Crack-Resistant Structural Systems Employing Nano-Composite Mortar–Filled Steel Tubes

Concrete-Filled Steel Tubes (CFSTs) are widely adopted in advanced structural and civil engineering applications due to their high load-carrying capacity, excellent ductility, and effective composite interaction between the confining steel tube and the infilled concrete or mortar core. However, differential thermal expansion between steel and the mortar core under elevated temperatures can generate high interfacial stresses that lead to microcracking, debonding and reduced durability. This study develops a coupled thermo-mechanical finite element framework in ANSYS Workbench to analyze CFST columns filled with plain and nano-composite mortars (nano-silica and graphene-oxide modified). The model integrates steady-state and transient thermal analyses, nonlinear structural response, contact mechanics (TARGE170–CONTA174), and fracture modelling using XFEM/CZM. A parametric study varies steel yield strength, mortar compressive strength, and support–load spacing. Results show that nano-modified mortars reduce thermal mismatch, delay crack initiation, and improve confinement. A crack-free envelope is proposed to guide design under combined thermal and mechanical loading.