Pullout Capacity Research Articles

Interface properties of a cement coated geocomposite

A new geocomposite material introduced by cement treatment of the surfaces of an ordinary woven geosynthetic. Thin layers of cementitious material created on the surfaces of geosynthetic spraying the portland cement on the surfaces of a saturated geosynthetic and coating with sand. The interface behavior of the proposed cement coated geocomposite and sand was investigated in the laboratory using a series of pullout tests. The pullout tests performed on both cement coated geocomposites and pristine geosynthetics then the results were compared. The results of laboratory tests indicated that the interface adhesion, interface friction angle and pullout capacity of cement coated geocomposite is higher than those of pristine geosynthetic. For a similar stress level and thicknesses, the average interface friction angle and pullout capacity of the cement coated geocomposite were 29% and 38% higher than those of pristine geosynthetic which was used to produce the cement coated geocomposite.

Moment-rotation response of cold-formed steel joist-to-ledger connections with variable-finishes in ledger-framed construction

Ledger framing is the dominant framing system in North American cold-formed steel (CFS) construction. In this system, the floor, which is typically sheathed with oriented strand board, is framed into the top of the wall via a rim track (ledger) and clip angle connection. The diaphragm is essentially hung from the walls. Recently completed experimental work involving full-scale shake table tests on a ledger-framed CFS building exhibited the presence of alternate load paths that contributed to the lateral force resisting system. Within the goal of quantifying this contribution to the overall diaphragm response, experimental tests on joist-to-ledger connection have demonstrated to have a complex behavior involving limit states such as ledger flange buckling, stud web crippling, and fastener pull-out. Current design practices do not account for these limit states. To improve design recommendations and understanding of load transfer mechanisms, a robust finite element model for a joist-to-ledger connection in ABAQUS, validated via existing experimental tests, is presented herein. Experimental testing on the pull-out capacity of screw-fastened connections was conducted for implementation into the finite element environment. Results were then implemented directly in ABAQUS as connection behavior. Generally, the modeling approach accurately captures connection capacity and behavior. In addition, influence of other floor sheathing materials, fiber cement board and steel deck, on the moment-rotation stiffness and strength of this connection is explored. In steel deck sheathing, effects of deck thickness and fastener spacing are explored. This work enables predictions for both design and system-scale characterization.

Pull-Out Capacity and Creep Behavior of Helical Piles in Frozen Ground

This paper presents pull-out capacity and creep behavior of a model helical pile and a model grouted shaft helical pile installed in frozen ice-rich silt in Gloucester, Ontario, Canada. The measured pull-out capacity of the model piles was compared to predicted capacities calculated using modified forms of previously published theoretical approaches based on the individual bearing model (IBM) and the cylindrical shear model (CSM). The modified IBM adequately captured the pull-out loading resistance of the helical pile; however, neither the modified IBM nor CSM could accurately predict the measured capacity of the grouted shaft helical pile in frozen ground. The creep behavior of the test piles in frozen soil was dependent on the applied creep stress and the frozen ground temperature. The pile creep rates increased when the ground exposure temperature increased, even under a constant creep loading condition. The pile creep rates measured in the current study were smaller compared to previously published results for similar stress and thermal boundary conditions. This could be attributed to creep rate hysteresis associated with ground warming, as well as the differences in the helix diameter. An improved graphical solution was also produced to predict creep rates for single-helix helical piles in frozen ground at various exposure temperatures.

Pull out and pre-tightening force tests for plastic dowel of the railway sleeper considering the influence of installing torque and frost force

The reliability connection of the plastic dowel and the bolt largely determines the normal function of the railway fastener system. However, the failure of the dowel and the uplift of the bolt are found during railway operation. Therefore, a series of pull-out and pre-tightening force tests for plastic dowel of the railway sleeper are carried out. Not only the relationship between the bolt ultimate pull-out capacity and the effective anchorage length is obtained, but the failure pattern of the plastic dowel is analysed. In addition, the relationship between pre-tightening force and installing torque, and the influence of freeze-thaw cycles on pre-tightening force are investigated. The above relationships could be described by linear equations, the failure of the dowel during pull-out test is dominated by bending failure pattern and the freeze-thaw cycles for the space between the bolt and the dowel with full of water (9 mL) could cause reduction of the pre-tightening force.

Experimental Study of Pulling-Out Capacity of Foundation for Solar Array Mounting Frames

Solar energy became the cheapest mode of energy generation in recent years because of the cost-effective techniques causing exponential reduction of solar installation cost. Solar arrays installed in these solar farms are susceptible to wind-driven forces, which may uplift array and mounting frame foundation. Due to high wind, extensive damages of the solar panels, array mounting frame, and foundations have been observed globally in the recent past. A number of the solar array foundation failed due to the uplifting of the foundation by intensive wind-induced lift forces. To improve pull-out resistance of solar array foundations, a comparative experimental study was done to determine the pull-out capacity of steel pile having varying diameter and length in three different soil conditions, i.e. clayey soil, sandy soil, and mixed soil. Helical piles were found to be a cost-effective improvement over plain piles to resist uplift forces. A mathematical expression is also proposed based on a number of soil and pile parameters, to determine the pulling-out capacity of helical piles, and analytically determined capacity is compared with experimental findings. Reliability analysis was also done to determine the effectiveness of the proposed mathematical expression to determine the pull-out load. Earlier, a numerical study has been carried out for the determination of wind loads over various solar arrays tilted at different angles and subjected to extreme wind. Computational fluid dynamics techniques for turbulent wind flow using Reynolds-averaged Navier–Stokes equations have been used to predict lift and drag coefficients on ground-mounted solar arrays with varied tilt angle and wind incidence. To effectively resist lift forces induced over the solar array, the foundation should be carefully designed with optimum pulling out capacity for precise lift forces determined using numerically obtained force coefficients.

Laboratory investigation of pullout behavior of hollow and solid shaft helical nail in frictional soil

Helical soil nails are passive elements installed in the soil which attains its bond strength through skin friction and bearing from helices. The present study examines the behavior of helical soil nail installed in cohesionless soil subjected to pullout force under varying parameters such as helical nail configuration (shaft diameter, helical diameter, helical pitch, number of helices), nail shaft types (roughness and stiffness), installation torque, and overburden pressure. The installation torque and corresponding nail pullout capacity can be established using a torque correlation factor (Kt). Kt value decreases with increasing embedded nail area and is inversely proportional to the nail shaft diameter. From pullout tests result, it is found that pitch in the range of 24.5–35.5 mm shows better pullout capacity. Also, results show that additional helices will only contribute to pullout capacity if located outside the region of soil mobilized in the failure mechanism of lower helix. Moreover, higher axial strains are found for hollow shaft nail, which alters with the increase in number of helices. Test results also indicate that various hollow shaft helical nails have nearly equal interaction friction angle to solid shaft helical soil nails with lesser shaft diameter. Therefore, it is concluded that solid shaft helical nails can be replaced by hollow nails without compromising on pullout capacity adding to reduction in construction cost. Tests results show linear correlation between maximum pullout shear stress and overburden pressure following a Mohr–Coulomb failure for different helical nail types.

Characterization of Model Uncertainty for the Vertical Pullout Capacity of Helical Anchors in Cohesive Soils

This paper conducts coupled Eulerian–Lagrangian (CEL) analysis to characterize the model uncertainty of using the cylindrical shear method (CSM) to predict the pullout capacity of helical anchors in cohesive soils. The model factor M is adopted to represent the model uncertainty, which is equal to the value of measured capacity divided by estimated solution. The model factor Mcel can be considered to be a random variable with a lognormal distribution, and its mean value and coefficient of variation (COV) are 1.02 and 0.1, respectively. Correction factor η is introduced when comparing CSM and CEL, which is found to be influenced by input parameters. The dependence on input parameters is removed by performing regression analysis and the regression equation f is obtained. Substituting the regression equation f into the original CSM constitutes the modified CSM (MCSM), and the model factor of MCSM can be modeled as a random variable with a lognormal distribution, and its mean value and COV are 1.02 and 0.13, respectively. Finally, 13 filed tests are collected to compare the prediction accuracy, the results show that the prediction error range of MCSM is mostly within 15%. The present findings might be helpful for engineers and designers to estimate the pullout capacity of helical anchors in cohesive soils more confidently.

Discrete mesoscale analysis of adhesive anchors under tensile load taking into account post-installed reinforcement

The utilization of post-installed anchors is growing fast to connect both structural and non-structural members. Adhesive anchors are one type of post-installed anchors which are formed as threaded bars. They can be post-placed into concrete with the help of epoxy adhesive. On the one hand, improvement of the performance of post-installed anchors, unlike cast-in-place anchors, has not drawn attention much. On the other hand, due to the complexity of their performance, a numerical study can be a supportive method for the experimental study. This paper addresses the effect of post-installed reinforcement (PR) on the adhesive anchors under tensile loading in both experimental and numerical studies. Reinforcing steel bars as post-installed reinforcement (fully embedded in concrete) were used to ameliorate the performance of the adhesive anchors under tensile force. Rigid Body Spring Model (RBSM) was developed as a simulation that is based on discrete analysis at mesoscale. Pull-out capacity, displacement, failure mode, and concrete cone geometry were measured by the experiments and the RBSM simulation. In addition, internal stress, strain, cracking patterns were investigated by the RBSM simulation. Moreover, some comparisons were conducted through the existing standard. In general, PR assist the anchors to have higher pull-out capacities, lower displacement as well as leading smaller size of concrete cone failure. Due to PR, the internal tensile stress of concrete changed to compressive stress resisting greater pull-out force. The higher strain is obtained at near the top of the anchors and at the mid-span of PR. Furthermore, cracking patterns in concrete were mostly within the area between the anchor and PR. Post-installed reinforcement can be considered as a method to improve the performance of adhesive anchors under tensile loading. This is validated by the RBSM simulation, which agrees with the experimental results.

Load-carrying capacity of timber joints with multiple glued-in steel rods loaded parallel to grain

The joints with glued-in steel rods are efficient joints in the design of timber structures, due to their high stiffness, strength and fire resistance. The ductile behaviour of joints can be achieved through designing the yielding of steel rods prior to wood failure. In practice, the joints are generally with multiple rods rather than single rod. In the case of multiple glued-in rods, the yielding of single rod is designed as prior failure by using mild steel rod, and the load-carrying capacity of joints is expected to be equal to the yield capacity of single rod multiplied by the number of rods. However, the actual pull-out capacity of single rod in timber joints with multiple glued-in rods can be less than that in timber joints with a single glued-in rod, due to the group effect of glued-in rods. Thus, the brittle failure of pull-out of rods can still occur prior to the yielding of steel rods in timber joints with multiple glued-in rods, though the yielding of single rod is designed as prior failure. The pull-out capacity of multiple rods can generally be considered as the pull-out capacity of single rod multiplied by the effective number of rods instead of the actual number of rods. Therefore, it is necessary to determine the effective number of rods in the case of pull-out of rod.This paper presented an experimental investigation on joints composed of multiple glued-in steel rods (two and four rods with different rod spacing) in glued-laminated timber with the pull-out failure mode. The actual experimental results combined with those from literatures, were used to analyze the influence of main factors, e.g. rod diameter, slenderness ratio of rods, number of rods and rod spacing to diameter, on the effective number of rods. Afterwards, based on these main factors, an empirical expression of the effective number of rods was derived. Finally, a model of load-carrying capacity for timber joints with multiple glued-in rods was proposed. The load-carrying capacity of timber joints with multiple rods should be calculated as the minimal value between yielding capacity of a single rod multiplied by the number of rods and pull-out capacity of a single rod multiplied by the effective number of rods. The proposed model is capable of predicting the failure mode and load-carrying capacity for multiple rods.

Study on the Uplift Resistance of a Joint Board Cable Foundation Considering the Critical Burial Depth

Joint board cable foundation is a kind of foundation form proposed by the author which is applied to transmission lines. In the study of pullout resistance of a joint board cable foundation, the most important factor is the critical depth of the anchor plate. Theoretical analyses, numerical simulations, and field tests were carried out to study the impact of the critical burial depth on the uplift capacity. Test results were corrected by the back-stepping cohesive force method. The theoretical analyses, numerical simulations, and field test results are consistent. It is found that the development of the plastic failure zone in the foundation is directly controlled by the shear strain. Through the field test, the pullout resistance of the anchor plate is studied, and it is found that the depth ratio has the most influence on the pullout capacity of the anchor plate. The field tests also provide valuable data for theoretical calculation, numerical simulation, and design of joint board cable foundations. The field test data analysis and numerical simulation results show that the optimal burial depth ratio of the joint board cable foundation is about 2.5–3.0. Therefore, in the design of the joint board cable foundation, 2.5 can be adopted as the critical depth ratio of the joint board cable.

New insights into the failure mechanisms of horizontal plate anchors in clay during pull-out

Offshore wind developments are moving towards deep-water regions where energy is abundant, visual impact is minimised and the larger turbine sizes can make the energy production more cost-effective. One of the key challenges facing the industry is the development of reliable substructures. While fixed foundation systems are widely used for shallow-water (<60 m) developments, permanent anchors are seen as one of the most viable mooring solutions for floating structures in deep water. In the current study, the pull-out behaviour of square plate anchors in clay was investigated using large-displacement finite-element analysis. The anchor capacity and failure mechanism were considered for a range of embedment ratios and undrained shear strengths. Three distinct modes of anchor failure identified in previous studies were examined through the analysis of four descriptors including: the pull-out capacity of the anchor, the pull-out displacement required to mobilise this capacity, the energy absorbed by the anchor during pull-out and the variation of the pull-out capacity with respect to a normalised overburden pressure. The findings of the study are presented in the form of a series of charts that can aid design through understanding of the factors controlling the development of anchor failure modes, in addition to identifying the transition point between different failure mechanisms.

Effect of Uneven Excavation Method on Pull-Out Capacity of Fully-Grouted Rock Bolt

Effect of Uneven Excavation Method on Pull-Out Capacity of Fully-Grouted Rock Bolt

Anchorage of Perfobond Leiste shaped shear connector composite dowel with carbon fibre reinforced polymer

This study focuses on the pullout behaviour of composite structures having closed shape geometry Perfobond Leiste (PBL) shear connectors wrapped with carbon fibre reinforced polymer (CFRP). Eight test specimens having PBL connectors with and without CFRP were used to perform the pullout tests. These tests were performed under static loading, and the concrete thickness and the embedment depth were the parameters used to evaluate the effects of CFRP jacketing on the pullout strength. The responses, that is, the initial cracking load, the ultimate pullout capacity and the displacement, were investigated. Failure modes were analysed, and a new model was proposed because of the unavailability of suitable models for PBL shear connectors with CFRP. The diagonally bonded CFRP jackets significantly delayed the onset of cracking and showed superior performance in terms of deformation capacity and ultimate pullout strength. A strength model was proposed to predict the ultimate pullout capacity of CFRP-confined PBL composite dowels. Overall, the study demonstrated that it is more efficient to use the proposed CFRP-confined PBL shear connectors than other connectors in practical engineering applications, given the improved deformation capacity and the ultimate shear strength.

Deformation and Stability Analyses of Hybrid Earth Retaining Structures

Hybrid earth retaining structure (HERS) is an efficient solution for earth retention problems that face spatial constraints. Deformation and stability analyses of the HERS have not been studied rigorously. The present study focuses on the development of predictive equations for the estimation of maximum lateral facing displacement and global factor of safety of the mechanically stabilized earth (MSE) over the soil nail (SN) hybrid retaining (MSE/SN) wall, a category of the HERS. Multiple linear regression is performed using the method of least squares to develop the predictive equations. The regression models for the MSE/SN wall are proposed using the data generated from the finite element model of the MSE wall of heights 6, 8 and 10 m. The adequacy of the predictive equations is verified by evaluating the summary of fit statistics. The failure surface of the MSE/SN wall consists of two parts: (i) a linear surface which propagates internally through the bottom nail of the SN wall starting at the toe of the MSE/SN wall and propagates externally through the remaining height of the SN wall, and (ii) continuation of the linear surface externally behind the reinforcement through the MSE wall. It is concluded that the predominant deformation modes are base sliding, rotation about the base and local bulging of the MSE wall. The failure surface always passes through the soil nails and therefore, it is recommended that the ultimate pullout capacity of the nails should be assessed during the design of the MSE/SN walls.

Testing of URM wall-to-diaphragm through-bolt plate anchor connections

The presence of effective wall-to-diaphragm connections has been shown to significantly improve the global seismic behavior of unreinforced masonry (URM) buildings. However, despite the importance of such connections, there remains a paucity of experimental research to provide physical validation of current recommendations in design standards and guidelines. The experimental study reported herein included a total of 18 tests which were undertaken in two phases, with Phase 1 testing being undertaken on existing vintage plate anchor connections in an existing URM building and Phase 2 testing involving newly installed plate anchor connections in two additional existing URM buildings. The tested buildings offered variation in material properties, levels of axial load, and wall thickness as test parameters. Attained failure modes and corresponding force-displacement curves are presented herein, as well as comparisons regarding the influence of varying test parameters on the ultimate pull-out capacity. Prediction of plate anchor capacity was undertaken using a basic mechanics approach, and comparisons to current strength recommendations in standards and guidelines are provided.

Anisotropy and bond behaviour of recycled Polyethylene terephthalate (PET) fibre as concrete reinforcement

This paper studied the anisotropy of the recycled Polyethylene terephthalate (PET) and as reinforcing fibres for concrete considering three experimental campaign e.g. uni-axial tension, pullout, and three point-bending. The study also relates parameters such as fibre position and embedded length. In total, 18 recycled PET samples with dog-bone shape are prepared for the uni-axial tension test, 54 samples (embedded recycled PET fibre in concrete) for the pullout test, and 12 recycled PET fibre reinforced concrete samples for the 3-point bending tests. The data were analysed using ANOVA and Tukey methods to get statistical confidence. Tensile results demonstrated anisotropy in recycled PET, but its effect was low in the recycled PET fibre-concrete interface behaviour. Also, the results show a weaker pullout capacity of the PET fibre-concrete interface than the PET tensile strength. The addition of recycled PET fibre showed about 6% increase in flexural strength of concrete.

Investigating the Effect of Grout on Improving the Performance of Helical Anchors Used in Wall Stabilization

The benefits of helical anchors have made them a good alternative to grouted soil anchors. However, as their bearing capacity depends on the length and number of helices, they are not economically justified or feasible in some projects. In this research, an attempt was made to propose a new method of implementing helical anchors and their application considering the advantages of helical and grouted anchors. This method, which was named “grouted helical anchor,” was tested in wet sandy soil. Since one of the most important parameters of anchor design is pull-out resistance, the parameters affecting the pull-out resistance of grouted helical anchor such as overburden pressure, helical anchor configuration, and grout were evaluated to determine the best conditions for constructing an anchor. The results show that in the helical anchor with a 100-mm helix, changing the helix spacing from 300 to 400 mm at 90 kPa increases the maximum pull-out force by less than 6%. At the same overburden pressure, if the helix spacing is 400 mm and the helix diameter is changed from 100 to 130 mm, the maximum pull-out force will increase by more than 29%. However, by injecting and modifying the anchor to the grouted helical anchor, the maximum pull-out force can be increased by more than 45%. Therefore, injection operations can help to increase the pull-out capacity of the helical members without changing their configuration.

Pull-Out Capacity and Failure Mechanisms of Strip Anchors in Clay

Plate anchors are a well-established solution for supporting the efforts of floating platforms for wind and marine renewable energies. The behavior of ultrathin rigid plate anchors buried in purely cohesive soils under undrained and plane-strain conditions is analyzed. As already known, a dimensional analysis shows that the pull-out capacity of the anchor may be expressed using a weightless break-out factor (Nc0) that only depends on the ratio between the depth and the anchor width (H/B). Using finite element analyses, tabulated values of the weightless break-out factor are provided in this paper and three different failure mechanisms are identified, namely very shallow (quasi-vertical), shallow or intermediate (semi-vertical), and deep (rotational). For very shallow failure mechanisms, the studied problem is completely equivalent to the trapdoor problem because immediate breakaway at the bottom part of the anchor is considered (vented conditions). The existing analytical solutions for the very shallow (Nc0 = 1.956 H/B) and deep cases (Nc = 3π + 2) using the slip-line method are reviewed and an analytical limit is proposed for the first time for the very shallow mechanism (H/B = 1.314). For shallow (intermediate) cases, the failure mechanism is identified and the angle of the main slip lines is numerically evaluated.

Experimental pull-out tests and design indications for strength anchors installed in masonry walls

This study deals with the identification of the mechanical behavior of chemical anchors embedded in masonry walls. 108 pull-out tests are carried out in five types of masonry walls built with clay brick or vertically perforated units with cement mortar. Different parameters are taken into account: embedment depths, masonry type, anchor position (injection either in brick units or in mortar joints). The axial load capacity and the failure mode are observed for each test. The results are examined by means of elastic and plastic models assessing the efficiency of anchors installed in headers, stretchers or mortar joints. The anchors injected in mortar joints are shown to have much greater pull-out capacity than that found for anchors in bricks. Passing from 90 to 160 mm of embedment depth, a minimum increase by 40% of pull-out strength is observed. The most common failure modes are the sliding failure, which occurs for short anchors or weak masonry, and mixed sliding/cone failure, for long anchors or strong masonry. An analytical model is proposed to design anchors in order to avoid or at least to limit brittle masonry failures and to identify the field of application of uniform stress models.

Horizontal Pullout Behavior of Novel Open-Ended Pipe Helical Soil Nail in Frictional Soil

The reinforcing action of soil nails is governed by its interaction with the surrounding soil generally investigated in terms of interface friction. The reported literature depicts that increase in interface friction enhances the reinforcing action of a soil nail. Thus, with the aim of utilizing additional interface friction from internal surface of a hollow pipe and bearing resistance from helical plates attached to it, the present work investigates the pullout behavior of newly developed open-ended pipe helical soil nails. The novel open-ended pipe helical soil nails are installed and subjected to pullout force in a test tank filled with frictional soil using installation/pullout machine. The present study also examined the effect of varying soil nail diameter, number of helices and phenomenon of soil plugging on pullout capacity. Additionally, torsional and axial strains developed during pullout are also observed. The installation torque and pullout capacity are correlated using a dimensionless factor called as ‘Torque factor (Kt)’ with values ranging from 27 to 55 m−1 in compression and 28.12–53.3 m−1 in tension. A theoretical torque model for open-ended helical soil nails is also developed and is verified by the laboratory test results. The test results indicate that soil plug contributes about 11.5% of the total mobilized skin friction during pullout. The pullout capacity increases with increase in the number of helices and nail shaft diameter. However, soil plug length is independent of number of helices. Besides, higher torsional and axial strains are found for helical nails with smaller diameter.