Torsional behavior and analysis of steel fiber reinforced concrete (SFRC) beams is investigated in this paper. The purpose of this study is twofold; to examine the torsion strength models for SFRC ...beams available in the literature and to address properly verified design formulations for SFRC beams under torsion. A total of 210 SFRC beams tested under torsion from 16 different experimental investigations around the world are compiled. The few strength models available from the literature are adapted herein and used to calculate the torsional strength of the beams. The predicted strength is compared with the experimental values measured by the performed torsional tests and these comparisons showed a room for improvement. First, a proposed model is based on optimizing the constants of the existing formulations using multi-linear regression. Further, a second model is proposed, which is based on modifying the American Concrete Institute (ACI) design code for reinforced concrete (RC) members to include the effect of steel fibers on the torsional capacity of SFRC beams. Applications of the proposed models showed better compliance and consistency with the experimental results compared to the available design models providing safe and verified predictions. Further, the second model implements the ACI code for RC using a simple and easy-to-apply formulation.
Experimental research has shown the extraordinary potential of the addition of short fibers to cement‐based materials by improving significantly the behavior of concrete structures for serviceability ...and ultimate limit states. Software based on the finite element method has been used for the simulation of the material nonlinear behavior of fiber‐reinforced concrete (FRC) structures. The applicability of the existing approaches has often been assessed by simulating experimental tests with structural elements, in general of a small scale, where the parameter values of the material constitutive laws are adjusted for the aimed predicting level, which constitutes an inverse technique of arguable utility for structural design practice. For assessing the predictive performance of these approaches, a blind simulation competition was organized. Two twin T‐cross section steel FRC beams, flexurally reinforced with steel bars and without conventional shear reinforcement in the critical shear span, were experimentally tested up to failure. Despite the experimental data provided for the definition of the relevant model parameters, inaccuracies on the load capacity, deflection, and strain at peak load attained 40, 113, and 600%, respectively. Inadequate failure modes and highly different results were estimated with the same commercial software, indicating the need for deeper analysis and understanding of the models and influence of their parameters on their predictive performance.
•A mechanically consistent model for the transfer of shear stresses across cracks in SFRC is presented.•The model relates the shear and normal stresses transferred across cracks in SFRC to crack ...kinematics.•The model accounts for the transfer of stresses via fibre bridging and aggregate interlock.•The model is shown to correlate well with available experimental data.
Existing models for the shear strength of steel fibre reinforced concrete (SFRC) in general, and for the transfer of shear stresses across cracks, typically assume that the shear strength of plain concrete is increased by a so-called “fibre contribution”. This is usually assumed to be independent of the roughness of the cracks. While being relatively simple to implement in practice, such approaches fail to capture the physical-mechanical behaviour of the transfer of shear stresses across cracks. Hence, in order to exploit the full potential of SFRC in shear, rational and mechanically consistent models capable of describing this behaviour are essential. This paper presents such a model, which relates the shear and normal stresses transferred across cracks in SFRC to the crack opening and slip displacements. The novelty of the proposed model consists in the fact that it not only accounts for fibre stresses bridging the crack, as done in many previous models, but also for the aggregate interlocking behaviour along the faces of the crack, and the interaction of these effects. Regardless of the aggregate interlock relationship used, the proposed model predicts that except at large crack openings (in the order of half the size of the maximum aggregate particle), only a minor portion of the applied shear stresses are resisted directly by inclined fibres crossing the crack, even for high fibre contents. Rather, it is shown herein that shear stresses are primarily transmitted via the interlocking of aggregates along the crack faces. Nonetheless, the addition of fibres to concrete is highly beneficial to the transfer of shear across cracks since fibre stresses normal to the crack plane are equilibrated by compressive stresses on the crack faces. These compressive stresses greatly enhance aggregate interlock. A comparison of predictions by the proposed model with a wide range of reported experimental data shows a good correlation. However, the results also indicate that existing relationships for aggregate interlock in plain concrete are highly variable, and their applicability to SFRC needs to be carefully examined.
•The use of synthetic fiber-enhanced mechanical properties on torsional hollow beams.•The enhancement in beam performance was relative to the fiber type and length.•The torsional ACI equation was ...modified to incorporate the synthetic fiber effect.
Past research has used synthetic fiber (SY.F) and steel fiber (ST.F) for decades to advance concrete mechanical characteristics, including shear, tensile, and flexural strengths. Nevertheless, there is limited information concerning the torsional concrete reinforced with SY.F and ST.F performance. This research aims to explore the torsional performance of hollow reinforcement concrete beams reinforced with various fiber types. The fiber content of 1% with three different lengths of SY.F, 19, 38, and 57 mm, along with 13 mm of ST.F, was used. Two specimens were cast with normal concrete without using fibers as control beams and four hollow beams with ST.F and SY.F. To use a pure torsional load on the tested samples, an innovative test method was employed. The twisting angle of tested beams was calculated at each interval of the load as well as the first crack load and failure load. Outcomes illustrated that the utilizing of SY.F and ST.F in the reinforced concrete beams (RCB) enhanced the overall performance under torsional load compared to the control beam behaviors. This enhancement in the performance was relative to the fiber type and length. For the first cracking load, the tested beams reinforced with the ST.F and SY.F of 19 and 37 mm lengths showed approximately the same value. Also, the beam reinforced with the SY.F length of 55 mm exhibited the highest first cracking load value, among other tested beams. As the fiber length increases of SY.F, the ultimate load capacity was raised by 4.7, 9.4, and 21.9% for beams cast with 19, 37, and 55 mm fiber length, respectively. For the ST.F reinforcement concrete beam, the ultimate load capacity was raised by 5.5%. Therefore, due to the significant impact of SY.F on the torsional performance, it is recommended using SY.F with normal concrete.
Engineering design problems are often multi-objective in nature, which means trade-offs are required between conflicting objectives. In this study, we examine the multi-objective algorithms for the ...optimal design of reinforced concrete structures. We begin with a review of multi-objective optimization approaches in general and then present a more focused review on multi-objective optimization of reinforced concrete structures. We note that the existing literature uses metaheuristic algorithms as the most common approaches to solve the multi-objective optimization problems. Other efficient approaches, such as derivative-free optimization and gradient-based methods, are often ignored in structural engineering discipline. This paper presents a multi-objective model for the optimal design of reinforced concrete beams where the optimal solution is interested in trade-off between cost and deflection. We then examine the efficiency of six established multi-objective optimization algorithms, including one method based on purely random point selection, on the design problem. Ranking and consistency of the result reveals a derivative-free optimization algorithm as the most efficient one.
•Multi-objective optimization (MOO) approaches in general and in Reinforced Concrete (RC) structures are reviewed.•A novel multi-objective model is developed for the optimal design of RC beams.•A set of algorithms are examined and compared through numerical testing.•This paper enlightens the merits of advanced MOO methods in structural engineering problems.
Fiber-reinforced concrete (FRC) is increasingly used in structural applications owing to its benefits in terms of toughness, durability, ductility, construction cost and time. However, research on ...the creep behavior of FRC has not kept pace with other areas such as short-term properties. Therefore, this study aims to present a comprehensive and critical review of literature on the creep properties and behavior of FRC with recommendations for future research. A transparent literature search and filtering methodology were used to identify studies regarding creep on the single fiber level, FRC material level, and level of structural behavior of FRC members. Both experimental and theoretical research are analyzed. The results of the review show that, at the single fiber level, pull-out creep should be considered for steel fiber-reinforced concrete, whereas fiber creep can be a governing design parameter in the case of polymeric fiber reinforced concrete subjected to permanent tensile stresses incompatible with the mechanical time-dependent performance of the fiber. On the material level of FRC, a wide variety of test parameters still hinders the formulation of comprehensive constitutive models that allow proper consideration of the creep in the design of FRC elements. Although significant research remains to be carried out, the experience gained so far confirms that both steel and polymeric fibers can be used as concrete reinforcement provided certain limitations in terms of structural applications are imposed. Finally, by providing recommendations for future research, this study aims to contribute to code development and industry uptake of structural FRC applications.
On the cover: The cover image is based on the Research Article A graph‐based method for quantifying crack patterns on reinforced concrete shear walls by Pedram Bazrafshan et al., ...https://doi.org/10.1111/mice.13009.
•Suggest a data-driven approach for the failure mode prediction of RC shear walls.•Construct an experimental database for RC shear walls.•Compare the performance of prediction models using various ...machine learning techniques.•Identify the critical input parameters affecting the failure mode of shear walls.•Propose the open-source data-driven classification model.
A reinforced concrete shear wall is one of the most critical structural members in buildings, in terms of carrying lateral loads. Despite its importance, post-earthquake reconnaissance and recent experimental studies have highlighted the insufficient safety margins of shear walls. The lack of empirical and mechanics-based models prevents rapid failure mode identification of existing shear walls. This study builds on recent advances in the area of machine learning to determine the failure mode of shear walls as a function of geometric configurations, material properties, and reinforcement details. This study assembles a comprehensive database consisting of 393 experimental results for shear walls with various geometric configurations. Eight machine learning models, including Naïve Bayes, K-Nearest Neighbors, Decision Tree, Random Forest, AdaBoost, XGBoost, LightGBM, and CatBoost were evaluated in this study, in order to establish the best prediction model. As a result of detailed evaluation, a machine learning model based on the Random Forest method is proposed in this paper. The proposed method has 86% accuracy in identifying the failure mode of shear walls. This study also demonstrates that aspect ratio, boundary element reinforcement indices, and wall length-to-wall thickness ratio are the critical parameters influencing the failure mode of shear walls. Finally, an open-source data-driven classification model that can be used in design offices across the world is provided in this paper. The proposed model has the flexibility to account for additional experimental results yielding new insights.
•Blast tests were conducted on UHPC filled CFDST columns.•Numerical models were validated against blast test results.•Parametric studies were carried out by using the numerical models.
In recent ...years, a large number of studies have been carried out to investigate behaviours of concrete filled double skin steel tube (CFDST) members due to its increasing popularity in the construction industry. This paper firstly presents an experimental study on ultra-high performance concrete filled double-skin tubes subjected to close-range blast loading with cross section being square for both inner and outer steel tubes. It is evident that the proposed CFDST column was able to withstand a large blast load without failure so that it has the potential to be used in high-value buildings as well as critical infrastructures. Then, to further investigate the behaviours of the proposed CFDST column, a number of parametric studies were carried out by using a numerical model which was developed and calibrated based on the data acquired from the blast test along with some laboratory tests. Parameters that affect the behaviours of concrete filled double skin steel tube (CFDST) members against blasts are characterised.
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