Strain serves as a direct indicator of bridge operational condition, playing a crucial role in the health monitoring and status assessment of bridge structures. However, measurement strain is significantly influenced by vehicle loads in small and medium span bridges, leading to the inability of the fixed pre-set warning indicators in the structural health monitoring system to provide effective warnings. In this context, this study proposes a deep learning-based anomaly detection approach aiming to improve the prediction accuracy and warning efficiency under vehicle loads. First, the grey wolf optimizer (GWO) algorithm is employed to optimize the Variational mode decomposition (VMD) decomposition parameters, adaptively decomposing the non-stationary measurement strain into several stationary sub-sequences at different time-scales. Next, a temporal convolutional network (TCN) and bidirectional gated recurrent unit (BiGRU) with attention mechanism (TCN-BiGRU-Attention) model is designed to predict strain with high precision, and the improved hybrid aquila optimizer and African vultures optimization (IHAOAVOA) algorithm is introduced to optimize the key parameters of the TCN-BiGRU-Attention to enhance the generalization performance. Finally, the prediction error is chosen as a warning indicator, and warning limits are developed using statistics and mean control chart theory. A small and medium span bridge analysis results demonstrate that the proposed approach can accurately predict fluctuations in bridge strain under vehicle loads, outperforming other comparative models in prediction accuracy. The proposed method can effectively improve the detectability of strain anomalies induced by vehicle loads and has promising potential for practical engineering applications.

With the development of long-span spatial structures utilizing bolted spherical joints (BSJs), the application of large-diameter high-strength bolts has gained widespread usage. Large-diameter high-strength bolts, as critical connecting elements in BSJs, are prone to fatigue failure under alternating loading. To investigate the fatigue behavior of Grade 9.8 M60 bolts, constant amplitude fatigue tests on 18 specimens of M60 bolt material and 27 M60 high-strength bolts were conducted. The investigation focuses on establishing S-N curves, analyzing the fatigue strength, identifying failure mechanisms, examining the progression of fatigue damage, and predicting fatigue life in these bolts. Furthermore, the experimental results were compared against current design standards to assess their applicability. The findings revealed that, under a 97.72 % survival probability, the fatigue limit at 2 & times; 106 cycles of M60 bolts was lower than the values specified in current codes. Two distinct fracture modes were observed during the tests, with the dominant one being fatigue failure at the first engaged thread between the bolt and the sphere, attributed to the maximum stress concentration at that location. Moreover, the fatigue damage propagation rate for M60 bolts was found to be faster than predicted by current design standards. Finally, the Heywood model was adopted to predict fatigue life of the M60 high-strength bolts in BSJs, while the modified Heywood model demonstrated superior accuracy in fatigue life estimation. These results would provide a reference for the fatigue-resistant design of large-diameter high-strength bolts in BSJs.

This paper proposes a stepped beam-column joint featuring with flush flange surfaces in the connecting segment. Due to the joints' innovative connection configuration, therefore, a serious of methods were adopted to illustrate its force transfer mechanism. Firstly, two full-scaled T-shaped joint specimens were designed. Through cyclic loading test, the failure modes of the joints were characterized as the opening deformation of endplate surfaces and the buckling of flange plates. Specifically, the hysteretic curves, skeleton curves and energy dissipation capacity of the specimens were analyzed. The test results indicated that the stepped joint exhibited favorable seismic performance. Consequently, detailed finite element (FE) models were established and verified against the test results. Furthermore, parametric analysis focused on endplate and flange thickness was conducted, illustrating that the increase of plate thickness caused variation in joint's stress distribution and load-bearing capacity. Finally, based on the finite element analysis results, the force transmission mechanism through the connecting surfaces was elucidated, while the horizontal connection surface contributed to force transmission in the plastic stage.

Bolted spherical joints (BSJs) are integral to large-span space grid structures commonly used in expansive public and industrial buildings. BSJs are susceptible to fatigue damage in high strength bolts due to variable random loads. This study summarized findings from prior fatigue tests, detailing the fatigue failure patterns and S-N curves for grade 10.9 M20, M30 high strength bolts, and grade 9.8 M39 high strength bolts in BSJs. By employing finite element analysis, the study determined the stress concentration factors for these bolts, which were then utilized in fatigue life estimations using the Heywood model and the local strain approach (LSA). Both methods could yield satisfactory predictions, but when it came to the Heywood model, particularly when modifying it in areas of high stress, it demonstrated superior accuracy in predicting the performance of M20, M30, and M39 high strength bolts. Additionally, incorporating initial defect considerations, fatigue life was predicted using the damage tolerance design method (DTDM). Finally, when comparing the fatigue life prediction results obtained from various methods, it became evident that the modified Heywood model outperformed the other methods. This not only provided a superior solution but also demonstrated user-friendliness, thereby establishing itself as the preferred option for predicting the lifespan of high strength bolts in BSJs.

Fatigue failure of high-strength bolts is one of the causes of collapse of steel structures. In this paper, six different machine learning models were used to analyze and predict the fatigue life of high-strength bolts, and the relationship between fatigue life of the bolts and the influencing factors was analyzed by SHAP method. During this process, a data set of fatigue life of high-strength bolts was presented, and 30 percent of the data was randomly selected as the test set. Geometric dimensions and stress states of bolts were as input features, and fatigue life was output label. After training the model, the errors of bolt fatigue life prediction of six machine learning models were compared. Finally, the most adverse factors affecting the fatigue life of the bolts are analyzed. It was found that XGBoost has the best performance on prediction of fatigue life of high-strength bolts, R2 reaches 0.881 and 0.788 in training set and test set, respectively. At the same time, the prediction result of the model is also better than that of the traditional fracture mechanics method. In addition, according to the analysis of SHAP value, the stress amplitude (SA) applied on the bolt has the greatest impact on the fatigue life. Larger SA value will accelerate the expansion of fatigue crack, thus increasing the degree of fatigue damage of the bolt. At the same time, the combination of MAXS (maximum stress applied on high-strength bolts) and SA is the most unfavorable factor to affect the fatigue life of the bolt. Increasing both factors can greatly reduce the fatigue life of the bolt. Finally, the current mainstream steel structure design codes have sufficient safety reserves, and M39 bolt has the best fatigue performance.

High-strength bolt connection is a kind of main connection mode of prefabricated steel structures. Due to the insufficient fatigue performance of high-strength bolts, the degree of damage in the steel structure is very serious, so the fatigue performance research of high strength bolts cannot be ignored. The research object of the paper is M24 twisted-shear high-strength bolts in a steel structure buildings. Some special tests and results analysis on the normal fatigue performance were carried out, establishing the fatigue S-N curve of M24 twisted-shear high-strength bolts, revealing the fatigue failure mechanism of M24 torsion-shear high-strength bolts; obtaining the fatigue S-N curve equation; and estimating the fatigue life of high-strength bolts by using the Paris formula. In addition, by comparing the test data in this paper with the constant fatigue test data of high-strength bolts in the existing research literature, it can be seen how the strength grade of the bolts and the pretension force have an impact on the fatigue strength. It is further revealed that the M24 torsion-shear high-strength bolt with full pretension force has twice as long fatigue life than the other two types of bolts. By comparing the test results of M24 and M20 bolts under full pretension, it is known the relation between the fatigue strength of the bolts and diameter decreases. The research data and useful conclusions can provide scientific basis and theoretical reference for the anti-fatigue design of M24 torsion-shear high-strength bolt connection.

Large-span spatial lattice structures generally have characteristics such as incomplete modal information, high modal density, and high degrees of freedom. To address the problem of misjudgment in the damage detection of large-span spatial structures caused by these characteristics, this paper proposed a damage identification method based on time series models. Firstly, the order of the autoregressive moving average (ARMA) model was selected based on the Akaike information criterion (AIC). Then, the long autoregressive method was used to estimate the parameters of the ARMA model and extract the residual sequence of the autocorrelation part of the model. Furthermore, principal component analysis (PCA) was introduced to reduce the dimensionality of the model while retaining the characteristic values. Finally, the Mahalanobis distance (MD) was used to construct the damage sensitive feature (DSF). The dome of Taiyuan Botanical Garden in China is one of the largest non-triangular timber lattice shells worldwide. Relying on the structural health monitoring (SHM) project of this structure, this paper verified the effectiveness of the damage identification model through numerical simulation and determined the damage degree of the dome structure through SHM measurement data. The results demonstrated that the proposed damage identification method can effectively identify the damage of large-span timber lattice structures, locate the damage position, and estimate the degree of damage. The constructed DSF had relatively strong robustness to small damage and environmental noise and has practical application value for SHM in engineering.

The high-strength bolts’ fatigue is critical for the bolt–sphere joints of grid structures under the action of suspended cranes. High-strength bolts with a huge diameter are used more commonly when the span of grid structures and the burden of suspended cranes increase. However, few works have explored the fatigue performance of high-strength bolts with a huge diameter in bolt–sphere joints of grid structures. Thus, this paper examines M60 high-strength bolts with a huge diameter used in the bolt–sphere joints of grid structures. To this end, an AMSLER fatigue testing machine performed fatigue tests on 27 specimens under constant amplitude. The stress–fatigue life (S–N) curve was obtained by regression analysis and the corresponding constant-amplitude fatigue design method was established. The test results were compared with those of high-strength bolts in other specifications. The results showed that the M60 high-strength bolt has a higher fatigue strength. Furthermore, scanning electron microscopy (SEM) analyzed the macroscopic and microscopic fatigue fracture of the specimens, and the mechanism of the fatigue failure was examined. Our findings provide important experimental data for revising relevant Chinese and international codes and promote the application of high-strength bolts with a huge diameter used in the bolt–sphere joints of grid structures with suspended cranes. This study could fill the gap of fatigue performance data of high-strength bolts in different specifications for bolt–sphere joint grid structures, and provide a basis for further studies.

The high-strength bolts of grid structures with bolted spherical joints under the action of suspension cranes are at risk of severe fatigue failure. Thus, this paper studies the variable-amplitude fatigue performance of M60 high-strength bolts. The test results for eight specimens in four loading modes are obtained using an Amsler fatigue testing machine. The fatigue life is also estimated based on Miner and Corten–Dolan’s theories, and the applicability of Corten–Dolan’s theory is verified. The fracture induced by the variable-amplitude fatigue is microscopically analyzed using scanning electron microscopy (SEM), revealing the mechanism of the variable-amplitude fatigue failure. Our findings provide valuable experimental data supporting the fatigue life estimation of grid structures with bolted spherical joints in service.

Grid structures with bolt-sphere joints are widely used in industrial plants. With the installation of suspension cranes, high-strength bolts are subjected to repeated alternating loads and cause fatigue problems. Due to their dispersive nature, the degree of difficulty and cost of fatigue tests are extremely high. Due to the lack of a recognized fatigue design method, engineering designers have encountered great difficulties, and the promotion and application of such methods are severely restricted. In this paper, we successfully implemented a constant-amplitude fatigue test of M39 high-strength bolt specimens on an American MTS Landmark 370.50 fatigue testing machine and obtained the corresponding S-N curve from the statistical analysis of the test data. Using the nominal stress amplitude Δσ and the hot point stress amplitude Δσk as the design parameters, we established a corresponding constant-amplitude fatigue design method. We performed a microscopic analysis of the fracture surface using a TESCAN Mira3 LMH scanning electron microscope and revealed the fatigue failure mechanism of the high-strength bolts.

为了研究网架结构在悬挂吊车荷载作用下的受力特点,对某网架结构在不同吊车运行工况下的应力响应进行了现场实测和有限元模拟.结果表明,吊车运行对腹杆受力影响最为显著,杆件的应力变化与吊车行驶位置和吊车吊重之间存在明显的线性变化关系;吊车刹车作用以及邻跨吊车运行对被测杆件受力影响较小;考虑重物起吊和卸载对杆件受力的影响时,建议其作用放大系数取1.4;给出了吊车运行荷载的简化模拟方法,能较好地反映悬挂吊车对网架结构的荷载作用,模拟值与实测值吻合较好.随后,考虑悬挂吊车使用吨位的增大,模拟得到了吊重增加后网架结构杆件在吊车荷载作用下的应力变化曲线.研究成果将为研究和编制网架结构在悬挂吊车作用下的疲劳载荷谱提供数据支撑和参考依据.

针对太原植物园原设计结构中应力较低、截面尺寸偏大的构件进行优化分析,利用MIDAS Gen 对优化后的结构进行计算,结果表明在最不利工况及地震作用下,优化后的结构仍能满足设计及相关规范要求.对于结构中构造复杂、受力较大的相贯节点,提出了不同的加强构造措施,利用 ABAQUS 软件进行节点的有限元分析,考察节点在控制工况下的受力状态.结果表明,在最不利工况下,节点区域容易出现应力屈服,但通过适当的节点域加强构造措施,可以有效改善其受力性能,提高承载能力,使其满足节点的受力性能要求,证明了结构的优化方案是可行的.

Fatigue failure of a grid structure using bolt-sphere joints is liable to occur in a high-strength bolt due to the alternating and reciprocal actions of a suspension crane. In this study, variable amplitude fatigue tests were carried out on 20 40 Cr steel alloy M30 high-strength bolts using an MTS fatigue testing machine, and four cyclic stress amplitude loading patterns, Low-High, High-Low, Low-High-Low, and High-Low-High, were tested. The scanning electron microscope images of bolt fatigue failure due to variable amplitude stress were obtained, and the fractographic analysis of fatigue fractures was performed to investigate the fatigue failure mechanisms. Based on the available data from the constant amplitude fatigue tests, the variable amplitude fatigue life of an M30 high-strength bolt in a bolt-sphere joint was estimated using both Miner's rule and the Corten-Dolan model. Since both cumulative damage models gave similar predictions, Miner's rule is suggested for estimating the variable-amplitude fatigue life of M30 high-strength bolts in a grid structure with bolt-sphere joints; the S-N fatigue curve of the M30 high-strength bolts under variable amplitude loading was derived using equivalent stress amplitude as a design parameter.

A grid structure with bolted spherical joints (BSJs) is one of the large-span space latticed structures and has been widely used in industrial buildings. Under the alternating actions of the suspension cranes, fatigue failure of BSJs is liable to occur in a high-strength bolt. In this paper, the constant amplitude fatigue tests of 39 40Cr steel alloy M30 high-strength bolts used in BSJs were carried out using an MTS fatigue testing machine. The corresponding fatigue S-N curves were developed with the stress range as the parameter, and the test results were discussed with the theoretical values of the current specifications. Then, by means of the finite element analysis, the stress state and fatigue failure position of bolts in BSJs in tension were discussed. The analysis of fracture morphology was performed to investigate the fatigue fracture characteristics. Finally, on basis of fatigue damage theory, a high-cycle fatigue damage model was adopted to describe the development process of fatigue damage.

Experimental study on constant amplitude fatigue performance of seven M30 high strength bolts with false twist is conducted.The fatigue failure modes of M30 high strength bolt under the condition of false twisting are obtained,the fracture morphology of the bolt rod is analyzed.And the corresponding S-N fatigue curves and expressions are established.Finally,compared with the fatigue test results of the existing M30 high strength bolts under the condition of full twisting,it is concluded that the fatigue strength of M30 high strength bolts controlled by 3 screw threads reduces by 75％.

With the wide application of self-tapping screws in prefabricated light-guage steel structure residence,the connection performance has obtained much attention.In this paper,the progress in research on shear,tensile and seismic properties of various components connected by self-tapping screws are summarized in details,which is based on the relevant research literature at home and abroad.And the design methods of shear and tensile strength of self-tapping screws in China,USA,Europe and other countries are compared.Finally,some suggestions are put forward about the problems of the self-tapping screw connection that need to conduct further study.

采用电阻率法定量研究土的孔隙特征,通过试验测量了不同孔隙率的饱和砂在不同电流频率下的交流电阻抗,然后研究电阻率、电流频率以及孔隙率之间的关系.结果表明:孔隙水的电阻率随频率的增加而减小;饱和砂的电阻率随电流频率的增加而减小;饱和砂的电阻率随孔隙率的增加而减小;结构因子随电流频率的增加而增加;结构因子随孔隙率的增加而减小;最后在分析等效电路的基础上建立了考虑电流频率变化的饱和砂电阻率模型.

Microstructures and mechanical properties of AM60 magnesium alloy with Sm and Ti addition were investigated through OM, SEM XRD and DNS100 electronic universal testing machines. The results show that the alloy grains can be rinfined by the addition of Sm and Ti.The morphology and distribution of beta-Mg17Al12 phase changed from continuous/discontinuous netlike or strip form to cobble or particulate form and even dispersed,respectively.The addition of Sm and Ti obviously improves the microstructure. There are some Al3Ti phase formed after the additon of Ti. Particle phase of Al2Sm,Mg41Sm5 and spherical phase of Al18Ti2Mg3 formed when the addition both of Sm and Ti. The Rod-shaped phase in the alloy dismissed or transformed roundly and massive particles become smaller after the inoculation of Ti and T-6 process subsequently. With addition of 1.0% Sm and 0.4%Ti both, the tensile strength and elongation reached 226MPa and 6.7% , elevated by 34.5% and 39.6% respectively;The heat tensile strength and elongation at 200 degrees C reached 170Mpa and 10.4%, elevated by 53.2% and 82.5% respectively. T6 process can further enhance the mechanical properties of AM(60).

Filling and solidification process of permanent mold casting Mg or Al alloy tensile testing bar were simulated by the ProCAST software to understand various physical field and to optimize gating system design. The simulated results are well in agreement with experimental ones. The results verify that the optimized gating system can effectively eliminate casting defects in the testing bar so that mechanical properties of the permanent mold casting bar are nearly the true value.

Factors that affect residual stress of tensile specimen such as pouring temperature,mold temperature and mold open time were analyzed by the methods of orthogonal test and numerical simulation.The results show that mold open time is the main factor that influences the residual stress.The residual stress can be reduced by adjusting the mold open time.Impact of mold temperature on the residual stress is less than that of mold open time,and the residual stress decreases with increasing of mold temperature.Residual stress is little affected by pouring temperature.