Dynamic response of tunnels in stochastic soils by the boundary element method

A stochastic boundary element method (SBEM) is developed in this work for evaluating the dynamic response of underground openings excited by seismically induced, horizontally polarized shear waves under steady-state conditions. The surrounding geological medium is viewed as an elastic continuum exhibiting large randomness in its mechanical properties, which implies that the wave number of the propagating signal is a function of a random variable. Suitable Green's functions are proposed and used within the context of the SBEM formulation. More specifically, a series expansion for the Green's functions is employed, where the basis functions are orthogonal polynomials of a random argument (polynomial chaos). These are subsequently incorporated in the SBEM formulation, which employs the usual quadratic, isoparametric line elements for modeling the surfaces of the problem in question. Finally, this formulation is used for the solution of a few problems of engineering interest involving buried cavities (tunnels). We note that the present approach departs from earlier boundary element derivations based on perturbations, which are valid for ‘small’ amounts of randomness in the elastic continuum.     

Ultrathin graphitic carbon nitride nanosheets and graphene composite material as high-performance PtRu catalyst support for methanol electro-oxidation

Graphitic carbon nitride (g-C₃N₄) has been demonstrated as an advanced support material for Pt nanoparticles (NPs) due to its excellent stability and abundant Lewis acid for anchoring metal NPs. However, its non-conductive nature and low surface areas still impede its application in electrochemical fields. Herein, a π–π stacking method is presented to prepare graphene/ultrathin g-C₃N₄ nanosheets composite support for PtRu catalyst. The weaknesses of g-C₃N₄ are greatly overcome by establishing a 2D layered structure. The significantly enhanced performance for this novel PtRu catalyst is ascribed to reasons as follows: the homogeneous dispersion of PtRu NPs on g-C₃N₄ nanosheets due to its abundant Lewis acid sites for anchoring PtRu NPs; the excellent mechanical resistance and stability of g-C₃N₄ nanosheets in acidic and oxidative environments; the increased electron conductivity of support by forming a layered structure and the strong metal-support interaction (SMSI) between metal NPs and g-C₃N₄ NS.     

板柱节点冲剪破坏后的精细有限元分析

按实际结构构造建立了板柱节点的精细有限元模型，采用实体单元和梁单元分别模拟混凝土和钢筋，采用生死单元技术模拟冲剪过程中混凝土开裂和冲剪后的钢筋断裂。3类典型冲剪试验的模拟验证表明该方法可以准确模拟冲剪和冲剪后的位移和承载力。基于该模型对约束节点的冲剪受力全过程进行了进一步的分析，结果表明:面内约束的板柱节点试验中，整体性钢筋和受弯钢筋对冲剪后承载力贡献为42%和58%；提高配筋率对节点冲剪前后的刚度均提升显著，而板厚增加仅对节点冲剪前的承载力和刚度有显著提升；欧美澳中四国规范在计算约束节点冲剪强度值时至少仍有36%的承载力储备，现有冲剪后承载力计算方法低估了负弯矩钢筋贡献，其冲剪后强度的计算值也都低于试验值。     

Additional deepwater sampling of prey fish in Lake Michigan annual bottom trawl survey reveals new insights for depth distribution dynamics

Beginning in 2013, sites at the 128-m bottom depth contour were added to the sampling design of the annual Lake Michigan bottom trawl survey for prey fish, which has been conducted by the U.S. Geological Survey Great Lakes Science Center (GLSC) each fall since 1973, to better assess fish depth distributions in a changing ecosystem. The standard sampling design included bottom depths from 9 to 110 m, although the GLSC also sporadically conducted bottom trawl tows at the 128-m bottom depth contour during 1973–1988. Enactment of this new sampling design in 2013 revealed that mean biomass density of deepwater sculpins (Myoxocephalus thompsonii) at the 128-m depth exceeded the sum of mean biomass densities at shallower depths, indicating that the bulk of the deepwater sculpin population is residing in waters deeper than 110 m. Thus, our findings supported the hypothesis that the depth distribution of the deepwater sculpin population had shifted to deeper waters beginning in 2007, thereby explaining, at least in part, the marked decline in deepwater sculpin abundance since 2006 based on the standard sampling design. In contrast, our results did not support the hypothesis that the slimy sculpin (Cottus cognatus) population had shifted to deeper waters sometime after 2000. A portion of the burbot (Lota lota) population may have also shifted in depth distribution to waters deeper than 110 m after 2007, based on our results. Our findings have served as an impetus to further expand the range of depths sampled in our bottom trawl survey.     

阻尼器响应放大技术研究与应用进展

目前，阻尼器在工程结构减隔震控制领域的应用已极为广泛，但存在中小地震作用下阻尼器的位移和速度等较小时，阻尼器难以充分发挥耗能能力的问题。因此近年来阻尼器响应放大技术得到了国内外学者的广泛重视，并利用连杆机构、齿轮机构、杠杆机构、跨层支撑等提出了多种阻尼器响应放大装置。全面综述国内外阻尼器响应放大技术的研究和应用进展，包括装置构造和作用机理等。同时，分析现有阻尼器响应放大技术在遭遇极罕遇地震作用时阻尼器更容易失效等方面的不足，指出响应放大技术的研究和发展方向，以期为阻尼器响应放大技术的发展和极罕遇地震作用下确保工程结构的安全提供有效思路。     

Performance evaluation of spaceborne cryocooler micro-vibration isolation system employing pseudoelastic SMA mesh washer

A spaceborne cryocooler produces undesirable micro-vibration disturbances during its on-orbit operation, which is one of the main sources of degradation of the image quality of high-resolution observation satellites. Therefore, to comply with the strict mission requirement for the acquisition of high-quality images, micro-vibration disturbances induced by cryocooler operation need to be isolated. In this study, we proposed a spaceborne cryocooler micro-vibration isolator that employs a pseudoelastic shape memory alloy (SMA) mesh washer, which guarantees vibration isolation performance in a severe launch vibration environment while effectively isolating the micro-vibrations from the cryocooler on-orbit. Basic characteristics of the cryocooler assembly integrated with the proposed isolators were measured through static tests and free vibration tests. The effectiveness of the isolator design was demonstrated by the micro-vibration measurement tests under qualification temperature limits.     

Ultrasonic broadband signals monitoring of glass-fiber reinforced cement (GRC) bending tests

In this study, complete ultrasonic monitoring of Glass-fiber Reinforced Cement plates under bending tests was addressed. In this kind of experiment, the mechanical properties of the specimen continuously change during the test, thus, the acquisition time of the ultrasonic signals is a critical variable. In order to overcome this drawback, a new ultrasonic procedure based on broadband signals (chirp) has been applied. Following this line of thought, the analysed ultrasonic parameters have been split into the parameters that only depend on time, and those that depend on both time and frequency. In particular, the frequency dependent attenuation parameter allows characterizing the evolution of the plate being damaged over a wide frequency range and significantly detecting the main two events happening during the experiment: the first crack and the maximum stress point. In short, this paper demonstrates the suitability of ultrasonic broadband signals for characterizing fiber-reinforced cementitious composites under bending stress.     

巨-子型结构控制体系抗震性能的试验研究

研究开发了一种新型的高阻尼比减隔震支座,设计了一个与实际工程结构相接近的Y字型巨-子结构钢模型,并分别对传统巨-子型结构抗震体系和采用新型减隔震支座连接的控制体系进行了振动台试验。结果表明,与传统的巨-子型结构抗震体系相比,新型的巨-子结构控制体系在地震作用下的反应显著降低,具有良好的减震效果。由试验观察到的该控制体系减震机理与理论分析结果相吻合,可为工程设计和应用提供参考。     

实时混合试验的自适应线性二次高斯时滞补偿方法研究

时滞补偿是实时混合试验(RTHS)成功非常关键的环节,传统时滞补偿方法主要针对建筑结构实时混合试验设计,主要关注低频的时滞补偿能力,但航空、交通等领域的结构频率较高,甚至超过10 Hz,高频信号对结构响应的影响不可忽略,较高的结构频率要求更小的时滞保证稳定性,对其进行实时混合试验需要在较宽频带上实现时滞补偿。该文提出了自适应线性二次高斯算法(ALQG)提高对高频信号的时滞补偿能力和稳定性。采用不同轨道梁截面刚度参数的桥梁作为数值子结构进行实时混合试验,检验ALQG算法在车桥耦合系统RTHS中时滞补偿的有效性和稳定性,并与采用ATS的结果进行比较。试验结果表明:ALQG算法能够较好补偿RTHS中的高频信号,补偿效果优于ATS算法。     

带约束拉杆壁式钢管混凝土柱拟静力试验研究

为避免在多高层钢结构建筑中柱凸出填充墙,提出了设置约束拉杆的截面高宽比为3.0的壁式钢管混凝土柱,通过2个带约束拉杆壁式钢管混凝土柱足尺试件的拟静力试验,研究其抗震性能。试验结果表明:约束拉杆可以有效抑制两侧柱壁局部屈曲;试件破坏模式为柱底四周钢板受压鼓曲、钢板间纵向焊缝撕裂;滞回曲线较为饱满,无明显的捏拢现象;屈服位移角在1/147 rad~1/121 rad,极限位移角在1/51 rad~1/41 rad,位移延性系数在2.61~3.11,承载力退化系数在0.86~1.04,破坏时的等效粘滞阻尼系数在0.3以上。在试验研究的基础上,建立了该类试件的精细化有限元模型,对比可知有限元结果与试验结果吻合较好,验证了模型的正确性,可为此类构件的数值模拟提供参考。研究成果丰富了矩形钢管混凝土组合构件的类型,促进装配式钢结构建筑的发展。