武汉城市桥梁管理与变形监测

本文根据国家《公路养护技术规范》(JTJ073-96)中对桥梁运营期间的管理要求,结合武汉市几座跨越长江和汉江的各类大型和特大型桥梁的结构特点,以及为了有效地保证大桥的行车安全,阐述了大桥管理中应实施变形监测主要内容;并结合武汉长江二桥等桥梁的监测实践,验证了变形监测在运营管理中的作用。文中还介绍了城市桥梁管理中的有关组织体系。     

The effect of plastic fines on the pore pressure generation characteristics of saturated sands

Pore water pressure generation during earthquake shaking initiates liquefaction and affects the shear strength, shear stiffness, deformation, and settlement characteristics of soil deposits. The effect of plastic fines (kaolinite) on pore pressure generation in saturated sands was studied through strain-controlled cyclic triaxial tests. In addition to pore pressure generation, this experimental study also focused on evaluating the threshold shear strain for pore pressure generation and the volumetric compressibility of specimens during pore pressure dissipation. The results reveal that specimens having up to 20% plastic fines content generated larger values of pore water pressure than clean sand specimens. At 30% fines content, the excess pore water pressure decreased below that of clean sand. The threshold shear strain, which indicates the strain level above which pore pressures begin to generate, was assessed for different kaolinite–sand mixtures. The threshold shear strain was similar for 0–20% fines (γ_t0.006–0.008%), but increased to about 0.025% for 30% fines. The volumetric compressibility, measured after pore pressure generation, was similar for all specimens. The transition of behavior at fines contents between 20% and 30% can be attributed to a change in the soil structure from one dominated by sand grains to one dominated by fines.     

Effect of linear alkylbenzene sulfonate (LAS) and atrazine on marine microalgae

Five marine microalgae (Tetraselmis chuii, Rhodomonas salina, Chaetoceros sp., Isochrysis galbana (T-iso) and Nannochloropsis gaditana), in the same biovolume quantity, were exposed to 72h growth-inhibition tests with atrazine and LAS. In all cases, the inhibition effect of atrazine was higher than that of LAS up to two orders of magnitude higher in the case of T. chuii. In a second part of the study, initial cellular densities for each microalga strain and fixed organic compound concentration were varied, and results show density has a clear influence in growth inhibition tests. Finally, the sum of all data obtained in the study was expressed in terms of "toxic cellular quota" (mass of chemical substance per cell). The result was a sigmoid curve with a good fit, including the two main factors in toxicity tests, initial cellular density and contaminant concentration. This toxic cellular quota exhibits a general tendency to increase with cell volume/size.     

Transient 3D numerical simulations of column collapse and pyroclastic density current scenarios at Vesuvius

Numerical simulations of column collapse and pyroclastic density current (PDC) scenarios at Vesuvius were carried out using a transient 3D flow model based on multiphase transport laws. The model describes the dynamics of the collapse as well as the effects of the 3D topography of the volcano on PDC propagation. Source conditions refer to a medium-scale sub-Plinian event and consider a pressure-balanced jet. Simulation results provide new insights into the complex dynamics of these phenomena. In particular: 1) column collapse can be characterized by different regimes, from incipient collapse to partial or nearly total collapse, thus confirming the possibility of a transitional field of behaviour of the column characterized by the contemporaneous and/or intermittent occurrence of ash fallout and PDCs; 2) the collapse regime can be characterized by its fraction of eruptive mass reaching the ground and generating PDCs; 3) within the range of the investigated source conditions, the propagation and hazard potential of PDCs appear to be directly correlated with the flow-rate of the mass collapsing to the ground, rather than to the collapse height of the column (this finding is in contrast with predictions based on the energy-line concept, which simply correlates the PDC runout and kinetic energy with the collapse height of the column); 4) first-order values of hazard variables associated with PDCs (i.e., dynamic pressure, temperature, airborne ash concentration) can be derived from simulation results, thereby providing initial estimates for the quantification of damage scenarios; 5) for scenarios assuming a location of the central vent coinciding with that of the present Gran Cono, Mount Somma significantly influences the propagation of PDCs, largely reducing their propagation in the northern sector, and diverting mass toward the west and southeast, accentuating runouts and hazard variables for these sectors; 6) the 2D modelling approximation can force an artificial radial propagation of the PDCs since it ignores azimuthal flows produced by real topographies that therefore need to be simulated in fully 3D conditions.     

高应力下砾质心墙料切线模量研究

使用高压大型三轴仪,对某300 m级土石坝的砾质土心墙料进行了最高围压5 MPa的三轴试验。试验结果表明砾质土的应力-应变关系符合双曲线关系,抗剪强度包络线呈非线性。根据参数的物理意义,初始模量Ei应在尽可能小的应变范围内取值,最大主应力差 应在大应变范围内取值,且实际工程的应变在1 %左右,建议在?a= 0 %～3 %下取Ei值,在?a = 5 %～15 %下取 值,数据拟合表明建议取值法比传统取值法拟合度高。由于试验的围压范围较大,提出把围压分0.2～1.0 MPa,1.5～3.0 MPa,3.5～5.0 MPa三段分别取切线模量,通过回归证明拟合较好。     

多筒系缆平台原型顶升试验研究

描述了位于渤海辽东湾93地区人工岛靠船系缆平台原型顶升的试验过程,系缆平台的基础采用三筒结构型式,这也是我国应用于海洋工程的第一座多筒型基础平台。尽管海上施工对筒型基础沉/拔过程有了一定的经验,但筒型基础平台在长期使用后的拔出复用还没有任何的工程经验,此次顶升试验验证了筒型基础平台移动复用的可行性,利用主要测试结果给出了筒基上拔顶升力的相关分析,对海上原型结构顶升施工的可行性及筒型基础使用过程中的动态抗拔力的变化具有直接的参考意义。     

固结比对砂土动剪切模量及地表反应谱的影响

采用共振柱试验方法,研究了固结比对砂土最大动剪切模量以及对动剪切模量比与剪应变非线性关系的影响。通过土层地震反应计算,初步给出了这种影响对地表反应谱作用的估计。对福建标准砂和哈尔滨砂进行了系统试验,提出了计算不同固结比砂土最大动剪切模量的建议公式,公式显示固结比kc>1、最大动剪切模量较kc=1时的增长程度明显比Hardin公式要大。同时,给出了固结比对动剪切模量比与剪应变非线性关系及其对地表反应谱的影响。结果表明,固结比对砂土动剪切模量比与剪应变非线性关系有一定影响。随着固结比增加,模量比非线性关系曲线有一定提高,在强地震动作用下的土层反应分析中应考虑实际固结比的影响。     

Hybrid simulation of a partial-strength steel–concrete composite moment-resisting frame endowed with hysteretic replaceable beam splices

This paper deals with the seismic response assessment of a steel–concrete moment-resisting frame (MRF) equipped with special dissipative replaceable components (DRCs): the dissipative replaceable beam splices (DRBeS), which combine large energy dissipation with ease of replacement. The evaluation of the full potential of DRBeS requires a system-level investigation, that is, a six-story MRF, whereby the hysteretic effects of beam splices partial-strength joints are considered on the global response of the structural system. Therefore, an OpenSees finite element (FE) frame model, based on previous experimental campaigns with cyclic displacements on partial-strength joints, and a Matlab model validated on OpenSees, were used for a more complex experimental activity via hybrid simulation (HS). The aim of the simulations was twofold: (i) to increase knowledge of the non-linear behaviour of steel-concrete composite partial-strength MRFs; and (ii) to study the effectiveness of the DRBeS components for increasing the recovery of functionality after a major seismic event. Therefore, to appreciate the performance of the partial-strength MRF at damage limitation (DL), significant damage (SD) and near collapse (NC) within the performance-based earthquake engineering (PBEE) approach, HSs were carried out. In such instances, the ground floor was physically tested at full scale in the laboratory and the remainder of the structure was numerically simulated. Relevant results showed that the DRBeS were capable of dissipating a significant amount of hysteretic energy and of protecting the non-dissipative parts of partial-strength joints and the overall structure with an ease of replacement.     

新型动力安装锚水动力学特性模型试验研究

相比于已有动力锚(鱼雷锚、多向受荷锚等),新型轻质动力安装锚借助助推器安装,具有质量轻、埋深大、承载效率高、在海床中下潜容易等特点。良好的水动力学特性(较小的拖曳阻力系数及稳定的下落垂直度)是确保动力安装锚准确、有效地安装到指定地点并贯入到设计深度的前提。通过4组10个工况的模型试验,研究了轻质动力安装锚的终端速度和拖曳阻力系数,及轻质动力安装锚和助推器的组合锚在水中自由下落时的方向稳定性。试验结果表明:优化后轻质动力安装锚的拖曳阻力系数为0.51~0.55,这有助于提高组合锚在水中的下落速度,从而提升组合锚的沉贯深度;增大助推器尾翼展弦比和选用轻质材料制作尾翼能减小组合锚的下落偏角,提高组合锚的方向稳定性。     

薄壁型钢管/胶合竹板复合柱抗震性能试验

对9根带约束拉杆的方形薄壁型钢管/胶合竹板复合空芯柱(SBCCB)试件进行低周反复拟静力测试,考察SBCCB的破坏过程和形态,分析试件的长细比、胶合竹净横截面面积、截面组合方式对其受力和抗震性能影响。结果表明:SBCCB破坏形态主要为柱脚胶合面的开裂破坏和胶合竹板断裂破坏,截面组合方式对其破坏模式有显著影响。SBCCB试件有较好的弹性变形能力和抗震耗能性能,增大复合柱截面尺寸和长细比能改善抗震性能;约束拉杆有效保证了试件的整体性,抑制基体开胶破坏,间接提高了抗震性能。