Aluminum has long promised architects a tempting bargain: structures that resist corrosion, never need painting, and weigh a fraction of their steel equivalents. The catch has always been strength. Conventional structural aluminum alloys simply cannot match the load-carrying demands of very large spans, forcing engineers to insert steel members into the most heavily stressed zones of aluminum reticulated shells. A new experimental and numerical study published in Case Studies in Construction Materials argues that a familiar aerospace alloy could finally dissolve that compromise. The research team, led by Feng Luo and colleagues, systematically tested 7075-T6 aluminum alloy and the gusset joints that connect its members, demonstrating that the material achieves an ultimate tensile strength of 541.2 megapascals, which exceeds that of ordinary structural steel while weighing only one third as much. The work also delivers design tools that engineers can use to model these joints realistically in full structural simulations.
The significance of joint behaviour in single-layer reticulated shells is difficult to overstate. These delicate-looking latticed domes and vaults rely on the stability of the entire shell rather than on the strength of individual members, and previous studies have repeatedly shown that the stiffness of the joints exerts a remarkable influence on overall buckling performance. Yet joints are never ideally pinned or perfectly rigid in practice. They behave semi-rigidly, deforming in complex nonlinear ways under load, and until now no universal model existed that designers could conveniently apply to capture this behaviour. For high-strength aluminum alloy gusset joints, often abbreviated as HHAA joints, the research record was particularly thin, which severely limited the engineering application of a material that appears ideally suited for ultra-large-span structures exceeding 300 meters, a scale at which conventional aluminum alloys fall short of material requirements.
The experimental campaign began at the most fundamental level: the material itself. Three coupon specimens of 7075-T6 aluminum alloy, all 12 millimeters thick and cut from the same batch used for the joint tests, were pulled to failure on an electronic universal testing machine under strain-rate control at room temperature, in accordance with Chinese national testing standards. For comparison, identical specimens of conventional alloys 6061-T6, 6063-T6, and 6082-T6 were tested under the same conditions. The resulting stress-strain curves were fitted with the classical Ramberg-Osgood constitutive law, achieving coefficients of determination above 0.96. The numbers told a striking story. While the elastic moduli of all four alloys were nearly identical, clustering near 72,000 megapascals, the 0.2 percent proof stress of 7075-T6 reached 510.18 megapascals, roughly double that of 6082-T6 and nearly triple that of 6063-T6. The high-strength bolts used in the joints, with an elastic modulus of 206,000 megapascals and an ultimate strength of 914.8 megapascals, were also characterized from earlier work.
With the material properties established, the team fabricated four full-scale gusset joint specimens, each assembling six H-shaped aluminum alloy beams around a circular cover plate connected by groups of 10-millimeter high-strength bolts. Three design variables were explored deliberately: cover plate diameter, plate thickness, and loading condition. Specimens A1 and A2 used 460-millimeter plates of 6- and 10-millimeter thickness respectively under axial compression; specimen A3 enlarged the plate to 560 millimeters while keeping the 10-millimeter thickness; and specimen B1, with a 2000-millimeter length, was loaded in out-of-plane bending. Servo press loading was applied under displacement control, beginning with a preload stage reaching approximately 30 percent of the estimated ultimate load, a step designed to settle the instrumentation and capture data during the critical bolt-slipping phase, before ramping to failure at a higher loading rate. Displacement gauges monitored the deformation response throughout.
The failure observations carried a clear engineering message. All four specimens failed in a brittle manner, dominated by shear fracture of the bolt groups, and in the bending specimen by additional block tearing of the top cover plate. The beams themselves never buckled, because the bolt groups gave way first, confirming that joint performance, not member performance, sets the ceiling. Quantitatively, the gusset joints built from 7075-T6 achieved an ultimate bearing capacity about 1.75 times that of conventional aluminum alloy gusset joints reported in earlier studies. The influence of geometry proved equally decisive: specimens A1 and A2, sharing the same bolt count, delivered essentially consistent shear resistance, but specimen A3, benefiting from its larger 560-millimeter plate and a greater number of bolts, reached a maximum capacity of 1514 kilonewtons, approximately 65 percent higher than joint A2. The authors conclude that enlarging plate diameter and increasing bolt quantity are the most effective practical levers for raising the axial capacity of these joints.
Beneath the headline numbers, strain-gauge data revealed how the joints actually work. In the axial tests, strains at the centre of the cover plate exceeded those elsewhere, because the central region of the joint resists load through the plate alone while the outer regions share load between plate and beam. Beam strains remained consistently lower than plate strains in the same directions, confirming that the joint domain is the most vulnerable element. The load-deformation curves, once the beam’s predictable elastic deformation was subtracted to isolate the true joint deformation, displayed a characteristic four-stage signature. Stage one showed linear elastic response, with friction between bolts, beams, and plates keeping everything working together. Stage two featured bolt slipping, as applied forces overcame maximum static friction, producing rapid deformation under slowly increasing load. Stage three, entered when bolts bore directly against hole walls, combined rising stiffness with progressive localization of stress and the onset of plasticity around the bolt holes. Stage four brought stiffness degradation, damage accumulation, and eventual fracture.
To translate these observations into design-ready tools, the researchers first validated a refined finite element model in Abaqus. Exploiting the symmetry of specimen, load, and boundary conditions, they built half-joint models using C3D8R solid elements with at least two elements through every thickness, a tangential friction coefficient of 0.3, and bolt preload explicitly included. The simulated load-deformation curves reproduced the experimental bolt-slipping phenomena and the multi-stage stiffness variation with convincing agreement, and computed stress concentrations appeared precisely at the bolt-hole contact positions predicted by theory. Deviations appeared only at extreme load levels approaching ultimate capacity, partly attributed to out-of-plane plate deformation, a regime the authors note is rarely reached in practice because standard safety factors keep working loads below half the joint’s maximum bearing capacity.
The analytical centrepiece of the study is a quadrilinear stiffness model constructed through the component method. The total joint deformation is decomposed into contributions from the beams, the cover plates, and the bolt groups, with bolt slippage formulated as a function of the ratio of applied load to the bolts’ total sliding friction force, which itself depends on bolt number, preload, and interfacial friction. Constant coefficients calibrated by regression against the experimental stiffness values and an extensive finite element parametric study captured the effects of bolt force, bolt gap, plate diameter, plate thickness, and beam depth. The parametric analysis showed, among other findings, that higher pre-tightening forces suppress bolt slipping and stabilize the initial stiffness, that larger bolt gaps slightly soften all stiffness stages while enhancing deformability, that plate diameter and thickness raise axial stiffness substantially, and that beam depth mainly improves bending stiffness rather than axial stiffness. Fitted curves describing the staged stiffnesses achieved coefficients of determination exceeding 0.99, and the model’s predicted load-deformation curves matched the test data closely.
Because multi-stage analytical formulas are inconvenient to embed directly in whole-structure simulations, the team then proposed an elegant simplification: an equivalent uniform H-shaped beam whose cross-sectional area, moment of inertia, and stress-dependent elastic modulus reproduce the joint’s full nonlinear behaviour. Implemented in ABAQUS through a custom user-defined material subroutine that switches the equivalent modulus according to the current stress level, the equivalent beam model tracked the experimental axial and bending responses with favourable consistency and outperformed an existing component-based model from the literature, particularly in reproducing bolt-slipping characteristics and predicting ultimate capacity. The authors acknowledge limitations, including the restriction to single loading conditions and the need for more refined models under combined loads, but they argue that the framework generalizes to analogous materials and joint types. For engineers contemplating aluminum domes on an unprecedented scale, the message is concrete: 7075-T6 gusset joints can be strong, stiff, and, crucially, predictable.
Subject of Research: Experimental and numerical investigation of 7075-T6 high-strength aluminum alloy and the mechanical behaviour of its matching gusset joints for large-span reticulated shell structures
Article Title: Experimental and numerical study on material performance of high-strength aluminum alloy and mechanical behaviour of its matching joints
Article References: Luo, F., Wang, G., Zheng, T., Zhao, C., Chen, Q., & Chen, M. (2026). Experimental and numerical study on material performance of high-strength aluminum alloy and mechanical behaviour of its matching joints. Case Studies in Construction Materials, 25, Article e06511. https://doi.org/10.1016/j.cscm.2026.e06511
Image Credits: AI Generated
DOI: 10.1016/j.cscm.2026.e06511
Keywords: high-strength aluminum alloy, 7075-T6, gusset joints, reticulated shells, semi-rigid joints, bolt slipping, quadrilinear stiffness model, equivalent beam model, finite element analysis, large-span structures, bearing capacity, structural stability
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Neil Sanderson. (September 23, 2026). High-Strength Aluminum Alloy Matches Steel Strength at One-Third the Weight, New Joint Tests Show. Scienmag. https://scienmag.com/high-strength-aluminum-alloy-matches-steel-strength-at-one-third-the-weight-new-joint-tests-show/
Neil Sanderson. “High-Strength Aluminum Alloy Matches Steel Strength at One-Third the Weight, New Joint Tests Show.” Scienmag, 23 September 2026, https://scienmag.com/high-strength-aluminum-alloy-matches-steel-strength-at-one-third-the-weight-new-joint-tests-show/. Accessed 23 September 2026.
Neil Sanderson. “High-Strength Aluminum Alloy Matches Steel Strength at One-Third the Weight, New Joint Tests Show.” Scienmag. September 23, 2026. https://scienmag.com/high-strength-aluminum-alloy-matches-steel-strength-at-one-third-the-weight-new-joint-tests-show/
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Tags: 7075-T6advanced joint testing in architectureaerospace aluminum applicationsaluminum alloy tensile strengthaluminum vs steel load capacitybearing capacitybolt slippingdurable corrosion-resistant structuresequivalent beam modelfinite element analysisgusset joint performancegusset jointshigh-strength aluminum alloylarge-span structureslightweight structural materialsnumerical modeling in constructionquadrilinear stiffness modelreticulated shell stabilityreticulated shellssemi-rigid jointssteel strength comparisonstructural engineering innovationsstructural stability
