1) Torsion occurs in the monolithic concrete construction primarily where the load acts at a distance from the longitudinal axis of the structural member. A spandrel beam, a canopy, peripheral beams or a helical staircase are all examples of structural elements subjected to twisting moments. These moments occasionally cause excessive shearing stresses. Most concrete beams subjected to twist are components of rectangles. They are usually flanged sections such as T beams and L beams.
2) The torsional moment acting on a particular structural component such as a spandrel beam can be calculated using normal structural analysis procedures. Design of the particular component needs to be based on the limit state of failure. Therefore, the nonlinear behavior of a structural system after torsional cracking must be identified in one of the following two conditions: I) no redistribution of torsional stress to other members after cracking and 2) redistribution of torsional stress and moments after cracking to effect deformation compatibility between intersecting members.
3) Stress resultants in statically determinate beams can be evaluated from equilibrium conditions alone. Such conditions require a design for the full-factored external torsional moment, because no redistribution of torsional stress is possible. This state is often termed equilibrium torsion.
4) The edge beam has to be designed to resist the total external factored twisting moment due to the cantilever slab; otherwise, the structure will collapse. Failure would be caused by the beam not satisfying conditions of equilibrium of forces and moments resulting from the large external torque.
5) In statically indeterminate systems, stiffness assumptions, compatibility of strains at the joints, and redistributions of stresses may affect the stress resultants, leading to a reduction in the resulting torsional shearing stress.
6) Neglect of the full effect of the total external torsional moment in this case does not lead to failure of the structure but may result in excessive cracking.
Задание 1. Прочитайте текст и письменно переведите абзацы 2, 3, 6.
Задание 2. Письменно ответьте на вопросы к тексту "Torsion":
1 What elements are subjected to twisting moments?
2 Where does torsion occur?
3 How can the torsional moment be calculated?
4 When can failure happen?
5 What may redistributions of stresses result in?
Задание 3. Найдите и выпишите из текста "Torsion" английские эквиваленты следующих выражений.
перераспределение напряжения кручения
главный вектор напряжений