Search Results (11)

Aluminum alloy frame is a novel structure system developed in recent years. In this article, the load-bearing performance of the beam-beam joint of the aluminum alloy frame is studied through numerical analysis and experiment and a safety monitoring method is developed. The impacts of the arch angle and bolt diameter on the beam-beam joint mechanical characteristics are explored through experiments under vertical load. When the diameter of the bolt was increased, the load-bearing performance of such joint displayed a pattern of first increasing and then decreasing. As the arch angle increased, the load-bearing performance on the joint gradually improved. Based on the experiments, numerical analysis models varying in arch angle were established, and the impacts of arch angles on the stiffness during the yield stage, ultimate load, and elastic stiffness of the aluminum alloy portal frame (AAPF) beam-beam joints were further explored through numerical simulation of the structure under vertical and horizontal loads. When the arching angle was increased, the elastic stiffness and yield stiffness of the beam-beam joint under vertical load showed a pattern of first increasing and then decreasing. When the arching angle was increased, the elastic stiffness and yield stiffness of the beam-beam joint under horizontal load significantly decreased. Based on the mechanical properties, a safety monitoring method for AAPF beam-beam joints based on displacement monitoring and frequency monitoring is proposed. Full article

This study explores the potential use of new connections to shape precast building geometries, focusing on connection performance, robotic fabrication, and foldable structural elements. Three connection types, including coupled-bolts, hinges, and steel tubes, were initially proposed and assessed in beam and portal frame geometries. In contrast, the study introduces conceptual ideas; initial experimental and numerical studies were conducted to estimate connection capacities. Robotic fabrication for connecting elements to reused concrete and converting floor elements into beams was detailed, showcasing robotic technology’s performance and potential. These connections were employed in designing new precast element geometries, ranging from simple beams to multi-story buildings. Geometric properties and volume quantities of folded and opened geometries were studied using 37 CAD models. To properly discuss the joint performance reference, monolithic elements with exact dimensions were created for comparison. Despite varied connection capacity ($38\%$ to $100\%$), the steel tube exhibited the most desirable performance, resembling a monolithic element with an exact size. Some proposed foldable geometries showed a significant reduction (up to $7\%$) in element dimensions to facilitate transport and construction. Full article

In the article, the semi-permanent aluminum alloy portal frame is used as the research background, beam-column joints are used as the research object, and experimental and numerical analyses are carried out. The influence of different bolt diameters and arch angles on the mechanical properties of beam-column joints under vertical load was analyzed using five sets of experiments. The experimental results show that the load–displacement curves of different bolt diameters in the elastic stage are basically consistent. After entering the plastic stage, the ultimate load first increases and then decreases, and the ultimate displacement is basically consistent. According to the experiment, there is no significant difference in the load–displacement curve when the arch angle increases from 90 degrees to 108 degrees. When the arch angle increases to 126 degrees, the stiffness and ultimate bearing capacity of the node under vertical load significantly increase. Then, a numerical analysis model was established to analyze the mechanical performance of beam-column joints under horizontal loads. The numerical analysis results indicate that under horizontal load, as the diameter of the bolt increases, the yield load, yield displacement, ultimate load, and ultimate displacement of the beam-column node exhibit no significant changes, and the change amplitude is minimal. When the beam-column node is subjected to horizontal loads, as the arch angle increases, the yield and ultimate displacement increase by 2.14 times and 2.78 times, respectively, and the yield and ultimate load decrease by 58% and 48%, respectively. Finally, a simplified design method for beam-column joints was proposed based on experiments and numerical analysis. Full article

Transforming the current food system into one which delivers healthy, sustainable diets will require some form of governance. Due to the complex nature of the food system, multi-stakeholder platforms (MSPs), which bring together actors from multiple sectors into a shared space for joint decision making, have been proposed as one potential governance structure. Using the Food Change Lab, a multi-stakeholder platform led by a local civil society organization in Fort Portal, Uganda, as a case study, this paper uses an explicit conceptual framework for food system governance to understand how such an MSP can support improved food system outcomes. Local-level, civil-society-led MSPs have a limited ability to support a system-based problem framing, due to a tension between a holistic view of the system and identifying concrete entry points for action. They can support boundary spanning by creating horizontal linkages but are less effective in creating vertical linkages due to their locally embedded nature. Because such MSPs are not dependent on formal policy processes, they can be very adaptable and flexible in prioritizing issues and focus areas. The greatest influence of such MSPs in food governance is in supporting inclusiveness, especially of marginalized voices. While such MSPs are unlikely to be able to achieve food system transformation alone, they do play a key role in engaging with marginalized groups, supporting inclusion of local issues and promoting alternative food system visions. Full article

The efficient utilization of robotic construction of structures requires a review of structural material, elements and details, while traditional construction methods face difficulties in producing some dry concrete joints, robotic methods can manufacture them efficiently. With the rapid advancement of new construction methods, more effort should be directed towards developing new types of joints manufactureable by Additive Manufacturing (AM) methods. Accordingly, considering the potentials of robotic techniques, this article proposes eight new concrete dry joints. Concrete portal frames with two identical joints at the end of the beam are cast and evaluated under bending and shear. The performance of each joint, evaluated by experimental and numerical studies based on the crack distribution and stresses, was discussed. Furthermore, various aspects of the process of robotic subtractive manufacturing of the connections are discussed through the selected printed/milled geometries; likewise, geometrical accuracy by microscanning was measured, proving this technique’s capability (methodology). Based on findings, some proposed joints that can be manufactured entirely and quickly by robotic additive and subtractive techniques structurally can produce the full strength of the monolithic reference section. The range of the capacities and initial stiffness is, accordingly, [50%, 106%] and [51%, 124%] of the monolithic elements. Full article

The study is part of the MOOVABAT project aiming at defining innovative technological buildings with low environmental impact and characterised by the capacity to constantly adapt to the changing of their users’ needs. In this context, the mechanical performance of a fibre-reinforced polymer (FRP) frame, chosen as a structural solution for the building assembly, was investigated. Specifically, the research study aims to experimentally define the moment–rotation behaviour of screw-connected joints by using steel plates. For this purpose, two different configurations, a beam-to-column joint and a whole portal frame, were tested to evaluate the strength and the stiffness of the connection. In addition, the beam-to-column element was also subjected to cyclic loads to assess the joint energy dissipation capacity. The experimental results show that the strength of the connection is higher than that required to satisfy both serviceability limit state (SLS) and ultimate limit state (ULS) loading conditions. Moreover, it also provided an accurate characterisation of the semi-rigid connection useful for designing purposes and raising the possibility of considering an optimisation of the system. All in all, with respect to mechanical aspects, the study confirms the suitability of pultrude FRP element assemblies for modular building applications and paves the way for further analysis aimed at enhancing their efficiency. Full article

Past earthquakes have highlighted the seismic vulnerability of prefabricated industrial sheds typical of past Italian building practices. Such buildings typically exhibited rigid collapse mechanisms due to the absence of rigid links between columns, beams, and roof elements. This study aims at presenting the experimental and numerical assessment of a novel dissipative connection system (DCS) designed to improve the seismic performance of prefabricated sheds. The device, which is placed on the top of columns, exploits the movement of a rigid slider on a sloped surface to dissipate seismic energy and control the lateral displacement of the beam, and to provide a recentering effect at the end of the earthquake. The backbone curve of the DCS, and the effect of vertical load, sliding velocity, and number of cycles were assessed in experimental tests conducted on a scaled prototype, according to a test protocol designed accounting for similarity requirements. In the second part of the study, non-linear dynamic analyses were performed on a finite element model of a portal frame implementing, at beam-column joints, either the DCS or a pure friction connection. The results highlighted the effectiveness of the DCS in controlling beam-to-column displacements, reducing shear forces on the top of columns, and limiting residual displacements that can accrue during ground motion sequences. Full article

Aluminium portal frames with a tension tie element are a commonly used type of aluminium structure. Due to the significant reduction in aluminium’s mechanical properties caused by welding, typical beam to column joints of such frames are formed using bolts and welded steel knee joints embedded in the structure. Expressions for the reliable assessment of the behaviour of such joints are lacking, thus limiting the use of aluminium portal frames. Although the behaviour of steel joints using hollow sections is well investigated, there are only a small number of studies regarding knee joints, none of which investigate the influence of the tie element on the joint behaviour. Therefore, the first stage of the research is focused on the flexural behaviour of steel knee joints with tension tie elements. Laboratory tests of three identical steel knee joints with a tension tie element were conducted as well as a parametric numerical study with variation of tie element stiffness. It was concluded that different stiffnesses of the tie element have little influence on moment–rotation behaviour of the knee joint, but greatly affect overall frame resistance to vertical loads. It was also concluded that different stiffnesses of the tie element can lead to different failure modes of the knee joint as well. Full article

The Rock Art Studies Bibliographic Database is an open access; online resource that fulfills the need for a searchable portal into the world’s rock art literature. Geared to the broadest interests of rock art researchers; students; cultural resource managers; and the general public; the RAS database makes rock art literature accessible through a simple search interface that facilitates inquiries into multiple data fields; including authors’ names; title and publication; place-name keyword; subject keyword; ISBN/ISSN number and abstract. The results of a data search can further be sorted by any of the data fields; including: authors’ names; date; title; and so forth. An ever increasing number of citations within the database include web links to online versions of the reference cited; and many citations include full author’s abstracts. The data compilation has been undertaken by Leigh Marymor with the year 2018 marking the 25th year of continuous revision and expansion of the data. Over 37,000 citations are currently contained in the database. The RAS database first launched online as a joint project of the Bay Area Rock Art Research Association and University of California’s Bancroft Library. After thirteen years of collaboration; the project found a new home and collaborator at the Anthropology Department at the Museum of Northern Arizona. The Paleolithic Rock Art bibliography results from an export of data from the RAS database and captures a freeze-frame in the state of the rock art literature for the world’s Paleolithic rock art as compiled here in the year 2018. The online version of the RAS Bibliographic Database at the Museum of Northern Arizona is updated annually; and we refer the reader to that resource for up-to-date bibliographic data revisions and additions. Researchers who consult the online database in concert with their reference to the Paleolithic Rock Art bibliography will discover a powerful ally in further refining geographic and thematic inquiries. Full article

The application of cold-formed steel channel sections for portal frames becomes more popular for industrial and residential purposes. Experimental tests showed that such structures with long-span up to 20 m can be achieved when knee brace joints are included. In this paper, the influence of knee brace configuration on the optimum design of long-span cold-formed steel portal frames is investigated. The cold-formed steel portal frames are designed using Eurocode 3 under ultimate limit states. A novel method in handling design constraints integrated with genetic algorithm is proposed for searching the optimum design of cold-formed steel portal frames. The result showed that the proposed routine for design optimization effectively searched the near global optimum solution with the computational time is approximate 50% faster than methods being popularly used in literature. The optimum configuration for knee brace joint can reduce the section size of rafter and so the lighter frame could be obtained especially for long-span portal frame. The minimum weight of main frame obtained from optimization process is approximate 19.72% lighter than a Benchmark Frame used in the full-scale experimental test. Full article

This paper examines the dynamic behaviour of timber framed buildings under wind and dynamic loads, focusing on the role of connections being experimentally tested. The main aim of this manuscript is to analyze the in-service dynamic behaviour of a semi-rigid moment-resisting dowel-type connection between timber beam and column. For this purpose, two laboratory tests have been performed, the first on a connection and another one on a portal frame. The results are used to validate a numerical model of the simple portal frame, analyzed in OpenSees. The obtained relationships are also discussed and compared with Eurocode rules. The main result is that the joint stiffness is calculated through the Eurocode (EC) formulation underestimates the experimental one. A mutual agreement is obtained between the numerical model, validated from the experimental stiffness value for the connections, and the experimental results on the portal frame. Full article