Slab Model Research Articles

Numerical analysis of high-speed railway slab tracks using calibrated and validated 3D time-domain modelling

Concrete slabs are widely used in modern railways to increase the inherent resilient quality of the tracks, provide safe and smooth rides, and reduce the maintenance frequency. In this paper, the elastic performance of a novel slab trackform for high-speed railways is investigated using three-dimensional finite element modelling in Abaqus. It is then compared to the performance of a ballasted track. First, slab and ballasted track models are developed to replicate the full-scale testing of track sections. Once the models are calibrated with the experimental results, the novel slab model is developed and compared against the calibrated slab track results. The slab and ballasted track models are then extended to create linear dynamic models, considering the track geodynamics, and simulating train passages at various speeds, for which the Ledsgård documented case was used to validate the models. Trains travelling at low and high speeds are analysed to investigate the track deflections and the wave propagation in the soil, considering the issues associated with critical speeds. Various train loading methods are discussed, and the most practical approach is retained and described. Moreover, correlations are made between the geotechnical parameters of modern high-speed rail and conventional standards. It is found that considering the same ground condition, the slab track deflections are considerably smaller than those of the ballasted track at high speeds, while they show similar behaviour at low speeds.

Influence of Spring Stiffness on the Loading Speed of the Falling Weight Deflectometer (FWD) in Bearing Capacity Evaluation of Cement Concrete Pavement

Introduction: The bearing capacity evaluation of cement concrete runway pavement is one of the most important contents in the airfield operation. Among the methods for estimating bearing capacity, the Falling Weight Deflectometer (FWD) is the most widely used method because it does not damage the pavement structure and spends so much time. The equipment for evaluation should have suitable parameters, such as. magnitude and loading speed, to the actual operating loads. Aims and Objectives: Currently, the equipment to assess the bearing capacity of cement concrete pavements of highways and airports by falling weight has been widely used in the world and is being applied in Vietnam. The loading system consists of a falling block through a spring system acting on the pressure plate under the pavement with a certain falling height. In particular, the spring system plays an important role in controlling the speed of the load on the pavement. In Vietnam, the test standards (Industry Standard 22TCN335-06, Vietnamese Standard TCVN 11365-2016) for assessing the pavement bearing capacity by FWD equipment do not specify the selection of spring stiffness corresponding to different operating speeds of the vehicle. Therefore, it is difficult to use the equipment for pavements with operating speeds different from the standard. In this paper, we study the effect of spring stiffness on the loading speed when considering different loading speeds corresponding to different speeds of vehicles moving in reality. This research is only limited to laboratory experiments. This study aims to determine the dependence of the loading magnitude and loading time on the damping spring stiffness of the dynamic loading equipment, that is, used as a basis for choosing the appropriate damping stiffness of FWD corresponding to actual vehicles. Methods: Among the methods for estimating the bearing capacity, the Falling Weight Deflectometer (FWD) is the most widely used method as it does not cause any damage to the pavement structure and spends much time. The equipment for evaluation should have suitable parameters, such as magnitude and loading speed, to the actual operating loads. Results: This paper presents the results of experimental research that determines the influence of the damping spring stiffness on the loading speed of the dynamic loading equipment on the model of the concrete slab in the laboratory. Conclusion: Based on the comparison of the FWD loading speed when using 02 damping springs with different stiffness, we propose the basis for choosing the damping system that conforms to the evaluation needs of different types of vehicles.

Enhanced radiative heat transfer via the coupling of multi-particle interactions with combined surface models

Radiative heat transfer (RHT) has been playing a pivotal role in the study of all length scales from macroscopic to microscopic. This work aims to theoretically enhance the RHT between nanoparticles in multi-particle and slab systems. The results show that the strong coupling between the multi-particle interactions and the combined slab surface modes including transmission and reflection can significantly enhance the inter-particle RHT at a proper slab thickness, and the maximum amplification ratio can reach up to two orders of magnitude. For larger thicknesses of the slab, the RHT decreases due to the weakening of coupled evanescent models. In addition, we show that adding graphene sheets to both sides of the middle slab produces a surface hybrid model, which can regulate the coupling properties of the multi-particle and slab by changing the chemical potential of graphene. When the resonance frequency of nanoparticles is higher than that of the slab model, the RHT between the particles at both ends increases. Instead, the conclusion is the opposite. This work may exhibit potential applications for enhancing, guiding, and regulating contactless energy management in complex many-body systems at mesoscopic scales.

Investigations on mechanical, thermodynamic and surface properties of U–Si alloys

The investigation of U–Si alloys as advanced technology fuels or accident tolerance fuels (ATFs) has gained momentum due to their higher uranium density and exceptional thermal conductivity. Density functional theory (DFT) calculations were used to examine the mechanical, thermodynamic and surface properties of U–Si alloys. Voigt-Reuss-Hill model was used to evaluate the mechanical properties such as Young's modulus, shear modulus, bulk modulus and so on. The results suggest that U3Si2 possesses an inherent brittleness, as opposed to the remaining U–Si alloys which demonstrate reliable ductility. In comparison to the hardness of other U–Si alloys (40–80 GPa), U3Si2 exhibits a significantly lower hardness (∼10 GPa). The results of anisotropy show that U3Si2 exhibits a lower anisotropy compared to USi2 (I41/amd) and U3Si (Pm-3m). Also, based on these mechanical properties, the sound velocity and Debye temperature are determined. Additionally, the study calculates the internal energy, Helmholtz free energy, entropy and heat capacity as a function of temperature, which is beneficial for fuel design and other applications. The surface energies and work function are investigated comprehensively for 161 surface slab models and used to obtain other surface properties, including equilibrium morphology, dominant surface orientations, area-weighted surface energy and area-weighted work function.

The modeling and identification of walking beam type slab reheating furnace based on immersion and invariance disturbance estimation

This paper presents the modeling and identification of a walking-beam-type slab reheating furnace in one of the biggest Iron and Steel Industry in Turkey. Firstly, the dynamical model of the furnace is established as it is running with 12 control zones based on energy balance equations in the zones. Secondly, a disturbance observer is designed to estimate the disturbances that represents unmeasurable energy losses and the effects of unknown dynamics of the system based on Immersion and Invariance (I&I) approach. Then, model is identified with real data collected from the running furnace. The model and real furnace outputs are compared zone by zone. The results demonstrate the validity of the model.

Band alignment and crystal stability of Y3Al5−xGaxO12 garnets using density functional theory with hybrid functional

In this study, the dependence of band gap, band alignment, and structural stability of Y3Al5−xGaxO12 garnet (YAGG) solid solutions on Ga content (x) have been investigated using density functional theory (DFT) with PBE0 hybrid functional. The most stable model of YAGG for each x is identified using evolutionary algorithm-based USPEX method. The band alignment was determined by connecting valence band maximum (VBM) and conduction band minimum (CBM) to vacuum level via macroscopic average electrostatic potential of the slab model. Solid solution formation energy as a function of x indicates that YAGG with x = 3.0 (Y3Al2Ga3O12) exhibits remarkable structural stability. At x = 3.0, the analysis of the formation energy contribution shows a dominant contribution from electronic charge redistribution energy while there is no contribution from distortion energy. Bader charge, electron localization function, as well as the projected density of state analysis reveal a strong covalent character of Ga under oxygen tetragonal environment. The calculated PBE0 band gap as a function of x agrees well with the experimental results. Ga admixing significantly lowers the CBM, which exhibits a potential to envelop the shallow electron traps from the forbidden gap. The YAGG band alignment calculated using the proposed vacuum-connecting method is consistent with VRBE results from experiment. The proposed methods used to model site-preferred solid solution and calculate the vacuum-connected band alignment are viable in predicting structural stability and band edge modification via compositional engineering of garnet solid solutions. We expect that this work provides a promising strategy for material design through compositional engineering in obtaining high stability and enhanced performance in garnet compounds.

A Truncated Transient Slab Model for a Reheating Furnace

This paper considers the steel reheating process, in which cold slabs are reheated to a temperature suitable for hot rolling operations. Temperature uniformity within the slab is very important during reheating, as non-uniformities often lead to quality concerns in the later stages of the production process. Attaining slab temperature uniformity is quite challenging, therefore, a thorough understanding of the reheating process becomes very important. Due to the extreme conditions inside the furnace, numerical tools like computational fluid dynamics are necessary for such situations. However, when applied to these complex installations, it often leads to very lengthy computational times. This paper develops a computationally efficient transient model to simulate the environment around a slab. This Truncated Transient Slab Model is a coupled model: it uses the temperature and flow profiles from a full-scale steady-state simulation and imposes those on a smaller domain that represents the immediate environment around the slab. The efficiency of the model is compared to the state of the art. With the simulations available in the literature, it was found that the proposed model can simulate a furnace seven times larger (grid size), with much higher grid and time resolutions, using only a third of the computational resources.

Two-dimensional carrier gas at a polar interface without surface band gap states: A first principles perspective

We present first principles calculations of the interface between GaN and strained AlN, using a slab model in which polarization is compensated via surface fractional-charge pseudo-hydrogen atoms. We show that an interface two-dimensional carrier electron or hole gas emerges naturally in response to different compensating surface charges, but that this need not involve in-gap surface states.

Tearing on the southward subducting Kelameili oceanic lithosphere in the early Devonian: Evidence from the magmatism in the Harlik arc, southern Altaids

The coexistence of adakites, high-Mg andesites (HMAs) and Nb-enriched basalts (NEBs) records special subduction geodynamics, for instance, subduction initiation, subduction of oceanic ridges or slab tearing, which are widespread in the circum-Pacific subduction zone. The Altaids in Central Asia shared similar tectonic evolution to the western Pacific. However, slab tearing has not been widely reported, which hinders a better comparison between the Altaids and the western Pacific. In this study, we report the contemporaneous early Devonian granodiorites and mafic microgranular enclaves (MMEs) in the Sidingheishan area of the Harlik arc, southern Altaids. The granodiorites have high Sr (534–683 ppm) but low Y (7.79–10.2 ppm) and Yb (0.71–1.68 ppm) contents, with corresponding high Sr/Y values (29.78–76.93). In combination with their juvenile isotopes (initial 87Sr/86Sr = 0.70333–0.70356, εNd(t) = +7.4 − +8.01) and high Mg# numbers (50.9–53), they indicate that their primitive magmas were derived from slab melting. The MMEs show similarly high Sr contents (507–696 ppm), and identically juvenile isotopic signatures (initial 87Sr/86Sr = 0.70346–0.70356, εNd(t) = +7.14 − +7.5) to their host granodiorites. However, their relatively low silica contents (55–60 wt%), evolved Mg# numbers (44.8–55.2) and high Nb contents (12.7–24.7 ppm) demonstrate that they are the fractionation products of NEBs, which were produced by the partial melting of the mantle that was previously metasomatized by these adakitic magmas. Considering all the available evidence, we propose a slab tearing model in which the southward subducting Kelameili oceanic lithosphere underneath the Harlik arc underwent rollback in the early Devonian and its differential rollback rates caused slab tearing. Subsequent asthenosphere upwelling stimulated the Kelameili oceanic lithosphere to melt, producing the adakitic magmas, some of which intruded the crust after limited interaction with the mantle peridotites and underwent crystallization of dominant amphibole in the crust. The rest reacted completely with the mantle peridotites, which underwent further melting to produce the Nb-enriched basaltic magmas. They intruded into the adakitic magma chamber after fractional crystallization of olivine, clinopyroxene and garnet in the deep, forming the MMEs and promoting the remobilization of those hornblendites. This study reveals the development of slab tearing that are closely associated with slab rollback in the Altaids, providing further evidence that argues for the similarity between the Altaids and the western Pacific.

Model for calculation of thermal stresses in concrete pavement slabs with refined non-linear deformation constraints

Few investigations have considered comprehensive deformation constraints when calculating thermal stress of concrete slab. In this paper, the comprehensive and refined non-linear deformation constraints model of concrete slab is firstly proposed by setting non-linear spring elements at bottom and side of the slab and the capacity of shear load transfer across joints is considered as well. The results show that thermal stresses calculated by refined non-linear deformation constraints model are in good consistent with experimental results. The foundation reaction modulus has little effect on thermal stresses, but has a significant effect on gap between slab and its foundation. The stiffer base results in higher curling stresses at bottom of slab, and the types of base have an important effect on frictional resistance in horizontal direction at bottom of slab. The larger shear stiffness of joints will increase thermal stresses and shear force along joints but decrease deflections of slab.

Shakedown limit analysis of railway slab track foundations under train loading

Shakedown limit analysis is used to calculate the factor of safety of a structure subject to cyclic moving loading. It is a promising approach for railway slab track structural design because it can help identify the required layer thicknesses and material strength properties. However, the approach is based on an underlying assumption that the stress field in the train passage direction is invariant, which is violated for slab tracks in the vicinity of expansion joints. To address this issue, this paper proposes a novel shakedown limit analysis implementation that enables its use for slab tracks with joints. Firstly, a 3D finite element slab track model is developed to calculate the stress field profiles exerted on the subgrade surface. Analytical equations describing the shape of these profiles are then derived, considering locations along the slab track, including those near and far from expansion joints. Relationships are also derived to describe the stress field profile variation with depth, including both train-induced and geostatic stresses. Next, a lower-bound shakedown limit method is used to calculate the elastic shakedown limit based on the Mohr-Coulomb criterion using the computed stress fields. After the model is validated, shakedown limits are examined, considering various friction angles, cohesions, and Poisson's ratios. It is shown that the limit is reduced when the geostatic stresses in the ground are ignored. Furthermore, the shakedown limit is not always directly proportional to subsoil cohesion and increases with Poisson's ratio.

Understanding the role of oxygen-vacancy defects in Cu2O(111) from first-principle calculations

The presence of defects, such as copper and oxygen vacancies, in cuprous oxide films determines their characteristic carrier conductivity and consequently their application as semiconducting systems. There are still open questions on the induced electronic re-distribution, including the formation of polarons. Indeed, to accurately reproduce the structural and electronic properties at the cuprous oxide surface, very large slab models and theoretical approaches that go beyond the standard generalized gradient corrected density functional theory are needed. In this work we investigate oxygen vacancies formed in proximity of a reconstructed Cu2O(111) surface, where the outermost unsaturated copper atoms are removed, thus forming non-stoichiometric surface layers with copper vacancies. We address simultaneously surface and bulk properties by modelling a thick and symmetric slab, to find that hybrid exchange-correlation functionals are needed to describe the oxygen vacancy in this system. Our simulations show that the formation of oxygen vacancies is favoured in the sub-surface layer. Moreover, the oxygen vacancy leads to a splitting and left-shift of the shallow hole states in the gap, which are associated with the deficiency of copper at the surface. These findings suggest that surface electronic structure and reactivity are sensitive to the presence of oxygen vacancies, also when the latter are formed deeper within the film.

First-Principles Investigation of the Diffusion of TM and the Nucleation and Growth of L12 Al3TM Particles in Al Alloys

The key parameters of growth and nucleation of Al3TM particles (TM = Sc-Zn, Y-Cd and Hf-Hg) have been calculated using the combination of the first principles calculations with the quasi-harmonic approximation (QHA). Herein, the diffusion rate Ds of TM elements in Al is calculated using the diffusion activation energy Q, and the results show that the Ds of all impurity atoms increases logarithmically with the increase in temperature. With the increase in atomic number of TM, the Ds of 3–5d TM elements decreases linearly from Sc, Y and Hf to Mn, Ru and Ir, and then increases to Zn, Ag and Au, respectively. The interface energy γα/β, strain energy ΔEcs, chemical formation energy variation ΔGV and surface energy Esurave were further computed from the based interface and slab models, respectively. It was found that, with the increase in the atomic number of TM, the interface energies γα/β of Al/Al3TM (TM = (Sc-Zn, Y-Cd)) decreased from Sc and Y to Mn and Tc and then increased to Zn and Cd, respectively (except for the (001) plane of Al/Al3(Fe-Co), the (111) plane of Al/Al3Pd and the (110) and (111) planes of Al/Al3Cd). The strain energies ΔEcs of Al/Al3TM (TM = (Sc-Zn)) increased at first, and then decreased for all cycles. The chemical formation energy ΔGV of all Al3TM changed slightly in the temperature range of 0~1000 K, except that the ΔGV of Al3Sc, Al3Cu, Al3(Y-Zr), Al3Cd, Al3Hf and Al3Hg increased nonlinearly. With the increase in atomic number at both 300 and 600 K, the ΔGV of 3–5d TM elements increased from Sc, Y and Hf to Mn, Tc and Re at first, and then decreased to Co, Rh and Ir, respectively, and slightly changes at the end. With the increase in atomic number of TM, the variation trends of the surface energies of Al3TM intermetallic compounds present similar changes for all cycles, and the (111) surface always has the lowest values.

A machine learning-based structural load estimation model for shear-critical RC beams and slabs using multifractal analysis

This paper presents a machine learning model for load-level estimation for shear-critical reinforced concrete (RC) beams and slabs using multifractal features of their characteristic crack patterns to automate and provide well-informed decisions for RC damage assessment. Multifractal analysis was conducted on a database of 508 images, of which critical features were extracted from the singularity and generalized dimension spectra. These features are used as predictors for the load-level estimation model. The extreme gradient boosting algorithm yielded the best performance among the four machine learning models considered. The mean of the predicted-to-true ratio for the developed model was 1.04 with a coefficient of variation of 0.27. Upon applying Shapley additive explanations, the fractal dimension, information dimension, correlation dimension and the area under the left branch of the singularity spectrum were the critical features influencing load-level estimation. The proposed model can be useful to RC building inspectors.

Planar frame models considering system‐level interactions of a two‐story low‐damage concrete wall building

AbstractA system‐level shake‐table test of a two‐story low‐damage concrete wall building was conducted in 2019. The test building consisted of unbonded post‐tensioned (UPT) walls with perimeter frames and different wall‐to‐floor connections to provide deformation compatibility. The test results highlighted that the measured lateral strength of the building notably exceeded the design value. This over‐strength was largely attributed to the compatibility deformations imposed on the floor systems. Previous simulation results from planar models also underestimated the building global response and lateral strength, so a modified model was developed to improve the accuracy by accounting for the system‐level interactions. The floor slab out‐of‐plane strength was assessed by the floor slab models using shell elements to quantify their response when subjected to deformations induced by the UPT wall uplift. In addition, the unintended effects of the beam‐to‐floor connection strength were also calculated. The strength contributions from the floor and connections were included in the planar frame models using lumped rotational springs located at the slotted‐beam joints. Lastly, the models were also updated to include flexibility in the connections of the energy dissipations at the wall bases based on test observations. Nonlinear time history analysis of the updated models for unidirectional loading cases demonstrated an improved calculation of the test results for both the global and local responses. When considering the floor interaction in the updated models, the absolute relative errors of peak overturning moments reduced from 35.4% to 15.6% averagely for the longitudinal direction, and from 23.1% to 14.1% averagely for the transverse direction.

The Effect of Voids on Flexural Capacity of Reinforced Concrete Slabs

The voided reinforced concrete slab system is mainly produced with polyester foam placed mostly at the bottom of the slab. The aim of the voids is to reduce the weight of the slab. In this paper behavior of the voided reinforced concrete slabs in which voids placed at the mid-height of the slab cross-section, is examined analytically. A series of models were created to come up with a lightweight slab. Two distinct slab models were analyzed using the ABAQUS software. In the first group, slabs had three layers, in which bottom and top layers were of solid reinforced concrete, but the mid layer was of voided unreinforced concrete. In the second layer, in order to increase the contact between top and bottom layers of the slab, crossties were utilized, and the mid layer was reinforced accordingly. Since all the layers were 5 cm thick, the total thickness of the slabs were 15 cm. Slabs were 100 cm wide and 200 cm long. They were simulated the three-point bending test. Concrete damaged plasticity material model (CDPM) for concrete and elastoplastic material model for steel was selected. From the results it was found that moment capacity decreased with the increase in the volume of the voids. There was a sudden decrease in strength after reaching the yield strength in voided slab without a crosstie. In addition, crossties enabled the reduction of the weight of the slabs without significant decrease in moment capacity.

Blast resistance of ECC and composite slabs subjected to near-field explosion

Due to the unfavorable blast resistance of reinforced concrete (RC) slabs, particularly with the frequent occurrence of penetration and spalling damage, engineered cementitious composite (ECC) provided a promising alternative for enhanced blast resistance through its direct application as a building material or by reinforcing existing RC slabs due to its excellent tensile ductility and toughness. In the present study, the blast resistance of the RC slab, the ECC slab, and the composite slab (RC slab reinforced by ECC layer) was investigated and compared through experimental and numerical approaches. Firstly, the material properties of the ECC were acquired through the quasi-static compressive test, as well as quasi-static and dynamic tensile tests, which felicitated the parameter calibration in the K&C model for ECC. Then the numerical models of the RC slab, the ECC slab, and the RC/ECC composite slab were established and validated with the blast test results. The test and numerical results showed that the ECC and composite slabs exhibited superior anti-blast performance in terms of failure mode, damage extent, and load mitigation compared to the RC slab. Owing to the remarkable ductility and toughness, the ECC and composite slabs could greatly reduce the possibility and severity of penetration and spalling damage. Furthermore, five significant parameters impacting the blast resistance of ECC and composite slabs were summarized through dimensional analysis including the tensile strength of ECC σt, the total explosive energy Q, the standoff distance R, the slab thickness H, and the slab span L. Then a dimensionless number was proposed to determine the failure mode and predict the residual deflection at the center of the ECC and composite slabs. The results could serve as a reference for the design of ECC and composite slabs to resist blast loading in the field of structural protection.

Failure Modes Behavior of Different Strengthening Types of RC Slabs Subjected to Low-Velocity Impact Loading: A Review

Concrete is brittle; hence, it is incredibly likely that concrete buildings may fail in both local and global ways under dynamic and impulsive stresses. An extensive review investigation was carried out to examine reinforced concrete (RC) slab behavior under low-velocity impact loading. Significant past research studies that dealt with experimental and numerical simulations and analytical modeling of the RC slabs under impact loading have been presented in this work. As a result, numerous attempts to define failure behavior and to assess concrete structures’ vulnerability to lateral impact loads have been made in the literature. Based on analytical, numerical, and experimental studies carried out in previous research, this article thoroughly reviewed the current state of the art regarding the responses and failure behaviors of various types of concrete structures and members subjected to low-velocity impact loading. The effects of different structural and load-related factors were examined regarding the impact strength and failure behavior of reinforced concrete slabs reinforced with various types of strengthening procedures and exposed to low-velocity impact loads. The reviews suggested that advanced composite materials, shear reinforcement, and hybrid techniques are promising for effectively strengthening concrete structures.

A mixed finite element model for FRP-strengthened RC slabs based on sequential linear analysis

The aim of the present study is to develop a quasi-3D finite element model for predicting the nonlinear behavior of reinforced concrete (RC) slabs strengthened with fiber-reinforced polymers (FRP). The equivalent layered concept is adopted for modelling the constituent parts of the slab, including steel reinforcements, FRP sheets, concrete, and adhesive layers. The kinematical relation of the FRP-strengthened RC slab is approximated by using a mixed stress-displacement field plate theory. Material nonlinearity of the slab's constituents is included in the formulation. To overcome the convergence problems that traditional nonlinear algorithms are usually encountered with them, the sequential linear analysis approach is employed for simulating the crack propagation process. To evaluate the accuracy, numerical results obtained from the presented sequential linear FE model are compared with other similar numerical and experimental results available in the literature. The comparisons show that the proposed formulation is a simple and efficient tool for predicting the nonlinear behavior of FRP-strengthened RC slabs.

Determination of NSC-UHPC interface properties for numerical modeling of UHPC-strengthened concrete beams and slabs

Normal-strength concrete (NSC) structural components strengthened with ultra-high-performance concrete (UHPC) overlays are widely studied and have demonstrated their efficiency in improving structural capacity and durability. The behavior of UHPC-strengthened beams or slabs is highly influenced by the properties of the NSC-UHPC interface. This project aimed to develop NSC-UHPC interface models by determining their detailed shear and tensile laws in UHPC-strengthened beams or slabs, which are missing presently in the literature. Determination of the interface models was realized through test data analysis of 700 interface characterization specimens found in the literature and inverse analysis with nonlinear finite element (FE) calculations of 14 UHPC-strengthened beams and slabs test results. Two interface models were proposed for two types of interfaces with good or poor surface preparations, respectively: a concrete fracture (CF) model and an interface sliding (IS) model. Results showed that FE calculations with CF and IS models provide accurate replication of the mechanical behavior of strengthened beams and slabs in terms of stiffness (K), ultimate shear capacity (P), and deflection at ultimate shear capacity (Δ), while the calculations with perfect bond model were not satisfactory. Parametric studies on the nine interface parameters indicated that peak cohesion stress, shear stiffness, and tensile stiffness greatly impact the shear behavior of strengthened beams in the CF model, while only shear stiffness had a significant effect on the shear behavior of strengthened slabs in the IS model. Suitable choices for interface model parameters, as in the proposed CF and IS models, provided accurate results for modeling the bending and shear behaviors of UHPC-strengthened concrete beams or slabs.