Combined Compressive Stresses Research Articles

Waterproofing performance of polypropylene – concrete wall of underground silo under combined compressive stress and water pressure

Safe, economical and high-quality storage of huge amount of grain for a longer duration under COVID-19 is a challenge and underground storage is a good alternative due to stable temperature, less cooling consumption and better pest control effect. However, the underground silo has very high requirement of waterproof and the performance of underground silo under combined compression and water pressure was rarely studied. In this study, a new composite structure, polypropylene – concrete wall (PPCW) for underground silo was proposed. Total three PPCWs with different size were manufactured to test the waterproofing features under joint effect of compression and hydropower of water. The strains, lateral displacement and cracking conditions of PPCWs were investigated. According to the experimental results, the PP board and concrete presented very good performance of interaction working under compression. The maximum water pressure of the specimens with stud spacing of 250mm increased by about 15.7% compared with that of the specimens with stud spacing of 350mm. The welding and strength of PP board has the greatest influence on the ultimate performance of PPCW. Based on the empirical coefficient method of concrete flat-slab and tested results, a new modified method was proposed to predict the bending moment at mid-span of PPCW by using an adjustment coefficient, Rm. Considering this experimental case only, the adopting a Rm = 0.64 could control the relative errors between test and analysis under 15.6%.

Damage mechanism of pier concrete subjected to combined compressive stress, freeze-thaw, and salt attacks in saline soil

This study experimentally investigates the damage mechanism of pier concrete under the combined action of axial compressive stress (CS), freeze–thaw (FT) cycles, and salt attacks (SA). An indoor accelerated corrosion test of pier concrete under the combined action of CS, FT, and SA was conducted based on field investigations of concrete corrosion of piers in the saline soil of Xinjiang province in China. The experimental results of macro and micro analyses showed that the durability degradation of the pier concrete could be attributed to the damage to the cement slurry, aggregates, interface areas, and pore structure. A new delamination damage model was established to describe the mechanism of the combined damage, including the deterioration of the mortar layer, the generation of microcracks in the interface zone, the deposition of corrosion products, and crack development. The quantitative assessment of the durability degradation of the pier concrete was more accurate when the mass loss (ML) and relative dynamic elastic modulus (RDEM) were considered. These unique findings provide an important reference for the design and durability evaluation of pier concrete in saline soils.

Evaluation of Bond Strength between Ultra-High-Performance Concrete and Normal Strength Concrete: An Overview

Ultra-high-performance concrete (UHPC) is an advanced, durable cementitious material with excellent mechanical properties, which makes it an appropriate material for strengthening, repair, and retrofitting of damaged concrete structures. The UHPC as a repair material on normal strength concrete (NSC) depends on the quality of the bond strength at the interface. The interface behavior of UHPC-NSC concrete has a significant impact on its overall durability performance. This paper reviews the studies conducted on the bond strength at the concrete interface to determine the effectiveness of different bond strength testing techniques. The review has shown that the bond strength is commonly evaluated through splitting tensile, slant shear, direct shear, pull-off, bi-surface shear, and third-point flexural tests. Slant shear and splitting tensile test methods are the most common techniques used to evaluate the performance of bond strength between UHPC and NSC. splitting tensile tests, stress is directly applied at the concrete interface, while in the slant shear test, the interface surface is subjected to combined compressive stress and shear stress. Thus, Splitting tensile tests produces more accurate results than the slant shear test. Bi-surface shear and third-point flexural tests are easy to conduct and give a result similar to splitting and direct shear tests. However, further investigations are required on the reliability of the test methods under different conditions. In terms of failure modes, splitting tensile tests produces a more consistent result compared to the pull-off test.

Effects of compressive stresses on torsional fatigue

Rolling contact fatigue (RCF) is the dominant failure mode in properly installed and maintained ball and roller element bearings. Lundberg and Palmgren in their seminal publication indicated that this failure is due to the alternating component of shear stress. Thus, torsional fatigue experiments have been used to predict the RCF behavior of bearing materials. In non-conformal contacts, due to Hertzian pressure the contact experiences large compressive stresses. Hence, it is critical to take into account the effect of these large compressive stresses in torsional fatigue to better simulate RCF conditions. This paper presents an investigation of torsional fatigue of bearing steels, while the effects of combined compressive stress and its relevance to material behavior in rolling contact fatigue is examined. An MTS test rig was used to investigate the fatigue life of several bearing steels and their failure mechanisms were evaluated through fractography. Then the effects of compressive stresses on torsional fatigue were investigated. A set of custom designed clamp fixtures were designed, developed and used to apply Hertzian pressures of up to 2.5GPa on the torsion specimens. The experimental results indicate that at high cycle fatigue, a combination of shear and biaxial compression, by application of Hertzian contact, is more detrimental to fatigue life than shear alone; however, as expected it has little to negligible effects in the low cycle fatigue regime. Also the failure mode changes such that fracture planes form a cup and cone pair with multiple internal cracks as opposed to helical planes observed in pure torsion which are formed by a single crack. A 3D finite element model (using ABAQUS) was developed to investigate the fatigue damage accumulation, crack initiation, and propagation in the material. The topology of steel microstructure is modeled employing a randomly generated Voronoi tessellation wherein each Voronoi cell represents a material grain and the boundaries between the cells are assumed to represent the weak plane in the steel matrix. Continuum damage mechanics (CDM) was used to model material degradation during the fatigue process. A comprehensive damage evolution equation is developed to account for the effect of mean stress on fatigue. The model predicts the fatigue lives and crack patterns successfully both in presence and absence of compressive stresses.

Finite element implementation of Puck’s failure theory for fibre-reinforced composites under three-dimensional stress

The objectives of this article are to apply Puck’s failure criteria to predict the failure of 12 test problems, proposed in Part A of the second World-Wide Failure Exercise. These problems include a polymer material, various unidirectional laminae and three multi-directional laminates under a variety of 3D stress loadings. The implementation was carried out through a commercial finite element code where material nonlinearities, due to material behaviour under shear and transverse and through-thickness loadings and due to post failure damage, were taken into account. This is the first time where the critertion has been stretched to its limits. Some of the challenges found include the need to determine the fracture angle of action plane under 3D stresses and the treatment of the strengthening effects on the nonlinear stress strain curves when a lamina is subjected to combined compressive stresses in both the transverse and through-thickness directions. The successful methodology developed here will be used to analyse the effects of boundary conditions in Part B of the second World-Wide Failure Exercise to improve correlation with experimental results for the test problems.

Mesoscale Approach to Modeling Concrete Subjected to Thermomechanical Loading

Concrete subjected to combined compressive stresses and temperature loading exhibits compressive strains, which are considerably greater than for concrete subjected to compressive stresses alone. This phenomenon is called transient thermal creep or load induced thermal strain and is usually modeled by macroscopic phenomenological constitutive laws which have only limited predictive capabilities. In the present study a mesoscale modeling approach is proposed in which the macroscopically observed transient thermal creep results from the mismatch of thermal expansions of the mesoscale constituents. The mesostructure of concrete is idealized as a two-dimensional three-phase material consisting of aggregates, matrix, and interfacial transition zones. The nonlinear material response of the phases is described by a plasticity interface model. The mesoscale approach was applied to analyze compressed concrete specimens subjected to uniform temperature histories and the analysis results were compared to experimental results reported in the literature.

A NEW APPARATUS TO SIMULATE ATHLETIC FIELD TRAFFIC: THE CADY TRAFFIC SIMULATOR

Realistic traffic simulation is crucial to the validity of athletic field research. Previously developed athletic field traffic simulators contain studded drums that turn at different speeds, creating shear forces at the playing surface. The Cady Traffic Simulator (CTS) (a modified walk‐behind core cultivation unit) was developed at Michigan State University in 2000. The objective of this study was to compare the magnitude and direction of the forces produced by two traffic simulators: the Brinkman Traffic Simulator (BTS), a pull‐behind unit, and the CTS. Both simulators were operated over an in‐ground force plate, which measured the forces in three directions: front to back, side to side, and vertical. The CTS produced a higher compressive stress and net shear stress when operated in either direction than the BTS. The average peak compressive stress produced by the feet of the CTS when operated in the forward direction was approximately 30 times higher than the combined compressive stresses of both BTS drums. The average peak net shear stress produced by the feet of the CTS when operated in the forward direction was approximately 15 times higher than the combined net shear stresses of both BTS drums. Operating in the reverse direction, the average peak compressive stress produced by the feet of the CTS was greater than five times the compressive stresses of both BTS drums combined. The average peak net shear stress produced by the feet of the CTS was approximately four times higher than the combined net shear stresses of both BTS drums.

Strength of Oil Well Cements at Downhole Pressure-Temperature Conditions

Abstract Triaxial compression tests with independently applied external confining pressures and internal pore pressures show that the ultimate compressive strengths of representative oil well cements are nearly linear functions of effective pressure the difference between external and internal pressures on the jacketed cylindrical specimens (to 15,000 psi). The strengths are little affected by the test temperature to 350F (not to be confused with the curing temperature). At an effective pressure of 15,000 psi, strengths are in the range of 30,000 to 50,000 psi, comparable to those of sedimentary rocks under similar conditions. The cements become very ductile even under low effective pressures; permanent shortenings of 30 per cent or more are attainable without rupture. Introduction Since the pioneering work of Richart, Brandtzaeg and Brown on the failure of cement under combined compressive stresses, it has been recognized that ultimate compressive strength is greatly enhanced by the application of confining pressure. More recently, McHenry showed that the strength of concrete was a linear function of the effective pressure (the difference between the external confining pressure on a jacketed specimen and the internal fluid pore pressure) at least for a range of 0 to 1,500 psi. The effect of temperature had not been investigated, and no previous systematic triaxial compression testing of materials used for oilwell cementing seems to have been done. The present work was suggested by the late J. M. Bugbee who stated that "consideration of the common application of high-pressure hydraulic fracturing to the initial completion or recompletion of wells, and the large pressure drawdowns in some producing wells, particularly those in abnormally high-pressure gas-condensate reservoirs, raises the question of what is a suitable cement strength for various completions. The intuitive belief exists that cement strength need be no greater than formation strength. Tests should, however, be conducted at downhole conditions."The ultimate compressive strengths of rocks penetrated by the borehole must rise several fold with increasing depth. This marked enhancement of strength is due to the influence of the effective pressure, the total weight per unit area of the overburden less the hydrostatic pore pressure. (The effect of temperature due to the geothermal gradients is relatively small for depths to 30,000 ft.) A significant comparison of the strengths of rocks and cements at downhole conditions requires knowledge of the confined compressive strengths of cements as well. EXPERIMENTAL PROCEDURES The theory and technique of triaxial compression testing are fully discussed in earlier reports. Briefly, cylindrical specimens 1-in. long and 0.5-in. in diameter are jacketed in thin copper tubes of negligible strength, placed in the test chamber and subjected to an external confining pressure of kerosene and loaded axially by the piston at a strain rate of 1 per cent per minute. Pore pressures of water (or kerosene) are applied independently through the hollow piston and are maintained constant during the shortening of the specimen. Tests at sensibly 0 pore pressure are arranged so that any free water in the cement can escape to the atmosphere. (If egress of water were denied, pore pressure would rapidly attain the value of the external confining pressure because of reduction of pore space.) The test chamber can be heated for high-temperature experiments. Unless other-wise noted, the cement samples were air dried for about a week. Recorded during a test are pore and confining pressures, shortening and axial differential force (total force less the product of the confining pressure and the area of the piston). SPEJ P. 341ˆ