Monotonic Compressive Loading Research Articles

Behavior of thin masonry arches repaired using composite materials

The innovative technique described in this article is the result of the evolution of a traditional building technique (tabicada technique or tile vaulting method) belonging to the constructive Spanish tradition. This technique consists in the realization of thin masonry vaults by placing several layers of thin bricks alternated with coatings of hydraulic mortar. Since the use of a modern technology may improve the mechanical performance of the traditional materials, the proposed strengthening system is based on the combination of the typical features of tabicada technique with the high mechanical properties of the composite materials. In order to provide extra tensile strength to the vaulted structure, composite grids were inserted between the brick layers into the mortar coating as well as on the outer surface of the vaults. Seventeen arch specimens were tested under a monotonic vertical compression load applied at the keystone. The influence of the type of strengthening arrangements, arch thickness and properties of hydraulic mortars were investigated. Test results are presented and discussed considering the mechanical behavior of the specimens and the axial stress-axial strain relationships.

Thermal-Mechanical Properties of Epoxy-Impregnated Bi-2212/Ag Composite

Knowledge of the thermal-mechanical properties of epoxy/superconductor/insulation composite is important for designing, fabricating, and operating epoxy impregnated high field superconducting magnets near their ultimate potentials. We report measurements of the modulus of elasticity, Poisson's ratio, and the coefficient of thermal contraction of epoxy-impregnated composite made from the state-of-the-art powder-in-tube multifilamentary Ag/Bi 2 Sr 2 CaCu 2 O x round wire at room temperature and cryogenic temperatures. Stress-strain curves of samples made from single-strand and Rutherford cables were tested under both monotonic and cyclic compressive loads, with single strands insulated using a thin TiO 2 insulation coating and the Rutherford cable insulated with a braided ceramic sleeve.

Compressive behavior of H-shaped brace strengthened with non-welded cold-formed element

As seismic design code was revised in Korea in 2009, the seismic performance of the structures which were not built in compliance with the code need to be reviewed. In middle and low-rise buildings, braces resist most of lateral force. Therefore, it is critical to decide how to reinforce the braces in middle and low-rise buildings to ensure structural safety when seismic load is applied repeatedly. This study suggests reinforcement details to restrain the flexural buckling of slender H-shaped braces and enable them to resist compressive force. In order to evaluate the behavior of the suggested reinforcing member, preliminary test and full-scale monotonic compressive loading test were carried out. The parameters in the test were slenderness ratio and reinforcement area ratio. It was observed from the test that the suggested reinforcing member restrained the flexural buckling of slender brace and induced stable behavior of the brace when compressive force was applied. According to the tests, the area of reinforcing member should be more than 1.7 times of that of core member and the length of the former should be at least 80% of that of the latter.

Confining concrete with sisal and jute FRP as alternatives for CFRP and GFRP

Abstract This research paper presents an experimental investigation on the confinement strength and confinement modulus of concrete cylinders confined using different types of natural fibre composites and a comparative performance analysis with different artificial fibre based composite materials. The paper also highlights the need to switch over from the utilization of artificial fibres, which are non-renewable and fossil fuel products, to environmental beneficial materials like green fibres. The utilization of plant products like sisal and jute fibres and their composites in various structural engineering applications addresses the issues of sustainability and renewability with constructional materials. The paper describes a suitable mechanical treatment method like high temperature conditioning, which aids us in further improving the properties of these woven natural materials like sisal and jute for composite fabrication and utilization. Heat treated natural fibres of woven sisal and jute were utilized for confining concrete cylinders similar to CFRP and GFRP confinement and their confinement characteristics were obtained and compared. All the cylinders were subjected to monotonic axial compressive loads, so as to evaluate the effect of confinement on the axial load carrying capacity and all their failure modes were discussed thoroughly. The results indicated superior performance by sisal FRP as well as jute FRP confined cylinders as compared to controlled or unconfined cylinders, also sisal FRP wrapped cylinders displayed ultimate axial load of comparable magnitude to CFRP confinement. Natural FRP confinement displayed superior confinement modulus and confinement strength, also the ultimate axial load of concrete cylinders confined with natural FRPs underwent 66% enhancement by sisal FRP and 48% enhancement by jute FRP, in comparison with controlled or unconfined cylinders. Enhancement in axial load carrying capacity was 83% with CFRP confinement and 180% with GFRP confinement. Although natural FRP displayed lower enhancement in axial load carrying capacity in comparison with artificial FRP confinement, but enhanced load carrying capabilities alongside superior sustainability and environmental friendly indices could be obtained using the same, because of various advantages associated with the use of natural fibres.

Material behavior modeling with multi-output support vector regression

Based on neural network material-modeling technologies, a new paradigm, called multi-output support vector regression, is developed to model complex stress/strain behavior of materials. The constitutive information generally implicitly contained in the results of experiments, i.e., the relationships between stresses and strains, can be captured by training a support vector regression model within a unified architecture from experimental data. This model, inheriting the merits of the neural network based models, can be employed to model the behavior of modern, complex materials such as composites. Moreover, the architectures of the support vector regression built in this research can be more easily determined than that of the neural network. Therefore, the proposed constitutive models can be more conveniently applied to finite element analysis and other application fields.As an illustration, the behaviors of concrete in the state of plane stress under monotonic biaxial loading and compressive uniaxial cycle loading are modeled with the multi-output and single-output support regression respectively. The excellent results show that the support vector regression provides another effective approach for material modeling.

Computational simulation of ratcheting in dented pipes due to monotonic and cyclic axial loading

This article presents a computational simulation framework developed to capture the ratcheting response of dented straight pipes. The results are compared against the results obtained from our previously conducted experiments. Ratcheting occurs when a structure is subjected to a primary axial load along with a secondary cyclic load, provided that the applied loads are sufficiently large in magnitude to cause the material to yield. The dented pipes investigated in this study were initially subjected to a monotonic axial compression load, which caused the initiation of small amplitude wrinkles, and were subsequently subjected to an axial cyclic loading regime. A nonlinear finite element analysis, using a combined hardening model, was adopted to model the response of the material during the entire loading regime. The parameters required by the material model were obtained from cyclic tests conducted on representative coupon specimens. The results of the numerical simulations were compared to experimentally obtained data. The results demonstrated that the ratcheting response of dented pipes could be numerically simulated with a reasonable accuracy. The results also revealed that the surface imperfections exerted a very pronounced effect on the ratcheting response of the dented pipes. The computational model was also used to investigate the influence of some key parameters, such as the initial strain level, stress amplitude, mean stress, loading regime, and material hardening properties, on the resulting ratcheting.

Mechanical behaviour of wood T-joints. Experimental and numerical investigation

Results of a double-shear single-dowel wood connection tested under monotonic quasi-static compression loading are presented and discussed in this paper. The wood used in this study was a pine wood, namely the Pinus pinaster species, which is one of the most important Portuguese species. Each connection (specimen) consists of three wood members: a centre member, loaded in compression along the parallel-tograin direction and two simply supported side members, loaded along the perpendicular-to-grain direction (Tconnection). The load transfer between wood members was assured by means of a steel dowel, which is representative of the most common joining technique applied for structural details in wooden structures. The complete load-slip behaviour of the joint is obtained until failure. In particular, the values of the stiffness, the ultimate loads and the ductility were evaluated. Additionally, this investigation proposed non-linear 3D finite element models to simulate the T-joint behaviour. The interaction between the dowel and the wood members was simulated using contact finite elements. A plasticity model, based on Hill’s criterion, was used to simulate the joint ductility and cohesive damage modelling was applied to simulate the brittle failure modes (splitting) observed in the side members of the joint. The simulation procedure allowed a satisfactory description of the non-linear behaviour of the T-joint including the collapse prediction.

Steel strap confined high strength concrete under uniaxial cyclic compression

This paper discusses an affordable and effective lateral confinement technique to enhance concrete’s compressive strength and ductility – the steel strapping tensioning technique (SSTT). Considerable studies have been done on the characteristics of SSTT-confined concrete under uniaxial monotonic compression loading, but none has addressed its uniaxial cyclic response. In this paper, 21 high-strength concrete specimens having diameter of 150mm and height of 300mm had been cast, laterally pre-tensioned with steel straps in different confining ratios, and tested to failure under uniaxial cyclic and monotonic compression loadings. Results indicated that the basic hypothesis of envelope curve is valid for SSTT-confined high-strength concrete specimens for uniaxial monotonic and cyclic loadings. The development of plastic strain is independent of the confining ratio when the envelope unloading strain exceeds 0.0025. Moreover, SSTT-confinement has the lowest plastic strain compared to several related existing plastic strain models. The stress deterioration ratio is independent of confining ratio and loading patterns. Lastly, the concept which neglects the effect of loading history on the permanent axial strain of the unloading and reloading paths of concrete is invalid because repeated unloading/reloading cycles have demonstrated a cumulative effect on the permanent strain and stress deterioration.

Notch Fracture Toughness Evaluation for a Brittle Graphite Material

Abstract First, several disc-type test samples weakened by a central bean-shaped slit with two U-shaped ends, called U-notched Brazilian disc (UNBD) specimens, made of commercial graphite, were prepared. Four notch tip radii were considered in the tests. Then, a monotonic compressive load was diametrally applied to each sample along the slit, resulting in pure mode I loading. After sudden fracture, the fracture loads were recorded and converted into the corresponding values of the notch fracture toughness (NFT) KIρ,c. The main advantage of the UNBD specimen is that the NTF test can be easily conducted without using complicated fixtures. The well-established brittle fracture model, namely the strain energy density (SED) over a specified control volume, which embraces the notch edge, was employed to estimate the fracture loads theoretically. A good agreement was found between experimental and theoretical results. Under Mode I loading, the SED and the NFT are linked by a simple relationship providing a powerful tool for the fracture assessment of different specimens and structural components weakened by notches.

Effect of Confining Layers of Steel Straps Confined High-Strength Concrete Cylinder under Uniaxial Cyclic Compression

The remarkable advantages and promising increment in concrete ultimate capacity as well as ductility by using steel straps as lateral confinement has brought the steel strapping tensioning technique (SSTT) as one of the most affordable confining technique in market. A number of studies have been reported the behaviour of SSTT-confined concrete under uniaxial monotonic compression loading but none of any study addressed the uniaxial cyclic response of such confinement. In this paper, twenty-one high-strength concrete cylinder specimens with diameter of 150 mm and 300 mm in height were cast, laterally pre-tensioned with steel strap in different confining layers and tested to failure under uniaxial cyclic and monotonic compression loading. A number of conclusions to be drawn from experimental results including the tangential validation of stress-strain curve for uniaxial monotonic and cyclic loading, independency of plastic strain to the amount of confining layers, the disagreement of uniqueness concept on the repeated uniaxial unloading and reloading cycles, and the promising effect of confining layers and loading patterns to the ultimate capacity of SSTT confinement. A plastic strain model is proposed and compared with existing plastic strain models. The result proved that SSTT confinement able to secure the lowest plastic strain among the others existing confinement method.

Effect of cyclic loadings on heated self-compacting concrete

This experimental study examines the effect of cyclic loadings on heated self-compacting concrete (SCC). One hundred and eight standard cylindrical specimens and one hundred and eight cubic specimens were tested. Compressive strength of the concrete specimens was within the normal range with strengths of 25, 35, and 45MPa. Test speed was within the quasi-static range. The cyclic loading was imposed within the compressive area. The concrete specimens were heated to 23°C, 100°C, 200°C, 400°C, 600°C and 800°C and then were exposed to monotonic compressive loading or cyclic loading. The stress–strain diagram, compressive strength, and SCC behavior under the cyclic and monotonic loadings before and after heating were compared. The results show that the heated concrete has a lower compressive strength. The heated concrete exhibits more strains in the cyclic loading. Development of cracks in all the heated and unheated specimens under cyclic loading is different.

Experimental study of non-circular concrete elements actively confined with shape memory alloy wires

This study focuses on developing a novel scheme for applying external active confinement to non-circular concrete elements that lack ductility using shape memory alloys (SMAs). A total of 13 concrete elements (prisms) are tested under monotonic and cyclic uniaxial compression load. The compressive stress–strain relationships of the SMA confined concrete elements are examined and compared with the behaviors of elements confined with conventional glass fiber reinforced polymer (GFRP) jackets. The results clearly show a significant improvement in the ultimate strain and residual (post-peak) strength of concrete elements actively confined with SMA compared to that of GFRP confined elements.

Effects of confinement level, cross-section shape and corner radius on the cyclic behavior of CFRCM confined concrete columns

The main results of an experimental research aiming to investigate the behavior of medium-size low-strength concrete columns wrapped with Carbon Fiber Reinforced Cementitious Matrix (CFRCM) under monotonic and cyclic compressive axial loads are presented. Thirty columns with circular, square and rectangular cross-sections were tested under monotonic and cyclic axial loads to investigate the effect of the confinement level, the cross-section shape and the corner radius on the stiffness, strength, and ductility of CFRCM confined concrete columns under cyclic loads. The results prove that CFRCM confining jackets provide substantial gain in compressive strength, deformability and absorbed energy.

Concrete confinement with steel-reinforced grout jackets

The potential of steel fiber reinforced jackets combined with inorganic matrix (cementitious grout matrix) as an alternative strengthening system to fiber-reinforced polymer (FRP) jackets was investigated experimentally in the current study. For this purpose, the novel jacketing device was applied on cylindrical specimens subjected to monotonic concentric uniaxial compression load. Parameters of investigation were the type of the steel fiber reinforced fabric, its density, the overlap length, and the concrete compressive strength. The 3 × 2 and 12× types of steel fabric were used with three alternative densities, characterized as high, medium and low density. Experimental evidence has shown that a single layer of SRG jacket has increased substantially both axial strength and deformation capacity. From the response of the SRG confined cylinders the degree of penetration of the grout matrix through the fabric as well as the overlap length are considered rather critical parameters for the effectiveness of the method. The experimental data were used for the derivation of a simple empirical confinement model which correlated well with other well-established FRP confinement models. The knowledge gained from this experimental study renders SRG jacketing a remarkably promising retrofit solution for reinforced concrete confinement.

Ratcheting response of dented pipes under monotonic and cyclic axial loadings

Offshore pipelines are usually subject to hostile environments. Temperature changes and repetitive start-up/shutdown in offshore pipelines generate cycles of axial compression and relaxation. Consequently, the pipes may become subject to loading magnitudes that could cause them to locally buckle and wrinkle, and if subject to repeated loading, they could undergo ratcheting. Pipelines could also be subject to damage in the form of dents. This form of damage would have a profound effect on a pipe’s ratcheting response when subjected to cyclic loading. In this article, the ratcheting response of locally dented pipes that were subject to axially applied cyclic loading has been experimentally investigated. Scaled pipes (tubes) were first laterally indented with a cylindrical indenter and then were subjected to a monotonic axial compressive load that initiated small amplitude wrinkles on them. The pipes were subsequently subjected to repeated axial strain. The experiments were conducted on low carbon steel pipes (API 5L-grade B), with Do/t ≃ 35, which were indented to three different indentation depths. Significant variation in pipes’ responses was observed, and the number of cycles prior to collapse dramatically decreased by as much as 75% when the indentation depth was marginally increased.

A model for damage analysis of concrete

The damage level in structures (global scale), elements (intermediate scale) and sections (local scale) can be evaluated using a single parameter called the Damage Index. Part of the damage attributed to the local scale relates to the damage sustained by the materials of which the section is made. This study investigates the damage of concrete subjected to monotonic compressive loading using four different damage models - one proposed here for the first time and three other well-known models. The analytical results show that the proposed model is promising yet simple and effective for evaluating the damage of concrete. The proposed damage model of concrete with its promising characteristics indicated, appears to be a useful tool in the damage assessment of structures made of concrete.

A model for damage analysis of concrete

The damage level in structures (global scale), elements (intermediate scale) and sections (local scale) can be evaluated using a single parameter called the "Damage Index". Part of the damage attributed to the local scale relates to the damage sustained by the materials of which the section is made. This study investigates the damage of concrete subjected to monotonic compressive loading using four different damage models - one proposed here for the first time and three other well-known models. The analytical results show that the proposed model is promising yet simple and effective for evaluating the damage of concrete. The proposed damage model of concrete with its promising characteristics indicated, appears to be a useful tool in the damage assessment of structures made of concrete.

Investigation of Compressive Damage Mechanisms in 3D Braided Composites by the Acoustic Emission Events Energy and Amplitude

The deformation behavior and damage mechanism of 3-D carbon/epoxy braided composites with different braiding angles under the monotonic compressive loading are investigated by the acoustic emission (AE) technique. The damage process is divided into several different regions based on the change of the accumulative AE event counts. Correlations between the damage mechanisms and the AE results are established in terms of the events energy and amplitude. These correlations can be used to monitor the fracture growth process in the braided composites. Experimental results reveal that the AE technique is an effective tool for identifying damage mechanisms.

Effects of Copper Slag as a Replacement for Fine Aggregate on the Behavior and Ultimate Strength of Reinforced Concrete Slender Columns

Use of copper slag (CS) as a replacement for fine aggregate (FA) in RC slender columns was experimentally investigated in this study. Twenty columns measuring 150 mm x150 mm x 2500 mm were tested for monotonic axial compression load until failure. The concrete mixture included ordinary Portland cement (OPC) cement, fine aggregate, 10 mm coarse aggregate, and CS. The cpercentage of cement, water and coarse aggregate were kept constant within the mixture, while the percentage of CS as a replacement for fine aggregate varied from 0 to 100%. Four 8 mm diameter high yield steel and 6 mm mild steel bars were used as longitudinal and transverse reinforcement, respectively. Five cubes measuring 100 mm x100 mm x100 mm, eight cylinders measuring 150 mm x 300 mm and five prisms measuring 100 mm x 100 mm x 500 mm were cast and tested for each mixture to determine the compressive and tensile strengths of the concrete. The results showed that the replacement of up to 40% of the fine aggregate with CS caused no major changes in concrete strength, column failure load, or measured flexural stiffness (EI). Further increasing the percentage reduced the concrete strength, column failure load, and flexural stiffness (EI), and increased concrete slump and lateral and vertical deflections of the column. The maximum difference in concrete strength between the mixes of 0% CS and 100% CS was 29%, with the difference between the measured/ control failure loads between the columns with 0 and 100% CS was 20% the maximum difference in the measured EI between the columns with 0 and 100% CS was 25%. The measured to calculated failure loads of all specimen varied between 91 and -100.02%. The measured steel strains were proportional to the failure loads. It was noted that columns with high percentages of CS (

Hyperelastic Analysis of High Density Polyethylene under Monotonic Compressive Load

In the past few decades, design development of high performance machines and devices encouraged industries to utilize advanced materials such as polymers. Special mechanical features of polymer materials such as high strength to weight ratio and etc have increased scientists demands to investigate the nonlinear behaviour of polymers. One of the challenges in mechanic of polymers is to introducing a model that is competent to predict hyperelastic deformations based on long-strain behaviour of polymers. In this study, a comprehensive research is performed on introduced mechanical models for polymer materials. The major attempt was on introducing an appropriate model among the existing models, capable enough to predict mechanical behaviour of high density polyethylene under monotonic compressive load. The procedures of simulation and experimental tests are performed to examine the load capability of the model for high density polyethylene. Several compression tests are performed on High Density Polyethylene cubic specimens to extract the full stress-strain response of the high density polyethylene. Moreover, strain gauge is used in experimental tensile test to determine Poisson’s ratio. Simulation procedure is performed using ABAQUS 6.9EF for a comprehensive analysis and discussion on hyperelastic deformation. The simulation procedure is confirmed and verified perfectly by experimental data. The comparison between experimental result of compression test under monotonic load and finite element simulation of this test is remarkable to know about behaviour of HDPE to use in other structural and mechanical application.