The Flat Jack Test (FJT) is a well-established technique for in-situ stress assessment in masonry and rock engineering, whereas its application to concrete structures remains limited due to the higher stiffness, heterogeneity, and stress redistribution mechanisms characteristic of concrete. This study proposes and preliminarily validates a combined experimental–numerical framework for investigating the applicability of the FJT to concrete elements. Controlled laboratory tests were performed on C20/25 unreinforced concrete blocks subjected to known compressive stress levels ranging from 2 to 4 MPa. Two circular-segment-shaped flat jacks with lengths of 25 cm and 33 cm were tested. The relative displacements measured between gage points during slot cutting and flat-jack re-pressurization were compared with three-dimensional finite element simulations. The numerical model was then used to analyse displacement fields, stress redistribution around the slot, and the influence of gage length and elastic modulus associated with common concrete classes, from C20/25 to C60/75. The comparison showed a fair agreement between experimental and numerical displacement responses within the repeatability and resolution of the measurement system. The results indicate that the reliability of the FJT in concrete is primarily governed by the measurability of the displacement field, which depends on slot geometry and gage length. For the investigated unreinforced block geometry and stress range, the 33 cm configuration provided a larger displacement signal and a higher signal-to-resolution ratio than the 25 cm configuration; however, this finding is configuration-dependent and should not be interpreted as a general recommendation to use larger flat jacks. Within the adopted linear-elastic framework, variations in elastic modulus mainly affected the amplitude of the displacement signal, without substantially changing the dominant role of the test geometry. The study provides an experimentally supported basis for the progressive extension of the FJT from masonry to selected applications in unreinforced concrete elements and massive concrete regions where the slot can be cut without interacting with reinforcement.
Earth masonry has attracted renewed interest as a low-emission construction system, yet its in-plane shear resistance at structural scale remains insufficiently quantified for design. This study addresses this gap through an experimental and analytical investigation of unstabilised load-bearing earth masonry walls. Nine full-scale shear wall tests were carried out under controlled combinations of vertical precompression and horizontal loading using an ESECMaSE-type setup (Enhanced Safety and Efficient Construction of Masonry Structures in Europe). Complementary material tests were conducted under laboratory climate, allowing moisture effects to be explicitly considered in the interpretation of the results. Shear failure was successfully induced in all tests. Depending on vertical precompression and overlap, the walls exhibited frictional joint failure, tensile block failure, and shear-compression failure. The results establish a characteristic shear resistance envelope where capacity initially scales with normal stress - governed by bed joint sliding - reaches a peak limited by the tensile strength of the units, and subsequently declines as compressive masonry crushing becomes dominant. Moisture-dependent changes in compressive and tensile strength were found to be essential for consistent interpretation of the results. The experimental peak loads and governing failure modes were compared with mechanically based analytical models according to Mann/Müller (1978) and subsequent extensions. Good overall agreement was obtained, with a mean ratio of experimental-to-calculated resistance of 1.05 when moisture effects were included. The results indicate that mechanically based shear design approaches developed for conventional masonry can, in principle, be transferred to earth masonry, provided that moisture-sensitive material properties are adequately accounted for.
To expedite the construction of nuclear power plants (NPPs), this study proposes two novel types of superposed slab-shear wall joints (SSSWJs) utilizing ultra-high-performance concrete (UHPC) and short lap-splice connections. Their seismic performance was systematically evaluated through experimental and numerical programs. Six full-scale joint specimens with low slab span-to-thickness ratios (STRs) of 4.63 and 3.08, including two reinforced concrete (RC) specimens, two partial UHPC SSSWJ specimens, and two full UHPC SSSWJ specimens, were tested under reversed cyclic loading. Test results revealed that the UHPC SSSWJs exhibited different UHPC-normal concrete (NC) interface damage and failure characteristics under different STRs. The UHPC SSSWJs exhibited satisfactory seismic performance at an STR of 4.63. The full UHPC SSSWJ achieved an average peak strength and ductility coefficient that were 6.4% and 12.7% higher, respectively, than those of the corresponding RC joint, with an ultimate drift ratio of 1/22. When the STR decreased to 3.08, the ductility coefficients of the UHPC SSSWJs decreased significantly owing to premature UHPC-NC interfacial failure. Notably, the full UHPC joint increased the average peak strength and average ultimate displacement by 21.2% and 43.2%, respectively, compared with the partial UHPC joint. Finally, a numerical parametric study was conducted based on the verification of test specimens. Results demonstrated that the STR, slab reinforcement ratio, UHPC length, and shear interfacial stiffness significantly influenced the seismic response of the UHPC SSSWJ. Based on these quantitative findings, specific design recommendations were given. This study highlights the necessity of strengthening UHPC-NC interfaces in low-STR applications to guarantee the reliable seismic performance of SSSWJs in NPP structures.
When activated by resistive heating, Fe-SMA rebars can introduce self-prestress into concrete beams; however, reliable electrical insulation is essential when they are tied together with conventional steel reinforcement and activated within reinforcement cages. In this study, textured epoxy-coated Fe-SMA rebars were used as embedded self-prestressing reinforcement. Twelve rectangular hybrid-reinforced beams were tested under four-point bending, considering the steel/Fe-SMA rebar ratio (2:1 and 1:1), Fe-SMA surface condition (uncoated and textured epoxy-coated), activation condition (non-activated and activated at 150 °C), and high–low temperature cycling (−20 °C to +80 °C for 60 d). A sectional model incorporating effective self-prestress was also developed to predict the cracking, yield, and ultimate moments. The results showed that the textured epoxy coating maintained visual integrity and electrical insulation after environmental heating at 80 °C and resistive-heating treatment at 100–300 °C. All specimens exhibited typical under-reinforced flexural failure; the coating did not change the failure mode and had limited influence on ultimate capacity. Activation at 150 °C consistently increased the cracking load by 30.9%–72.3% and the load corresponding to a 0.3 mm crack width by 12.5%–40.0%, while limiting the change in ultimate capacity to within ±3%. After 60 d cycling, the ultimate capacity variation remained within ±5%, and good crack resistance was retained. The theoretical predictions agreed well with the test results, with conservative ultimate moment estimates. Overall, textured epoxy-coated Fe-SMA rebars enabled safe and controllable resistive-heating activation and retained their crack-control benefits in hybrid-reinforced beams after high–low temperature cycling.
The complex surface geometries and mesh topology of free-form single-layer grid shells present substantial challenges for uniform mesh generation and structural stability optimization. To address these issues, this study proposes a mesh generation and structural optimization framework based on NURBS parametric domain coordinates. The main conclusions are as follows: 1) the proposed method can generate meshes for surfaces with different curvature characteristics while maintaining high member-length uniformity and element regularity; 2) a local mesh optimization strategy is developed by minimizing a weighted sum comprising the squared relative length deviations and element quality penalty terms; 3) the radial basis function (RBF) based surrogate model shows high predictive accuracy and can effectively capture the nonlinear relationship between mesh size and ultimate load-bearing capacity; 4) the structural stability generally increases first and then decreases with increasing mesh size, and reasonable mesh-size ranges are identified. These findings provide theoretical support and practical guidance for the integrated architectural and structural design of free-form single-layer grid shells.
