Deformations Of Slab Research Articles

Influence of large-diameter shield tunneling on deformation of adjacent high-speed railway subgrade in soft soils and effectiveness of protective measures

The excavation of large-diameter shield tunnels in soft soils inevitably impacts adjacent high-speed railway infrastructure. This study investigates the effects of constructing a 14.02 m large-diameter shield tunnel on the deformation of a nearby high-speed railway subgrade in soft soils of Shanghai, and evaluates the effectiveness of various protective measures. A numerical model was developed to simulate the horizontal deformations of railway subgrade piles, as well as the vertical and horizontal deformations of track slab resulting from shield excavation. Comprehensive real-time monitoring of track slab displacements in both vertical and horizontal directions, along with ground surface deformation, was conducted. The accuracy of the computational model and the effectiveness of the implemented protective measures were validated through field measurements. The results demonstrate that isolation piles with coupling beams proved to be the most effective method for protecting the railway subgrade. The maximum observed ground settlement above the tunnel reached −20.3 mm, while the peak heave was recorded at 3.7 mm. Notably, the additional vertical and horizontal deformations of the high-speed railway track were successfully constrained within the 2-mm threshold. These findings provide valuable insights for safety assessments and the implementation of protective measures in similar projects.

Geosynthetic reinforcement of backfill behind integral abutments to mitigate approach slab distresses

An approach slab typically has a negligible settlement on one end supported by an integral bridge abutment, but a considerable settlement on the other end underlain by a sleeper slab on the backfill due to factors including seasonal temperature changes and traffic loading. As a result, a differential settlement develops between the two ends of the approach slab, resulting in an abrupt change of the pavement gradient. Furthermore, the concave deformations of the approach slab under traffic loads exacerbate this abrupt gradient change, which creates a hazardous condition for vehicles. Four physical model tests were conducted to investigate the feasibility of using geogrids in the backfill to mitigate these approach slab problems due to simulated seasonal temperature changes and traffic loading. The test results showed that geogrids could significantly reduce the settlements of the backfill away from the abutment, which were mainly caused by traffic loading. Horizontal geogrids increased the backfill surface settlements near the abutment, while wrap-around geogrids significantly reduced these settlements. Longer top geogrid layers with wrap-around facing could further reduce the backfill surface settlements near the abutment.

NUMERICAL STUDY OF REINFORCED CONCRETE PLATES IN THE PRESSURE AREA

Here is the description of fi nite elementmodels of joints between reinforced concrete slab and column, made in the SIMULIA ABAQUS software package. The variable parameters were the ratio of the sides of the column cmax/cmin and the ratio of the side of the column to the eff ective depth c/h0. The calculation is performed in a non-linear formulation. Finite elementmodels showed realistic behavior: a punching shear pyramid was detected. It was found a signifi cant unevenness in the distribution of tangential deformations, as well as the main compressive deformations of the concrete slab near the column. The nature of the formation and development of the punching shear pyramid depends on the value of the ratio of the sides of the column cmax/cmin and the ratio of the side of the column to the eff ective depth slab c/h0.

Modeling snow slab avalanches caused by weak-layer failure – Part 1: Slabs on compliant and collapsible weak layers

Abstract. Dry-snow slab avalanche release is preceded by a fracture process within the snowpack. Recognizing weak-layer collapse as an integral part of the fracture process is crucial and explains phenomena such as whumpf sounds and remote triggering of avalanches from low-angle terrain. In this two-part work we propose a novel closed-form analytical model for a snowpack under skier loading and a mixed-mode failure criterion for the nucleation of weak-layer failure. In the first part of this two-part series we introduce a closed-form analytical model of a snowpack accounting for the deformable layer. Despite the importance of persistent weak layers for slab avalanche release, no simple analytical model considering weak-layer deformations is available. The proposed model provides deformations of the snow slab, weak-layer stresses and energy release rates of cracks within the weak layer. It generally applies to skier-loaded slopes as well as stability tests such as the propagation saw test. A validation with a numerical reference model shows very good agreement of the stress and energy release rate results in several parametric studies including analyses of the bridging effect and slope angle dependence. The proposed model is used to analyze 93 propagation saw tests. Computed weak-layer fracture toughness values are physically meaningful and in excellent agreement with finite element analyses. In the second part of the series (Rosendahl and Weißgraeber, 2020) we make use of the present mechanical model to establish a novel failure criterion crack nucleation in weak layers. The code used for the analyses in both parts is publicly available under https://github.com/2phi/weac (last access: 6 January 2020) (2phi, 2020).

Geotechical support for building construction with changed design considerations of the superstructure

The paper presents a system for the safe construction assessment of a building and its structures with a developed substructure and with a crucially changed superstructure at the late stage of construction under the conditions of the completed substructure at the early stage of construction. The main specific feature of above-mentioned construction is to ensure the continuity of the superstructure erection in case of the high increased loads on the foundation (mainly on the foundation slab) until it is strengthened. All values of the settlements and deformations of the building were find by using the verified program “STARK ES” and due to the results of the geotechnical monitoring. The paper proposes a verification system for acquired data proceeding to the monitoring and calculated values of settlements and deformations of the foundation slab which ensure the operational safety using the convenient "traffic light" method and the instructions for its successful use.

Natural thermal loads and their influence on airfield concrete slabs

The article presents theoretical aspects of the influence of environmental changes on the extent of the recognized stress in the case of airfield concrete slab. Analyses included actual measurement data from 34 weather stations located within the area of Poland. The results obtained between 2000 and 2016 were used to prepare climatic data base of the selected regions. The analyses included maps of typical values taking into consideration daily, monthly and annual variations. In case of exemplary data from Kielce station, the influence of external conditions on the extent of the registered stress and deformations of airfield concrete slab was determined. According to the obtained test results, the significant influence of environmental conditions on changes of concrete slab strains was confirmed. Recommendations aiming at limiting negative influence of environmental conditions on concrete slab strains were suggested in case of the analysed area.

Embankment Filling Loads on an Assembled Concrete Culvert beneath High Embankment

A culvert with prefabricated and assembled structural components is introduced to speed up the progress of highway construction in China. In order to clear the behavior of the prefabricated and assembled slab culvert, the center line section and the shoulder section of the embankment are selected for field tests. In the tests, the distribution and the growth of the earth pressures on the top slab and the lateral walls and the displacements and the deformations of the top slab and lateral walls are investigated, thereafter, the tested earth pressures are linearly fitted, and the formulas of fitting lines are obtained. The results show that the deflections of the lateral walls and of the cover slab are very small, and the variation of distribution and growth of the earth pressures presents significantly nonlinear characters, which is totally different from the linear earth pressure theory proposed by the current Chinese code. The vertical pressure is much smaller in the middle part of the top slab than that on both ends, and it is much larger than the linear theory results. The distribution curve of the lateral earth pressures on the lateral walls is approximately “3” in shape, and the maximum earth pressure locates at the junction of the cap and the lateral wall. The formula of the fitted line obtained from the primary stage pressure can be employed to estimate the earth pressure of embankment completion. The results of the field tests can provide references for the calculations of the components and the strength in the junctions of the assembled culverts.

Formation Mechanism of Voids around Hard Inclusion during Hot Rolling Processes

Abstract To investigate the mechanism by which voids form around hard inclusions, the deformations of a plastic slab with hard and soft inclusions that form inside it during the hot rolling process have been simulated with a finite element method. By comparing plastic strain distributions, the relative displacements of contact surfaces, and the deformations between hard and soft inclusions have preceded analysis of the formation mechanism of these voids. The variations of strain measurements between the matrix and hard inclusions cause relative displacement of their contact surfaces. Therefore, voids occur at the front and rear of the hard inclusions. Trials on the slab deformations using a titanium ball instead of the soft inclusion inside the slab during the hot rolling process are conducted. The simulated shapes of the soft inclusions with different reductions mostly agree with the experimental results.

Temperature-induced deformation of CRTS II slab track and its effect on track dynamical properties

Two finite-element models of the CRTS II slab track are presented to simulate temperature-induced deformations of the concrete track slab with no deterioration or with a deteriorated cement asphalt mortar (CAM). One model, which considers the fully bonding interface between the slab and the CAM layer, could applied to a track that is in good condition; the other model uses cohesive zone elements to simulate the deteriorated CAM with some possible interfacial separation and slip. Utilizing both of the models, temperature-induced warp deformations of track under various temperature loads are investigated. The influence of temperature deformation on the dynamic properties of the track is analyzed based on the train-track coupled dynamics. Numerical results show that the deteriorated CAM layer can significantly increase temperature deformations of a CRTS II track slab, which would produce tiny rail irregularities. There are clear differences between the deformation shapes of the track slabs that have an inseparable mortar layer and those have a separable mortar layer. The track slab with a deteriorated mortar layer showed more open curl distortion than the track slab in good condition. The dynamical response index of the slab track is intensified to a certain level due to the temperature deformation; with an increase of the train speed, the track dynamical responses increased linearly. However, rail irregularities due to the temperature deformations are very tiny. Even if a track is exposed to extreme temperature loads and the mortar layer is deteriorated, temperature deformation can have a negligible effect on the track’s dynamical properties.

Research on Post-Tensioned Unbonded Prestressed Concrete Hollowed Floor

In order to study the mechanical behaviors of post-tensioned unbonded prestressed concrete hollowed floors, a 1/4 scale post-tensioned unbonded prestressed reinforced concrete hollow slab-column structure model is used to act uniform distributed load on the floor. The test results showed that the load carrying capacity is enough. The points of maximum displacement are at the centers of slabs. By means of the experimental studies and elastic finite element analysis methods, the results showed that post-tensioned unbonded prestressed concrete hollowed floor presents anisotropy with layout of circular-tubes in one way. In direction parallel to layout of hollowed tubes, the continuity of floor is destruction and bending stiffness of slab is weakened. For studying the deformations of slab, it can still be considered continuous cross-slab in two directions.

Shrinkage Deformations of Composite Slabs with Open Trapezoidal Sheeting

Composite steel-concrete slabs that have integral steel shuttering at the soffit of a reinforced concrete slab are commonplace in building infrastructure. Inevitable shrinkage of the concrete represents an indirect (or non-mechanical) strain that results in deformations of the composite slab, resulting in long-term effects in which creep of the concrete also plays a role. Because the impervious steel sheeting prevents moisture egress at the slab soffit whereas at the top of the slab such moisture egress can occur, there is a variation of the shrinkage strain through the depth of the slab, resulting in warping-type deformations. In addition, the composite action between the steel and concrete results in partial shear interaction between these elements, and this interacts with the shrinkage response. Surprisingly little appears in the published literature on rational modelling of the behaviour of composite slabs incorporating partial interaction that are subjected to shrinkage straining, despite its practical importance and significance. Based on fundamental principles of mechanics, a theoretical model of this shrinkage behaviour that includes partial interaction is developed, and prescriptive equations are derived. These may be used to assess the deflections and stresses in the concrete due to restrained shrinkage which may lead to cracking of the slab. It is also shown that the two effects of partial interaction and shrinkage straining counteract each other when slab deflections are considered.

Service-Stage Analysis of Curved Composite Steel-Concrete Bridge Beams

The long term behavior of composite steel-concrete bridge beams with a circular axis is discussed. The time evolution of strains and stresses arising in the composite section and the main aspects of the structural behavior are investigated, by assuming perfect bond between the steel beam and concrete slab and by considering the sections as thin-walled. The warping theory according to sectorial areas has been adopted for the analysis, extending it to the viscoelastic domain. The problem, governed by a set of sixth-order integro-differential equations, is solved in a general way recurring to a numerical algorithm carried out by the writers. A significant case study is finally worked out, allowing us to point out the most important prerequisites of the deferred behavior of composite steel-concrete curved bridges, in particular the interaction between the different components of internal actions due both to the curved geometry of the beam and to the delayed deformations of the concrete slab induced by creep.

Local Bifurcation Analysis of a Second Gradient Model for Deformations of a Rectangular Slab

In this paper we carry out a derivation of the equilibrium equations of nonlinear elasticity with an added second-gradient term proportional to a small parameter \(\varepsilon>0\). These equations are given by a fourth order semilinear system of pdes. We discuss different types of possible boundary conditions for these equations. We then specialize the equations to a rectangular slab and study the linearized problem about a homogenous deformation. We show that these equations admit solutions representable as Fourier series in one of the independent variables. Furthermore, we obtain the characteristic equation for the eigenvalues (possible bifurcation points) for the linear problem and derive asymptotic representations for this equation for small \(\varepsilon\). We used these expressions to show that in the limit as \(\varepsilon \to 0\) the characteristic equation for \(\varepsilon>0\) converges uniformly (in certain regions of the parameter space) to the corresponding characteristic equation for \(\varepsilon=0\). When the base material (\(\varepsilon=0\)) is that of a Blatz–Ko type, we get conditions for the existence of eigenvalues of the linear problem with \(\varepsilon>0\) and small. Our numerical results in this case indicate that the number of bifurcation points is finite when \(\varepsilon>0\) and that this number monotonically increases as \(\varepsilon \to 0\). For the problem with \(\varepsilon>0\) we get conditions for the existence of local branches of non-trivial solutions.

Analytical solutions for the time-dependent behaviour of composite beams with partial interaction

This paper presents a generic modelling for the time-dependent analysis of composite steel–concrete beams with partial shear interaction that occurs due to the deformation of the shear connection. The time effects considered in this modelling are those that arise from shrinkage and creep deformations of the concrete slab, and these effects are modelled using algebraic representations such as those of the age-adjusted effective modulus method (AEMM) and the mean stress method (MS), which are viscoelastic models for concrete deformation that can be stated algebraically. The generic model lends itself to closed form solutions for the analysis of composite beams subjected to a generic applied loading under a variety of end conditions. In this paper, the generic model is applied for the time-dependent analysis of composite beams that are simply supported and encastré, and to a propped cantilever, that are subjected to uniformly distributed loading and shrinkage deformations. Various representations of the structural behaviour of these beams are given in closed form which can also be used to benchmark available modelling techniques, i.e. finite element and finite difference formulations, which require a spatial discretisation to be specified as well as the time discretisation to perform a time analysis.

Time dependent service load behaviour of prestressed composite tee beams

This paper is concerned with the time dependent service load behaviour of prestressed composite tee beams. The effects of creep and shrinkage of the concrete slab are modelled using the age adjusted effective modulus method and a relaxation approach. The tendon strain is determined considering compatibility of deformations and equilibrium of forces between the tendon and the composite tee beam. A parametric study is undertaken to study the influence of various aspects on the stress, strain and deformations of the concrete slab, steel beam and prestressing tendon. The effect of loading type and tendon relaxation has also been considered for various types of prestressing tendon materials. Recommendations are then made in relation to adequate span to depth ratios for varying levels of prestressing force.