Anchor Support Research Articles

Anchorage of shear reinforcement in beams and slabs

Anchorage of shear reinforcement, such as links or stirrups, can be performed by providing hooks, bends or heads at their ends, by welding transverse reinforcement or by closing open stirrups with pins. Hooks and bends, also used to enhance the anchorage of flexural reinforcement at the end regions of beams and slabs, have often been preferred because of their simple and cost-effective production. Such anchorages present nevertheless several peculiarities that shall be accounted for. They are relatively sensitive to their detailing (mandrel diameter, length of the tail segment between bar end and bent region) as well as to the cracking state of the surrounding concrete. Also, brittle failures can occur due to spalling of the concrete cover in case of bars near to a free surface.The anchorage with hooks and bends is currently still widely designed according to old detailing rules, based on the results of tests performed in many cases with materials whose properties are significantly different than those of nowadays. Also, no mechanical models are available for a consistent verification and detailing, acknowledging the different potential failure modes and their interaction with the surrounding concrete. In an effort to provide a consistent approach to its design and verification, this paper presents an investigation addressed at understanding the mechanical response and performance of bend and hook anchorages. To that aim, the results of an experimental programme performed with state-of-the-art instrumentation are introduced. By means of analysis of Digital Image Correlation and Fibre-Optic Measurements, the complete transfer of forces is analysed under different circumstances. On that basis, a consistent mechanical model is developed and validated, also reproducing a large variety of tests found in the literature. The paper introduces eventually several practical considerations on the activation of shear reinforcement in beams, and the level of performance required at its anchorages.

Study on Antiweathering Support Technology of Thin Spray-On Liners in Shallowly Buried Coal Seam Roadway under Corrosion Condition

The thin spray-on liner is an inorganic polymer product that has been widely used to support mine perimeter rock roadways, but it is mainly used in metallic hard rock roadways with high rock strength and is less used in roadways affected by roadway corrosion and weathering in shallowly buried coal seams. Therefore, this study studies the thin spray-on liner support technology under such geological conditions. First, the causes of anchor support failure in this condition are analyzed, and it is concluded that alkaline ionized water corrodes the anchor rods, and chloride ions in the water play a role in accelerating the degree of anchor rod corrosion. Next, microscopic testing was used to determine the content of weathering and swelling minerals contained in the roof rock and the development of tectonic fissures. Third, the loosening circle of the surrounding rock is theoretically calculated and used as a basis to design the anchor mesh rope support parameters for the roadway. Finally, the construction process of a thin spray-on liner anticorrosion and antiweathering support technology is introduced. This technology improves the anchor force environment of anchor rods while incorporating anchor rods (ropes)—rock—metal mesh into the support system to play a coupling support role. On-site monitoring is performed to derive the optimum thickness of the spraying layer in different environments. At the same time, the deformation of the roadway surrounding rock and the anchor force can be improved to meet the requirements of anticorrosion and antiweathering and tighten the roadway surrounding rock. Compared with concrete support technology, the economic and environmental benefits of this support technology are apparent, and it helps to promote the application in shallowly buried coal seam mines.

Unified approach for reinforcement development length using the partly cracked elastic stage for bond strength

Current structural design codes in the United States treat the development of straight bars/lap splices, standard hooks, and deformed headed bars with separate equations. The fib Model Code 2010, on the other hand, uses a more unified approach. Recent changes to the standard hook and headed bar equations in the ACI 318–19 Building Code Requirements for Structural Concrete have sparked conversation about the discrepancies between ACI 318–19 and the AASHTO LRFD Bridge Design Specifications within the bridge design community. The objective of this research was to develop and validate a unified approach for the design/evaluation of reinforcement anchorage. A procedure based on the partly cracked elastic stage of bond was proposed. The proposed procedure was validated with 1006 tests from the literature.

Simple rebar anchorage slip macromodel considering corrosion

Reinforcement slip in the footing of a reinforced concrete (RC) column can significantly influence the lateral displacement of the column, a critical structural response under lateral loads such as seismic loading. Many past researchers studied and developed models to capture the anchorage slip of rebar; however, there is still a need for a model that can reflect the actual bond-slip relationship (especially in the presence of corrosion) and yet is simple-to-use for structural analysis. In this study, a simple bar stress-slip macromodel is developed to predict reinforcement anchorage slip given a rebar stress. The proposed rebar anchorage slip model is derived by implementing a macromodel solution based on a simple bond stress distribution function that captures the bond stress distribution numerically obtained from a real bond-slip relationship. Available experimental bond stress-slip data collected from literature are used to optimize the model parameter in the proposed bond stress distribution function, which reflects the impact of the structural parameters on the rebar slippage such as concrete strength and corrosion level. The proposed rebar slip model is then incorporated into a fiber beam-column model for numerical analysis, and is further validated by comparing flexural behavior of several RC columns (with and without corrosion) based on the numerical model with the experimental data. The results demonstrate the importance of incorporating rebar slippage and corrosion effect on bond. Using this fiber beam-column model, seismic performance of an example RC bridge column is evaluated, and one can conclude the rebar slip plays a critical role in the seismic evaluation. As the proposed rebar slip macromodel provides simple formulation and it is explicitly expressed with a model parameter that can be updated easily to incorporate new information, it is practical for structural analysis applications.

Analytical Studies on Retrofitted Anchorage System in Concrete using Strut and Tie Method

Analytical studies were conducted on force transfer mechanism of retrofitted anchorage system in structural concrete by Strut-and-Tie modeling (STM). Post Installation of Headed anchorage (PIHA) as supplementary system introduced for implicit strengthening of anchorage system. The boundaries of STM are considered under direct tension pull-out test. Five different configurations of conventional reinforcement anchorage in concrete with straight bar, 90-degree bend, 180-degree hook, single head and double head bars are retrofitted by using PIHA technique. The mechanics of force transfer in anchorage system was analyzed by STM and validated the results by experimental program. The study parameters considered are (i) location of nodal zone, (ii) strut angle, (iii) size of strut (concrete) contributed during failure. The study variables are (i) configuration of anchorage system (ii) characteristic node formation and (iii) presence of supplementary reinforcement. The result shows good agreement with experimental findings against failure mode, stress pattern, and location of critical zone in conventional and retrofitted anchorage system. Use of this study may further extended to assess theoretical evaluation of failure mode, formation of critical section and stressed regions of discrete RC elements such as corbel projection, bracket connections and beam-column joints.

Sanctions and the Exchange Rate

Stabilising the exchange rate allows the Russian government to anchor inflation expectations and support consumption but comes at the cost of the financial repression of domestic savers.

Shear capacity of inverted-U reinforced concrete bridge beams

ABSTRACT Existing reinforced concrete inverted-U beam bridges in Western Australia built using standard beams designed by Public Works Department between 1957 and 1969 were found to have reinforcement anchorage detail at supports not adequate when assessed using recent design standards. Tests were carried out on six full-size bridge beams recovered from a bridge scheduled for replacement to determine whether the deficient detailing adversely affects the shear capacities of these beams. These beams were the longest of the series designed in 1957. In addition, the mean shear strengths of the five bridge beams to AS 5100.5–2004 and to the most recent design standard AS 5100.5–2017 were determined and these were compared with their corresponding test values. It was found from testing that the detail does not affect the shear strength much. The predicted mean shear capacities using AS 5100.5–2017 were found to be more conservative than the corresponding values using AS 5100.5–2004. This suggests the likelihood of low load ratings for shear using the latest design standard (based on the Modified Compression Field Theory) for existing reinforced concrete bridges designed to previous standards.

Stability of expansive soil slopes reinforced with anchor cables based on rotational-translational mechanisms

Expansive soil slopes are usually characterized with conspicuous fissures. Pre-stressed anchor cables are effective techniques in improving the slope stability. Explicit considerations of the fissures and the suction effect become crucial in producing more realistic solutions. Based on the kinematic limit analysis theorem, this paper performs a limit analysis of the stability for expansive soil slopes stabilized by anchor cables. The upper bound solution to the slope stability was optimized and compared with the published solutions, demonstrating the applicability of the proposed method. An illustrative slope reinforced with two different reinforcement patterns was investigated to show the role of soil suction and anchor reinforcement in the safety assessments of expansive soil slopes. The results indicate that the slope stability and anchor reinforcement relate closely to the fissures. A threshold value of the fissure height exists, beyond which the slope stability is significantly reduced. An optimum inclination angle (ξopt) of anchors exists universally and is reduced as the anchor height, the internal friction angle and the surcharge load increase.

Shaking Table Tests and Simulations of Grouting Sleeve Connecting Prefabricated Bridge Piers

To investigate the seismic performance of prefabricated piers with a grouting sleeve connection, two scaled model specimens of symmetrical prefabricated piers with different reinforcement anchorage lengths, and two cast-in-place (CIP) comparison symmetrical specimens, were designed and manufactured. The fabricated specimens were connected by a grouting sleeve, which was in the column of the pier. The height of the pier column of the test piece was 1.425 m, the diameter of the pier column was 0.25 m, and the size of the bearing platform was 0.85 m × 0.85 m × 0.5 m. Shake table tests were performed on the specimens to evaluate crack development, dynamic characteristics, acceleration response and relative displacement of the pier tops, as well as strain in the plastic hinge area. The results revealed the dominant failure mode of the test piers was bending failure, while the cracks were generally horizontal through-cracks. The failure location of the prefabricated specimens with the grouting sleeve was concentrated within one diameter of the pier in the upper sleeve region. Compared with the CIP specimens, the plastic hinge exhibited an obvious upward movement. Under a maximum test loading condition, the peak acceleration at the pier top of the fabricated pier was 11.0% smaller than that of the CIP specimen, the peak relative displacement was 34.2% smaller than that of the CIP specimen, and the peak tensile strain of the pier body was 46.8% smaller. The seismic performance of the prefabricated pier connected via the grouting sleeves was barely affected by changing the anchoring length of the reinforcements in the grouting sleeves. An ABAQUS finite element model was established for the specimens, with good agreement between the model and experimental results. When the seismic load was 0.65 g, the difference between the peak acceleration of the pier top in the X direction and the Y direction of the numerical simulation and the experimental data was less than 15%.

Performance Assessment of Soil Moisture Meter under Sandy Clay Loam Soil

Background: Irrigation performs a substantial function for the growth of Agricultural vegetation. Soil supplies essential nutrients for the growth of plant and provides anchor support to the roots of the crops. Soil Moisture permits the requirement for water system to be measured ahead of a yield giving indications of misery. Knowing the soil moisture status empowers exceptionally productive water system, giving the water as and when required and wiping out the inefficient utilization of water when water system isn’t required. Methods: Sandy clay loam soil contains a decent arrangement of plant supplements and supports most sorts of plants and yields. So in the field plentiful accessibility of this soil its texture is discovered by estimating soil moisture. Result: Within the research we developed a soil moisture meter based on capacitive type sensor the output is analog voltage which is calibrated to soil moisture percentage and its performance is comparatively investigated with different moisture sensor under sandy clay loam soil. The proposed model is highly emphasized on the soil moisture percentage that is the level of water content in the soil. The percentage value is displayed in the LCD. The deployment cost is highly reduced in the proposed model.

Cast – in anchor channels used to support curtain wall facades – numerical study of additional anchor reinforcement

As the architectural trend for ever greater spans for glass framing elements keeps its momentum, we are dealing with larger reaction loads onto the elements connecting these to the concrete slab, respectively onto the anchoring system. Therefore, this numerical study has the scope of researching the use of standard cast-in anchor channels, commonly used to support curtain wall façade systems, that are positioned and cast-in relatively close to the edge of the reinforced concrete slab; as well as researching the evolution of the relationship between the concrete strength, slab thickness, anchorage length, the distances between the anchors, the T-bolt positioning, (lever arm of shear force on t-bolt), and the geometry of the “ski plates”. Whilst many studies have been performed regarding the performance of both the concrete and these fastening systems, there is not sufficient information/classification relating to the influence of the welded “skis “, and as to what the optimal sizes and geometries are, when used in a class of concrete where this is critical. The main conclusion desired to be achieved is to find the optimal reinforcement plate (ski) shape and position for the given concrete and anchorage depth, allowing for a more accurate connection design, and to provide options for the instances where clashes occur.

DETERMINING THE PATTERNS OF STABILITY OF MINE WORKINGS FOR CALCULATION ROOF BOLTING PARAMETERS

Purpose. The published studies are aimed at determining the mechanism of deformation of the rocks of the contour around the workings in terms of the parameters of the emerging fracturing and their dependence on the indicators of the strength of the rocks and the depth of occurrence in the massif. The tasks of the study include the installation of fracture indicators, the determination of the parameters of the development of the deformation process around the working, including the effect of longwall mining and taking into account the possibility of reuse of the workings.
 Methodology. To solve the set tasks, the method of field observations was used together with the use of regression dependencies to determine the dependences of the parameters on the influencing factors. In addition, the method of full-scale pull-out tests of anchor support was used, which made it possible to determine the clamping forces of the anchors.
 Originality. In the course of the research, the dependences of stresses and deformation along the K7 coal seam in the conditions of the mine named after Kuzembaev CD JSC "ArcelorMittal Temirtau" for the massif around the mine with fastening. Rational parameters for the use of roof bolting in preparatory mine workings have been established. This type of fastening provides direct contact between rocks and lining. Analysis of the results of calculating the parameters of the roof bolting showed that to maintain the roof in the development workings, it is necessary to take into account the parameters of the roof bolting. The main parameters include the length of the anchors, the total resistance of the roof bolting and the density of the anchors. Anchor support forms laminated rock beams in the roof rocks, which ensure the stability of the workings.
 Conclusions and practical significance. The results of studies devoted to the establishment of the influence of mining-geological and mining-technical factors on the formation of zones of inelastic deformation in the host rocks were considered. Significant dependences of the deformation processes of rocks in the massif around the workings were obtained, and the parabolic zone of destruction of rocks was determined. The practical significance of the research consists in determining the actual indicators of the required bearing capacity of the anchorage at two levels in the conditions of the development of the coal seam k7 of the Kuzembaev mine. 

Shaking table test on single segment prefabricated concrete bridge pier connected by grouting sleeve

PurposePrefabricated pier technology has the advantages of quick construction time, relatively little traffic interference and relatively small environmental impact. However, its applicability under earthquake conditions is not yet fully understood. The seismic performance and influence parameters of a prefabricated concrete pier connected by embedded grouting sleeve (GS) in a pile cap are investigated in this study.Design/methodology/approachTwo prefabricated pier scale model specimens with different reinforcement anchorage lengths and two comparative cast-in-place (CIP) pier model specimens are designed and manufactured for a seismic simulation shaking table. With the continuous increase of input ground motion strength, the changes in basic dynamic characteristics, damage development, acceleration and displacement variation laws, and pier bottom strain responses are compared among the specimen. The finite element software ABAQUS is used to simulate the test pier.FindingsThe crack location of the two prefabricated pier specimens is almost the same as that of the CIP pier specimens; CIP pier specimens show more penetrated cracks than prefabricated pier specimens, as well as an earlier crack penetration time. The acceleration, displacement and strain response of the CIP pier specimens are more affected by earthquake activity than those of the prefabricated pier specimens. The acceleration, displacement and strain responses of the two prefabricated piers are nearly identical. The finite element results are in close agreement with the acceleration and displacement response data collected from the test, which verifies the feasibility of the finite element model established in ABAQUS.Originality/valueA GS connection method is adopted for the prefabricated pier, and on the premise of meeting the minimum reinforcement anchorage length required by the code, this study explores the influences of different reinforcement anchorage lengths on the seismic performance of prefabricated piers in high-intensity areas. A shaking table loading test is used to simulate the real changes of the structure under the earthquake. This work may provide a valuable reference for the design and seismic performance analysis of prefabricated pier, particularly in terms of seismic stability.

STUDY ON BONDING PROPERTY OF POLYURETHANE CEMENT (PUC) TO STEEL BAR

The pull-out test of the bar and PUC is carried out in this paper, the effects of protective layer thickness, reinforcement anchorage length, diameter and shape of reinforcement on bonding properties were studied. The results show that the bond strength between reinforcement and PUC material increases with the increase of the thickness of the protective layer, but decreases with the increase of the anchorage length and diameter of reinforcement. The bond strength of bare round steel is significantly lower than that of ribbed steel, and the maximum bond strength is about 47.4% of ribbed steel. By analyzing the bond slip curve obtained from the pull-out test, the stress process of bond anchorage between reinforcement bar and PUC material is mainly summarized into three stages: the rising stage, the falling stage and the residual stage. The characteristics of the curve, the stress process and the failure mode of specimen at each stage are analyzed.

Model experimental study on GFRP anchor reinforcement and soil deformation

Due to the application of reinforced anchor technology in soil reinforcement, the anchor after long-term use will have serious corrosion, which greatly affects the safety of the engineering structure, leading to engineering accidents. In this paper, GFRP (Glass Fiber Reinforced Polymer) anchor is used instead of reinforced bolt for the pull-out experiment. In order to investigate the deformation of the soil around the GFRP anchor solid in the process of drawing, this paper improves the traditional indoor model pull-out experiment of GFRP anchor and introduces PIV (Particle Image Velocimetry) technology and its application to the analysis of soil deformation in the process of drawing.

A new analytical solution for deep-buried circular cavern with anchor reinforcement under seepage field

This paper presents a new method for assessing the stability of an underground cavern with anchor reinforcement under the seepage field. Firstly, the reinforcement effect of the anchor is considered as a set of clamping forces acting on both sides of the anchored rock mass, besides, whose strength parameters are also considered to be improved. Secondly, a mechanics model for a deep-buried circular cavern with anchor reinforcement under the seepage field is established, and the analytical solution incorporating the characteristics of dilatancy and strain softening of the surrounding rock are derived based on the unified strength theory. Finally, the validity and accuracy of the present solution are examined via comparison with published researches and field monitoring data. Subsequently, extensive parameter investigation is performed to systematically discuss the influence of the intermediate principal stress, dilatancy, strain softening, and seepage force on the cavern deformation and study the variation of the axial force of anchors. The results show that the surrounding rock stresses increase significantly but its radical displacement and the anchor axial force decreased as the intermediate principal stress coefficient increases. With the increase in dilatancy angle, the surrounding rock radial displacement and the anchor axial force increase sharply, but the plastic zone radius and the stresses are almost constant. Moreover, considering the seepage field, the peak value of maximum tangential stress and the stresses in the elastic zone increases but the radial stress in the plastic zone decreases, and the radial and tangential stress distributions are no longer asymptotic with the initial ground stress.

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.

The influence of bottom-up anchors pre-tension optimization on the prediction of pit walls rockfall displacements

Introduction. Currently in Russia, innovations in urban subsoil facilities construction are among the key factors of economic development. To improve the efficiency of holding a pit wall in restraint urban conditions and prevent soil loosening around the pit, it is proposed to optimize the pre-tension forces of the bottom-up anchors. It has been determined that the pre-tension forces of the active anchors create extra retention forces in the sliding wedge and, in some specified sense, reinforce the walled soil. Research methodology. When modeling the complex calculation of a pit wall, 4 main stages of the pit excavation and 3 stages of preliminary level tensions of anchor ties were preset. The numerical solution of the beam bending problem is the basic method of calculating the walling strength; the beam laying on the elastoplastic base and retained by the anchors as bonds. The bottom-up anchor structure is modeled in the operating environment of GeoWall software. The values of bottom-up anchors pre-tension are set following the ordinates of forces in the anchors, obtained from the walling stability calculation by the deterministic approach. Experimental research was carried out of the impact made by pit opening stages on the walling stress strained state. Results. Analysis and discussion. The efficiency of bottom-up anchors optimal pre-tension, according to the research results, is obtained by constructing the diagrams reflecting the correlation dependence between the anchors loading and the walling displacement. An obvious advantage of the software is the opportunity to calculate walling and retaining structures stage by stage ignoring their construction technologies. Experimental calculation in GeoWall has shown a high bearing capacity of the bottom-up anchor support. Summary. The nature of the obtained dependence between the anchor longitudinal forces and the pit walling horizontal displacement reflects the actual situation. Thus, for a quiet expectable value of horizontal displacement, it is required to correct the optimal value of pre-tension using the empiricalformula dependences.

Study on the interaction mechanism between deep displacement of soil and internal force of anchor cable under pile-anchor support system of ultra-deep foundation pit

Based on a concrete engineering example, the change law of soil deep displacement and internal force of anchor cable in the excavation process of foundation pit under pile and anchor support system is simulated by numerical analysis method, and compared with the measured results, and the synergistic action law of soil deep displacement and internal force of anchor cable is discussed. The comparison between the results of finite element numerical analysis and the field measurement shows that the two-dimensional finite element numerical analysis can reflect the variation law of the deep displacement of soil and the internal force of anchor cable in the field to some extent.

Modeling the lateral behavior of freeze-thaw damaged reinforced concrete columns including reinforcement slip and shear effects

This paper focuses on modeling the lateral load-deformation response of reinforced concrete columns subjected to freeze-thaw cycles (FTCs). Freeze-thaw effects are accounted for by means of a non-uniform reduction in concrete strength and bond deterioration between the steel and concrete. The new column response model that is proposed includes deformations due to flexure, reinforcement slip, and shear effects, and the influence of freeze-thaw effects on each of these aspects. The slip displacement is formulated and solved using governing equations among four bond fields. The moment-rotation relationship is then developed and introduced into the zero-length spring element to compromise the rotations caused by reinforcement anchorage slip and by curvatures over the column height. A shear spring element is used in series to represent the shear backbone curve and to capture the onset of shear failure. The proposed model is validated using experimental data on freeze-thaw damaged columns with a wide range of typical design parameters. Overall, the proposed column model accurately simulates the cyclic behavior of both flexure and flexure-shear columns that experience freeze-thaw cycles.