and its sensitivity to seismicity model

Conventional design methodology for the earthquake‐resistant structures is based on the concept of ensuring ‘no collapse’ during the most severe earthquake event. This methodology does not envisage the possibility of continuous damage accumulation during several not‐so‐severe earthquake events, as may be the case in the areas of moderate to high seismicity, particularly when it is economically infeasible to carry out repairs after damaging events. As a result, the structure may collapse or may necessitate large scale repairs much before the design life of the structure is over. This study considers the use of design force ratio (DFR) spectrum for taking an informed decision on the extent to which yield strength levels should be raised to avoid such a scenario. DFR spectrum gives the ratios by which the yield strength levels of single‐degree‐of‐freedom oscillators of different initial periods should be increased in order to limit the total damage caused by all earthquake events during the lifetime to a specified level. The DFR spectra are compared for three different seismicity models in case of elasto‐plastic oscillators: one corresponding to the exponential distribution for return periods of large events and the other two corresponding to the lognormal and Weibull distributions. It is shown through numerical study for a hypothetical seismic region that the use of simple exponential model may be acceptable only for small values of the seismic gap length. For moderately large to large seismic gap lengths, it may be conservative to use the lognormal model, while the Weibull model may be assumed for very large seismic gap lengths. Copyright © 2006 John Wiley & Sons, Ltd.     

Interaction of a Dynamic Rupture on a Fault Plane with Short Frictionless Fault Branches

Spontaneous bilateral mode II shear ruptures were nucleated on faults in photoelastic Homalite plates loaded in uniaxial compression. Rupture velocities were measured and the interaction between the rupture front and short fault branches was observed using high-speed digital photography. Fault branches were formed by machining slits of varying lengths that intersected the fault plane over a range of angles. These branches were frictionless because they did not close under static loading prior to shear rupture nucleation. Three types of behavior were observed. First, the velocity of both rupture fronts was unaffected when the fault branches were oriented 45° to the main slip surface and the length of the branches were less than or equal to ~0.75 R₀* (where R₀* is the slip-weakening distance in the limit of low rupture speed and an infinitely long slip-pulse). Second, rupture propagation stopped at the branch on the compressive side of the rupture tip but was unaffected by the branch on the tensile side when the branches were ~1.5 R₀* in length and remained oriented 45° to the principle slip surface. Third, branches on the tensile side of the rupture tip nucleated tensile ``wing tip' extensions when the branches were oriented at 70° to the interface. Third, when the branches were oriented at 70° to the interface, branches on the tensile side of the rupture tip nucleated tensile ``wing-crack' extensions. We explain these observations using a model in which the initial uniaxial load produces stress concentrations at the tips of the branches, which perturb the initial stress field on the rupture plane. These stress perturbations affect both the resolved shear stress driving the rupture and the fault-normal stress that controls the fault strength, and together they explain the observed changes in rupture speed.     

Probabilistic Assessment of Earthquake Insurance Rates for Turkey

A probabilistic model is presented to obtain a realistic estimate of earthquake insurance rates for reinforced concrete buildings in Turkey. The model integrates information on seismic hazard and information on expected earthquake damage on engineering facilities in a systematic way, yielding to estimates of earthquake insurance premiums. In order to demonstrate the application of the proposed probabilistic method, earthquake insurance rates are computed for reinforced concrete buildings constructed in five cities located in different seismic zones of Turkey. The resulting rates are compared with the rates currently charged by the insurance companies. The earthquake insurance rates are observed to be sensitive to the assumptions on seismic hazard and damage probability matrices and to increase significantly with increasing violation of the code requirements.     

Reevaluation of the earthquakes of 10 March and 19 May 1951 in southern Spain

Damage and parameters of the earthquakes of 10 March and 19 May 1951 in southern Spain have been reevaluated. Data available do not allow accurate depth determinations and previous estimates of larger depths are not confirmed, so depths have been fixed at 30 km for both shocks. Magnitudes (Ms) have been determined as 5.4 and 5.6, respectively. Intensities estimated at 22 and 29 sites from contemporary documentary sources give maximum values of VI–VII and VI (EMS Scale), lower than previous estimates. The focal mechanism for the May shock is right-lateral strike-slip with a normal component of motion, with planes with strikes 273° and 169°; seismic moment 1.9 × 10¹⁶ Nm and dimension 6 km (radius of circular fault). Shocks are located near the boundary between the Iberian plateau and the Guadalquivir Basin and may be related to faults connected with this boundary.     

地震人员伤亡估算方法研究

本文将目前国内外地震人员伤亡的评估方法区分为将生命损失用货币单位来衡量和单独估算人员伤亡数量两大类,并对评估方法进行了系统归纳总结,在此基础上,利用以倒塌率为主要影响因素的6种估算方法对1976年唐山地震,1996年云南丽江7．0级地震及内蒙古包头西6．4级地震的人员伤亡进行了评估,并与三次地震人员伤亡的实际统计结构进行了比较,最后,提出了一种较精确,适用的伤亡评估方法。     

拉应力条件下岩石细观力学本构模型和渗透系数张量研究(Ⅱ):各向异性渗透系数张量及算例

建立了同时考虑微裂纹发展过程、渗透压和变形影响的岩石各向异性渗透系数张量,推导了所建立本构模型和渗透系数张量的单轴拉伸方程,并和实验结果进行了对比。结果表明,建立的本构模型能够反映岩石的弹性阶段、非线性强化阶段、应力跌落阶段和应变软化阶段的特征;能够很好地反映有渗流时岩石抗拉强度降低等渗流岩石力学特征;建立的渗透系数张量正确反映了随着岩石损伤的发展岩石中渗流的各向异性规律。该模型也适用于岩体。     

塔克拉玛干沙漠公路气象灾害及其防御对策

通过对沙漠公路周围１６个气象站３０多年资料分析,结合近几年沙漠腹地的气象观测资料,指出大风、沙尘暴、高温等是沙漠公路一线主要的气象灾害,分析了灾害性天气的时空分布,并提出了相应的防御措施。     

Ambient vibration tests of a seven-story reinforced concrete building in Van Nuys, California, damaged by the 1994 Northridge earthquake

Results of two detailed ambient vibration surveys of a 7-story reinforced concrete building in Van Nuys, California, are presented. Both surveys were conducted after the building was severely damaged by the 17 January 1994, Northridge earthquake (M_L=5.3, epicenter 1.5 km west from the building site) and its early aftershocks. The first survey was conducted on 4 and 5 February 1994, and the second one on 19 and 20 April 1994, about one month after the 20 March aftershock (M_L=5.3, epicenter 1.2 km north–west from the building site). The apparent frequencies and two- and three-dimensional mode shapes for longitudinal, transverse and vertical vibrations were calculated. The attempts to detect the highly localized damage by simple spectral analyses of the ambient noise data were not successful. It is suggested that very high spatial resolution of recording points is required to identify localized column and beam damage, due to the complex building behavior, with many interacting structural components. The loss of the axial capacity of the damaged columns could be seen in the vertical response of the columns, but similar moderate or weak damage typically would not be noticed in ambient vibration surveys. Previous analysis of the recorded response of this building to 12 earthquakes suggests that, during large response of the foundation and piles, the soil is pushed sideways and gaps form between the foundation and the soil. These gaps appear to be closing during “dynamic compaction” when the building site is shaken by many small aftershocks. The apparent frequencies of the soil–foundation–structure system appear to be influenced significantly by variations in the effective soil–foundation stiffness. These variations can be monitored by a sequence of specialized ambient vibration tests.