Finite element model for predicting the shear behavior of FRP-strengthened RC members

The shear behavior of FRP strengthened reinforced concrete (FRP strengthened RC) membrane elements can be predicted by developing logical models that satisfy the principles of mechanics of materials namely stress equilibrium, strain compatibility, and constitutive relationships of concrete, steel and, FRP reinforcements. The Softened Membrane Model (SMM), which was developed for predicting the shear behavior of reinforced concrete (RC) membrane elements, is extended to FRP strengthened RC members subjected to shear. This new analytical model, referred to as the Softened Membrane Model for FRP strengthened RC members (SMM-FRP), considers new constitutive laws for each material component of the member. Similar to the case of the SMM model for RC, this new SMM-FRP model can predict the entire stress-strain curve, including pre- and post-cracking, and the ascending and descending branches. The SMM-FRP is implemented into an OpenSees-based finite element program for a membrane 2-D element that will allow structural engineers to predict the monotonic responses of FRP strengthened RC members subjected to shear. The developed program is validated in this paper by the prediction of the monotonic responses of 10 FRP strengthened RC panels subjected to pure shear stresses. The good agreement between the experimental and analytical results confirms the validity of the analytical model in predicting the shear behavior of RC members strengthened with FRP sheets

Existence results for impulsive dynamic inclusions on time scales

In this paper, we investigate the existence of solutions and extremal solutions for a first order impulsive dynamic inclusion on time scales. By using suitable fixed point theorems, we study the case when the right hand side has convex as well as nonconvex values

Behavior of FRP-strengthened RC elements subjected to pure shear

The shear behavior of fiber reinforced polymer strengthened reinforced concrete (FRP-strengthened RC) has been the focus of extensive research studies. However, the mechanism of this complex phenomenon has not been fully clarified. Recent analytical models which were developed for predicting the shear capacity of FRP strengthened RC girders were based on test results of simply supported beam specimens with various shear span-to-depth (a/d) ratios. In such tests no region of the specimen is subjected to uniform stress conditions, Therefore, the results of such tests cannot predict the true pure shear behavior due to non-uniformity of stresses, the presence of flexural and other non-shear related effects such as a/d ratio that cannot be filtered out. Therefore, proper design of shear strengthening using FRP requires testing of elements that are subjected to pure shear case primary before adding other governing effects. This allows a careful investigation and full understanding of the behavior at the element level. In order to accomplish this task, panel testing of representative RC specimens strengthened with FRP sheets were needed. This paper reports the testing of 10 FRP strengthened RC panels subjected to pure shear stress field. The tests were carried out to evaluate the effects of three variables: FRP stiffness, FRP wrapping scheme, and transverse steel reinforcement ratio. The test results showed that these three variables greatly affected the shear behavior due to various types of failure modes associated with FRP strengthening. In addition, it was observed that the magnitude of increased shear capacity associated with the application of FRP sheets depends not only upon the stiffness of FRP, but also on the stiffness of internal shear reinforcement. With the increase of internal steel shear reinforcement, the effectiveness of shear gain due to externally bonded FRP decreases

Internationalization of Education and the Brain Drain Paradox: Case of the Mena Region

This paper discusses how the internationalization of higher education has brought about its impact in terms of spreading standardized academic programs, scientific research, innovation, culture exchange, and strengthening ties between involved higher education institutions and countries to resolve mutual benefit challenges. Among these challenges, the brain drain paradox remains an annoying problem for developing countries. The paper sheds light on these related issues through witnessed education system reform, research efforts exchange, and cooperation between collaborating countries in the MENA region to diminish the impact of the brain drain paradox

Experimental assessment of the variability of concrete air permeability: repeatability, reproducibility and spatial variability

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Uniaxial Tensile Stress-Strain Relationships of RC Elements Strengthened with FRP Sheets

The shear behavior of fiber-reinforced-polymer–strengthened reinforced concrete (FRP-strengthened RC) members is not fully developed and accurately predicted because of the lack of accurate constitutive laws for the components of the composite members. This paper presents experimental and analytical investigations of tensile stress-strain relationships of concrete and steel in FRP-strengthened RC members. These stress-strain relationships are required in formulations of softened truss models to predict the shear behavior of the FRP-strengthened RC element. Thirteen full-scale FRP-strengthened RC prismatic specimens with different FRP reinforcement ratios, steel reinforcement ratios, and FRP wrapping schemes were tested under uniaxial tension loading. The results show that the tensile behavior of the concrete and steel is altered because of the externally bonded FRP sheets. Modified constitutive laws are proposed and incorporated in the softened membrane model (SMM) to demonstrate through two tests the behavior of FRP-strengthened RC element subjected to pure shear. Moreover, crack spacing and crack width were studied and compared with existing code provisions

Influence of Fiber-Reinforced Polymer Sheets on the Constitutive Relationships of Reinforced Concrete Elements

Fiber-reinforced polymer (FRP) started to find its way as an economical alternative material in civil engineering in the early 1970s. The behavior and failure modes for FRP composite structures were studied through extensive experimental and analytical investigations. Although research related to the flexural behavior of FRP-strengthened elements has reached a mature phase, studies related to FRP shear strengthening are less advanced. In all proposed models to predict shear capacity, the constitutive behaviors of concrete and FRP are described independently. The true behavior, however, should account for the high level of interaction between the two materials. Constitutive relations for FRP-strengthened reinforced concrete (RC) elements should provide a better understanding of the shear behavior of the composite structure. To generate these relations, large-scale tests of a series of FRP-strengthened RC panel elements subjected to pure shear were conducted. This paper presents the results of the test program and the calibration of the parameters of the constitutive model. These constitutive laws could easily be implemented in finite-element models to predict the behavior of externally bonded FRP-strengthened beams. The focus in this work is on elements failing because of concrete crushing and not because of FRP debonding. The newly developed model provides a good level of accuracy when compared with experimental results

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

Stress intensity solutions for cracked plates by the dual boundary method

This paper presents the application o f the dual boundary element method for the determination o f stress intensity factors in plate bending problems. The loadings considered include internal pressure, and also combined bending and tension. Mixed mode stress intensity factors are evaluated by a crack surface displacement extrapolation technique and the J-integral technique. The boundary element results for the case studies considered in the paper have been compared with either analytical or finite element results and in all cases good agreement has been achieved.Описано застосування методу подвійних граничних елементів для визначення коефіцієнтів інтенсивності напружень у задачах, що пов’язані зі згином пластин. Умови навантаження включають внутрішній тиск та комбінацію згину з розтягом. Коефіцієнти інтенсивності напружень для змішаних мод оцінюються за допомогою методу екстраполяції переміщення поверхні тріщини та методу J-інтеграла. Результати розрахунків методом граничних елементів для досліджуваних випадків навантаження порівнюються із даними аналітичних чи скінченноелементних розрахунків. Отримано їх хорошу збіжність.Описано применение метода двойных граничных элементов для определения коэффициентов интенсивности напряжений в задачах, связанных с изгибом пластин. Исследуемые условия нагружения включают внутреннее давление и комбинацию изгиба с растяжением. Коэффициенты интенсивности напряжений для смешанных мод оцениваются с помощью метода экстраполяции перемещения поверхности трещины и метода J-интеграла. Результаты расчетов методом граничных элементов, полученные для рассматриваемых случаев нагружения, сравниваются с данными аналитических или конечноэлементных расчетов. Получено их хорошее соответствие

Continuous Concrete Beams Reinforced With CFRP Bars.

yesThis paper reports the testing of three continuously and two simply supported concrete beams reinforced with carbon fibre reinforced polymer (CFRP) bars. The amount of CFRP reinforcement in beams tested was the main parameter investigated. A continuous concrete beam reinforced with steel bars was also tested for comparison purposes. The ACI 440.1R-06 equations are validated against the beam test results. Test results show that increasing the CFRP reinforcement ratio of the bottom layer of simply and continuously supported concrete beams is a key factor in enhancing the load capacity and controlling deflection. Continuous concrete beams reinforced with CFRP bars exhibited a remarkable wide crack over the middle support that significantly influenced their behaviour. The load capacity and deflection of CFRP simply supported concrete beams are reasonably predicted using the ACI 440.1R-06 equations. However, the potential capabilities of these equations for predicting the load capacity and deflection of continuous CFRP reinforced concrete beams have been adversely affected by the de-bonding of top CFRP bars from concrete