The cable-net structural system of FAST is a flexible tension cable net, consisting of a main cable net, several hydraulic actuators and controllers, which is the world’s largest span, the highest precision, and the first active shape-changing cable-net system. Its characteristic is that the cable net form can be adjusted according to requirements, but it also results in the cable boundary conditions constantly changing with the cable net form, which brings huge challenges to cable force identification. In order to accurately identify cable forces of the active shape-changing cable-net system, a method for identifying cable forces of variable elastic boundary supports is proposed. An equivalent single-degree-of-freedom model of the cable is established, and the mathematical expressions of the cable frequencies between ideal hinge and elastic boundary support are derived. The first-order frequency is then corrected based on the first-order mode values at the mid-point and both ends of the cable. The cable force identification method of the active shape-changing cable-net system which is based on the string vibration theory is proposed. Numerical simulations are carried out to verify the accuracy of the proposed method, and parametric analyses are also conducted. The method is proved to be practicable and applicable through numerical simulations and field measurements to identify the cable force of the FAST cable net.The results show that the relative errors of cable force identification are within 1% in the numerical simulation and less than 5% in the field measurement. The method takes into account the complex boundary conditions of cables, avoids solving for unknown boundary constraint stiffnesses, and extends the engineering applicability of the traditional string vibration theory.

The deflection influence line and strain influence line can integrally reflect the flexural stiffness of beam bridge section. In the process of obtaining the measured time-history response of beam bridge, the response of beam bridge involves the influence line information and structural dynamic components, and is interfered by the multi-axis effect of loading vehicle under vehicle moving load. In order to identify the influence line of beam bridge structure accurately, the empirical mode decomposition was proposed to eliminate the dynamic component in the measured data of beam bridge, and the quasi-static response data of beam bridge containing the multi-axis effect was obtained. Combined with the sampling frequency and vehicle wheelbase, a mathematical model was established to identify the influence line, and the multi-axis effect of vehicle was converted into unit concentrated load. Tikhonov regularization method was used to accurately solve the stable solution of the influence line of the beam bridge. Through the establishment of numerical simulation models of 1/2 two-axle vehicle-crossing simply-supported beam bridge and three-span continuous beam bridge with variable section, the deflection and strain time-history responses of simply-supported beam bridge and three-span continuous beam bridge at different vehicle speeds were extracted, and the feasibility and effectiveness of identifying influence lines of beam bridge based on empirical mode decomposition and Tikhonov regularization method were verified. The deflection influence lines and strain influence lines of the structural examples of the beam bridge were identified accurately, and the identification effect of the influence lines was evaluated quantitatively by establishing error index. The research also found that the identification effect of the influence lines of the beam bridge decreased with the increase of the loading vehicle speed.

In the seismic design of bridge structures, the influence of local site conditions at piers on the seismic response should be considered. The multi-support response spectrum method is a common method for seismic performance analysis of bridge structures under spatial ground motion. For deep-water bridge, the existing method cannot include the water-structure interaction.Based on the radiation wave theory, this paper proposed a multi-support response spectrum considering the water-structure interaction by introducing the term of hydrodynamic pressure into the vibration equation of the bridge. The correctness of the method was verified. Taking a typical five-span continuous girder bridge as an example, the seismic response of the bridge under different site conditions is studied by changing the site type of the pier, seismic intensity, and design seismic group. The influence law of local site effect on the seismic response of the multi-span continuous girder bridge is revealed. The results show that with the softening of site of pier 3, the relative displacement at top of pier 3 decreases by up to 93.0% at most. The influence of site type on pier displacement is greater than that of the axial force of girder and the bending moment at bottom of pier. With the increase of seismic intensity, the relative displacement at top of pier, axial force of girder and bending moment at bottom of pier increase by 7 times. With the increase of epicenter distance, the relative displacement at top of pier increases by 41.0%, the axial force of girder increases approximately by 18.0%, and the bending moment at bottom of pier increases approximately by 30.0%.

In order to investigate the dynamic response law of concrete-filled steel tubular composite single pile with large diameter and variable section under different types of seismic waves, 5010 wave, 1004 wave, Kobe wave and El-Centro wave with ground motion intensity of 0.15g were selected through indoor shaking table test relying on Xiangan Bridge project of Xiamen Second East Passage. The pile acceleration, horizontal displacement, bending moment and pile foundation damage of large diameter variable section concrete filled steel tube composite pile are studied. The test results show that the dynamic response characteristics of large diameter variable section concrete filled steel tube composite pile are different due to the different spectral characteristics of different seismic waves. Pile top acceleration maximum, pile top horizontal displacement maximum and pile bending moment maximum are the maximum under 1004 wave, and the minimum under Kobe wave. The maximum bending moment of pile body did not exceed the designed flexural bearing capacity of pile foundation. In the design of flexural bearing capacity of pile foundation under the action of earthquake force, the design of flexural bearing capacity at the interface of soft and hard soil layer is emphasized.

To investigate the influences of charge structures on the blast-induced ground vibration characteristics in hydraulic blasting, several onsite experiments were conducted in the context of Xinbin tunnel at the Shenyang to Jilin Expressway. Based on the onsite experiments, the peak particle velocity (PPV) and dominant frequency (DF) were analyzed under different kinds of charge structures, which includes the normal charge structure, the water bags located in the top of blasthole, the water bags located in the blasthole collar and the water bags located in the both ends of blasthole. In addition, the distribution laws of ground vibration under different charge structures were further studied using numerical simulation. The research results indicated that, compared with the normal charge structures, less explosive energy is converted into vibration energy in hydraulic blasting, resulting in smaller PPVs and higher DFs. Within 5 m of the cross section along the tunnel excavation face, the PPVs of blasting vibration under the normal charge structure exceed the vibration safety criteria, which is adverse for the safety control of ground structures. The converted vibration energy is relatively smaller along the direction of water bags in blasthole, but on the opposite direction of the blastholes more explosive energy is converted into vibration energy. In tunnel blasting excavation, the charge structure of the water bags located in the both ends of blasthole was recommended to promote the uniform distribution of vibration energy and minimize the disturbance to the surrounding structures.

In the realm of engineering structures, the distribution of structural parameters often remains uncertain due to a lack of sufficient data, presenting a common and intricate challenge in structural reliability analysis. This paper presents a novel linear moment method for assessing the seismic reliability of random structures with unknown distributions. A random dynamic system is constructed using only two basic random variables: (1) the first four-order linear moments derived from the structural random parameters, expressed as a univariate cubic polynomial with a random function involving standard normal random variables; (2) A random function-spectral representation model is utilized to describe the non-stationary seismic ground motion. On this basis, representative point sets for the two basic random variables are determined using number-theoretical methods. Through time-domain analysis, extreme structural responses are computed to evaluate the samples of the performance function and its linear moments within the specified limit state. The seismic reliability index derived from linear moments is established by solving the univariate cubic equation roots. To demonstrate the proposed method’s applicability, a nonlinear single-degree-of-freedom system with unknown parameter distributions is analyzed, and its effectiveness is verified by comparing the results with those obtained using Monte Carlo simulation.

Railway bridges must have sufficient stiffness to ensure high-speed train safety, increasing seismic response. The Sichuan-Tibet Railway network has extended westward. This research analyzes the fourth level of high-speed railway bridges.Three 1/5 and six 1/8 scaled-down high-speed rail(HSR) round-ended rectangular-shaped cross-section solid(RERSCSS) concrete pier were tested and evaluated. The piers survived the earthquake with a peak acceleration 0.96g (prototype 0.32g, seven degrees high-level earthquake). Bridge pier specimens showed no concrete cracking or spalling. The code-designed bridge is seismically safe. When the seismic energy reached 1.71g (prototype 0.57g, eight degrees high-level earthquake), the bridge piers showed moderate to severe damage in the cis-bridge direction. At giant earthquake 1.86g, no bridge abutments collapsed. The study shows that increasing longitudinal reinforcement rate increases structural energy dissipation under the same ground shaking, but increasing seismic protection level increases it more, indicating that test piers can take larger earthquake loads. The bridge pier’s energy dissipation and hysteresis curve depend on the longitudinal reinforcement rate. High-speed rail piers are not designed for ductility. Therefore, their volume hoop rate and hysteresis performance are low. Based on the analysis, the seismic design classification may be upgraded from the third to forth levels.

There are several shortcomings in the assessment of human-induced vibration in walkways, including a focus on structural response rather than pedestrian comfort, the reliance on structural vibration response to evaluate pedestrian comfort, and the limitations of data collection methods. To address these problems, this paper proposes a more comprehensive approach, namely human-induced vibration serviceability assessment of full-path footbridge based on computer vision with source-path-receiver. The proposed method captures video sequences of both the footbridge and pedestrian movements under pedestrian excitation using computer vision techniques, and then utilizes the segmental optical flow method and the MMTracking algorithm to obtain the vibration response of both. The acceleration responses of the pedestrians obtained from the above extractions and transformations are used as an evaluation index for the vibration comfort of the pedestrian bridge in terms of the root mean square value of acceleration. To validate the feasibility and accuracy of this method, experiments were conducted on the pedestrian bridge in the laboratory. The results show that the computer vision technology can accurately and contactlessly capture the pedestrian dynamic information of the footbridge, which is more reasonable than the conventional method which only evaluates the vibration comfort of the footbridge based on the structural vibration response. By addressing the shortcomings of current assessment standards and methods, this approach provides a more comprehensive and accurate means of evaluating the vibration serviceability of footbridges, considering both the structural response and the actual experience of pedestrians.

The aerodynamic interference between tandem square cylinders is strongly influenced by their geometric shape. The change of corner shape of square cylinders will lead to the change of flow field, which will affect the aerodynamic performance of square cylinders. The influence and mechanism of wind load interference effect of tandem square cylinders need to be further studied.In this paper, the large eddy simulation method is used to investigate the impact and mechanism of corner cutting measures on the wind load of tandem square cylinders with subcritical spacing ratio and supercritical spacing ratio under two typical spacing ratios. The upstream and downstream cylinders are considered with or without corner cutting(the corner cutting rate is 10%). The wind pressure coefficient of standard tandem square cylinders is compared with the wind tunnel test results in literature to verify the effectiveness of the simulation method and parameter setting. effects of different corner cutting measures on the aerodynamic performance of tandem square cylinders under two typical spacing ratios are compared and analyzed from the perspectives of aerodynamic coefficient statistics and auto-spectrum, average and fluctuating wind pressure coefficient distribution. The mechanism analysis is carried out from the perspective of time-average and transient flow field.The results show that under the two typical spacing ratios, the corner cutting measures at different positions will affect the flow separation around the square cylinder, resulting in the change of flow pattern. The average and fluctuating wind loads of the square cylinder can be reduced more effectively by the corner cutting measures at both upstream and downstream square cylinders.Under the subcritical spacing, the shielding effect is significant, and the corner cutting measures change the separation and reattachment position of the separation vortex, and reduce the lift and drag of the downstream square cylinder significantly.

Ground motion simulation can provide reference for buildings seismic design in areas lacking earthquake records. High frequency attenuating factor （κ） is an important parameter in ground motion simulation，controlling the drop of Fourier spectrum shape in the high frequency interval. Luring magnitude 6.8 earthquake records within 150 km of the epicenter are selected to develop κ. Parzen window is used to smooth the cluttered Fourier amplitude spectrums （FAS）. The frequency interval in FAS with the smallest p^H function is selected to fit the κ. The approach improves accuracy of identifying lowest and upper frequency，and the stability of the calculation. κ are calculated based on 20 stations of horizontal records and the distribution trend of κ is analyzed. The results show that FAS is gradually smooth with the increase of the window width，and it is significantly different from the original spectrum when the window width is larger than 1 Hz. Compared with 12 window widths，the window width of 0.4 Hz is the best. The window of 0.4 Hz width makes the curve smooth and the error of κ small. There is a significant directional difference in κ distribution. κ in EW direction increases with respect to epicenter distance，and κ in NS direction decreases with respect to PGA.