Influence Of Concrete Creep Research Articles

Performance of RC Beams with NSM Fe-SMA after Eight-Year Exposure and Sustained Loading

Low-cost iron-based shape memory alloys (Fe-SMAs) have emerged as a viable alternative to carbon fiber reinforced polymers (CFRP) for near-surface mounted strengthening of reinforced concrete (RC) structures, particularly due to their ease of prestressing and their plastic behavior similar to reinforcing steel. The short-term behavior has already been investigated in detail, yet the durability of such systems still remain a relatively unexplored area, as there is a scarcity of long-term experimental studies available. To address this gap, two RC beams strengthened with NSM Fe-SMA were subjected to natural environmental conditions for an extended period of 8 years, during which they were subjected to sustained loading beyond their cracking load level. Subsequently, the beams were subjected to four-point bending loading until failure. Results were compared with a previous short-term study involving identical specimens that had not been exposed to environmental factors or sustained loading. A comprehensive cross-section analysis (CSA) further complements the experimental results, which effectively captured both the long-term and bending behavior. Influence of concrete creep and shrinkage, as well as Fe-SMA relaxation is discussed by employing the CSA. Lastly, influential parameters and their impact on structural performance were identified via sensitivity analysis.

Dynamic Responses of Train-Symmetry-Bridge System Considering Concrete Creep and the Creep-Induced Track Irregularity

This work considers the influence of concrete creep on track irregularities and establishes the dynamic motion equation of the train-track-bridge coupling system. The track irregularity is obtained by superposition of the initial geometric irregularity and additional geometric irregularity of the steel rail caused by creep. When high-speed railway trains pass through bridges; the vertical acceleration and vertical displacement of continuous beam bridges are related to the train’s operating speed, and the influence of creep camber is relatively small. At the same time, considering the randomness of track irregularities, the dynamic responses of the train track bridge coupling system under the action of random track irregularities are analyzed, and the dynamic responses of trains at different operating speeds are obtained. The deterministic and uncertain dynamic responses of the train track bridge system were compared and analyzed to verify the accuracy of the Karhunen Loéve expansion (KLE)-Point estimate method (PEM) calculation results. The results indicate that the random characteristics of track irregularities have a significant impact on train dynamic response. Based on the random system vibration analysis and considering the safety and comfort indicators of high-speed railway trains, the creep deformation limit of a continuous beam bridge with a length of 48 m + 80 m + 48 m is obtained to be 19 mm. This is the first time that the dynamic responses of train-symmetry-bridge system are calculated by considering concrete creep and the creep-induced track irregularity, which has certain significance for understanding the dynamics of train -bridge system. In addition, the proposed creep threshold is also of great significance to ensure the safety of traveling.

Influence of Concrete Creep on the Bending of a Prestressed Bridge Beam

By present time significant experimental and theoretical material on concrete creep has been accumulated. At the same time, the known approaches to calculation of concrete and reinforced concrete structures with regard to creep are oriented mainly to solving problems with relatively simple geometry of the product. Moreover, there are no mechanic-mathematical models of hereditary type oriented to the finite-element method.The concept of modelling of long-term deformation of reinforced concrete structures in a three-dimensional statement, based on the use of the integral deformation modulus of concrete, does not allow one to carry out designing considering the technological prehistory. Therefore, the problem of developing a finite-element algorithm and corresponding software allowing the modelling of the volumetric stress-strain state of large-span prestressed reinforced concrete structures within the framework of the theory of hereditary aging is relevant.

Collapse analysis of real RC spatial structures using known failure schemes of ferro-cement shell models

Large-span reinforced concrete (RC) shells collapses that occurred in the last decade caused many death toll as well as significant losses to national economies. The most famous cases were the collapse of the aqua park cover in Moscow on February 2004 and the 2E terminal roof destruction at Charles de Gaulle Airport near Paris on May 2004. Following the publications of the appropriate commissions that have studied the reasons of these events, the influence of concrete creep and changes in the shell geometry on buckling of RC thin-walled shells was not properly considered in the design. This study is focused on buckling of such shells, taking into account geometrical and physical nonlinear behaviour of compressed concrete. Other important reasons of concrete shells collapse are also analysed. The study is based on available experimental and theoretical investigations of ferro-cement shells' models previously performed by the first author. The results of these investigations, obtained for small-scale ferro-cement models of thin-walled shallow RC shells, are discussed. Behaviour of the tested models is compared with that of the above-mentioned real shells and similar structures, which also collapsed. The critical buckling loads for the shells are obtained. It is shown that these loads are lower than the actual ones; thus, the shells buckling was unavoidable. To prevent brittle shell failure, they should be designed using other dominant failure modes that appear before the buckling. Possible failure schemes of real RC shells can be predicted using dominant failure modes obtained by laboratory testing of scaled models. Copyright © 2012 John Wiley & Sons, Ltd.

The Influence of Concrete Creep on Deflection of Box Beam with Sectional Joints in Continuous Rigid Frame Bridge

Over-deflection of beam in continuous rigid frame bridge has become an serious problem in recent years. The reason is complex. Some reseachers think that the bad quality of sectional joints in cantilever construction will cause additional shearing deformation and affect the beam deflection, this idea need to be further studied. In the paper, two three-dimensional models are built up based on a factual bridge, the simulation method of sectinoal joints is studied. The influence of concrete creep on the deflection of box beam with sectional joints is analysed being compared to beam without sectional joints . In order to simulate concrete creep, a method of effective elastic modulus adjusted with concrete age was applied. The study shows that the shearing deformation of sectional joints has obvious influence on the long-term deflection , and different calcultion method of concrete creep has different effect on it. It shouldn’t be ignored in the bridge design.

The Influence of Concrete Creep on Deflection of Box Beam with Sectional Joints in Continuous Rigid Frame Bridge

Over-deflection of beam in continuous rigid frame bridge has become an serious problem in recent years. The reason is complex. Some reseachers think that the bad quality of sectional joints in cantilever construction will cause additional shearing deformation and affect the beam deflection, this idea need to be further studied. In the paper, two three-dimensional models are built up based on a factual bridge, the simulation method of sectinoal joints is studied. The influence of concrete creep on the deflection of box beam with sectional joints is analysed being compared to beam without sectional joints . In order to simulate concrete creep, a method of effective elastic modulus adjusted with concrete age was applied. The study shows that the shearing deformation of sectional joints has obvious influence on the long-term deflection , and different calcultion method of concrete creep has different effect on it. It shouldn’t be ignored in the bridge design.

Creep effects on dynamic behavior of concrete filled steel tube arch bridge

Long-term properties of concrete affect structures in many respects, not excepting dynamic behaviors. This paper investigates the influence of concrete creep on the dynamic behaviors of concrete filled steel tube (CFT) arch bridges, by means of combining the analytical method for the creep of axially compressed CFT members, which is based on Model B3 for concrete creep, with the finite element model of CFT arch bridges. By this approach, the changes of the stress and strain of each element in the bridge with time can be obtained and then transformed into damping and stiffness matrices in the dynamic equation involved in the finite element model at different times. A numerical example of a long-span half- through CFT arch bridge shows that creep influences the natural vibration characteristics and seismic responses of the bridge considerably, especially in the early age. In addition, parameter analysis demonstrates that concrete composition, compressive strength and steel ratio have an obvious effect on the seismic response of the CFT arch bridge.

Creep Stress Analysis of PC Composed Box Girder Bridge with Corrugated Steel Webs

According to the forced load-bearing characteristics of the prestressed concrete girder bridge with corrugated steel webs, the cross-section internal forces and stress redistribution of box-girder were studied under the influence of concrete creep. And the internal force redistribution formula on concrete creep was derived through the establishment of the compatibility equation of bending deformation; the stress redistribution formulas of the top slab and the bottom slab of box-girder at any time were also derived, through the establishment of the compatibility equation of the axial displacement and angular deformation of the top slab and the bottom slab of box-girder under the influence of concrete creep at any time. These show that the creep stress is only related to the box height and it’s the geometric properties of top slab and bottom slab concrete section, but not to the steel web’s size.

Creep influence on buckling resistance of reinforced concrete shells

The influence of concrete creep on the response of shallow reinforced concrete shells is analyzed in this contribution in the context of time-dependent shell buckling. The classical time-invariant stability analysis is extended to account for the long-term creep buckling, which is characterized by a continuous increase of deformation and time-dependent stability failure, if a certain critical load factor is exceeded. For a systematic study of these phenomena on a cylindrical roof shell, a recently proposed time-invariant and a time-dependent material model for concrete are combined in the framework of the long-term multi-level simulation concept, taking into account elasto-plastic deformation, crack damage and nonlinear basic creep of concrete. The performed numerical analyses provide an insight into the mechanisms of creep buckling of reinforced concrete shells as well as its sensitivity with respect to main influence factors and emphasize the relevance of interaction mechanisms between short- and long-term loadings.