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

Seismic Test Methods for Architectural Glazing Systems

An ongoing effort is being made at the University of Missouri-Rolla to develop standard laboratory test methods and codified design procedures for architectural glass under seismic loadings. Recent laboratory work has yielded some promising results regarding the development of an appropriate seismic test method for architectural glass, as well as identifying ultimate limit states that quantify the seismic performance and damage thresholds of various glass types. Specifically, a straightforward crescendo-like in-plane dynamic racking test, performed at a constant frequency, has been employed successfully. Two ultimate limit states for architectural glass have been defined: (1) a lower ultimate limit state corresponding to major glass crack pattern formation; and (2) an upper limit state corresponding to significant glass fallout. Early crescendo tests have yielded distinct and repeatable ultimate limit state data for various storefront glass types tested under dynamic racking motions. Crescendo tests will also be used to identify and quantify serviceability limit states for architectural glass and associated glazing components under dynamic loadings. These limit state data will support the development of rational design procedures for architectural glass under seismic loadings

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

International audienc

Comparison of Linear and Nonlinear Seismic Drift Histories for Midrise Steel Frames

The linear and nonlinear seismic responses for two midrise office buildings of five- and 24-storeys were generated by two independent research groups using three commercial analysis packages, ABAQUS, SAP90 and DRAIN-2DX. The results indicate that a variability of up to 25% occurred between the independent research groups\u27 seismic responses. Originally, these models and analyses were generated for the purpose of aiding in the development of load histories for the seismic testing of architectural glass at the University of Missouri-Rolla. The independent researchers were provided with the same structures, accelerograms and basic modelling assumptions and were directed to perform both linear and nonlinear seismic analyses. The variability in the results is of interest since it is indicative of the differences that may be seen between two independent consulting firms\u27 analyses. The linear analysis results using ABAQUS and SAP90, the nonlinear analysis results using ABAQUS and DRAIN-2DX and the linear and nonlinear results using ABAQUS and DRAIN-2DX are compared and contrasted. Copyright © 1996 Elsevier Science Ltd

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

Development of a Loading History for Seismic Testing of Architectural Glass in a Shop-Front Wall System

Moderate earthquakes can pose significant threats to the serviceability and structural integrity of the architectural glazing systems that are included in most building envelope systems. Building envelope damage can cause considerable economic losses due to operational disruptions for extended periods following an earthquake. Furthermore, glazing system structural failures are potentially hazardous to both building occupants and pedestrians. In this paper a systematic analytical study of the effect of the SOOE component of the 1940 El Centro earthquake on the response of a one-storey glass and aluminum shop-front wall system is presented. The seismic response of a one-storey commercial building comprised of three reinforced masonry walls, a glass and aluminum shop-front wall system, and a steel bar joist metal deck roof system was determined using the ABAQUS and SAP 90 finite element packages. In this study, the roof was considered incapable of transferring lateral forces to the walls and therefore its stiffness was ignored. Significant differences in the natural frequencies obtained from the two models were observed. These differences can be traced to different elements, different number of elements, different number of concentrated mass and nonstructural mass distribution, and variations in the number of supports used in the two models. For the El Centro ground motions perpendicular to the plane of the shop-front wall, displacements and drifts calculated by the ABAQUS and SAP 90 models differed considerably. This variation was probably due to modelling differences in the front steel frame. For El Centro ground motions parallel to the plane of the shop-front wall, displacements and drifts calculated by the ABAQUS and SAP 90 models were in much better agreement. It should be noted that for testing architectural glass the inplane drifts are more important. Typical values of inplane displacement reached 2.0% of the overall building height of 6.10 m, while the drifts reached 2.8% of the 1.83 m glazing opening. Copyright © 1996 Elsevier Science Ltd

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