Search

This study focused on the in-plane rocking behavior of unreinforced masonry (URM) walls. Three URM wall specimens were designed and fabricated based on a typical masonry house in Korea. The experimental parameters were the layout of openings (its presence or absence) and configuration of openings (window or door). Static cyclic loading tests were conducted to investigate nonlinear performance curves of masonry walls subjected to a rocking behavior in the in-plane direction. In this paper, the mortar-joint tensile crack strength and rocking strength of masonry walls (i.e., peak and residual strengths) were evaluated, and the effects of opening configurations on the masonry wall strength were examined, due to the proposed procedure. The deformation capacity of a rocking behavior was also identified by the procedure. As a result, specimens without initial cracks showed the rocking behavior after mortar-joint tensile crack failure, whereas a specimen with initial cracks exhibited only the rocking behavior. Since no remarkable strength deterioration was found until final loading in all specimens, an in-plane rocking URM wall may have very good deformation performance. The estimated mortar-joint tensile crack strength, rocking strength, stiffness, and ultimate deformation were in good agreement with the experimental results, regardless of the layout and configuration of openings.

The mechanisms of dynamic disasters around underground roadways/tunnels were examined by adopting split Hopkinson pressure bar (SHPB) laboratory tests to reproduce the failure process of the surrounding rock subjected to incident stress waves. On the basis of ensuring the consistency of numerical simulations with the experimental results, the failure mechanisms of the surrounding rock and spatiotemporal evolution of the hoop stress around the hole were studied by using a two-dimensional particle flow code (PFC2D). The results of the numerical simulation indicate that tensile stress and compressive stress concentrate along the horizontal and vertical directions around the hole, respectively, owing to the instantaneous incidence of compressive stress waves. The failure modes of surrounding rocks are significantly different when the hole is subjected to various intensities of incident stress waves. In addition, the stability of the surrounding rock of the hole is greatly affected by the amplitude and wavelength of the incident wave and the elastic modulus of the surrounding rock.

The mechanical behavior of loess is highly predicated on variation in its moisture content. While the impacts of the water content on the shearing behavior and collapsibility of loess have been extensively studied, its effect on tensile characteristics has received relatively little attention. In this study, a series of tensile tests were conducted on remolded specimens of a clayey loess that were collected from Ili Valley in China. Two sets of loess specimens with varying water contents were prepared separately using wetting and drying methods. The influence of the water content on the tensile stress–strain response, failure mode and tensile strength was investigated by combining the tensile test results and particle image velocimetry (PIV) analysis. On this basis, a nuclear magnetic resonance (NMR) test and scanning electron microscopy (SEM) observations were implemented in order to assist with the interpretation of the underlying mechanism. The test results indicate that the tensile failure process and the variation of tensile strength with varying water contents differ for specimens that are prepared with wetting and drying methods; a finding which arises from the differences in the soil microstructure, clay–water interaction and the distribution of capillary and adsorbed water. This research has shown that the tensile strength of clayey loess is essentially dominated by the clay’s hydration/cementation and the development of capillary and adsorption suction as well as the microstructural evolution that occurs with the change in the water content. Based on the experimental observations, a conceptual model is proposed in order to interpret the effect of water content on loess’ tensile behavior.