Creep Of Concrete Research Articles

Impact of PVA-coated aggregate on concrete impermeability and creep characteristics under hydraulic pressure and development of a creep model

Impact of PVA-coated aggregate on concrete impermeability and creep characteristics under hydraulic pressure and development of a creep model

The impact of relative humidity on the nanoindentation relaxation in calcium silicate hydrates

Despite extensive research efforts, understanding the time-dependent behavior of concrete remains an enigma due to the complex nature of cement microstructure. In this study, the statistical nanoindentation was employed to investigate the influence of relative humidity (RH) on the relaxation behavior of calcium silicate hydrates (C-S-H) in a cement paste. Our experiments, performed at RH levels of 33 % and 86 %, revealed significant enhancements in both the indentation modulus and hardness of the C-S-H as RH increased. Remarkably, the internal water exerted a significant influence on the asymptotic relaxation behavior, displaying a clear power-law fashion. Further analysis identified the presence of short- and long-term viscoelastic behaviors within the C-S-H, distinguished by a transition observed within the initial seconds. These findings advance the understanding of nanoscale mechanisms driving concrete creep under different humidity conditions.

Interpretable machine‐learning models for predicting creep recovery of concrete

AbstractCreep recovery of concrete is essential for accurately assessing the performance of concrete structures over service time. Existing creep recovery models exhibit low accuracy, and the influencing factors of creep recovery remain inadequately elucidated. In this paper, interpretable machine learning (ML) techniques were employed to develop a prediction model for concrete creep recovery. Several ML techniques were selected including random forest (RF), support vector regression (SVR), extreme gradient boosting (XGBoost) and light gradient boosting machine (LGBM). In order to maximize the sample size of the dataset, 109 sets of creep recovery data were collected from existing literatures for model training. Feature selection is utilized to determine the input parameters for ML models, and 12 input variables were selected. The model is fine‐tuned using Bayesian optimization techniques. To ensure the reliability of ML models, 10‐fold cross‐validation and random data splitting were implemented. The results indicate that the ML models exhibited higher accuracy compared to the existing creep recovery model. Among these ML models, LGBM demonstrated superior accuracy, efficiency and stability (with R2 = 0.993, 0.978, and 0.973 for the training, testing, and validation sets, respectively). Shapley additive explanations (SHAP) were employed to interpret the significance of each input parameter on ML model prediction. Duration after unloading, stress magnitude, and ambient relative humidity were the main feature variables influencing concrete creep recovery. Upon comparing the influencing factors, it was discerned that there exists a distinct difference between creep and creep recovery of concrete.

Effects of thermal cycles and time-dependent behavior of the deck on steel network arch bridges

Network arches are a type of arch bridges with inclined hangers, in which some hangers cross each other at least twice. This paper aims to evaluate the effects of thermal fluctuations and volumetric changes of the concrete deck on steel network arches. Fifty-nine variants of a reference network arch bridge were developed, assuming identical arch geometries but varying hanger arrangements. Each bridge was modeled using the finite element method and subjected to heat flux due to solar radiation and changes in ambient temperature in addition to heat transfer via conduction, convection, and radiation. The time-dependent deformations of the concrete deck were implemented using a rate-type formulation. Results obtained during a one-year period after the assumed end of construction showed that stress changes in the arch bridge due to ambient and time-dependent effects were not very sensitive to the hanger layout. Neglecting concrete creep and shrinkage was found to cause a 15-20% underestimation of maximum stresses in the concrete deck, whereas a 40-60% error was observed in both the deck and rib when thermal effects were ignored. The radial arrangement of hangers, already known to perform favorably under live loads, was also found to provide the smallest bending moments and the fewest number of relaxed hangers due to thermal and time-dependent effects.

Numerical Simulations of Nonlinear Creep of Concrete at Mesoscale

Numerical Simulations of Nonlinear Creep of Concrete at Mesoscale

Методы прогнозирования долгосрочного поведения преднапряженных железобетонных мостов

Purpose: to analyze the causes of long-term deformations of prestressed concrete bridge spans and the problems associated with their prediction. To provide a brief overview of existing methods for predicting the long-term behavior of prestressed concrete bridges. The relevance of the problem is due to the need to ensure the reliability and durability of these structures, which are widely used in modern bridge construction. The objective of this paper is to identify factors that influence the development of long-term deformations and to develop approaches for their accurate prediction. Methods: the study examines the long-term deformations of prestressed concrete bridge spans and the problems associated with their prediction using existing bridge structures as examples. Existing methods for predicting long-term deformations in prestressed concrete are evaluated. In particular, the effects of high-strength reinforcement relaxation and the effects of concrete creep and shrinkage are analyzed. Results: accurate prediction of long-term deformations is a complex task that requires consideration of many factors, such as prestress losses, environmental conditions, material properties, and structural characteristics of bridges. The methods discussed in this paper, including the multiplier method and the approximate time interval method, demonstrate their effectiveness in evaluating long-term deformations. However, further research is needed to improve the prediction methods and increase the efficiency of prestressed concrete bridge design. Practical significance: provides design engineers with specific methods and approaches for evaluating the long-term behavior of prestressed concrete bridges. Application of these methods can reduce the risk of excessive deformations and deflections, ultimately ensuring the safety and reliability of bridge structures.

Hybrid model-driven and data-driven method for predicting concrete creep considering uncertainty quantification

Hybrid model-driven and data-driven method for predicting concrete creep considering uncertainty quantification

Proposal of a Creep-Experiment Method and Superficial Creep Coefficient Model of CFT Considering a Stress-Redistribution Effect

Existing concrete creep coefficient prediction models have the limitation of not considering the structural characteristics of CFT. For this reason, these models tend to overestimate the creep deformation of CFT. Therefore, in order to overcome the limitations of existing CFT creep experiments, this study proposes a creep-experiment method involving the use of CFT that passively changes the load applied to a single concrete specimen by calculating the stress redistribution between the concrete and a steel tube in CFT based on a step-by-step method. Furthermore, by actually applying the proposed experimental method, a creep experiment of CFT lasting for approximately 163 days was performed and a superficial creep coefficient model of CFT was proposed based on long-term strain data from the experiment. In order to verify the proposed superficial creep coefficient model, it was compared with two design criteria (CEB-FIP and ACI) based on the experimental results of this study and references. As a result, compared to the existing design criteria, the value predicted by the proposed superficial creep coefficient model showed good agreement with the experimental results of this study and the references, proving that the proposed creep-experiment method of CFT and superficial creep coefficient model are reasonable.

A time-series deep learning model for predicting concrete shrinkage and creep verified with in-situ and laboratory test data

This paper proposed a time series prediction method for concrete shrinkage and creep based on deep learning and the accuracy of the method was verified by field tests. Based on the experiment data in the Northwestern University (NU database), a deep learning model considering the material, environment, and history was constructed by integrating Gated Recurrent Units and Self-Attention mechanism (GSA model). To validated the model, short-term indoor and outdoor field tests of concrete shrinkage and creep were conducted. The proposed GSA model outperformed the LSTM model for both creep and shrinkage predictions. Moreover, the comparison between the GSA model prediction and the outdoor test data indicated that the model can accurately capture the real-time outdoor temperature and humidity variation through historical data. To predict the ten-year shrinkage and creep of concrete, a recursive multi-step method was proposed to extrapolate the short-term predictions of the GSA model. The effectiveness of the recursive multi-step method was validated against the long-term test data in the NU database. Overall, the proposed GSA model demonstrated high accuracy in both short-term and long-term predictions.

Numerical model for time-dependent cracking and deflection of large-span concrete bridge structures

A new computational framework is proposed to analyse the simultaneous occurrence of multiple physical processes affecting the long-term behavior of large-scale concrete structures. Relying on the additivity of small strain, the framework comprehensively takes the nonlinearity of concrete creep, cyclic creep induced by traffic load, concrete shrinkage, concrete cracking, normal-strength steel rebars and prestressing strands relaxation into account, and other physical processes are further imagined. The algorithm is implemented with Abaqus/Standard with the aid of several user-supplied subroutines. The implicit time integration scheme is deemed appropriate for large-scale structures. The framework is systematically validated by several classical experimental results. Finally, a three-dimensional study of a three-span continuous rigid frame bridge with 270 m main span is performed. Comparison between the experimental and numerical results further reveals the contributions of various potential influencing factors. The proposed model shows promise for predicting the time-dependent performance of large-scale reinforcement concrete (RC) structures.

Tensile Creep and Cracking Resistance of High-Strength Concrete with Shrinkage Reducing Admixture under Uniaxial Restrained Condition at Early Age

Tensile Creep and Cracking Resistance of High-Strength Concrete with Shrinkage Reducing Admixture under Uniaxial Restrained Condition at Early Age

Modeling time-dependent deformation in concrete: A fractional calculus method with finite element implementation

This study presents a novel numerical method to simulate the time-dependent behavior of concrete materials. The deformation response of both traditional and fractional calculus (FC) viscoelastic models is analyzed by the proposed method, in which models’ one-dimensional constitutive relationships are extended to the three-dimensional form. By applying numerical and finite difference methods based on Caputo-type fractional integration, the stress-strain behavior of the FC viscoelastic model is discretized over the time scale. This method exhibits broad application prospects, and can be employed to represent various forms of viscoelastic models. For the concrete material, suitable FC viscoelastic models are developed. To facilitate practical engineering applications of the proposed model, a numerical solution algorithm is implemented in the finite element (FE) analysis through the User-defined Material Mechanical Behavior (UMAT) interface of the commercial FE software ABAQUS. Finally, FE results are compared with the experimental results from several concrete creep tests. The consistency between the FE results and experimental data confirms the effectiveness of the proposed model in describing concrete behavior. The proposed method and model provide theoretical and numerical support for a more profound understanding and simulation of the time-dependent deformation of RC specimens in practical engineering applications.

A Failure Analysis of the Long-Term Overturning Stability of Concrete Continuous Single-Column Pier Bridges Considering Creep and Overloaded Vehicles

Several single-column pier girder bridges have been involved in overturning accidents, resulting in significant economic losses and casualties, thus necessitating a risk assessment of the overturning stability. To date, the effect of structural degradation due to concrete creep on the long-term stability of bridges has not been demonstrated. In this study, a full-scale nonlinear analysis of the lateral overturning process of a collapsed concrete box girder based on the explicit dynamic finite element method (EFEM) was conducted to verify the reliability of the numerical method. An EFEM model incorporating concrete creep was developed to demonstrate the effect of structural degradation on the long-term stability of bridges. The synthesis overturning axis method (SOAM) was proposed to evaluate the long-term overturning stability of concrete continuous bridges, aiming to address the deficiencies in existing methods, particularly for curved bridges, and was compared with conventional methods. The results show that the variations in bearing reaction forces between curved and straight bridges under creep and self-weight are minimal, staying within 2%. An increase in the creep terminal coefficient results in the opposite trend in the ultimate vehicle weight of curved bridges and straight bridges, but fluctuations remain within 2%, indicating that long-term creep has a limited effect on the overall overturning stability. A failure analysis of 20 single-column pier bridges reveals significant differences in the ultimate vehicle weight between the rigid overturning axis method (ROAM) and folded overturning axis method (FOAM), with error ranges of −14.2% to 567.4% and −99.1% to −32.1%, respectively. The SOAM results have the smallest error range compared to those of the EFEM, with an error range of −38.8% to 33.9%. Despite these errors, the SOAM demonstrates a significant improvement in characterizing the trend and assessment accuracy of the overall overturning stability of single-column pier bridges.

Shrinkage separation prediction of concrete-filled steel tube arch bridge: A coupling model concerning multiple factors

The shrinkage separation is one of the key factors restricting the development of concrete-filled steel tube (CFST) arch bridge. In this paper, its mechanism and evaluation method concerning multiple factors, including structure, environment, material and construction were investigated. Firstly, the hydration process of in-tube concrete was simulated using the hydration degree as a basic state parameter. Then with the consideration of energy and mass conservation, as well as the moisture and heat transmission effects, the temperature and relative humidity fields, early-age mechanical properties, basic creep, and total deformation of in-tube concrete were further calculated. On the basis, in accordance with the stress criterion and displacement coordination, a multi-field (hydro-thermo-hygro-constraint) coupling model was finally established, taking the ratio of normal stress to bonding strength at the steel-concrete interface as the shrinkage separation risk index. The simulation results obtained from the model were in good agreements with the full-scale CFST model test.

Theoretical and simulation study on the vibration modes of shear walls in prefabricated modular construction

Abstract As prefabricated construction advances, the enhanced informatization and the industrialized modular construction method of MIC (Modular integrated construction) shear walls have been widely applied in real projects. MIC shear walls are generally made up of prefabricated wall modules with varying strength grades, using concrete of various ages, and are combined with cast-in-place concrete. Due to the unique construction requirements of these walls, defects such as interfacial delamination and internal voids might occur, arising from factors like concrete shrinkage and creep, complex interfacial structures, inadequate compaction during vibration, and construction process issues. Since these interfacial defects cannot be visually inspected from the exterior, developing non-destructive testing (NDT) methods specifically for detecting such defects in shear walls becomes an urgent necessity. This paper utilizes a combination of theoretical analysis and numerical simulation to explore the vibration modes of MIC shear walls with hidden defects. First, a theoretical model is proposed for the local vibration modes of MIC shear wall shells with consideration of interfacial delamination defects. Then, a numerical simulation model is established based on MIC shear wall construction and defect features to simulate the vibration behavior accurately. Finally, after examining the theoretical and simulated vibration characteristics of MIC shear walls, a significant theoretical foundation is established for identifying interfacial defects in MIC shear walls.

Long-Term Behavior of Timber–Concrete Composite Structures: A Literature Review on Experimental and Numerical Investigations

Timber–concrete composite structure is a type of efficient combination form composed of concrete floors and timber beams or floors through shear connectors, and shows good application potential in the floor system of timber buildings. The long-term performance of the timber–concrete composite structures is complex and is affected by the creep of timber and concrete, as well as the long-term slip of the shear connectors. This article presents a comprehensive overview of the research status on the long-term behavior of timber–concrete composite members and different shear connectors. For the shear connectors, the effects of loading levels, environments, and component materials on their creep coefficients are summarized. As to the timber–concrete composite members, both the experimental and numerical investigations are gathered into discussions: the connection types, component materials, loading conditions, and durations in the long-term tests are also discussed; various models for describing long-term behavior of timber, concrete, and connection systems are provided, and then a comprehensive description of the progress of numerical investigations over the last decades is made. In addition, the suggestions for future research are proposed to reach a clearer understanding of the bending mechanisms and mechanical characteristics of timber–concrete composite structures.

CALCULATED DETERMINATION OF CHARACTERISTICS OF SHRINKAGE AND TOUCH OF CONCRETE

Raising of problem. When calculating concrete and reinforced concrete structures, it is necessary to take into account the shrinkage and creep of concrete, which are not a minor factor. Because during long-term operation of such structures, these factors can significantly change the stress-strain state of structures over time and lead to the appearance of extreme deformations, cracks and their destruction. Therefore, when designing concrete and reinforced concrete structures, it is necessary to take into account the influence of shrinkage and creep of concrete. To do this, the designer must have the parameters included in the equations and calculation formulas. There are numerous of parameters and they are determined experimentally and depend on many factors. However, the designer must have these parameters even when there is no experimental data on the material and design, but when the material (strength class) has already been specified. Thus, there is a need to calculate the required parameters based on the main factors. The simplest computational determination of the creep characteristics of concrete is possible using the theory of aging at a constant modulus of elasticity of concrete, which partially takes into account the aftereffect (reversibility) of creep deformations. We will call such a theory the technical theory of aging and it operates with the smallest number of parameters (2 in total) and only one creep curve at the initial load age t0, and not with a family of these curves. Purpose. Development of theoretical solutions and practical methods for taking into account the design characteristics of shrinkage and creep of concrete in building design standards. Conclusion. The work resulted in the development of a convenient for practical use linear theory of concrete creep − the technical theory of aging and the development on its basis of theoretical solutions and practical methods for taking into account the calculated characteristics of shrinkage and creep of concrete in building design standards.

Characterization of the static and dynamic response of a post-tensioned concrete box girder bridge with vertically prestressed joints showing vertical deflections due to concrete creep deformation

Characterization of the static and dynamic response of a post-tensioned concrete box girder bridge with vertically prestressed joints showing vertical deflections due to concrete creep deformation

A memory-dependent three-dimensional creep model for concrete

The study of creep models for concrete is of great significance in analyzing and predicting the long-term stability of concrete structures. Based on the theory of memory-dependent derivatives, memory-dependent viscous dashpots that can describe the characteristics of decaying creep and accelerating creep are constructed based on the varying characteristics of the creep process in different stages. The Kelvin body was replaced with a stable memory-dependent dashpot and the Newtonian dashpot in the visco-plastic body was transformed into an unstable memory-dependent dashpot by drawing on the component combination form of the Nishihara model. A three-dimensional concrete creep model based on memory-dependent derivatives was established. By adjusting the model parameters of stable and unstable memory-dependent viscous dashpots, the model can simulate the creep process of concrete with different decaying creep characteristics and accelerating creep characteristics, and it has good universality. Multiple sets of experimental data on concrete creep verify that the memory-dependent concrete creep model corresponds well to the experimental data. Compared with five other concrete creep models, this model has fewer parameters and higher fitting accuracy, especially in characterizing the accelerating creep characteristics of concrete.

Dynamic serviceability and safety reliability analysis of aging PC girder bridges with non-prestressed reinforcement considering concrete shrinkage, creep and stochastic vehicle load flows

Prestressed concrete (PC) bridges’ service performance displays time-dependency due to several factors including concrete shrinkage, creep, resistance degradation, and stochastic vehicle load flows. These non-stationary vehicle load flows, combined with concrete shrinkage, creep, and resistance degradation, result in sequential alterations of internal forces and deformations in simply supported PC girder bridges, ultimately influencing their dynamic reliability. This study proposes a robust methodology that considers the impact of traffic loading, shrinkage, and creep to analyze the dynamic reliability of simply supported PC girder bridges through the development of a load probability model. A stochastic model for truck loads is generated using motion measurement data, which can be used to calculate bridge internal forces and subsequent quantitative analysis of structural deformation due to shrinkage and creep. Subsequently, the formula for the first exceedance probability under resistance degradation is presented and validated through Monte Carlo simulation. Reliability analysis is conducted for both serviceability and load carrying capacity limit states to assess the impact of shrinkage, creep, and increased mean vehicle load on structural reliability. The proposed method offers the theoretical foundation and practical guidance for assessing the structural health status of in-service bridges, thereby providing valuable insights into their long-term performance and maintenance requirements.