Concentrated Load Research Articles

Research on the Application of Cushion and Isolation Materials in Protecting the over Shield Tunnel

The portal frame, as an innovative subway protection structure, primarily serves the development of underground spaces above shield tunneling for subways. It comprises foundation piles along both sides of the tunnel and a transition thick plate. When the transfer thick plate sustains loads at its midspan, deformation occurs, interacting with the underlying soil to generate additional stresses, thereby potentially impacting the subway tunnel beneath negatively. This study, anchored in the real-case scenario of Qianhai Exchange Square, employs finite element analysis to investigate the interaction mechanisms between the transfer thick plate under midspan loading and soils of varying properties. Findings revealed a characteristic distribution pattern of additional stresses in the soil—smaller at the edges and larger at the center. Furthermore, under equal loading conditions, there's a positive correlation between soil stiffness and induced additional stress, while an inverse relationship exists with the vertical deformation of the transfer thick plate. In response to this issue, the paper innovatively proposes embedding a cushioning and isolation layer under the transfer thick plate. Based on the results of full-scale tunnel tests carried out during the early stages of the project, and by employing high-precision finite element simulations, the bearing capacity of the tunnel was determined. This analysis, in turn, informed the formulation of selection principles for the cushioning and isolation materials in a feedback manner. Computational verifications showed that appropriately designing the cushioning and isolation layer can significantly reduce additional stresses in the foundation soil, thereby effectively alleviating the impact of concentrated upper loads on the shield tunnel.

Forced vibrations of an elastic triangular plate supported around its perimeter by a unilateral support via the Chebyshev polynomial expansion

The present study introduces static and dynamic analysis of an elastic triangular plate on unilateral edge supports, including forced vibrations due to loading and unloading excitation. The plate is assumed to be subjected to a uniformly distributed load and an eccentrically applied concentrated load. Furthermore, the loads are assumed to display dynamic variations. The governing equation of the problem is derived by considering the static and the dynamic responses of the plate by including inertia forces. The analytical solution is conducted by employing a series of Chebyshev polynomials for the admissible displacement functions and using Lagrange’s equations of motion. Having found the governing equation of the problem, an approximate numerical solution is accomplished using an iterative process due to the non-linear properties of the unilateral edge supports. The static behavior of the plate under a concentrated load is investigated in detail numerically by considering a wide range of parameters of the plate geometry and the stiffness of the support. In deriving the governing equation of the problem and in the numerical solution, special care is taken to use nondimensional parameters. This approach ensures that the analysis and conclusions remain valid across a wide range of parameter values. Dynamic treatment of the problem is carried out in the time domain by assuming a stepwise time variation of the concentrated load and by employing the constant acceleration procedure in the numerical solution of the system of governing differential equations derived from the equation of motion. Time variations of the displacements, the contact points, and the reactions of the plate’s support are presented in figures for various values of the parameters of the plate, as well as those of the supports, particularly focusing on the non-linearity of the problem due to the plate liftoff from the unilateral support. The effects of the parameters and the loading are investigated in detail. The results reveal that the unilateral property of the support stiffness significantly affects the static and dynamic behavior of the triangular plate. The analysis can be extended easily to cover a general type of loading as well. The main issues addressed in this study include: the analysis of a triangular plate with unilateral perimeter support that does not resist tensile forces; the use of Chebyshev polynomials as admissible functions in both directions; the consideration of static and dynamic loads; the determination of lifting areas of the support in both cases and the assessment of the global vertical force balance in the plate, including inertia forces in the dynamic case.

Numerical modeling of the punching shear behavior of biaxially loaded RC footings

In this study, the punching shear behavior of footings under biaxial eccentric loads is numerically investigated. Load eccentricities usually encountered in practice were primarily investigated on flat slabs, whereby the research on footings is still limited. Since the structural behavior of thick footings is significantly different compared to that of thin ones due to fracture mechanics, further investigations are required. To gain a deep understanding of the punching shear behavior of footings under biaxial eccentric loads, a numerical investigation was conducted. A finite element model was developed and validated against multiple experimental results in terms of load-deflection behavior and crack patterns. The validated model was then employed to examine the effect of different biaxial load eccentricities, different shear spans to effective depth ratios, column sizes, and column shapes. Finally, the numerical results were used for analyzing the design approach of the latest version of Eurocode 2 (FprEC2-2023). The numerical results showed a gradual transition between a fully developed punching shear cone to a partially formed cone without shear crack formation on the less loaded side with increasing load eccentricities. Additionally, larger load eccentricities lead to significantly increased rotation of the footing accompanied by a reduction of the punching shear capacity. A more pronounced influence of the effect of unbalanced moments on the punching shear capacity was identified in footings with a larger shear span to effective depth ratio. Furthermore, the effect of column size was more pronounced in small shear spans under concentric loads, while the effect was greater in footings with a larger shear span to depth ratio under eccentric loads. However, the beneficial effect of a larger column size was more pronounced for eccentric loads compared to concentric loading. Overall, the results indicate a good agreement with the design approach of Eurocode (FprEC2) for square columns. However, in some cases, the prediction was underestimated. Modified approaches from the literature for considering the effect of load eccentricity were found to address the underestimated cases safely. The results of this study demonstrated the applicability of the new design approaches for eccentric punching shear in footings under biaxial eccentric loads.

Design, simulation and experiment study of a snap-fit spatial self-locking system for energy absorption

Due to the strong destructiveness and poor predictability of the impact loading, energy absorption structures are easy to cause secondary damage in emergency situations. The proposed self-locking system for energy absorption can effectively solve this problem, but also can realize fast installation, disassembly and free editing. In this paper, a new snap-fit spatial self-locking energy absorption system is designed according to the self-locking idea of mortise and tenon structure. Firstly, the effects of concentrated loading, uniform distributed loading and friction properties on the self-locking characteristics under nine different spatial directions are studied by finite element simulation. Then, the crushing mechanism is revealed by impact experiment, and the performance and engineering adaptability of the existing self-locking energy absorption systems are compared. Finally, the design criteria for the system is derived. The results show that the system will not fly away under the impact loading in any spatial direction, and has good self-locking characteristics, while the friction properties have little effect on the self-locking characteristics of the system. In addition, under the uniform distributed loading, the deformation mode is the most regular in the direction 3, and the specific energy absorption in the direction 9 is as high as 7.07 J/g. Furthermore, when the total number of the structural unit in the self-locking energy absorption system is not less than twelve, the total energy absorption is linear with the number of layers, width and total number of the structural unit. Consequently, this study provides a new research idea for the design and feasibility of the self-locking energy absorption system.

Edge-selective reconfiguration in polarized lattices with magnet-enabled bistability

The signature topological feature of Maxwell lattices is their polarization, which manifests as an unbalance in stiffness between opposite edges of a finite domain. The manifestation of this asymmetry is especially dramatic in the case of soft lattices undergoing large nonlinear deformation under concentrated loads, where the excess of softness at the soft edge can result in the activation of sharp indentations. This study explores how this mechanical dichotomy between edges can be tuned and possibly extremized by working with soft magneto-mechanical metamaterials. The magneto-mechanical coupling is obtained by endowing the lattice sites with permanent magnets, which activate a network of magnetic forces that can interact with – either augmenting or competing with – the elasticity of the material. Specifically, under sufficiently large deformation that macroscopically alters the equilibrium positions of the sites, the attractive forces between the magnets can trigger bistable reconfiguration mechanisms. The strength of such mechanisms depends on the landscapes of elastic reaction forces exhibited by the edges, which are different due to the polarization, and is therefore inherently edge-selective. We show that, on the soft edge, the addition of magnets simply enhances the softness of the edge. In contrast, on the stiff edge, the magnets activate snapping mechanisms that locally reconfigure the cells and produce a lattice response reminiscent of plasticity, characterized by residual deformation that persists upon unloading.

Response of group piles subjected to coupled vertical-eccentric lateral-seismic loads

In seismic prone regions, analyzing loaded pile groups can be challenging because of limitations in conventional design methods and the inability of small-scale laboratory tests to accurately replicate the real behavior. Studying how pile group response is affected by the combined impact of vertical, concentric, and seismic loads is challenging. One of the limitations pertains to the intricacy of scaling up experiments, particularly in creating large-scale laboratory models. Thus, a numerical analysis may be appropriate for capturing the response. This study aimed to understand the pile group response in dense sand subjected to vertical, eccentric lateral, and seismic loadings via a large-scale 3D nonlinear finite element model. The validation results indicate that the numerical approach accurately predicts the behavior of pile groups in dense sand. Then, two different layouts of pile groups are analyzed under various loading scenarios on the basis of the recorded data from the El Centro earthquake. The results revealed that the number and arrangement of piles significantly affect the induced settlement. Compared with the 5-pile groups, the 3-pile groups presented higher maximum bending moments under vertical loading. However, the response of the 5-pile groups varied, as they experienced higher bending moment values without vertical loading. The peak lateral soil pressures were higher in the 3-pile groups. Some significant variations appeared in the induced torque resistances when the 5-pile groups were compared with the 3-pile groups. This study demonstrated the reliability of the used numerical approach for analyzing the response of pile groups in dense sand, as an alternative to laboratory test models.

Structural response reconstruction of beam-like bridge based on equivalent loads under moving forces

Response reconstruction has advantages in enriching monitoring data with high quality and it is of great importance to bridge structural health monitoring. However, there still are many current difficulties with response reconstruction due to the complex operation of bridges, e.g., hard to deal with time-varying positions of vehicles and inefficient reconstruction for cases with a long time. According to the theory of equivalent load identification, this paper proposes a model-based method for reconstructing responses induced by moving forces. The proposed method introduces moving time windows to extract the measured responses in an orderly manner and re-organizes them into a matrix form. The measured responses, expressed in matrix form, then serve as the input data to identify both equivalent loads and structural initial conditions, but not to estimate the actual moving forces. Herein, the equivalent loads represent some concentrated loads with time-invariant acting positions and are employed to approximately re-express the main information of moving forces. Matrix regularization with a sparse penalty term is used to ensure the robustness of identified results. Since the structural inputs have been estimated, the structural responses happening at the validation sensors then can be calculated as a forward problem. In this process, the role of identified structural inputs is an intermediate variable connecting the measuring sensors and the validation sensors so that, the transmissibility function (TF) discussed in the proposed method is expressed in an implicit pattern. Compared to the response reconstruction methods developed from moving force identification (MFI), an obvious characteristic is that information on the actual moving forces is no longer necessary. Therefore, it can bring convenience in practical application such as the time-varying positions of moving vehicles are not needed in advance. In addition, the application of matrix regularization has the potential for efficient computation. To verify the feasibility and effectiveness of the proposed method, both numerical simulations and experimental studies are finally carried out. The illustrated results indicate that the proposed method can accurately reconstruct the structural response. In addition, some related issues are also discussed.

Numerical Analysis of the Cylindrical Shell Pipe with Preformed Holes Subjected to a Compressive Load Using Non-Uniform Rational B-Splines and T-Splines for an Isogeometric Analysis Approach

In this paper, we implement the finite detail technique primarily based on T-Splines for approximating solutions to the linear elasticity equations in the connected and bounded Lipschitz domain. Both theoretical and numerical analyses of the Dirichlet and Neumann boundary problems are presented. The Reissner–Mindlin (RM) hypothesis is considered for the investigation of the mechanical performance of a 3D cylindrical shell pipe without and with preformed hole problems under concentrated and compression loading in the linear elastic behavior for trimmed and untrimmed surfaces in structural engineering problems. Bézier extraction from T-Splines is integrated for an isogeometric analysis (IGA) approach. The numerical results obtained, particularly for the displacement and von Mises stress, are compared with and validated against the literature results, particularly with those for Non-Uniform Rational B-Spline (NURBS) IGA and the finite element method (FEM) Abaqus methods. The obtained results show that the computation time of the IGA based on the T-Spline method is shorter than that of the IGA NURBS and FEM Abaqus/CAE (computer-aided engineering) methods. Furthermore, the highlighted results confirm that the IGA approach based on the T-Spline method shows more success than numerical reference methods. We observed that the NURBS IGA method is very limited for studying trimmed surfaces. The T-Spline method shows its power and capability in computing trimmed and untrimmed surfaces.

Acoustic Radiation Characteristics of a Forced Vibrating Elastic Panel Under Thermal Environments

This paper presents the thermo-acoustic frequency response of an un-baffled rectangular panel subjected to an external excitation load. A boundary element method BEM has been employed taking into account the Kirchhoff-Helmholtz K-H integral equation for the acoustic pressure and with the fluid-plate interface boundary condition the acoustic pressure jump over the panel is calculated. The thermal effects are considered regarding in the form of a uniform increment of temperature of the panel and are analysed in order to prevent the buckling phenomena. The excitation force considered is in the form of a concentrated load at some point of the panel and the deformation modes correspond to the vacuum case. Applying a collocation method for the panel equation, a frequency transfer function is obtained that relates the deflexion of the panel with the applied load. The effect of several geometric parameters, different thermal loads and location of the load applied on the acoustic radiated power and the acoustic efficiency spectrum are evaluated. Furthermore, the influence of the excitation frequency on the sound directivity is evaluated. The verification of the method is proven with other works.

On two contact problems for a half-plane with static friction

Abstract Exact solutions of two contact problems are constructed for a half-plane, when a finite number of absolutely rigid flat punches with friction are pressed into the half-plane under the influence of different concentrated loads, and when a periodic system of absolutely rigid flat punches with friction is pressed into the half-plane. It is assumed that friction in contact zones is associated with normal contact pressure by the generalized law of dry friction, in which the coefficient of friction depends on the coordinates of the contacting points of the contacting bodies and is directly proportional to the difference between the coordinates of these points and the coordinates of the middle points of the contact zones. The governing equations of the posed problems were obtained in the form of singular integral equations with variable coefficients relative to the contact pressure and their closed solutions were constructed.

Response surface test simulation of locking system reliability considering kinematic pair wear evolution

The concentrated load endured by the locking system during the weapon mounting and release procedures may lead to mechanical wear in hinges and kinematic pairs, thereby influencing the functional reliability of the weapon rack mechanism system. This study aims to investigate the impact of kinematic pair wear evolution on the reliability of the locking system. Firstly, a rigid-flexible coupling multi-body dynamics model of the locking system was established to simulate the dynamic behaviors of the rack under different loading conditions. Moreover, the wear amounts of the main kinematic pairs were precisely calculated by the Archard wear model to provide data support for the subsequent reliability analysis. Subsequently, the response surface method was employed to design the orthogonal experiments for the reliability analysis of the locking system, and the reliability degradation law of the locking system within the design lifespan was obtained through the Monte Carlo method simulation. The research findings indicate that the wear of kinematic pairs has a significant effect on the motion function and accuracy of the mechanism. The motion reliability of the mechanism can be maintained above 99% within the design lifespan. Nevertheless, when the usage time exceeds twice the design lifespan, the reliability drops significantly to approximately 85%, and the influence degrees of different wear positions on the reliability were obtained through the sensitivity analysis. The research results not only provide a scientific basis for the optimal design of the locking system but also offer a novel perspective and method for the reliability assessment and maintenance strategy of the weapon rack locking system.

Elastica-plastica theory of Euler-Bernoulli beams subjected to concentrated loads

Elastica theory plays an important role in the study of large displacements of slender rods. However, the majority of the studies are still limited to elastic material only. In this paper, the traditional elastica theory is extended to an elastica-plastica theory.For the Euler-Bernoulli beams subjected to concentrated loads, the Legendre elliptic integral solution to elastic rods and the plastica solution to elastic-perfectly plastic rods are used. The deformations of elastic-perfectly plastic rods are classified into several cases, and the classification criteria are given. Furthermore, general solving methods that are applicable to various loading conditions are proposed. For an initial value problem, the highly efficient and accurate solution is completely analytical, while for a boundary value problem, the solution adopts a combination of the shooting method and the quasi-Newton method. The accuracy of the current elastica-plastica theory is verified by the corresponding two-dimensional FE simulations.

Experimental investigation of flexural and punching behavior for plain PE-ECC slabs with different fiber volume fractions and span-depth ratios

Engineered Cementitious Composite (ECC) exhibits superior tensile ductility, shear capacity, and crack-control ability in comparison to traditional concrete and fiber reinforced concrete. These attributes render ECC a suitable candidate for addressing the brittle punching shear behavior commonly observed in reinforced concrete (RC) flat slabs. To verify the feasibility of using ECC for strengthening the punching shear capacity of concrete slabs, an investigation on the punching behavior of plain ECC slabs was conducted to ascertain their crack patterns, failure mode, strength and energy absorption capacity by means of experiments on twenty-seven 400 mm×400 mm square slabs. The plain ECC slabs were simply supported on a bespoke steel framework with eight supports, centrically loaded with a concentrated load. The fiber volume fraction (FVF) and span-depth ratio (SDR) are the two variables to be examined for their effects on the punching behavior of ECC slabs. Test results revealed that the incorporation of fibers significantly improved the load-bearing capacity, ductility and energy absorption capacity, while it altered the failure mechanism from brittle to ductile. The critical punching shear angles of all tested plain ECC slabs ranged from 40° to 50°. The ECC specimens possessing an FVF of 2 % exhibited markedly superior tensile capabilities compared to those with a 1 % FVF, as evidenced by direct tensile tests. Nevertheless, the ECC slabs with an FVF of 2 % did not demonstrate commensurate improvements in load-bearing capacity relative to their counterparts containing 1 % FVF. The span-depth ratio significantly impacted the failure mode of plain ECC slabs, yielding to punching shear failure at an SDR of 1, and to flexural failure at SDRs of 2 and 3. Moreover, an increase in the SDR value led to a reduction in both the initial cracking load and the ultimate load, concurrently increasing the associated deflection. In addition, a preliminary theoretical analysis was conducted to estimate the bearing capacity of plain ECC slabs. Flexural strength was estimated by yield line theory (YLT) and punching shear resistance was estimated by the model based on theory of plasticity in slab-column systems. The experimental and theoretical investigations could provide insights into the punching and flexural behavior of ECC slabs, laying a groundwork for the design and development of flat systems strengthened with ECC.

Study on the Damage Evolution and Failure Mechanism of Floor Strata under Coupled Static-Dynamic Loading Disturbance

In the field test, we found that the failure depth of the goaf floor strata tends to be further because the periodic breaking and caving of the immediate roof, upper roof, and roof key stratum has dynamic stress disturbance effects on the floor. To further analyze its formation mechanism, this paper studies the damage evolution and fracture mechanism of goaf floor rock under the coupled static-dynamic loading disturbance caused by roof caving, based on the stress distribution state, the damage evolution equation of coal measure rock, the damage constitutive model, and the fracture criterion of floor rock. The main conclusions are listed as follows: 1. Based on the mining floor stress distribution, the floor beam model establishes the response mechanism of floor rock stress distribution. Also, the equation of stress distribution at any position in floor strata under mining dynamic load is given. 2. Combining the advantages of Bingham and the Generalized-Boydin model, the B-G damage constitutive model is established, which can describe the constitutive characteristics of coal measure rock under the coupled static-dynamic loading disturbance well. Furthermore, the variation law of parameters changing with strain rate is analyzed. 3. According to the twin-shear unified strength yield theory and the B-G damage constitutive model, coal measure rock’s twin-shear unified strength damage fracture criterion is established. Finally, the stress distribution expression of floor strata under concentrated and uniform dynamic loads is introduced, and the fracture criterion of goaf floor strata under a coupled static-dynamic loading disturbance is proposed.

Strain Behavior of Short Concrete Columns Reinforced with GFRP Spirals

This paper presents a comprehensive study focused on evaluating the strain generated within short concrete columns reinforced with glass-fiber-reinforced polymer (GFRP) bars and spirals under concentric compressive axial loads. This research was motivated by the lack of sufficient data in the literature regarding strain in such columns. Five full-scale RC columns were cast and tested, comprising four strengthened with GFRP reinforcement and one reference column reinforced with steel bars and spirals. This study thoroughly examined the influence of various test parameters, such as the reinforcement type, longitudinal reinforcement ratio, and spacing of spiral reinforcement, on the strain in concrete, GFRP bars, and spirals. The experimental results showed that GFRP–RC columns exhibited similar strain behavior to steel–RC columns up to 85% of their peak loads. The study also highlighted that the bearing capacity of the columns increased by up to 25% with optimized reinforcement ratios and spiral spacing, while the failure mode transitioned from a ductile to a more brittle nature as the reinforcement ratio increased. Additionally, it is preferable to limit the compressive strain in GFRP bars to less than 20% of their ultimate tensile strain and the strain in GFRP spirals to less than 12% of their ultimate strain to ensure the safe and reliable use of these materials in RC columns. This research also considers the prediction of the axial load capacities using established design standards permitting the use of FRP bars in compressive members, namely ACI 440.11-22, CSA-S806-12, and JSCE-97, and underscores their limitations in accurately predicting GFRP–RC columns’ failure capacities. This study proposes an equation to enhance the prediction accuracy for GFRP–RC columns, considering the contributions of concrete, spiral confinement, and the axial stiffness of longitudinal GFRP bars. This equation addresses the shortcomings of existing design standards and provides a more accurate assessment of the axial load capacities for GFRP–RC columns. The proposed equation outperformed numerous other equations suggested by various researchers when employed to estimate the strength of 42 columns gathered from the literature.

Upgrading the capacity of foundations by using a hybrid expanded footing-micropile system

This paper introduces an innovative approach, where a hybrid expanded footing-micropile system is utilized to improve the load-bearing capacity of shallow footings on loose sand. Finite element analyses were carried out with a validated numerical model to simulate a shallow foundation on loose sand supporting a concentric vertical load. The simulated foundation was then upgraded by expanding its area and underpinning the additional area with pressure-grouted micropiles. The micropile installation process was treated as a pressure-controlled cavity expansion problem in the numerical simulation to account for the associated increase in radial stresses in the adjacent soil. A comprehensive parametric study was conducted, focusing on the primary determining factors: number of micropiles, micropile diameter, micropile bond length, grouting pressure, width of the additional area around the perimeter of the footing, and footing aspect ratio. The results showed that the micropiles acted as excellent settlement reducers once installed. If reducing the settlement is a high priority, when designing an expanded footing, the hybrid expanded footing-micropile system should be preferred rather than expanding the footing without the use of micropiles. The load capacity of the underpinned foundations was highly dependent on the grouting pressure applied during micropile construction.

Mechanical Properties of Adjacent Pile Bases in Collapsible Loess under Metro Depot

Metro transit construction has begun to develop rapidly in northwest China because of the acceleration of urbanization. Accordingly, metro depots are also regarded as an essential auxiliary facility for stopping, operation, and maintenance of trains. Meanwhile, many commercial buildings are constructed over metro depots to improve the utilization rate of land due to the increasingly scarce urban land resources, known as transit-oriented development (TOD). These buildings have a large covered area and transfer concentrated loads to the bases. Therefore, pile bases under metro depots have the bearing characteristics of undertaking large concentrated loads, while lesser loads are placed on the soil between the adjacent pile bases. Additionally, the main ground in northwest China is collapsible loess, so the collapsibility should also be considered. Based on the above background, this research performed static loading tests with and without immersion in a reduced scale of adjacent pile bases under a metro depot in Xi’an. The remolding process of natural loess could destroy its structure and the anisotropy of natural loess could also affect the test results. Therefore, four kinds of artificial collapsible loess with different mass ratios of barite powder, kaolin, river sand, cement, industrial salt, and calcium oxide were made by the free-drop method. This method could make the artificial loess simulate the structure of natural loess reasonably. Then, the artificial loess with the most similar properties to intact loess was selected by comparison. Finally, static loading tests with this artificial loess were implemented. The results showed that the ultimate bearing capacity was 4.5 kN. At the same time, the axial force decreased along depth, since the pile shaft friction was positive, and the load sharing ratio of pile tip force increased to 0.58 when the load exceeded 4.5 kN in the situation without immersion; the settlement of pile bases increased significantly after immersion, while the negative shaft friction occurred at the depth of −8 cm~−35 cm, and the load sharing ratio of pile tip force reached 0.92.

Spatially resolved capacitance-based stress self-sensing in concrete

Spatially resolved capacitance-based stress self-sensing in unmodified concrete has been demonstrated. The spatial resolution is 45 mm in one dimension, which is in the direction of the capacitance measurement. Parallel coplanar component electrodes (aluminum, 5-mm wide), attached to the concrete using double-sided adhesive tape) separated by 45 mm are used to measure the in-plane capacitance in the direction perpendicular to the length of the electrodes. Combinations of component electrodes are electrically connected to form an electrode. The capacitance ranges from ∼200 pF to ∼750 pF. The greater is the number of component electrodes in an electrode, the higher is the capacitance. The compressive loading is applied at selected areas located between adjacent component electrodes. The stress (defined as load divided by the 300 ×300-mm2 concrete area) is up to 3000 Pa. The load decreases the capacitance monotonically and reversibly. The fractional decrease in capacitance ranges from ∼0.1 % to ∼0.5 %. More spatially concentrated loading, as for loading near the edges of the specimen, gives greater fractional decrease in capacitance. The capacitance decreases with increasing inter-electrode distance. Embedded steel rebars with a 20.0-mm concrete cover do not affect the capacitance or capacitance-based sensing.

Review on Stamping Shear Properties of Foam Board

Bubbled slabs are introduced to decrease the self-weight of the slab by decreasing the amount of concrete in the slab's middle. This decrease results in cost savings, a reduction in the time needed for construction, improvements in structural performance, and an increase in the slab's efficiency. Despite the many benefits that this form of slab offers, it is similar to flat slabs. The more concentrated load at the column connection causes it to experience failure-punching shear. In addition, the design equations for bubbling slabs suggested by building rules derive from experiments conducted on flat slabs. Previous investigations of bubbled slabs have shown that the punching shear of bubbled slabs is different from that of flat slabs.

RESEARCH OF THE STRESS-STRAIN STATE OF PRECAST REINFORCED CONCRETE HOLLOW CORE SLABS UNDER THE ACTION OF A CONCENTRATED AND UNIFORMLY DISTRIBUTED LOAD

The scientific work is devoted to a comprehensive study of the stress-strain state of prefabricated hollow-core floor slabs, establishing the nature of deformation, as well as determining the characteristics of crack resistance, deformability and load-bearing capacity experimentally under short-term loads. The experimental data obtained were confirmed by theoretical calculations. The scientific novelty of the experiments carried out within the framework of the presented work lies in the improvement of the principles of direct design of floor slabs from commercially produced beam slabs, the possibility of determining the stress-strain behavior of a slab structure using the formed ends. The method of monitoring the stressed behavior of a slab structure was also further developed. For the first time, the results of full-scale experimental studies of the stress-strain behavior of a prefabricated slab, carried out using the hydraulic loading method, have been obtained, and the features of the deformation of a slab embedded in the wall of a multi-story building have been experimentally established. The article provides recommendations for the practical use of the research results obtained, and also develops technical specifications for the production of concrete slabs during design and construction. The developed proposals were used in the construction of residential buildings in Kharkiv. When using the recommended grade of concrete C25/30 (instead of the actual grade C20/25 tested), the rigidity of the slab increases and its deflections will be smaller. Based on the data obtained from the experimental testing of the slabs, a generally positive test result should be stated. During further serial production of slabs, periodic testing of batches of slabs should be carried out in accordance with DSTU B V.2.6-53:2008. In this case, the slabs are accepted according to the indicators of strength, rigidity, crack resistance, fire resistance limits, frost resistance limits, as well as water resistance of slabs intended for use in aggressive environments. Keywords: concentrated load, testing, concrete, calculation, deflection, transverse force.