SIMULATION OF RIDGE-WEATHERING EFFECTS ON THE GROUND MOTION CHARACTERISTICS

Seismic responses of weathered ridge model with various types of weathering materials/soils and thickness were simulated, using double-couple point shear dislocation sources to evaluate the significance of ridge-weathering effects on the ground motion characteristics. 2.5D finite difference modeling was adopted for simulating the ground motion using parsimonious staggered grid scheme. The analysis of responses of weathered and non-weathered ridge models reveals that surface waves were generated near the top of the ridge. The surface waves were not dominating on the top of the ridge but at some lower elevation. Results also revealed ground motion amplification with elevation. Maximum amplitude of ground displacement was observed on the top of the ridge, when it was not very much weathered, but the reverse was the case (surface waves were dominating near the base) when weathering velocity was more than three times lesser than the underlying rock. An important conclusion was drawn based on simulated results that the thickness of weathering in terms of wavelength (λ) play a vital role in the generation of very strong surface wave with long duration, i.e. when the thickness is equal to or more than λ/8. The decrease of weathering-velocity further increased the amplitude and duration of surfaces waves. On the other hand, surface waves caused by the ridge itself or by weathered materials having thickness less than λ/12 have amplitudes similar or somewhat more than the incoming waves and with much smaller duration. Therefore, special measure for weathering thickness and its velocity is recommended on the basis of simulated results during the construction of buildings on the ridge topography.     

GROUND MOTION DOMINANT FREQUENCY EFFECT ON THE DESIGN OF MULTIPLE TUNED MASS DAMPERS

Utilising the Kanai-Tajimi and Clough-Penzien spectrums and the pseudo-excitation algorithm in the frequency domain, parametric study is performed to examine the effect of the dominant frequency of ground motion on the optimum parameters and effective-ness of multiple tuned mass dampers (MTMD) with identical stiffness and damping coefficient but with unequal mass. The examination of the optimum parameters is con-ducted through the minimisation of the minimum values of the maximum displacement and acceleration dynamic magnification factors of the structure with the MTMD. The optimum parameters of the MTMD include the optimum frequency spacing reflecting the robustness, the average damping ratio and the tuning frequency ratio. Minimisation of the minimum values of the maximum displacement and acceleration dynamic mag-nification factors, nondimensionalised respectively by the maximum displacement and acceleration dynamic magnification factors of the structure without the MTMD, is used to measure the effectiveness of the MTMD. The results indicate that in the two cases where both the total mass ratio is below 0.02 and the total mass ratio is above 0.02, but the dominant frequency ratio of ground motion is below unity (including unity), the earthquake ground motion can be modelled by a white noise. It is worth noting, however, that for the total mass ratio above 0.02, the Kanai-Tajimi Spectrum or Clough-Penzien spectrum needs to be employed to design the MTMD for seismic structures in situations where the dominant frequency ratio of ground motion is beyond unity.     

EMPIRICAL EVALUATION OF SITE EFFECTS BY MEANS OF H/V SPECTRAL RATIOS AT THE LOCATIONS OF STRONG MOTION ACCELEROMETERS IN ISRAEL

Acceleration data from local and regional earthquakes is of prime importance in evaluating the seismic hazard. Consequently, strong motion accelerometers are currently installed at more than 60 locations in Israel. We have explored the possibility of site amplification effects at 10 sites where local earthquakes triggered strong motion accelerometers by integrating empirical and analytical estimations. Implementing H/V spectral ratio techniques using 15 accelerograms from nine earthquakes, 105 seismograms shear-wave records of 35 local and regional earthquakes and seismograms of microtremors were used in the empirical evaluations. The subsurface models were constructed by integrating available geological and geophysical information at the analysed site with empirically evaluated site response functions. Amplification effects of factor 3-6 are observed at various frequencies in the 0.8-6.0 Hz band. Through the analysis process it became evident that the instant availability of many useful time windows of microtremors provides systematic estimations of the fundamental resonance frequency of each site and their associated amplification levels, which are similar to those obtained from H/V spectral ratios of seismograms and accelerograms and to those inferred from the subsurface geology. Analytical transfer functions should be reviewed with respect to empirical site response evaluations. Estimations that are based on only one approach may be totally misleading.     

SIGNIFICANT GROUND MOTION PARAMETERS FOR EVALUATION OF THE SEISMIC PERFORMANCE OF SLENDER MASONRY TOWERS

The evaluation of seismic risk of masonry monuments requires to study the combination of vulnerability and hazard. In the present work, the global seismic response of slender masonry towers has been studied by means of a specific 3-D fibre model. Accounting for the particular behaviour of such structures, the hazard should also be described by a suitable measure of intensity of the seismic action. A variety of different parameters relating with the ground acceleration recordings have been investigated for what regards their correlation with the damage indicators of the model. The combination of the peak ground velocity of the horizontal component and of the significant duration is an effective measure of intensity. This measure can be improved by considering the accord of the frequency content of the ground motion with the dynamical characteristics of the tower. Since in some cases the effect of the vertical component proved to be important, a further improvement can be obtained by taking into account also the vertical ground motion intensity.     

NOTE ON THE INCLUSION OF SITE CLASSIFICATION INFORMATION IN EQUATIONS TO ESTIMATE STRONG GROUND MOTIONS

Two main regression methods have been proposed for using site category information within ground motion prediction equations, these are: (a) joint estimation of the site category coefficients and the magnitude and distance coefficients; or (b) estimation of site category coefficients by using the residuals from the equation derived without considering soil conditions. Method (a) requires each record be assigned a site category whereas for method (b), because it relies on residuals, site information can be missing for some records. This short note finds that if the mean of the transformed distances within each site category is the same then the two methods give the same site coefficients. If, however, these means are significantly different then method (b) can yield incorrect site coefficients.     

COUPLED P-Y T-Z ANALYSIS OF SINGLE PILES IN COHESIONLESS SOIL UNDER VERTICAL AND/OR HORIZONTAL GROUND MOTION

Various approaches are currently used for the analysis of piles under vertical and lateral loading. Among these, the beam-on-a-nonlinear Winkler foundation (BNWF) approach using published P-y, T-z and Q-z curves is widely used in practice. In this approach, the P-y and T-z responses are generally uncoupled from each other. The objective of this paper is to investigate the influence that the coupling of the P-y and T-z responses has.on the cyclic and dynamic response of piles in cohesionless soil. A cyclic model is first developed and a parametric study is conducted to investigate the effect the initial confining pressure, angle of wall friction and effective vertical stiffness have on the lateral cyclic hysteretic response. A dynamic model is then developed, and used to study the response of a single pile in cohesionless soil under horizontal and/or vertical ground motion. Results from the parametric study showed that the three parameters did not have a significant influence on the lateral cyclic hysteretic response. Under horizontal and/or vertical ground motion, the horizontal ground motion was observed to dominate the inertial interaction response, and significantly affected both the horizontal and vertical displacement response, mainly due to second-order P-Δ and gapping effects.     

基于社会学视野的黄山市汤口镇旅游城市化特征和机制研究

改革开放以来,旅游城市化成为汤口镇城市化发展的主要路径之一。基于社会学视野考察黄山市汤口镇旅游城市化发展特征并探讨其机制。发现伴随旅游业发展,汤口镇产业结构由第一产业为主向以旅游业占主导的第三产业为主的产业结构转变,居民收入主要来自于旅游业,居民就业主要向旅游业及其相关产业集中;居民的居住条件、生活习惯和邻里关系呈现城市社区特点,居民的经营理念、教育观念和生活态度等思想观念发生很大转变,显现出城市居民的特点;居民的社会角色向现代企业家转变;汤口镇城镇性质和职能也由农业社区向旅游社区演变。而优越的区位条件、良好的资源禀赋、政府的推动以及居民的积极参与等是汤口镇旅游城市化发展的主要因素。     

港澳与珠江三角洲文化特色及其关系比较

港澳文化与珠江三角洲文化都以岭南文化为本根,由于历史原因,形成不同文化特色;港澳文化与珠江三角洲文化之间是互动关系,这种互动性在时空分布上是一个动态过程;港澳与珠江三角洲文化的交流与融合,最终将导致文化的趋同。     

重庆市公租房居民职住时空特征研究

近年来公共租赁住房政策成效显著,住房困难人群安居问题得到明显改善,其乐业与否也逐步受到关注。本文以重庆市主城区为例,选取网络公示配租数据,探讨2015—2020年公租房配租居民就业空间分布以及职住分离演变特征。研究发现：①公租房居民就业少量分散于地铁站点以及公租房小区附近,多数居民就业分布在内外以内,呈中心大集聚、边缘小分散态势。②2015—2020年就业集聚于内环以内的态势未发生改变,局部变化受到了城市发展布局与配租数量的影响。③公租房居民通勤平均直线距离在14—17 km之间,距离经历小幅下降后持续上涨,居民内部分化明显,部分人群距离超过30 km,面临愈趋严重的职住分离问题。④居民职住分离程度在个体和社区层面上具有差异性,区位条件好的公租房小区居民职住分离程度较低,男性和收入较高的居民分离程度更高。