This study investigates the effect of varying tennis racket string tension on stroke effect and the dynamic response of the racket. Using the YSV dynamic acceleration signal acquisition system and a portable radar speed gun collect data on racket acceleration, stress-strain signals, and ball speed from 15 male athletes. Stroke accuracy and depth were assessed according to the International Tennis Number. The recorded stroke speeds were 108.87±13.57 km/h, 111.83±16.34 km/h, and 107.76±12.53 km/h for the low, medium, and high tension, respectively. A significantly higher ball speed was observed at 54lbs compared to both 48lbs and 60lbs (P <0.05). Control scores were 4.90±0.61,5.46±0.84, and 4.64±0.69 for the respective tensions. The control at 54lbs was significantly higher than at 60lbs (P<0.05). Deformation measurements were 18.53±4.90με, 16.31±4.42με, and 20.90±3.53με, with significantly lower deformation at 54lbs compared to 60lbs (P<0.05). The impact forces recorded were 381.81±48.51m/s2, 380.53±50.47m/s2, and 380.04±53.70m/s2, with no significant effect of string tension on impact force. Racket vibration frequencies were 44.14±0.48Hz, 44.08±0.35Hz, and 44.14±0.25Hz, with no significant difference among three string tensions. Rackets with three string tensions showed significantly higher vibration frequencies during the collision phase compared to before or after (P<0.01). In conclusion, string tension affect the stroke effect, racket strung at medium tension can optimize stroke effect while got milder dynamic impact, suggesting that racket strung at medium tension is recommended for tennis enthusiasts to enhance stroke performance and to decrease the risk of resonance damage in the forearm soft tissues.

With the rapid development of urban construction and infrastructure, bridges serve as critical transportation hubs, and their structural integrity is directly linked to public safety. This paper presents a bridge structural damage detection method based on Covariance-driven Stochastic Subspace Identification (Cov-SSI) and hypothesis testing. A vibration sensor network is deployed to collect bridge vibration data, providing high-quality input for subsequent modal analysis. The proposed method performs modal identification using the long-term bridge vibration data, extracts stable modal frequencies using the Density-Based Spatial Clustering of Applications with Noise (DBSCAN) algorithm, and ultimately applies the two-sample two-tailed t-test to determine the damage state of the bridge. This study utilizes data from the Swiss Z24 bridge for validation. Experimental results demonstrate that the proposed method effectively mitigates the influence of environmental factors, accurately identifies bridge damage in a timely manner, and provides a reliable basis for preventive maintenance. The proposed method can be applied to the long-term health monitoring of various critical infrastructures, enhancing safety assessments and maintenance decision-making.

This paper proposes a method for identifying damage in bridge structures by combining frequency-domain analysis with hypothesis testing. Vibration signals are continuously collected through a strategically deployed sensor network on the bridge. The method first transforms the vibration signals into the frequency domain, extracting characteristic frequencies from both the healthy and monitored states. The paired-sample t-test is then applied to determine whether the frequency changes are statistically significant, thereby identifying potential damage in the structure. This approach integrates the sensitivity of frequency characteristics with statistical objectivity, allowing for efficient damage detection without relying on complex modal analysis. Experimental results demonstrate that the proposed method performs effectively across a variety of damage scenarios, showing robustness and strong practical applicability. It is particularly suitable for long-term monitoring, periodic evaluation, and rapid post-event screening of bridge structures. Additionally, this method can be applied to stiffness-sensitive structures such as railway bridges, urban overpasses and light rail tracks, offering a quantitative assessment of their condition to ensure operational safety and stability.

Wind engineering has made significant strides in addressing the challenges posed by exceptional terrains, where traditional methodologies often fall short. This paper reviews the advances in wind tunnel technology and computational fluid dynamics (CFD) that have revolutionized the understanding and prediction of wind effects on bridges, particularly in complex environments. The integration of advanced measurement techniques with wind tunnel experiments has provided deeper insights into wind characteristics, leading to more accurate aerodynamic designs for bridges. The application of these technologies in unique terrains has been instrumental in ensuring the safety and stability of critical infrastructures. The paper reviews the importance of continuous research and collaboration in wind engineering to address the evolving demands of infrastructure in challenging terrains. The article also introduces the wind tunnel facilities at Chang’an University, detailing their capabilities and contributions to research in wind engineering, including the study of aerodynamic performance and control measures for bridges. It is concluded by reflecting on the research team’s 20-year journey at Chang’an University, noting their growth, achievements, and contributions to the field of wind engineering.

The [Formula: see text]-shaped open section girder is a very common section, which has been widely used in the construction of modern bridges. However, compared with a streamlined box girder, it is easy to cause vortex-induced vibration (VIV) in bridges due to its bluff section shape and poor aerodynamic stability. In this paper, a typical open section with a height–width ratio of 10:1 is taken as the research object. Through wind tunnel tests and numerical simulation technology, the time-history data of VIV of the [Formula: see text]-shaped section are obtained. By selecting three different neural network models to establish the relationship between external parameters (wind attack angle, wind speed, turbulence) and structural response parameters (the onset wind speed of VIV, the length of the lock-in interval). After comparing different machine learning methods, the most suitable machine learning model is selected to predict the VIV response characteristics of the main girder. The research results show that the typical open section has a serious VIV phenomenon. The BP neural network model has the best performance in predicting the VIV performance of the open section in terms of calculation speed, prediction accuracy and solving nonlinear adaptability. At the same time, it is found that different characteristic parameters of the incoming wind field have different influences on the prediction results of the VIV response. Among them, the wind attack angle is the key parameter that affects the onset wind speed of VIV, but the turbulence intensity has a greater impact on the maximum amplitude of VIV. At the same time, the optimized BP model can predict the characteristic parameters of VIV response under unknown wind fields. This paper provides a new idea to study the effect of different incoming flow parameters on the performance of section VIV and further improves people’s understanding of VIV system.

As a high-rise structure, the tower of a suspension bridge has low stiffness due to the lack of cable system constraints when it is self-supporting. Wind-induced vibration is one of the key factors in design and construction. In this paper, the wind tunnel test of the bridge tower aeroelastic model is carried out in two different flow fields, and the wind vibration response under a self-supporting state is systematically studied. Meanwhile, numerical simulation of the unsteady flow field around the tower section is carried out, and the dynamic modal decomposition (DMD) method is used to study the modal frequency of the flow field, the surface pressure of the section, flow field reconstruction error, and the stability of the flow field around tower section is discussed. The results show that in the self-supporting state, the displacement of the tower top presents a quadratic curve relationship with the wind speed, and no galloping phenomenon occurs under the test wind speed. However, in the uniform flow, when the wind attack angle is 90°, the bridge tower has an obvious vortex-induced vibration (VIV) phenomenon. After decomposing the flow field by the DMD method, it is found that there is strong aerodynamic interference between the double rectangular column sections, the first seven orders of modal energy play a major role in the flow field, and when the main modal energy accounts for more than 90%, the reconstruction can realize the accurate restoration of the information such as the surface pressure. For the complex flow field structure, it shows that the method can more accurately identify the coherent structure and background part in the unsteady flow field. This paper provides an idea for future research on the characteristics of the flow field around complex sections and helps to further improve the understanding of the VIV mechanism.

Compared with traditional streamlined box girders, girders with a typical open section have a highly bluff aerodynamic shape and are prone to cause vortex-induced vibration (VIV), which will affect the safety and serviceability of a bridge. In this study, the surface pressure distribution and aerodynamic nonlinearity characteristics of a typical open section are studied through wind tunnel tests and numerical simulations. Based on the synchronous measurement technology, the evolution characteristics of the surface pressure distribution in different periods of the VIV lock-in region are analyzed, and the numerical simulation of the section was performed by a user-defined function (UDF) program. The numerical simulation results are in good agreement with the wind tunnel test results. Furthermore, the multi-order components of aerodynamic force in the VIV process were decomposed by the Hilbert vibration decomposition (HVD) method. Our study found that the average pressure of the open section’s surface at the leading edge was negative, as this is where the air flow is separated. At the extreme point of the VIV lock-in region, the fluctuating pressure changes most drastically in the region ([Formula: see text]), indicating that the intensity of vortex shedding is the greatest in this region. High-order components of the aerodynamic forces acting on an open section girder can be identified by analysis. The aerodynamic damping of the open section girder is significantly reduced in the VIV lock-in region, and reaches its minimum near the extreme point of VIV. Due to the presence of high-order harmonic components, the degree of aerodynamic nonlinearity continues to increase. Moreover, the work performed by each aerodynamic component throughout the whole vibration period has different characteristics, and the influence of the third-order and above components on the VIV system can be ignored. This study can help us to further understand the aerodynamic nonlinear energy evolution characteristics of the open section, and further improve people’s understanding of the VIV system.

Wind tunnel test is often adopted to assess the site-specific wind characteristics for the design of bridges as suggested by current design standards. To investigate the wind characteristics of flat and mountainous terrain, two topographic models are tested in a boundary layer wind tunnel. The wind characteristics, including the vertical and horizontal mean wind speed distributions, the turbulence intensity, and the wind power spectra, are presented. They are investigated intensively in present study with the discussions on the effect of wind direction and the effect of topography. It is indicated that for flat terrain, the wind direction has negligible effect on the wind characteristics, however, the assumption of a homogenous wind field for the mountainous terrain is not applicable. Further, the non-homogeneous wind field can be defined based on a proposed approach if the wind tunnel test or on-site measurement is performed. The calculated turbulence intensities and wind power spectra by using the measured wind speeds are also given. It is shown that for the mountainous terrain, engineers should take into account the variability of the wind characteristics for design considerations.

This paper investigated the aerodynamic response features of an asymmetric cable-stayed bridge. The wind resistance design parameters for judging the response were first determined, afterwards the bridge dynamic characteristics were analyzed for subsequent aerodynamic analysis. The vortex-induced vibrations (VIV) and flutter response at various wind fairing angles were then examined by using a 1:50 sectional model in the wind tunnel test. Finally, a 1:150 full bridge aeroelastic model was employed to explore the aerodynamic stability and characteristics of the whole asymmetric bridge under different wind attack angles in various flow fields. The results show that the sharp wind fairings could reduce the VIV amplitude of the steel box girder cable-stayed bridge to some extent, and the example bridge has examined to have enough flutter stability through sectional and full bridge aeroelastic model wind tunnel tests. Unlike symmetric bridges, the bridge's maximum displacement of first torsion mode shape is at the closure rather than the mid-span, which is the essential reason to lead this unique vibration feature. The results from the present study could highlight the important effect of structural asymmetry and fairing shape to the wind-induced bridge vibration and hence may facilitate more appropriate wind design of asymmetric cable-stayed bridges.

The influence of key parameters of transverse seismic isolation system, which consisted of steel dampers and wind bearings, on transverse seismic response of cable-stayed bridges is investigated in this paper. An asymmetric cable-stayed bridge with unequal height towers is taken an example bridge, and orthogonal test design method is used to set test conditions for synchronous optimization of the key parameters. The results show that significant parameter coupling is observed from internal force of auxiliary pier and left deck end displacement, so synchronous optimization should be considered. Moreover, steel dampers have little effect on the internal force of towers while internal force of auxiliary pier and deck end displacement can be significantly decreased by setting steel dampers.

为探究由钢阻尼器与抗风支座组成的横向减震体系关键参数对斜拉桥横向地震响应的影响,以某高矮塔斜拉桥为例,基于结构内力与位移响应相平衡的原则,运用正交试验设计法设定参数联合优化的分析工况,分别以结构内力与位移响应、钢阻尼器耗能为优化指标,探究算例中减震体系关键参数钢阻尼器屈服力及抗风支座初始间隙对优化指标的影响.结果表明:辅助墩内力及高塔侧边跨主梁梁端位移响应的控制因子具有显著的参数耦合效应,参数优化时需联合考虑;在墩台设置钢阻尼器可显著降低辅助墩内力及梁端位移响应,但不能有效降低桥塔内力响应.

以某斜拉桥为算例,通过非线性动力时程分析,研究横向支承体系关键力学参数对结构地震响应的影响.分别运用正交试验设计法和控制变量法对桥墩单向可动支座屈服力和桥塔抗风支座初始间隙进行参数联合优化.结果表明:多因子优化时,控制变量法已无法适用,而正交试验设计法不但有效且计算效率高;双因子优化时,两种方法结果相同,但正交试验设计法可量化参数之间的正交与耦合性.高墩上支座的屈服力与桥塔抗风支座初始间隙具有较强的正交性,互相影响的显著性较低,参数优化时可以单独考虑;矮墩上支座的屈服力与桥塔抗风支座初始间隙表现出较强的耦合性,参数优化时需联合考虑.

In Chinese seismic design codes, soils are divided into four sites (I -IV), and each site is divided into three groups (G1 similar to G3) according to the design characteristic period (T-g) again. The current studies only present the near-fault inelastic input energy (SEI) spectra corresponding to each site, while those corresponding to G1 similar to G3 of each site have not been reported. Therefore, in this study, 210 near-fault ground motion (GM) records were selected and classified according to G1 similar to G3 of Sites I similar to IV. By inputting the records into the BISPEC software, the effects of the characteristics of near-fault GMs and the parameters of hysteretic models on the near-fault SEI spectra were studied, and then the near-fault S-EI design spectra corresponding to G1 similar to G3 of Sites I similar to IV were established. Moreover, by improving the previous procedure and using the near-fault S-EI design spectra, an energy-based procedure for estimating the near-fault input energy of beam bridges was proposed, and its feasibility and safety were verified through a case study.

The S(EI)smically isolated simply-supported beam bridge (SISBB) with the S(EI)smic isolation bearing (SIB) is converted into an equivalent bilinear single-degree-of-freedom system. Then, by inputting the 139 near-fault ground motion (GM) records into the equivalent system, the parametric study on the near-fault S(EI)smic input energy spectra (S-EI) of the SISBB is conducted by considering the equivalent system parameters and the near-fault GM characteristics. So, it can be found that: the increase of post-yield stiffness ratio (eta(e)) can slightly increase the peak values of the near-fault S-EI, and eta(e) = 0.2 can be used to calculate the near-fault S-EI design spectra of the SISBB; with the increase of the damping ratio (eta(e)) (or ductility ratio (mu e)), the spectral values of the near-fault S-EI increases, the hysteretic energy dissipation capacity of the SIB decreases, and the damping energy dissipation capacity of the equivalent system increases; when mu(e) > 10, the effect of mu(e) on the near-fault S-EI can be ignored; the softer the site soil or the smaller the Joyner-Boore distance to rupture plane (R-jb) is, the greater the near-fault S-EI is; if the near-fault S-EI with a standard peak ground acceleration (PGA) is known, the near-fault S-EI with other PGAs can be obtained by multiplying the (PGA(Other)/PGA(Standard))(2) by the spectral values of the near-fault S-EI with a standard PGA. Finally, the near-fault S-EI design spectra of the SISBB are obtained, and the seismic isolation design for SISBB based on the energy balance method is proposed, the feasibility of which is verified by a case study.

以HDR隔震梁桥多自由度(MDOF)模型和等效双线性单自由度(SDOF)模型为研究对象,以典型近场地震动作为输入,研究HDR支座双向耦合效应对HDR隔震梁桥地震响应的影响.研究结果表明:不考虑双向耦合效应的HDR支座滞回曲线呈典型双线性;考虑双向耦合效应的HDR支座滞回曲线面积小于不考虑双向耦合效应的HDR支座滞回曲线面积.不考虑双向耦合效应的顺桥向HDR支座位移峰值db大于考虑双向耦合效应时,但横桥向的结果相反.近场地震作用下,对梁桥进行HDR支座隔震设计时,忽略双向耦合效应计算得到的墩底剪力峰值和弯矩峰值均偏于保守.可忽略HDR支座双向耦合效应对HDR隔震梁桥近场地震能量的影响.

为研究脉冲型近场地震动作用下简支梁桥设计参数对其隔震后地震响应的影响,采用结构分析软件SAP2000建立设置高阻尼橡胶(HDR)支座的隔震简支梁桥等效单墩模型,以典型近场地震动作为输入,得出桥墩高度、桥墩质量和等效隔震度对HDR隔震简支梁桥的近场地震动响应的变化曲线.研究结果表明:桥墩越矮,HDR隔震简支梁桥的等效周期增幅就越大;桥墩越高,HDR隔震简支梁桥的梁体位移峰值也就越大;当墩高大于35 m,HDR隔震效果不明显;桥墩质量的增大对HDR隔震效果不利;HDR隔震简支梁桥的近场地震动响应与等效隔震度有很强相关性,即当等效隔震度小于2.0时,HDR隔震效果较差;而当等效隔震度大于3.0时,HDR隔震效果则随等效隔震度增加而增强.

For studying the effects of turbulence characteristic parameters on the wind tunnel test results of different structures,the parameters of local turbulent wind field produced by different grille shapes were measured and the influences of the distance between two grilles and the widths of grilles on the turbulence intensity,turbulence integral scale and fluctuating wind power spectra at different cross section were analysed by means of wind tunnel tests.The results show that the local turbulent wind field with good uniformity can be developed at the cross section 3.5 meters away from grilles. The turbulence intensity generated by grilles changes little with the change of wind velocity.Smaller widths of grilles and lower turbulence intensity can make better the stability of data.The size of turbulence integral scale is nearly the same as the distance between the two grilles.To facilitate the local turbulent wind adjustment,the estimation formula for turbulence intensity and turbulence integral scale according to the width and space of grilles was provided.

Homotopy methods are globally convergent under weak conditions and robust; however, the efficiency of a homotopy method is closely related with the construction of the homotopy map and the path tracing algorithm. Different homotopies may behave very different in performance even though they are all theoretically convergent. In this paper, a spline smoothing homotopy method for nonconvex nonlinear programming is developed using cubic spline to smooth the max function of the constraints of nonlinear programming. Some properties of spline smoothing function are discussed and the global convergence of spline smoothing homotopy under the weak normal cone condition is proven. The spline smoothing technique uses a smooth constraint instead of m constraints and acts also as an active set technique. So the spline smoothing homotopy method is more efficient than previous homotopy methods like combined homotopy interior point method, aggregate constraint homotopy method and other probability one homotopy methods. Numerical tests with the comparisons to some other methods show that the new method is very efficient for nonlinear programming with large number of complicated constraints.

Based on the wind tunnel experiment for aerostatic force of section model of Jianghai direct ship channel bridge of Hongkong-zhuhai-macau great bridge in its finished stage, one calculation program considering the geometric nonlinearity and aerostatic nonlinearity is prepared by using ANSYS parametric design language in order to calculate the nonlinear aerostatic response for long-span cable-stay bridges. Then, the FEA model of Jianghai direct ship channel bridge of Hongkong-zhuhai-macau great bridge in its finished stage is established to analyze the three-dimensional nonlinear aerostatic stability. And the aerostatic response with different position of bridge is also calculated. The research result indicates that the aerostatic instability can not occur in Jianghai direct ship channel bridge of Hongkong-zhuhai-macau great bridge in its finished stage. And, the max torsion deformation, transverse and vertical displacements of finished stage occur in the mid-span of each span and decrease gradually near to both sides.

Based on Hangzhou Zhijiang Bridge, FEA models of arch steel tower in construction and completed stages are established by using ANSYS software. Before closed and completed are considered to compute the dynamic characteristics of different structural system for arch steel tower. The results show that the wind-reduced vibration can be generated easily. It can cause some bad effect on the construction, equipments and the safety of staff. So, some proper measures should be adopted to decrease the wind-induced vibration of arch steel tower in construction and completed stages. So, some meaningful references are provided for the further research on control of wind-Induced vibration for arch steel tower.