Effects Of Concrete Shrinkage Research Articles

Finite-Element Performance Degradation Behavior of a Suspension Prestressed Concrete Arch Bridge with Grouting Defects

In response to the difficulty in effectively dealing with grouting defects in corrugated pipes within a suspension prestressed concrete arch bridge, a method for assessing the deterioration in the performance of prestressed concrete girders afflicted with grouting defects was established in the present study. Specifically, a time-varying model of steel strand corrosion within grouting defects was constructed by investigating the corrosion theory of steel strands. In addition, a full-scale numerical simulation model of the long-span prestressed concrete bridge was established based on a practical project. Through the described means, the long-term impact of steel strand corrosion at various locations, lengths, and quantities on the vertical displacement and axial stress of girders was elucidated. The results reveal that in the presence of corrosion affecting 16 steel strands located in the midspan bottom plate, a vertical displacement alteration of 17.55 mm was observed in the midpoint region of the girder over a 30-year period following the bridge’s construction. Further, when considering the combined effects of concrete shrinkage, creep, and the corrosion of 16 steel strands in the midspan bottom plate, the axial compressive stress within the midpoint region of the girder decreased from an initial 6.30 MPa to 0.79 MPa over the same 30-year timeframe post-construction. It was observed that two indicators of vertical displacement and axial stress can be employed to evaluate the performance degradation of prestressed concrete bridge girders with grouting defects. The present findings may provide a reference for the operation and management of bridges with grouting defects.

Shear transfer at the steel‐concrete interface using different mechanical connectors

AbstractThe present article is dealing with an assessment of the longitudinal shear at the steel‐concrete interface using several types of mechanical connections. Experimental and numerical tests have been performed to understand better the short and long‐term effects of the influence of the newly defined connectors.Experimental tests consisted of 12‐column push‐out tests (CoPOT). In the test campaign, four types of surface finishing have been tested: i) reference tests (0v2) without any mechanical shear connectors, (ii) angled, V‐shaped, variant of the novel flat shear connector (Av2), (iii) transversal variant of the novel flat shear connector (Bv2) and (iv) multiple ribs on the flanges having a height of 0.7mm (Cv2). Three specimens for each configuration were tested in short‐term loading. The loading procedure defined in EN1994‐1‐1:2004 Annex B was applied for all the tests. Also, one of each specimen was tested in long‐term loading to observe the effect of concrete shrinkage on the quality of bond performance. No significant differences in behavior were observed between both load sequences and the test results after shrinkage is within the short‐term tests’ margin of variation. Numerical simulations performed using FE software Abaqus®, while applying a simplified definition of the bond, supported the results of the previous investigation.

Tension Stiffening and Cracking Behavior of Axially Loaded Alkali-Activated Concrete.

Alkali-activated concrete is an eco-friendly construction material that is used to preserve natural resources and promote sustainability in the construction industry. This emerging concrete consists of fine and coarse aggregates and fly ash that constitute the binder when mixed with alkaline activators, such as sodium hydroxide (NaOH) and sodium silicate (Na2SiO3). However, understanding its tension stiffening and crack spacing and width is of critical importance in fulfilling serviceability requirements. Therefore, this research aims to evaluate the tension stiffening and cracking performance of alkali-activated (AA) concrete. The variables considered in this study were compressive strength (fc) and concrete cover-to-bar diameter (Cc/db) ratios. After casting the specimen, they were cured before testing at ambient curing conditions for 180 days to reduce the effects of concrete shrinkage and obtain more realistic cracking results. The results showed that both AA and OPC concrete prisms develop slightly similar axial cracking force and corresponding cracking strain, but OPC concrete prisms exhibited a brittle behavior, resulting in a sudden drop in the load-strain curves at the crack location. In contrast, AA concrete prisms developed more than one crack simultaneously, suggesting a more uniform tensile strength compared to OPC specimens. The tension-stiffening factor (β) of AA concrete exhibited better ductile behavior than OPC concrete due to the strain compatibility between concrete and steel even after crack ignition. It was also observed that increasing the confinement (Cc/db ratio) around the steel bar delays internal crack formation and enhances tension stiffening in AAC. Comparing the experimental crack spacing and width with the values predicted using OPC codes of practice, such as EC2 and ACI 224R, revealed that EC2 tends to underestimate the maximum crack width, while ACI 224R provided better predictions. Thus, models to predict crack spacing and width have been proposed accordingly.

Time-Varying Evolution Behaviors of Steel–Concrete Composite Girders with Differentiated Connectors

To improve the cracking resistance of a concrete slab in the hogging moment region, a new concept called uplift-restricted and slip-permitted (URSP) connection technology has been proposed. Several studies have been conducted on URSP connectors, but investigations into the time-varying evolution behaviors of composite beams with URSP connectors are still lacking. In this paper, three types of elaborate finite element models of composite girders with differentiated connectors and different construction methods were established. Simulation of the concrete shrinkage and creep effect was realized using a user subroutine based on an improved rate-type formulation. The performances of the composite girders in three schemes were analyzed and compared in both the construction and service stages. The results demonstrated that the URSP connection technique can effectively increase the prestressing efficiency and decrease the tensile stress of the concrete induced by dead loads and vehicle loads. With an increasing service time, the concrete shrinkage effect will enhance the advantage of the URSP connection technique, and the creep effect will reduce this advantage. Finally, parametric analyses were conducted, and a value of 0.2 is recommended for the URSP length ratio to promote practical applications.

Characterization of concrete shrinkage induced strains in internally-restrained RC structures by distributed optical fiber sensing

The present paper reports the result of an inter-university experimental investigation on concrete shrinkage induced strains on embedded rebars instrumented with Distributed Optical Fiber Sensors (DOFS). The monitoring was performed for a standard 28 days drying time and for a shorter 6 days time span (reflecting realistic constructions schedules accelerations to meet set deadlines). The tested specimens were Reinforced Concrete (RC) tensile members differing in their geometry, DOFS employed and fiber/rebar bonding techniques. Regarding the latter, a combination of cyanoacrylate (for gluing) and silicone (protection) was found to be the optimal one for deployments inside RC structures. The DOFS-reported combined effect of concrete shrinkage and creep on the embedded rebars is compared with the Model Code 2010's predictions and employed to extract conclusions on the residual performance of the RC members at the end of their drying phase.

Calculation method steel reinforced concrete continuous bridge spans with two reinforced concrete slabs on the effect of concrete shrinkage

The article is considered calculation method steel reinforced concrete continuous bridge spans with two reinforced concrete slabs on the effect of concrete shrinkage. For long-term processes that must be considered when calculating the span structures of bridges, besides creep, concrete shrinkage applies. Object of study: composite steel and concrete span beam bridge with two reinforced concrete slabs. Purpose: to develop a calculation method the cross section steel reinforced concrete bridges with two reinforced concrete slabs on the effect of concrete shrinkage considering concrete creep. Continuous spans of steel reinforced concrete bridges with two reinforced concrete slabs over intermediate supports much more economically, in terms of metal consumption, compared to steel reinforced concrete bridges with one concrete slab. Cross section of a reinforced reinforced concrete beam consists of a steel part that combined with two reinforced concrete slabs. The article presents the results of the calculation of continuous steel-concrete superstructure of a road bridge with two reinforced concrete slabs by the above method.

Automation in the Construction of a 3D-Printed Concrete Wall with the Use of a Lintel Gripper.

Developments in the automation of construction processes, observable in recent years, is focused on speeding up the construction of buildings and structures. Additive manufacturing using concrete mixes are among the most promising technologies in this respect. 3D concrete printing allows the building up of structure by extruding a mix layer by layer. However, the mix initially has low capacity to transfer loads, which can be particularly troublesome in cases of external components that need to be placed on top such as precast lintels or floor beams. This article describes the application of additive manufacturing technology in the fabrication of a building wall model, in which the door opening was finished with automatic lintel installation. The research adjusts the wall design and printing process, accounting for the rheological and mechanical properties of the fresh concrete, as well as design requirements of Eurocode. The article demonstrates that the process can be planned precisely and how the growth of stress in fresh concrete can be simulated, against the strength level developed. The conclusions drawn from this research will be of use in designing larger civil structures. Furthermore, the adverse effects of concrete shrinkage on structures is also presented, together with appropriate methods of control.

Analysis and correction of stress error in construction monitoring of cantilever cast prestressed beam bridge

In order to correct the monitoring stress of long-span prestressed concrete girder more accurately, and consider the characteristics of bridge load gradually applied during cantilever construction, this paper proposes an accurate correction method for monitoring stress of long-span prestressed concrete bridge. Based on the linear creep theory and Bauer boltzmann (L.B oltzman) superposition principle, the invariant elastic mode of traditional calculation isreplaced by the equivalent elastic modulus from load-to-pre-calculation, and the formula of concrete creep, and the time-varying elastic mode is taken into account. The effect of concrete shrinkage and temperature change softer on the real stress value of the structure is accurately corrected by separating and removing stress-free strain from the measured strain. This method is applied to the calculation of the measured stress in the key section of the main beam of a long-span continuous beam of a high-speed railway. The results show that the modified stress value is in good agreement with the theoretical value and the error is significantly reduced, which verifies the reliability and accuracy of the modified method.

Analysis of the concrete shrinkage effects on the real behavior of the spatial concrete and reinforced concrete structures using the thermal analogy

PurposeThis paper aims to present an approach for the numerical simulation of concrete shrinkage. First, some physical mechanisms of shrinkage are described and then the developed numerical model for the analysis of shrinkage of spatial three-dimensional structures using thermal analogy is presented. Results of the real behavior of structures because of concrete shrinkage using the developed numerical model are compared with the experimental and it is clearly shown that the developed numerical model is an efficient tool in predicting the time-dependent behavior of all concrete structures.Design/methodology/approachIn this paper, Fib Model Code 2010 to predict shrinkage deformation of concrete is used, and it was incorporated in the three-dimensional numerical model using the thermal analogy. Mentioned three-dimensional numerical model uses the modified Rankine material law to describe concrete behavior in tension and modified Mohr-Coulomb material law to describe concrete behavior in compression. The developed three-dimensional numerical model successfully analyzes the behavior of reinforced and/or prestressed concrete structures including time-dependent deformations of concrete as well.FindingsResults are shown in this paper clearly demonstrate the reliability of the developed numerical model in predicting the shrinkage strain, as well as its impact on concrete and reinforced concrete structures. The results obtained using the developed numerical model are in better agreement with the experimental results, than the results obtained using the numerical models from literature that also use the Fib Model Code 2010 to predict the shrinkage strain. So, it can be concluded that for a real simulation of concrete structures, alongside the model for predicting the shrinkage strain, the models for concrete behavior in tension and compression have a very important role.Originality/valueResults of the developed three-dimensional numerical model were compared with experimental results from literature and with theoretical foundations, and it can be talked that this numerical model presents a good tool for analysis of reinforced and prestressed concrete structures including shrinkage deformation of concrete. Results obtained using the developed three-dimensional numerical model are better agreed with experimental than results of other numerical model from literature.

Hygrothermal performance of timber-concrete composite panels – theoretical investigation

The concrete layer as a part of the timber-concrete composite (TCC) element makes it possible to maintain the accumulated heat and thus reduce the energy required for heating. Especially for buildings used for a sauna, swimming pools or wellness. In the TCC cross-section due to uneven thermal and humidity deformation of both materials, additional stresses occur. It can lead to the failure of partial cross-sections or composite connection. The aim of the research is to investigate the influence of changing humidity and temperature conditions of the environment on the composite adhesively bonded TCC panels without the influence of other phenomena such as mechanical stress or the effect of concrete shrinkage. The paper presents the results of the preliminary theoretical investigation before the realization of measurements on prepared specimens.

Measured temperature effects during the construction of a prestressed precast concrete bridge beam

Prestress losses in precast concrete beams include the short-term effects of elastic shortening and the long-term effects of concrete shrinkage, concrete creep and steel relaxation. Temperature effects are, however, excluded. The aim of this research was to monitor the behaviour of a prestressed precast concrete bridge beam, focussing on temperature effects and destressing. Successful monitoring assists in comparing the real performance of a structure to the expected design performance, and in managing the durability of the monitored structure. The effect of temperature variation on strains in prestressed beams was investigated by instrumenting a precast beam. Temperature and strains were monitored from the day of casting up to and including the cutting of the pretensioning strands. Daily temperature variations causing vertical non-linear temperature profiles resulted in internal strains of up to 28 % of the strains caused by destressing. It was therefore concluded that thermal effects before destressing resulting from elevated curing temperatures and daily temperature changes should be considered in the calculation of prestress losses. The monitoring techniques used were successful in determining the stresses and strains within the beam, which can be used to compare real prestress losses with the losses assumed in design.

Coupled Effects of Concrete Shrinkage, Creep, and Cracking on the Performance of Postconnected Prestressed Steel-Concrete Composite Girders

Coupled Effects of Concrete Shrinkage, Creep, and Cracking on the Performance of Postconnected Prestressed Steel-Concrete Composite Girders

Quantifying the influence of elliptical ring geometry on the degree of restraint in a ring test

A novel elliptical ring test method has been proposed to replace the traditional circular ring test method for the purpose of shortening test duration for assessing cracking tendency of concrete and more conveniently examining crack evolution in concrete rings. To further explore the mechanism of this new test method, a numerical model was established to analyse stress development and crack initiation in concrete rings in which a fictitious temperature field simulated the externally applied mechanical effects of concrete shrinkage on concrete causing the same strain as shrinkage does. The proposed numerical model was validated against experimental results and was then used to evaluate the effects of ring geometry on the degree of restraint to concrete. Moreover, a series of numerical experiments were conducted to derive the expression of the degree of restraint to elliptical rings. Through the error analysis of the degree of restraint on concrete properties and ring geometry, the expression was verified so that it can be used to calculate the degree of restraint provided by the internal steel ring. According to the derived expression, the restrained elliptical ring test can be designed to quantitatively simulate the service condition of concrete in an engineering structure more accurately.

Experimental Study on the Long-Term Behaviour of RBPC T-Beams

This study compares the mechanical properties of the retard-bonded and conventionally bonded prestressed concrete (RBPC and BPC, respectively) under uniform loads. Results show that the prestressed strands and concrete of the RBPC T-beams are firmly bonded with harden of retard-bonded materials, thereby exhibiting the same mechanical properties as that of the BPC beams. The growth rate of the long-term deflections of the RBPC T-beam is slightly lower than that of the BPC T-beam. Given the effect of concrete shrinkage, creep and time variation of prestress loss, the regular patterns of deflection growth of the RBPC T-beam mid-spans are analysed based on the age-adjusted effective modulus method, method of equivalent prestress load and calculation model of prestress loss. Accordingly, the long-term deflection development curves of the RBPC T-beam mid-spans under self-weight, prestressing force and external loads are obtained. Calculation results are in good agreement with the test results. This method has immense applicability for the computation of the RBPC T-beams, and can be used to estimate the long-term deflection growth of regular patterns of the RBPC components.

Damage in glass-concrete composite panels

The evolution of damage of a glass-concrete façade panel is presented and discussed. The phenomenon is strongly influenced by the mutual interaction between three materials (concrete, steel rebars and glass) having different mechanical and rheological properties.To assess the possible causes of the observed damages, detailed 3D finite element numerical analyses were conducted considering the effects of thermal loads, due to difference of temperature outside and inside of the building, and the effects of concrete shrinkage. Furthermore, a construction stages analysis was implemented to consider the loading history during the production process of the panel.The analyses were performed both in linear elastic and non-linear conditions to assess the stress redistributions in the panel due to concrete cracking. In particular, the analyses showed that the shrinkage of concrete was the main reason of the detected damage in a case study, even considering the creep that mitigates the phenomenon leading to a delayed cracking. Finally, a parametric study is presented assuming different factors (concrete rib sizes, different shrinkage laws, as a consequence of the addition of shrinkage-reducing admixtures (SRA), different bond between glass and concrete and different reinforcement ratio). The results of this parametric study suggest interesting remarks about suitable design principles of glass-concrete façade panels.

Coupling model for calculating prestress loss caused by relaxation loss, shrinkage, and creep of concrete

The calculation model for the relaxation loss of concrete mentioned in the Code for Design of Highway Reinforced Concrete and Prestressed Concrete Bridges and Culverts (JTG D62—2004) was modified according to experimental data. Time-varying relaxation loss was considered in the new model. Moreover, prestressed reinforcement with varying lengths (caused by the shrinkage and creep of concrete) might influence the final values and the time-varying function of the forecast relaxation loss. Hence, the effects of concrete shrinkage and creep were considered when calculating prestress loss, which reflected the coupling relation between these effects and relaxation loss in concrete. Hence, the forecast relaxation loss of prestressed reinforcement under the effects of different initial stress levels at any time point can be calculated using the modified model. To simplify the calculation, the integral expression of the model can be changed into an algebraic equation. The accuracy of the result is related to the division of the periods within the ending time of deriving the final value of the relaxation loss of prestressed reinforcement. When the time division is reasonable, result accuracy is high. The modified model works excellently according to the comparison of the test results. The calculation result of the modified model mainly reflects the prestress loss values of prestressed reinforcement at each time point, which confirms that adopting the finding in practical applications is reasonable.

Analysis of Shrinkage and Creep Effects on New Steel-Concrete Composite Deck System for Suspension Bridge

AbstractTo study the shrinkage and creep of the new steel-concrete composite deck system of a suspension bridge, an equivalent calculation method based on the existing calculation theory of shrinkage and creep with changing temperatures and creep guidelines was proposed. Two different validation analysis models were established for the same structure using two largely popular finite element programs. The validity and accuracy of the equivalent results were verified, and the equivalent method was found to be practical, feasible, and highly accurate. A fine segment model for the steel-concrete composite bridge deck system of a suspension bridge was created with the use of the ANSYS finite element program. Further research was conducted on the effect of shrinkage and creep on a composite structure using the proposed equivalent calculation method. Research results for the new class of steel-concrete composite bridge deck indicate that the concrete shrinkage effect is dominant, but the creep effect is relative...

The influence of concrete shrinkage on durability of reinforced structural members

Abstract The aim of the paper was to present the author’s novel approach to the problem of the influence of concrete shrinkage on the static-strength performance of reinforced structures. The problem of concrete shrinkage has been known in concrete technology for years, mainly in the theoretical and experimental aspects. However, there are few works in which the effect of concrete shrinkage in real reinforced structural members and structures is shown. In the present article the author performs an analysis of these effects on a macro-scale, useful in the assessment of the influence of concrete shrinkage on limit states of bearing capacity and serviceability of reinforced concrete structures. An important distinction is made between shrinkage stresses imposed in RC members by external and internal (reinforcement induced) constraints and residual shrinkage stresses inside members (massive especially) resulting from non-stationary and non-linear moisture fields. The article concludes with a way of calculating the necessary, near-surface anti-shrinkage reinforcement in such members.

Theoretical Calculation and Experimental Research of Shrinkage of High Strength Concrete an High-Speed Railway Bridges

Concrete bridges on high-speed railway are usually constructed with high strength concrete. Because of shrinkage of concrete, large stress and deformation always appear in construction and operation process of bridges. It even leads to concrete cracking. So as to guarantee the safety of structures and smoothness of tracks, correct calculation of concrete shrinkage effect must be done. Concrete shrinkage effect is a very complex non-stress strain problem which is influenced by numerous factors and difficult to calculate. According to the factors considered from different emphasis aspects, a variety of patterns or specifications are formed based on different domestic and foreign models of concrete shrinkage calculation. Combined with the construction of Jiangshan Harbor Bridge (75+2×135+75) m prestressed concrete continuous beam bridge on Hangzhou-Changsha high-speed railway, concrete shrinkage field tests and measurements were carried in which the same mix of high strength concrete as that of the bridge was used. The results of tests and measurements were compared with results of different theoretical models. The effects of high strength concrete shrinkage on high-speed railway concrete bridges were studied and some useful conclusions were obtained.

Experimental and Numerical Assessment of Restrained Shrinkage Cracking of Concrete Using Elliptical Ring Specimens

AbstractA new experimental method is proposed for assessing the cracking tendency of concrete using elliptical ring specimens subject to restrained shrinkage. To explore the mechanism of this method, a numerical model is developed to analyze stress development and crack initiation in concrete rings in which the effect of concrete shrinkage is simulated by a fictitious temperature drop applied on concrete causing the same strain as that induced by shrinkage. Stress developed in a concrete ring is then obtained through a combined thermal and structural analysis. Based on the maximum tensile stress cracking criterion, numerical results are in accordance with experimental results on cracking age for a range of circular and elliptical concrete rings with different geometries. Geometrical factor, i.e., the ratio between the major and minor semiaxes of an elliptical ring, is the main factor that affects tensile stress developed and consequently concrete cracking age in restrained ring specimens. Elliptical rings...