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

Load-bearing behaviour of anchors in fibre-reinforced concrete – A state of the art review

Contemporary construction heavily relies on advanced techniques for connecting and assembling structures. The most common example of construction assemblies is connecting structural and non-structural elements to a concrete substrate, often using cast-in and post-installed anchors. The widespread adoption of advanced concrete materials with high compressive strengths, such as Steel Fibre Reinforced Concrete (SFRC), in practical applications have led to challenges. Most of these stem from the absence of established standards and limited understanding of their impact on other structural elements, such as anchorage systems embedded in these types of substrates. This is because existing guidelines for anchorage design primarily rely on studies and test outcomes conducted on anchors embedded in Plain Normal-Strength Concrete (NPC). This creates a research gap when applying the CCD method to SFRC, particularly Ultra-High-Performance Fibre Reinforced Concrete (UHPFRC), where compressive strength can exceed 120 MPa. In this work, a comprehensive evaluation of the literature on anchorages in SFRC is conducted. Several parameters relating to the behaviour of anchorage in SFRC are listed and discussed in this work. Factors such as the fibre content, fibre homogeneity and orientation, and fibre type are determined to influence the capacity of anchors. The results of a total of 916 tests on the performance of anchorages in SFRC are carefully collated, classified, critically reviewed and analysed. The synthesised data highlights the trends, gaps, and evolutions on the research on anchorage in SFRC and illustrates the relationships and connections that emerge from the collective literature. The evaluation of the test results indicates that the scope of the CCD method can potentially be expanded to be used for the design of anchors in SFRC, with some modifications. Consequently, a modification factor is suggested for the CCD method using the analysed dataset. The insights from this comprehensive review on anchorages in SFRC can drive future research, guide revisions to industry standards and enhance practical construction applications

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

Protein Synthesis Adaptation to the AU-Rich Transcriptome of Plasmodium falciparum

The process of protein synthesis whereby a messenger RNA is decoded into an amino acid chainis conserved among the domains. Fastidious protein synthesis is necessary for organism survival. However, exceptions negatively affecting the mRNA translation cycle – inadvertently or by design – may occur. Polyadenosine tracts are one such motif causing ribosomal stalling and frameshifting in almost all organisms tested thus far; save Plasmodium spp. Thus, with ~60% of their protein-coding genome harboring polyadenosine tracts, the elucidation of such paradigm-breaking adaptations enabling Plasmodium spp. to translate this typically problematic motif without issue is salient from both basic science and clinical perspectives. Using biochemical and structural approaches, I report on the parasite ability to express polyA motifs and ribosome alterations enabling polylysine synthesis. The developed PP7-mRIP assay reveals RBP differences among varying mRNA substrates, revealing a previously uncharacterized, parasite-specific AU-rich binding protein bound to polyA tract reporter mRNA. Finally, the parasite exhibits altered binding of the essential ribosomal protein RACK1, vital for translation cap-dependent initiation and quality control activation, that would invariably alter ribosome- associated quality control pathway signaling, ostensibly aiding polyA translation

Experimental and numerical investigation of screw anchors in large crack width

In predicting the capacity of screw anchors under static tensile loading, the Concrete Capacity (CC) method is the state-of-the-art prediction model which covers concrete cone capacities in uncracked and cracked concrete up to 0.3 mm crack width. However, in seismic applications, anchors may be subjected to large crack widths of up to 0.8 mm. With large crack width, the behaviour of small-sized (typically 6 mm) screw anchors has not been studied. In this study, experimental investigations were conducted for a total of 29 anchors in uncracked and cracked concrete with large crack widths up to 0.8 mm. The experimental results showed that the load-carrying capacity of screw anchors significantly dropped resulting in a reduction factor of 0.13–0.47 for cracked concrete with 0.8 mm crack width (significantly lower than 0.7 assumed by the CC method for a crack width of up to 0.3 mm). This paper focused on developing modelling technique for predicting the performance of screw anchors in cracked concrete with a crack width of up to 0.8 mm since screw anchor in cracked concrete has not been studied using finite element analysis. Three-dimensional finite element models were developed for screw anchors in uncracked and cracked concrete and validated by the experimental results. Further, parametric analysis showed that dilation angle and shape factor are the two most influencing parameters among other of the concrete damage plasticity model.</p

Development and challenges in finite element modelling of post-installed anchors in concrete

Finite element analysis (FEA) has been used as a successful supplement to experimental testing in various studies for simulation of anchorage behaviour. Throughout the years, researchers have employed different modelling techniques in various FEA packages to capture the behaviour of post-installed anchors. However, the vast amount of knowledge accrued is yet to be reviewed. This article critically reviews all aspects of FEA from pre-processing to post-processing and provides a comprehensive review of published literature on FEA studies for predicting the behaviour of post-installed anchorage systems. Most current efforts focus on investigating failure mechanism of anchors in uncracked concrete under tensile loading. Findings show that developing finite element model for post-installed anchorage in concrete is very challenging due to complex geometrical configuration of anchors, difficulty in modelling concrete–anchor interface and lack of reliable information on selecting material properties and parameters. The analysis identified key gaps in research related to the effect of geometrical simplification, anchor subjected to dynamic loading and anchor performance in cracked concrete which needs attention in future research. This review article is a valuable resource in facilitating future research on assessing the performance of post-installed anchorage in concrete with FEA.</p

Development and challenges in finite element modelling of post-installed anchors in concrete

Finite element analysis (FEA) has been used as a successful supplement to experimental testing in various studies for simulation of anchorage behaviour. Throughout the years, researchers have employed different modelling techniques in various FEA packages to capture the behaviour of post-installed anchors. However, the vast amount of knowledge accrued is yet to be reviewed. This article critically reviews all aspects of FEA from pre-processing to post-processing and provides a comprehensive review of published literature on FEA studies for predicting the behaviour of post-installed anchorage systems. Most current efforts focus on investigating failure mechanism of anchors in uncracked concrete under tensile loading. Findings show that developing finite element model for post-installed anchorage in concrete is very challenging due to complex geometrical configuration of anchors, difficulty in modelling concrete–anchor interface and lack of reliable information on selecting material properties and parameters. The analysis identified key gaps in research related to the effect of geometrical simplification, anchor subjected to dynamic loading and anchor performance in cracked concrete which needs attention in future research. This review article is a valuable resource in facilitating future research on assessing the performance of post-installed anchorage in concrete with FEA.</p

Imaging and Identification of Waterborne Parasites Using a Chip-Scale Microscope

We demonstrate a compact portable imaging system for the detection of waterborne parasites in resource-limited settings. The previously demonstrated sub-pixel sweeping microscopy (SPSM) technique is a lens-less imaging scheme that can achieve high-resolution (<1 µm) bright-field imaging over a large field-of-view (5.7 mm×4.3 mm). A chip-scale microscope system, based on the SPSM technique, can be used for automated and high-throughput imaging of protozoan parasite cysts for the effective diagnosis of waterborne enteric parasite infection. We successfully imaged and identified three major types of enteric parasite cysts, Giardia, Cryptosporidium, and Entamoeba, which can be found in fecal samples from infected patients. We believe that this compact imaging system can serve well as a diagnostic device in challenging environments, such as rural settings or emergency outbreaks

Blind bolted connections for steel hollow section columns in low rise structures

© 2011 Dr. Jessey LeeHollow sections have become increasingly popular in structural applications due to their superior load bearing capacity and natural aesthetic appeal. However, their use in low rise residential and commercial structures is hampered by the limited means of providing fully bolted site connections. This limitation can be overcome by using single sided or blind bolting. The merit of blind bolts is that installation requires access to one side only. This eliminates both the problem of lack of access and also the need to weld various accessories to the hollow sections. This research project focuses on the development of a range of connections to hollow sections using blind bolts. A series of tests have been performed to determine the behaviour of various configurations of blind bolted connections, exploring connections to the (i) face of the hollow section column, (ii) side wall of the column and (iii) front and back face of the column. This has resulted in the development of blind bolted moment connections for hollow section columns without concrete infill. Comprehensive three-dimensional finite element (FE) models have been developed to predict the behaviour of the developed connection with sufficient accuracy. Extensive parametric studies have been conducted to explore the effects of various parameters on the performance of these connections with specific focus on the stiffness. Simplified theoretical models based on the component model method proposed by Eurocode 3 have been formulated. These provide a quick and easy way for practising engineers to determine the stiffness of the proposed connections. Both the FE and theoretical models have been thoroughly validated against the experimental results. The successful development of the proposed blind bolted moment connections offers a convenient and efficient alternative for beam-to-hollow section column connections in low rise structures