Concrete Tension Research Articles

Shear strength of fiber-reinforced high-strength steel ultra-high-performance concrete beams based on refined calculation of compression zone depth considering concrete tension

This article presents an experimental and theoretical investigation on the shear behavior of fiber-reinforced ultra-high-performance concrete beams reinforced with high-strength steel. The test parameters included the fiber volume fraction, fiber type, and stirrup ratio. The test results indicate that the shear failure in ultra-high-performance concrete beams is not brittle and catastrophic but has ductility characteristics. A moderate quantity of stirrups can significantly improve the shear behavior of ultra-high-performance concrete beams, as reflected in the thorough propagation of cracks in both shear span and pure bending zone. The depth of the compression zone considering concrete tension was derived based on the deformation compatibility and force equilibrium equations for both serviceability limit state and ultimate limit state. The comparison of the proposed method and classical beam theory shows that the concrete tension should not be neglected in the serviceability limit state analysis. After cracking, the concrete tension can be neglected for simplicity when the beam is heavily reinforced and should be considered when the beam is lightly reinforced. Then, a shear strength model was established based on Rankine’s failure criteria, the truss model, and Association Francaise de Génie Civil-Sétra. Finally, the proposed shear strength equation was verified by the test results and compared with other shear strength equations.

Size Effect of the Post-Peak Cyclic Behavior of Plain Concrete in Uniaxial Tension with Acoustic Emission Technique

Abstract At present, studies about the size effect of concrete mainly focus on macroscopic mechanical behaviors like strength and fracture energy, while research on the size effect of the cyclic nonlinear properties of concrete is very rare. To further analyze the ambiguous concept of specimen size, three types of precut cylindrical concrete specimens with the same diameter but different heights, the same height but different crack depths, and the same aspect ratio but different volumes are used for the uniaxial post-peak cyclic tensile test. At the same time, the acoustic emission (AE) device is used to monitor and collect the AE signals in the loading process. According to the test results, no size effect exists in the accumulation of residual deformation, but the degradation of the unloading modulus is related to the specimen diameter. Meanwhile, the Kaiser effect is found in the analysis of AE signals. After the data analysis, a post-peak cyclic tensile model of concrete is proposed based on the size effect and damage evolution. The quantitative relationship among the model parameter, specimen aspect ratio, and damage is calculated. Finally, a good comparison is found between the predicted model and experimental result.

Results on the long-term performance and effectiveness of a galvanic CP system applied on a lightweight concrete bridge with prestressed steel as determined by depolarisation values and current densities

This paper gives insight in the research and investigations which were undertaken on a post tensioned light-weight concrete box girder bridge in the Netherlands. This project started in the first half of 2013 and measurements are still executed regularly. Due to long-term leakage of a longitudinal joint between 2 parts of the bridge, chlorides had penetrated into the concrete up to the level of the reinforcement and beyond, causing severe corrosion of the steel, spalling of the concrete cover and eventually causing danger for the shipping underneath the bridge due to falling lumps of concrete. To solve this problem, Galvanic Cathodic Protection (GCP) was applied in 2 stages. Firstly, in 2013, zinc based anode strips were applied on the soffit of 2 post tensioned lightweight bridge segments for the purpose of testing and monitoring. After obtaining good results from the test, in 2014/2015 the remaining 29 bridge segments were repaired and protected with the same GCP system as well. This paper reviews subsequent potential decay and current densities measurements, which have provided valuable information on GCP performance and throwing power. The results of anode performance at different locations and depths are reviewed. Concrete resistivity has shown a major influence on the effectiveness of the installed GCP system.

Quality Control of a Pos Tensioned Concrete Tower for Wind Turbine Assembly

More than 30 years ago, ENERCON created a unique technology patent in the form of gearless Wind Energy Converter technology. Ever since then, our engineers and specialists have been working continuously to further develop the products and manufacturing processes. We guarantee our customers maximum agility and excellent solutions which make good economic sense and comply with market requirements.Innovations are fundamental to success here. We want to be the first to establish new ideas on the market and new standards in the industry. The expertise of our employees and their interdisciplinary working partnerships form are the essence of our technological excellence.Every day we work to live up to our claim to perform as technology leader. We are leading the way in developing new technologies and taking an active and responsible role in shaping the future of energy generation and supply from renewables.For that we aim to develop and produce the highest-quality wind energy converter on the market. We do not define ourselves primarily in terms of the purchase price, but instead offer turbines with the lowest running costs per unit generated. Content and well-qualified employees are essential for long-term success. That is why we make huge investments in training and advanced training and measures to promote healthy workplaces. The successful further development of our high-tech products relies on us working together. Hybrid towers for ENERCON wind energy converters comprise individual precast concrete elements and steel sections that form the top end of the tower. Concrete segments with large diameters are produced in two or three shells so that they can also be transported to locations which are complex to reach. After all segments and sections have been assembled, the bottom steel section, the concrete segments and the foundation are joined together and tensioned to form one unit by means of prestressing tendons.

Insight into the tension stiffening behavior of reinforced concrete tension members revealed by finite element modeling

The disasters happened in recent past pointed out the need of design criteria, ensuring adequate safety levels against progressive collapse. The attention was focused on the behavior of composite beam-to-column joint components in the field of large displacements. This article presents the experimental and numerical study enabling the simulation of the RC elements under tension. This has helped in understanding the non-negligible contribution of concrete in tension stiffening response up to failure especially in the case of discontinuous geometry marked in composite structures. The finite element model proposed may be considered a mid-way between smeared and discrete crack modeling approaches.

Numerical Estimation of the Mechanical Properties of a Steel-Fiber-Reinforced Geopolymer Composite

A mesoscale model for modeling a geopolymer concrete (GPC) in tension and compression using the Drucker–Prager yield criterion for the GPC in compression and Rankin’s criterion in tension is proposed. The von Mises isotropic plasticity model with a negative hardening modulus is used for modeling the short-steel-fiber pull-out behavior. A computationally efficient fiber generator that takes into account the specific fiber orientation near surfaces is developed. An uncoupled upscaling method of mesoscale simulation is proposed for an efficient and accurate modeling of macroscale structural elements. Results showed that the numerical models proposed exhibited a good agreement with experimental measurements in tensile, compression, and flexural tests. The numerical models can be used to estimate the load-bearing capacity of structural elements, such as beams, where short fibers and a macroscopic reinforcement are mixed in a GPC matrix.

Finite Element-Smeared Crack Combined Algorithm based Bridge Corbel Analysis

A practical combined algorithm for the corbel of common reinforced concrete bridge is put forward. Based on material nonlinearity, combining the professional finite element software Midas Civil and MIDAS FEA with Smeared crack model, the Thorenfeldt and Constant curves are used as concrete compression and tension constitutive model to numerical analyze the corbel’s stress and crack. Example results show that the normal stress of the corbel and crack are greater than design value of C35 concrete tensile strength, and part areas are in the plastic state. The groove corner region of the corbel has abrupt stress. The crack of the corbel is firstly generated at the groove and the top plate, and gradually expands with the increase of the load coefficient. It develops sufficiently in the groove region, but there is not any full-length crack. The corbel has a group-strip-like crack farther from groove corner region. The calculation results are consistent with the bridge disease condition, which shows that Finite Element-Smeared Crack Combined Algorithm proposed in this paper is effective for the analysis of corbel.

Field performance of large section concrete pipes cracking during jacking in Chongqing – A case study

Long-distance large-section pipe jacking inevitably encounters a variety of complex engineering problems in the construction process, one of which is the pipe concrete cracking during jacking. A large-area rupture and leakage occurred at pipe No. 61 during the large-section concrete pipe jacking adopted in the project studied in this paper. After a detailed field investigation and on-site pipe strain monitoring, the possible causes of pipe cracking were analysed. First, a direct compression failure of the pipes was ruled out. Additionally, a large number of pores were found inside the concrete fragments falling from pipe No. 61’s site. Thus, we suspected that the pipe cracking was attributed to the conversion of the pipe’s compressive stress into the concentrated tensile stress by the substantial pores inside the pipes, which resulted in a concrete tension fracture. The core sampling results of the pipes after monitoring confirmed that there were indeed plenty of small pores in multiple pipe concretes, while the strain monitoring results indicated that the compressive stress of the pipes during normal jacking had the potential to produce the tensile stress that could crack the concrete. Combining this with the jacking deviation monitoring curves, it could be deduced that the upper right side of the pipes was most prone to failing initially. This coincided with the rupture area of pipe section No. 61 but was also consistent with the prediction of pipe No. 60 cracking, thus proving the rationality of the pipe rupture cause hypothesis. Finally, no cracking occurred after improving the production quality of the pipes. This not only shows that the pipe quality is indeed the root cause of cracking but also effectively solves the engineering problems and provides an excellent reference for similar projects.

Fiber Beam Analysis of Reinforced Concrete Members with Cyclic Constitutive and Material Laws

This paper presents a non-linear Timoshenko beam element with axial, bending, and shear force interaction for nonlinear analysis of reinforced concrete structures. The structural material tangent stiffness matrix, which relates the increments of load to corresponding increments of displacement, is properly formulated. Appropriate simplified cyclic uniaxial constitutive laws are developed for cracked concrete in compression and tension. The model also includes the softening effect of the concrete due to lateral tensile strain. To establish the validity of the proposed model, correlation studies with experimentally-tested concrete specimens have been conducted.

Durability of ultra-high performance concrete in tension under cold weather conditions

Freezing and thawing resistance is a key characteristic for concrete materials in cold weather conditions. In this study, the tensile properties and elastic modulus of ultra-high performance concrete (UHPC) under accelerated freeze-thaw cycles are characterized. Six series of UHPC specimens are experimentally tested with a well-designed direct tension test (DTT) method to capture complete tensile stress-strain responses. Both the dynamic and wave moduli of elasticity of UHPC are measured at specific cycles using the standard impact test and self-designed “smart aggregate” technology, respectively. Long term freezing and thawing cyclic conditioning of UHPC samples results in reductions of elastic modulus, tensile strength, strain capacity, and energy absorption capacity. The tensile stress-strain curves of UHPC demonstrate distinct descending with increasing freeze-thaw cycles, particularly in the strain softening region. The energy-based approach is found to be more sensitive and effective than the elastic modulus-based approach when evaluating material deterioration over time and capturing accumulative material degradation subjected to rapidly-repeated freezing and thawing actions. As from the test results, UHPC is characterized as a very durable cementitious material, but it is not inherently unconquerable. Extended freezing and thawing actions can still lead to deterioration of the material, with respect to its elastic modulus, tensile strength, energy absorption capacity, etc. As demonstrated, the DTT method can be used to effectively characterize the long-term performance of UHPC in tension under cold weather conditions.

Geometry, material properties and bond performance of prototype titanium reinforcing bars

The use of titanium as a concrete reinforcing bar material has been proposed. This study summarizes measured geometric and experimentally determined material properties of 6Al-4V titanium reinforcing bars and comparable properties of ASTM A615 steel. All bars are nominally #5 bars. Bond characteristics of the titanium bars were assessed through ASTM D7913 pull-out tests, ASTM A944 beam-end tests and four concrete prism tension tests. The nature of reinforcing bar bond to concrete is such that deformed bars exhibit very similar patterns of bond stress-slip behaviour. Provided adequate deformations are provided, the bond-slip relationship is dominated by concrete behaviour. The bond performance of the 6Al-4V titanium bars was similar to that of A615 steel bars and, as expected, clearly affected by the rib ratio. The results presented reinforce the ASTM A615-implied lower limit for the rib ratio, Rr > 0.05. The implication of a similar bond-stress behaviour is that existing bond relationships for steel-reinforced concrete likely apply to titanium bars provided they meet the deformation requirements of ASTM A615 – the standard for which steel reinforcing bars, and therefore their bond characterisation – is calibrated. Both the pull-out and beam-end test results reinforce the conclusion that bond behaviour of titanium bars is essentially the same as that steel bars. The bond stresses, normalised to account for variation in concrete strength, are similar and the calculated development lengths are essentially in the ratio of yield strengths of the materials. The prism tension tests demonstrated that concrete crack width is proportional to modular ratio of the reinforcing material, while spacing is inversely proportional to the stiffness of the initial bond-slip response.

Performance of Fiber-reinforced Self-consolidating Concrete for Repair of Bridge Substructures

The main objective of this study was to investigate the structural properties of bridge substructures retrofitted with fiber-reinforced self-consolidating concrete (FR-SCC) tension zones. The testing program compared FR-SCC repair mix designs at two different replacement levels of Type-K shrinkage compensating cement (10 and 15% of the total cementitious content).Both small and full-scale tests were conducted. The small-scale repair tests included third point loading composite prism tests as well as bond strength tests. The full-scale tests included a total of nine beam specimens. One set of three control beams (CC), and two sets of three repair beams representing either 10% (C-10) or 15% (C-15) Type K cement replacement. Results of this study showed that the two repair concretes examined throughout this study, C-10 and C-15, showed comparable load-carrying capacities to the monolithic control beams.

Effect of graded fibers on stress strain behaviour of Glass Fiber Reinforced Concrete in tension

Effective blending of short length and long length fibers in concrete is termed as Graded fiber reinforced concrete. Earlier research shows that short length fibers primarily control the propagation of micro cracks, and improve the ultimate strength whereas, long length fibers arrest the macro cracks and improve the post crack deformation of concrete. Thus different combinations of short and long length fibers would help in arresting the micro and as well as macro cracks to improve both pre and post crack performances of concrete. An attempt has been made to study the effect of addition of Graded Glass Fibers with different fiber length and volume fraction in Glass Fiber Reinforced Concrete. The experimental work was carried out under uni-axial tension for M30 grade of concrete with the 0.1%, 0.2%, 0.3%, 0.4% & 0.50% fiber volume of Mono Glass Fibers (3 mm, 6 mm, 12 mm and 20 mm length fiber). In 0.3% fiber volume, different fiber volume combination of Glass fibers in Short Graded form (3 mm + 6 mm length fiber), combination of Glass fibers in Long Graded form (12 mm + 20 mm length fiber) and combination of Short Graded + Long Graded fibers to form Combined Graded fibers (3 mm + 6 mm + 12 mm + 20 mm length fiber) were studied. The results shows that the strength, deformation capacity and energy absorption capacity is higher for Graded Glass Fiber Reinforced concrete than Mono Glass Fiber Reinforced Concrete. Graded fibers improved the workability. Fiber efficiency characteristics (Fiber length, Fiber dispersion, fiber orientation) were quantified to investigate their effect on the tensile strength of Glass Fiber Reinforced Concrete (GFRC). For this purpose, optical microscopic study and an image analysis technique is used to examine the failed specimens of GFRC. The results of image analysis shows that the strength of fiber reinforced composite are dependent on the fiber efficiency characteristics.

Flexural Response of Reinforced Concrete Beams Strengthened with Near-Surface-Mounted Fe-Based Shape-Memory Alloy Strips

This paper proposes an advanced near-surface-mounted (NSM) technique with an Fe-based shape-memory alloy (Fe-SMA) strip which can solve issues of low workability and reduced ductility of reinforced concrete (RC) beams strengthened with an NSM technique using prestressed fiber-reinforced polymer (FRP) strips in the concrete tension section. The flexural behavior of the RC beam strengthened by the NSM technique with the Fe-SMA strip was investigated. A total of seven RC beams were tested by four-point bending tests under displacement control. The type of reinforcements, the quantity of Fe-SMA strips, and the pre-straining level of the Fe-SMA strips were considered as experimental variables. Cracking load, yielding load, and ultimate load increased, respectively, with larger quantities of Fe-SMA strip. In addition, activation of embedded Fe-SMA in the concrete by electrical resistance heating effectively induces a prestressing force on the concrete beam, resulting in a cambering effect. The introduced prestressing force to the RC beam by activation of the Fe-SMA increased the crack and yielding loads, and did not decrease the ductility of the RC beam compared to the RC beam with non-activated Fe-SMA. It can be concluded from the test results that the strengthening technique using the recovery stress of the Fe-SMA strip as the prestressing force solves the various problems of the existing prestressing strengthening systems, meaning that Fe-SMA can be used as a substitute for conventional prestressing strengthening systems.

Interaction between matrix crack and circular capsule under uniaxial tension in encapsulation-based self-healing concrete

This paper investigates the fracture process of a capsule when subjected to uniaxial tension in encapsulation-based self-healing concrete. A circular capsule embedded in the mortar matrix is considered along with different ratios of core-shell thickness. To represent potential cracks, zero thickness cohesive elements are pre-inserted throughout element boundaries. The effects of fracture strength around the interfacial transition zone of the capsule are analyzed. The crack nucleation, propagation, and fracture mode of capsule are also discussed. The numerical results indicate that increasing the strength of the interfacial transition zone around the capsule can increase the load-carrying capacity of self-healing concrete. Moreover, given a similar fracture strength around the interface of the capsule, the fracture probability of capsule in encapsulation-based self-healing concrete is strongly dependent on the core–shell thickness ratio..

Erratum for “Fatigue Behavior of Steel Fiber Concrete in Direct Tension” by Bernard Isojeh, Maria El-Zeghayar, and Frank J. Vecchio

Erratum for “Fatigue Behavior of Steel Fiber Concrete in Direct Tension” by Bernard Isojeh, Maria El-Zeghayar, and Frank J. Vecchio

Post-yield behavior of fixed steel beams encased in concrete with plastic rotation capability under monotonic loads

Flexural strength calculated based on only curvature at sections shows some inconsistencies at large strains compared with nonlinear finite element analyses which considered damaged concrete plasticity. The prediction of the post-yield behavior of steel–concrete composite structures has been a complex issue, rendering analytically inaccurate prediction of the post-yield deflection of composite beams when plastic flows were not considered. The accurate prediction of the post-yield deformation of composite steel beams encased in structural concrete should account for the strain based on plastic rotation. The plastic rotation is influenced by the inelastic energy dissipation. The post-yield behavior of steel–concrete composite structures is affected by the inclination of diagonal cracks of concrete, and the stiffening effect of concrete tension between cracks. Plastic strain occurring in the steel section also contributes to in-elastic behavior of composite structures. The aim of this study was to idealize plastic flow of steel beams encased in structural concrete at fixed foundation. Plastic flows were calculated by non-linear finite element analysis including the consideration of concrete plasticity. The post-yield deflection was, then, predicted in a manner reflecting plastic deformation. The proposed idealization agreed well with numerical data obtained by means of nonlinear finite element analysis, providing a simplified but reliable procedure for practicing engineers designing composite structures in the inelastic region.

EXPERIMENTAL INVESTIGATIONS OF THE BEARING CAPACITY OF TWO-PASS’S NON-SEPARABLE REINFORCED CONCRETE BEAMS UNDER THE INFLUENCE OF LOW-CYCLIC REPETITIVE AND SIGN-LOADED LOADINGS

The results of tests of the bearing capacity of two-pass’s non-separable reinforced concrete beams under the influence of low-cyclic repetitive and sign-loaded loadings, in which features of change of reference reactions, bending moments and deformations of concrete and reinforcement are revealed. It is established that the process of changing these parameters is stabilized by 5-6 load cycles. The changes in the voltage of the deformed state of normal and inclined sections of experimental samples by the values of the indicated loads are also revealed and analyzed.Test results showed that there has been repeated cyclic alternating loadings and impact on the carrying capacity, reducing its straightforward compared to static loadings. The reasons of the bearing capacity’s reducing are determined by the concrete tension of both extended and compressed zones, as well as the formation of microcracks in concrete even at high loadings’ levels. Taking into account the specified features of changing the stress-strain state for the above-mentioned loadings will increase the reliability of reinforced concrete non-separable constructions during their operation.

Micromechanical modeling of tension stiffening in FRP-strengthened concrete elements

This article presents a micromodeling computational framework for simulating the tensile response and tension-stiffening behavior of fiber reinforced polymer–strengthened reinforced concrete elements. The total response of strengthened elements is computed based on the local stress transfer mechanisms at the crack plane including concrete bridging stress, reinforcing bars stress, FRP stress, and the bond stresses at the bars-to-concrete and fiber reinforced polymer-to-concrete interfaces. The developed model provides the possibility of calculating the average response of fiber reinforced polymer, reinforcing bars, and concrete as well as the crack spacing and crack widths. The model, after validation with experimental results, is used for a systematic parameter study and development of micromechanics-based relations for calculating the crack spacing, fiber reinforced polymer critical ratio, debonding strength, and effective bond length. Constitutive models are also proposed for concrete tension stiffening and average response of steel reinforcing bars in fiber reinforced polymer–strengthened members as the main inputs of smeared crack modeling approaches.

A 5 year track record on a galvanic CP system applied on a light weight concrete bridge with prestressed steel – Developments in time of the effectiveness as determined by depolarisation values and current densities

This paper gives insight in the research and investigations which were undertaken on a post tensioned light-weight concrete box girder bridge in the Netherlands. This project started in the first half of 2013 and measurements are still executed regularly. Due to long-term leakage of a longitudinal joint between 2 parts of the bridge, chlorides had penetrated into the concrete up to the level of the reinforcement and beyond, causing severe corrosion of the steel, spalling of the concrete cover and eventually causing danger for the shipping underneath the bridge due to falling lumps of concrete. To solve this problem, Galvanic Cathodic Protection (GCP) was applied in 2 stages. Firstly, in 2013, zinc based anode strips were applied on the soffit of 2 post tensioned lightweight bridge segments for the purpose of testing and monitoring. After obtaining good results from the test, in 2014/2015 the remaining 29 bridge segments were repaired and protected with the same GCP system as well. This paper reviews subsequent potential decay and current densities measurements, which have provided valuable information on GCP performance and throwing power. The results of anode performance at different locations and depths are reviewed. Concrete resistivity have shown a major influence on the effectiveness of the installed GCP system.