How Does the Strength Test of Double-Curved GRC Panels Differ from Flat Panels?

The strength testing methods for double-curved GRC panels differ fundamentally from those for standard flat panels, because the stress state shifts from two-dimensional plane stress to three-dimensional spatial stress, and a significant "shell effect" is present. The Quality Testing Center of Qinglong Group has established a comprehensive evaluation system tailored to the characteristics of double-curved GRC—comprising "material property testing, full-scale component testing, and numerical simulation"—to ensure structural safety.

The most fundamental difference lies in specimen preparation and testing methods. Flat GRC panels can typically have standard rectangular specimens cut directly from the panel for three-point or four-point bending tests, measuring parameters such as flexural strength and ultimate flexural strain. Double-curved GRC panels, however, due to their curved surfaces, cannot yield representative standard flat specimens. Qinglong's solution is: 1) Simultaneous casting of conformal specimens: when producing large double-curved panels, a small conformal specimen matching the product's curvature is made simultaneously using the same materials and processes. 2) Design of dedicated test fixtures: for the conformal specimens, custom loading heads and support devices are fabricated so that the stress state simulates actual service conditions as closely as possible. During testing, the load-displacement curve must be precisely recorded to analyze the cracking load, ultimate load, and failure mode.

Testing and evaluation indicators need additional dimensions. For flat panels, the main focus is on in-plane flexural strength. For double-curved panels, in addition to in-plane stiffness and strength, particular attention must be paid to "out-of-plane stability" and the distribution of "membrane stresses." The excellent shell effect of the double-curved surface enables it to carry most of the load through membrane stresses, exhibiting stiffness and load-bearing capacity far exceeding those of flat panels. Therefore, testing must focus on the buckling behavior of the shell under load. Qinglong employs optical measurement technology (such as DIC—digital image correlation) to monitor the full-field strain distribution of double-curved panels during loading, verifying whether the load paths match the design model.

The combination of full-scale testing and numerical simulation is the final means of verification. For critical or new types of double-curved GRC components, Qinglong conducts 1:1 full-scale performance tests simulating the most unfavorable conditions such as wind pressure and snow loads, directly examining their load-bearing capacity and deformation performance. At the same time, precise three-dimensional models are built with finite element software for numerical simulation, and the simulation results are compared and calibrated against the test data, forming a reliable analytical method that can be used to guide the design of similar products. This rigorous testing system is the technical guarantee enabling Qinglong's double-curved GRC products to be safely applied in large-scale landmark projects.