الفهرس 
Behavior of Concrete Beams under TorsionOnly 14 pages are availabe for public view
 |  | from | 232 |  |  |
| | | from | 232 | | |
Abstract
Torsional moment is considered as a non-basic force effect on structure, but in some cases, it becomes the basic effective force, such as ring beams, spiral stairs, and curved elements in bridges. In addition, its difficulty
in studying and testing it in the laboratory led to a lack of research on torsion compared with shear and bending moment forces. Reinforced concrete box
girders are considered one of the best systems resisting torsional moments.
Due to changes in service loads or aging through time as well as changes of
use of the structure, strengthening and rehabilitation will be necessary to
retrofit box girders using different materials and methods. An experimental test program consisting of eleven reinforced concrete box girders with cross-section of 350 x 350 mm, a length of 1300 mm and an inner cross-section 200 x 200 mm was carried out. Four control specimens were tested; two as box girders, one solid beam and one box girder with an opening. Two specimens with opening were strengthened with steel plates and CFRP around the opening. Two specimens were strengthened
longitudinally with steel plates and CFRP sheets. Two specimens were
strengthened with U-shaped steel plates and CFRP sheets. One specimen was
strengthened with longitudinal and U-shaped CFRP sheets. All specimens
were tested under pure torsion up to failure. Crack patterns, modes of failure and torsional moments versus angles of twist were investigated and
discussed. Numerical models by finite element method using ANSYS program
were suggested and compared with experimental results in order to verify the finite element model. After verification, different variables were studied such as influence of opening location, number of openings, area of the opening, change in longitudinal and transverse steel amount, and strengthening around the opening. The comparative study showed good agreement between experimental and FEM results. The results indicated that the main factors affecting the torsional moment are the number of openings and their dimensions. Also, the strengthening around the opening compensates the torsional strength that was lost due to the opening.