Innovative testing technique of rock subjected to coupled static and dynamic loads

A new testing technique, which relates the physical stress state of rock subjected to simultaneous coupled static and dynamic stresses, is presented. The method involves modification of a split Hopkinson pressure bar, such that the test specimen is subjected to coupled axial static pre-stress, axial impact loading, and optional confining pressure. Tests on siltstone specimens with different coupling loads showed that the strength of the specimens under coupling loads was higher than their corresponding individual static or dynamic strengths. In the grade size distribution, the percentage of small size particles of fractured specimen increases with higher coupling loads. The strength of rock under coupling loads decreases rapidly when the axial pre-compression stress is greater than 70% of the static strength of rock (with identical impact loading). However, with constant axial pre-compression stress and increasing impact loading, the strength of siltstone increases initially and reaches a maximum constant value.     

Non-preloaded bolted ring flange connections subjected to static loads

The ultimate behaviour of bolted connections in tubular members, such as chimneys, is studied and the interaction M-N curves are plotted, taking into account the main parameters of the problem. The proposed methodology is based on a classification of failure patterns of the L-stub main component (segmental behaviour) under compressive or axial tensile forces, considering non-preloaded bolts. Besides, the results of the theoretical analysis of the main L-shape component ultimate behaviour are compared with the corresponding obtained through finite element analysis of the constructed 3D models. Extending the local behaviour of the individual L-shape segments along the ring flange, the ultimate bearing capacity is derived, for each level of axial force, through a proposed analytical procedure and the corresponding interaction M-N curves are obtained. The parameters considered are the size and thickness of the flange and the tubular shell, the size and the location of the bolts, the quality of the materials and the amount of the applied axial load on the tubular element.     

Stability analysis of shallow tunnels subjected to eccentric loads by a boundary element method

In this paper, stress behavior of shallow tunnels under simultaneous non-uniform surface traction and symmetric gravity loading was studied using a direct boundary element method(BEM). The existing fullplane elastostatic fundamental solutions to displacement and stress fields were used and implemented in a developed algorithm. The cross-section of the tunnel was considered in circular, square, and horseshoe shapes and the lateral coefficient of the domain was assumed as unit quantity. Double-node procedure of the BEM was applied at the corners to improve the model including sudden traction changes. The results showed that the method used was a powerful tool for modeling underground openings under various external as well as internal loads. Eccentric loads significantly influenced the stress pattern of the surrounding tunnel. The achievements can be practically used in completing and modifying regulations for stability investigation of shallow tunnels.     

轴向荷载作用下梁结构动力特性的随机分析

传统梁结构动力特性分析方法由于忽略结构参数的不确定性而不能满足实际工程设计需要,因此,将响应面法(RSM)、有限元法(FEM)和蒙特卡罗法各自的优点相结合,提出一种新的结构随机动力特性计算方法-混合分析法。该方法的最大特点是有效地利用响应面法(RSM)、有限元法(FEM)和蒙特卡罗法(MCS)各自的优点,并将其充分地结合起来。然后,运用该方法分析一简支梁自振频率的统计值。结果表明基于确定性模型的梁结构频率响应分析仅能给出频率响应的均值,忽略结构随机参数对频率响应的影响。为获得准确的频率响应值,有必要在今后的结构动力特性分析中考虑结构参数随机性的影响。最后,进行梁结构随机动力特性计算的敏感性因素分析,并指明影响梁结构动力特性的主要随机因素。     

Analysis and optimization of laminated composite circular cylindrical shell subjected to compressive axial and transverse transient dynamic loads

Optimization is one of the important stages in the design process. In this paper the genetic algorithms method is applied for weight and transient dynamic response and two constraints including critical buckling loads and principle strains optimization of laminated composite cylindrical shells. The multi-objective function seeks the minimum structural weight and transient dynamic response. Nine design variables including material properties (fibre and matrix), volume fraction of fibre, fibre orientation and thickness of each layer are considered. In analytical solution, vibration of composite circular cylindrical shells are investigated based on the first-order shear deformation shell theory. The boundary conditions are assumed to be fully simply support. The dynamic response of the composite shells is studied under transverse impulse and axial compressive loads. The modal technique is used to develop the analytical solution of the composite cylindrical shell. The solution for the shell under the given loading conditions can be found using the convolution integrals. An example of simply supported laminated composite cylindrical shells is given to demonstrate the optimality of the solution obtained by the genetic algorithms technique. Results are shown that the weight coefficient of multi-objective function and the type of the constraints have considerable effect on the optimum weight and dynamic response.     

隧洞岩爆风险评估应用研究

结合岩爆发生的条件及影响因素,从岩性、地质构造、隧洞埋深等方面,对岩爆发生的风险程度进行了综合评估,并在准确的风险评估基础上,采取合理的施工措施有效防治岩爆的发生,进而保障施工人员生命安全,减少设备财产损失。     

循环荷载下天津吹填土动应力应变关系研究

通过对天津滨海吹填土开展的循环荷载下的室内动三轴试验,研究了振动频率、固结比、动应力幅值的大小、静偏应力、循环振次等因素对动应力—应变关系的影响,试验结果表明,天津滨海吹填土存在临界循环应力比,且与固结围压成线性关系,以临界动应力作为归一化因子,建立了考虑固结围压与循环振次的动应力—应变关系曲线方程。     

The behaviour of tunnels at great depth under large static and dynamic pressures

The main objective of the paper is to illustrate the range of conditions that can result from the presence of tunnels in, and the activity of driving tunnels through, competent hard rock under conditions of very high rock pressure. After briefly examining differences and similarities between the support design philosophies applied in these circumstances and those prevailing in most civil engineering tunnels, the paper goes on to suggest concepts that might prove useful in civil works under great depth of cover. The conviction is clearly explained and illustrated that the rock-anchoring tendons used under these conditions must possess sufficient yieldability to avoid tensile fracture under conditions of large and violent rock deformation. The containment support must also be appropriately compliant and must be properly coupled to the retaining rock tendons. Environmental impact statement: The environment in which tunnelling is undertaken through hard rock at great depth is harsh and sometimes dangerous. It has the potential to affect the health and safety of the workforce who constructed the tunnel and continue to use it after completion. There is no possibility that the underground situation can have any effect on the surface environment or any direct impact on the health and safety of its community. Insofar as they would have the objective of controlling the fracturing and potential disruption of the surrounding rock, the technologies implied or explicity advocated in the paper would improve the underground environment and substantially benefit the safety of the workforce.     

Analysis and design of steel-concrete composite sandwich systems subjected to extreme loads

This paper presents the design guide based on analytical, numerical and experimental investigation of Steel-concrete-steel (SCS) sandwich structural members comprising a lightweight concrete core with density ranged from 1300 to 1445 kg/m³ subjected to static, impact and blast loads. The performance of lightweight sandwich members is also compared with similar members with normal weight concrete core and ultra high strength concrete core (f _c = 180 MPa). Novel J-hook shear connectors were invented to prevent the separation of face plates from the concrete core under extreme loads and their uses are not restricted by the concrete core thickness. Flexural and punching are the primary modes of failure under static point load. Impact test results show that the SCS sandwich panels with the J-hook connectors are capable of resisting impact load with less damage in comparison than equivalent stiffened steel plate panels. Blast tests with 100 kg TNT were performed on SCS sandwich specimens to investigate the key parameters that affect the blast resistance of SCS sandwich structure. Plastic yield line method is proposed to predict the plastic capacity and post peak large deflection of the sandwich plates. Finally, an energy balanced model is developed to analyze the global behavior of SCS sandwich panels subjected to dynamic load.     

Ships and tunnels: particular loads

The author deals with the impact of three types of phenomena on the design and immersed tunnels: (1) the occurrence of sinking or sunken ships; (2) a falling anchor; (3) a dragging anchor. The article discusses ways of calculating the effects of these phenomena, and design factors that should be considered to minimize these effects.     

Energy absorption capability of fibreglass composite square frusta subjected to static and dynamic axial collapse

The crashworthy behaviour of square frusta of fibreglass composite material subjected to axial compression at various strain rates is reported. The effect of specimen geometry and the loading rate on the energy absorbing capability was experimentally studied. The mechanics of the axial crumbling process from macroscopic and microscopic points of view were also investigated theoretically and experimentally. The collapse modes at macroscopic and microscopic scale during the failure process were observed and analysed. A theoretical analysis of the observed stable collapse mechanism of the components crushed under axial compression, for calculating crushing loads and energy absorbed during collapse, is proposed. A good agreement between theoretical and experimental results was obtained indicating the efficiency of the theoretical model in predicting the energy absorbing capacity of the collapsed shell.     

On the shear failure mode of granular column embedded unit cells subjected to static and cyclic shear loads

Since the initial conception of geosynthetic encased columns (GECs), exhaustion of column capacity due to vertical loads in bulging and punching failure modes were readily recognized. This lead to a vast majority of the available research on GECs to be about the behavior of columns under the action of vertical loads. Recently, two other likely and perhaps more dominant failure modes for granular columns namely, shear and bending failure modes, were identified. The purpose of this paper is to study the behavior of unit cells containing ordinary stone columns (OSCs) and GECs under static and cyclic lateral loads where shear failure of the column is imminent. 1-g physical tests are conducted with a novel apparatus, designated as Unit Cell Shear Device (UCSD), to model the behavior of the unit cells located close to the toe of an embankment where OSCs and GECs experience significant lateral loading. Overall failure envelope and strength parameters for GECs with varying reinforcement stiffnesses are quantified under static and cyclic lateral loading conditions. The distribution and magnitude of reinforcement strains in horizontal (hoop) and vertical direction of the columns are also considered.     

连续刚构桥静动载试验研究

介绍了预应力混凝土连续刚构桥静动载试验的主要内容和测点布置以及理论计算的方法等，并给出了试验中的3个主要工况的理论与试验结果对比值，最后得出了有益的结论。