A Feasibility Study of BBP for predicting shear capacity of FRP reinforced concrete beams without stirrups.

yesShear failure of concrete elements reinforced with Fiber Reinforced Polymer (FRP) bars is generally brittle, requiring accurate predictions to avoid it. In the last decade, a variety of artificial intelligence based approaches have been successfully applied to predict the shear capacity of FRP Reinforced Concrete (FRP-RC). In this paper, a new approach, namely, biogeography-based programming (BBP) is introduced for predicting the shear capacity of FRP-RC beams based on test results available in the literature. The performance of the BBP model is compared with several shear design equations, two previously developed artificial intelligence models and experimental results. It was found that the proposed model provides the most accurate results in calculating the shear capacity of FRP-RC beams among the considered shear capacity models. The proposed BBP model can also correctly predict the trend of different influencing variables on the shear capacity of FRP-RC beams

The compression chord capacity model for the shear design and assessment of reinforced and prestressed concrete beams

This is the accepted version of the following article: [Cladera, A., Marí, A., Bairán, J. M., Ribas, C., Oller, E. and Duarte, N. (2016), The compression chord capacity model for the shear design and assessment of reinforced and prestressed concrete beams. Structural Concrete, 17: 1017–1032. doi:10.1002/suco.201500214], which has been published in final form at http://onlinelibrary.wiley.com/doi/10.1002/suco.201500214/fullA simplified mechanical model is presented for the shear strength prediction of reinforced and prestressed concrete members with and without transverse reinforcement, with I, T or rectangular cross-section. The model, derived with further simplifications from a previous one developed by the authors, incorporates the contributions of the concrete compression chord, the cracked web, the dowel action and the shear reinforcement in a compact formulation. The mechanical character of the model provides valuable information about the physics of the problem and incorporates the most relevant parameters governing the shear strength of structural concrete members. The predictions of the model fit very well the experimental results collected in the ACI-DAfStb databases of shear tests on slender reinforced and prestressed concrete beams with and without stirrups. Due to this fact and the simplicity of the derived equations it may become a very useful tool for structural design and assessment in engineering practice.Peer ReviewedPostprint (author's final draft

Design equations for reinforced concrete members strengthened in shear with external FRP reinforcement formulated in an evolutionary multi-objective framework

Methods for predicting the shear capacity of FRP shear strengthened RC beams assume the traditional approach of superimposing the contribution of the FRP reinforcing to the contributions from the reinforcing steel and the concrete. These methods become the basis for most guides for the design of externally bonded FRP systems for strengthening concrete structures. The variations among them come from the way they account for the effect of basic shear design parameters on shear capacity. This paper presents a simple method for defining improved equations to calculate the shear capacity of reinforced concrete beams externally shear strengthened with FRP. For the first time, the equations are obtained in a multiobjective optimization framework solved by using genetic algorithms, resulting from considering simultaneously the experimental results of beams with and without FRP external reinforcement. The performance of the new proposed equations is compared to the predictions with some of the current shear design guidelines for strengthening concrete structures using FRPs. The proposed procedure is also reformulated as a constrained optimization problem to provide more conservative shear predictions

Machine Learning Prediction of Shear Capacity of Steel Fiber Reinforced Concrete

The use of steel fibers for concrete reinforcement has been growing in recent years owing to the improved shear strength and post-cracking toughness imparted by fiber inclusion. Yet, there is still lack of design provisions for steel fiber-reinforced concrete (SFRC) in building codes. This is mainly due to the complex shear transfer mechanism in SFRC. Existing empirical equations for SFRC shear strength have been developed with relatively limited data examples, making their accuracy restricted to specific ranges. To overcome this drawback, the present study suggests novel machine learning models based on artificial neural network (ANN) and genetic programming (GP) to predict the shear strength of SFRC beams with great accuracy. Different statistical metrics were employed to assess the reliability of the proposed models. The suggested models have been benchmarked against various soft-computing models and existing empirical equations. Sensitivity analysis has also been conducted to identify the most influential parameters to the SFRC shear strength

Shear strength assessment of reinforced recycled aggregate concrete beams without stirrups using soft computing techniques

This paper presents a study to predict the shear strength of reinforced recycled aggregate concrete beams without stirrups using soft computing techniques. The methodology involves the development of a Multi-Objective Genetic Algorithm Evolutionary Polynomial Regression (MOGA-EPR) and Gene Expression Programming (GEP) models. The input variables considered are the longitudinal reinforcement ratio, recycled coarse aggregate ratio, beam cross-section dimensions, and concrete compressive strength. Data collected from the literature were used to train and validate the models. The results showed that the MOGA-EPR and GEP models can accurately predict the shear strength of beams without stirrups. The models also performed better than equations from the codes and literature. This study provides an alternative approach to accurately predict the shear strength of reinforced recycled aggregate concrete beams without stirrups

NUMERICAL SIMULATION OF CONCRETE BEAMS WITH DISCONTINUITY REGIONS REINFORCED WITH NONMETALLIC REINFORCING BARS

Nonmetallic Glass Fiber-Reinforced Polymer (GFRP) reinforcing bars are considered a viable alternative to the conventional steel reinforcement because of their high strength-to-weight ratio and noncorrosive nature. This research aimed to investigate the nonlinear structural behavior of GFRP-reinforced concrete beams with discontinuity regions (D-regions) through numerical analysis. Three-dimensional (3D) numerical models were developed to simulate the nonlinear structural behavior of GFRP-reinforced deep beams with and without web openings. The models adopted realistic constitutive laws that accounted for the nonlinear behavior of the materials used. Predictions of the numerical models were validated against published experimental data. A parametric study was conducted to examine the effect of key variables on the structural behavior of GFRP-reinforced deep beams with and without web openings. The interaction between the concrete compressive strength (fc’), shear span-to-depth ratio (a/h), size and location of the web opening was elucidated. Simplified analytical formulas capable of predicting the shear capacity of GFRP-reinforced beams with D-regions were introduced based on an inverse analysis of results of the numerical simulation models. Predictions of the proposed analytical formulas were in good agreement with the results of the simulation models

Shear strength of concrete beams reinforced with glass fiber reinforced polymer bars without stirrups

The use of fiber reinforced polymer (FRP) bars as an alternative to steel bars for reinforced concrete (RC) structures is gaining acceptance among the structural engineers. The investigation of structure performance of FRP-RC members has become a critical issue. Extensive researches have been conducted to investigate the shear behavior of RC members with FRP bar. However, the shear strength design of FRPRC beams is similar to that of RC beams with steel bar except that the mechanical properties of FRP bars which affect the shear strength design shall be considered. The focus of this research is to investigate the shear behavior of FRP-RC beams. A total of 18 RC beams were constructed and tested up to failure, the test beams included 10 GFRP-RC beams and 8 steel-RC beams. In order to realize the occurrence of the shear failure, all tested beams were designed without stirrups. The test variables were the reinforcement ratio (ρ), shear span to depth ratio (a/d), depth of beam (d), and concrete compressive strength

Modelo mecánico para la resistencia a cortante de vigas de hormigón armado reforzado con fibras, sin armadura de cortante

Despite the numerous studies made showing that the addition of steel fibres to concrete enhances the shear strength of RC beams, current design formulations are still empirical and present large scatter in front of the test results. In this paper, the previously developed Multi-Action Shear Model is extended to SFRC beams without stirrups, adopting an analytical formulation to evaluate the residual tensile stress of SFRC and incorporating the effects of the crack bridging capacity of SFRC in the shear resisted trough the different shear-transfer mechanisms. The proposed model predicts the tests results included in a recently published database with 448 shear tests with less scatter than any of the existing models.The financial support provided by the University of Messina (Italy), through the scholarship granted for a two-months research and teaching stage of the first author, is acknowledged. This work is part of the Research Projects BIA2015-64672-C4-1-R, funded by the Spanish Ministry of Economy and competitiveness, and RTI2018-097314-B-C21, funded by the Spanish Ministry of Science and Innovation.Postprint (published version

Experimental and analytical study of concrete structures reinforced with GFRP bars

The rational use of natural, economic and social resources in order to ensure the sustainability and a long-term balance has become one of the largest global concerns. In the civil engineering field, the limited durability of steel reinforced concrete structures, especially in aggressive environments, and the high costs of the repair and maintenance operations have motivated the search for alternative materials and solutions to steel. One of these alternative reinforcements is the glass fibre reinforced polymer (GFRP) bars due to their immunity to corrosion, which is an important advantage when comparing to steel. However, several factors such as the novelty in the market, the high fabrication costs, the different design philosophies and the uncertainties of its behaviour with the concrete have been delaying the use of the GFRP bars in a larger scale. This thesis aims to contribute to the scientific knowledge of the GFRP reinforced concrete, as it studies its behaviour and design. The research work is mainly experimental and is based on a campaign with 24 full-scale reinforced concrete (RC) beams 4.30 m long and rectangular crosssection of 0.25 x 0.40 m2, divided into two groups with different purposes: - 18 beams to study the performance of different GFRP bar layouts as shear reinforcement; - 6 beams to assess the behaviour of a rehabilitation solution with GFRP bars to replace the deteriorated flexural steel reinforcement. The specimens of the first group were designed to fail due to shear with four different GFRP shear reinforcement solutions: 1) closed hoop GFRP stirrups, 2) two C shaped GFRP bars forming a stirrup, 3) two double headed GFRP bars and 4) two simple straight GFRP bars. Two shear reinforcement ratios with different spacing were also tested with the closed hoop GFRP stirrups. For each GFRP shear reinforcement layout, three different longitudinal stiffnesses were considered using steel and GFRP bars with different ratios. The beam specimens were tested until failure under a four point loading set-up and both the serviceability and the ultimate performance were analysed. The results were reported in terms of deflections, crack pattern, crack width, strains in the longitudinal and shear reinforcements, ultimate load capacity and failure modes. The different shear layouts were compared regarding their load carrying performance and their field implementation easiness. The design of the beams and their result predictions were made according to the existing guidelines and codes. It was concluded that the closed hoop stirrups and the C-stirrups were the most efficient and that the beams load capacity was highly underestimated by the GFRP codes. To improve the design formulas of these codes, different values for the limit strains and for the strut angle were proposed. The double headed bars as shear reinforcement were also efficient in the cases with higher longitudinal stiffness because it contributed to keep the integrity of the beam by exhibiting low deflections and crack widths. It was observed that a wide crack at the end of these bars highly compromises the anchorage function of the head. The solution of the simple straight bars was not effective because of the lack of anchorage length. The idea for the second group of beams was inspired on the RC structures with deteriorated bottom concrete due to the corrosion of the longitudinal steel reinforcement. Actually, no steel corrosion was considered in these specimens, but they were concreted in two phases to simulate the replacement of the deteriorated concrete, starting at the stage after its complete removal. The rehabilitation procedure consisted on the insertion of the longitudinal GFRP bars and the concreting of a new bottom layer in the beam. Two solutions with different GFRP longitudinal cross-section areas were designed according to the existing guidelines, one to restore the ultimate load capacity of the original beam, and the other to maintain the deflection of the original beam. The ends of the GFRP bars were conic heads to compensate their lower anchorage length. The rehabilitated beam specimens were subjected to 3 point bending tests until failure, and their service and ultimate behaviour were analysed. Results are presented in terms of deflection, crack pattern, mid-span crack width, reinforcement strains, ultimate flexural capacity and failure modes. It was concluded that this technique was effective for both the serviceability and ultimate limit states of the rehabilitated beam, as it was able to restore the deflection and the load capacity of the original beam, and that the existing GFRP design documents can be used. Although this was mainly an experimental research work, a simple but reliable two-dimensional finite element (FE) model was defined using ATENA software to simulate the tests, which helped to better understand some issues regarding the specimens behaviour and enabled to extrapolate some results of non-tested possibilities. The linear and nonlinear behaviour of all materials was adequately modelled by appropriate constitutive laws. Furthermore, numerical results were compared with the experimental results. Results show that, in general there was a good agreement between the overall modelling results and the experimental ones. The constructed models were able to predict the experimental behaviour in terms of ultimate capacity and load-deflection curves. Regarding the first group of beams, two additional stirrups spacing were modelled in order to clarify its influence in the shear capacity. It was simulated different longitudinal reinforcement ratios to assess its influence in the shear capacity. As a final remark, the results of the present work show that the use of GFRP bars is viable in RC structures, which contributes to more durable structures in long-term. This material can be used as longitudinal and shear reinforcement of new structures and as a rehabilitation solution to replace the corroded steel in deteriorated structures

Модель сопротивления срезу бетонных элементов, армированных стержнями из полимерных композитов

V. V. Tur, A. P. Varabei. MODEL OF SHEAR RESISTANCE OF CONCRETE ELEMENTS REINFORCED WITH FRP BARSВведение. Проблема сопротивления срезу железобетонных элементов без поперечного армирования по-прежнему остаётся одной из наиболее дис-куссионных в теории конструкций из бетона. Новый интерес к проблеме возник в связи применением в конструкциях из бетона в качестве продольной арматуры стержней из полимерных композитов (FRP). Рассмотрены модели сопротивления срезу, внесенные в нормативные документы и сформулированные в виде предложений для элементов, армированных стальными стержнями и стержнями из FRP. Показано, что для формулирования модели сопротивления срезу элементов, армированных FRP в качестве основы, может быть принята теория критической наклонной трещины (CSCT). Однако её положения не могут быть применены напрямую без соответствующих корректировок, в частно-сти касающихся определения ширины раскрытия критической наклонной трещины. Материалы и методы. Для определения сопротивления срезу самонапряженных бетонных элементов, армированных стержнями из полимерных композитов, разработана модифицированная модель. Данная модель, использующая итерационную процедуру, позволяет определять отдельный вклад в полное сопротивление срезу каждой из основных его составляющих, с учетом формы потенциальной наклонной трещины, принятой в соот-ветствии с положениями теории критической трещины среза (CSCT), а также ширины раскрытия наклонной трещины на уровне продольного армирования, определенной по закону «сцепление-проскальзывание» для FRP-стержней. Результаты: Предложенная модифицированная модель сопротивления срезу верифицирована на фоне опытных данных, полученных как в собственных исследованиях, так и другими авторами (база данных включала 374 элемента). Основываясь на результатах параметрического исследования, предложен феноменологический критерий сопротивления срезу для гибких элементов, армированных стержнями из полимерных композитов, на основе которого разработана упрощенная расчетная модель, позволяющая определять сопротивление срезу бетонных элементов, армированных FRP-стержнями, без необходимости расчета всех составляющих перерезывающей силы. Выводы: Представленная модель сопротивления срезу гибких самонапряженных элементов, армированных стержнями из полимерных композитов, отражает физическую сущность явления среза, применима к различным случаям и схемам нагружения