Single Anchors Research Articles

The influence of child restraint lower attachment method on protection offered by forward facing child restraint systems in oblique loading conditions

ABSTRACTObjective: The research objective was to quantify the influence of child restraint lower attachment method on head kinematics, head impact potential, and head, neck, and thorax injury metrics for a child occupant secured in a forward-facing child restraint system (FFCRS) in oblique side impacts.Methods: Fifteen sled tests were conducted with a Q3s seated in an FFCRS secured to the center position on a production small SUV bench seat. Three lower attachment methods were evaluated: rigid ISOFIX, a flexible single loop lower anchors and tethers for children (LATCH) webbing routed through the vehicle belt path of the FFCRS, and dual flexible LATCH webbing attachments on either side of the FFCRS. All were tested with and without a tether with one repeat test in each test condition. The same model FFCRS was used for all tests; only the attachment method varied. The vehicle bench seat was fixed on the sled carriage at 80° (from full frontal). The input pulse was the proposed FMVSS 213 side impact pulse scaled to a 35 km/h delta-v. Two-way analysis of variance (ANOVA) was used to evaluate the effect of lower attachment and tether use on 3 outcome metrics: lateral head excursion, neck tension, and neck lateral bending. Data included anthropomorphic test dummy (ATD) head excursions, head linear accelerations and angular velocities, neck loads and moments, thoracic accelerations, lateral chest deflections, lower anchor loads, and tether webbing loads. ATD head kinematics were collected from 3-dimensional motion capture cameras.Results: Results demonstrated a reduction in injury measures with the rigid ISOFIX and dual webbing attachment compared to the single webbing attachment with decreased lateral head excursions (331, 356, and 441 mm for the rigid ISOFIX, dual webbing, and single webbing systems, respectively, P <.0001), neck tension (1.4, 1.6, and 2.2 kN, P <.01), and neck lateral bending (31.8, 38.7, and 38.0 Nm, P =.002). The tether had a greater influence on lateral head excursion for the FFCRS with flexible webbing attachments than those with the rigid attachment, with the tether forces being highest with the single webbing attachment. Lateral head excursions were significantly lower and lateral neck bending moments were significantly higher with tether use (P <.0001) across all lower attachments. The effect of tether on neck tension was mixed, only showing an increased effect with the rigid ISOFIX system.Conclusion: The CRS lower attachment system influenced occupant kinetics. The results indicate that CRS attached to the vehicle via rigid and dual webbing systems exhibit improved kinematics by reducing the rotation and tipping seen with the single webbing attachment. This leads to reduced lateral head excursions and neck tension values. The advantages of the tether in reducing lateral head excursion in side impacts are most pronounced with the flexible webbing attachments. With tether use low in the United States, a dual webbing type FFCRS attachment system may be a better attachment method than single webbing and provide a simpler engineering solution than rigid ISOFIX attachment.

Horizontal Pullout Capacity of a Group of Two Vertical Square Anchors Embedded in Medium Dense Sand

In the present study an attempt is made to evaluate the ultimate horizontal pullout capacity of group of two square anchors embedded in medium dense sand by conducting laboratory model tests. The size of the model box used in the present study is 1.2m lengthx0.75m width and 1.5m height. A series of experiments were conducted on single and group of anchors subjected to horizontal pullout load on mild steel square plates of size 10 cm and 15 cm were used .Clean dry local river sand was used in the present study. All the tests were carried out on dry clean sand with a relative density of 55% corresponding to medium dense state. The raining technique was adopted to prepare the sample in the model box to achieve the desired density. In the present study the ratio of H/B is equal to 5 and 6; where H = depth of embedment from top of tank to bottom of lower anchor, B=width of anchor. The parameter S/B is equal to 0,1,2; where S = clear spacing between the anchor, and B= width of anchor. It was found from the present study as H/B ratio increases the pull out capacity increases and also for each H/B ratio as the S/B ratio increases pull out capacity decreases due to decrease in passive resistance. In the present study the group efficiency factor was found which is defined as the ratio pull out capacity of group of anchors to the pull out capacity of single anchor. It was found that the group efficiency factor was found to be greater than 1 and further as S/B ratio increases the group efficiency factor decreases for same H/B ratio. Also as H/B increases the efficiency factor also increases. The anchor breakout factor (Nγ) was also found which tends to increase with increase in depth of embedment and decreases with clear spacing between the anchors. The present data was compared with that of published literature on single anchors and it was found to compare well.

Experimental study on concrete edge failure of single headed stud anchors after fire exposure

In the present study different single headed stud anchors are exposed to various durations of fire and loaded in shear perpendicular to and towards the free concrete edge up to failure after cooling. The effects of concrete edge distance, nominal diameter, embedment depth and concrete compressive strength on the load-bearing behaviour of the anchors at various durations of fire are experimentally investigated. The standard fire curves ISO-834 with the corresponding durations of 15 min and 60 min are employed to study the effect of fire on the residual capacities of the anchors. Even more than expected, the results demonstrate that the anchor behaviour is significantly influenced by the fire exposure. Under ambient conditions, the influence of the edge distance on anchor resistance is very strong while the influence of the anchor diameter and the embedment depth is relatively weak. However, after fire exposure the influence of the edge distance reduces and the influence of the diameter and the embedment depth on the shear resistance increases. The influence of fire exposure is significant on the concrete edge capacity of the anchors. After only 15 min of fire duration, the reduction of more than 50% of the reference value is reported.

Fiber Reinforced Polymer as External Reinforcement for Single Cast-in Anchors in Plastic Hinge Zones

This paper presents a test of cast-in anchors in the plastic hinge zone of a reinforced concrete column. Design codes, such as ACI 318-11, do not allow concrete anchors in concrete that could be substantially damaged during an earthquake unless special reinforcement is provided. Steel reinforcement has been proven effective in protecting core concrete; however, it does not protect cover concrete, which is critical to the shear behavior of anchors. Fiber reinforced polymer (FRP) composite material was used in this study to protect cover concrete around the test anchors. The column specimens were subjected to quasi-static cyclic loading while the single anchors were loaded in cyclic shear. Compared with the anchors in unprotected concrete, the FRP reinforced anchors developed a higher shear capacity at a much smaller displacement. This indicates that FRP fabrics can be effective as external reinforcement for concrete anchors. Meanwhile, a systematic study is needed before practical applications.

Behaviour of undercut anchors subjected to high strain rate loading

Abstract The increase in global terrorism has culminated in the protection of high profile buildings and monuments against the effects of blast loading – a high strain rate loading event. Depending on the design basis threat, the level of protection can range from facade and fenestration upgrade to retrofit of the structural systems. Post-event surveys after the Oklahoma City Bombing and other similar events indicated widespread window glass damage. Most of the injuries reported were attributed to the glass shards, especially in buildings proximate to the target building. Thus, the least protection recommended for buildings is to retrofit window glass against glass shard injury. When the window retrofit consists of anti-shattered film anchored to the window frames, blast loads are transferred to the window frames and ultimately to the structure of the facade through discrete window retention steel anchors. A lot of research has been conducted to investigate the response of upgraded windows however little research is available on the load transfer from the window frames to the facade structure through the window retention anchors. This paper presents results from a finite element analysis program to investigate the tensile behaviour of post-installed undercut anchors under high strain rates. Strain rates varying from 10-5 to 103 s-1 were applied to single undercut steel anchors embedded in concrete blocks. Anchor diameters of 12 mm, 16 mm and 20 mm with various embedment depths were selected for the analyses. The analyses results show increased tensile capacity of undercut anchors with increase in strain rate. The maximum dynamic increase factor for tension of undercut anchors at strain rate of 103 s-1 was about 1.60 for the anchors investigated.

Toward tightly bound carboxylic acid-based organic dyes for DSCs: relative TiO2 binding strengths of benzoic acid, cyanoacrylic acid, and conjugated double carboxylic acid anchoring dyes

Strong anchoring groups are essential in the fabrication of the highest efficiency dye-sensitized solar cell (DSC) devices and for promoting long-term stability of photosensitizers in DSCs. While many metal-based sensitizers frequently make use of multiple anchors, synthesizing purely organic dyes with multiple anchors, especially those with anchors in direct conjugation with donor structures, has proved challenging. Novel quinoxaline-based dyes utilizing double donor/double acceptor structures can fill this gap in dye design understanding through a novel double donor-π-bridge-double acceptor (DD-π-AA) dye. These dyes have been synthesized with the optical and electrochemical properties, electron injection efficiencies, and relative binding strengths characterized. Fluorescence lifetime measurements show favorable electron injections from all dyes. Submersing dye-sensitized TiO2 plates in a hydrolytic solution reveals desorption rates up to 180 times slower for dyes containing multiple carboxylic acid anchors compared to single acid anchors.

Uplift response of multi-plate helical anchors in cohesive soil

The use of helical anchors has been extensively beyond their traditional use in the electrical power industry in recent years. They are commonly used in more traditional civil engineering infrastructure applications so that the advantages of rapid installation and immediate loading capability. The majority of the research has been directed toward the tensile uplift behaviour of single anchors (only one plate) by far. However, anchors commonly have more than one plate. Moreover, no thorough numerical and experimental analyses have been performed to determine the ultimate pullout loads of multi-plate anchors. The understanding of behavior of these anchors is unsatisfactory and the existing design methods have shown to be largely inappropriate and inadequate for a framework adopted by engineers. So, a better understanding of helical anchor behavior will lead to increased confidence in design, a wider acceptance as a foundation alternative, and more economic and safer designs. The main aim of this research is to use numerical modeling techniques to better understand multi-plate helical anchor foundation behavior in soft clay soils. Experimental and numerical investigations into the uplift capacity of helical anchor in soft clay have been conducted in this study. A total of 6 laboratory tests were carried out using helical anchor plate with a diameter of 0.05 m. The results of physical and computational studies investigating the uplift response of helical anchors in soft clay show that maximum resistances depend on anchor embedment ratio and anchor spacing ratio S/D. Agreement between uplift capacities from laboratory tests and finite element modelling using PLAXIS is excellent for anchors up to embedment ratios of 6.

Pryout failure capacity of single headed stud anchors

Concrete pryout failure mode, which occurs for relatively short and stocky cast-in headed studs or post installed anchorages, has been investigated only to a limited extent in the past. The increasing use of such anchorages in engineering practice emphasizes the need to clarify the pryout failure mechanism and to formulate design rules that assure safe and economical structural design. Currently used design provisions are based mostly on analysing push off test data, which were focusing on composite beam design. The database (Jebara and Ožbolt in Vergleichsanalyse von Bemessungskonzepten fur Querbelastung und Scherversuche mit ruckwartigem Betonausbruch (pryout). (Literature review of design concepts for shear loaded tests with pryout failure), Internal Report/November 2011) including recently reported shear tests is lacking in pryout in-the-field tests with systematic variation of anchor embedment depth and diameter. In order to clarify the behaviour of cast-in headed studs and anchor bolts, shear tests were performed on single cast-in headed studs (Jebara and Ožbolt in Tragverhalten von angeschweistem gedrungenen Kopfbolzenverankerungen in der Flache unter Querlast, experimentelle Untersuchung, (Bearing mechanism of stocky studs in-the-field under shear load, experimental Investigation), Internal Report/November 2013). In the present article the experimental results, pryout failure mechanism and proposed pryout capacity equation for single anchor under pure shear load are presented, discussed and compared with current design formula.

Assessment of shear capacity of adhesive anchors for structures using neural network based model

In this study, an artificial neural network (NN) based explicit formulation for predicting the edge breakout shear capacity of single adhesive anchors post-installed into concrete member was proposed. To this aim, a comprehensive experimental database of 98 specimens tested in shear was used to train and test NN model as well as to assess the accuracy of the existing equations given by American Concrete Institute and prestressed/precast concrete Institute. Moreover, the proposed NN model was compared with another existing model which had been derived from gene expression programming by the authors in a previous study. The prediction parameters utilized for derivation of the model were anchor diameter, type of anchor, edge distance, embedment depth, clear clearance of the anchor, type of chemical adhesive, method of injection of the chemical, and compressive strength of the concrete. The proposed model yielded correlation coefficients of 0.983 and 0.984 for training and testing data sets, respectively. It was found that the predictions obtained from NN agreed well with experimental observations, yielding approximately 5 % mean absolute percent error. Moreover, in comparison to the existing models, the proposed NN model had all of the predicted values in ±20 % error bands while the others estimated up to %160 error.

Behaviour of Group of Helical Screw Anchors Under Compressive Loads

In this paper experimental investigations on the behaviour of single, double and triple helical screw anchors under the influence of vertical compressive loads are presented. The testing program was conducted on one, two, three and four numbers of model anchors in sand for different depths of embedment keeping shallow and deep mode of behaviour in mind. The experimental setup was instrumented to measure the compressive load and the downward displacement of the anchor. It was observed that the compressive load varied significantly with the installation depth of the anchor and the number of anchors. Based on experimental results, non-dimensional graphs were plotted normalizing the deformation and load axis both and simple equations are proposed correlating load and deformation. Ultimate compressive capacity of multiple anchors was plotted against that of single anchor and simple equations were proposed correlating them. Using these equations an anchor foundation for a particular structure can be easily designed. A 3-D finite element model, PLAXIS, was used to confirm the results obtained from laboratory tests and the agreement is excellent.

How Multiple Anchors Affect Judgment: Evidence from the Lab and eBay

The vast majority of anchoring research has found that judgments assimilate toward single anchors, but no papers have directly compared the impact of one anchor with that of multiple anchors. We hypothesized that the presence of additional anchors can reverse the usual anchoring effect. When one anchor is paired with a second, moderate anchor, people rely more on the additional anchor when the original anchor is extreme than when it is moderate. Extreme original anchors therefore generate less extreme estimates than moderate original anchors do in the two-anchor case — a reversed anchoring effect. Three controlled experiments verified that although estimates assimilated to single anchors, the reverse occurred when people were simultaneously given a second anchor: extremely low (high) anchors generated higher (lower) estimates than moderately low (high) anchors. A natural experiment using eBay auctions in the U.S. and China provided corroborating evidence. This research has implications for pricing strategies when there is more than one price cue available.

Behavior and strengths of single cast-in anchors in Ultra-High-Performance Fiber-Reinforced Concrete (UHPFRC) subjected to a monotonic tension or shear

Ultra-High-Performance Fiber-Reinforced Concrete (UHPFRC) exhibits improved compressive and tensile strengths and strain capacity far superior to those of conventional concrete. The anchors used in UHPFRC are expected to have much higher strengths in concrete-related failure modes and to show a very reliable performance. A total of thirty-three tests, seventeen tension tests and sixteen shear tests, were conducted on anchors in UHPFRC of a 199 MPa compressive strength. The load capacities and displacement capacities of these anchors in UHPFRC were significantly improved compared with the anchors in normal concrete, in both tension and shear. The average ratios of the measured strengths to the predictions by the Concrete Capacity Design (CCD) method were 1.40 for the breakout strength in tension, 1.07 for the breakout strength in shear, and 2.62 for the pryout strength. The enhanced capacities can be attributed to the improved strain capacity and tensile strength of UHPFRC: the improved tensile strength enlarged the projected concrete failure area as well as enhanced the resisting strength and the improved strain capacity secured a reliable performance with low variance, i.e., a higher safety factor than a factor for normal concrete. Three design equations, i.e. breakout strength in tension, breakout strength in shear, and pryout strength, for anchors in UHPFRC were proposed by modifying design equations of ACI 318-11 through regression analyses of the tests, and using the 5% fractile coefficient, they have the same reliability as the design equations of ACI 318-11.

Testing of rock climbing anchors in weak sandstone

Climbers sometimes rely on fixed anchors which are secured in drilled holes by mechanical expansion or with glue. Most rock climbing takes place on high strength rock and there has been considerable testing of anchors worldwide. However, there has only been limited testing of anchors in weaker rock. Over 60 anchors were tested in weak rock, failure loads of 8–48 kN were achieved. Chemically bonded anchors were the strongest, the 10 mm rings and 10 mm U-bolts were the only anchors that passed the European standard (EN 959). Older style anchors showed low strength and high variability. The relative strengths of single and twin holes anchors followed predictions based on interaction theory. The results also confirm the prediction of mixed glue/rock failure. The cyclic loading behaviour of anchors was explored, anchor with higher stiffness appeared to perform better; the U-bolts had the best fatigue performance.

Button Fixation Technique for Achilles Tendon Reinsertion: A Biomechanical Study

Chronic insertional tendinopathy of the Achilles tendon is a frequent and disabling pathologic entity. Operative treatment is indicated for patients for whom nonoperative management has failed. The treatment can consist of the complete detachment of the tendon insertion and extensive debridement. We biomechanically tested a new operative technique that uses buttons for fixation of the Achilles tendon insertion on the posterior calcaneal tuberosity and compared it with 2 standard bone anchor techniques. A total of 40 fresh-frozen cadaver specimens were used to compare 3 fixation techniques for reinserting the Achilles tendon: single row anchors, double row anchors, and buttons. The ultimate loads and failure mechanisms were recorded. The button assembly (median load 764 N, range 713 to 888) yielded a median fixation strength equal to 202% (range 137% to 251%) of that obtained with the double row anchors (median load 412 N, range 301 to 571) and 255% (range 213% to 317%) of that obtained with the single row anchors (median load 338 N, range 241 to 433N). The most common failure mechanisms were suture breakage with the buttons (55%) and pull out of the implant with the double row (70%) and single row (85%) anchors. The results of the present biomechanical cadaver study have shown that Achilles tendon reinsertion fixation using the button technique provides superior pull out strength than the bone anchors tested.

Vertical Pullout Capacity of a Group of Helical Screw Anchors in Sand: An Empirical Approach

In this paper experimental investigations on the behavior of a group of single, double and triple helical screw anchors under the influence of vertical uplift loads are presented. The testing program were conducted on one, two, three and four numbers of anchors in sand for different depths of embedment keeping shallow and deep mode of behavior in mind. It was observed that the pullout load varied significantly with the installation depth of the anchor and the number of anchors. It had been shown that the load displacement relationships for all groups may be reduced to a common curve. The graphs of ultimate pullout capacity a group of two, three and four numbers of anchors with respect to one anchor were plotted and design equations had been proposed to design a group of anchors based on ultimate pullout capacity of one anchor.

Modeling and analysis of the shear capacity of adhesive anchors post-installed into uncracked concrete

This paper reports the results of an analytical study to predict the edge breakout shear capacity of single adhesive anchors post-installed into uncracked hardened concrete. For this purpose, an experimental database for the adhesive anchors compiled by the ACI Committee 355 was obtained and utilized to construct training and test sets so as to derive the closed-form solution by means of gene expression programming (GEP). The independent variables used for development of the prediction model were anchor diameter, type of anchor, edge distance, embedment depth, clear clearance of the anchor, type of chemical adhesive, method of injection of the chemical, and compressive strength of the concrete. The generated prediction model yielded correlation coefficients of 0.98 and 0.92 for training and testing data sets, respectively. Moreover, the performance of the proposed model was compared with the existing models proposed by American Concrete Institute (ACI) and Prestressed/Precast Concrete Institute (PCI). The analyses showed that the proposed GEP model provided much more accurate estimation of the observed values as compared to the other models.

Estimation of Tensile Capacity of Single Anchors Including Edge Effect Using Neural Networks

The demand for more flexibility in the design and strengthening of concrete structures has resulted in an increased use of anchoring systems. Adhesive anchors are widely used in seismic strengthening applications to add new structural members or sections to existing concrete members. To safely design such anchors, it is very important to know their tensile capacity under axial tensile forces. This paper explores the pullout capacity of single adhesive anchors loaded in tension in un-cracked concrete. To this end 142 single anchor tests including edge effect (located near a concrete edge) were obtained from literature. The formulated three-layered artificial neural network method (ANN) was trained using 75% of the data set by using different learning algorithms. The methods were tested with the remaining 25% of the data set. The variables taken into account in this study are anchor diameter, embedment length, concrete body height and edge distance. It was determined that experimental data can be estimated to a notably close extent via the ANN model.

Axisymmetric Lower-Bound Limit Analysis Using Finite Elements and Second-Order Cone Programming

AbstractIn this paper, the formulation of a lower-bound limit analysis for axisymmetric problems by means of finite elements leads to an optimization problem with a large number of variables and constraints. For the Mohr-Coulomb criterion, it is shown that these axisymmetric problems can be solved by second-order cone programming (SOCP). First, a brief introduction to SOCP is given and how axisymmetric lower-bound limit analysis can be formulated in this way is described. Through the use of an efficient toolbox (MOSEK or SDPT3), large-scale SOCP problems can be solved in minutes on a desktop computer. The method is then applied to estimate the collapse load of circular footings and uplift capacity of single or multiplate circular anchors. By comparing the present analysis with the results reported in the literature, it is shown that the results obtained from the proposed method are accurate and computationally more efficient than the numerical lower-bound limit analysis incorporated with linear programming.

Vertical Uplift Capacity of a Group of Helical Screw Anchors in Sand

In this paper experimental investigations on the behavior of single, double and triple helical screw anchors under the influence of vertical uplift loads are presented. The testing program was conducted on three model anchors having single, double and triple helical screws installed in sand. The experimental setup was instrumented to measure the pullout load and the upward displacement of the anchor. It was observed that the pullout load varied significantly with the installation depth of the anchor and the number of anchors. A mathematical model was developed using the limit-equilibrium method of analysis. Based on experimental results, non-dimensional graphs were plotted normalizing the deformation and load axis both and simple equations are proposed correlating load and deformation. Using these equations an anchor foundation for a particular structure can be designed. Comparison of the pullout load values obtained from the theory developed and the present experimental results showed good agreement.

Prediction of tensile capacity of adhesive anchors including edge and group effects using neural networks

AbstractAdhesive anchors are widely used in seismic strengthening applications to add new structural members or sections to existing concrete members due to their high tensile and compressive strengths, low cost, and easy and fast installation. To safely design such anchors, it is very important to know their pullout capacity under axial tensile forces. This paper explores the pullout capacity of both single and groups of adhesive anchors loaded in tension in uncracked concrete. Quadruple anchor groups were considered for group effect. To this end, 142 single anchor tests including edge effect (located near a concrete edge) and 175 quadruple group anchor tests (totally 317 tests) were obtained from literature. The formulated three-layered artificial neural network method (ANN) was trained using 75% of the data set by using different learning algorithms. The methods were tested with the remaining 25%. The variables taken into account in this study are anchor diameter, embedment length, concrete compressive strength, concrete body height, edge distance (for single anchors), and anchor spacing (for group anchors). It was determined that experimental data can be estimated to a notably close extent via the ANN model.