Anchor Bolts Research Articles

Cyclic Shear-Lag Model of Steel Bolt for Concrete Subjected to Impact Loading

AbstractThis paper presents a new cyclic piecewise linear pull-out push-in shear-lag material model representing the local bond behavior of preconstruction-installed steel anchor bolts for concrete...

Failure mechanism of surrounding rock with high stress and confined concrete support system

Surrounding rock control is a big challenge in roadway with high stress in deep underground engineering. To address this issue, Zhaolou coal mine – a typical kilometer deep well is taken as engineering background to monitor and analyze the original support scheme. The analysis shows that the following main reasons lead to the support failure in roadway with high stress in deep underground coal mine. Roadway deformation is large and lasts longer with a large extent of damage; all anchor bolts are in severely damaged surrounding rock zone without reliable adhesive basis; and U-shaped steel arch unevenly contacts with surrounding rock without sufficient bearing capacity. With summary of support failure mechanisms on-site, a concept of “high-strength and integrity support” is put forward; a support system with square steel confined concrete (SQCC) is developed; and a full scale in-door comparative test is conducted on its core component – SQCC arch and also on the conventional U29 arch. The research shows the bent and damaged legs of U29 arch result in dramatic reduction of bearing capacity of arch. However, the SQCC arch with similar steel content has a bearing capacity of 2.15 times of that of U29 arch and still has a higher post bearing capacity even after the arch is deformed dramatically. Quantitative evaluation index is established such as vault displacement control rate and bolt strength utilization rate; comparative analysis is made on surrounding rock control mechanism and the mechanical properties of support components under the influence from the four factors – arch strength, geostress, lateral pressure coefficient and surrounding rock mechanical parameters; and good control effect on surrounding rock of SQCC support is verified. Comparative tests are conducted on site. The monitoring results show the roadway surrounding rock deformation on the test section of SQCC support is only 21.2% of that on test section of U29 arch support; and no yield and damage occurs on the test section of SQCC support. Therefore, the SQCC support system is proved to be effective on surrounding rock control.

Comparison of Pigtail with J Anchor Bolt in Normal Concrete

Anchor bolts have been used to attach the steel structure of concrete and transfer load into the concrete. Anchor bolts in concrete are to withstand the shear force as they connect steel beams to the reinforced concrete foundations. The research was carried out to increase the understanding and investigating the performance of anchor bolts Pigtail since there is a lack of research on the bolt and to compare it with anchor bolts J which have been widely used by the industry. According to the methodology, testing the tensile load was used in this research to get a maximum load capacity of the anchor bolt in concrete. The sample was embedded in concrete cylinders of 75mm radius and 300mm height. Depths of embedment were 200mm, 230mm, and 260mm. The Universal Testing Machine, UTM was used to test the strength of tensile. 12 samples were used, each type and depth used two samples to get the average value using concrete grade 30. The samples underwent the process of curing for 28 days. The anchor bolts J used a 40mm bending radius and the length of hook was 100mm. Anchor bolts pigtail also used the 10 bending radius with depth of 8mm that have been compressed using 16mm radius rigs with a load of 500kN. Results of the research showed the depth of 260mm for Pigtail almost the same with J 60.529kN and 53.628kN and anchor bolts J were 75.557kN and 76.332kN. Difference of the values was not too far vary when compared with the 200mm and 230mm depths. Each comparison showed the ability of each bolt and anchor bolt failure occurred. Performance of the anchor bolts pigtail can be used on a structure or a higher load at an embedment of 260mm. Embedment of 200mm and 230mm can be used on a lighter load if steel material saving is a priority in every usage.

Peridynamic Model for the Numerical Simulation of Anchor Bolt Pullout in Concrete

Predictive simulation of anchor pullout from concrete structures is not only a serious problem in structural mechanics but also very important in structural design safety. In the finite element method (FEM), the crack paths or the points of crack initiation usually need to be assumed in advance. Otherwise, some special crack growth treatment or adaptive remeshing algorithm is normally used. In this paper, an extended peridynamic method was introduced to avoid the difficulties found in FEM, and its application on anchor bolt pullout in plain concrete is studied. In the analysis, the interaction between the anchor bolt and concrete is represented by a modified short-range force and an extended bond-level model for concrete is developed. Numerical analysis results indicate that the peak pullout load obtained and the crack branching of the anchoring system agreed well with the experimental investigations.

Evaluating the pull-out load capacity of steel bolt using Schmidt hammer and ultrasonic pulse velocity test

Steel bolts are used in the construction industry for a large variety of applications that range from fixing permanent installations to temporary fixtures. In the past much research has been focused on developing destructive testing techniques to estimate their pull-out load carrying capacity with very little attention to develop non-destructive techniques. In this regards the presented research work details the combined use of ultrasonic pulse velocity and Schmidt hammer tests to identify anchor bolts with faculty installation and to estimate their pull-out strength by relating it to the Schmidt hammer rebound value. From experimentation, it was observed that the load capacity of bolt depends on its embedment length, diameter, bond quality/concrete strength and alignment. Ultrasonic pulse velocity test is used to judge the quality of bond of embedded anchor bolt by relating the increase in ultrasonic pulse transit time to the presence of internal pours and cracks in the vicinity of steel bolt and the surrounding concrete. This information combined with the Schmidt hammer rebound number, R, can be used to accurately identify defective bolts which resulted in lower pull-out strength. 12 mm diameter bolts with embedment length of 70 mm and 50 mm were investigated using constant strength concrete. Pull-out load capacity versus the Schmidt hammer rebound number for each embedment length is presented.

Developing a water discharge anchor & trap bolt to prevent basic salt from penetrating to harbor structures

Developing a water discharge anchor & trap bolt to prevent basic salt from penetrating to harbor structures

Developing an improved water discharge anchor & trap bolt to prevent basic salt penetration to harbor structures

Developing an improved water discharge anchor & trap bolt to prevent basic salt penetration to harbor structures

Occurrence Mechanism of Roof‐Fall Accidents in Large‐Section Coal Seam Roadways and Related Support Design for Bayangaole Coal Mine, China

This study focused on large‐scale roof‐fall accidents occurred in large‐section coal seam roadways of Bayangaole Coal Mine, Inner Mongolia, China, and investigated the occurrence mechanism of roof‐fall and the related supporting control method in detail. Firstly, the fracture characteristics of the surrounding rocks on the roadway roof were measured using a stratum detector. The results showed that the roadway roof underwent the most severe failure with a maximum deformation of 3.53 m; the bedding separation and fracture zones were distributed at irregular intervals. Accordingly, the entire stratum was separated into several thin sublayers, significantly reducing the stability of roof. In addition, the roof medium grained sandstone of roadway is water‐rich strata, and water aggravates the damage of roof. Next, the mechanism of the occurrence of roof‐fall accidents in the roadway was elucidated in detail. The following three reasons are mainly attributed to the occurrence of roof‐fall accidents: (i) effects of mining‐induced stress and tectonic stress, (ii) existence of equipment cavern on the side of roadway, and (iii) unreasonable support parameters. On that basis, a new supporting design is proposed, including a more reasonable arrangement of anchor cables and bolts, bolts with full‐length anchorage which are applicable in cracked and water‐rich roadway, high‐strength anchor cables, and crisscrossed steel bands. Moreover, high pretightening force was applied. Finally, a field test was performed, and the mining‐induced roof displacement and stress on anchor cable (bolt) were monitored in the test section. The maximum roof displacements at the two monitoring sections were 143 mm and 204 mm, respectively, far smaller than the roadway’s allowable deformation. Moreover, the stress on roof anchor cables (bolts) was normal, and no anchorage‐dragging and tensile failure phenomena were observed. The monitoring data indicated that the new supporting design was remarkable on the control of large‐section coal seam roadway roof deformation.

Experimental Study on Bond‐Slip Behavior of Bamboo Bolt‐Modified Slurry Interface under Pull‐Out Load

This paper presents an analysis of bamboo bolt‐modified slurry interfaces based on 26 in situ axial pull‐out tests intended to highlight the mechanical behavior of interface under a fracture mode. Three impact factors are analyzed: anchorage length, bolt diameter, and bolt hole diameter, using the same materials of bamboo and modified slurry. The result shows that the interface between the bamboo bolt and anchoring agent is the control interface of an anchorage system, and the local behavior of the interface involves four stages: elastic, soften, friction, and decoupling. Distribution law and change trend of slippage, stress, and strain of anchoring interface along with the axial direction of an anchor bolt were analyzed. The result shows that there is effective anchoring length limit in this kind of interface, and that the complete decoupling phenomenon should not be neglected. Through a comparative analysis of the existing bond‐slip model and interface bond‐slip curve, and considering the correspondence of the strain‐slip curve and trilinear bond‐slip model simultaneously, a modified trilinear bond‐slip model has been proposed. The friction section of this model is limited, and shearing stress in the complete decoupling section is zero.

Experimental Study on Load-Displacement Relationship of Prestressed Cable in Red Clay Stratum

The P-S curves of prestressed anchor cable are obtained by field pull-out tests in the red-clay stratum in Guiyang area. The P-S curves of different theoretical models are discussed base on the theoretical analysis. The elastic and plastic displacement of prestressed anchor cable are analyzed. The results shows that, the anchoring effect are mainly effected by the red-clay mechanic properties in the red-clay stratum; the P-S curve of anchor bolt can be fitted well by the exponential model and conformed to the actual; the plastic displacement is used to anchor’s damage index are more truthfulness in the red-clay stratum.

Application of EEMD and neural network in stress prediction of anchor bolt

An estimation method for free bolt stress is described. Acoustic stress wave signals of free bolt were collected under different tensile forces and analysed in time domain and frequency domain after cross-correlation. The variations of wave propagation time, fundamental and secondary frequency of signals' spectrum are studied. Then signals are decomposed into intrinsic mode functions (IMFs) by ensemble empirical mode decomposition (EEMD). The normalised energy ratios and correlation coefficients of IMFs are also discussed. Propagation time, fundamental and secondary frequency of signals' spectrum, energy ratios and correlation coefficients of IMFs are influenced by applied tensile force. Thus they are selected as the components of eigenvector for inputs of neural network. Back propagation neural network (BPNN) and genetic algorithm (GA) optimised BPNN are used for tensile force prediction. Eleven sets of data were used to test the stress prediction effect of BPNN after training. The results indicate that the BPNN optimised by GA can achieve small errors for stress prediction.

Bolt quality testing research using weighted fusion algorithm based on correlation function

Bolt length is an important factor for quality evaluation of anchors. Because of the harsh detection environment and the interference caused by instruments, bolt testing signal contains a lot of noises that make it difficult to analyse and predict the parameters of anchor bolts accurately. In this paper, a non-destructive method based on information fusion of pseudo random signals is presented for bolt quality testing. After pseudo-random signals are generated by multiple sources, weighted fusion algorithm based on correlation function is proposed for fusion processing. Compared with the D-S fusion algorithm and average weighted fusion approach, the correlation fusion is verified to have higher accuracy and better retention of frequency characteristic. Finally, this proposed approach is proved to be more suitable for random signal fusion.

Application of EEMD and neural network in stress prediction of anchor bolt

An estimation method for free bolt stress is described. Acoustic stress wave signals of free bolt were collected under different tensile forces and analysed in time domain and frequency domain after cross-correlation. The variations of wave propagation time, fundamental and secondary frequency of signals' spectrum are studied. Then signals are decomposed into intrinsic mode functions (IMFs) by ensemble empirical mode decomposition (EEMD). The normalised energy ratios and correlation coefficients of IMFs are also discussed. Propagation time, fundamental and secondary frequency of signals' spectrum, energy ratios and correlation coefficients of IMFs are influenced by applied tensile force. Thus they are selected as the components of eigenvector for inputs of neural network. Back propagation neural network (BPNN) and genetic algorithm (GA) optimised BPNN are used for tensile force prediction. Eleven sets of data were used to test the stress prediction effect of BPNN after training. The results indicate that the BPNN optimised by GA can achieve small errors for stress prediction.

基于锚栓联接的装配式挡墙设计与施工工艺研究

基于锚栓联接的装配式挡墙设计与施工工艺研究

Seismic vulnerability assessment of a case study anchored liquid storage tank by considering fixed and flexible base restraints

Liquid storage tanks are among vital infrastructures, and their seismic vulnerability assessment plays a pivotal role in uninterrupted operation of an industrial plant. Technically, vulnerability notion relates capacity of each tank component's resistance to failure subjected to different seismic hazard levels. The predominant source of damage to liquid-containing tanks is steel shell buckling which can be intensified by base flexibility of fully anchored tanks. This flexibility is mainly resulted from anchor bolt failure and base concrete damage. In other words, the presence of anchors does not necessarily preclude anchorage failure or loss of concrete support, especially during large earthquake events.A case study on a liquid storage tank is introduced in this paper to highlight the influence of base flexibility on the seismic performance of fully anchored tanks. The tank is initially designed in accordance with the requirements of American Petroleum Institute, API-650. Fluid-structure interaction (FSI) is simulated by means of so-called added-mass approach. Two sets of finite element models are constructed, namely; fixed base (FB) and flexible base (FLB) tank. Nonlinear time history analysis based on a suite of twenty-two multi-directional spectrally matched acceleration time histories are conducted. Simultaneous input motions of two horizontal components are of particular importance as they shift the position of failure mechanism to directions being more affected by combined accelerations. Critical intensity measures (IMs) according to incremental dynamic analysis are then determined. Fragility curves are obtained by introducing conditional probability of failure as a function of critical IM. Results reveal that modelling base flexibility may contribute to lower value of critical IMs compared to that obtained from restrained support model. More specifically, FLB model demonstrates lower value of endurable peak ground acceleration (PGA) compared to the initial value selected for the tank design as per API requirements.

Experimental Study on Determining Design Parameters of Non-Prestressed BFRP Anchor for Supporting Soil Slope

Basalt fiber-reinforced polymer (BFRP) is a high-strength, lightweight material with an anti-corrosion property and a thermal expansion coefficient that is close to that of concrete. When used as an anchor bolt material, the corrosion problem of steel anchors can be solved fundamentally. In recent years, the BFRP bar has been applied in geotechnical anchorage engineering. In this study, the mechanical properties of the BFRP bar were studied by tensile, shear, corrosion resistance, and bonding strength tests with cement-based materials. In accordance with the design specifications of the steel anchor and existing research results, the design parameters of the non-prestressed BFRP anchor in supporting soil slope were proposed. To examine the reinforcing effect of the BFRP anchor, this study adopted the recommended parameters to design a BFRP anchor in an actual soil slope. A field contrast test of the steel anchor was also carried out. Experimental studies yielded the following conclusions. First, the tensile-strength safety factor of the non-prestressed BFRP bar should not be less than 1.6 (permanent) and 1.4 (temporary). The tensile-strength standard value was 80% of the ultimate tensile strength, and the value of the BFRP bar (diameter ≥ 12 mm) commonly used as an anchor was 710 MPa. The bonding-strength standard value between the BFRP bar and cement was equal to the average value divided by 2.1 of the pull-out test, and the common value was 2.8 MPa. The monitoring field test data proved that the designed BFRP anchor demonstrates better control displacement and can effectively retain soil slope. Moreover, the reinforcing effect of the BFRP anchor was equivalent to that of the steel anchor. Thus, the design of the BFRP anchor is reasonable, and the equal strength substitution method can be used to design the BFRP anchor.

Field experimental study on the retrofit of cracked onshore wind turbine foundations using externally prestressed anchor bolts

Inserted rings are considered as a crucial element of onshore wind turbine foundations to resist uplift and compressive forces at the interface of the steel towers and concrete foundations. These inserted rings can be deficient because of the crushing of the concrete and the occurrence of cracks as the result of the vibration of the tower and the shrinkage of the concrete. Therefore, it is very important to develop an efficient retrofitting system in order to restore the lost capacity and/or even outperform it. The objective of this paper is to develop a retrofit strategy for the deficient foundations using external prestressing technique and verify it using field data. A field test was conducted on two onshore wind turbine foundations with almost the same level of cracks. One of them was retrofitted using externally prestressed anchor bolts after the appearance of cracks, and the other was the control foundation. Strain sensors were installed in the foundation and strain signals were recorded in the period of construction, prestressing, and operation. Field test results showed that the prestressing technique can limit the crack width and improve the section stiffness.

Cyclic loading tests on exposed column-base plate weak-axis connections of small-size steel structures

Research on evaluating the seismic performance of exposed column-base plate weak-axis connections of small-size steel structures is substantially limited. Therefore, in this study, six exposed column-base plate weak-axis connection specimens with L-shaped anchor bolts under cyclic loading were tested. The primary test variables were the thickness of base plates, the presence of rib plates, and the number and embedment length of anchor bolts. Furthermore, round and threaded rods with L-shape were used as anchor bolts to assess the effect of bond performance. It was found that the structural performance of the connections was influenced by the thickness of base plate and the bond performance of anchor bolts. It should be noted that although base plate meets the minimum thickness requirements by the current design code, if the base plate yields before the moment capacity of steel column reaches the plastic moment, the structural performance of the connection will decrease. The connection details in this study can be considered semi-rigid connections. Threaded anchor bolts with L-shape are more preferred over the smooth round anchors for increased bond strength. Furthermore, equations for required tensile capacity and cross-sectional area for anchor bolts were derived in this study.

03.18: Anchor bolt tensile load distribution: Effects of the column base‐plate design: Wide flange column bases – loading on additional line of bolts

ABSTRACTThe designer of column base elements usually considers that the uplift force existing in the column member is equally distributed on its anchor bolts. While this simplified approach may be used for the most common cases of a steel structures (for instance, when only 4 equally spaced anchor bolts exist in the column base design), it may lead the designer to overlook that the distribution of uplift loads is highly influenced by factors such as the rigidity of the base plate, the positioning of its stiffeners and the number and geometric arrangement of the anchor bolts. This unequal distribution of uplift loads on the anchor bolts may cause overloading on some of the anchor bolts, leading to diverting failure. This paper analyses through finite element several different wide‐flange column base elements, with varying plate thicknesses and geometry. The conclusion summarizes that the distribution of the loads on the anchor bolts largely depend on the typology of the base plate and suggests a revision of the codes to be more precise on when unequal axial tensile loads may arise on the anchor bolts and recommend more refined methods for the estimation of those unequally distributed loads.

03.14: Steel connections with thermal barrier for nearly zero‐energy buildings (NZEB)

ABSTRACTThis paper summarises the results of a study assessing the thermal and mechanical performances of two solutions of thermal breaks for external steel structures (balconies, passageways …) attached on a façade with external thermal insulation. The first solution is composed of a PVC plate and an acoustic insulation between the end‐plates of the attached beams and the support (floor slab, concrete wall …). The second one is composed of a PVC plate between a saddle and the support and an acoustic insulation under the beam flange. This solution should be used only in the case of a steel structure with supporting elements (columns, cables…) as it does not transfer bending moments. The thermal performances were evaluated by numerical simulations. They showed a reduction by 30 to 65% of the thermal bridge at the attached steel structure connections. The rate of reduction depends on the configuration of thermal break (thickness of insulation, anchor bolts…). As deformable layers are used, between the steel plates and the facade support, the thermal breaks are unconventional steel connections with mechanical performances to be deeply investigated. Thus, an experimental program including static and cyclic tests is performed on various configurations of end‐plates and saddle with thermal breaks to evaluate their mechanical behaviour considering the stiffness and the resistance.