Monotonic Loading Conditions Research Articles

Experimental investigation of the breaking load of a dowel-pinned connection in granite cladding

A dowel-pinned anchorage in granite cladding has been widely used in modern granite cladding systems. However, current studies on the breaking loads of dowel-pinned connections are limited, and the damage behavior is not yet clear as a result of insufficient experimental studies. In accordance with current code provisions, monotonic static loading tests were carried out to investigate the breaking load and failure modes of a dowel-pinned cladding connection. The specimens were 200 × 200 × 30 mm granite panel with holes drilled in the middle of each side for steel pins with three different diameters, that is, 5 mm, 6 mm, and 7 mm. The results show that when using the 5 mm steel dowel pin, the steel pin yielded with a certain plastic deformation prior to the V-shape fracture of the granite near the dowel hole. When using the 7 mm and 8 mm steel pins, the U-shape fracture of the granite panel occurred first. Then only slight bending deformations of the steel pins were observed. The experimental breaking load was compared to the computational results following the formula recommended in the literature. A conceptual loading skeleton curve was developed to illustrate the damage progress of the connection. It revealed the load redistribution mechanism in the connection in a representative manner with which the calculated stress in the steel pin is corresponded to the experimental breaking load. This study is helpful for understanding the damage behavior of the novel connection in stone claddings.

Cyclic stress–strain rate-dependent response of rubberised concrete

This paper presents an experimental investigation into the constitutive response of rubberised concrete materials under monotonic and cyclic compression. After describing the test specimens and experimental arrangement, a detailed account of the stress–strain response of rubberised concrete materials, as well as their reference high strength conventional concrete, is given. The volumetric rubber content is varied between 0 and 40% of both fine and coarse aggregates. Both monotonic and cyclic loading conditions are considered for comparison, and three strain rate levels, simulating static, moderate and severe seismic action, are examined. The increase in rubber content is shown to have a detrimental effect on the stiffness and strength, as expected. However, with the increase in rubber content, rubberised concrete materials are shown to exhibit improved compressive recovery under cyclic loading, coupled with a higher energy accumulation rate, enhanced inter-cycle stability and lower inter-cycle degradation. It is also shown that the increase in strain rate, from static to severe seismic, leads to a notable increase in the stiffness and strength, with these enhancements becoming less significant with the increase in rubber content. Based on the results and observations, expressions for determining the unloading stiffness and residual strain, as a function of rubber content and strain rate, are proposed within the ranges considered. The suggested relationships enable the characterisation of rubberised concrete materials within widely used cyclic constitutive models.

Experimental and numerical investigation of timber formwork beam under different loading type

With the developing construction technologies, the formwork systems used in the manufacturing of the structures have also changed and developed significantly. Especially in the production of high-rise buildings, a special sliding formwork system that is quick-installation, resistant to external loads, can be used more than once, are widely used and preferred. Timber and composite timber materials are preferred due to their durability, ease of installation, lightness compared to steel systems, and easy to use more than one time. Within the scope of this study, it was aimed to investigate the performance and behaviors of timber beams of 1800 and 2450 mm length experimentally under the influence of different loading types in H20 top P-type, which is among the products of DOKA Company. During the use of timber formwork beams, various loading types such as static, fatigue, and sudden dynamic impact load can be affected. For this reason, an experimental study was carried out, and general load-displacement behaviors, initial stiffness, displacement ductility ratios, energy dissipation capacities, collapse mechanisms, acceleration, displacement, and impact load-time behaviors under the effect of monotonic static, repetitive fatigue and impact loading of two different length timber formwork specimens were examined. In addition to experimental study, nonlinear numerical analysis is made by using ABAQUS software for experimental specimens and compared with results with an experimental study.

Approximate cutting pattern optimization of frame-supported and pneumatic membrane structures

A simple iterative method is presented for cutting pattern optimization of frame-supported and pneumatic membrane structures for minimizing the variation of stresses from the target values. The plane cutting sheet is generated by minimizing the error from the shape obtained by reducing the target stress from the desired curved shape of surface. The equilibrium shape is obtained using an energy approach to minimize of total strain energy under forced deformation at the boundary nodes. The external work done by the pressure is also incorporated for analysis of pneumatic membrane structures. An approximate method is also proposed to derive a discretized form for analysis of an ethylene tetrafluoroethylene (ETFE) film, where elasto-plastic behavior under monotonic loading condition is modeled as a nonlinear elastic material under monotonic loading condition. The proposed method is applied to examples of a frame-supported polyvinyl chloride membrane structure and an air pressured square ETFE film.

Stress–strain behaviour of bio-desaturated sand under undrained monotonic and cyclic loading

Microbial (or bio-) desaturation is a new method for mitigation of the liquefaction hazard of sand. In this paper, a series of monotonic and cyclic triaxial tests was performed on bio-desaturated sand under undrained conditions to demonstrate that the bio-desaturation method is effective in enhancing the liquefaction resistance of sand under either monotonic or cyclic loading conditions. The test results showed that, under monotonic loading, the undrained shear strength increased by more than two times and the behaviour of soil changed from strain softening to strain hardening when the degree of saturation (Sr) reduced from 100% to 86·4%. The undrained shear strength ratio (su/p′0) has a unique relationship with the peak excess pore water pressure ratio (Δumax/σ′c) regardless of different effective confining stress conditions. Under the applied cyclic load, the liquefaction resistance showed a significant increase when the sample was slightly desaturated. For the same cyclic stress ratio and number of cycles, the accumulated excess pore water pressure (Δu) in the sample with a degree of saturation of 96% was only a quarter of that in the fully saturated sample. The instability behaviour of sand was also studied. The results showed that the slope of the instability line, which is a measurement of the resistance of sand to collapse, also increased with the reduction in degree of saturation under monotonic loading. The failure stresses obtained in cyclic triaxial tests conducted under different cyclic stress ratios coincide with the instability line obtained under monotonic conditions for sand with the same degree of saturation. This provides good support for the use of the instability line to predict the failure stress state of sand for both monotonic and cyclic loading conditions.

Experimental study of stress anisotropy and noncoaxiality of dense sand subjected to monotonic and cyclic loading

Abstract The noncoaxiality of the principal stress direction and plastic principal strain increment has been broadly recognized as an influencing parameter for design of soil structures. Here we performed a series of systematic hollow cylinder experiments to study the effects of stress anisotropy on the noncoaxiality of dense Babolsar and Toyoura sands. A total of 25 undrained torsional shear tests were carried out under constant mean confining pressure, and fixed principal stress directions, α. We investigated the stress-strain behavior of dense sands for different α-directions, and cyclic stress ratio, CSR, under monotonic and cyclic loading conditions. The results show that the noncoaxiality value depends on the CSR, the level of plastic strain, and α-direction. Independent of the principal stress direction, maximum noncoaxiality value was observed at peak shear strength when there is most interlock between sand particles. Minimum noncoaxiality was recorded in α = 45° tests, in which the direction of maximum shear stress coincided with the horizontal bedding plane direction (weakest plane).

Behaviour of reinforced concrete beam strengthened in shear with geosynthetic

The primary objective of this article is to focus on the experimental investigation of shear-deficient and geosynthetic-strengthened reinforced concrete beams. In this study, two varieties of geosynthetic, namely geogrid and geotextile, are used. The performances of shear-deficient reinforced concrete beams strengthened with geosynthetics under the single-point static monotonic loading are studied. It is observed that shear failure occurs in shear-deficient beam, but after strengthening the brittle shear failure changes to ductile flexure failure. A significant increment in flexural strength, ductility, energy absorption capacity and inelastic performance is observed in strengthened beams. The performance of geogrid is better in all respects when compared to the geotextile. The test results reveal that the use of geosynthetic not only increases the shear capacity but also remarkably improves the ductile behaviour of RC beams. In addition, conventional analytical methods are applied for the evaluation of the ultimate load, and the results are compared with the experimental findings, which show a good agreement between the analytical and experimental results.

Experimental characterization and numerical analysis of additively manufactured mild steel under monotonic loading conditions

Additive Manufacturing (AM), for the case of metals, is a technology developed to create 3D products by following a layer-by-layer welding procedure. In this work, the tensile behavior of wire arc additively manufactured mild steel is studied experimentally and numerically. The microstructure of the metal is strongly influenced by the AM process that involves several heating and cooling cycles; therefore, it is first analyzed with optical microscopy, scanning electron microscopy, energy-dispersive X-ray spectroscopy and X-ray diffraction to identify the different phases and to extract the grain properties. With this information, two approaches are used to build the Representative Volume Element, which will be part of a multi-scale material model. The first approach constitutes a synthetic generation of grains according to a Voronoi Tessellation and the second one an image-based representation. Afterwards, a virtual tensile test for the determination of the stress–strain relation of the material is performed, which is later compared with the measurements of a real tensile test carried out on several specimens that were obtained using the wire arc additive manufacturing technique. It can be observed that the influence of the welding direction on the stiffness and the ductility of the additively manufactured steel product is rather low, yielding similar results in both parallel and perpendicular directions. Additionally, a softening behavior of the material is noticed.

Structural behavior and design of high-strength steel welded tubular connections under extreme loading

The present work is motivated by the increasing need for cost-efficient solutions in offshore structural systems for wind energy production and for improvement of their structural performance. The structural behavior and design of high-strength steel welded tubular connections (yield strength higher than 700 MPa) subjected to monotonic and strong cyclic loading is investigated. In the first part of the paper, an experimental investigation is presented on high-strength steel tubular X-joints subjected to monotonic and cyclic loading far beyond the elastic limit of the material, leading to weld fracture. Two grades of weld metal material are employed in the welding process of the specimens. The experimental results indicate that the weld material grade has a significant influence on the deformation capacity of the welded connection under monotonic loading conditions, and its low-cycle fatigue life. The experimental procedure is simulated using advanced finite element models, elucidating several features of joint behavior and complementing the experimental results. Overall, a good agreement is found between numerical simulations and experimental results, in terms of both global response and local strains at the vicinity of the welds. Furthermore, the structural performance of the welded tubular joints under consideration is assessed using available design methodologies in terms of both ultimate strength and low-cycle fatigue resistance, in an attempt to validate an efficient design methodology for low-cycle fatigue. The results from this research effort are aimed at developing the necessary background for the possible use of high-strength steel in tubular steel lattice structures, particularly in offshore platforms for renewable energy production. They can also be used as a basis for the possible amendment of relevant design specifications and recommendations for including special provisions for high-strength steel structural systems.

Characteristics of Crack Growth in Rock-Like Materials under Monotonic and Cyclic Loading Conditions

Experiments with gypsum as a model rock material were conducted to investigate the characteristics of crack growth under monotonic and cyclic loading. The specimens had two pre-existing flaws that were placed at different inclination angle, spacing and continuity. Tensile or wing cracks and secondary or shear cracks were observed in both the monotonic and cyclic tests. Wing cracks or tensile cracks initiated at (or near) the tips of flaws and grew parallel to the loading direction. Secondary or shear cracks occurred after initiation of the wing crack and culminated in a final failure. Secondary cracks started at the tips of flaws and propagated in the colinear direction of flaws or perpendicular to loading. Six types of coalescence were observed. Both the monotonic and cyclic tests showed almost identical coalescence types. Coalescence occurred due to the internal shear cracks in specimens containing colinear flaws, while it occurred through combinations of internal shear cracks, internal wing cracks and tension cracks in specimens with non-colinear flaws. Fatigue cracks occurred in tests under cyclic loads. Finally, the subcritical crack growth parameters under monotonic and cyclic loading were determined. Although there were variations in the parameters, the parameter “n” showed similar values.

Failure mode of truss system concrete beams strengthened with tensile reinforcement

Cracks usually precede beams failures. Cracks occurred due to the applied load exceeds the capacity of the cross-section in carrying the load. The use of a diagonal reinforcement or truss system can increase the flexural capacity of the beams. The previous research of using truss system reinforcement in the beam without concrete in the tension zone causes a decrease in flexural capacity due to the cracks in the area near the support. Therefore, it is necessary to add tensile reinforcement in the zone. This study uses a truss reinforced concrete beam specimen with dimensions of 15 cm x 20 m x 330 cm. There are four variations of the specimens, namely Normal Beams (BN) as control beam, BTRP 40D, BTRP 60D, and BTRP 80D. The flexural test is carried out by monotonic static loading. The results showed that the flexural capacity of BTRP 40D, BTRP 60D, and BTRP 80D increased due to the addition of tensile reinforcement in the support zone. Moreover, the failure mode of BTRP 60D and BTRP 80D are under reinforced and cracking does not occur in the support zone. Meanwhile, the BTRP 40D beam shows wide cracks in the support zone.

Numerical study of bracing section variations in an eccentrically braced frame

Eccentrically Braced Frame (EBF) is a better option for the earthquake-prone country due to it having a better strength, stiffness, energy dissipation and ductility than Moment Resisting Frame (MRF) structure and more so than structures made of concrete. The structure’s ductility was influenced by the cross-sectional dimension and link element of the frame. This study aims to determine the relation behavior of EBF with the varied link element and cross-sectional of bracing with the ultimate load and ductility of the structure. The analysis was done using MSC. PATRAN/NASTRAN student edition software. A total of three-link model variations, each one represents the three-link variations of EBF; short link, intermediate link, and long link. As for the cross-sectional, variation was made on the flange and web thickness of the IWF profile and web thickness of the HSS profile. The most optimum performance of the structure was determined by displacement control and static monotonic loading. The result indicates that variations in the crosssectional of bracing effects the short link EBF the most, while the intermediate and long link EBF doesn’t show a significant change in terms of ultimate load. Meanwhile, ductility is not bound by the increase of bracing thickness.

Experimental and numerical assessment of the end of the thermoelastic effect during static traction test

In the last thirty years Infrared Thermography has been widely adopted as a technique able to predict the fatigue life of materials in a short amount of time. In the recent years, Risitano and Risitano proposed the Static Thermographic Method as a rapid test procedure able to predict the fatigue limit of the material from a static traction test, evaluating the end of the thermoelastic phase. In this work, the energetic release during a uniaxial static test of a medium carbon steel C45 has been experimentally investigated. A numerical finite element model has been developed in order to predict the temperature evolution of the material under the same monotonic load conditions. A comparison between the experimental and numerical temperature evolution has been carried out showing how the end of the thermoelastic phase is reached before the macroscopic yielding stress of the material. The Static Thermographic Method may be adopted as a novel energetic approach to assess the macroscopic stress value that introduce in the material the first micro plasticization, hence will lead it to fatigue failure.

Tensile and fatigue behavior of a Pb-Sn-Sb alloy investigated via small-scale in-situ mechanical testing in SEM

Pb-Sn-Sb alloys (E-alloy) are commonly used in subsea power cable sheathing. Due to the relatively low melting temperature, i.e. around 600 K, this type of alloy is prone to experience microstructural time-dependent evolution such as recovery, relaxation, recrystallization and creep deformation even at room temperature, in contrast to other conventional materials for which involve these mechanisms are activated only at high temperatures. To better understand the deformation mechanisms of Pb-Sn-Sb alloys, small-scale in-situ mechanical testing inside a scanning electron microscope (SEM) has been conducted under both monotonic loading and cyclic loading conditions. Thanks to the in-situ imaging technique, the deformation behavior as well as the damage mechanisms were revealed with high resolution. The possible deformation mechanisms, including the creep behavior, has been discussed and the results can provide necessary input to damage calculations and modelling work of the studied alloy system used for cable sheathing.

Influence of CFRP Strengthening on the Behavior of Concavely-Curved Soffit Concrete Bridge Girders

Over the last few decades, fiber reinforced polymer (FRP) has been increasingly used in strengthening different structural concrete members. The main objective of this research is to study the influence of curvature on the performance of curved soffit reinforced concrete (RC) bridge girders that have been strengthened with carbon fiber reinforced polymers (CFRP). This experimental program was designed to evaluate the effect of concavity and soffit curvature on the CFRP laminate utilization and load capacity, compared to flat soffit RC beams strengthened with the same CFRP system. Accordingly, five beams, 2.7 m in length and having the same degree of soffit curvature (20 mm per 1 meter) extending over 2 meters of the span length, were tested under three-point monotonic static loading up to failure. CFRP pre-cured laminates were used for external strengthening in flexure. It was observed that 20 mm/m degree of curvature reduced the load-carrying capacity of strengthened concavely curved RC beams by 15.9 – 17.8%.

Numerical and experimental study on flexural behavior of reinforced concrete beams: Digital image correlation approach

Understanding the realistic behavior of concrete up to failure under different loading conditions within the framework of damage mechanics and plasticity would lead to an enhanced design of concrete structures. In the present investigation, QR (Quick Response) code based random speckle pattern is used as a non-contact sensor, which is an innovative approach in the field of digital image correlation (DIC). A four-point bending test was performed on RC beams of size 1800 mm x 150 mm x 200 mm. Image processing was done using an open source Ncorr algorithm for the results obtained using random speckle pattern and QR code based random speckle pattern. Load-deflection curves of RC beams were plotted for the results obtained using both contact and non-contact (DIC) sensors, and further, Moment (M)-Curvature (k) relationship of RC beams was developed. The loading curves obtained were used as input data for material model parameters in finite element analysis. In finite element method (FEM) based software, concrete damage plasticity (CDP) constitutive model is used to predict the realistic nonlinear quasi-static flexural behavior of RC beams for monotonic loading condition. The results obtained using QR code based DIC are observed to be on par with conventional results and FEM results.

Constitutive models for nonlinear analysis of SFRC corbels

In this paper, nonlinear constitutive models are proposed for steel fiber reinforced concrete (SFRC) in compression and tension. The models were implemented in the finite element computer program ANSYS for 3-D nonlinear analysis of SFRC corbels under monotonic static loading. Several validation studies have been performed for normal-strength and high-strength SFRC corbels with constant or variable depth. Good agreement is generally achieved between experimental and numerical results for the load-deflection curves and crack patterns. Additionally, parametric studies have been performed in order to investigate the effect of structural parameters on the performance of SFRC corbels. It was found that: (1) increasing the concrete compressive strength (fc’) improves corbel shear capacity and toughness, (2) the inclusion of steel fiber (Vf) delays premature shear failure for corbels and enhances strain ductility, (3) an enhancement in shear capacity and strain ductility is noticed by increasing the ratio of horizontal stirrups (ρh), and finally, (4) increasing the shear span-to-depth ratio (a/d) reduces the shear capacity of SFRC corbels. Corbel shear capacity increases by 27% due to a 33% increase in (fc’), by 31% due to Vf = 1% inclusion, by 20% due to a 1% increase in (ρh), and by 20% due to a 39% decrease in (a/d) ratio. The proposed nonlinear finite element approach is efficient in determining the expected enhancement in shear capacity and ductility of SFRC corbels, and consequently in optimizing design parameters for such elements.

A framework to model the fatigue behavior of brittle materials based on a variational phase-field approach

A novel variational framework to model the fatigue behavior of brittle materials based on a phase-field approach to fracture is presented. The standard regularized free energy functional is modified introducing a fatigue degradation function that effectively reduces the fracture toughness as a proper history variable accumulates. This macroscopic approach allows to reproduce the main known features of fatigue crack growth in brittle materials. Numerical experiments show that the Wöhler curve, the crack growth rate curve and the Paris law are naturally recovered, while the approximate Palmgren–Miner criterion and the monotonic loading condition are obtained as special cases.

Flexural performance of steel-reinforced engineered cementitious composites with different reinforcing ratios and steel types

Reinforced engineered cementitious composites (ECC) flexural members fail either after a dominant crack forms (i.e., crack localization) or after gradual strain hardening of reinforcing steel. These two failure paths represent distinct ductility ranges and load reduction mechanisms that have not been fully characterized. This study experimentally investigates the two failure paths of flexural members with different reinforcing ratios (0.53%–2.10%), two types of reinforcing steel (A615 Grade 60 and A1035 Grade 100), and under monotonic and cyclic loading conditions. A total of twelve simply-supported beams are tested including two conventional concrete beams for baseline comparisons. Based on the experimental results, a recently-developed flexural strength prediction method is validated. Results show that (1) the two failure paths are affected by the reinforcing ratio and steel type, (2) ECC sustains a maximum compressive strain that is larger than 1.0% before crushing, (3) ECC effectively restrains crack width opening for flexural members using high strength (Grade 100) steel reinforcement, and (4) a recently proposed flexural strength prediction method is able to predict the experimentally observed flexural strength of the beams with an error less than 5%.

A damage evolution model based on micro-structural characteristics for an additive manufactured superalloy under monotonic and cyclic loading conditions

In the present work the superalloy Inconel 718 manufactured by selective laser melting (SLM) was investigated with focus on micro-structural damage evolution under both monotonic and cyclic loading conditions. Material testing and characterization reveal significantly accelerated damage evolution of the SLM material, in comparing with the forged Inconel 718. An accumulated plastic strain based damage model was proposed to predict the damage evolution in the alloys under both monotonic and cyclic loading. The damage mechanism related to detrimental precipitate particles and porous defects in the material was discussed and considered in the model, which can predict both monotonic and cyclic material degradation processes with agreement.