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ABSTRACTAluminium alloy 5083 plates were joined using friction stir welding (FSW) technique individually or in combination with boron carbide (B4C) and carbon nanotubes (CNTs). The effect of these reinforcements on mechanical properties, microstructure evolution and corrosion behaviour after FSW has been investigated. Radiography confirmed good fusion in the welded zone and the absence of surface or subsurface defects. The tensile testing results indicated a 35% decrease in tensile strength after FSW of the Al-5083 plates compared to the base metal, but it increased once again after the addition of individual reinforcements of B4C and CNTs due to grain refinement and second phase strengthening. In the sample with hybrid reinforcement, premature failure was observed due to lack of fusion and improper bonding between the two reinforcing materials. A similar trend was observed in the case of flexural testing. Severe plastic deformation and reduced grain size increased the micro-Vickers’ hardness values of reinforced samples. Evolution of the aluminium grain structure was analyzed using optical and stereo microscopy, while uniform dispersion of reinforcements and chemical composition was characterised by scanning electron microscope (SEM) and energy-dispersive X-ray spectroscopy (EDS), respectively. Increase in corrosion resistance was also observed after FSW and addition of reinforcements.

Disproportionate or progressive collapse is a phenomenon in which entire structure or large part of it collapses because of the local failure of a structure. Resistance to such progressive collapse depends on continuity between elements and ductility of the connections. The ductility of commonly used bolted end plate connections may depend on the T-stub component of the connection. The aim of this paper is to study the behaviour of T-stub components of beam to column end plate bolted connections under large deformation demands associated with column loss scenario. For this purpose, a parametric study is carried out to evaluate the ultimate strength and deformation capacity considering two parameters i.e. distance between the bolts and endplate thickness. Based on the experimental data, numerical model has been validated and employed in a parametric numerical study aimed at improving the response under large deformation demands. The study indicate significant role of bolts in development of catenary forces since the ultimate tensile capacity of T-stub after undergoing large deformation in a ductile failure mode was controlled by the failure of the bolts. Parametric study reveals much higher bolt force in comparison with displacement controlled induced axial force in the T-stub indicating failure of the bolts at much lower applied axial force.

The role of community building portfolios in socio-economic development and the growth of the built environment cannot be overstated. Damage to these structures can have far-reaching consequences on socio-economic and environmental aspects, requiring a long-term perspective for recovery. As communities aim to enhance their resilience and sustainability, there is a cost burden that needs to be considered. To address this issue, this paper proposes a community-level performance enhancement approach that focuses on optimizing the long-term resilience and sustainability of community building portfolios, taking into account recurrent seismic hazards. A Gaussian process surrogate-based multi-objective optimization framework is utilized to optimize the cost objective while considering performance indicators for resilience and sustainability. The proposed framework involves using performance-based assessment methods to evaluate the socioeconomic and environmental consequences under stochastic and recurrent seismic hazard scenarios. These evaluated indicators are then used to efficiently optimize the community resilience and sustainability, taking into account the retrofit costs. Finally, approximate Pareto-optimal solutions are extracted and utilized for decision-making. In summary, this paper presents a novel approach for optimizing the long-term resilience and sustainability of community building portfolios by considering recurrent seismic hazards. The proposed framework incorporates performance-based assessment methods and multi-objective optimization techniques to achieve an optimal balance between cost, resilience, and sustainability, with the ultimate goal of enhancing community well-being and decision-making in the face of seismic hazards.