Design Method Research On Progressive Collapse Prevention Of Steel Frame

When a load bearing element fails, load will be transmitted to other elements around it. If the corresponding elements cannot bear the transmitted load and reach a new balance, the elements will be damaged progressively, which always lead to an uncontrollable progressive collapse. China takes on high risks of progressive collapse for four reasons:the great number of super high-rise buildings, the high probability of terrorist attack, dense population with high mobility and big vehicle holdings. However, China has not yet a professional code for progressive collapse resistance. Procedure and parameters for progressive collapse prevention, which are suitable for China’s building codes, is really meaningful to be studied.This paper, with an example of 4-floor,9×3 cross steel frame office without one bottom column, introduces the linear static design procedure in progressive collapse resistance code published by General Services Administration in Oct.2013. Some parameters in GSA code is modified to fit China’s structural code. All components are divided into five groups:outside longitudinal beam, medial longitudinal beam, transverse beam, structural lateral column and medial column. Each group’s section is changed 6-9 times. The relationships between section modulus and stress ratio is studied. The effect of degradation in stiffness of middle or corner bottom column, which is simulated by progressively reducing the Young modulus, on other components’ stress ratio is also studied. The conclusions are:(a) The frame designed by China’s code in this paper cannot resist progressive collapse. The stress ratio of beam and column in deformation controlled criteria and shear ratio of column in force controlled criteria is overrun.(b) In the plane containing the removal column, all components can reduce stress ratio obviously by extending any group’s component sections in this plane. But in planes including no removal columns, extending a group’s component sections in this plane can only reduce its own stress ratio.(c) As stiffness of failed columns decreased gradually, stress ratio of the adjacent beam and column is increased. The increasing velocity is slow-fast-slow. For coaxial column above the failed one, the stress ratio curve can be divided into the falling or rising part.And the curve of the second floor first rises then falls in the falling part.