Study on Safety Performance of Building Finish Layer under Thermomechanical Coupling Condition

The building finish layer is a comprehensive structural system including the building exterior insulation system and building exterior finish. Combining with buildings has the advantage of reducing wall heat loss and building deformation caused by large temperature differences. Since the building finish layer is prone to cracking, hollowing, and peeling, during the application process, its safety needs to be studied and certified. This study prepares 20 groups of specimens, 15 anchor bolts in each group. The anchor bolt pull-out strength test is carried out. Anchoring damage evolution law and failure mode of anchor bolts are investigated. And the influence of anchoring methods on the pull-out bearing capacity is analyzed. In addition, ABAQUS finite element data simulation is carried out. The stress state of finish in thermomechanical coupling condition and without the effect of temperature are compared and analyzed. The influence factors of anchor bolt pull-out strength and the influence of temperature load on the long-term performance of building finish layer are obtained. The durability of the building finish layer is analyzed. The results show that the anchoring strength of the anchor bolt is positively correlated with the anchoring depth. The anchoring strength is influenced significantly by anchoring construction sequence and temperature. The stress under the coupled effect of temperature and load is greater than that of the single effect of load, and the stress distribution changes significantly. Due to thermal expansion and contraction, the anchor bolt would loosen, which is more prone to damage the building finish layer in a low temperature environment. The weight relationship of each influencing factor of the building finish layer is proposed. A systematic evaluation index system is established. The results of this study provide a basis for subsequent related research work and engineering applications.

An Analytical Study on the Pull-Out Strength of Anchor Bolts Embedded in Concrete Members by SPH Method

As an important method for connecting structural members, anchor bolts have been installed in many situations. Therefore, accurate evaluation of the pull-out strength of anchor bolts has always been an important issue, considering the complicated actual installation conditions and the problem of aging deterioration of the structural members. In general, the patterns of pull-out failure of anchor bolts can be classified into three types: adhesion failure, cone failure, and bolt break. However, it sometimes shows a mixed fracture pattern, and it is not always easy to predict the accurate pull-out strength. In this study, we attempted to evaluate the pull-out strength of anchor bolts under various installation conditions using SPH, which can analyze the crack growth process in the concrete. In particular, the anchor bolt-concrete interface model was introduced to SPH analysis in order to consider the bond failure, and it was confirmed that various failure patterns and the load capacity could be predicted by proposed SPH method. After that, the influence of several parameters, such as bond stress limit, anchor bolt diameter, and the anchor bolt embedment depth on the failure patterns and the load capacity, were investigated by numerical calculation. Furthermore, several useful suggestions on the pull-out strength of anchor bolts under improper installation conditions, such as the ends of members for the purpose of seismic retrofitting, are presented.

Electrochemical Study of Stainless Steel Anchor Bolt Corrosion Initiation in Corrosive Underground Water

Application of low-nickel stainless steel anchor was one of the economical and effective methods to solve the durability problem of slope engineering. At present, there are scarce reports about corrosion characteristics of low-nickel stainless steel in various underground waters. For investigating the corrosion initiation of stainless steel anchor bolt in corrosive underground water, the effect of SO42−, HCO3− and pH value on the corrosion behavior of 201 low-nickel stainless steel was studied via electrochemical methods. As the SO42− concentration, HCO3− concentration or pH value increase, the open circuit potential and polarization resistance increase, while the double-layer capacitance, donor density and passive current density decrease. The results indicate that corrosion is inhibited by SO42−, HCO3− and OH− in underground water. In addition, the inhibitive efficiency of SO42− and HCO3− increases with the SO42− and HCO3− concentration.

Assessment of Rotational Stiffness for Metallic Hinged Base Plates under Axial Loads and Moments

Pinned base plate connections are the most common base connection used in low-rise steel buildings. In this research, an extensive parametric study is performed using the Finite Element (FE) software Abaqus to determine the elastic rotational stiffness, moment resistance, and energy absorption of the pinned base plate connection connected to a reinforced concrete footing and subjected to an eccentric axial load. The developed FE model is validated using experimental results from the literature. Moreover, an intensive parametric study is conducted to understand the behavior of these connections better. The investigated parameters include the base plate thickness, anchor bolt diameter, and arrangement and number of bolts. The most effective parameters that affect the elastic rotational stiffness and moment resistance of pinned base connections are the anchor bolt arrangement and diameter. The maximum increase in the rotational stiffness was 53% for the anchor bolt diameter of 30 mm when the base plate thickness increased from 12 mm to 30 mm. Based on the base plate thickness, the moment resistance is improved by 150–260% when the bolt diameter increases from 12 mm to 30 mm.

Fault Feature Extraction for Anchor Bolt Loosening of Escalator Based on EWT and Bispectrum Analysis

Escalator is an essential large-scale public transportation equipment. Once the failure occurs, it will inevitably affect the operation and even cause safety accidents. As an important part of the structure of escalator, the loosening of the anchor bolt will lead to abnormal operation of escalator. Aiming at the current difficultyin extracting the fault features of anchor bolt loosening, a fault feature extraction method of escalator anchor loosening is constructed based on empirical wavelet transform (EWT) and bispectrum analysis. First, perform EWT decomposition of the original footing vibration acceleration signal to obtain a series of empirical mode functions(EMFs).Then, for each empirical mode function, the bispectrum was calculated by using bispectrum analysis method, and six texture features of the bispectrum were extracted as fault feature vectors by means of gray-gradient co-occurrence matrix. Finally, the extracted multi-scale fault feature vectors and bi-directional longshort-term memory (BI-LSTM) were used to classify and identify the four types of fault signals with different degrees of foot loosening, and the fault types of foot loosening were determined. The results show that the feature extraction method based on empirical wavelet decomposition and bispectrum analysis can more effectively identify the loosening level of anchor bolts.

A Study of Safety Coefficient Determination and Support Parameter Optimization Based on Vulnerability Preevaluation

The preevaluation to the vulnerability of the surrounding rocks is proposed as one of the reliable indicators of the safety coefficient of gateway support and a foundation to optimize the support design parameters. In this study, taking the surrounding rocks, stress, geological environment, and service time into consideration, the safety coefficient is determined based on the vulnerability scores calculated by the vulnerability preevaluation model of the surrounding rock. Applying the safety coefficient to the instability evaluation of the composite rock-bolt bearing structure, the strength required to maintain the stability of the gateway is calculated, which further provides references and guidance to the optimization of the anchor support parameters. This method has been successfully adopted by the GuCheng coal mining project in N1303 tailgate to strengthen the anchor-bolt structure in the roof watering area especially the main inclined shaft. Applying more accurately calculated strength to the anchor-bolt structure can effectively avoid the issue of overcompensation, thus reducing the cost and increasing the driving speed. Furthermore, this method provides insights into optimizing design parameters of the gateway. This method provides a reliable basis for the optimization design of bolt support parameters in coal mine gateway.