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951.
Wan Zheng 《地震工程与工程振动(英文版)》2015,14(2):229-238
A simple cyclic elastoplastic constitutive model for sand is proposed based on the UH model for overconsolidated clay. The proposed model has the following features. First, in order to describe the stress-induced anisotropy in sand, a rotational hardening rule is introduced for the evolution of the yield surface axis with development of plastic deviatoric strain in the principal stress space. Second, the relationship between the rotational axis and stress-induced anisotropy is modeled by introducing the slope of rotational axis into the yield function. The fl atness of the yield surface can be determined by the slope of rotational axis. Finally, a revised unifi ed hardening parameter is proposed to incorporate the stress-induced anisotropy. The model capability in describing the cyclic response of sand is verifi ed by comparing the simulations with available test results. 相似文献
952.
Different values have been assigned to the ratio of the defl ection amplifi cation factor(Cd) to the response modifi cation factor(R) for a specifi ed force-resisting system in the seismic design provisions while the same application is defi ned for it. An analytical study of the seismic responses of several reinforced concrete frames subjected to a suite of earthquake records performed in this research indicate that the stories’ overstrength and stiffness distribution along the structural height can affect local defl ections more than global ones. Therefore, the Cd/R ratio is calculated based on the ratio of both maximum inelastic to maximum elastic displacements and interstory drifts. Due to damage concentration in some specifi c stories, the defl ection amplifi cation factor calculated based on inelastic interstory drifts was larger than that of the inelastic displacements. Consequently, a minimum value of 1.0 is recommended for the Cd/R ratio in order to estimate maximum inelastic drifts. The ratio of inelastic to elastic displacement was generally found to increase slightly along the structural height for the studied RC models. In addition, it was detected that the story damage indices of the studied RC frames decrease when the inverted value of inelastic interstory drift ratios are increased through a(negative) power form. 相似文献
953.
Continuum model is a useful tool for approximate analysis of tall structures including moment-resisting frames and shear wall-frame
systems. In continuum model, discrete buildings are simplified such that their overall behavior is described through the contributions
of flexural and shear stiffnesses at the story levels. Therefore, accurate determination of these lateral stiffness components
constitutes one of the major issues in establishing reliable continuum models even if the proposed solution is an approximation
to actual structural behavior. This study first examines the previous literature on the calculation of lateral stiffness components
(i.e. flexural and shear stiffnesses) through comparisons with exact results obtained from discrete models. A new methodology
for adapting the heightwise variation of lateral stiffness to continuum model is presented based on these comparisons. The
proposed methodology is then extended for estimating the nonlinear global capacity of moment resisting frames. The verifications
that compare the nonlinear behavior of real systems with those estimated from the proposed procedure suggest its effective
use for the performance assessment of large building stocks that exhibit similar structural features. This conclusion is further
justified by comparing nonlinear response history analyses of single-degree-of-freedom (sdof) systems that are obtained from
the global capacity curves of actual systems and their approximations computed by the proposed procedure. 相似文献
954.
Liverpool Bay is a region of freshwater influence which receives significant freshwater loading from a number of major English
and Welsh rivers. Strong tidal current flow interacts with a persistent freshwater-induced horizontal density gradient to
produce strain-induced periodic stratification (SIPS). Recent work (Palmer in Ocean Dyn 60:219–226, 2010; Verspecht et al. in Geophys Res Lett 37:L18602, 2010) has identified significant modification to tidal ellipses in Liverpool Bay during stratification due to an associated reduction
in pycnocline eddy viscosity. Palmer (Ocean Dyn 60:219–226, 2010) identified that this modification results in asymmetry in flow in the upper and lower layers capable of permanently transporting
freshwater away from the Welsh coastline via a SIPS pumping mechanism. Observational data from a new set of observations from
the Irish Sea Observatory site B confirm these results; the measured residual flow is 4.0 cm s−1 to the north in the surface mixed layer and 2.4 cm s−1 to the south in the bottom mixed layer. A realistically forced 3D hydrodynamic ocean model POLCOMS succeeds in reproducing
many of the characteristics of flow and vertical density structure at site B and is used to estimate the transport of water
through a transect WT that runs parallel with the Welsh coast. Model results show that SIPS is the dominant steady state,
occurring for 78.2% of the time whilst enduring stratification exists only 21.0% of the year and enduring mixed periods, <1%.
SIPS produces a persistent offshore flow of freshened surface water throughout the year. The estimated net flux of water in
the surface mixed layer is 327 km3 year
−1, of which 281 km3 year−1 is attributable to SIPS periods. Whilst the freshwater component of this flux is small, the net flux of freshwater through
WT during SIPS is significant, the model estimates 1.69 km3 year−1 of freshwater to be transported away from the coast attributable to SIPS periods equivalent to 23% of annual average river
flow from the four catchment areas feeding Liverpool Bay. The results show SIPS pumping to be an important process in determining
the fate of freshwater and associated loads entering Liverpool Bay. 相似文献
955.
结合深圳地铁2号线盾构过富水砂层施工实际,考虑流-固藕合水土本构关系,用FLAC3D软件建立了盾构施工数值分析模型。计算结果与工程实测数据对比验证了数值模型的合理性。进一步研究了盾构过富水砂层对地表不同位置建筑的影响:建筑物基础在隧道正上方时产生沉降最大且较均匀,水平位移最小;盾构机开挖下穿时建筑物差异沉降最大,建筑物倾向盾构开挖方向;建筑物基础横向上离隧道中心一倍隧道埋深时,建筑物水平移动最大,易受剪切破坏,倾向垂直盾构开挖方向,周边地表沉降差最大;建筑物离隧道中心横向距离超过两倍隧道埋深时,盾构开挖对建筑物基础沉降的影响较小,建筑物沉降与其周边地表沉降较均匀。 相似文献
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