- Volume:18 Issue: 5, 2020
- تاریخ انتشار: 1399/01/18
- تعداد عناوین: 8
Effect of Recycled PET (Polyethylene Terephthalate) on the Electrochemical Properties of Rebar in ConcretePages 487-500
This research is focused on the use of recycled PET (Polyethylene terephthalate) as an aggregate to improve the electrochemical properties of reinforcing steel in concrete. Samples were made with different PET geometries such as: fibers (F), rectangles (R), and mixture of fiber and rectangle (F–R). The PET was added as a substitute for sand with a PET/sand ratio by volume percent of 3%/97%, 5%/95%, and 8%/92%. Specimens were exposed to an aggressive solution of sodium chloride at 3%, simulating a marine environment, and were evaluated for 300 days through various electrochemical techniques such as: open-circuit potential, electrochemical noise, electrochemical impedance spectroscopy, and linear polarization resistance. Samples with PET reached more noble values of potential compared to the control sample. The highest values of noise resistance (Rn) and polarization resistance (Rp) were reached for the reinforcing steel in concrete samples prepared with particle of rectangles and fiber–rectangle mix. Likewise, these samples maintained a diffusive behavior for a longer time. At the end of the test period, the favorable effect of the rectangles and the mixture of fibers and rectangles in the concrete samples are evident, since they remain in the negligible range of corrosion rate, with values below 1 × 10−1 μA/cm2. This behavior was not noticeable for samples with only PET fibers, due to the fact that they reach the moderate range of corrosion rate, with values between 2 × 10−1 and 5 × 10−1 μA/cm2, similar to the control sample.
RC Beam–Column Connections Retrofitted by Steel Prop: Experimental and Analytical StudiesPages 501-518
This paper studies the efficiency of a proposed retrofit technique to boost the seismic behavior of beam–column connections in existing deficient reinforced concrete (RC) moment frame systems with the consideration of constraint conditions such as the height of beams, using analytical, experimental, and numerical methods. The proposed retrofit method, called the “single steel prop and curbs”, consists of a diagonal steel prop element and two steel curbs that to the beam and column are laterally mounted. The internal force diagrams of the retrofitted exterior beam–column connections by analytical formulations are investigated and design strategies for promoting the efficiency of the single steel prop to achieve the expected efficiency proposed. To assay the validity and reliability of the proposed analytical procedure, experimental and numerical assessments were also conducted independently. Therefore, four deficient RC beam–column connections by single steel prop were retrofitted using three different cross-sectional areas and revival sheets and then accompanied by a control specimen subjected to cyclic loading. Next, numerical models were calibrated in ABAQUS software. Finally, by derivation of the props’ average axial force from experimental and numerical results, the beam shear coefficient, β, is calculated based on the analytical relations. These results confirmed good conformity between the experimental and numerical outputs as well as reliability of the analytical formulations. Also, the output results indicated that the retrofitted specimens had 53–78% bearing capacity and 146–217% dissipated energy more than the control specimen.
A Bayesian Network Framework for Comparing Project Delivery MethodsPages 519-537
Public–Private Partnerships (PPPs) are innovative and evolving project delivery methods that have enabled public entities, such as local, state, and federal government agencies to pursue projects that were otherwise infeasible. Value for Money (VfM) is commonly used as a tool to evaluate PPP project delivery with traditional project delivery. In this work, a BN framework is presented for supplementing VfM analysis that allows for the combination of the quantitative and qualitative components of project delivery. The framework includes steps to develop BNs, analyze network scenarios and interpret the results. The proposed BN framework reduces the subjectivity and bias inherent in VfM assessment. It, therefore, has the potential to supplement the decision-making process. We demonstrate the application of the proposed framework to California’s Presidio Parkway Project as a case study. The results corroborate the findings from the VfM assessment and conclude that for the Presidio Parkway project, design–build–finance–operate–maintain is a better method than the traditional design–bid–build project delivery method.
Numerical and Physical Modeling of the Effect of Roughness Height on Cavitation Index in Chute SpillwaysPages 539-550
This study presents the results of physical and numerical modeling of the effect of bed roughness height of chute spillways on the cavitation index. A 1:50-scale physical hydraulic model of the chute spillway of Surk Dam was constructed at the hydraulic laboratory of Shahrekord University, Iran. The experiments were conducted for different flow rates and the parameters of pressure, velocity, and flow depth in 26 positions along the chute. Finally, the ANSYS-FLUENT model was calibrated in the chute spillway using the experimental data by assumptions of two-phase volume of fluid and k–ε (RNG) turbulence models. The cavitation index in different sections of the chute spillway was calculated for different values of bed roughness including the roughness heights of 1, 2, and 2.5 mm. Results showed that the minimum values of the cavitation index were 0.2906, 0.2733, and 0.2471 for the roughness heights of 1, 2, and 2.5 mm, respectively. The statistical significance analysis showed that reducing the roughness height from 2.5 to 1 mm would not change significantly the value of the cavitation index at 95% confidence interval.
Nonlinear Dynamic Response of a RC Frame for Different Structural Conditions Including the Effect of FE Model UpdatingPages 551-567
After destructive events such as earthquakes, attempts have generally been made to repair and strengthen structures using such methods as filling cracks by injection, wrapping structural elements with fiber-reinforced polymer (FRP). These applications can allow the recovery of lost structural performance. In this paper, the aim was to investigate the structural performance of an RC frame under different conditions—undamaged, damaged, repaired, and strengthened—by comparing results of nonlinear dynamic analyses. In addition, finite-element (FE) model updating effects were investigated in the case of the undamaged condition. To this end, an RC frame model was first constructed in the laboratory, and then, the model was damaged by lateral forces, repaired with epoxy injection, and lastly strengthened by wrapping with FRP. To obtain the dynamic characteristics of the RC frame under the different conditions, ambient vibration tests were performed for each condition. The FE model of the RC frame, obtained through global and local model updating using the ambient vibration test results, was modeled to achieve the nonlinear dynamic analyses. The results of the analyses were presented in the form of maximum displacements, principal stresses, and strains with contours diagrams. The maximum displacement increased significantly (133%) with the degree of damage, sharply decreased with the repaired (32%), and strengthened (36%) applications. The maximum and minimum principal stresses decreased by 24% and 35%, respectively, with the damaged condition. In addition, maximum differences between the undamaged and strengthened conditions were calculated as 17% for the maximum principal stress and 38% for the minimum principal stress. Findings indicated that the epoxy injection with FRP wrapping eliminates effect of the damage and recovers the model’s performance to its initial state. In addition, it is demonstrated in this paper that the updating procedure considerably changes the dynamic analysis results.
Horizontal Cyclic Performances of Hook-End U-Shaped High-Damping Rubber Jointed Precast FramePages 569-584
In the past few decades, many efforts have been carried out to investigate and improve the cyclic performance of the precast structure joints using high-strength steel bars and plates. However, the utilization of high-damping rubber (HDR) is mainly limited as the bearing pad below the structural components to dissipate the cyclic energy. Hence, a new hook-end connection precast beam–column joint embedded with U-shaped HDR is developed in this study to investigate energy dissipation capacity and equivalent viscous damping ratio in a precast frame. The horizontal cyclic performance of the new connection is experimentally tested, numerically analyzed, and evaluated by comparing to precast reinforced concrete frame specimens built with monolithic and conventional pinned dowel connections. The experimental results showed that the precast frame with newly developed connection exhibited fatter hysteretic curves, approximately 15% and 13% higher cumulative energy dissipation capacity, and equivalent viscous damping ratio than the control specimen with conventional pinned dowel connection, respectively. Besides, it also attained similar yield force and approximately 6% lower maximum force compared to the monolithic specimen. The force–displacement backbone curves obtained from the numerical analysis also showed satisfactory matching in yield force, maximum force and maximum displacement when compared to the experimental results.
Performance of RC Beam Strengthened with NSM-CFRP Strip Under Pure Torsion: Experimental and Numerical StudyPages 585-593
This paper presents experimental and finite element model (FEM) on reinforced concrete (RC) beam behavior strengthened by near-surface mounted (NSM) carbon fiber-reinforced polymer (CFRP) strips subjected to pure torsional loading. Seven rectangular reinforced concrete RC beams of 250 mm × 250 mm × 1600 mm were constructed and tested considering the effect of length, inclination, arrangement of longitudinal and scheme of NSM-CFRP strips. The outcomes of the tests indicated remarkable enhancement in the behavior of torsional strengthened beams using NSM-CFRP strips. In general, the beams strengthening with inclined CFRP-NSM strips exhibited an increase in torsion moment strength and angle of twist more than the beams strengthening with vertical CFRP-NSM strips. The experimental measured results are validated with a 3D numerical simulation carried out using nonlinear finite element (FE) modeling. Finally, it can be seen that the calculated numerical torsional moment–angle of twist behavior is in agreement with the experimental results for all RC beams.
Three-Dimensional Nonlinear Finite Element Modeling for Bond Performance of Ribbed Steel Bars in Concrete Under Lateral TensionsPages 595-617
Development of experimental studies in bond behavior between deformed bar and concrete under complex stress conditions in the last 2 decades is significantly affecting the concrete design specification. This article presents a rib-scale finite element model (FEM) to study the bond behavior of deformed bar in concrete under lateral tensions. In this model, detailed modeling including the reinforcing bar ribs and the concrete keys in contact region is realized with real geometric parameters. At the concrete–bar interface, surface-to-surface contacts with tie constraints are used and relative sliding or separation between contact surfaces are inhibited; adhesion between concrete and deformed bar is ignored. A user-defined subroutine named VUSDFLD in ABAQUS software was incorporated into the concrete damaged plasticity (CDP) model to acquire more accurate concrete constitutive relations. The FEM is calibrated using pullout test data from published papers. The simulation results show that all specimens failed in splitting mode. The lateral tension is an adverse factor on the bond property between steel bar and concrete, both the ultimate bond strength and the slip at the peak bond stress decrease with the increase of the lateral tensions. Comparison of computational simulation with the experimental data indicates that the proposed model gives a reasonable prediction of the bond stress–slip curves as well as the concrete crack patterns.