Numerical Finite Element Analysis Research Articles

On the resonance frequency of the irregular shaped visco-acoustic Helmholtz cavity problem

In this paper we develop a closed-form mathematical solution for the resonance frequency of the axisymmetric irregular shaped visco-acoustic Helmholtz cavity problem. The solution is based on a conformal mapping that transforms the governing visco-acoustic equations of motion for the irregular cavity geometry into a new domain described by a set of orthogonal curvilinear coordinates. These orthogonal curvilinear coordinates have an important characteristic relative to the transformation of the physical boundary: the mapped domain is constructed such that the locus of all points for the length-wise profile of the physical boundary coincides with a constant value for a (quasi radial) coordinate in the new mapped domain. In these orthogonal curvilinear coordinates we obtain an analytical solution for the visco-acoustic equations of motion and exactly satisfy the no-slip fluid boundary conditions over the irregular shaped cavity walls by matching the coefficients of an orthogonal Legendre polynomial series representation for the non-uniform velocity on the cavity walls. The mathematical solution is an approximation to the extent that the scale factors chosen for the mapping consist of strictly the mutual-coupling terms of the true scale factors. Thus we analyze some results to understand the correlation of the analytical solution frequency response spectra with numerical finite element analyses of the idealized boundary conditions with various irregular shaped cavity geometries. The results for fundamental resonance frequency were found to exhibit good correlation with the results of finite element analyses over a significant range of fluid properties with different irregular cavity geometries. As the primary motivation for the derivation stems from the lack of a rapid yet accurate alternative to computationally intensive MultiPhysics FEA in the formulation of acoustic trendlines for sensor development, the solution’s acoustic impedance was applied as dispersive loading in a simple lumped parameter model of a fluid identification sensor for comparison. The resulting acoustic trendlines of the reduced (5 DOF) model were found to exhibit good correlation with the results of the MultiPhysics FEA (>105 DOF). Thus the solution was found to enable a closed-form analytical method for rapid construction of parametric studies in the practical design of fluid analysis sensors based on complex resonant cavity geometries.

Mechanised deep tunnel excavation in saturated clayey soils: a pre-design hydro-mechanically coupled method for the assessment of both spoil and face volume loss

Mechanised tunnel excavation in soils causes over-excavations, potentially leading to large amounts of spoil and settlements at ground level. An accurate estimation of over-excavations is crucial in the pre-design phase for assessing costs, determining the appropriate excavation method and choosing the muck management strategy. Currently, the estimation is based on experience and data from similar projects, but this becomes difficult when project conditions are heterogeneous. As an alternative, finite-element analyses are time-consuming and not suitable for early design stages; therefore, simplified tools are needed. In this paper, the authors present a simplified approach putting in relation face extrusion with estimated spoil mass and face volume loss. This approach, conceived for deep tunnels, is the extension to the case of mechanised tunnelling of a hydro-mechanical coupled meta-model derived from finite-element numerical analyses for tunnels in clayey soils excavated by using conventional techniques (i.e. without any use of tunnel-boring machines). The model has been validated against field data relative to a case study. The approach can be used in the early design process to identify tunnel-boring machine characteristics and provide preliminary cost estimates. In addition, during the construction phase, the method can be employed to interpret monitoring data and pre-design mitigation measures for unforeseen soil profile variations.

Biomechanical changes in the proximal femur before and after removal of femoral neck system

BackgroundAs an innovative internal fixation system, FNS (femoral neck system) is increasingly being utilized by surgeons for the treatment of femoral neck fractures. At present, there have been numerous finite element analysis experiments studying the immediate stability of FNS and CSS in treating femoral neck fractures. However, there is scarce mechanical analysis available regarding the effects post internal fixation removal. This study aimed to investigate the alterations in mechanical parameters of the proximal femur before and after the removal of FNS (femoral neck system), and to assess potential distinctions in indicators following the extraction of CSS (Cannulated Screws).MethodsA proximal femur model was reconstructed using finite element numerical techniques. The models for CSS and FNS were formulated utilizing characteristics and parametric definitions. The internal fixation was combined with a normal proximal femur model to simulate the healing state after fracture surgery. Within the framework of static analysis, consistent stress burdens were applied across the entirety of the models. The total deformation and equivalent stress of the proximal femur were recorded before and after the removal of internal fixation.ResultsUnder the standing condition, the total deformation of the model before and after removing CSS was 0.99 mm and 1.10 mm, respectively, indicating an increase of 12%. The total deformation of the model before and after removing FNS was 0.65 mm and 0.76 mm, respectively, indicating an increase of 17%. The equivalent stress for CSS and FNS were 55.21 MPa and 250.67 MPa, respectively. The average equivalent stress on the cross-section of the femoral neck before and after removal of CSS was 7.76 MPa and 6.11 MPa, respectively. The average equivalent stress on the cross-section of the femoral neck before and after removal of FNS was 9.89 MPa and 8.79 MPa, respectively.ConclusionsThe retention of internal fixation may contribute to improved stability of the proximal femur. However, there still existed risks of stress concentration in internal fixation and stress shielding in the proximal femur. Compared to CSS, the removal of FNS results in larger bone tunnels and insufficient model stability. Further clinical interventions are recommended to address this issue.

Numerical simulation and experimental study on the compression performance of a double layer cross-lattice-core sandwich structure

Lattice sandwich structures are widely used in many engineering fields for their excellent mechanical properties, such as aerospace, transportation, construction and so on. In this paper, a new type of double layer cross-lattice-core sandwich structure is proposed. Firstly, based on the nonlinear finite element software ABAQUS, a finite element numerical simulation analysis is processed to the sandwich structure unite cell under flat compression. The deflection pattern, load-displacement curve and internal energy-displacement curve are obtained to discuss the compression performance of the unite cell with some specific geometric parameters, such as arm length ratio, clamped angle and thickness of the cross-lattice-core. It is found that the compression performance of the lattice sandwich structure with an arm length ratio of 1 and an included angle of 90° is optimal. The energy absorption effect decreases slightly with the increases of the arm length ratio increases, which will be greatly reduced when the core angle is lower than 90°. Then the unite cell model of the structure is prepared using 3D printing technology, and its compression performance is investigated by flat compression tests and verified in comparison with the numerical analysis results. Finally, the load-bearing property of the structure is further verified by compression analysis of a plate structure consisting of several unite cells. The results provide a reference for the design and engineering application of the structure.

Estimating sliding displacement of slopes induced by earthquake sequences based on the finite element method

After shocks trigger or worsen landslides by exacerbating damage to slopes. In this study, slope sliding displacements induced by seismic sequences were calculated. The combined effects of mainshocks and aftershocks on slope sliding were examined in this study using 273 ground motion records from real seismic sequences. A three-layer clayey slope was modeled in OpenSees. The ground motions were input for dynamic analysis to calculate the corresponding sliding displacements. More than 20% of the seismic sequences caused slope instability. The Arias intensity (Ia) of the mainshock had the strongest correlation with sliding displacements. The strength reduction technique was used for the pseudo-static stability analysis of the slope whose yield acceleration (ky ) value was 0.23g. The Newmark method computed smaller displacements compared to the finite element method which calculated the dynamic behavior of the slope more accurately when Ts/Tm > 0.1. The Ia of the mainshock was the optimal parameter. An empirical model based on finite element numerical analysis was proposed for predicting slope sliding displacements induced by seismic sequences. The predictive model, unlike the traditional rigid sliding block method, prevented some unrealistic assumptions. The proposed model was more conservative than numerical algorithm-based predictive models that compute only the mainshock effect.

Tests and Seismic Response Analysis of Guided-Rail-Type Anti-Tensile Rubber Bearing

When subjected to seismic activity, tall isolated buildings with a high aspect ratio are susceptible to overturning as a result of the failure of rubber isolation bearings under tension. In order to address this issue, a guided-rail tension device (GR) has been developed to enhance the tensile strength of rubber bearings. Furthermore, a novel guided-rail isolation rubber bearing (GR&RB) has been proposed as a potential solution. Quasi-static tests have been conducted to investigate the mechanical properties of the GR, as well as the GR&LNR600 and LNR600. Additionally, numerical finite element analysis has been employed to study the seismic response of the GR&RB under El Centro seismic action in a high-rise building with an aspect ratio of approximately 4. The experimental results suggest that the inclusion of GRs has a limited effect on the horizontal mechanical attributes of rubber isolation bearings. Nevertheless, it simultaneously enhances their tensile strength, demonstrating a significant augmentation of 4.23 times. Moreover, the mechanical behavior of the GR aligns with the Hook model. The numerical analysis suggests that the utilization of GR&RB can mitigate the tensile stress levels of rubber isolators. Furthermore, it is recommended to augment the elastic tensile stiffness of the GR while reducing the open value to enhance the tensile efficiency, with the potential to attain up to 75% efficiency in tensile performance.

Research on Restoring Force Model Characteristics of Prestressed Steel Reinforced Concrete Frames

On the basis of reasonable selection of material constitutive model, the numerical model of singlebay prestressed section steel-concrete frame. was constructed by using ABAQUS and Open SEES finite element software, respectively, and numerical analyses of the whole process of monotonic and hysteretic force were carried out, and the hysteretic characteristics of this type of frame. structure were analyzed. The main parameters affecting the hysteresis characteristics of this type of frame. were determined through parametric analysis, and the restoring force model was established as a result. The results show that: the numerical model constructed by ABAQUS software can intuitively reflect the damage morphology and stress distribution of the frame, and the simulated peak load is 191kN, with an error of 10% from the test; the numerical model constructed by OPENSEES finite element software can macroscopically reflect the energy-consuming capacity of the frame, and the simulated peak load is 186kN, with an error of 12% from the test; both the axial compression ratio and the length to slenderness ratio are sensitive parameters of prestressed steel and concrete members, the load capacity of the specimen increases with the increase of the design axial compression ratio, and decreases with the increase of the length and slenderness ratio, but too small length and slenderness ratio leads to the destruction of the specimen faster, which is not conducive to the ductility of the specimen; the prestressing effect on the ductility of the hysteresis curve is not obvious; according to the mechanical properties of the section, the geometrical parameters of the member, the restoring force constructed by means of linear regression can be a good fit for this type of frame.

Experimental and Numerical Study on Flexural Behavior of Concrete Beams Using Notches and Repair Materials

In a concrete beam, cracking is generated on the tension side under the effect of flexure, shear, and torsional loadings. Accordingly, these weak concrete members require repair and/or strengthening to increase or restore their internal load capacity. In the current experimental and numerical investigations on concrete beams, the impact of using notches with different width to depth ratios on the ultimate flexural load under a three-point test was considered. Further, the flexural behavior performance of a notched concrete beam repaired using the three repair materials—cement mortar, bacterial mortar, and adhesive—was also examined. Consequently, a comparative study was implemented between the experimental and numerical results. A concrete damage plasticity (CDP) model was used for the finite element numerical analysis of the beams. The differences in numerical and experimental measured results ranged from 0.65 to 22.20% for the ultimate load carrying capacity. As the notch size increased, the ultimate load carrying capacity of the beam reduced. Additionally, a linear regression model was used to predict the ultimate load values at a notch width interval of 5 mm up to a maximum notch width of 100 mm. It was observed that the ultimate load capacity for a repaired beam increased as compared to the notched beam for all three repair materials under consideration. And the maximum ultimate load increased in the case of notched beams repaired using adhesive. Furthermore, in comparison to the cement mortar, the performance of the bacterial mortar in terms of the ultimate load was more. The bacterial mortar was found to be more sustainable and more durable as a repair material for concrete structures.

Experimental and numerical study on mechanical performance of single shear bolted connections with novel elliptical one-sided bolts

One-sided bolts, which typically employed for connecting components with closed cross section, often present complexities in both construction and installation. Addressing the limitations of conventional one-sided bolts, this study introduces a novel variant distinguished by its elliptical head, offering ease of installation without the need for specialized tools. Due to the special shape of the bolt head, the mechanical properties of the bolt need to be studied in depth. To investigate the shear properties of the novel elliptical one-sided bolts, three sets of single lap shear experiments were conducted. Subsequently, finite element numerical analyses were employed to simulate these experiments, facilitating the development of a reliable finite element model. Furthermore, parametric analyses were undertaken to examine the influence of various parameters on the ultimate shearing capacity and displacement of joints. The findings indicate that the shear capacity of the single lap joint employing novel elliptical one-sided bolts closely rivals that of ordinary hexagonal bolts with equivalent diameters. However, an enhancement in slip resistance capacity is observed in the novel elliptical one-sided bolt joints compared to hexagonal bolts. Notably, the parameters of the bolt exert a more pronounced impact on the ultimate shearing capacity and displacement of joints when contrasted with parameters associated with the plates. The recommended torque coefficient for the novel elliptical one-sided bolt is established as 0.2, and it is recommended to use appropriate torque to ensure the slip performance of the joint during practical application.

The prediction of residual stress of welding process based on deep neural network

The welding process has been an efficient method for producing essential and complex manufacturing parts in various industrial design fields. The post-weld residual stress can have detrimental effects on welded components. Therefore, systematic studies of residual stress are essential for evaluating welding behaviors and mechanisms in welded structures. They can provide a valuable reference and optimization for addressing residual stress relief. Numerical finite element analyses based on thermal-mechanical models offer a comprehensive approach to simulate real welding, providing a reliable means to determine and quantify the distribution of residual stress based on welding parameters and material properties. Furthermore, the finite element analysis is capable of generating adequate and dependable datasets in relation to the classical experiment. However, the finite element simulation is not considered an efficient method for predicting the magnitude and distortion of residual stress due to its high computational cost. A deep learning framework with powerful automatic learning abilities could potentially be used as an alternative method to efficiently predict residual stress. The purpose of the current study is to propose an innovative modeling approach for accurately and effectively predicting residual stress. A deep network model with Convolutional Neural Network using Adam optimization is integrated with numerical finite element analyses of a single-pass beam weld in SUS304 stainless steel. Finite element analysis is used to generate extensive residual stress datasets, which are partly used to train the deep network model and partly used for model validation. The deep network model aligns closely with the finite element analysis results, with a root-mean-square error (RMSE) of less than 12, an absolute fraction of variation (R2) of greater than 0.95, a mean absolute error (MAE) of less than 6.8 and a mean absolute percentage error (MAPE) of less than 1.1. Furthermore, this study highlights the potential advantage of using a deep network model with strong memory capabilities to directly predict residual stress for identical structural components and welding processes.

Finite Element Analysis and Fatigue Test of INTEGRA Dental Implant System.

The study involved numerical FEA (finite element analysis) of dental implants. Based on this, fatigue tests were conducted according to the PN-EN 14801 standard required for the certification of dental products. Thanks to the research methodology developed by the authors, it was possible to conduct a thorough analysis of the impact of external and internal factors such as material, geometry, loading, and assembly of the dental system on the achieved value of fatigue strength limit in the examined object. For this purpose, FEM studies were based on identifying potential sites of fatigue crack initiation in reference to the results of the test conducted on a real model. The actions described in the study helped in the final evaluation of the dental system design process named by the manufacturer as INTEGRA OPTIMA 3.35. The objective of the research was to identify potential sites for fatigue crack initiation in a selected dental system built on the INTEGRA OPTIMA 3.35 set. The material used in the research was titanium grade 4. A map of reduced von Mises stresses was used to search for potential fatigue crack areas. The research [loading] was conducted on two mutually perpendicular planes positioned in such a way that the edge intersecting the planes coincided with the axis of the system. The research indicated that the connecting screw showed the least sensitivity (stress change) to the change in the loading plane, while the value of preload has a significant impact on the achieved fatigue strength of the system. In contrast, the endosteal implant (root) and the prosthetic connector showed the greatest sensitivity to the change in the loading plane. The method of mounting [securing] the endosteal implant using a holder, despite meeting the standards, may contribute to generating excessive stress concentration in the threaded part. Observation of the prosthetic connector in the Optima 3.35 system, cyclically loaded with a force of F ≈ 300 N in the area of the upper hexagonal peg, revealed a fatigue fracture. The observed change in stress peak in the dental connector for two different force application surfaces shows that the positioning of the dental system (setting of the socket in relation to the force action plane) is significantly decisive in estimating the limited fatigue strength.

Efficient technique for evaluation of three-dimensional elastic–plastic fracture mechanics parameters based on equivalent distributed stress concept

This study proposes an efficient technique for the evaluation of the elastic–plastic fracture mechanics (EPFM) parameters of three-dimensional (3D) cracks based on the modified crack cohesive force (CCF) model. In the current method, the 3D crack’s EPFM parameters are analyzed by applying the pseudo crack face traction (CFT) to a two-dimensional (2D) center crack in an infinite plate. This pseudo traction is called the equivalent distributed stress (EDS). The EDS to be applied on the 2D center crack is determined in a manner that reproduces the relationship between crack length and stress intensity factor (SIF) of the intended 3D crack. Once EDS is determined, EPFM parameters for 3D cracks can be obtained instantly by using the center crack’s analytical closed-form solutions. This approach can compute the 3D crack’s EPFM parameters in dramatically less computation time than 3D finite element (FE) analysis. The effectiveness of the proposed method is validated by comparing the EPFM parameters of a 3D penny-shape crack obtained from this method against the reference analytical solutions and numerical FE analysis results. The parameters determined by the present method show excellent agreement with the reference solutions.

Numerical biomechanical finite element analysis of different trimming line designs of orthodontic aligners: An in silico study

A finite element model was used to investigate the effect of different designs and thicknesses of orthodontic aligner margins on their biomechanical behavior. A three-dimensional data set of an upper jaw was imported into the 3-matic software. The upper right central incisor tooth (Tooth 11) was separated from the remaining model, and its periodontal ligament and surrounding bone were designed. Aligners were designed with four different trimming lines (scalloped, straight, scalloped extended, straight extended), each with four different thicknesses (0.3, 0.4, 0.5, and 0.6 mm). The models were imported into a finite element package (Marc/Mentat). A linear elastic constitutive material model was applied. A facial 0.2 mm bodily malalignment of tooth 11 was simulated. The maximum resultant force was in the range of 1.0 N to 2.2 N. The straight trimming designs deliver higher resultant forces compared with scalloped trimming designs. Increasing the aligner thickness and/or extending the aligner edge beyond the gingival line leads to an increase in the resultant force. All designs showed an uneven distribution of the normal contact forces over the tooth surface with a predominant concentration toward the cervical third and distal third, particularly with the extended trimming designs. All designs showed uncontrolled tipping of the tooth. Based on the current model outcomes, the use of a straight extended trimming line design for aligners is favored because of its positive impact on force distribution and, consequently, the control of tooth movement. These findings provide aligner companies and orthodontists a valuable biomechanical evidence and guidance to enhance control over tooth movement and therefore optimize treatment outcomes. This can be achieved by trimming the edges of aligners with a straight extended design and selecting the appropriate aligner thickness.

Numerical Simulations of Failure Mechanism for Silty Clay Slopes in Seasonally Frozen Ground

Landslide damage to soil graben slopes in seasonal freezing zones is a crucial concern for highway slope safety, particularly in the northeast region of China where permafrost thawing is significant during the spring. The region has abundant seasonal permafrost and mostly comprises powdery clay soil that is susceptible to landslides due to persistent frost and thaw cycles. The collapse of a slope due to thawing and sliding not only disrupts highway operations but also generates lasting implications for environmental stability, economic resilience, and social well-being. By understanding and addressing the underlying mechanisms causing such events, we can directly contribute to the sustainable development of the region. Based on the Suihua–Beian highway graben slope landslide-management project, this paper establishes a three-dimensional finite element model of a seasonal permafrost slope using COMSOL Multiphysics 6.1 finite element numerical analysis software. Additionally, the PDE mathematical module of the software is redeveloped to perform hydrothermal-coupling calculations of seasonal permafrost slopes. The simulation results yielded the dynamic distribution characteristics of the temperature and seepage field on the slope during the F–T process. The mechanism behind the slope thawing and sliding was also unveiled. The findings provide crucial technical support for the rational analysis of slope stability, prevention of sliding, and effective control measures, establishing a direct linkage to the promotion of sustainable infrastructure development in the context of transportation and roadway engineering.

Structural optimization of trays in bolt support systems

Abstract Fiber reinforced polymer (FRP) have the advantages of high strength, corrosion resistance, and low density, which are widely used to serve as tray products in bolt support systems. As a key component, the low mechanical load-bearing capacity of trays significantly limits their widespread application. Besides, there is no corresponding theoretical calculations and strength analysis methods for the structural design. The aim of this study is to optimize the tray structure and improve its load-bearing capacity. Through theoretical calculations and finite element numerical analysis, the effect of inner surface taper and stiffener height on the load-bearing capacity of the tray under the application of constant axial force is investigated. The results show that first of all, the larger the inner surface taper is, the better the load capacity of the tray. Second, the special-shaped truncated cone type displayed better load capacity than the stiffener tray. Third, the higher the design height of the stiffener is, the smaller the deformation and shear stress on the top of the inner surface of the tray, and better load capacity is achieved. We believe that this study provides theoretical guidance for the structural design of high-performance FRP trays.

Enhanced Mechanical Properties of Lattice Structures Enabled by Tailoring Oblique Truss Orientation Angle

The significant effect of the strut angle on the mechanical properties of strut‐based lattice structures is systematically explored through experimental and numerical investigations. The highest values of elastic modulus and yield strength, surpassing those observed in cubic lattices with the same relative density, have been experimentally observed at the strut angle of 71.76°. A correlation among elastic modulus, yield strength, and strut angles in lattices, validated by experimental tests, has been identified through developing a theoretical modelling and conducting a detailed finite element analysis. Transition from a bending dominated deformation mechanism to one dominated by compression within the lattice structures has been realized, contingent upon the tailoring of the strut angle. The deformation mechanism of these lattices is significantly influenced by the interplay between ductile bending and brittle failure of the struts. The superior energy absorption and yield strength demonstrated by the optimized lattice design have been underscored through a comparative analysis with other previously reported lattices. These lightweight structures hold promise for applications in the development of mechanical metamaterials with on‐demand mechanical properties.

Seismic performance and vulnerability analysis for bifurcated tunnels in soft soil

This paper investigates the seismic performance of complex comprehensive interchange underground structures. As an example, the seismic performance of Nanjing underground bifurcated tunnels constructed in soft soil is analyzed. A three-dimensional (3D) numerical finite element analysis model is established considering soil-tunnel interaction to analyze the seismic response characteristics and failure mechanism of the bifurcated tunnels. The results show that the tunnel damage degree is closely associated with the deformation response, and that the inter-story drift ratio of the lower layer is significantly greater than that of the upper layer. The pushover analysis method is used to obtain the seismic performance curve of the tunnel, and inter-story drift ratio limits are defined. The IDA procedure is then used to conduct multiple non-linear dynamic time history analyses based on the 3D finite element model, and IDA curve clusters are drawn with peak ground acceleration (PGA) as the earthquake intensity measures and the peak inter-story drift ratio as the damage measures of tunnels. The corresponding IDA percentiles lines are calculated, and the seismic fragility curves of the bifurcated tunnels are established. The post-earthquake functional failure probability of the bifurcated tunnels is obtained under different seismic fortification performance level.

Research on the suppression method of sensor impact vibration parasitic effects in surface reflection pressure measurement.

Ground reflection pressure plays a crucial role in evaluating the destructive power of ammunition explosions. Accurately measuring this pressure is essential for assessing ammunition's destructive capability and guiding ammunition design. In this study, a theoretical analysis of the parasitic effect of shock and vibration was conducted and COMSOL was employed for performing a multi-physics finite element numerical simulation analysis to elucidate the attenuation characteristics of stress waves in commonly used shock- and vibration-resistant materials. Furthermore, a device was designed using aluminum foam and polytetrafluoroethylene to mitigate the parasitic effects on the ground reflection pressure sensor. Experimental testing was conducted to validate the device's effectiveness. The results demonstrated that the device successfully reduced the intensity of stress waves reaching the ground reflection pressure sensor, with a relative attenuation rate of 29.6% in peak stress values. The sensor measurements obtained with the suppression device exhibited smoother curves and higher signal-to-noise ratios, significantly improving the reliability of the measurement results. Our study holds considerable engineering application value in enhancing the accuracy of shock wave pressure measurements in explosive fields.

Thermal insulation performance of buildings with phase-change energy-storage wall structures

Considering that improving the energy efficiency of buildings is crucial to achieving China's carbon neutrality goal, the application of phase-change energy-storage (PCES) technology could be considered a practical and feasible approach. Currently, the heat transfer characteristics of PCES walls and their influence mechanisms on the indoor building environment are the key issues to be solved in this field. Based on gypsum-based phase-change materials (PCMs), outdoor, indoor and central PCES walls are designed in this study. Unsteady heat transfer experiments, finite element numerical simulations and energy consumption analyses were used to study the thermal behaviour of PCES walls, and the thermal insulation performance of the buildings utilizing these wall structures were assessed. The results show that the maximum temperature of inner surface of wall with PCMs applying at the interior side is reduced by 0.6 °C, and the maximum temperature lag is reduced by 0.8 h. The results also prove that buildings employing this PCES walls as envelope have a reduction of annual cooling energy consumption about 7.6%, and a reduction of annual carbon dioxide emissions by about 2%, comparing with conventional buildings. Thus, these results suggest that the use of PCES walls can effectively enhance the thermal insulation performance of buildings in summer. This research could provide an innovative idea for the design of PCES walls, which is of significance for the application of PCES walls in severe cold regions.

Calibration and verification of creep parameters for concrete

Concrete is a material which undergoes slow increasing deformation while subjected to persistent mechanical stress. This phenomenon is known as creep. In concrete material, creep occurs at all stress levels. Additional deformation of concrete structures at the end of their design working life caused by creep is usually two to three times of the immediate elastic deformation value, but might be even more in some cases. The value is dependent on many parameters, e.g. concrete grade, cement class, ambient environment relative humidity, geometry of the structure (drying surface of concrete in contact with air) and also the age of concrete at the time of loading. According to corresponding European standard, the effects of creep are evaluated using creep coefficient, and should be considered for verification of serviceability limit states, and if significant, also at ultimate limit states. In order to evaluate the creep effects in geometrically more complex structures, numerical finite element (FEM) analyses might be conducted. In commercially available software ANSYS, there is a library of several implicit creep equations, with several input parameters. These parameters need to be calibrated in order to match the assumptions of the creep effects over time in accordance with the corresponding European standard. In this study, calibration process of European standard concrete C35/45 parameters for selected implicit creep equation from ANSYS library is presented. The parameters are calibrated for two different ambient relative humidity (RH) levels, 78.8% and 90%, each for concrete loaded in 28 days (also 90 days for RH 78.8% and 50 days for RH 90%) after its casting, and suitable for finite element analysis of creep effects within the first year after loading of the concrete structure. The calibration process is split into two parts, analytical one conducted in table processor, where approximate estimations of suitable parameter values are determined. The second part consist of the subsequent optimization process in OptiSLang software, where the optimal parameter values are determined in order to achieve the best match between the time dependent Eurocode standard creep coefficient and the creep coefficient based on the results of one solid element uniaxial compression test in ANSYS finite element software. The obtained parameters are then verified on an analysis of a simply-supported concrete beam modelled of solid 3D finite elements. The values of selected creep equation parameters are summarized in the table, and might be used in the subsequent ongoing research.