Stability Analysis Of Cross Brace Systems

Steel braces as a stable unit to improve the stability of the structures besides it significantly improve the lateral stiffness of the structure.Cross bracing system is the most common form of steel braces.Usually,cross braces were slender,in order to simplify the calculation,the design assuming that compression strut of cross braces doesn’t work,only consider tension rod’s effect.This design assumption may bring risks to structure,caused the oblique compression bar buckling will bring larger deformation,thus a spate of second-order effect can cause structural damaged.So the oblique compression bar instability of the critical force should be an important indicator of structure design.Current specification are given calculation formula for the same length,cross section and the same intersection in the middle(standard)of the cross braces,but for the non-standard cross braces,there are no corresponding calculation formula or chart to calculate.This paper research on the present situation,derived and solved the critical equation of non-standard cross braces by using the method of balance and second-order displacement.In order to rapid calculation in engineering,with the thousands of transcendental equation solved,this paper received a large amount of data,and plotted nomographs(dimensionless)to solve the critical force of cross braces.The most valuable achievements of this paper are these nomograghs(figure 3.10,figure 3.19,figure 4.6 and figure 4.11)to solve critical force of non-standard cross braces.The correctness and reliability of the nomographs have stood the test of finite element calculation,and it has a high precision.It is a good tools to rapid calculation the critical force of non-standard cross braces,that is also a supplement with the fact that the steel structure design code is not yet have the corresponding calculation form or formula.In addition,this paper also do some research in the approximate calculation method of non-standard cross braces of the critical force,such as use deflection method to get the approximation equation of calculating the critical force,such as formula(5.6),formula(5.7),formula(5.8),and formula(5.9).These formulas also were checked by using finite element calculation,the accuracy is also high,and more convenient to use.