## 3.1. _Introduction_  
Topology Optimisation (TO) has reached maturity for practical applications in numerous industries after almost thirty-five years of cutting-edge research [1, 2, 3, 4]. This era was leveraged by seminal research by [PERSON] and [PERSON] in developing the now classic homogenisation methods [5, 6], and by [PERSON] and [PERSON] [7], who solved [PERSON] and [PERSON]'s material distribution problem [8, 9, 10, 11]. However, despite significant developments, the current density-based TO algorithms continue to create optimised structures that are non-manufacturable. Hence, the latest research has been pursuing other solutions for attaining smoother edges and potential manufacturable outcomes. Within these endeavours, one option is the Smooth-Edged Material Distribution for Optimising Topology (SEMDOT) algorithm [12] and its subsequent non-penalisation (np-SEMDOT) version [13].  
Considering the promising results delivered by np-SEMDOT in terms of both optimisation and surface quality [13], its usage in real-world applications and the validation of its ultimate behaviour have been regarded as vital with regard to its adoption within the industry sector.  
While TO is already a fundamental step in the industrial design of products for such sectors as automotive, defence, aerospace, medical devices, and new materials design, it is yet to become commonplace in civil and large structural engineering endeavours. Hence,as we face the dawn of TO usage for construction [14], influenced not only by architects' taste for genuine and meaningful shapes [15; 16; 17; 18] but also by the progress made in code-compliant TO [19; 20; 21] and TO for multiple loadings [22; 23; 24; 25; 26; 27; 28; 29], civil engineering structures can be regarded as the ideal ground for testing new TO solutions.  
To address the need for assessment with physically nonlinear analyses of topologically optimised parts subjected to extreme loading for each TO method, this paper investigated the optimisation of the well-known Sheikh-Ibrahim [30] connection's tension plate. The np-SEMDOT method was benchmarked against the ubiquitous and reliable Solid Isotropic Material with Penalisation (SIMP)-based optimisation tool provided by TOSCA software. The benchmark used the conditions depicted in [21] and the solutions were compared with the Physical Nonlinear Finite Element Analyses (PhNLFEA) solution.  
The novel results were expected to provide significant and well-founded conclusions on the usability of TO in steel design, as well as on the prospects of np-SEMDOT.  
This work's main contributions can be considered to validate the use of the np-SEMDOT algorithm for a real-world case study. It was found that np-SEMDOT optimisations slightly outperformed SIMP-based optimisations for the current case, and showed that np-SEMDOT solutions performed adequately in nonlinear conditions until collapse with a remarkable displacement capacity. It was concluded that performing a preliminary parametric analysis was essential to ensure np-SEMDOT solution quality and that the np-SEMDOT solution enhanced the smoothness of the internal voids' edges, facilitating its manufacture.  
In this paper, after introducing the theme and related work and providing a brief on np-SEMDOT in Section 3, the case study is depicted in Section 4. Research methods, including the general methodology for structural code compliant TO and the specific protocol for SEMDOT optimisation and parametric analyses, are explained in Section 5. The results are presented and discussed in Section 6, and conclusions are detailed in Section 7.