Anchors In Concrete Research Articles

Analytical and numerical investigation of gravity anchors for floating photovoltaic systems

Gravity anchors are a widely used anchoring solution for floating photovoltaic systems but can be costly and difficult to transport and install. To address this issue, 3D printed concrete gravity anchors can be fabricated offsite into a custom shape that optimizes the bearing resistance then filled with ballast onsite. This study evaluates the performance of gravity anchors with novel geometries enabled by 3D printing in representative sandy (drained) and clayey (undrained) soil layers for mooring angles ranging from 0 to 70°. The failure modes of gravity anchors were explored using numerical simulations with the goal of validating simpler analytical methods suitable for design. Results indicate that sliding primarily affects anchor efficiency (pullout capacity divided by buoyant weight) at small mooring angles, while overturning and plowing become dominant at larger mooring angles. Greater anchor efficiency is gained when using a skirt to enhance the passive bearing resistance, but difficulties may arise in the penetration of the skirt into sand. A C-shaped anchor with a padeye close to the center of gravity promoted plowing at high mooring angles. Analytical models are suitable fat lower mooring angles, but numerical simulations are recommended when evaluating anchor performance at mooring angles greater than 30°.

Influence of Polymer Fibre Reinforcement on Concrete Anchor Breakout Failure Capacity.

With the increasing use of fibre-reinforced concrete, e.g., in industrial floor and tunnel construction, the associated fastening technology in this material has increasingly become the focus of scientific attention in recent years. Over 25 years ago, design and assessment guidelines for anchoring systems in reinforced concrete were established, which have since evolved into comprehensive regulatory standards. However, these standards only address plain and rebar-reinforced concrete as anchoring bases, neglecting fibre-reinforced concrete. The design of anchorage systems in fibre-reinforced concrete has not yet been standardised. Recent studies and product certifications accounting for steel fibre reinforcement are now seeing their way to publication, supported by a fair amount of scientific research studies. This paper aims to elucidate the effects of polymer fibre reinforcement in this application through a systematic investigation. Experimental studies were conducted to evaluate the system's load-bearing behaviour failing with concrete breakouts under tensile loading. By incorporating the determined material properties of polymer fibre-reinforced concrete and their mathematical interpretation, alternative model proposals are presented to assess concrete breakout resistance. The addition of polymer fibres significantly improves the load-bearing capacity and ductility of concrete under tensile loads, transforming its quasi-brittle response into a more ductile behaviour. Although the fibres had a minor impact on overall material strength, their influence on the tensile capacity of the anchors reveal a 15-20% increase in load resistance and up to a doubling of the failure displacements.

Frontier, not boundary: The use of amenities around communities

In the field of urban governance, the concept of community is often regarded as the fundamental unit for the delivery of public services. People strive to tackle diverse challenges, such as social segregation and rigid bureaucracy, through the lens of community development. Hence, a precise articulation of this concept is crucial. However, “community” can refer to either a physical area or a group of people, resulting in multiple definitions. The boundary of a community may be defined in various ways. Consequently, a paradox arises: people may enthusiastically explore the suitability of a community for providing public services, but without exactly clarifying where the discussed community itself is. This ambiguity can cause confusion in practical applications of the concept of community, resulting in a decrease in the effectiveness of community governance, the neglect of social attributes, and the undermining of public nature. This conceptual article advocates for a new approach to defining communities, one that integrates sociological components while also having a concrete spatial anchor. It proposes substituting the idea of a clear-cut “boundary” with a buffer “frontier” (or “boundary,” depending on the author’s intended meaning) as a means of demarcating the community. By comparing the conceptual characteristics of “frontier” and “boundary,” we believe that this substitution can eliminate the yes-or-no binary determination inherent in the traditional community concept. In addition, by adopting the concept of “amenity,” we aim to provide a more tangible anchor for identifying the boundaries of a community, clarifying ambiguities, and offering guidance for subsequent research operationalization.

Seismic Performance of Drop-In Anchors in Concrete under Shear and Tension

This paper presents an experimental study conducted on the behavior of drop-in anchors in uncracked concrete slabs. Both seismic (cyclic) load tests and static load tests to collapse are performed on drop-in anchors subjected to tension or shear forces. Three different anchor sizes are subjected to seismic qualification testing, followed by a static load test to collapse. The test results confirm the capability of the tested anchors to sustain simulated pulsating seismic tension and shear loading with frequency ranges between 0.1 and 2.0 Hz. It was observed that no tension failure occurred at the end of the cyclic load tests for all the tested anchors, and their residual inelastic maximum displacement at the end of the cyclic tension test was relatively small. Moreover, the experimental results show that the anchors’ ultimate capacities are higher than those specified by the anchor manufacturer. Finally, the anchors’ experimental pullout shear capacities are compared with the failure prediction equations in the literature and design codes. It is found that the theoretical models provide a conservative prediction of the concrete breakout of anchors in tension compared to the experimental ultimate loads. The coefficient for pry-out strength (kcp) equal to 2 or slightly smaller than 2 is likely to predict a better pry-out capacity with the experimental results compared to the application of the high conservative value of kcp equal to 1, as given in the code.

Tensile and shear capacity of post-installed chemical adhesive anchors in lightweight concrete

Due to construction efficiency and performance, chemical anchors have been widely applied to long-span or high-rise structures or infrastructures. This study investigates the capacity of post-installed anchors in concrete with lightweight aggregates. Extensive static experiments are conducted to investigate tensile and shear capacities of chemical adhesive anchors in lightweight concrete. Both confined and unconfined tensile conditions are considered. In total, 102 tests are performed with various anchor diameters (12–30 mm), embedment depths (80–300 mm), and types of concrete. The test results show that cone breakout and combined failures dominate the unconfined tensile tests, which have about 40% capacity for the anchors in normal-weight concrete. Chemical adhesive anchor failure models in lightweight concrete are also summarized with respect to the input parameters. Finally, multiple nonlinear regression analyses are further performed, and revised empirical and analytical equations are proposed for lightweight concrete to accommodate different failure modes.

МОДЕРНИЗАЦИЯ СТРОИТЕЛЬНО-МОНТАЖНОГО ПИСТОЛЕТА ДЛЯ ДОБЫЧИ ПРИРОДНОГО КАМНЯ

The possibility of mechanizing the operation of wedging for the extraction of natural stone was reviewed. The goal is to reduce the weight of the wedges to several kg and reduce the diameter of the holes in the stone where the wedges are installed. The weight of one hydraulic wedge used is 26 kg, not counting the weight of the hydraulic pump with pressure hoses. Among the options for mechanizing stone mining with wedges, the following approaches are considered – the use of the electro-hydraulic effect; application of liquid nitrogen evaporation in a closed volume; use of electromechanical wedge drive. The fourth option was chosen – modernization of the powder actuated fastening tool for the new task. A calculation has been made for a modernized fastening tool. Several fastening tools chambered for a 7,62 × 54,00 mm rifle cartridge with a charge of moderated propagation gunpowder can split a large stone block. Shallow holes are drilled into the stone block into which wedges are inserted. Measures have been taken to compensate for the recoil of a shot. A shot is fired and the wedges, much larger than a concrete anchor, split the stone. The wedges are reusable. The synchronized operation of several tools is ensured by electric firing from one circuit. A modernized tool with an electric triggering for stone mining can weigh below 3,5 kg. The technical details of the proposal are discussed.

Comparison of types of grouting to guarantee zero tendon slip with post-tension system prestressed concrete bridge anchors

Prestressed concrete is internal stresses of appropriate magnitude and distribution are given in such a way that the stresses caused by external loads are resisted to a desired level. The use of prestressed concrete is mostly applied in bridge construction, especially in the bridge girders. During the stressing girder process, grouting is carried out to prevent the anchor from slipping. The strength of the adhesion of the grouting material used determines the homogeneous nature and whether the prestressed concrete section next to it can meet the anchor load. If the bond strength does not meet the requirements, it will cause slippage in the anchors which will ultimately affect the strength of the prestressed concrete structure due to quite large prestress losses due to slippage. The method used is to test the adhesive strength of the strands that have been grouted with f.a.s. 1:3 using each grouting material such as PCC (Portland Composite Cement), PPC (Portland Pozzoland Cement), OPC (Ordinary Portland Cement) and Sika Grout 215 which is then compared with the grouting material that adheres best. The results obtained were Sika Grout 215 bond strength of 3.6629 MPa, PCC bond strength of 3.2986 MPa, PPC bond strength of 2.5743 MPa and OPC bond strength of 2.307MPa.

Assessment of shear capacity in NSM prestressed FRP strengthening with anchorage conditions

Efforts to achieve a defect-free flat groove in near-surface-mounted prestressed fiber-reinforced polymer (FRP) strengthening systems have proven challenging. Despite attempts, attaining an ideal groove remains formidable. In this system, anchorage device installation involves injecting epoxy resin into groove defects to achieve planarity. Structural behavior analysis and optimization of the anchorage device were conducted based on device type, anchor type, and defect depth through shear loading tests. The mechanical anchor demonstrated an ultimate load of 261 kN, with failure modes including concrete cracking, concrete compression failure, and anchor tensile failure. The chemical anchor exhibited an ultimate load of 390 kN, with its final failure attributed to anchor tensile failure. The ultimate load capacity of anchorage device surpassed that of a carbon FRP(CFRP) bar by up to 62.5%. In a parametric study, the shear strength of the anchorage device was explored concerning concrete compressive strength and anchor diameter. The ultimate load of the proposed model with low concrete compressive strength proved insufficient compared to the strength of CFRP rebar.

Supporting innovation and growth through entrepreneurship: reflections on the German Federal Government's “startup strategy”

PurposeAll over the world, countries are searching for ways to foster innovation and growth through startups. This viewpoint paper presents the aims, development procedure and contents of Germany's “Startup Strategy,” published for the first time in 2022, along with a fundamental assessment of its potential usefulness.Design/methodology/approachIn this opinionated viewpoint paper, the authors provide an overview of the strategy's contents and discuss it against established policy frameworks focusing on the determinants of innovative entrepreneurial activity and the potential consequences of the strategy on the micro-, meso- and macro levels of the German economy. Additionally, the authors evaluate and analyze the strategy's proposed fields of action to illustrate its potential impact on innovative entrepreneurial activity.FindingsThe strategy's development avoids considering an evidence-based, fundamental framework to structure its fields of action and instead relies on diverse input from various entrepreneurial agents. As a result, it emphasizes access to finance for startups and building entrepreneurial capabilities as its main fields of action. On the one hand, the authors show how the contents of the German “Startup Strategy” can be matched with the OECD (2017) framework. On the other hand, the authors offer detailed insights into how the “Startup Strategy's” fields of action might influence the German economy's micro, meso and macro levels.Research limitations/implicationsTo the best of the authors' knowledge, this article is the first one commenting on the German government's first-ever published startup strategy. Hence, this might offer several starting points for other researchers to analyze future startup strategies. Also, comparing such strategic approaches in other European countries and beyond might be a starting point for developing public policies in this field. Also, researchers on entrepreneurial ecosystems and innovation ecosystems will find concrete anchor points for these subject areas.Practical implicationsPolicymakers can use this viewpoint paper to devise future actions. The paper provides concrete fields of action on the individual and company levels, as well as on a national economic and regional ecosystem level, to derive such recommendations.Originality/valueGermany is one of the strongest economic nations in the world and by far in Europe. Hence, this startup strategy comes with the potential for substantial impact. This viewpoint paper may inspire the development of other national strategies to create a positive economic and societal environment supporting the emergence of more innovative startups. In particular, the strategy's focus on diversity and social entrepreneurship seems promising.

Preparation of polyurethane concrete and its novel application in bridge expansion joint anchorage zone

The frequent damage and repair of bridge expansion joint anchorage zone has caused a great burden to the bridge maintenance work. The objective of this study is to prepare a steel fiber reinforced polyurethane concrete (SFPUC) with balanced multi-properties of workability, compressive strength, and flexural strength for the application in bridge expansion joint anchorage zone. A four-factor, five-level orthogonal experimental design was carried out to investigate the effects of the binder-aggregate ratio ( BA), cement content ( C), fine-coarse aggregate ratio ( FC), and steel fiber dosing ( SF) on the workability, compressive strength, and flexural strength, respectively. The multi-criteria decision-making (MCDM) method was used to transform the multi-response problem in the orthogonal experimental design into a single-response problem. Finally, a real engineering application and a finite element method were used to verify the feasibility of SFPUC for the expansion joint anchorage zone. The results show that the optimum proportion of SFPUC is BA (25%), C (20%), FC (20%), and SF (2.5%). The maximum principal stress in SFPUC anchorage zone is less than that in C50 steel fiber concrete anchorage zone under the same load. SFPUC is a highly promising material for bridge expansion joint anchorage zone repair.

Investigation of Helix-Pultruded CFRP Rebar Geometry Variants for Carbon-Reinforced Concrete Structures.

Carbon concrete is a new, promising class of materials in the construction industry. This corrosion-resistant reinforcement material leads to a reduction in the concrete cover required for medial shielding. This enables lean construction and the conservation of concrete and energy-intensive cement manufacturing. Bar-type reinforcement is essential for heavily loaded structures. The newly developed helix pultrusion is the first process capable of producing carbon fiber-reinforced polymer (CFRP) reinforcement bars with a topological surface in a single pultrusion process step, with fiber orientation tailored to the specific loads. The manufacturing feasibility and load-bearing capacity were thoroughly tested and compared with other design and process variants. Approaches to increase stiffness and strength while maintaining good concrete anchorage have been presented and fabricated. Tensile testing of the helical rebar variants with a 7.2 mm lead-bearing cross-section was conducted using adapted wedge grips with a 300 mm restraint length. The new helix geometry variants achieved, on average, 40% higher strengths and almost reached the values of the base material. Concrete pull-out tests were carried out to evaluate the bond properties. The helix contour design caused the bar to twist out of the concrete test specimen. Utilizing the Rilem beam test setup, the helical contour bars could also be tested. Compared with the original helix variant, the pull-out forces could be increased from 8.5 kN to up to 22.4 kN, i.e., by a factor of 2.5. It was thus possible to derive a preferred solution that is optimally suited for use in carbon concrete.

Influence of surface cracking, anchor head profile, and anchor head size on cast-in headed anchors in geopolymer concrete

In this study, the concrete cone capacity, concrete cone angle, and load–displacement response of cast-in headed anchors in geopolymer concrete are explored using numerical analyses. The concrete damaged plasticity (CDP) model in ABAQUS is used to simulate the behavior of concrete substrates. The tensile behavior of anchors in geopolymer concrete is compared with that in normal concrete as well as that predicted by the linear fracture mechanics (LFM) and concrete capacity design (CCD) models. The results show that the capacity of the anchors in geopolymer concrete is 30%–40% lower than that in normal concrete. The results also indicate that the CCD model overestimates the capacity of the anchors in geopolymer concrete, whereas the LFM model provides a much more conservative prediction. The extent of the difference between the predictions by the numerical analysis and those of the above prediction models depends on the effective embedment depth of the anchor and the anchor head size. The influence of concrete surface cracking on the capacity of the anchor is shown to depend on the location of the crack and the effective embedment depth. The influence of the anchor head profile on the tensile capacity of the anchors is found to be insignificant.

Response of Embedded Plates in Reinforced Concrete Loaded in Eccentric Shear towards an Edge

Embedded plates (EPs) are commonly used to connect steel to reinforced concrete elements. Due to a lack of industry-wide standard designs, EPs are custom designed for every instance in each project. This leads to many inefficiencies in the construction process and introduces susceptibilities to error. North American design standards based on the concrete capacity design (CCD) philosophy require many assumptions to predict EP capacity, which then lead to inconsistencies in their application. CCD is also well suited for analysis as it depends on a considerable numbers of variables (e.g., edge distances, anchor size, number, and length) to check capacity. The sheer number of variables makes it difficult for designers to come up with a trial design to fit a situation. This study aims to improve the efficiency of this process by proposing standard EPs. A subset of these proposed standard EPs are then experimentally tested to verify predicted capacities and evaluate design assumptions using existing CCD approaches in North America. Four- and six-anchor proposed standard EPs with shear tab connections were placed at four distances from the concrete edge (75–250 mm) and tested in shear towards the edge. North American provisions for concrete anchorage were adequate in predicting the failure loads if connection eccentricity, caused by the gap between the shear tab bolt line and the exposed surface of the plate, is considered in capacity predictions. Mean test-to-predicted ratios of 0.92 and 1.05 were obtained, respectively, when not considering and considering this eccentricity. Rotations of these connections during testing (0.01 to 0.02 rad at peak load with further rotations post-peak) and signs of secondary tension breakout cones suggest that connection eccentricity significantly affects the behavior of EPs and should be considered in design.

Debonding Analysis of Fibre Reinforced Polymer Anchors in Concrete via In-Situ X-Ray Microtomography Tests Coupled to Volume and Digital Image Correlation

Debonding Analysis of Fibre Reinforced Polymer Anchors in Concrete via In-Situ X-Ray Microtomography Tests Coupled to Volume and Digital Image Correlation

Prediction of concrete anchor pull-out failure using cohesive zone modeling

Concrete anchor pull-out failure is predicted using the cohesive zone-based finite element analysis. For anchor pull-out tests, two sets of concrete specimens are prepared according to the curing temperatures. The displacement of an anchor steel bar is measured using the digital image correlation technique, and the cone failure surface is reconstructed using a 3D scanner. For each test set of concrete specimens, material properties such as the fracture energy, compressive strength, tensile strength, and elastic modulus are obtained from the three-point bending, cylindrical compression and indirect tension tests. Based on the measured material properties, the cohesive zone-based finite element analysis captures the load–displacement relationship of the anchor pull-out and three-point bending tests without the calibration of material properties. The experimental results demonstrate that the fracture energy is an essential material property to predict the concrete anchor pull-out failure, and thus the cohesive zone-based finite element analysis can provide accurate prediction of the anchor pull-out failure.

Predictive models for concrete cone capacity of cast-in headed anchors in geopolymer concrete

The scope of current state-of-the-art prediction models for concrete cone capacity of cast-in headed anchors is limited to normal concrete. In this study, the difference in the tensile performance of cast-in headed anchors embedded in ambient-temperature cured fly ash-based geopolymer concrete and normal concrete is investigated using both experimental and numerical analysis. The concrete cone capacity obtained for anchors investigated in this study is compared with current prediction models namely: Concrete Capacity Design (CCD) model, which overestimated the results by a maximum of 41%, and Linear Fracture Mechanics (LFM), which underestimated the results by a maximum of 53%. Anchors of sizes 1.3T, 2.5T and 5T are tested at effective embedment depths of 40 mm, 70 mm and 90 mm. Finally, based on the experimental results obtained in this study and other research [1,2], modification factors are suggested to be incorporated in the CCD and LFM models so the application of the two models can be expanded to predict the concrete cone capacity of anchors in geopolymer concrete. The modification factors are validated using over 60 numerical analyses on similar anchors with effective embedment depths ranging between 40 mm and 180 mm. The modified CCD model shows an average numerical-to-prediction ratio of 1.09 and a COV of 7%, whereas, the modified LFM model shows an average numerical-to-prediction ratio of 1.02 and a COV of 3%. This indicates that the proposed modification factors are able to predict the concrete cone capacity of anchors in geopolymer concrete investigated in this study with good accuracy.

Tensile performance of cast-in headed anchors in ambient-temperature cured fly ash-based geopolymer concretes with varying fracture energies

The performance of cast-in headed anchors subjected to tensile loading in ambient-temperature cured fly ash-based geopolymer concrete was investigated in this research. Varying sizes of anchors were installed in geopolymer concrete at effective embedment depths ranging between 40 mm and 90 mm. The new experimental results were compared with those of a previous study on the tensile performance of anchors in geopolymer concrete with similar compressive and tensile strengths, but different fracture energy and elastic modulus. The influence on the concrete cone capacity and its angle due to the varying anchor head size ratio and fracture energy were evaluated in detail. A 43% difference in fracture energy between the two geopolymer concrete mixes translated to 17% increase in concrete cone capacity of the tested anchors. Moreover, the obtained results were compared with the existing prediction models, the Linear Fracture Mechanics (LFM), and Concrete Capacity Design (CCD) models, as well as the design models by ACI 318 and AS 3850.1. The results showed that most of the existing models overestimate the concrete cone capacity of anchors tested in this study and the test-to-prediction ratios depend on the effective embedment depth of anchors. After statistical analysis of experimental results, a new modified equation was proposed to extend the use of the existing CCD model to anchors installed in geopolymer concrete studied in this article.

Three-dimensional finite element analysis of a vertical anchor embedded in granular soil

ABSTRACT The present study aims at investigating the behaviour of concrete anchor blocks in cohesionless soil through numerical modelling. A three-dimensional finite element analysis using PLAXIS 3D was conducted to examine the effect of various factors, including anchor shape, embedment depth, and the presence of a groundwater table, on the pullout resistance of anchor blocks. The results showed that anchor shape affects the pullout resistance, particularly for anchor blocks with small aspect ratios. The presence of groundwater table between the ground surface and the base of the anchor block affects the pullout resistance of the anchor block. Based on the results, an empirical correlation was developed to account for the effect of the groundwater table on pullout capacity. The study also compared different pullout capacity prediction models with the results of the numerical simulations for varying embedment depth ratios. The failure modes of the soil body were critically observed and discussed.

Experience from design & construction of a stable feature MSE wall in Dubai

There has been continued development of various methods for mechanically stabilized earth (MSE) wall construction, often by specialized system providers, to solve problems when the available width of reinforced fill is highly restricted. The design manual FHWA-NHI-10-024 permits to reduce the length of soil reinforcements up to 30% of wall height in shored or stable featured walls. There are many instances where the available width is much less than the limits by design standards, necessitating innovative approaches. The current project involves constructing a link road as a diversion at the middle of an existing 6m high ramp made of concrete wall. The new ramp will be retained by MSE wall that will be joined to the old concrete wall within tight space limitations. To accomplish this 'stable feature MSE wall' within narrow space, it was imperative to adopt a novel method of actively connecting geogrid reinforcements and modular block fascia to existing concrete wall. This paper presents the challenges in designing a stable feature MSE wall in extremely narrow space. The presented approach of connecting the soil reinforcement to the concrete anchors was a determining factor in the project and could therefore be adopted for future projects under similar conditions.

Analysis of Temperature Sensitivity and Cracking Causes in Suspension Bridge Anchorage Based on Numerical Simulation

Mass concrete, a common structure in bridge engineering, is frequently threatened by cracking. Based on the gravity anchorage of a long-span suspension bridge that has been in operation for more than ten years, the causes of the cracks growing year by year in the anchorage were analyzed in this paper. The refined numerical model of the anchorage was established using the space finite-element software. Taking full account of the environmental characteristics of the bridge site, the temperature sensitivity of the anchorage was simulated and analyzed, as well as the stress distributions on the surface of each side of the anchorage at different temperatures. The calculation results showed that there is little correlation between anchorage cracking and anchorage bolt force. Under condition two, the temperature increased 20°C, the principal tensile stress of anchorage reached to 1.5 times of the allowable stress. Under condition six, the anchorage surface temperature at 40°C suddenly dropped to 20°C, and the principal tensile stress reached 2.4 times the allowable stress. Thus, under the dual effects of internal and external constraints, the cold hit effect of the mass concrete anchorage resulted in the sudden drop of the surface temperature of the anchorage concrete to produce “internal constraint cracks”, and the overall temperature rise caused the expansion of the anchorage concrete to produce “external constraint cracks.” The two types of cracks led to the vertical cracks of the anchorage. Additionally, the environmental and construction factors were the main causes of the cracking in transverse construction joints. Finally, the anchorage was reinforced with high-performance concrete with an anticrack reinforcement mesh, which presented good results in the follow-up observation, providing a certain reference value for similar projects.