Short Specimens Research Articles

Behavior of FRP-interlayer-steel confined concrete columns subjected to eccentric compression

Fiber reinforced polymer (FRP)-interlayer-steel confined concrete (FISC) columns are proposed by bonding a filament-wound FRP tube with a concrete-filled steel tube (CFST) using grouting material to increase the corrosion resistance of CFST columns. FISC columns have high bearing capacity, benefiting from the dual confinement provided by both FRP and steel tubes on the core concrete. Despite this, the current research on the behaviors of FISC columns is limited, particularly regarding the confinement mechanism in FISC columns under eccentric compression. In this paper, a total of twenty short specimens were tested under eccentric compression, including seventeen FISC specimens, two FRP confined concrete-filled steel tubular (CCFT) columns, and one CFST specimen. Failure modes, load versus deflection curves and strain development for FISC specimens were presented and discussed, considering variations in eccentricity, FRP types, FRP thicknesses, and the ratio of FRP and steel confining indexes. Additionally, confining stresses of the FRP and steel tubes were obtained, revealing a non-uniform distribution of confinement on concrete along the sectional circumference, which decreased with increasing eccentricity. Furthermore, by regarding the concrete and grouting material as a whole unity and accounting for the influence of eccentricity, a sectional numerical analysis model for FISC columns was established and validated against test results, and the influences of steel thickness, FRP thickness, and concrete-grouting strength on the N-M correlation curves of FISC columns were investigated.

Direct Tensile Capacity of Steel-Tube Connections in a Precast Concrete Double-Wall System

This study introduces a new precast concrete (PC) double-wall system designed to simplify the complex fabrication process of existing PC double-wall systems and eliminate laitance and other defects that can occur during the manufacture of concrete panels. An experiment and finite element analysis were conducted on 11 specimens to determine the tensile resistance performance of rectangular steel tubes that maintain spacing to avoid damage to the PC panels during transportation or on-site installation. Specimens varied in terms of the end details of the rectangular steel tubes, such as the presence of welded steel plates or embedded concrete and total length in terms of whether longer or shorter specimens were used. As a result, the specimens showed a 20–30% increase in maximum tensile strength compared to the control specimen according to the end details, except for the case where side steel plates were cut and bent inward. The control specimen filled with concrete was the most suitable for connections when constructing PC double-wall systems. It has significant tensile resistance according to the experiment and finite element analysis and does not require additional construction steps or costs.

Hybrid FRP-concrete-steel double-skin tubular columns of varying slenderness ratios under eccentric compression

Hybrid fiber reinforced polymer (FRP)-concrete-steel double-skin tubular columns (DSTCs) are an emerging form of hybrid column with excellent mechanical performance and durability. Such columns consist of an outer FRP tube, an inner steel tube and a concrete infill between the two tubes. While extensive experimental and theoretical studies have been conducted on such columns, these studies have been focused on short specimens under concentric compression. This paper presents the results of a series of tests on hybrid DSTCs of varying slenderness ratios subjected to eccentric compression. The effects of FRP confinement stiffness, load eccentricity, and slenderness ratio on the behavior of hybrid DSTCs were examined. The test results showed that the test hybrid DSTCs exhibited excellent performance with great ductility. A theoretical model with incorporations of existing stress-strain models for FRP-confined concrete was then adapted to simulate the behavior of the test hybrid DSTCs. The comparisons showed that the direct use of a concentric loading stress-strain model led to underestimation of the deformation capacity of the test hybrid DSTCs. Compared with the other two models, the eccentric-loading stress-strain model previously developed by the authors' group provided more accurate predictions for the ultimate deformation of the test hybrid DSTCs.

Effect of Samples Size on the Water Removal and Shrinkage of Eucalyptus urophylla × E. grandis Wood during Supercritical CO2 Dewatering

Eucalyptus urophydis E. grandis green wood with different lengths were dewatered using CO2 that was cyclically alternated between the supercritical fluid and gas phases. The results indicate that shorter specimens can be dewatered to below the fiber saturation point (FSP). There was no significant difference in the dewatering rate between the specimens of 20 and 50 mm in length. The dewatering was faster when the moisture content (MC) was over the FSP, leading to a greater gradient and a non-uniform distribution of moisture. The MC distributions in all specimens had no clear differences between in tangential and radial directions. Supercritical CO2 dewatering generated a different moisture gradient than conventional kiln drying. Most water was dewatered from the end-grain section of the wood along the fiber direction, but a small amount of water was also removed in the transverse directions. There was no deformation in the specimens when the MC was above the FSP.

Freeze-thaw behaviour of basalt fibre reinforced recycled aggregate concrete filled CFRP tube specimens

This paper is focused on the behaviour of basalt fibre reinforced recycled aggregate concrete (BFRC) short specimens confined by carbon fibre reinforced polymer (CFRP) tubes under freeze–thaw conditions. The main parameters investigated are the replacement rate of recycled coarse aggregate (RCA), the number of freeze–thaw cycle (FTC), the related temperature range, and the shape of short specimen section. The failure mode, dynamic elastic modulus, ultimate bearing capacity and the load–strain response of the specimens are studied. The results show that the failure mode and the load–strain response of CFRP tube confined recycled aggregate concrete (RAC) specimen have insignificant change due to FTCs. However, with the increase of the FTCs, the bearing capacity of the specimen decreases, and the specimen with square cross-section is much more sensitive than that of the circular cross-section counterpart. The smaller the range of freeze–thaw temperature changed, the smaller loss of the dynamic modulus and the smaller decrease range of the ultimate bearing capacity after FTCs.

Numerical and analytical investigation of square timber columns confined with steel and carbon fiber reinforced polymer external jacket

This paper numerically investigated the timber confinement of columns with carbon fiber reinforced polymer (CFRP) and steel tubes under axial compression. An elastic-plastic model with linear hardening, a CFRP hashin damage, and a timber damaged anisotropic elastic-plastic model, respectively, are used to simulate the inelastic behavior of the steel tube, CFRP layers, and timber core. In addition, a comprehensive numerical study was conducted using a wide range of cross-sections, thicknesses, lengths, and the number of CFRP layers developed to varying degrees (0, 45, and 90). To confirm the accuracy of the current FEM model, numerical data is compared to the experimental model’s final strengths, behavior, and failure mechanisms. Additionally, the ultimate strengths of timber-steel and CFRP are compared to various standards and design formulas. The results reveal that columns with thicker steel tubes and more CFRP layers have an average of about 42% and 12% greater load-bearing capacity and ductility. The degree of CFRP affected the load-bearing capacity of timber columns, which increased by around 10% from 45 to 90. In comparison to specimens with equal cross-sections and thickness, shorter specimens with greater cross-sections typically have 40% higher stiffness. According to parameter studies, the AISC 360-16 American standard design approaches can be safely extended to anticipate the ultimate strength of timber-steel columns. Meanwhile, both the ACI-440 and Ilki et al. design formula predictions are the most precise, particularly at 45° with high ultimate strength.

MO42-3 The stability of angiogenesis-related factors in angiogenesis panel: a prospective observational study

Angiogenesis-related factors, especially vascular endothelial growth factor (VEGF)-A and -D, have been reported to be possible biomarkers for angiogenesis inhibitors of the second-line treatment of advanced colorectal cancer. Currently, the angiogenesis panel (AP), which analyzes 17 angiogenesis-related factors by the multiplex assay with Luminex technology, is under development. Clinical studies using AP are ongoing or planned for advanced colorectal cancer. However, AP is inconvenient at the point of its short specimen processing time.

Rehabilitation of Composite Column Subjected to Axial Load

Concrete Filled Double Steel Tube (CFDST) columns are a modern technique of composite structural element that has fire resistance and has been adopted in high-rise building structures. The Concrete Filled Steel Tube (CFST) columns also have high strength and ductility due to composite action. This type of column CFST can sustain a heavy load with high performance and has been adopted in recent years in many countries around the world. The aim of the present work is to study the behavior and strength of rehabilitation of composite columns that are made from concrete core and surrounded steel tubes under the effect of axial compression loads with different height to diameter ratios such as 5.46, 10.91, and 16.37, respectively, by experimental tests. Double skin methodology is adopted to repair the damaged columns that were tested up to 85% of the ultimate load. Strength column capacity of double skin columns, axial and buckling deformations with axial and buckling strains are investigated. Test results showed that the repaired specimens up to 85% of the ultimate load had the same strength carrying capacity as compared with the control specimens, which had the same geometry. The ductility of an 800 mm specimen’s height is greater than the other tested specimens, while the stiffness of short specimens becomes high. Doi: 10.28991/CEJ-2022-08-03-013 Full Text: PDF

Hysteretic Behavior and Multi-Wave Buckling of Assembled Buckling-Restrained Braces Wrapped with Fiber Clothes

To rapidly repair the damaged buckling-restrained brace serving as energy absorption member during earthquake, the assembled method of wrapping the component with FRP cloth is proposed. In this research, a series of cyclic tests on six assembled buckling-restrained brace (ABRB) wrapped with three kinds of FRPs (carbon fiber, glass fiber and basalt fiber) were performed. The tested results show that all the specimens show excellent hysteretic performance and similar damage mode, namely core unit fracture, whilst short specimens show better ductility, but worse energy dissipation ability than the long specimen. A parametric analysis is performed based on a finite element model validated against the test result. The effects of the gap and friction force between core unit and infilled concrete and the thickness of FRP cloth are analyzed. The modes of multi-wave buckling of core units are exhibited, and the influence of multi-wave buckling on component performance is evaluated. Based on the test and simulation analysis, CFRP is suggested to be used in the wrapped buckling-restrained brace.

Correction factors for in-plane shear strength and stiffness testing of flat angle-ply composite laminates with high Poisson’s ratios

In this paper, a method to obtain correction factors for in-plane shear properties in fibre-reinforced polymers with high Poisson’s ratio under biaxial load conditions and at high loads is presented. Experimental testing shows the deviations from classical laminate theory for such cases. The transverse deformation ratio is a general form of Poisson’s ratio and, for a ±45° angle-ply laminate, increases with strain. This effect is shown to exist for long and short test specimens, where significant biaxiality in the stress state is present. Reasons for this include fibre rotation at higher loads in tensile load conditions, and matrix plasticity and damage initiation. Test results show that the expanded formulas compensate errors in shear strength calculation of angle-ply laminates which arise from using nominal parameters with standard formulas. The results are also applicable to structures under biaxial load and when transverse contraction is inhibited, e.g. in shear panels. Further potential uses are in the presence of high shear strains and to detect the onset of damage under shear loading.

The Influence of Specimen Geometry and Loading Conditions on the Mechanical Properties of Porous Brittle Media

Dynamic tests of fine-grained fired dioxide-zirconia ceramics under compression under uniaxial stress conditions were carried out. The influence of the specimen length on the obtained strength and deformation properties of ceramics is investigated. The thickness of the specimen has a significant impact on the course of the obtained dynamic stress–strain diagrams: short specimens have a much more sloping area of active loading branch. The main contribution to the modulus of the load branch resulting from tests of brittle porous media is made by the geometry of the specimens and the porosity of the material. When choosing the length of specimens for dynamic tests, the optimal geometry of the tested specimens is preferable in accordance with the Davies–Hunter criterion, when the contributions of axial and radial inertia are mutually compensated, and the contribution of the effects of friction in the resulting diagram is minimal. When choosing the geometry of specimens of brittle porous media, the structure of the material should be taken into account so that the size of the specimen (both length and diameter) exceeds the size of the internal fractions of the material by at least five times.

An algorithm for statistical evaluation of weld toe geometries using laser triangulation

Commonly, to evaluate the influence of the local weld geometry in fatigue test, small-scale specimens are used, assuming those represent a longer weld adequately. In this study, a comparison between short specimens and a long weld is performed. A method is developed for the statistical evaluation of weld toe radii and angles, stress concentration factors and weld quality classes. The results show a strong sampling rate dependence and lower ISO 5817:2014 weld quality results for higher sampling rates. Comparable results between short specimens and a long weld can be achieved using modal values of the parameters assuming a lognormal distribution.

Flexural Behavior of 3D printed Concrete Beam with Fiber Reinforcement

3D printing with concrete is a promising new method for rapid, low cost construction. The flexural strengths for reinforced/unreinforced and 3D printed/cast concrete Warren trusses were tabulated and the failure mechanisms were reported. The types of reinforcement used were rebar(basalt and steel), and mesh (basalt and aramid). The effect of loading geometry and loading speed was measured for basalt mesh and aramid mesh composite, respectively. Due to the expected variation in flexure between samples, it cannot be said whether small differences for various tests are significant. Variation stems from a microscopically uneven surface and random inhomogeneities in the bulk of the tested material which act as a microcrack catalyst and propagator. Since the tested beams are short specimens the numerical findings of other studies will vary based on the intended design. This paper is intended to assess the performance of various reinforcements in a qualitative sense by comparing basalt reinforcement with other reinforcements. It was found that cast beams tolerated deflection better but had a similar flexure strength compared as the printed beams. The steel and basalt rebar reinforced beams had the highest flexure strengths where the traditional steel rebar reinforcement outperformed the basalt in flexure by 36% and the basalt outperformed the steel in deflection by 40%. The basalt mesh outperformed the cast and printed unreinforced bars by a small margin but had only 25% of steel rebars’ deflection at maximum flexure strength. The aramid mesh tolerated the biggest deflection out of any sample at 2.26 cm.

Factors Affecting Lymph Node Yield in Surgically Resected Colorectal Cancer Specimens

Background: Currently, the CAP protocol mandates evaluation of ≥12 Lymph nodes as a quality indicator for the adequacy of pathologic examination of colorectal cancer resection specimens. Aim: To identify factors that may influence the lymph node yield in colorectal cancer specimens and to compare with the relevant publications. 
 
 Methods: The retrospective study of seventy patients with loco-regional colorectal adenocarcinomas treated by standard surgical resection from April 2015- April 2017 was included. All cases with inadequate lymph nodes had been re-grossed by another pathologist. Variables like age, gender, primary site, type of surgery, specimen length, tumour size, grade and stage, neoadjuvant therapy and tumour site perforation were evaluated for their impact on the average total number of nodes examined.
 Results: Out of seventy, eleven [15.71%] patients had inadequate mean nodal yield [MNY]. Of these eleven patients, MNY was greater in males [6.6] than in females [6.4]. MNY was lesser in patients with age >50years [5.71] than patients ≤ 50 years [8]. The yield increased exponentially with increasing tumour stage and tumour size. Yield was higher in tumours with perforation. Specimens longer than 20cm had a higher yield [7.29] than in shorter specimens [5.25]. The yield was lesser when tumour is located more distally [APR:4.5 and AR &sigmoid colectomy:7.7]. Seven patients had taken neoadjuvant therapy [63.6%] of whom, six had moderately differentiated adenocarcinoma & one had no tumour.
 Conclusion: Factors like neoadjuvant therapy, age & gender of the patient, type of surgery, length of the specimen, tumour size, grade, stage, site & perforation, affect the MNY in colorectal cancers.

Experimental study of concrete filled steel tube composite beam under hogging moment

The main objective of this work is an experimental study of the concrete filled steel tube (CFST) composite beam under the influence of a hogging moment. The specimens are consisting of a steel tube filled with lightweight or normal concrete (CFST) and a reinforced concrete slab, perfobond connector is used to connect the steel tube and concrete slab. Seven specimens were cast and tested, five parameters are studied, specimen length, the strength of concrete which filling the steel tube, the influence of filling the steel tube, and existing of a concrete slab. To study the behavior of specimens the flexure test was done under hogging (negative) moment. The testing results including ultimate load, crack, load-deflection curve, and slip at the end and one-third span of the tested beam. The short specimen has a greater ultimate load than other specimens but a smaller bending moment. The local buckling appeared in the steel tube at a load ranged from 83.7% to 96.7% of the ultimate load, the ultimate load of the hollow steel tube composite beam is decreasing by 75.69% compared with the reference specimen, also the ultimate load was increased when the concrete compressive strength which filled steel tube increased. The slip was measured in two locations of the specimen, the slip at the end of the specimens is less than the slip in one-third of the specimens at the ultimate load.

Multi-leaf masonry walls: Load transfer mechanisms sensitivity to mechanic and geometric parameters

The apparent monolithic behaviour of multi-leaf walls is compromised by the discontinuity planes that the load transfer mechanisms generate for the following reasons: i) difference between mechanical characteristics of layers; ii) lack or weakness of the structural interaction between core and external layers. The goal of this paper is to evaluate through parametric analysis the dimensional ratios by reference to core confinement effects of multi-leaf masonry walls with several interface and mechanical characteristics of layers. The study was carried out through the finite element analysis performed in non-linear field on two-dimensional plain strain models calibrated on experimental basis and numerical results are presented and discussed. The horizontal interfaces hand the load transfer and structural performances of multi-leaf walls. The behaviour of short specimens is controlled by confinement of external layers while for slender masonry walls the out of plane mechanisms affect the confinement effect.

Effect of Strain Rate on the Tensile Mechanical Properties of Electron Beam Welded OFE Copper and High-Purity Niobium for SRF Applications

An investigation of the tensile mechanical properties of electron beam welded OFE copper and high-purity niobium sheets is presented. Specimens were deformed in tension at strain rates ranging from 10−3 to ~ 1600 s−1. The 0.2% yield stress and ultimate tensile strength (UTS) of the welded niobium specimens are similar to those of unwelded specimens at strain rates lower or equal to 20 s−1. At higher strain rates, these mechanical properties are lower for welded niobium specimens. The 0.2% yield stress of welded OFE copper specimens is consistently lower than unwelded specimens over the range of strain rates studied, while the UTS is comparable at all strain rates. The elongation to failure of welded OFE copper specimens remains unchanged at all strain rates while the ductility of niobium specimens reduces at strain rates greater or equal to 20 s−1 and reaches a minimum at ~ 400 s−1. The effects of the weld on a non-standardized short specimen geometry, developed for this study to obtain strain rates in the order of 103 s−1, are more pronounced for niobium due to large grain sizes (up to 1200 μm) in the fusion region. However, comparable strength and ductility trends, with respect to a standard specimen, were measured at low strain rates. The conservation of strength and the relatively high ductility of the welded sheets, especially for OFE copper, suggest that bent and electron beam welded tubes could be used for the fabrication of seamless superconducting radiofrequency (SRF) cavities. These results are promising for the use of high-speed forming techniques, like electro-hydraulic forming, for the manufacturing of parts using welded tubes and sheets.

On the interplay of microstructure and residual stress in LPBF IN718

The relationship between residual stresses and microstructure associated with a laser powder bed fusion (LPBF) IN718 alloy has been investigated on specimens produced with three different scanning strategies (unidirectional Y-scan, 90° XY-scan, and 67° Rot-scan). Synchrotron X-ray energy-dispersive diffraction (EDXRD) combined with optical profilometry was used to study residual stress (RS) distribution and distortion upon removal of the specimens from the baseplate. The microstructural characterization of both the bulk and the near-surface regions was conducted using scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD). On the top surfaces of the specimens, the highest RS values are observed in the Y-scan specimen and the lowest in the Rot-scan specimen, while the tendency is inversed on the side lateral surfaces. A considerable amount of RS remains in the specimens after their removal from the baseplate, especially in the Y- and Z-direction (short specimen dimension and building direction (BD), respectively). The distortion measured on the top surface following baseplate thinning and subsequent removal is mainly attributed to the amount of RS released in the build direction. Importantly, it is observed that the additive manufacturing microstructures challenge the use of classic theoretical models for the calculation of diffraction elastic constants (DEC) required for diffraction-based RS analysis. It is found that when the Reuß model is used for the calculation of RS for different crystal planes, as opposed to the conventionally used Kröner model, the results exhibit lower scatter. This is discussed in context of experimental measurements of DEC available in the literature for conventional and additively manufactured Ni-base alloys.

Drying Characteristics of Eucalyptus urophylla × E. grandis with Supercritical CO2.

Supercritical CO2 (ScCO2) is a drying medium with excellent solubility and mass transfer efficiency. Supercritical CO2 drying (SCD) can remove the water of wood rapidly and prevent a change of microstructure caused by capillary tension in the drying process. In this study, Eucalyptus urophylla × E. grandis specimens with lengths of 50 and 100 mm were dried with ScCO2. Conventional kiln drying (CKD) and oven-drying (OD) were used as control. After 1 h, the drying rate, shrinkage, moisture distribution, drying stress were measured to explore the influence of drying methods and specimen length for drying characteristics during the early drying stage. The results showed that compared with CKD and OD, water removal was the fastest under SCD, and the drying rate was nine times of CKD and one time of OD. The shrinkage of SCD was the lowest among the three drying methods. Moisture distribution of SCD and OD was uneven. The drying stress of SCD was relatively high, the drying stress index of it was almost five times of CKD and three times of OD. Regardless of the drying method, shorter specimens had a shorter drying period but greater drying defects than the long specimens.

Tests of bond between concrete and steel bars – literature background and program of own research

This article deals with the issue of the bond between concrete and reinforcement. The bond is crucial for reinforced concrete elements because it is possible to transfer forces (stresses) from concrete to the reinforcement. Basic information related to the cooperation of concrete and rebars was recalled in the article. Selected issues concerning theoretical and numerical analysis as well as experiments of the bond phenomenon were presented. The article also proposes its own concept of experimental studies on the bond on two types of specimens: so-called short specimen and large specimen that will be subjected to pull-out tests. The described concept is ultimately to form the basis for creating a numerical model, enabling the simulation of bond in various reinforced concrete elements, calibrated based on the results of experimental studies.