الفهرس 
INTRODUCTIONOnly 14 pages are availabe for public view
 |  | from | 337 |  |  |
| | | from | 337 | | |
Abstract
Nowadays, many authorities and public agencies in North America have considered glass/carbon FRP bars and stirrups as a good material that can resist corrosion in harsh climate. Accordingly, experimental tests are the best way to understand the behavior of concrete beams reinforced in flexure and shear with CFRP and subjected to pure torsion. Although some experimental tests are mentioned in the literature, there is a significant lack of experimental research on concrete members reinforced with FRP and subjected to torsion. Many concrete codes and design guidelines have no provisions on torsion such as [ACI 440.1 R-06; JSCE 1997; CAN/CSA S6-06]. As a result, JSCE 1997 stated that the design of torsion capacity for RC members should be investigated experimentally and analytically based on reliable techniques.
In the current study, the behavior of concrete beams reinforced in flexure and shear with CFRP bars and subjected to pure torsion is investigated experimentally and numerically. Seven half-scale RC beams with rectangular sections are tested to failure and the cracking and ultimate moment, the angle of twist along with crack pattern are obtained. The main goal of this study is to investigate the effect of concrete compressive strength, stirrup bar size, and stirrup spacing on the torsional capacity. A numerical investigation using the non-linear finite element (FE) modeling is conducted using ATENA program. The displacement control is used in the numerical simulation to apply the load in two opposite cantilevers and the failure criteria is proposed to predict the failure in concrete and CFRP bars. The validity and accuracy of the formulations and the procedure adopted in ATENA are checked through holding a comparison between the proposed numerical models and experimental results of RC beams subjected to pure torsion gathered from the literature. The comparison showed good agreement between experimental and numerical models with average difference of 7%.
The experimental results show that the ultimate and cracking torque for RC beam with concrete compressive strength 42.5 MPa increased by 20% and 23%, respectively than the RC beam with concrete compressive strength of 30 MPa. The results also indicate that the stirrup spacing, and stirrup size do not affect cracking moment but have a significant effect on the ultimate moment. The ultimate torque for RC beams with stirrup spacing 170, 125, and 85 mm is higher than that without stirrups by 31%, 56% and 77%, respectively. The ultimate torque of tested specimens increased with the increase of stirrup bar size by 28% and 45% for sizes 9.5 mm, and 11.5 mm, respectively than that of 7.5 mm. It is found that the studied parameters have a major effect on the deformability index.
The numerical results indicated that the concrete compressive strength and beam depth-to-width ratio had a significant effect on cracking moment while, stirrup spacing, and stirrup bar size had an insignificant effect on cracking moment. It is found that all studied parameters had a noticeable effect on ultimate moment. The numerical results also showed that RC beams with closer stirrup spacing had a lower stirrups effective stress while RC beams with larger stirrup spacing had a high stirrups effective stress which approximately reached or higher than bend stress of CFRP stirrups. The failure of concrete beams reinforced with CFRP bars under pure torsion governed by concrete crushing or followed by rupture in stirrups at bent portion without using the capacity of straight portion.
The proposed models are introduced based on the regression analysis of the numerical outcomes. The proposed models are used to predict both cracking and ultimate moments for concrete beams reinforced in flexure and shear with CFRP and subjected to pure torsion. To check the validity of proposed model, the predicted results using proposed models are compared to their counterparts either from experimental work or data gathered from literature. The numerical results are in good agreement with their counterparts predicted by proposed models. The predicted models improved predicting both cracking and ultimate torsional moments and the mean values of numerical-to-predicted are 1.016 and 1.08, respectively.