Ratios Of Shear Research Articles

Torsional strengthening using carbon fiber reinforced polymer of reinforced concrete beams subject to combined bending, shear and torsion

The results of an experimental investigation of six large scale rectangular reinforced concrete (RC) beams subject to different ratios of combined bending, shear, and torsion strengthened with externally-bonded carbon fiber reinforced polymer (CFRP) U-wraps are presented. All beams exhibited torsion-dominated behaviour. The presence of discrete CFRP U-wrap strips controlled the cracks well and the resulting torsional cracks were observed to be oriented at about 50°. Regardless of loading ratio, strengthened beams exhibited a 70% increase in torsional capacity. Before cracking, torsion to flexure ratio had a small effect on the flexural and torsional stiffness indicating that twist and deflection have a small counteracting effect on each other. Existing beam capacities were assessed using ACI 318-19 and GB 50010-2010 while CFRP strengthening was assessed based on fib Bulletin 14. Main findings are as follows: the ACI 318-19-predicted torsional capacity was conservative while GB 50010-2010 appeared to result in better capacity-prediction of unstrengthened RC beams. Even though load capacities derived from GB 50010-2010 are consistent with torsion-dominated behaviour, neither standard-based approach addresses the complete interaction of internal forces which is necessary to determine existing in situ strength for FRP strengthening applications. The fib Bulletin 14 approach to FRP strengthening for torsion was extrapolated to U-wraps and shown to overestimate the strengthening effect of the CFRP system applied. Critically, the assumed angle of inclination of torsional cracking was increased by the presence of the U-wraps, reducing the efficacy of the CFRP application.

Characterization and modeling of continuous carbon fiber-reinforced polycarbonate under multiaxial loads

The presented work considers the characterization of a continuous fiber-reinforced thermoplastic (FRTP) with unidirectional plies under quasi-static, multiaxial loading conditions and the modeling of the non-linear mechanical behavior. For the experimental investigation, hoop wound tubular specimens fabricated from carbon fiber-reinforced polycarbonate (CF-PC) tape were tested on an electromechanical static testing machine with an axial and torsional drive. The multiaxial material response was determined for an extensive set of tests performed at several load ratios of in-plane shear to transverse stress. For modeling the non-linear mechanical response, an elasto-plastic framework is used which is kept preferably simple in order to facilitate the application in numerical analysis. Based on the generated experimental data, suitable criteria for fracture and yielding are proposed. The defined yield criterion respects the special characteristics of a FRTP such as the different mechanical behavior under transverse tensile and compressive loading as well as a linear material response in the direction of the fiber reinforcement . Furthermore, the implementation of the proposed model as a user-defined material (UMAT) routine for implicit finite element analysis (FEA) using Abaqus /Standard is described and the calibration of the plasticity approach using only the data of the in-plane shear and transverse compression tests is discussed. The model predictions for multiaxial loads are validated using the determined biaxial material data. • Multiaxial experimental data for a continuous fiber-reinforced thermoplastic • Full dataset of the arithmetic mean stress–strain curves is provided • Selection of a suitable fracture criterion and definition of a yield criterion • Development and implementation of a non-linear elasto-plastic material model • Calibration and validation of the material model using the determined multiaxial data

Shear strengthening of RC short columns with CFRP grid-reinforced FRC matrix: Cyclic loading tests

This study investigated the shear behaviors of reinforced concrete (RC) short columns retrofitted with a new textile-reinforced mortar (TRM) system made of carbon fiber-reinforced polymer (CFRP) grid-reinforced short-fiber-reinforced concrete (FRC) (referred to as “TR-FRC”). Six RC specimens, including two control specimens and four specimens strengthened with TR-FRC jacket, were tested under the combined action of constant axial load and cyclic horizontal load. The experimental parameters were the reinforcement ratios of CFRP grid and shear span-to-depth ratios. The test results indicated that the shear capacity, deformability, ductility and energy dissipation capacity of the strengthened columns were superior to those of as-built counterparts. The stiffness degradation of the strengthened columns was further delayed as the reinforcement ratio of the CFRP grid in composites overlay increased. Under smaller shear span-to-depth ratio, the TR-FRC system was still very effective in increasing the shear capacity of the RC columns. Moreover, based on the current code and superposition principle, considering the effective strain of the fiber grid, a design equation was proposed to predict the shear capacity of strengthened members.

INFLUENCE OF LONGITUDINAL REINFORCEMENT RATIO ON SHEAR CAPACITY OF NO COARSE-AGGREGATE CONCRETE

The study investigated the effect of longitudinal reinforcement ratio on the shear capacity of concrete beams without transverse steel. The concrete mixture did not include coarse aggregate. The Joint ACI–ASCE Committee 426 (1973) has shown that the shear is transferred across the surface where there is slip and it is called the aggregate interlock. To study the effect of longitudinal reinforcement ratio on the shear capacity of concrete without coarse aggregate, six beam specimens with the size of 110 × 7 × 12.5 cm and a/d ratio of 45/10.5 were investigated. The longitudinal reinforcement ratios were set from the minimum to the maximum, i.e. 0.0073, 0.0132, 0.0213, 0.0302, 0.0547, and 0.0782. The ratios of the ultimate shear to the shear capacity of concrete (Vu/Vc) were found between 1.0705 and 2.8748. When the longitudinal reinforcement ratio increases particularly from the minimum ratio, the value of Vu/Vc also significantly increases. The values of Vu/Vc were found less than 2, thus Vs is required. When the longitudinal reinforcement ratio approaches maximum, Vu/Vc becomes relatively constant and was found more than 2. This concludes that the ratio of Vu/Vc of the concrete without coarse aggregate is lower than normal concrete. The existing ACI’s formula for computing the shear capacity contributed by concrete, which has not been changed for decades, is only applicable for normal concrete (with coarse aggregate). This research proposes a theory to develop a new shear capacity formula specifically for concrete without coarse aggregate.

Параметры акустической неоднородности для неразрушающей оценки влияния технологии изготовления и эксплуатационной поврежденности на структуру металла

In this paper, we propose a non-destructive acoustic method for assessing microstructural alterations produced in metals as a result of processing and exploitation damage. The method is based on measuring ratios of longitudinal and shear ultrasound waves velocities with subsequent normalization of these ratios to their counterparts corresponding to a “baseline state” of the metal. The choice of the baseline state depends of the particular problem and corresponds to either the pre-exploitation metal state for the object to be monitored, or the state of reference samples, for which the strength characteristics fall into acceptable range according to the results of conventional strength-evaluation methods. For the introduced Microstructure-Sensitive Acoustic parameters (MSA-parameters) characterizing alterations in the metal microstructure, we discuss the reasons of the difference between the baseline and current states of the metal in terms of the total values of the normal and tangential compliances imparted to the metal due to the appearance of microstructural heterogeneities. The efficiency of utilization of the proposed acoustic diagnostic parameters is demonstrated using experimental data for two types of metal samples with essentially different microstructure (isotropic and anisotropic heterogeneity). Measurements of the proposed microstructure-sensitive acoustic parameters can be used in a variety of applications: (i) non-destructive quality control of manufacturing technologies in metallurgy and mechanical engineering (ii) evaluation of damage accumulation during exploitation manufactured constructions/samples; (iii) evaluation of mechanical properties, fracture resistance and other physical parameters of metals.

Relationship between fractures, stress, strike-slip fault and reservoir productivity, China Shunbei oil field, Tarim Basin

It is becoming widely recognized that a relationship exists between stress, stress heterogeneity, and the permeability of subsurface fractures and faults. We present an analysis of the Shunbei oil gas field, developed mainly in fractured carbonate, where active deformation has partitioned the reservoir into distinct structural and stress domains. These domains have differing geomechanical and structural attributes that control the permeability architecture of the field. The field is a composite of Caledonian contractional elements that have been modified by Hercynian contraction to produce basement-rooted strike-slip faults. Reservoir scale faults were interpreted in detail. Bulk reservoir performance is governed by the local stress architecture that acts on existing faults and their fracture damage zones to alter their permeability and, hence, their access to distributed oil. Reservoir potential is most enhanced in areas that have large numbers of fractures with high ratios of shear to normal stress. This occurs in areas of the field that are in a normal stress style. Comparatively, reservoir potential is lower in areas of the field that are in a strike-slip stress style where fewer fractures with high shear-to-normal stress ratios exist. Achieving the highest well productivity relies on tapping into critically stressed faults and their associated fracture damage zones. One wellbore has been drilled based on this concept, and shows an obvious improvement in petroleum productivity.

Moment Tensor Analysis of Acoustic Emissions for Cracking Mechanisms During Schist Strain Burst

Acoustic emission (AE) location technique and moment tensor analysis were used to evaluate the temporal–spatial evolution and damage of micro-cracks of schist during true triaxial compression and strain burst tests. The results show that the AE locations coincide with the macroscopic cracks for true triaxial compression while they are scattered during unloading strain burst tests. A shearing concentration occurs at the bottom of ejection position, but a tensile zone is located in the fracture plane of the ejection block. The ratios of shear and mixed-mode micro-cracks to total micro-cracks for true triaxial compression are both larger than those for strain burst. However, the strain burst has more tensile micro-cracks. Additionally, the damage caused by tensile micro-cracks for a strain burst is larger than that for a true triaxial compression. Moreover, for strain burst, the difference of damage between shear and tensile micro-cracks is in direct proportion to the loading rates after unloading.

Direct determination of resonant properties of near-surface sediments using microtremor

This article describes a method of direct determination of the resonant properties of the near-surface sediments using microtremor records and results of testing the method on the test area. It is shown that the averaging amplitude spectra of a large number of microtremor records makes it possible to extract reliably several lowest modes of compressional and shear standing waves in the near-surface layer. Examples of mapping frequencies of these modes (natural frequencies of the layer) for an area of observations are given. For the fundamental mode of horizontal oscillations, a map of the amplification factors relative to the reference point located on the hard rock is also constructed. In addition, we present the maps of calculated from the natural frequencies, the effective (averaged over the near-surface layer thickness) ratios of shear and compressional velocities Vs/Vp and Poisson ratios. The obtained results were compared with the results of processing the same data using the Nakamura's technique.

Unsteady heat transfer in non-axisymmetric Homann stagnation-point flows towards a stretching /shrinking sheet

Abstract We have studied the unsteady non-axisymmetric Homann’s stagnation point flow and heat transfer of an incompressible viscous fluid over a stretching/shrinking sheet in the presence of time dependent free stream. In a very recent paper Mahapatra and Sidui (2017) show a modification of Homann’s stagnation point flow over a rigid plate. Now if the plate is not rigid but linearly stretched as well as shrunk with velocities in x and y -directions, then there is a new family of asymmetric viscous stagnation-point flows depending on the unsteadiness parameter δ ( = σ ∕ | c | ) and the ratios of shear to the rate of linear stretching/shrinking of the sheet γ ( = b ∕ | c | ) , the strain-rate to the rate of linear stretching/shrinking of the sheet λ ( = a ∕ | c | ) in the range − ∞ γ , λ ∞ . Here a and b are the strain rate and shear rate of the stagnation-point flow respectively, σ is a positive constant whose dimension is t i m e − 1 and c is the rate of linear stretching/shrinking of the sheet along x - and y -axes at unit distance from origin when time, t = 0 . We have also studied the heat transfer in the flow. The temperature of the sheet is assumed to be higher than the ambient fluid temperature. The governing momentum equations are solved numerically using fourth order Runge–Kutta method with shooting technique. The effect of the various parameters on wall shear stress parameters, dimensionless velocities, displacement thicknesses and temperature distributions are analysed. A good agreement is found when we compare our numerical results of wall shear stress, displacement thickness and temperature distributions with their corresponding asymptotic value behaviours. For the flow past a shrinking sheet dual solutions are found to exist. Here we have made a stability analysis in the case of non-unique solutions to identify the stable solution.

On the Method of Source Images for the Wedge Problem Solution in Ocean Acoustics: Some Corrections and Appendices

In this study the method of source images for the problem of sound propagation in a penetrable wedge [G. Deane and M. Buckingham, J. Acoust. Soc. Am. 93 (1993) 1319–1328] is revisited. This solution is very important three-dimensional (3D) benchmark in computational underwater acoustics, since a wedge bounded from above by the sea surface and overlying a sloping penetrable bottom is the simplest model of a shallow-sea waveguide near the coastline. The corrected formulae for the positions of the source images and bottom images are presented together with the explanation of their derivation. The problem of branch choice in the reflection coefficient is thoroughly discussed, and the corresponding explicit formulae are given. In addition, numerical validation of the proposed branch choice schemes and the resulting wedge problem solutions are presented. Finally, source images solution is computed for a series of examples with different ratios of shear and bulk moduli in the bottom. The interplay between the acoustic-elastic waves coupling and the horizontal refraction in the wedge is demonstrated.

Seismic Testing of the Connecting Joint in a Buckling-Restrained K-Braced RC Frame

In this study, a 12-story reinforced concrete (RC) building with buckling-restrained braces (BRBs) arranged in a zigzag configuration is proposed as a prototype building. The beam-column joint at the tenth floor selected as the sub-assemblage specimen and its details including the BRB gusset bracket and RC corbels were designed following the model building codes. The full-scale sub-assemblage of the structural system was tested using cyclic loading procedure. Test results show that the proposed BRB-to-RC connection details performed very well without failure in the steel gusset bracket or the RC corbels. In order to further study the seismic performance of the 12-story buckling-restrained braced RC frame, nonlinear response history analyses are conducted using a total of 240 (SLE, DBE and MCE) ground accelerations. Analysis results indicate that the maximum ratios of total BRB shear to base shear are about 23% (SLE), 21% (DBE) and 19% (MCE). The maximum inter-story drift ratios under MCE and DBE events are 2.32% and 1.82%, respectively. Analysis results also suggest that the high mode effect is not significant. It is found that the peak demand of the horizontal tension force on the steel gusset bracket can be estimated by considering 70% of the sum of the two horizontal force components computed from the two adjacent BRB maximum tension strengths.

Experimental study of shear strength and failure mechanisms in RC beams scaled along height or length

The paper presents results of laboratory experiments carried out on longitudinally reinforced concrete beams subjected to four-point bending. Beams of separately varying height and length were analyzed to investigate the size effect on nominal strength and post-critical brittleness. Beams were scaled in the height direction in the first test series and in the length direction in the second series. Due to lack of geometrical similarity, different failure mechanisms were exhibited. Load-deflection diagrams and crack paths were registered during experiments. The digital image correlation technique was applied to visualize strain localization on the concrete surface. The crack opening and crack slip displacements were also measured. The beam response was characterized by two non-dimensional parameters ηa = a/D and ηb = b/D defined as the ratios of shear and bending spans to the beam depth D assumed as the size parameter and the reinforcement position parameter ηc = c′/D. Two major failure mechanisms were observed: flexural failure in the central beam zone combined with plastic yielding of the reinforcement and the diagonal shear crack failure in external shear zones. Two distinct modes of shear failure can be specified depending on the dominance of crack opening or crack closure contact zones. Two different effective stresses associated with failure mechanisms were defined to specify the beam strength’s dependence on ηa, ηb, ηc and D. Some analytical formulae specifying the critical shear stress dependence on ηa, ηc and strengths ratio of reinforcement and concrete were presented at the end of paper and compared with experimental data.

Heat transfer in non-axisymmetric Homann stagnation-point flows towards a stretching sheet

We have studied heat transfer in non-axisymmetric Homann stagnation-point flows towards a stretching sheet. In a recent paper, Weidman (2012) has modified Homann stagnation point flow and made it non-axisymmetric over a rigid plate. Now, if the plate is not rigid but linearly stretched with velocities in the x- and y-directions, and heat is transferred from the plate to the ambient fluid, then there is a new family of asymmetric viscous stagnation-point flows depending on the ratios of shear to strain rate at the plate γ(=b∕c), and the strain-rate of the ambient fluid to strain-rate at the plate λ(=a∕c) in the range −∞<γ,λ<∞. Here, a, b are the strain rate, shear rate of the stagnation-point flow, and c is the strain-rate at the plate. We have also studied the heat transfer in the flow. The governing momentum equations are solved numerically using a fourth order Runge–Kutta method with a shooting technique. The effect of the various parameters on the wall shear–stress parameters, dimensionless velocities, displacement thicknesses and temperature distributions are analysed. Numerical results of wall shear–stress and displacement thickness are compared with their large value behaviours and those behaviours give a good agreement with the corresponding numerical solutions.

Torsion strength of single-box multi-cell concrete box girder subjected to combined action of shear and torsion

A model has been proposed that can predict the ultimate torsional strength of single-box multi-cell reinforced concrete box girder under combined loading of bending, shear and torsion. Compared with the single-cell box girder, this model takes the influence of inner webs on the distribution of shear flow into account. According to the softening truss theory and thin walled tube theory, a failure criterion is presented and a ultimate torsional strength calculating procedure is established for single-box multi-cell reinforced concrete box girder under combined actions, which considers the effect of tensile stress among the concrete cracks, Mohr stress compatibility and the softened constitutive law of concrete. In this paper the computer program is also compiled to speed up the calculation. The model has been validated by comparing the predicted and experimental members loaded under torsion combined with different ratios of bending and shear. The theoretical torsional strength was in good agreement with the experimental results.

Crystal thermoelasticity at extreme loading rates and pressures: Analysis of higher-order energy potentials

Several finite elastic strain measures are evaluated for use in constitutive models of crystalline elasticity and elasto-plasticity. These include the Green material strain tensor, the Eulerian material strain tensor, and the logarithmic material strain tensor, all of which are referred to locally relaxed coordinates invariant under spatial rotations. New applications of logarithmic strain-based theory towards shock compression of aluminum, copper, and magnesium single crystals and polycrystals are presented. Solutions to the planar shock problem from previous work are summarized and compared with the present results. Consideration of these new results in conjunction with previous analysis for a number of different metals, ceramics, and minerals suggests that Eulerian strain-based theory is most accurate for modeling the dynamic high-pressure response of ductile metallic crystals wherein ratios of elastic shear to bulk moduli tend to be relatively small, while logarithmic strain-based theory is recommended for modeling shocks in ceramics and minerals with larger ratios of effective elastic shear to bulk modulus.

Advances in elucidating mechanochemical complexities via implementation of a simple organic system.

Mechanochemistry is becoming increasingly popular amongst both the academic and industrial communities as an alternative method for inducing physical and chemical reactions. Despite its rapidly expanding application, little is understood of its mechanisms, greatly limiting its capacity. In the present work the application of specialty devices allowed submission of the simple organic system, α-glycine + β-malonic acid, to isolated shearing and impact treatment. In doing so, unique products were observed to result from each of these major mechanical actions; shear inducing formation of the known salt, glycinium semi-malonate (GSM), and impact yielding formation of a novel phase. Correlation of these isolated treatments with a more common ball mill indicated two unique regions within the milling jar, each characterised by varying ratios of shear and impact, leading to different products being observed. It is widely accepted that, particularly when considering organic systems, mechanical treatment often acts by inducing increases in local temperature, leading to volatilisation or melting. A combination of DSC and TGA were used to investigate the role of temperature on the system in question. Invariably, heating induced formation of GSM, with evidence supporting a eutectic melt, rather than a gas-phase reaction. Shear heating alone is unable to describe formation of the novel phase obtained through impact treatment. By considering the formation and character of mechanically produced tablets, a model is described that may account for formation of this novel phase. This system and methodology for mechanochemical study offers intriguing opportunities for continued study of this widely used and exciting field.

Buckling behavior of strengthened perforated plates under shear loading

This paper is dedicated to the buckling behaviors of strengthened perforated plates under edge shear loading, which is a typical load pattern of steel plates in civil engineering, especially in plate and box girders. The square plates considered each has a centric circular hole and is simply supported on four edges in the out-of-plane direction. Three types of strengthening stiffeners named ringed stiffener (RS), flat stiffener (FSA and FSB) and strip stiffener (SSA, SSB and SSC) are mainly discussed. The finite element method (FEM) has been employed to analyse the elastic and elasto-plastic buckling behavior of unstrengthened and strengthened perforated plates. Results show that most of the strengthened perforated plates behave higher buckling strengths than the unstrengthened ones, while the enhancements in elastic buckling stress and elastoplastic ultimate strength are closely related to sti ffener types as well as plate geometric parameters including plate slenderness ratio and hole diameter to plate width ratio. The critical slenderness ratios of shear loaded strengthened perforated plates, which determine the practical buckling pattern (i.e., elastic or elasto-plastic buckling) of the plates, are also studied. Based on the contrastive analyses of strengthening efficiency considering the influence of stiffener consumption, the most efficient cutout-strengthening methods for shear loaded perforated square plates with different slenderness ratios and circular hole diameter to plate width ratios are preliminarily identified.

Relationship between fractures, fault zones, stress, and reservoir productivity in the Suban gas field, Sumatra, Indonesia

It is becoming widely recognized that a relationship exists between stress, stress heterogeneity, and the permeability of subsurface fractures and faults. We present an analysis of the South Sumatra Suban gas field, developed mainly in fractured carbonate and crystalline basement, where active deformation has partitioned the reservoir into distinct structural and stress domains. These domains have differing geomechanical and structural attributes that control the permeability architecture of the field. The field is a composite of Paleogene extensional elements that have been modified by Neogene contraction to produce basement-rooted forced folds and neoformed thrusts. Reservoir-scale faults were interpreted in detail along the western flank of the field and reveal a classic oblique-compressional geometry. Bulk reservoir performance is governed by the local stress architecture that acts on existing faults and their fracture damage zones to alter their permeability and, hence, their access to distributed gas. Reservoir potential is most enhanced in areas that have large numbers of fractures with high ratios of shear to normal stress. This occurs in areas of the field that are in a strike-slip stress style. Comparatively, reservoir potential is lower in areas of the field that are in a thrust-fault stress style where fewer fractures with high shear-to-normal stress ratios exist. Achieving the highest well productivity relies on tapping into critically stressed faults and their associated fracture damage zones. Two wellbores have been drilled based on this concept, and each shows a three- to seven-fold improvement in flow potential.

Consistency of field-theoretical and kinetic calculations of viscous transport coefficients for a relativistic fluid

We investigate the ratios βη≡η/τπ and βζ≡ζ/τΠ, i.e., the ratios of shear, η, and bulk, ζ, viscosities to the relaxation times τπ, τΠ of the shear stress tensor and bulk viscous pressure, respectively, in the framework of causal relativistic dissipative fluid dynamics. These viscous transport coefficients are computed both in a field-theoretical and a kinetic approach based on the Boltzmann equation. Our results differ from those of the traditional Boltzmann calculation by Israel and Stewart. The new expressions for the viscous transport coefficients agree with the results obtained in the field-theoretical approach when the contributions from pair annihilation and creation (PAC) are neglected. The latter induce non-negligible corrections to the viscous transport coefficients.

Fundamentals of elasticity of (Mg1−x, Fex)2SiO4 olivine

We study the influence of iron on the elasticity of (Mg1−x, Fex)2SiO4 olivine (0 ≤ x ≤ 0.125), a major constituent of the Earth's upper mantle. We calculate static elastic properties by first principles for this solid solution and investigate the effect of atomic arrangement, an artifact of supercell calculations, on all single crystal and poly‐crystalline elastic moduli. From calculated wave propagation velocities we find the heterogeneity ratios of shear to compressional wave velocity, and bulk sound to shear wave velocity. Their values are, though limited to composition considerations, marginally consistent with seismic tomography.