Fiber Anchors Research Articles

Ion Channels Activated by Mechanical Forces in Bacterial and Eukaryotic Cells.

Since the first discovery of mechanosensitive ion channel (MSC) in non-sensory cells in 1984, a variety of MSCs has been identified both in prokaryotic and eukaryotic cells. One of the central issues concerning MSCs is to understand the molecular and biophysical mechanisms of how mechanical forces activate/open MSCs. It has been well established that prokaryotic (mostly bacterial) MSCs are activated exclusively by membrane tension. Thus the problem to be solved with prokaryotic MSCs is the mechanisms how the MSC proteins receive tensile forces from the lipid bilayer and utilize them for channel opening. On the other hand, the activation of many eukaryotic MSCs crucially depends on tension in the actin cytoskeleton. By using the actin cytoskeleton as a force sensing antenna, eukaryotic MSCs have obtained sophisticated functions such as remote force sensing and force-direction sensing, which bacterial MSCs do not have. Actin cytoskeletons also give eukaryotic MSCs an interesting and important function called "active touch sensing", by which cells can sense rigidity of their substrates. The contractile actin cytoskeleton stress fiber (SF) anchors its each end to a focal adhesion (FA) and pulls the substrate to generate substrate-rigidity-dependent stresses in the FA. It has been found that those stresses are sensed by some Ca2+-permeable MSCs existing in the vicinity of FAs, thus the MSCs work as a substrate rigidity sensor that can transduce the rigidity into intracellular Ca2+ levels. This short review, roughly constituting of two parts, deals with molecular and biophysical mechanisms underlying the MSC activation process mostly based on our recent studies; (1) structure-function in bacterial MSCs activation at the atomic level, and (2) roles of actin cytoskeletons in the activation of eukaryotic MSCs.

Digital Image Correlation Analysis of CFRP to Brick Bonded Joints Fastened by Fiber Anchor

In the framework of the reinforcement of masonry structures by FRP sheets (Fiber Reinforced Polymer), the use of “Fiber Anchor” is an innovative performing solution to increase the peak load and the dissipation capability of the strengthened system. To analyze the performance of this new technology an experimental campaign composed by 36 tests has been conducted. Six series of CFRP to brick bonded joint fastened by different configurations of fiber anchor have been tested. To deeply describe the measure fields, the Digital Image Correlation (DIC) has been used. The strain fields obtained in the series not fastened by anchors have permitted to define the bond stress field and the advancement of the stress transfer zone. The DIC appears as a performing methodology to use in a lot of civil engineering experimental problems.

Strengthening of Multibay Reinforced Concrete Flat Slabs to Mitigate Progressive Collapse

Unable to generate sufficient ductility and continuity, RC flat slab structures are vulnerable to progressive collapse, in which the relatively brittle failure mechanism attributable to punching shear failure may lead to catastrophic consequences. Thus, it is necessary to evaluate the effectiveness of approaches for improving the ability of flat slabs to mitigate progressive collapse. Previous studies have indicated that integrity reinforcement may enhance the behavior, particularly postpunching behavior, of newly designed flat slab structures. However, limited tests have been conducted to determine reliable approaches for strengthening existing flat slab structures to resist progressive collapse. In this study, a series of seven multibay flat slab substructures were cast and tested to assess the effectiveness of proposed glass fiber-reinforced polymer (GFRP) strengthening schemes for improving the progressive collapse behavior of existing flat slab structures, owing to its low density, high strength, rigidity, and excellent resistance to corrosion. Three specimens without strengthening were used as control specimens and the remaining four specimens were strengthened by GFRP strips. Test results indicated that proposed strengthening schemes effectively improved the initial stiffness and flexural resistance of flat slab structures. However, they did not sufficiently enhance the postfailure resistance and deformation capacity: there was significant debonding of the GFRP strips from the concrete interface in the large displacement stage, even when specially designed fiber anchors were employed.

Experimental global analysis of the efficiency of carbon fiber anchors applied over CFRP strengthened bricks

The study focuses on the improvement of the cohesion strength of CFRP-to-substrate bonded joint by means of mechanical anchors built with the same fibers as the composite and plugged, in the substrate, like “nails”. Research on the use of this typology of anchor for masonry substrates has been limited. The aim of this study is to provide experimental data to quantify the efficiency of the carbon fiber anchors on the strength of a reinforced brick. The research demonstrates that the use of CFRP anchors increases the resistance and the dissipation capability of the reinforcement if the anchors are properly placed.

Chromatophore radial muscle fibers anchor in flexible squid skin

AbstractCephalopod skin is soft, flexible, and produces rapid color changes for camouflage and signaling primarily by regulating the shapes of its numerous chromatophore organs. Each chromatophore has 10–30 radial muscle cells, termed fibers, under central nervous system control. Each fiber contains myofilaments that contract in concert to stretch the pigment‐containing cell from its punctate, spherical state to a fully expanded thin disk of color. Expansion occurs in less than one second and can result in a 14‐fold expansion in pigment cell diameter. We investigated the anchoring mechanism of radial muscle fibers that expand pigment cells in the longfin squid,Doryteuthis (Loligo) pealeii. The proximal Active Zone of a radial muscle fiber adheres to the pigment cell within an ensheathing sinus. The distal portion forms terminal arbors, thereby increasing the surface area, to adhere it to the dermal extracellular matrix (ECM). While the muscle fiber is attached to the pigment cell with haptosomes, the remainder of the fiber is adhered to the surrounding basal lamina (part of theECM) by numerous, closely spaced, small costamere‐like projections. Branching of the radial muscle fiber termini and the costamere‐like attachments are key anatomical specializations that anchor the radial muscle fibers in the pliable skin while allowing the freedom of movement required for large changes in pigment cell diameter. We postulate that these features may be relevant for the development of soft actuation models in materials science.

Repair of Reinforced Concrete Bridge Columns Containing Buckled and Fractured Reinforcement by Plastic Hinge Relocation

AbstractThis paper describes a new repair technique that involves the use of plastic hinge relocation to restore strength and deformation capacity of RC bridge columns. Summarized is the overall repair concept and experimental results that include the reversed cyclic testing of three large-scale bridge columns that were previously damaged, repaired using the proposed methodology, and then subsequently retested. To date, two different repair alternatives were executed using unidirectional carbon fiber sheets in the hoop and longitudinal directions, the latter anchored into the RC footing with 30-mm-diameter carbon fiber anchors. A method for predicting the force-displacement responses of columns repaired in this manner was also developed and found to give reasonable results. Also included in this paper are design considerations, which are carried out in the steps needed to design a repair system to relocate the plastic hinge in a column containing buckled longitudinal reinforcement. The responses show that...

Experimental Testing of CFRP-Strengthened Reinforced Concrete Slab Elements Loaded by Close-In Blast

Strengthening reinforced concrete slab or wall structural elements with carbon fiber-reinforced polymer (CFRP) can improve their blast resistance. However, close-in blasts (blasts with a scaled range of less than 0.4 m/kg1/3) may undermine the effectiveness of the CFRP strengthening. This paper presents an experimental testing program on CFRP-strengthened reinforced concrete slab specimens that utilized fiber anchors. Two CFRP mitigation designs were tested under blast loads with a scaled range of 0.4 and 0.6 m/kg1/3. Tests on unmitigated reinforced concrete slab specimens provided baseline comparisons. The experimental results showed that the use of CFRP strengthening improved the blast resistance of reinforced concrete slab specimens. For a larger scaled range, 0.6 m/kg1/3, the CFRP successfully prevented flying debris and reduced the overall deflections of the slab specimens. However, for the closer scaled range, 0.4 m/kg1/3, the high shock blast pressures shattered the concrete through the thickness of the slab specimen and tore through the back-face CFRP. However, back-face velocity and overall deflections were reduced by about 75% compared to the baseline test slab specimen.

Experimental investigation of CFRP anchorage systems used for strengthening RC joints

Fibre-reinforced polymer (FRP) composite materials are widely used for strengthening existing reinforced concrete structures because of their light weight, easy implementation and high efficiency. However, recent seismic studies have revealed that FRP-strengthened specimens underperform due to the debonding of the FRP strips in the vicinity of L-shaped structural joints, resulting from the lack of an anchoring system to transfer loads from the FRP strips to the supporting structural element. To address this issue, four new anchorage techniques are presented in this paper, and experimental results for each are analysed in the form of failure modes, load displacement curves, longitudinal strain distribution curves, hysteresis loops and the ultimate capacity. This research paper concludes that these Carbon Fiber (CF) anchor systems enhance the overall seismic performance of FRP-strengthened specimens.

Retrofitting Earthquake-Damaged RC Structural Walls with Openings by Externally Bonded FRP Strips and Sheets

The majority of research studies on the behavior of reinforced concrete members with externally bonded fiber reinforced polymer (FRP) sheets have been focused on beams, columns, and beam-column joints. However, limited experimental studies have been conducted to investigate the performance of structural walls retrofitted by wrapping FRP strips or sheets, especially on structural walls with openings. The validated retrofitting schemes for strengthening damaged walls without openings may not be suitable for walls with openings. Therefore, a series of experimental studies were carried out at Nanyang Technological University, Singapore, to study the effectiveness of the proposed repair and strengthening schemes in recovering the seismic performance of the damaged walls with irregular or regularly distributed openings. The strut-and-tie approach was utilized to design the repair schemes. The repaired walls managed to recover their strength, dissipated energy, and stiffness reasonably, indicating that the strut-and-tie approach can be a good design tool for FRP-strengthening of structural walls with openings. Moreover, the shear and sliding capacities of repaired walls were enhanced by using fiber anchors. The repaired walls failed primarily because of debonding of the fiber reinforced polymer at the base of the walls.

탄소섬유 앵커 X-브레이싱으로 보강된 철근콘크리트 기둥의 구조거동 및 내진보강 효과

This paper presents a new strengthening method on concrete column against seismic loads for structural per- formance tests. An X-bracing using high performance carbon fiber threads called the Carbon fiber anchor X-bracing is used to connect RC frames internally. The carbon fiber sheet is wrapped around the column to fix the top and bottom of the column after Super anchor was installed by drilling hole on the column. The structural performance was evaluated experimentally and ana- lytically. Two types of columns specimens were made; flexure fracture scaled model and shear fracture scaled model. For the per- formance evaluation, cyclic loading tests were conducted on moment and shear resisting columns with and without X bracing. Test results confirmed that the bracing system installed on RC columns enhanced the strength capacity and provided adequate ductility.

Design Considerations of Carbon Fiber Anchors

Carbon fiber-reinforced polymer (CFRP) sheets can be used to strengthen existing reinforced concrete members. However, debonding (separation of the CFRP sheet from the concrete surface) may occur at less than 50% of CFRP sheet’s tensile capacity, implying that half of the CFRP material is ineffective in increasing the strength of a concrete member. The use of carbon fiber anchors can increase the amount of tension carried in the CFRP sheets. Forty specimens were tested to develop initial design parameters of carbon fiber anchors. Tests showed that by providing anchors with a total cross-sectional area at least two times greater than that of the longitudinal sheet, it was possible to fracture the CFRP sheets. The best results were obtained using a greater number of smaller anchors. Further, surface preparation is unimportant when the CFRP sheets were well anchored and a 1:4 transition slope can manage any offsets in surface level. The general anchor design was then implemented on a series of long beams and demonstrated that the full CFRP sheet tensile capacity can be realized without incurring limitations due to debonding.

Time-Lapse Analysis and Mathematical Characterization Elucidate Novel Mechanisms Underlying Muscle Morphogenesis

Skeletal muscle morphogenesis transforms short muscle precursor cells into long, multinucleate myotubes that anchor to tendons via the myotendinous junction (MTJ). In vertebrates, a great deal is known about muscle specification as well as how somitic cells, as a cohort, generate the early myotome. However, the cellular mechanisms that generate long muscle fibers from short cells and the molecular factors that limit elongation are unknown. We show that zebrafish fast muscle fiber morphogenesis consists of three discrete phases: short precursor cells, intercalation/elongation, and boundary capture/myotube formation. In the first phase, cells exhibit randomly directed protrusive activity. The second phase, intercalation/elongation, proceeds via a two-step process: protrusion extension and filling. This repetition of protrusion extension and filling continues until both the anterior and posterior ends of the muscle fiber reach the MTJ. Finally, both ends of the muscle fiber anchor to the MTJ (boundary capture) and undergo further morphogenetic changes as they adopt the stereotypical, cylindrical shape of myotubes. We find that the basement membrane protein laminin is required for efficient elongation, proper fiber orientation, and boundary capture. These early muscle defects in the absence of either lamininβ1 or lamininγ1 contrast with later dystrophic phenotypes in lamininα2 mutant embryos, indicating discrete roles for different laminin chains during early muscle development. Surprisingly, genetic mosaic analysis suggests that boundary capture is a cell-autonomous phenomenon. Taken together, our results define three phases of muscle fiber morphogenesis and show that the critical second phase of elongation proceeds by a repetitive process of protrusion extension and protrusion filling. Furthermore, we show that laminin is a novel and critical molecular cue mediating fiber orientation and limiting muscle cell length.

Rapid Repair of Earthquake Damaged RC Interior Beam-Wide Column Joints and Beam-Wall Joints Using FRP Composites

This paper studies the seismic performance of FRP-strengthened RC interior non-seismically detailed beam-wide column and beam-wall joints after limited seismic damage. Four eccentric and concentric beam-wide column joints and two beam-wall joints, initially damaged in a previous study, were repaired and tested under constant axial loads (0.1 and 0.35 ) and lateral cyclic loading. The rapid repair technique developed, aimed to restore the original strength and to provide minimum drift capacity. The repair schemes were characterized by the use of : 1) epoxy injection and polymer modified cementitious mortar to seal the cracks and replace spalled concrete and 2) glass (GFRP) and carbon (CFRP) sheets to enhance the joint performance. The FRP sheets were effectively prevented against possible debonding through the use of fiber anchors. Comparison between responses of specimens before and after repair clearly indicated reasonable restoration in strength, drift capacity, stiffness and cumulative energy dissipation capacity. All specimens failed with delamination of FRP sheets at beam-column joint interfaces. The rapid repair technique developed in this study is recommended for mass upgrading or repair of earthquake damaged beam-column joints.

Flexural Fatigue Behavior of Reinforced Concrete Beams Strengthened with FRP Fabric and Precured Laminate Systems

Rehabilitation of existing structures with carbon fiber reinforced polymers (CFRP) has been growing in popularity because they offer resistance to corrosion and a high stiffness-to-weight ratio. This paper presents the flexural strengthening of seven reinforced concrete (RC) beams with two FRP systems. Two beams were maintained as unstrengthened control samples. Three of the RC beams were strengthened with CFRP fabrics, whereas the remaining two were strengthened using FRP precured laminates. Glass fiber anchor spikes were applied in one of the CFRP fabric strengthened beams. One of the FRP precured laminate strengthened beams was bonded with epoxy adhesive and the other one was attached by using mechanical fasteners. Five of the beams were tested under fatigue loading for two million cycles. All of the beams survived fatigue testing. The results showed that use of anchor spikes in fabric strengthening increase ultimate strength, and mechanical fasteners can be an alternative to epoxy bonded precured lami...

Interface debonding failure in beams strengthened with externally bonded GFRP

Although strengthened concrete members with Fiber Reinforced Polymer Plastic (FRP) are well-known to improve both strength and stiffness of constructions, relatively little is known about their premature failure, and specially, the development of interface debonding when flexural macro cracks at the mid-point of a strengthened beam reach a critical state and an interface crack propagates to the end-block. Herein, an experimental study using GFRP-strengthened beams is performed, in which the effects of length, thickness, and plate width on interface debonding failure were examined. According as strengthening length is increased, failure pattern changed from ripoff to interface debonding, and there was comparatively smaller effect in which failure pattern by the strengthening amount changes. From the comparison of anchoring schemes in end-block of FRP, U-wrap anchoring is more effectively resistant to shear stress than fiber anchor. As flexural cracks developed near the mid-point of the beams, horizontal interface debonding cracks between the concrete and GFRP propagated to the end-blocks of the plates after the tensile rebars yielded. In this study, a semi-empirical equation is developed to predict debonding loads, based on the test results. The proposed theory, which is based on nonlinear analysis and the critical flexural crack width, predicted the debonding failure loads of the specimens relatively well, and can be used for the analysis and design of GFRP-strengthened RC beams.

Anchorage Systems for Masonry Walls Strengthened with FRP Composite Laminates

This study examined the anchorage of FRP systems in strengthening masonry walls against out-of-plane lateral loads. The anchorage methods utilized (i) improved bond; (ii) a fiber anchor bolt system; and (iii) an embedded bar system. Tests were carried out on eight walls of half-brick thickness and seven walls of full-brick thickness, strengthened with two different types of glass and one carbon FRP systems. Each wall was placed in a horizontal plane and simply supported along four sides without edge restraint, and then subjected to a uniformly distributed pressure applied using an air bag over a square area at its centre. Test results indicated that specimens without any anchorage measures showed premature failure by FRP debonding, while those provided with an anchorage system, failed by brick crushing or by punching shear at a much higher load. An analytical model is also presented to predict the failure load of FRP reinforced masonry walls failing in flexural compression or punching shear, and was found to predict test results well.

Actin Cable Dynamics and Rho/Rock Orchestrate a Polarized Cytoskeletal Architecture in the Early Steps of Assembling a Stratified Epithelium

To enable stratification and barrier function, the epidermis must permit self-renewal while maintaining adhesive connections. By generating K14-GFP-actin mice to monitor actin dynamics in cultured primary keratinocytes, we uncovered a role for the actin cytoskeleton in establishing cellular organization. During epidermal sheet formation, a polarized network of nascent intercellular junctions and radial actin cables assemble in the apical plane of the monolayer. These actin fibers anchor to a central actin-myosin network, creating a tension-based plane of cytoskeleton across the apical surface of the sheet. Movement of the sheet surface relative to its base expands the zone of intercellular overlap, catalyzing new sites for nascent intercellular junctions. This polarized cytoskeleton is dependent upon α-catenin, Rho, and Rock, and its regulation may be important for wound healing and/or stratification, where coordinated tissue movements are involved.

Strength Enhancement of Rectangular Reinforced Concrete Columns using Fiber-Reinforced Polymer

The strength enhancement of concentrically loaded columns bonded with external fiber-reinforced polymer (FRP) systems arises from two sources. First, the confinement effect of transverse fiber sheets leads to an increase in the uniaxial compressive strength of the confined concrete, resulting subsequently in an increase in the contribution of concrete to the load-carrying capacity of the column. Second, the longitudinal fiber sheets contribute directly to the load-carrying capacity of the column. The confinement effect of the externally bonded FRP systems in rectangular columns is known to be less than that in circular or square columns. This study specifically examines the case of rectangular reinforced concrete columns with a section aspect ratio of 3.65, which are typical in construction of monolithic housing apartments. A total of 52 half-scale, short columns were fabricated and tested to failure under a concentric load to investigate the effect of fiber type and configuration and fiber anchors on the...

Strength of RC Cantilever Slabs Bonded with GFRP Strips

Strengthening of RC cantilever slabs using bonded glass-fiber–reinforced plastic (GFRP) strips has recently been explored. That work led to the proposal that the GFRP strips should be anchored to the supporting wall using epoxy-mortar–filled horizontal slots and to the slab using fiber anchors, to prevent or limit debonding. This paper focuses on the strength of RC cantilever slabs strengthened using this method. Experimental work on model cantilever slabs with steel reinforcement of different amounts and different positions is presented. Because of the presence of fiber anchors, all strengthened slabs failed by tensile rupture of the fiber-reinforced plastic (FRP), although in some of the slabs partial debonding had appeared before the FRP rupture took place. Flexural strength equations based on the conventional plane section assumption are next described and shown to predict the test results well, even for slabs with partially debonded FRP strips. Finally, the effect of preloading on the strength of strengthened slabs is discussed.

Retrofitting of Deficient RC Cantilever Slabs Using GFRP Strips

Despite many studies on beams and slabs strengthened using fiber-reinforced plastic (FRP) plates, no study has been reported on the strengthening of RC cantilever slabs (e.g., canopies and balconies) using FRP materials. This paper presents the results of an experimental study of the feasibility of strengthening deficient RC cantilever slabs by bonding glass FRP (GFRP) strips/sheets on the top surface (the tension side). As the key to the success of this strengthening method is a proper way of anchoring the GFRP strips into the supporting wall and the slab, the effectiveness of different anchorage systems was the focus of the experiments. Based on the test results, a simple and effective method is identified in which the GFRP strips are anchored into the walls through horizontal slots and onto the slab using fiber anchors.