Relationships between internal forces, bracing patterns and lateral stiffnesses of a simple frame

For a braced frame it is important to understand the relationships between the lateral stiffnesses, internal forces and bracing patterns in order to achieve an efficient design. This paper studies these relationships based on a four-bay and four-storey braced frame using both hand and computer analyses. Assuming that two bracing members can be placed arbitrarily in each of the four stories, there are 331,776 possible bracing arrangements. The best and the worst patterns of the total patterns are reviewed, with their characteristics summarized. All possible 256 symmetrically braced frames are further studied, allowing a more detailed examination of these relationships. Criteria for selecting bracing panels and bracing orientations are suggested based on the findings of this study and basic concepts, which may be applicable to the design of other braced frames. It is also found that the mega X brace or the double inversed V brace is the stiffest brace pattern, dependent on the aspect ratio of the braced panel and the size ratio of the columns to beams. This finding is confirmed using evolutionary structural optimization.