# Parametric Analysis of Outrigger Systems for High-Rise Buildings with Different Geometric Shapes
## 3 Refined Modeling for Outrigger Systems
### Model Description  
For comparative purposes, the structural characteristics of the refined models align with those detailed in Section 3. Specifically, a 200 m tall building (50 stories) with a 40 m square plan footprint was adopted. An internal modular grid portions the plan to facilitate the positioning of the RC shear wall core and the arrangement of the perimeter columns (as illustrated in Figure 9). Key characteristics of the reference structure are summarized in Table 5.  
To isolate the effects of geometric configuration, identical design attributes were adopted across all models, including member sizes for beams, columns, core, and outriggers. Each refined model incorporates a single double-story steel outrigger with a steel belt-truss, positioned at mid-height (between the 24 th and 26 th floors). Outrigger and belt-truss configurations were adjusted to accommodate rotational floor displacements in the twisted model and elongation/shortening of spaces near the central core due to horizontal floor translations in the tilted models. Gravity loads comprise dead loads of 7 kN/m\({}^{2}\) and live loads of 2 kN/m\({}^{2}\). Composite slabs, designed for office tower applications, were dimensioned to support live loads. Steel  
Figure 9: Typical floor plan. \begin{table}
\begin{tabular}{c c} \hline \hline \multicolumn{2}{c}{**Refined Model’s Characteristics**} \\ \hline Height (H) & 200 m \\ Story levels & 50 \\ Inter-story height & 4 m \\ Plan dimension & 40 \(\times\) 40 m \\ Inner core dimension & 20 \(\times\) 20 m \\ Primary resisting system & RC MRF and RC core shear walls \\ Secondary resisting system & Steel outrigger and belt-truss system \\ Outrigger location & \(\gtrsim\)2 H = 100 m \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Main characteristics of refined models. beams were dimensioned uniformly across all three models, reflecting the consistent slab typology, with minor variations in beam length present in the tilted and twisted models. Within the scope of the present study, wind action was calculated according to the Italian technical code (NTC2018) by assuming a base speed of 40 m/s. Member cross-sections were sized to comply with code-based stiffness and strength criteria for the relevant combination of wind and gravity loads. To facilitate comparisons between refined and simplified models, column tapering was neglected, and column sizes remained constant throughout the building height. The structural properties of the refined models are shown in Table 6 and Figure 9.  
In the refined models, RC columns and steel beams were modeled as frame elements. The RC core shear walls were represented using an equivalent frame approach, which employs infinitely rigid beams to simulate shear wall stiffness and connect axial centerlines. Core shear walls and columns were fixed at the base, and outriggers were rigidly connected to the core and perimeter columns. Slabs were not explicitly modeled but their influence was accounted for by applying uniform distributed loads directly to the floor beams. In the design of tall buildings, it is common practice to assume rigid floor diaphragms, whereby the mass of each floor is concentrated at its geometric center. Thus, lateral wind loads were applied at the floor center of mass. This simplification facilitates computational efficiency and is a reasonable approximation of the structural behavior. As far as the comparative analysis between refined and simplified models is concerned, a uniformly distributed lateral wind load was assumed along the building height, calibrated to produce an equivalent base shear of 30,000 kN, consistent with the code-based provisions. This base shear corresponds to the value obtained by applying a unit load of 150 kN/m to the core in both model types. Gravity loads and load combinations were neglected within this specific comparison. Figure 10 depicts the refined models alongside their corresponding simplified counterparts.