Anchor Stiffness Research Articles

Pull-out behavior and failure mechanism of steel expansion anchors in high-performance steel fiber reinforced concrete(HPSFRC)

Past research on the pull-out performance of anchors mainly focuses on normal concrete(NC) concretes. New design methods are needed for the pull-out performance of anchors in the concretes of new cementitious materials with high strength and toughness. Accordingly, the pull-out behavior of torque-controlled expansion anchor(TCE) in high-performance steel fiber reinforced concrete(HPSFRC) concrete with different fiber content and installation conditions(embedment depth and anchor diameter) was investigated. The focus was on the failure modes, crack morphology, and load-displacement behavior(including pull-out load-bearing capacity, anchorage stiffness, and anchorage toughness). The addition of fibers leads to increased load-bearing capacity and toughness, reduced stiffness, and all failure modes exhibited ductile cracking and sufficient tensile ductility. Both diameter and depth had a positive impact on load-bearing capacity. A broader database based on literature and this study was analyzed for further exploration of the effects of fibers. The accuracy of predicting load-bearing capacity was compared between two empirical models(concrete capacity design-CCD and Toth models) and the proposed modified model. The CCD model greatly underestimates capacity, and the Toth model is unsuitable for high fiber content(exceeds 2.0 %) HPSFRC scenarios. The modified model showed the best bearing capacity prediction for anchors on HPSFRC concretes, with a mean ratio of predicted values to experimental values reaching 1.01–1.08 and a coefficient of dispersion below 15.0 %.

Numerical analysis of the displacement of retaining wall in the Carpathian flysch region

This paper presents a numerical analysis of the displacement of the substructure for the construction of the S1 route bypassing Węgierska Górka. The numerical analysis includes displacement calculations taking into account the ground anchor stiffness obtained in acceptance tests. The results of the analysis were compared with monitoring measurements. A sensitivity analysis was carried out in relation to the soil parameters used and the achieved ground anchor stiffnesses

Design method of prestressed anchor bolt system for wind turbine foundation

SummaryThe prestressed anchor bolt system is a reasonable connection mode between the upper steel tower and the bottom concrete foundation for multi‐megawatt wind turbines. This prestressed anchor bolt connection with forged flanges has a similar form to the prestressed high‐strength bolt connection with forged flanges between steel tubes for the tower. However, their mechanical performances have a great difference because of the influence of the stiffness of the anchorage zone in the concrete foundation. Based on the Petersen's method, the engineering calculation method of the prestressed anchor bolt system for wind turbine foundation is derived. The tensile force of the anchor bolt, the anchorage stiffness and clamping force of the base are all deduced according to the theories of mechanics of materials. The numerical models of the segment foundation with the unfavorable anchor bolt and the overall foundation with all anchor bolts are developed for researching the influence of the spatial effect of adjacent segments on the restraint stiffness of the concrete foundation. The numerical analyses of four engineering cases designed by engineering calculation method are carried out for verifying the effectiveness of engineering calculation method. The analysis results show the spatial effect of adjacent segments can be neglected and the Petersen's method can be directly applied for the design of the prestressed anchor bolt system for wind turbine foundation in engineering practice. The engineering calculation method meets the accuracy requirements in engineering practice and can be used to design the prestressed anchor bolt system of wind turbine foundation.

Assessment of Post-Installed Anchor Stiffnesses in Uncracked Concrete with Different Types of Coarse Aggregates

This paper investigates the potential influence of different aggregates in the concrete mix design on the concrete cone resistance of different types of anchors as well as the anchor stiffness. In fact, bonded anchors with three different adhesives and mechanical anchors and concrete screws of two types were installed in five different concrete mixes and tested in a standard tensile configuration using pull-out tests with wide support resulting in concrete cone failure. A rigorous analysis of both the initial and secant stiffness values of the different anchor types is carried out in a comparative manner. The results of the experimental program show that the anchor stiffnesses are not influenced by the different aggregates in the concrete mixes, but rather by the type of anchor. Finally, this manuscript provides a narrow range of both initial and secant stiffness values with respect to anchor type only.

Shear stability and resistance design of novel vertically-flexible stiffened steel plate shear walls

Steel plate shear walls (SPSWs) have been widely employed in practical engineering projects. The steel plates inevitably endure axial loads due to the gravitational forces and structural settling. However, vertical pre-compressive loads have detrimental effects on the buckling behavior and shear resistance of the steel plates. Instead of strengthening the SPSWs to resist the vertical loads, a new type of vertically-flexible stiffened steel plate shear wall (VFS-SPSW) is proposed to minimize these adverse effects. The incorporation of hollow steel tube reduces the vertical compressive stiffness of the VFS-SPSW, leading to a decrease in the proportion of axial compressive loads transmitted to the steel plate wall from the boundary frame. Consequently, this feature facilitates the installation of VFS-SPSW without the necessity of awaiting the completion of the upper structure. In this paper, finite element (FE) analysis is conducted to obtain a threshold out-of-plane bending stiffness ratio for the stability of the VFS-SPSW. Subsequently, a formula for threshold out-of-plane bending stiffness ratio is proposed, including parameters of the ratio of torsional to bending stiffness and aspect ratio of the subpanel. Then, the anchoring mechanism of hollow steel tube to the tensile field of the steel plate is investigated. The threshold in-plane anchor stiffness ratio is defined to ensure the full development of the tension field in the steel plate. A formula for predicting this ratio is proposed by theoretical and numerical analysis. Finally, the reduction factor of vertical compressive stiffness for the VFS-SPSW at the threshold in-plane anchor stiffness ratio is calculated. The results indicate that the vertical compressive stiffness of the VFS-SPSW, which meets the threshold stiffness design requirements, can be decreased to below 50% of the traditional stiffened SPSW, while ensuring that the reduction in ultimate shear stress remains within the limit of 5%.

Tensile behavior and failure modes of expansion anchors in High-Performance Steel Fiber Reinforced Concrete (HPSFRC)

To investigate the tensile(pullout) behavior of expansion anchors in High-Performance Steel Fiber Reinforced Concrete(HPSFRC), 30 valid unconfined tension(pullout) tests on expansion anchors, studying the effects of different steel fiber content(0.0 %, 0.5 %, 1.0 %, and 1.5 %), embedment depths(25 mm, 35 mm, and 45 mm), and anchor diameters(10 mm and 12 mm) on the tensile behavior of anchors. A total of seven failure modes, including different types of mixed modes, are observed. The incorporation of fibers reduces the anchorage stiffness, increases the ductility, and improves the post-peak performance of the tensile behavior of anchors. Effective embedment depth(Hef)exerts a great influence on the failure mode; as Hef increases, the dominant failure mode transits from the concrete breakout to the pull-through and mixed failure modes, and finally the steel failure mode. The increase in Hef also leads to increases in the ultimate tensile strength of the anchor(Nu) and the anchorage ductile. For the same Hef and fiber content, compared to the smaller diameter(D), Nu for the larger diameter is larger but the pullout ductility is weaker. A modified model considering the influence of steel fibers is proposed to predict Nu of CB mode in HPSFRC, and it results in more accurate predictions compared to the existing prediction models(CCD model, Toth model). An existing prediction model for PT mode in normal concrete has been proven to be applicable for anchors HPC/HPSFRC.

A numerical analysis on anchored sheet pile wall subjected to surcharge strip loading

Anchored sheet pile walls are practically subjected to a surcharge load that exists on the field in the form of vehicles, buildings, and storage areas, those additional surcharge loads on the ground surface produce additional stress on the wall. In the present investigation, a three-dimensional finite element method is implemented to study the behavior of an anchored sheet pile wall under a uniform surcharge strip load. The influence of surcharge load and foundation soil types on wall deflections, bending moments, anchor forces, and backfill ground settlement are examined. A parametric study is performed by varying the wall stiffness, anchor stiffness, number of anchors and magnitude of surcharge load. The results show that medium dense foundation soil increases the passive resistance, so it reduces wall deflections, bending moments, anchor forces and ground settlement. Moreover, double anchorage effectively reduces wall deflections, bending moments, anchor forces and ground settlement than single anchorage.

Dynamic response and breakage of trees subject to a landslide-induced air blast

Abstract. Landslides have been known to generate powerful air blasts capable of causing destruction and casualties far beyond the runout of sliding mass. The extent of tree damage provides valuable information on air blast intensity and impact region. However, little attention has been paid to the air blast–tree interaction. In this study, we proposed a framework to assess the tree destruction caused by powerful air blasts, including the eigenfrequency prediction method, tree motion equations and the breakage conditions. The tree is modeled as a flexible beam with variable cross-sections, and the anchorage stiffness is introduced to describe the tilt of the tree base. Large tree deflection is regarded when calculating the air blast loading, and two failure modes (bending and overturning) and the associated failure criteria are defined. Modeling results indicate that although the anchorage properties are of importance to the tree eigenfrequency, tree eigenfrequency is always close to the air blast frequency, causing a dynamic magnification effect for the tree deformation. This magnification effect is significant in cases with a low air blast velocity, while the large tree deflection caused by strong air blast loading would weaken this effect. Furthermore, failure modes of a specific forest subject to a powerful air blast depend heavily on the trunk bending strength and anchorage characteristics. The large variation in biometric and mechanical properties of trees necessitates the establishment of a regional database of tree parameters. Our work and the proposed method are expected to provide a better understanding of air blast power and to be of great use for air blast risk assessment in mountainous regions worldwide.

Overall pull-out behavior of group anchored steel strands with 90-degree hooked type

The Precast Prestressed Assembled Structural (PPAS) system is a novel prefabricated structure system, which mainly adopts the group anchor technology for 90-degree hooked steel strands in the connection of beam-column members. For this connection, however, the anchorage performance of the group anchored steel strands with 90-degree hooked type has not been fully understood. For this reason, the overall pull-out tests on the 12 test specimens of group anchored 90-degree hooked steel strands were carried out by adopting the overall pull-out test device. The test results indicated that with the increase of the layout quantity of the steel strands in the concrete column from one row of one column (1 steel strand) to three rows of four columns (12 steel strands), the anchorage capacity, anchorage stiffness and energy dissipation capacity of the group anchor specimens were significantly improved, but its anchoring efficiency presents a three-stage change rule of slow attenuation (0.065) - gentle attenuation (0.025) - fast attenuation (0.105). The variation of the anchorage depth of the steel strands in the concrete column has more pronounced effects on the failure mode and pull-out load-overall slip response, indirectly affecting its ultimate anchorage capacity, overall slip, anchorage stiffness, and anchoring efficiency, but hardly affecting its energy dissipation capacity. Additionally, the anchoring efficiency is strongly related to the failure mode of the test specimens. For the failure mode of the steel strand fracture, the anchoring efficiency is always not less than 0.85, which is significantly higher than that of the overall pulling out of the steel strands, always between 0.70 and 0.80. • The overall pull-out tests on the group anchored 90-degree hooked steel strands were successfully carried out. • The multiple 90-degree hooked steel strands with smaller anchorage lengths tended to be overall pulled out. • Increasing the layout quantity of steel strands in the concrete column can effectively improve the anchoring capacity. • Group anchored 90-degree hooked steel strands exhibited higher anchoring efficiency. • The influence of the group anchor effect on its anchorage performance cannot be negligible.

An experimental and numerical investigation of concrete pry-out failure after fire exposure: Group effects and failure mechanism

In the present study, the load-bearing capacity for concrete pry-out failure of the single stud anchor and multi-stud anchor groups after fire exposure is investigated experimentally and numerically. The main topic of the investigation is the influence of fire duration on the resistance and failure mode and the group effect on the load-bearing behaviour. The standard ISO 834 fire curve was employed. The numerical simulations were conducted using the thermo-mechanical model based on the microplane constitutive model for concrete, which was implemented into a 3D finite element (FE) code. The numerical model was first verified based on the performed experimental tests. Subsequently, the parametric study was performed in order to analyse the failure mechanism and the load distribution over the studs of the anchor group. It was shown that the employed numerical modelling technique can successfully predict the pry-out failure mode and the load-bearing behaviour of anchor groups after fire exposure. The results show that the group effect on the shear stiffness of anchors is strong at ambient temperature, but moderated after fire exposure. The group effect on the pry-out failure load of anchors, both before and after fire exposure, is significant. The evaluation of the load distribution at the interfaces between anchor and concrete contributes to a better understanding of the concrete pry-out failure mechanism before and after fire exposure.

Experimental response of cold-formed steel stud shear wall with hardboard sheathing under seismic loading

In the design of cold-formed steel (CFS) buildings, sheathings are used to provide lateral resistance to seismic or wind load. Many researchers have thoroughly studied the basic behavior of different sheathing (including walls sheathed with plywood, oriented strand board, gypsum wallboard, gypsum sheathing board, steel sheet sheathing, and fiberboard) with different thicknesses. However, despite many studies, the examination of existing experimental studies demonstrates that the lateral bracing and stiffness provided by the sheathing are generally ignored, and sheathing is provided as a non-structural component. This study aims at that neglected aspect. In this study, cold-formed steel shear wall (CFSSW) response has been investigated with varied thickness of hardboard sheathing used as a structural element. The main aim was to determine the contribution of sheathing in resisting lateral forces. For this purpose, three full-scale specimens (i) frame without sheathing, (ii) frame sheathed with 4 mm thick hardboard, (iii) frame sheathed with 10 mm thick hardboard were tested using a uni-directional shake table. The sheathing was screw-fastened to the cold-formed studs and tracked for the development of shear stiffness and strength in the wall system. The test results revealed that in addition to increasing the lateral stiffness of the structure, the hardboard sheathing also acts as an efficient bracing system. However, some minor but recoverable damages were also noticed. In addition, stud local buckling failure mode was observed, and it could be caused by the low anchor stiffness of using cleats instead of hold-downs. It is also important to mention that the number of tests performed in the current study was limited, and further similar research needs to be carried out before generalizing the results.

Influence of the rocking behavior of shearwalls on the fundamental period of CLT structures

AbstractThe comparison of results obtained from on‐site modal tests and numerical analyses presented in recent studies showed that Cross Laminated Timber (CLT) buildings may exhibit a significant shift of fundamental period from the condition when rocking does not occur to the condition which the shearwall rocking is activated for. The objective of the current study is to establish a relationship between the fundamental period of CLT structures and the lateral drift of their global dynamic response. The influence of the activation of rocking behavior on the fundamental period was investigated by using experimental modal testing and Finite Element (FE) numerical analyses. The results from an experimental campaign were adopted to validate an FE numerical model used to perform an extended parametric analysis. The shift of the fundamental period from the value of period representing the condition for which the rocking of shearwall does not occur is investigated via elastic nonlinear incremental dynamic analyses. The effects of vertical load, stiffness, and yield displacement of mechanical anchors and geometrical dimensions of CLT shearwalls are analyzed and discussed. An analytical expression to predict the maximum range of fundamental period which a CLT shearwall may exhibit under different levels of the dynamic lateral response is reported as a function of the vertical load and the equivalent rocking slenderness.

ПОСТРОЕНИЕ ГРАНИЦ ОБЛАСТЕЙ УСТОЙЧИВОСТИ РЕЖИМА СТАЦИОНАРНОГО ВРАЩЕНИЯ РОТОРНОЙ СИСТЕМЫ С ЖИДКОСТЬЮ, ОСЬ КОТОРОЙ РАСПОЛОЖЕНА В АНИЗОТРОПНЫХ ЗАКРЕПЛЕНИЯХ

Earlier, the authors generalized the original method for studying the stability of stationary rotation of rotor systems containing a viscous incompressible fluid, the axis of which is located in isotropic anchors, in the case when the viscoelastic anchors of the axis of the rotor system are anisotropic. The generalization is based on two theorems that say that finding the stability conditions of such systems is associated with the possibility of elliptical precession-type motion, and with such motion there is a special non-inertial reference frame in which the hydrodynamic elements of the system periodically change in time. The study of such movements allows us to construct the boundaries of regions with different degrees of instability, in particular, the boundaries of the stability regions of the stationary rotation regime in the parameter space of the problem. The boundaries of the stability regions are constructed for cases when the anchoring of the rotor axis is anisotropic. In the space of the anchorage parameters, a parametrically defined D-curve is obtained as a function of the dimensionless frequency of the rotor precession. The two most interesting cases are considered – anisotropic stiffness of anchors (damping is isotropic in this case) and the opposite situation: isotropic stiffness of anchors with anisotropic damping. The obtained results are compared with the known results for the case of isotropic anchoring of the rotor axis. It is shown that the anisotropy of anchors, which is always present in real rotary systems due to the imperfection of technologies for the production of anchors, does not lead to negative effects. Moreover, using the obtained D-curves, it is possible to obtain technological tolerances for the production of fasteners, using what is known as the permissible deviation of the stiffness or damping value along the axes.

Modified Algorithm of Anchor Cable Force in a Suspension Bridge Based on the Cable-beam Composite Structure

Traditional vibrating cable methods usually omit the influence of the bending stiffness of anchor threaded rods when measuring the cable force in suspension bridge tunnel-type anchorage, causing a great deviation in the measurement and calculation of the cable force. The cable tension in the anchorage was calculated using the cable–beam composite structure to improve the accuracy of the main cable force. Based on Hamilton’s principle and the assumption of cable–beam composite structure, a new measuring method was proposed by using the vibrating matrix equation of the cable–beam composite structure. Then, the matrix was solved using Mathematica. With the Qingjiang Suspension Bridge as a case study, the modified precision of the proposed method was verified by comparing its results with those of the conventional method and the finite-element method. Results indicate that using the cable–beam model to calculate the cable force can well describe the relationship among the cable force, the bending stiffness of the threaded rod, and the frequency of the cable. It also reduces the deviation induced by the bending stiffness of the threaded rod, which contributes to obtaining precise results about the actual cable state.

水下爆炸冲击作用下悬浮隧道响应参数分析

To investigate the dynamic responses of submerged floating tunnels (SFTs) subjected to near-field non-contact explosions, the SFT was simplified as a constant-section-and-stiffness Bernoulli-Euler elastic-support beam to establish the SFT dynamic model under underwater shock load. The differential equation for the vibration was resolved with the Galerkin method. The displacement, velocity and acceleration were analyzed for the SFT, the influences of the explosive quantity, the blasting distance and the vertical stiffness of anchor cables were discussed, and the results were also used to analyze the damage of tunnels and human bodies. The results show that, the impact of the blasting distance on the kinematic parameters of the SFT is significant. Moreover, the maximum displacement of the tunnel decreases in inverse proportion to the blasting distance. Compared with those of the blasting distance of 10 m, the displacements of the tunnel body of 20m and 30 m decrease by 50.7% and 66.6%, respectively. The impact of the explosive quantity on the kinematic parameters of the SFT is significant. Also, the maximum displacement of the tunnel decreases approximately in a low-order power function with the explosive quantity. Compared with those of the explosive of 20 kg, the displacements of the tunnel body of 40 kg and 60 kg increase by 29.8% and 51.3%, respectively. The impact of the vertical stiffness of anchor cables on the kinematic parameters of the SFT is significant. Besides, the maximum displacement of the tunnel decreases approximately in a step-like form with the vertical stiffness of anchor cables. Compared with those of the vertical anchor stiffness of 5×105 N/m, the maximum displacement of the tunnel body of 5×10⁶ N/m and 5×10⁷ N/m decrease by 53.0% and 86.2%, respectively. However, there is an efficiently acting interval for the anchor cable stiffness. The stiffness has significant influence on the displacement of the tunnel body within the interval, but has little influence outside the interval (large or small).

Influence of Anchor Connector Stiffness on Displacement-Internal Force of Steel-Concrete Frame

In the article, the author introduces how to determine the equivalent hardness of steel-concrete composite beam element, stiffness matrix and nodal load vector of steel-concrete beam element. Thereby, to build and solve the problem of analyzing the structural steel frame of concrete considering the anchor stiffness, programming and clarifying the impact of anchor stiffness associated with displacement - internal force of the frame.

Analyzing key factors of roots and soil contributing to tree anchorage of Pinus species

Tree anchorage is a primary function for plant survival which may reach its limit under extreme conditions such as windstorms. To better understand the processes and influential factors underlying tree anchorage, we analyzed the mechanical effects of root morphology and the material properties of roots and soil on the tree-overturning process with the recently developed finite element model RootAnchor. The root system was represented by a simplified 3D root pattern derived from an ensemble average of seven measured root systems of 19-year-old Pinus pinaster grown in sandy spodosol. Soil properties were measured by direct shear tests. Taguchi orthogonal arrays were used to examine the sensitivity of the geometric and material factors of roots and soil to tree anchorage. Tree anchorage was characterized by anchorage strength TMc and anchorage stiffness K0. Using a small number of numerical experiments, the sensitivity analysis prioritized only two key factors contributing to tree anchorage among the 34 factors considered. The results showed root morphological traits that played a dominant role in the material properties of roots and soil in tree anchorage. Taproot depth, the dimensions of the Zone of Rapid Taper (ZRT) and basal diameter of the windward shallow roots were the key factors contributing to TMc (variations > 8%). The dimensions of the taproot, root and soil stiffness, and the basal diameter of the leeward shallow roots were the most active factors for K0 (variations > 10%). These results provide insight into simplified tree anchorage expressions for the prediction of wind-induced uprooting.

Composite steel joist analysis using experimental stiffness factor from push-out tests

The stud anchor stiffness coefficient is vital for computing the deflections of composite steel joists (CSJ), although the way to capture this value can be challenging. A commonly used experimental method to compute this coefficient is the push-out test presented in EN-1994. However, the method does not address the incorporation of the steel metal deck currently used in the vast majority of composite decks. In order to tackle this problem, we present a modified version of the push-out experiment to better determine the stiffness coefficient when the stud anchor is placed in the weak or strong side with respect to the steel deck stiffener. Furthermore, 13mm and 16mm diameter studs are used in order to investigate lower capacities and to compare with the standard 19mm diameter connector. An analytical solution of the CSJ system which incorporates the stud anchor stiffness coefficient is utilized to predict the overall system deflection when the effective composite moment of inertia of the joist is included. Results demonstrate the effectiveness of placing the stud in the strong side, and the accuracy of the enhanced push-out test.

Experimental evaluation of tensile behaviour of single cast-in-place anchor bolts in plain and steel fibre-reinforced normal- and high-strength concrete

Abstract Cast-in-place anchor bolts embedded in plain and steel fibre-reinforced normal- and high-strength concrete members were subjected to monotonic tensile loads. The influence of the concrete member thickness, concrete strength, and the addition of steel fibres to the concrete mixture, on the anchorage capacity and performance was evaluated. The experimental results were evaluated in terms of anchorage capacity, anchorage ductility and stiffness as well as failure mode and geometry. Furthermore, the validity of Concrete Capacity (CC) method for predicting the tensile breakout capacity of anchor bolts in plain and steel fibre-reinforced normal- and high-strength concrete members was evaluated. The anchorage capacity and ductility increased slightly with increasing member thickness, whereas the anchorage stiffness decreased slightly. In contrast to the anchorage ductility, the anchorage capacity and stiffness increased considerably with increasing concrete compressive strength. The anchorage capacity and ductility also increased significantly with the addition of steel fibres to the concrete mixtures. This enhanced capacity and ductility resulted from the improved flexural tensile strength and post-peak cracking behaviour of steel fibre-reinforced concrete. The average ratio of measured strengths to those predicted by the CC method for anchors in plain concrete members was increased from 1.0 to 1.17 with increasing member thickness. In steel fibre-reinforced concrete, this ratio varied from 1.29 to 1.51, depending on the member thickness and the concrete strength.

Spatial dynamic response of submerged floating tunnel under impact load

AbstractIn order to analyze the global spatial dynamic response of a submerged floating tunnel (SFT) under the impact load, the tube is treated as a beam on elastic foundation (BOEF) with three degrees of freedom (horizontal displacement, vertical displacement, and torsion angle). The governing differential equations of the tube are derived based on the Hamilton principle considering the non-linear hydraulic resistance. The spatial displacement responses of the SFT are presented by the modal superposition method and Runge-Kutta method. The coupling motion of the horizontal displacement and torsion angle is also investigated. A finite element model of the SFT is established in ABAQUS to verify the results of the BOEF model, and the UAMP subroutine is used to simulate the effect of hydraulic resistance. Finally, the effects of the parameters, such as the anchorage stiffness, inclined angle of the cable, buoyancy-weight ratio, and hydraulic resistance on the impact response are studied. The results show the BOEF model is validated to be a suitable simplified method for the global impact response analysis. The coupling motion between the horizontal displacement and torsion angle has a significant influence on the torsion. The change of buoyancy-weight ratio has effect on displacement results and the natural frequency of the tube. It suggests the reasonable inclined angle of cable is between 45° and 60°. The hydraulic resistance considered in this paper had an effect of more than 20% on the maximum displacement, so it should not be ignored in analyses.