Search Results (35)

This study investigates the elastoplastic behavior of phenol formaldehyde/polyvinyl butyral matrix (70% PF/30% PVB) reinforced with Kevlar^® fibers through comprehensive in-plane tensile testing. Cyclic loading–unloading tests were conducted at a 100%/min strain rate using a universal testing system at room temperature on $\left(0_4\right)$, $\left({90}_4\right)$, and ${\left(\pm 45\right)}_s$ laminates. The experimental results revealed significant nonlinear hardening behavior beyond yield stress, accompanied by yarn stiffening effects during loading cycles. A novel elastoplastic constitutive model was developed, incorporating Hill’s yield criterion adapted for orthotropic materials and an isotropic hardening function that accounts for equivalent plastic strains and progressive yarn stiffening. Laminates with other stacking sequences were also tested and the accuracy of the predictions of the nonlinear behavior was assessed. In these laminates, delaminations took place and the model provided an overestimation of the stress–strain response. Since the model could not predict delamination onset and propagation, an adaptation of the model considering fully delaminated interfaces brought a lower bound of this response. Despite the limitations of the model, it can be used to provide reasonable limits to the stress–strain response of laminates accounting for plastic strains within plies. This study provides essential mechanical properties and constitutive relationships for designing Kevlar^® composite structures with tailored stiffness characteristics for impact-resistant applications. Full article

Sustainability in the construction and building sector with the use of greener and more eco-friendly building materials can minimize carbon footprint, which is one of the prime goals of the twenty-first century. The use of natural fibers in ancient and traditional buildings and structures is not new, but in the last fifty years, only man-made fibers have predominantly occupied the market for structural retrofitting or upgrading. This research investigated the potential of utilizing natural fibers, particularly jute fiber products, to enhance masonry’s thermal and structural characteristics. The study meticulously investigated the utilization of materials such as jute net (with a mesh size of 2.5 cm × 1.25 cm), jute fiber diatons, and jute fiber composite mortar (with 1% jute fiber with respect to the dry mortar mass) in the context of masonry upgrading. The research evaluated the structural and thermal performance of these upgraded walls. Notably, the implementation of natural fiber textile-reinforced mortar (NFTRM) resulted in an astounding increase of over 500% in the load-bearing capacity of the walls, while simultaneously enhancing insulation by more than 36%. Furthermore, the study involved a meticulous analysis of crack patterns during in-plane cyclic testing utilizing the advanced Digital Image Correlation (DIC) tool. The upgraded/retrofitted wall exhibited a maximum crack width of approximately 7.84 mm, primarily along the diagonal region. Full article

Ground texture-based localization leverages environment-invariant, planar-constrained features to enhance pose estimation robustness, thus offering inherent advantages for seamless localization. However, traditional feature extraction methods struggle with reliable performance under large-scale rotations and texture sparsity in the case of ground texture-based localization. This study addresses these challenges through a learning-based feature extraction framework—Ground Texture Rotation-Equivariant Keypoints and Descriptors (GT-REKD). The GT-REKD framework employs group-equivariant convolutions over the cyclic rotation group, augmented with directional attention and orientation-encoding heads, to produce dense keypoints and descriptors that are exactly invariant to 0–360° in-plane rotations. The experimental results for ground texture localization show that GT-REKD achieves 96.14% matching in pure rotation tests, 94.08% in incremental localization, and relocalization errors of 5.55° and 4.41 px (≈0.1 cm), consistently outperforming baseline methods under extreme rotations and sparse textures, highlighting its applicability to visual localization and simultaneous localization and mapping (SLAM) tasks. Full article

This study investigates the scale effects on the experimental shear strength of earthen walls, a critical parameter influencing the seismic performance of adobe and rammed-earth (RE) buildings. Recognized for their historical significance and sustainable construction practices, earthen structures require a comprehensive understanding of their mechanical behavior under shear loads to ensure effective design and preservation. This research compiles data from over 120 in-plane shear wall tests (adobe and RE), nearly 20 direct shear tests from the scientific and technical literature, and new cyclic direct shear tests performed on large cubic specimens (300 mm side length) made from the same material as a previously tested two-story RE wall. Based on the findings, this study recommends a minimum specimen cross-sectional area of 0.5 m² for reliable shear strength testing of earthen walls in structural laboratories. This recommendation aims to prevent the unconservative overestimation of shear strength commonly observed in smaller specimens, including direct shear tests. Furthermore, the Mohr–Coulomb failure criterion outlined in the AIS-610 Colombian standard is validated as a conservative lower bound for all compiled shear strength data. Cyclic direct shear tests on nine 300 mm cubic specimens produced a Mohr–Coulomb envelope with an apparent cohesion of 0.0715 MPa and a slope of 0.66, whereas the full-scale two-story wall (5.95 × 6.20 × 0.65 m) constructed with the same material exhibited a much lower cohesion of 0.0139 MPa and a slope of 0.26. The analysis reveals significant scale effects, as small-scale specimens consistently overestimate shear strength due to their inability to capture macro-structural behaviors such as compaction layer interactions, construction joint weaknesses, and stress redistributions. Based on the analysis of the compiled data, the novelty of this study lies in defining a strength reduction factor for direct shear tests (3.4–3.8 for rammed earth, ~3.0 for adobe) to align with full-scale wall behavior, as well as establishing a minimum specimen size (≥0.5 m²) for reliable in-plane shear testing of earthen walls, ensuring accurate structural assessments of shear strength. This study provides a first approach to the shear behavior of unstabilized earth. To expand its application, future research should explore how the scale of specimens with different stabilizers affects their shear strength. Full article

Precast structures are widely used in many parts of the world. This construction technique is more commonly preferred for low-rise industrial buildings than multi-story structures. The most commonly used column–beam connection in precast buildings is the dowel connection (DC). Past earthquakes in various parts of the world have shown that these connections do not provide sufficient resistance. The main deficiencies of such connections are that they are sheared or stripped due to the shear force demand from the in-plane effects of large earthquakes, and that they do not provide sufficient resistance to the overturning moments from the out-of-plane effects of the earthquakes. Correspondingly, many prefabricated buildings have collapsed during earthquakes, causing loss of life and property. This study proposes using post-tensioning tendon (PT) systems and systems created by adding steel springs (PTS) to eliminate the weaknesses in column–beam connections in precast structures. To this end, real-sized column and beam specimens used in precast buildings were produced, and experiments were conducted under the cyclic loads defined by the American Concrete Institute (ACI) Committee, Report 374, simulating earthquake effects for three different connection types (DC, PT, and PTS). It was observed that the proposed PTS connection type dissipated approximately one-third of the energy transferred to the joint through elastic deformation in the springs, compared to the DC and PT connection types. This indicates that the PTS specimens transferred significantly less energy to the column–beam connection region. Consequently, the PTS system exhibited much less damage in the column foundation and especially the column–beam connection areas than other test specimens. In conclusion, it can be stated that the use of the PTS connection type in prefabricated structures has high potential to reduce damages due to dynamic loads such as earthquakes. Full article

The tailings microcrystalline foamed plate (TMF plate), produced from industrial waste tailings, has limited research regarding its use in high-performance building walls. Its brittleness under stress poses challenges. To improve its mechanical properties, a prefabricated light steel-tailings microcrystalline foamed plate composite wall (LS-TMF composite wall) has been proposed. This LS-TMF composite wall system integrates assembly, sustainability, insulation, and decorative functions, making it a promising market option. To study the in-plane performance of the composite wall, compression and seismic performance tests were conducted. The findings indicate that the light steel keel, steel bar, and TMF plate in the composite wall demonstrated good working performance. Strengthening the TMF plate enhanced the restraint on the light steel keel and improved the composite wall’s compressive performance. Increasing the thickness of the light steel keel further improved the compressive stability. Under horizontal cyclic loading, failure occurred at the light steel keel embedding location. Increasing the strength of the TMF plate was beneficial for the seismic performance of the composite wall. This structural configuration—incorporating light steel keels, TMF plates, and fly ash blocks—enhanced thermal insulation and significantly improved in-plane stress performance. However, the splicing plate structure adversely affected the seismic performance of the composite wall. Full article

A new macro model for the finite element modeling of unreinforced masonry (URM) exhibiting in-plane nonlinear cyclic behavior is proposed. The ultimate objective is to predict the seismic response of multi-story URM buildings. The macro model enables the modeling of URM shear walls with a limited number of degrees of freedom (DOF) at low computation times. The macro model consists of a deformable elastic frame supported by diagonal struts with nonlinear behavior aiming to capture all dissipative phenomena occurring during seismic events. The nonlinear constitutive behavior of diagonal struts is inspired by models documented in the literature, ensuring a robust foundation for the proposed approach. This paper first provides a comprehensive review of the principal models currently available for URM analysis. It then articulates the rationale behind the development of this new numerical model, aiming to address the limitations encountered in existing methodologies and to offer a simple and fast tool for predicting the seismic behavior of URM buildings. Afterward, the new model is presented and tested with the simulations of two experimental campaigns performed on different URM walls. The comparison between experimental and numerical results shows that with a limited number of DOF and parameters, it is possible to obtain a prediction of the experimental results with satisfying accuracy. Full article

This paper presents a study on the seismic performance of rectangular hollow section (RHS) X-joints subjected to in-plane bending moment (IPBM). The study began by testing two RHS joint specimens with varying brace-to-chord width ratios (β) under quasi-static cyclic IPBM loading. The results showed that the final failure mode of the specimen with the large β value (β = 1.0) is the tearing of the weld near the brace root, while the specimen with the medium β value (β = 0.83) failed due to the tearing of both the weld and the adjacent chord face. The seismic performance of the X-joints depended considerably on the β value. The increase in β remarkably improved the strength of the X-joints but at the cost of energy dissipation capability, deformability and ductility. Our experimental results also demonstrated that the current code equations remarkably underestimate the flexural strength of RHS X-joints, while the modified equations that take the weld size into account can predict it well. In addition, the reason behind the experimental observation can be further explained by FE analysis and the proposed elastic-support plate analytical model. Full article

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. Full article

The interfaces between masonry infill and reinforced concrete (MI-RC) frames are identified as the weakest regions under lateral loads. Hence, the behavior of such frames under lateral loads can be understood mainly through experimental investigations. The deformation demands induced by horizontal loads on RC frames with infill masonry walls change due to contact losses between the infill masonry and the RC frames. This can be controlled by providing proper reinforcements at the interfaces. In the present experimental investigation, three half-scaled models subjected to reversed cyclic lateral in-plane loads were tested. In detail, the specimens considered are the MI-RC frame model, an MI-RC frame with geo-fabric reinforcement at the interface and an MI-RC frame with geo-fabric reinforcement at interfaces with an open ground story. The models were subjected to reversed cyclic lateral in-plane loads, and the post-yield responses of the models with respect to stiffness degradation, drift, energy dissipation, ductility and failure mode have been discussed. Full article

Damage to adobe constructions might occur due to a long wall and a lack of effective restraint in the middle of the wall, causing it to collapse under an earthquake. Aiming at these problems, a technology for improving the seismic performance of a modified adobe-brick-masonry composite wall with a wooden-construction center column is proposed. It uses modified mud, a wooden center column, steel-wire mesh, and nylon ropes to reinforce the wall. On this basis, four specimens of composite wall and one specimen of modified adobe wall were subjected to proposed quasistatic, cyclic in-plane loading tests to study their failure modes and seismic performance indicators. The results show that the failure modes of all walls were shear failure. The difference is that the modified adobe wall had horizontal cracks in the middle, whereas the composite walls were largely intact. Moreover, the composite walls relied on the modified mud to improve the seismic bearing capacity of each wall. They relied on the center column and the tie materials to form a second line of defense that would increase the wall ductility and collapse residual area. As a result, the phenomenon that caused wall damage and stiffness degradation was lessened. Full article

Innovative solutions for seismic-retrofitting existing structures are currently required, as often traditional strategies are expensive, non-reversible, highly invasive, and/or fail to address both serviceability and ultimate limit states together. The present paper describes a preliminary experimental campaign performed at TU Delft to investigate an innovative structural glass window for strengthening masonry buildings. To this purpose, a prototype composed of a timber frame, a semi-rigid adhesive, and a 20 mm thick structural glazing layer was designed. The prototype aimed to improve the structure’s behavior against minor but more frequent service vibrations (SLS), as well as against ultimate ones (ULS). Specifically, an increase in the structure’s in-plane capacity and stiffness was targeted to reduce cracking at low drifts/displacements, while at larger drifts, the adhesive’s tearing and timber crushing were used to activate damping. To evaluate the prototype’s performance, a quasi-static, cyclic, in-plane test on a strengthened full-scale wall was performed and compared with available data on a similar, yet unstrengthened, wall. Although the benefits were not pronounced in terms of cracking and energy dissipation, the implementation of the proposed strategy provided an increase in terms of initial stiffness (18%), force capacity (8%, 36%), and ductility (220%, 135%). This outcome provides the ground for numerical studies that will help better delineate the proposed strategy and improve the current design. Full article

Since the Japanese Building Standards Act was revised in 2000, the installation of steel timber connectors (STCs) to reinforce timber frame (TF) connections has been mandated for new-build TF houses in Japan. However, for the TF houses built before then, more than 40% do not have sufficient STCs and are considered earthquake-prone. This study proposed a simple and easy seismic retrofit technique for such earthquake-prone existing houses. The proposed technique can reinforce TF connections using only plywood and common nails and achieve equivalent performance to the benchmark STCs used in Japanese TF houses, such as the “CP-T type” or the combination of “VP type” and “BP type” STCs. Experiments were performed to compare the proposed technique with the STCs using pullout and full-scale in-plane cyclic tests. The experimental results showed that the proposed technique had a higher seismic performance than the STCs, which was particularly excellent in displacement ductility to prevent a collapse of the TF house without damaging the timbers. The proposed technique will be accepted by many carpenters when retrofitting earthquake-prone existing houses because simple and easy. Full article

The purpose of this study is to utilize timber material to enhance the in-plane shear strength and deformation capacity of a brick wall. The proposed strengthening method is light-weight and easy to assemble and includes a timber frame, plywood panel, M12 threaded rod with chemical epoxy, and the hold-down anchor. To evaluate the effectiveness of the reinforced brick wall, three walls were tested under a cyclic horizontal load and static compression stress: the brick wall (BW wall), the reinforced brick wall with timber (BW-T wall), and the reinforced brick wall with timber and the hold-down anchor (BW-TA wall). The proposed prediction method of the Kamiya and Inayama Murakami models assessed the BW-TA wall. The rocking was caused by the failure of BW and BW-T walls. However, because the BW-T wall failed in the lowest part of the wall, the timber part retained the original shape of the brick wall. When the diagonal on the BW-TA wall failed, the horizontal load at maximum load increased by 22%, and the drift angle calculated from the diagonal measurement increased 4.6 times. Full article

Unreinforced masonry structures are vulnerable to seismic loading due to their brittle behavior, and must therefore be strengthened. This paper presents the seismic performance of brick masonry strengthened with steel and plastic meshes. For this purpose, twenty masonry wallets of (600 × 600 × 113 mm) were constructed, keeping the same materials and workmanship. Fifteen of them were reinforced using steel and plastic meshes. These specimens were tested for in-plane static cyclic diagonal tension (shear) behavior. The critical parameters, such as shear stress, strain, failure modes, ductility, energy dissipation, and stiffness degradation were investigated. Compared to reference and plastic-reinforced specimens, the steel-reinforced samples were found to be highly effective. Furthermore, the recommended category of steel increased the shear capacity, energy dissipation, and ductility ratio by 1.3, 14, and 6.3 times, respectively. Full article