Gongcheng Kexue Yu Jishu/Advanced Engineering Science

The composite strengthening method with near surface mounted steel bars and wrapped fiber reinforced polymer strips can improve the bearing capacity and deformation behavior of timber columns effectively, and enhance their working performance greatly. To propose the load-bearing capacity formula of short timber columns strengthened with near surface mounted steel bars and wrapped carbon fiber reinforced polymer (CFRP) strips, a total of 42 reinforced specimens (12 groups) were tested under axial compression. The test results indicated that the failure of timber columns mainly occurred where the initial defects concentrated , and the bearing capacity and deformation performance of timber columns could be improved through the composite strengthening, showing significant strengthening effectiveness.Based on the typical strength model of concrete columns wrapped with fiber reinforced polymer strips, three strength models of timber columns with wrapped CFRP strips by analyzing and fitting the relevant experiment data were proposed. Through the comparison between theoretical and test values, the feasible strength model for the calculation of timber columns confined by CFRP strips was selected, and then the calculation formula of bearing capacity for the circular timber columns with composite reinforcement method was obtained. According to the additional experiment results and the comparison calculation for test data in existed research, it can be obtained that the theoretical calculation was able to predict the test results,which verified the reliability of the formula for the calculation of the strengthened timber columns' load-bearing capacity.

A water–soil coupling model of channel fluid movement is established considering the interaction of gully bed erosion, slope confluence, and rainfall, which can provide theoretical basis for watershed risk assessment, disaster prevention and mitigation, and identification of potential debris flow gully. By analyzing the erosion process of the channel fluid on the movable solid source of the gully bed, and coupling it with the slope confluence and the rainfall over the channel with temporal and spatial variability, the water–soil coupling model of the channel fluid movement in the small watershed can be established. The finite difference method was used to discretize the water–soil coupling model of fluid movement in time and space. A computer code for the coupling model of fluid motion was written in MATLAB. Meanwhile, laboratory experiments were carried out with varying flow rates and groove slopes to observe the evolution of fluid flow depth, flow velocity and fluid bulk density under different working conditions. By analyzing the results of the 12 sets of experiments, it was found that under the condition that the slope of the groove remains unchanged, the fluid flow depth and the fluid velocity were positively correlated with the flow and the bulk density was negatively correlated with the flow. At the same time, the numerical simulation results of the fluid flow depth, flow velocity and fluid bulk density at the control point of the groove were compared to and analyzed with the experimental results. It was found that the simulation accuracy of the fluid flow velocity and fluid bulk density were higher than 90%, and the simulation accuracy of the fluid flow depth was higher than 80%. The results revealed that the established water–soil coupling model of the channel fluid movement in the small watershed is accurate.

The base isolation structure has a high requirement for integrity of the isolation layer, and the connection behavior of the isolation layer members affects the integrity and the seismic behavior of the isolation layer directly. In this paper, the welding connection mode between longitudinal reinforcements at the bottom of the beam was improved, the tensile tests were also carried out, and a new frame joint was proposed of the isolation layer for prefabricated concrete base isolation structure. Then, the finite element models of the new frame joint and traditional cast-in-place joint were established to simulate the seismic behavior and the structural integrity under the lateral repeated loads in ABAQUS. Finally, an improved connection mode for the new frame joint was proposed by comparing the difference of seismic behavior between the two kinds of joints. The results showed that the tensile strength of the specimen which connected by grooving and welding on the steel plate was close to that of the complete reinforcement, and could significantly reduce the bending deformation of the connecting steel plate. The bearing capacity, stiffness and energy dissipation capacity of the prefabricated frame joint were lower than that of the cast-in-place joint, but the deformation capacity was stronger. The bearing capacity, stiffness, and deformation capacity of the new frame joint on the prefabricated isolation layer increased when some anchored rebars were added to the ends of the prefabricated beam, the reinforcement ratio at the end of beams also increased, at the same time, the plastic development of the longitudinal reinforcement was delayed by the anchored rebars, so the energy dissipation capacity decreased. The load-bearing capacity, stiffness and deformation capacity of the improved prefabricated frame joint were all stronger than that of cast-in-place joint, so the improved new frame joint had an excellent structural integrity, and it could be used in practical engineering widely.

To meet the demand for green construction of power grids in the new era, it is urgent to develop and apply a new type of environment-friendly foundation for power grid projects. For this purpose, an improved thin-walled tapered-end grouted miniature steel pipe pile was proposed, and the uplift bearing characteristics of this pile were studied through field tests. With the project background of the 220 kV line Shuanglou-Jiaohe Dongguang north substation, 18 steel pipe piles with two pile diameters of 159 mm and 203 mm, two burial depths of 5 m and 8 m were designed under two conditions of grouting and no grouting. The effects of grouting on the load–displacement curves, uplift bearing capacities, and soil failure modes for different test piles were analyzed through on-site uplift bearing characteristic tests. Based on the failure mechanism of pile–soil interface obtained through the field tests, a finite element model incorporated the pile–soil interaction for the tests was established, and the uplift deformation and failure process of the steel pipe pile was numerically simulated and analyzed. The simulation results showed that the failure modes of the pile–soil interface were consistent with the field tests. By comparing the shear strength parameters and microstructure of the soil around the pile before and after grouting, the macroscopic and microscopic mechanism of the influence of grouting on the soil around the pile was analyzed. The test results are as follows: 1) The load–displacement curve of steel pipe pile changed from steep drop type to slow change type after grouting, and the grouting enhanced the ability of the pile foundation to resist plastic deformation. 2) The uplift capacity of steel pipe pile increased by 59%～148% after grouting, and the increase range was negatively related to the slenderness ratio of test pile. 3) There were few cracks in the surface soil at the failure state of uplift tests for the non-grouting steel pipe piles. The pile body was almost extracted, and the surface soil appeared radial and circumferential cracks at the failure state of the grouting steel pipe piles. 4) Many voids in soil were filled in the process of grouting, which improved the soil strength around the pile. Cement consolidation was formed around the steel pipe pile after grouting, and a shear surface was formed between the cement consolidation and soil. This conclusion was also supported by the numerical simulation results. The influence mechanism of grouting on the uplift bearing capacity of steel pipe pile was mainly reflected in the increase of shear area and side friction of soil around the pile. The engineering application showed that the proposed steel pipe pile had a short construction period, a high bearing capacity, and a low impact on the surrounding environment. These steel pipe piles have been well popularized and applied in the 220 kV line project Shuanglou-Jiaohe Dongguang north substation.

Generally, the noise transmitted in the optical path mainly includes the influence of optical power, external vibration interference, the intrinsic noise of the optical path, and the influence of thermal motion caused by environmental temperature changes. The optical fiber is extremely sensitive to environmental interference, and any environmental disturbance will bring corresponding phase errors. At the same time, if the signal is preprocessed and filtered, it is easy to cause some small information to be lost and increase reconstruction errors. Aiming at the problem of internal common mode noise affecting measurement accuracy and increasing reconstruction error in micron-level vibration measurement, a differential measurement system based on all-fiber Fabry–Perot (F–P) interference is established. Firstly, according to the phase equation of the F–P interference principle and the 2×2 single-mode fiber coupler during the transmission process, the through arm and the coupling arm have a phase difference of 90°. It is deduced that the signals received by the two output detectors are equal in amplitude and opposite in direct. Then the difference between the two signals can increase the overall signal amplitude, weaken the influence of common mode noise on the signal, and enhance the signal quality. Through the reconstruction displacement analysis of the interference signal, the experimental results show that the reconstruction error of the synthesized signal is reduced by 0.4% in the 2 μm sinusoidal vibration of the mirror. Under 1.4 μm vibration measurement on rough surface, the reconstruction error is reduced by 2.8%. The experimental results also show that the differential structure can reduce the vibration measurement reconstruction error, and the reconstructed waveform is smoother.