Design Methods Of The Horizontal Braces Unlocated At Mid-height Of Columns Based On The Monte Carlo Method

The horizontal braces located at mid-height of the columns are usually used to reduce the out-of-plant effective length of the columns in the longitudinal column-bracing systems. The design methods of the horizontal braces located at mid-height of the columns have been comprehensively developed by domestic and foreign scholars, no studies of the horizontal braces unlocated at mid-height of the columns has not been carried out. In addition, the studies of the horizontal braces under the vertical loads which ensures stability was more, the studies of the horizontal braces under both of the horizontal loads and the vertical loads was less, according to the "Code for design of steel structures"(GB50017-2003) that the bracing forces has not add to the axial forces and took the larger between these two forces to calculate, it did not accord with the actual stress of the horizontal braces and no foundation in science. Therefore, it was necessary to research the design methods of the horizontal braces unlocated at mid-height of the columns and combined effect under both of the horizontal loads and the vertical loads for the horizontal braces.The initial imperfections of both the columns and the horizontal bracing bars are random variables in the longitudinal column-bracing systems, and the random combination of the initial imperfections between the columns and the horizontal. bracing bars can lead to the randomness of horizontal bracing bars in compression or in tension. However, in past studies, the longitudinal column-bracing systems were usually analyzed according to the worst combination of the above two initial imperfections and the horizontal bracing bars were only assumed to be in compression, so it was not in conformity with actual situations. Therefore, the various analyses on the longitudinal column-bracing systems with random distributions of the initial imperfections should be carried out and the rational design method should be sought.A large number of simulation analyses for the longitudinal column-bracing systems when the horizontal braces located at0.6L and0.7L of the column with pin-ended column bases had been studies using the ANSYS finite element program, in which the random combination of the initial imperfections between the columns and the horizontal bracing bars was well considered by the Monte Carlo method, and the design bracing forces was also obtained, then compared with the design bracing forces located at mid-height horizontal bracing, so the result indicated:the design bracing forces located at0.7L horizontal bracing bars was the highest, the design bracing forces located at0.5L horizontal bracing bars was in the middle and the design bracing forces located at0.6L horizontal bracing bars was the lowest.A large number of simulation analyses for the longitudinal column-bracing systems with the horizontal braces located at0.6L and0.7L of the columns height L with fixed-ended column bases have been studies using the ANSYS finite element program, in which the random combination of the initial imperfections between the columns and the horizontal bracing bars was well considered by the Monte Carlo method, the comparative studies on the design requirements of located at0.6L and0.7L horizontal bracing bars were carried out between the systems with fixed-ended column bases and pin-ended column bases, the reasons that the former are lower than the latter were analyzed.The researches on the design methods of the horizontal braces located at mid-height of the columns which combined effect under both of the horizontal loads and the vertical loads, confirmed combination principle of the braced forces and the horizontal loads, then the corresponding design recommendations were proposed. The results proved that the above design requirements were compared with the design methods of the horizontal braces which only under the functions with vertical loads and the horizontal loads simply added to axial forces, then the corresponding design recommendations were proposed, and the reasons that the former are higher than the both of which were analyzed, it was different from current national code.