## 8 Technical Challenges and Potential Solutions
### Columns Stability Issues  
The structural stability of columns under axial compression loading and their design method has always been the fundamental problem for steel structures in the analysis and design process. Direct analysis/second-order analysis [144] and an effective length/K-factor method are the widely accepted design methods for a steel column's design. In taller building systems, modeling geometric imperfections are preferred to include the notional load and out-of-plumbness of columns; second-order analysis is therefore adapted for the stability analysis. Alignment charts [145] and simplified equations [146] are used to calculate the rigid frames' effective length factor. Many researchers researched rigidly [147; 148] and flexibly [149; 150] connected traditional multi-story sway/unbraced and non-sway/braced steel frames. Additionally, the inelastic critical and post-critical behavior of the unbraced flexibly joined frame is investigated under different loading conditions [151]. However, both techniques are based on traditional steel frames with continuous columns.  
Because the IMC joining techniques, column discontinuities, and construction details of PFISB structures differ from traditional steel buildings, this results in complex end-boundary conditions for the members. Therefore, using conventional steel standards and design methods can incorrectly formulate the effective length factor and an uneconomical design approach. For example, [PERSON] et al. [152] observed the multi-column PFISB wall's buckling behavior. It was found that buckling can be reduced by concrete sheathing and the wall acted as a continuous one; the effective length was therefore found to be greater than 1.0. However, the study considered the uniform load distribution among all of the columns. [PERSON] et al. [153] studied the column tenon IMC. They used the theoretical design for the effective length coefficient. However, [PERSON] et al. [47; 48; 49] discovered that the traditional standards overestimate the compressive strengths of multi-column PFISBs' walls with SHS tubes because the IMUs' uniqueness is ignored. Similar research was carried out by [PERSON] et al. [154] by proposing a theoretical equation with a bending stiffness ratio, column-to-tenon length ratio, and column-to-beam rotational stiffness ratio. These investigations, however, assumed that column ends would be fully welded to endplates, which is not practicable in interior IMC. Likewise, a simple tenoned column cannot be used to construct additional columns, nor can it be used to create multi-story or multi-bay frames. The effective length in a sway and non-sway rigid IMU was derived in a study [155]. [PERSON] et al. derived equations for calculating the effective length factors for the sway [156] and non-sway frames [157]. However, they were entirely based on the theoretical approaches of [PERSON] et al. [147; 148] for rigid and [PERSON] et al. [149; 150] for semi-rigid frames based on the stability factors model proposed by [PERSON] et al. [158] for traditional steel structures. The study is appropriate for single-bay PFISB-infilled frames with continuous columns at the ends but not for discontinuous volumetric multi-bay and multi-story PFISBs. Unlike traditional or infilled frames, the IMUs' column ends are discontinuous at the IMC and supported by beams. PFISBs have a considerable impact on the column's stability as a result of a rigid internal IMC, the varying rigidities of the horizontal and vertical external connections, and the impact of the neighboring members. However, the above studies have not yet considered all of the details. This could also account for the effect of different stiffnesses of the exterior, middle, and interior joints, floor and ceiling beams, and group columns' mutual influence.