Reversible Rail Shear Apparatus Applied to the Study of Woven Laminate Shear Behavior

The multitude of in-plane shear tests existing in the literature seems to demonstrate the complexity of developing a test adapted to all experimental works. In a general framework of investigation of translaminar cracks in thin laminates, a test able to reproduce a pure in-plane shear loading was required. The laminate studied is notably employed as helicopter blade skin, and cyclic torsion induced by aerodynamic load involves cyclic in-plane shear. This particular application established some specifications for the test needed to carry out this study. To comply with them, an original technological solution has been developed from a three-rail shear test apparatus. This paper describes the resulting “reversible rail shear test” solution and its application to the study of in-plane shear behavior of a thin glass-epoxy laminate. The results concern plain and notched coupons under quasi-static loading, and crack growth tests under cyclic loading

Influence of post-cyclic loading on hemic peat

Construction on peat soils has proven to be a challenging task to civil engineers since this soil type has a significant issue that arises from common problems construction of roads, housing and embankment construction with regard to peat are stability, settlements and major problems were encountered especially on deep peat. For many years, in road design as an example, static loading method was applied in road designed by considering soil shear strength through static load and do not take into account the vehicular dynamic loading and shear strength thereafter. This fact is related to the shear strength of peat soil after dynamically loaded. The aim of this research is to establish the post-cyclic behaviour of peat soil after cyclically loaded and to assess the effect of parameters changes on static and post-cyclic behaviour of peat soil. 200 specimens are tested, and prepared under consolidated undrained triaxial with effective stresses at 25kPa, 50 kPa, and 100 kPa with different location from Parit Nipah, Johor, Parit Sulong, Batu Pahat, Johor and Beaufort, Sabah. These specimens tested using GDS Enterprise Level Dynamic Triaxial Testing System (ELDYN) apparatus. Whereas, dynamic load tests are carried out in different frequencies to simulate the loading type such as vibration of machineries, wind, traffic load and earthquake in field from 1.0 Hz, 2.0 Hz and 3.0 Hz with 100 numbers of loading cycles. Post-cyclic monotonic shear strength results and then compared to the static monotonic results. Significantly, showed some vital changes that leads to the changes of stress-strain behaviour. Apparently, the result shows that post-cyclic shear strength decreases with the increase of frequencies. Prior to critical yield strain level, the peat specimen experience a significant deformation. The deformation of peats triggers changes in soil structures that causes reduction in stress-strain behaviour. Thus, it can be concluded that the stress-strain behaviour of peat soil decreased after 100 numbers of cyclic loading in post-cyclic test as compared to the static tests, and it decreased substantially when frequencies were applied. The post-cyclic specimen had a lower undrained parameters than did the static. Reduction of cohesion value in postcylic compared to static almost 70% and reduction of friction angle is about 46.34%

Pore Pressure in Silty Sand under Cyclic Shear

In order to study the liquefaction phenomena of silty sand, saturated specimens prepared in the laboratory according to the dry unit weight of undisturbed samples are used to examine the cyclic shear resistance, pore pressure and residual shear strain developed in these specimens under cyclic loading. These tests are accomplished with a cyclic simple shear test apparatus developed in Nanjing Hydraulic Research Institute. Based on results of these tests expressions of cyclic shear resistance, pore pressure, dynamic shear modulus and residual shear strain as functions of number of cycles, consolidation pressure, initial and cyclic shear stress etc. have been developed

Strength Degradation Characteristics of the Steel-Concrete Interface Under Cyclic Shear

The shear capacity of the steel-concrete interface (SCI) of concrete-filled steel tubular piles (CFSTs) degrades due to the cyclic shear action of external loading and unloading and can result in a reduction in the bearing capacity. To explore the shear strength degradation characteristics of the steel-concrete interface under cyclic shear, cyclic shear tests for three roughness types and under four different normal stresses were carried out by using a large-scale repeated direct shear test system. The characteristics of the shear load-displacement curve and failure mode of the SCI under external cyclic shear were analyzed, and the influence of the roughness and normal stress on the SCI shear strength degradation was explored. The results indicate that the CFSTs experienced shear failure in the first three shear cycles and then exhibited wear failure. The peak shear load of the SCI increases exponentially with increasing normal stress and decreases logarithmically with increasing cyclic shear time. A larger interfacial roughness and normal stress results in a faster interfacial shear strength ratio (τfn/τf1) weakening during the first three shear cycles, and with an increase of the cyclic shear times, the weakening rate is reduced

Analytical modeling of reinforced concrete columns subjected to bidirectional shear

Under general seismic loading, reinforced concrete columns may be subjected to lateral loads in more than one direction. Available experimental data on columns subjected to bidirectional forces indicate that higher levels of damage and a higher loss of ductility and strength have been observed compared to similar tests under unidirectional shear forces. In this study, an experimental program was conducted in which six lightly reinforced concrete columns were subjected to unidirectional and bidirectional cyclic shear forces. This observation was used to identify the mechanisms and parameters governing the behavior of columns subjected to cyclic bidirectional lateral loads. Hence, a new conceptual model was developed to obtain the capacity of member. The shear forces were analyzed and an analytical formulation was derived to account for the effects in the concrete stress-strain relationship, the moment-curvature diagram and the plastic hinge length. These equations were used along with a structural model with concentrated plastic hinges to obtain the capacity curve of the column. The results of the formulations developed were verified using the results of the experiments performed on columns subjected to unidirectional and bidirectional cyclic lateral forces.Peer ReviewedPostprint (author's final draft

Threshold Shear Strain for Cyclic Degradation of Three Clays

Cyclic threshold shear strain, γt, is small cyclic shear strain amplitude above which soil properties significantly change with the number of cycles, N, and below which such changes are for all practical purposes negligible. To date, three cyclic threshold shear strains have been experimentally verified: for cyclic settlement (cyclic compression), for residual cyclic pore water pressure, and for cyclic stiffening. Subject of the paper is testing of fourth cyclic threshold shear strain for cyclic degradation, γtd. When fully saturated soil is subjected in undrained conditions to moderate or large cyclic strain-controlled loading, its secant shear modulus, Gs, decreases with N. This is quantified for given cyclic shear strain amplitude, γc, by degradation index, δ = GsN /Gs1, where GsN = Gs at cycle N. Index δ and N are related via degradation parameter t = −(logδ / logN) which measures the rate of cyclic degradation. At γc \u3c γtd there is no cyclic degradation and t = 0. If γc \u3e γtd cyclic degradation takes place and t \u3e 0. With a special simple shear device for small-strain testing the variation of t with γc was examined and γtd evaluated for three clayey soils. Results show that γtd increases with plasticity index, PI. For PI=12 γtd=0.015%, for PI=26 γtd=0.04, and for PI=47 clay γtd=0.05%. Testing procedure and comparison to other types of γt are presented

Cyclic and Post-cyclic Shear Behaviour of a Granite Residual Soil - Geogrid Interface

The dynamic frictional properties of the soil-geosynthetic interface play an important role in the design and stability analysis of geosynthetic-reinforced soil structures under repeated loadings, such as those induced by compaction, traffic and earthquakes. This paper describes a laboratory study carried out using a large-scale direct shear test device, aiming to investigate the cyclic and post-cyclic behaviour of an interface between a granite residual soil and a biaxial woven geogrid. In the cyclic direct shear tests, the interface was subjected to 40 cycles of sinusoidal displacement, with semiamplitude and frequency ranging from 1-10 mm and 0.05-0.5 Hz, respectively. To evaluate the effect of the cyclic loading on the interface shear strength, monotonic direct shear tests were performed immediately following the cyclic tests. The results indicated that the loading frequency has little impact on the interface shear stiffness during the loading cycles. In contrast, the influence of the displacement semi-amplitude on the interface stiffness was found to be significant. The cyclic loading did not lead to the degradation of the post-cyclic interface shear strength. The post-cyclic peak shear strength tended to increase with the semi-amplitude of the shear displacement, which may be associated with an increase in soil density

Cyclic Simple Shear Behavior of Fine Grained Soils

Consolidated, constant volume (CCV), cyclic laboratory shear tests were performed on marine clay soils. The Norwegian Geotechnical Institute (NGI) direct simple shear device, modified for cyclic loading (square wave) capabilities, was used for these tests. Two clays were investigated; a natural undisturbed Gulf of Mexico clay and a reconstituted Pacific Illite. The cyclic shear tests were performed with two way loading (complete stress reversal). Models are presented to predict the pore pressure behavior during a cyclic test, or to predict the strain or pore pressure behavior of tests with varying cyclic shear stress levels. A unique relationship between shear strain and pore pressure for the tests in this investigation is presented

Characterization of crack growth under combined loading

Room-temperature static and cyclic tests were made on 21 aluminum plates in the shape of a 91.4x91.4-cm Maltese cross with 45 deg flaws to develop crack growth and fracture toughness data under mixed-mode conditions. During cyclic testing, it was impossible to maintain a high proportion of shear-mode deformation on the crack tips. Cracks either branched or turned. Under static loading, cracks remained straight if shear stress intensity exceeded normal stress intensity. Mixed-mode crack growth rate data compared reasonably well with published single-mode data, and measured crack displacements agreed with the straight and branched crack analyses. Values of critical strain energy release rate at fracture for pure shear were approximately 50% higher than for pure normal opening, and there was a large reduction in normal stress intensity at fracture in the presence of high shear stress intensity. Net section stresses were well into the inelastic range when fracture occurred under high shear on the cracks