Hydrostatic Loading Research Articles

Approaches and Challenges in FEED and Detailed Design Process of Floating Substructures

Abstract In the FEED or detailed design phases, the floating foundation designers have to deal with complex structural design aspects and meet certification or class requirements for structural verifications, such as yield and buckling checks as well as fatigue checks for steel structures. The designer faces several challenges during the structural verification process, starting with the accurate definition of the complex external load state with the simultaneous action of aerodynamic, hydrostatic and hydrodynamic loads, inertia and mooring loads, followed by the processing and handling of very large load case tables required for the analysis of floating wind turbines, down to time efficient post-processing of the analysis results compatible with typical commercial project schedules. The paper discusses some of the currently existing and applied methodologies on how the structural checks are typically performed in these circumstances, and addresses their advantages and shortcomings. In addition, a new Global Influence Superposition (GIS) methodology that has been developed by Ramboll is presented, which is able to address many of the existing challenges in an efficient manner.

The location of cationic substitutions in carbonated biomimetic apatites significantly affects crystal nanomechanics

Bone and teeth are comprised of carbonate-substituted apatites with cationic substitutions, like sodium and potassium. Cations substitute for calcium in the apatite lattice but it is unclear whether they substitute for Ca(1) or Ca(2). Additionally, although we know that anionic substitutions affect the mineral mechanics, it is unclear how cationic substitutions affect mineral stiffness. Here, a combined experimental and theoretical approach using in situ fluid-mediated hydrostatic loading with synchrotron Wide Angle X-ray Scattering (WAXS) and Density Functional Theory (DFT) is used to elucidate the role of CO32− and Na+ or K+ co-substitutions on the atomic structure and mechanics of biomimetic apatites. Comparison of WAXS and DFT results showed that preferential substitutions at the Ca(1) and Ca(2) sites depended on cationic type and concentration, with a preference for Ca(1) at higher levels of co-substitution. Substitution levels and location of the cationic substitution both significantly affected the modulus of the minerals. This presents a new paradigm for the development of biomimetic apatites with multi-property tunability by considering composition and atomic organization.

Better than linear strength scaling of multifunctional ceramic truss lattice materials

Driven by the goal of creating exceptionally strong and lightweight thermal insulators to enable the operation of a vacuum airship on Venus, conditions where ceramic truss lattice materials provide better than linear scaling of strength with respect to variations in relative density have been found. This enhanced scaling relationship is a consequence of the pressure sensitive shear strength of ceramic materials. A new Gibson-Ashby type scaling relationship is developed between strength and relative density. Elementary analysis is used to formulate theoretical limits for the compressive strength, minimum density, and minimum thermal conductivity for truss lattice materials subjected to hydrostatic pressure loads. Shape optimization using the covariance matrix adopted evolutionary strategy (CMA-ES) and highly resolved finite element models is conducted on silicon carbide Kelvin cells with variable cross-section axisymmetric struts considering three failure modes: buckling, tensile rupture, and shear failure. The optimized designs closely adhere to and validate the newly developed analytical scaling relationship with better than linear strength scaling. These optimized designs are found to withstand the extreme loading conditions on Venus while providing up to 43 kgm3 of buoyancy. The thermal conductivity of the optimized designs are computed and found to be less than 0.5 WmK, with one design outperforming silica aerogels at elevated temperature.

The Effect of Hydrate Formation Conditions on the Mechanics of Laboratory Methane Hydrate‐Bearing Sediments

AbstractThe mechanics of methane hydrate‐bearing sediments (MHBS) have been broadly investigated over recent years in the context of methane‐gas production or climate‐change effects. Their mechanical investigation has mainly been carried out using models constructed from experimental data obtained for laboratory‐formed MHBS. Along with the dominant effects of hydrate saturation and morphology within the host soil pores, this study recognizes the effective pressure at which the hydrate is formed as a key factor in the MHBS mechanics. A state‐of‐the‐art experimental study has been conducted in order to isolate the effect of the hydrate formation pressure, for use as a model parameter. Two generalized mechanical prediction models that incorporate the effect of the hydrate formation pressure are developed in this work: (a) an analytical shear strength prediction, and (b) an empiric graphical model for predicting volumetric changes along a given stress path. The models are related to a novel data representation which enables the analysis of a few individual test outcomes as a whole, through a volume‐change mapping that describes the complex influence of the volumetric effect of hydrate in MHBS, under combined hydrostatic and deviatoric loading scenarios. In this study, we delve into a specific configuration of hydrate morphology, hydrate saturation, and host soil type, enabling a distinctive fundamental geotechnical investigation and the development of a conceptual modeling approach. The paper describes the approaches by which the MHBS properties can be extracted for other MHBS samples (than those examined in this work) having different host soils and hydrate pore‐space morphologies.

In situ study of microstructure evolution and α → ω phase transition in annealed and pre-deformed Zr under hydrostatic loading

The detailed study of the effect of the initial microstructure on its evolution under hydrostatic compression before, during, and after the irreversible α→ω phase transformation and during pressure release in Zr using in situ x-ray diffraction is presented. Two samples were studied: one is plastically pre-deformed Zr with saturated hardness and the other is annealed. Phase transformation α→ω initiates at lower pressure for a pre-deformed sample but for a volume fraction of ω Zr, c>0.7, a larger volume fraction is observed for the annealed sample. This implies that the proportionality between the athermal resistance to the transformation and the yield strength in the continuum phase transformation theory is invalid; an advanced version of the theory is outlined. Phenomenological plasticity theory under hydrostatic loading is outlined in terms of microstructural parameters, and plastic strain is estimated. During transformation, the first rule is suggested, i.e., the average domain size, microstrain, and dislocation density in ω Zr for c<0.8 are functions of the volume fraction, c of ω Zr only, which are independent of the plastic strain tensor prior to transformation and pressure. The microstructure is not inherited during phase transformation. Surprisingly, for the annealed sample, the final dislocation density and the average microstrain after pressure release in the ω phase are larger than for the severely pre-deformed sample. The results suggest that an extended experimental basis is required for the predictive models for the combined pressure-induced phase transformations and microstructure evolutions.

Stress–strain hysteresis during hydrostatic loading of porous rocks

A micro-mechanical model is proposed to predict the stress–strain hysteresis during the cyclic hydrostatic loading of fluid-saturated rocks under drained or undrained conditions. A spherical pore is surrounded by a multi-cracked shell where local deviatoric stress develops despite the remote hydrostatic loading. The effective properties of the material composing the shell are constructed assuming an isotropic distribution of cracks with no interaction, and the overall properties thanks to the spherical assemblage approach. The fluid pressure in drained and undrained conditions is assumed to be uniform throughout the assemblage. A new analytical solution is proposed, assuming all cracks are closed and slipping either forwardly or reversely. It is shown with numerical simulations for drained conditions that this assumption is indeed respected for sufficiently small values of the crack friction angle. However, for reasonable values, the closed cracks during the unloading phase could slip in either direction: reversely close to the pore and still forwardly away from the pore. Moreover, at critical radii, the slip could occur in either direction depending on the crack orientation. A similar micro-structural response is observed for undrained conditions, although the remote confining stress required to close the cracks is much larger. The model’s predictions compare favourably with recent experimental data on dry sandstones and carbonates, which were presented in a study on the influence of strain amplitude on the transition between static and dynamic properties. The crack density and matrix elasticity modulus are sufficient fitting parameters to accurately predict the hysteresis loops, especially for porosity levels above 10%.

Production And Improvement Productivity Of An Oil Well By Water Restraining And Penetration Using PLT

As any operation that delays water to reach and enter the production wells. Water production is one of the major technical, environmental, and economic problems associated with oil and gas production. Water production not only limits the productive life of the oil and gas wells but also causes several problems including corrosion of tubular, fines migration, and hydrostatic loading. The conventional water shutoff method has been applied in Sharara field for the wellbore isolation by cement plug in the watered out zone, fortunately it was successful. In this project as PLT calculation was done by using water hold-up sensor as following: shut – in the well and run PLT Log was correlated for depth matching of well X 1 to 5250 ft end of last perforation, then full-bore Spinner passes were consistent and repeated and did not show any cross flow between perforations The Changes in spinner rotation at few intervals is corresponding to change in caliper readings. Flowing the well Full-bore Spinner passes were consistent and repeated, Passes also indicated the inflow zones, was consistent and repeated and illustrated the fluid distribution in the wellbore, show that the main hydrocarbon bubble entry at the wellbore filled with water. Final result showing that for A-06 well first and last perforation (4810 ft – 4840 ft) & (4852 ft 4916 ft) producing water with (5.17) % & (87.72) % WC

Natural Vibrations and Stability of Composite Cylindrical Shells Containing a Quiescent Fluid

This paper presents the results of investigation of the natural vibrations and stability of circular vertical multilayered cylindrical shells, fully or partially filled with a quiescent compressible fluid subjected to hydrostatic and external static loads. The behavior of the elastic structure and fluid medium is described based on the classical shell theory and Euler’s equations. The linearized equations of motion of the shell, together with the corresponding geometrical and physical relations are reduced to a system of ordinary differential equations with respect to new unknowns. The acoustic wave equation is transformed to a system of differential equations using the method of generalized differential quadrature. The solution of the formulated boundary value problem is developed using Godunov’s orthogonal sweep method. The dependences of the lowest vibration frequencies and critical external pressure on the ply angle and the filling level of two-layer and three-layer cylindrical shells are analyzed in detail. It is demonstrated that, in contrast to the ply angle and a given combination of boundary conditions, the lay-up scheme of composite materials plays different parts in the problems of maximizing the fundamental frequency of vibrations and extending the stability boundaries.

An Experimental Investigation on the Effects of Temperature and Confining Pressure on the Static and Dynamic Behaviors of Shale Rocks

Abstract To better understand the associated thermal and mechanical effects on the elastic behaviors of shale rocks, we examine the shale rocks at reservoir stress (static) and elastic conditions (dynamic) at varying temperature (25–110°C) and pressure (5–55 MPa) conditions through coupling dynamic–static experimental measurements. The results illustrate that the shale’s P- and S-wave velocities increase with the increasing confining pressure but decrease with the elevated temperature. For the pressure history, ultrasonic P-wave velocities upon hydrostatic unloading are slightly larger than the loading ones, whereas S-wave velocities are almost overlapping together. Meanwhile, the temperature elevation causes much less velocity reduction at a higher confining pressure than lower confining pressure. The measured data demonstrate that the static bulk modulus is more sensitive to the confining pressure than the dynamic bulk modulus. Moreover, with the elevated temperature, the dynamic bulk moduli separate by showing a decreasing trend in either hydrostatic loading or unloading. The loading–unloading cycle shows that the static bulk moduli present values approaching the dynamic ones at all temperature levels when the confining pressure is initially unloaded from the maximum pressure. Both static and dynamic bulk moduli decrease with the continued unloading, with more decrement for the static bulk modulus. The coupling effects of the pressure and temperature on the static and elastic properties of shale samples imply that, in the practical shale reservoir characterization process, temperature and pressure influences should be considered to characterize the relation of dynamic and static properties of shale rocks. The laboratory investigations on shales imply that the relation of dynamic and static properties is pressure dependent mainly due to the intrinsic behavior of fracture, soft pore, and microstructure in the rock frame.

Analytical study on hybrid thrust foil bearing, structural characterization and measurement of static performance

This work presents a novel hybrid foil thrust bearing (HFTB) with an outer diameter of 154 mm, along with simulation and test results. The HFTB incorporates a high-pressure air/gas injection to the taper portion of the thrust foil bearing, boosting the hydrodynamic effect on the main bearing surface and hydrostatic load capacity at zero speed. The bearing has high load capacity, low power loss, and no friction/wear during startup and shutdown. Firstly, push-pull tests were conducted on a double-acting HFTB configuration to evaluate the nonlinear structural stiffness of the bump foil structure. The measured nonlinear stiffness model was adopted to predict the overall bearing performance under various speeds and loads. The simulation uses an advanced model which predicts the 2D plate top foil deflection with physical bump locations mapped from the actual hardware. The simulation confirms that the hybrid operation significantly increases the load capacity compared to hydrodynamic bearing due to the boost effect of hydrostatic pressure in the main film. Tests were conducted at 10krpm, 15krpm, and 20krpm to measure load capacity, power loss, and average film thickness. At 20krpm, a maximum axial load of 1711 N was achieved before bearing failure. Ultimately, the novel HFTB shows excellent static performance with potential for use in Organic Rankine Cycle (ORC) generators and other large oil-free turbomachines.

Dynamic Analysis of the De-Ballasting Operations of a Floating Dock with a Malfunctioning Pump

AbstractDuring normal de-ballasting operations for floating docks, each ballast pump independently manages a specific group of ballast tanks. However, when a pump malfunctions, a connection valve between the two groups of ballast water systems is opened. This allows the adjacent pump to serve as a helper pump, simultaneously controlling two groups of ballast water systems. This study explores a full-scale floating dock’s dynamic behaviours during the de-ballasting operations under this situation through a numerical model. In the developed numerical model, the dock is described as a six-degree-of-freedom rigid body which is subjected to hydrostatic, hydrodynamic, and mooring loads. A hydraulic model of the piping network of the malfunctioning pump and the helper pump is proposed. A modified P-controller regulates opening angles of all tank valves for minimal pitch and roll. Two configurations of the floating dock, i. e., a single floating dock and a floating dock with an onboard vessel, are considered. The numerical results show that the optimal helper pumps can be identified regarding the pumps’ total de-ballasting capacity and the dock’s stability. The most severe scenarios can be determined in term of the dock’s maximum draught differences caused by its roll and pitch. The observed maximum draught differences remain small relative to the dock’s width, indicating the effectiveness of employing helper pumps and the proposed automatic ballast control strategy for one-pump malfunction scenarios.

Nonlinear Static and Dynamic Responses of a Floating Rod Pendulum

Abstract A novel nonlinear dynamics model is developed in this paper to describe the static and dynamic nonlinear behaviors of a rod pendulum partially immersed in still water. The pendulum is hinged above the water level and subject to nonlinear gravity, hydrostatic, and hydrodynamic loads, all of which are incorporated into the system dynamics. The nonlinear static behavior and stability of the pendulum have been characterized by analyzing the fixed points. It is found that Pitchfork bifurcation governs the relationship between the rod density (the control parameter) and the static equilibrium angle. The pendulum's nonlinear response to external harmonic torque is obtained using Harmonic Balance Method (HBM). The influence of system parameters, including hinge height, rod diameter, and rod density, on the nonlinear frequency response is examined. Upon altering the system parameters, particularly the rod density, it is found that the system exhibits either a softening or a hardening effect.

Dynamic and structural analyses of floating dock operations considering dock-vessel coupling loads

Floating docks are important for increasing the capacity of land-based shipyards and serve as essential platforms for vessel construction, maintenance, and repair. As the size of modern vessels increases, ensuring the structural safety of the floating docks becomes challenging. To enhance the operational safety of the floating docks, this study aims to develop an in-house code for a comprehensive global response assessment of a full-scale floating dock. The code is developed under a quasi-static assumption and enables dynamic and structural response assessments for the floating dock and docked vessel during the vessel-docking operations. The floating dock and docked vessel are represented as rigid bodies with six degrees of freedom and subjected to hydrostatic, hydrodynamic, mooring, and contact loads. The piping network of the floating dock's ballast water system is modelled to calculate the flow rates out of all ballast tanks. A modified proportional controller (P-controller) is employed to achieve automatic ballast control, regulating opening angles of ballast tank valves to minimize roll and pitch motions of the floating dock and docked vessel. For structural response assessment, a bending model is proposed to evaluate the bending deformation of the floating dock based on the load distribution along the dock's length. Results show that the present code can successfully simulate the vessel-docking process. The automatic ballast control strategy effectively minimizes roll and pitch for both the floating dock and docked vessel, ensuring stable control of the entire system. Minimal discrepancies are observed in the dynamic responses and bending of the floating dock between one- and two-way couplings. The longitudinal shift of the docked vessel's centre of gravity (CoG) increases the relative motions between the docked vessel and the floating dock, especially in surge, sway and pitch. A significant shift distance might cause the mooring rope breakage. Positioning the vessel's CoG closer to the dock's CoG proves safer for vessel-docking operations. In general, the developed code can support the decision-making for dock masters and optimize the docking plan.

EXPERIMENTAL DETERMINATION OF FLOOR PANELS DEFORMABILITY OF A LARGE-PANEL SYSTEM BUILDING AFTER RENOVATION

This paper deals with a field tests of prefabricated reinforced concrete floor panels of a multistory building by the method of hydrostatic loading. Object of study is presented by 3 damaged floor slabs of a 9-storey residential building which was hit during the russian invasion. After renovation of panels using the constructive solution which consists of a reinforced build-up layer in the compressed zone (upper part) and additional external reinforcement in the stretched zone (lower part) connected to each other with the help of anchor connections, a series of tests with water loading were set. For creation of loading an inventory pool was used, which was gradually filled with water at a step of 1kN/m2. Maximum created loading level was 5kN/m2 which corresponds to the operational load. After reaching the maximum load, the panels were left under load for 15 hours and then fully unloaded in steps of 1kN/m2. For each panel two type of tests were established: first when panel had both upper and lower part of reinforcement, and second – when lower reinforcement within steel beams was removed. The idea of dismantling of steel beams connected with previously performed numerical analysis which gave to little difference in deflections of panels for these two cases. Deflection measurements at critical locations along with thorough visual inspection were conducted during the loading and unloading cycles. No damage was observed during the in-situ loading and unloading cycles. Maximum vertical deflection for panel before dismantling of beams lies in the diapason of 1.95-2.1mm and 2.31-2.4mm after they were removed. These results meet the requirements of regulatory restrictions on the maximum deflection equal to 20 mm for this structure. Difference in deflection for two cases doesn’t exceed 20% which allows to abandon the use of lower reinforcement in the form of steel beams in the future. As the size of the pool doesn’t cover the whole panel area, the equivalent uniformly distributed load was also calculated using Lira software. Keywords. Large panel system house, reinforcement, floor panel, method of hydrostatic loading, deflection.

Behavior of stressed skin corrugated sheet under hydrostatic loads

Water storage in buildings is an integral part of water supply, which can be used for firefighting and drinking. It can be divided into three categories: elevated, rooftop, and underground water tanks. This paper presents a novel water storage system consisting of thin-walled corrugated steel sheets, which can be installed in a multi-story building on any floor. Compared with a reinforced concrete tank, the integrated steel water tank can be fabricated and installed much faster and store freshwater more easily. To develop the system, a finite element model is developed, which is validated using the on-site measurements. Next, the model is used to conduct a parametric study to evaluate the effects of boundary conditions, panel depth, sheet thickness, trough-to-crest width ratio, and corrugation angle on the behavior of integrated steel water tanks. The model is further used to evaluate the water tank subjected to lateral diaphragm loads and report the tank stiffness under combined loads. Finally, an implementation guide for the steel tank is presented, showing the supporting system, vacuum and magnetic handling of steel panels, robotic welding techniques, and delivery. It can be concluded that the paneled steel tank can be an efficient solution for water storage inside buildings.

Environmental cell for USANS/SANS studies with aggressive fluids at high pressures and temperatures

The new (Ultra) Small Angle Neutron (USANS/SANS) cell provides in-situ monitoring capability of the evolving microstructure and physical properties of a wide range of natural and artificial materials. This modular, portable compact environmental cell is designed for thermal, mechanical and chemical loading measurements compatible with all neutron and X-ray-based research facilities worldwide that is fine-tuned to a specific beamline. A seamless integration of time-lapse structural information, on scales ranging from the sub-nano to the micrometre has been demonstrated in a series of USANS/SANS experiments performed on rock samples subjected to hydrostatic and uniaxial load, reactive fluid flow and elevated temperatures. The modular design of the cell allows optimisation for specific applications, ranging from cryogenic to temperatures over 500 °C, with plans for further extensions of this range in the future. Uniaxial mechanical stress up to 1000 bar, and sample surrounding fluid/gas pressure of up to 1000 bar in the constant pressure or constant flow rate mode can be applied independently to the sample during data acquisition. Due to the modular design, components such as windows, seals and pistons can be interchanged optimising the cell for use with chemically aggressive (including ultra-supercritical) fluids. This development supports research initiatives in geology, energy and minerals, resource engineering, civil engineering, material sciences, biotechnology, and medical sciences. The cell is also extendable for use in neutron diffraction and tomographic experiments.

Comparatively Design and Analyze Elevated Rectangular Water Reservoir with and without Bracing for Different Stagging Height

A water tank, like a container that stores liquids, are categorized based on shape studies predict the analysis and design of rectangular as well as circular overhead water tanks through the usage of STADD PRO software. Storage reservoirs, especially overhead tanks, serve the purpose of storing and distributing water to consumers. Water supply planning may not have been adequately done for the recently built Overhead Circular Tank to meet the increasing demands of the expanding urban population. Branched distribution systems could be in several scenarios, including rural irrigation and the distribution of reclaimed water. Time is approaching when the need to conserve and store water becomes so essential. In such moments, it is crucial to develop cost-effective methods for storing and distributing water. The water that is stored in overhead water tanks is strategically placed. The overhead tank is vital as it serves as a common public utility structure. The distribution to nearby areas can be done without the need for pumping!!! The cost efficiency of overhead storage water tanks relies significantly on the quantity of concrete and steel needed for tank construction. As an initial resolution to this issue, it is essential to develop a water storage project based on STAAD principles, famously known as Overhead Water Reservoir. The current study covers the analysis and design of an elevated circular water tank using STAAD.Pro V8i. The design involves manual load calculations and the analysis of the entire structure using STAAD Pro V8i. The method of design used in the STAAD.Pro analysis is Limit State Design; the water tank is being subjected to various loads such as wind load, deadload, self-weight, and hydrostatic load due to water.

Hydrostatic pressure mediates epithelial-mesenchymal transition of cholangiocytes through RhoA/ROCK and TGF-β/smad pathways.

Biomechanical cue within the tissue microenvironment is known to play a critical role in regulating cell behaviors and maintaining tissue homeostasis. As hydrostatic pressure often increases in biliary system under pathological states, we investigated the effect of the moderate elevation of the hydrostatic pressure on biliary epithelial cells, especially on the epithelial-mesenchymal transition (EMT). Human intrahepatic biliary epithelial cells were loaded to hydrostatic pressure using a commercial device. We found that loading the cells to 50 mmHg hydrostatic pressure induced obvious morphological changes and significantly upregulated vimentin, ZEB1, and pSmad2/3, fibronectin, and collagen 1α. All changes induced by hydrostatic pressure loading were effectively mitigated by either ROCK inhibitor (Y-27632) or ALK5 inhibitor (SB-431542). Our in vitro experimental data suggests that hydrostatic pressure loading induces EMT of cholangiocytes through RhoA/ROCK and TGF-β/Smad pathways. Elevated hydrostatic pressure in biliary duct system under pathological states may promote the biliary epithelial cells shifting to profibrotic and mesenchymal characteristics.

STUDY OF THE STRESS-STRAIN STATE OF A REINFORCED CONCRETE SLAB USING HYDROSTATIC METHOD

The scientific article is devoted to a complex study of the stress-strain state of a monolithic slab, implemented using the author’s method of hydrostatic loading, which involves setting the load by the weight of water and regulating its value by the height of the water column. To implement the given procedure, we used a tank-shaped facility for field tests of structures for vertical short-term and long-term loads. To determine the deflections of the loaded slab system, we installed mechanical deflection gauges of the 6PAO brand under the slab at pre-planned places. The short-term loading of the selected section of the monolithic reinforced concrete slab involved three stages. The first two stages of loading were carried out step by step, with a load step of 1–2 kN/m2 and a time delay until the arrows of the deflection gauges stopped. The maximum load on the slab was 5 kN/m2. The maximum deflection was recorded for point 2 (conventional centre of the tank) and was equal to 1.27 mm. The third stage of slab loading proceeded by analogy with the previous two. The maximum load on the slab was 8 kN/m2. The maximum deflection was recorded for point 2 and equalled 1.57 mm. After completing the stepped loading, the water tank was left on the slab to track vertical deflections for 32 days. The study experimentally established that the displacement of the examined slab in the span and support zones under increased load did not exceed the normative values. We carried out numerical verification using finite-element modelling followed by calculations in a linear and non-linear model. The theoretical and experimental calculation results showed a qualitative and quantitative data match (the difference did not exceed 15–20%). The nature of the change in the deflections remained practically linear and closely correlated with the experimental data (the values of the maximum deflections were equal to 1.16 and 1.57 mm, respectively, which was less than the maximum allowable deflection of 30 mm). Based on the results of the comprehensive study, we have made proposals for further safe operation of the investigated slab system through the use of lightweight floor elements (lighter filling, reduction of screed thickness, and others) to limit the total load on the overlapping to 10 kN/m2 (taking into account dead weight of the slab, load from floor structure and partitions, load from people and various types of construction and other equipment). Keywords: hydrostatic loading, testing, concrete, calculation, deflection, modelling.

A new yield criterion based constitutive model for porous materials

In the present work, a new explicit expression of macroscopic yield criterion is derived for porous materials, such as soil, rock and cement-based materials. To consider the asymmetric behavior between tensile and compression loading, the matrix is assumed to obey to a Drucker–Prager local criterion. The influence of porosity and the effect of matrix properties are well taken into account by this criterion. By using the stress variational approach with a suitable statically admissible stress field, a new more accurate estimation with a simple expression has been obtained for the case of purely deviatoric loading. The exact solutions can be retrieved by this criterion in the case of hydrostatic loading. It also resolves the problem of discontinuity between tension and compression. The weaknesses of the main existing criteria have been overcome by this new yield criterion. By comparing with the finite element numerical results with a wide range values of porosity and frictional parameter of the matrix, the proposed macroscopic yield criterion has a great accuracy and improves the existing ones. Based on this yield criterion, a complete constitutive model is constructed and implemented. This micro-mechanics based model is then applied to describe the mechanical behavior of porous sandstone, and validated by the comparisons with experimental results at different confining pressures.