Gongcheng Kexue Yu Jishu/Advanced Engineering Science

The bolted prefabricated concrete wall is widely used in construction due to its simple connection and rapid construction. The quasi-static tests of seven full-scale dry-type bolted prefabricated concrete walls (including four steel-plate-type bolted walls and three through-connection-type bolted walls) were conducted. The test results indicated that the bolted prefabricated wall would spread out at horizontal connection firstly and then the wall had rigid rotation, resulting in a lower lateral stiffness than the cast-in-place wall panel. Based on the elastic theoretical researches and finite numerical analyse, the horizontal deformation feature of the bolted prefabricated concrete wall was revealed, and the effect factors of lateral stiffness were analyzed. Moreover, the calculation formula of initial lateral stiffness of bolted prefabricated concrete wall was derived and its reliability was verified by numerical analyse and test results. In addition, through parameter analyse, a simplified calculation formula for initial lateral stiffness reducing the coefficient of bolted prefabricated concrete wall considering four effect factors (steel ratio of connection, height-width ratio of wall, axial compression ratio, and relative position of connection) was proposed. The error between the results by simplified formula and numerical analysis results is within 20%, indicating that the predicated results by the proposed simplified formula have high precision

The stability of coastal soft soil stratum is dramatically affected by external construction. To clarify the disturbance mechanism of the shallow shield tunnel engineering to the stratum, a refined numerical model for simulation of shield dynamic excavation was established based on the finite difference scheme, and the disturbance effect of every construction factor on the stratum was studied according to the modeling results. In the model, the combined effects of four factors on surrounding soil, including cutter head friction, excavation supporting force, grouting pressure, and shield friction, were considered. Referring to the behavior change of the grouting layer in the practical project, the relationship between pressure dissipation and slurry solidification during the shield tail grouting was divided into three stages to simulate the flowing state, the initial setting state and the final setting state of the slurry, respectively, and the corresponding parameters were sectionally assigned to the grouting layer of the newly-built tunnel and adjusted in real-time along with the excavation process. This model can realistically reflect the whole process of shield tunneling and realize the refined simulation of the construction. The numerical model was verified by comparison with the results from the field monitoring of the shield tunnel project with 1.0D (D is the outer diameter of the tunnel) burial depth in Xiamen Metro, and the influence of the above four construction factors on the soft soil stratum disturbance during the shallow excavation process was calculated and compared, and the effect of the factors on the disturbance deformation was summarized. The results show that the cutter head pushing causes the radial expansion of the forward soil. In the grouting process, a settlement groove is formed within 1.0D on both sides of the excavation space, and the near-field rebound and far-field expansion occur to the soil lateral displacements on two sides of the tunnel during the solidification of the grouting layer. The increase of the cutter head friction and shield friction will further aggravate the stratum disturbance deformation, and with the increase of the excavation supporting force and grouting pressure, the surface settlement slightly slows down and the stratum lateral displacement significantly increases. The results are of guiding significance for disturbance prediction and parameter selection in shallow shield excavation

The reliability of three-dimensional discrete element numerical simulation of granular materials depends on the reasonable calibration of mesoscopic parameters. At present, systematic research on the calibration method of mesoscopic parameters is lacking. Based on the comparative analysis of indoor direct shear test and numerical simulation, the correlation between the macroscopic mechanical parameters of granular materials and the mesoscopic parameters of particles was revealed. Besides, the calibration method of the meso parameters of the numerical simulation of granular materials was proposed, and the rationality of the calibration method was verified. The research result showed that: in the linear model, the macro elastic constant of the sample was positively correlated with the normal contact stiffness of the particles, but not sensitive to the change of the tangential contact stiffness. Based on this, the calibration method of contact stiffness (normal and tangential) of particles was proposed. The shear stress-shear displacement curve of the numerical direct shear test was well agreed with the experimental value, so the reliability and rationality of the calibration method were verified; Through the numerical test of the direct shear of gravel, it was found that the internal force chain network of the particles deflected from the vertical direction to the diagonal direction of the shear box with the increase of shear displacement, and the shear shrinkage and expansion occurred with the change of the overall velocity field of the particles during the shear process. The meso parameter calibration method proposed was used to conduct a numerical simulation of an indoor landslide motion test. The morphology of landslide gravel accumulation in the numerical simulation was consistent with the indoor test result, which verified the applicability of the calibration method in the simulation analysis of accumulated gravel landslide.

In the real world, many problems have the need to conduct relevant operations at a specific time. Timed-release encryption (TRE) is a cryptographic primitive in which the sender specifies the decryption time of the receiver, which can meet the above requirement. To address the problem that the current TRE schemes based on the periodic broadcast time trapdoor of the non-interactive time server cannot meet the user’s arbitrary specified decryption time, and the interactive time server mode meets the arbitrary decryption time but cannot guarantee the user’s identity privacy, a TRE scheme using onion routing network was proposed. In the scheme, when the decryption time approaches, the time trapdoor request was taken as the innermost onion, and the layer by layer encrypted onion was constructed and transmitted to the time server. The time server generates the corresponding time trapdoor and returns it to the receiver according to the original route, so that the user can hide the identity information when making a trapdoor query at any time. Meanwhile, for the node failure problem in the process of onion routing delivery, a method for constructing each layer of onion based on broadcast encryption was proposed, so that each layer of onion node can decrypt that layer of onion. The scheme achieves the trapdoor of successfully querying arbitrary time to the time server while ensuring the anonymity of user’s identity. Security analysis showed that the scheme is secure and robust against possible single-point speculation, monitoring attacks, replay attacks, and collusion attacks. Efficiency analysis showed that compared with the pairing-based onion routing scheme, the proposed scheme reduces the time consumption of solving the node failure problem by about 59%, thus realizing efficient anonymous query

With the development of seismic isolation technology, the service environment of the isolated bridge is becoming increasingly complicated, and the effect of ambient temperature on the seismic performance of isolated bridge should be considered urgently. To reduce the maximum response and residual deformation of the bridge under the action of an earthquake, combining the advantages of the lead rubber bearing (LRB) and shape memory alloy (SMA), a self-resetting SMA–LRB bearing was formed. In view of the temperature sensitivity of rubber and SMA materials, based on a 4–span SMA–LRB seismic isolation continuous girder bridge, the nonlinear dynamic time history analysis of isolated continuous girder bridges under different ambient temperatures was performed to obtain the dynamic response of the key parts of the structure, while the mechanical properties of SMA–LRB bearings at different ambient temperatures were considered. The results showed that the addition of SMA to LRB increased the horizontal rigidity and effectively controls the displacement response of the bearing. At the same time, the self-reset characteristic of SMA made the residual displacement control effective. As the ambient temperature decreases, the peak displacement and residual displacement of the LRB and SMA–LRB bearings would decrease, but the displacement control ability and self-reset ability of the SMA–LRB bearing would decrease compared with normal temperature. The stiffness of the bearing increased with the decrease of the ambient temperature, which caused an increment in the displacement of the top of the pier and the shear force at the bottom of the pier, and the shear force at the bottom of the lower pier was more sensitive to temperature changes. The qualitative evaluation of the influence of ambient temperature on the seismic performance of SMA–LRB isolated bridge can provide reference for the analysis and design of such bridges.