Tension-Stiffening Effect Consideration for Modeling Deflection of Cracked Reinforced UHPC Beams

Tension-stiffening effects can significantly influence the flexural performance of cracked reinforced concrete specimens. Such effect is amplified for fiber-reinforced concrete, given the fact that fibers can bridge the cracks. The objective of this study was to develop a model to predict the deflection of cracked reinforced ultra-high performance concrete (R-UHPC) beam elements. The modeling approach characterized the average bending moment of inertia by combining the existing model used for conventional reinforced concrete and the analytical model of stress distribution of UHPC along the cross-section. The finite element analysis (FEA) was employed to evaluate the flexural deflection based on the average bending moment of inertia. The calculated load-deflection relationships have been compared to experimental results. The results indicated that the relative errors of deflection between predicted and experimental results can be controlled within 15%, compared to values ranging from 5% to 50% calculated by neglecting the tensile properties of cracked UHPC and values ranging from 5% to 30% calculated by effective inertia of bending moment of ACI code. Therefore, the developed model can be used in practice because it can secure the accuracy of deflection prediction of the R-UHPC beams. Such a simplified model also has higher sustainability compared to FEA using solid elements since it is easier and time-saving to be established and calculated.

Finite Element Modeling of Tension Stiffening and Cracking of Reinforced Concrete Components: State of Art

The scientific community has been debating the vulnerability of structures to progressive collapse and how to mitigate the impact of local damages leading to un-proportional collapse. Recent tragedies have highlighted the necessity for particular design requirements to provide appropriate safety levels against progressive collapse as a result of damages caused by unusual loads. The performance of composite and reinforced concrete components in the realm of large displacements is presently the focus of study. The behaviour of reinforced concrete (RC) components, as well as the finite element model used to simulate RC parts under tension, were critically examined. This has aided in the understanding of concrete’s non-negligible contribution to tension stiffening response up to failure, particularly in the case of composite constructions with discontinuous geometry. The extensive study of literature provided insight into various modelling techniques and advised that experimental and numerical research be used to enhance diverse possibilities of model exploration.

Effects of Freeze-Thaw and Wet-Dry Cycles on Tension Stiffening Behavior of Reinforced RAC Elements

In the last several decades, the growth of Construction and Demolition Waste (CDW) production and the increased consumption of natural resources have led to promoting the use of secondary raw materials for a more sustainable construction. Specifically, the use of Recycled Concrete Aggregate (RCA), derived from waste concrete, for the production of Recycled Aggregate Concrete (RAC) has attracted a significant interest both in industry and in academia. However, the use of RAC in field applications still finds some barriers. In this context, the present study investigates experimentally the effects of freeze-thaw and wet-dry cycles on the stress transfer mechanisms of reinforced RAC elements through tension stiffening tests. First of all, the paper presents a detailed analysis of the degradation due to the aging process of RAC with RCAs obtained from different sources. Particularly, the results of tension stiffening tests are analyzed in terms of crack formation and propagation, matrix tensile strength contribution and steel-to-concrete bond. The results highlight that the pre-cracking elastic modulus, the first crack strength as well as the maximum concrete strength are strongly influenced by the presence of the Attached Mortar (AM) in RCA, as the former affects the concrete’s open porosity. Therefore, the amount of AM is identified as the key parameter for the evaluation of durability of reinforced RAC members: a degradation-law is also proposed which correlates the initial concrete open porosity with the damage observed in reinforced RAC elements.

Influence of Tension Stiffening and Cracked Shear Modulus Models on Non-Linear Analysis of High Strength Fibrous Reinforced Concrete Slabs

In the present study, new models are proposed for tension stiffening and cracked shear modulus to study their effect on the response of the slab. These models are used in the nonlinear analysis of High Strength Steel Fiber Reinforced Concrete (HSSFRC) slabs. The suggested models have multiple shapes depending on the curvature factor, these models are compared with the well-known formulas used in previous studies and great agreements are achieved. The Serendipity “eight-node” element type has been adopted for representing the concrete and layered approach is used to simulate the concrete elements and a smeared layer approach is used to represent the steel reinforcement. The concrete compression behavior is modeled using strain hardening plasticity method, the first two stress invariants of the yield condition is used. For finite element analysis, a computer program coded in Fortran 90 is developed and used for performing nonlinear analysis on the slabs. In order to check the validity of the current models, many actual results for testing slabs “in the laboratory” are compared with the results from the present study and a great agreement is achieved. All studied slabs were simply supported from four sides and loaded with concentrated load at the middle of the slab, but slab S5 is simply supported by two opposite parallel sides with line load parallel to the supports at the middle of the span of the slab. For the curvature factors (Bt, Bg) it is found that the values (Bt =0.005-0.5, Bg =0.001-0.05) give the best simulation for the slab. The effect of tension stiffening model is more than the effect of cracked shear modulus model and there is an interaction between tension stiffening and cracked shear modulus models.

Cyclic Behavior of Reinforced High Strain-Hardening UHPC under Axial Tension

The cyclic tensile behavior of steel-reinforced high strain-hardening ultrahigh-performance concrete (HSHUHPC) was investigated in this paper. In the experimental program, 12 HSHUHPC specimens concentrically placed in a single steel reinforcement under cyclic uniaxial tension were tested, accompanied by acoustic emission (AE) source locating technology, and 4 identical specimens under monotonic uniaxial tension were tested as references. The experimental variables mainly include the loading pattern, the diameter of the embedded steel rebar, and the level of target strain at each cycle. The tensile responses of the steel-reinforced HSHUHPC specimens were evaluated using multiple performance measures, including the failure pattern, load–strain response, residual strain, stiffness degradation, and the tension-stiffening behavior. The test results showed that the enhanced bond strength due to the inclusion of steel fibers transformed the failure pattern of the steel-reinforced HSHUHPC into a single, localized macro-crack in conjunction with a sprinkling of narrow and closely spaced micro-cracks, which intensified the strain concentration in the embedded steel rebar. Besides, it was observed that the larger the diameter of the embedded steel rebar, the smaller the maximum accumulative tensile strain under cyclic tension, which indicated that the larger the diameter of the embedded steel rebar, the greater the contribution to the tensile stiffness of steel-reinforced HSHUHPC specimens in the elastic–plastic stage. In addition, it was found that a larger embedded steel rebar appeared to reduce the tension-stiffening effect (peak tensile strength) of the HSHUHPC. Moreover, the residual strain and the stiffness of the steel-reinforced HSHUHPC were reduced by increasing the number of cycles and finally tended toward stability. Nevertheless, different target strain rates in each cycle resulted in different eventual cumulative tensile strain rates; hence the rules about failure pattern, residual strain, and loading stiffness were divergent. Finally, the relationship between the accumulative tensile strain and the loading stiffness degradation ratio under cyclic tension was proposed and the tension-stiffening effect was analyzed.

Tension Stiffening Behavior of Polypropylene Fiber- Reinforced Concrete Tension Members

This paper focuses on comparing the behavior of RC tension members with and without the addition of polypropylene fibers at various corrosion levels. Eight cylindrical tensile specimens were tested to evaluate their tension-stiffening and cracking behavior. The content of polypropylene fiber added into the concrete mix was the main variable (0.25%, 0.50%, 0.75%, and 1.0% of total volume). The corrosion level was varied from slight (5%), medium (10%) to severe (30%) and, like the other variables, applied only to 1.0% polypropylene fiber-reinforced concrete (PFRC) specimens. The test results showed that the fiber addition significantly increased the tension-stiffening effect but was largely unable to reduce the effect of bond degradation caused by corrosion. Moreover, the addition of polypropylene fibers was able to improve the cracking behavior in terms of crack propagation, as shown by smaller crack spacing compared to the specimen without fiber addition at the same corrosion level.