Efficiency-based design of bending-active tied arches

[EN] Active bending is recently attracting considerable attention as a new paradigm to build lightweight structures both in research and practice. While there are many references dealing with form-finding methods for bending-active structures, the literature on their performance in relation to their shape and member proportioning is still scarce. This paper addresses the relationship between configuration finding and structural performance in bending-active tied arches: planar arches composed of a bent (active) rod, lower spanning cables and secondary struts that are joined to the rod and act as cable deviators. This simple bending-active arrangement allows to state key relationships between shape, proportion and performance. Starting from the fact that rod segments between struts behave as elastica segments, and selecting the mechanical slenderness of the rod as key parameter, scale-independent relationships between rise-to-span ratio, rod slenderness and stresses after activation have been established for a three-strut tied arch. The limitations posed by keeping stresses in cables after the activation within an acceptable range have been also addressed. Span-deflection ratios corresponding to Eurocode loads for the serviceability limit state have been obtained for a set of three-strut configurations using a non-linear structural model. Results have been represented in terms of rod slenderness, cable slenderness and rise-to-span ratio. The same procedure has been used to determine and represent proper utilization ratios for rod cross-sections in ultimate limit state. All the results have been combined to show the design space corresponding to the given constraints and to exemplify how to extract from it a suitable structural configuration. Finally, we explain how to extend the proposed method to design bending-active tied arches with an arbitrary number and proportion of deviators.The authors gratefully acknowledge the financial support from the Spanish Ministry of Economy and Competitiveness through grant BIA2015-69330-P (MINECO) and the support from CALTER Ingenieria and SOFiSTiK AG for providing a software license.Bessini, J.; Lazaro, C.; Casanova Colón, J.; Monleón Cremades, S. (2019). Efficiency-based design of bending-active tied arches. Engineering Structures. 200:1-11. https://doi.org/10.1016/j.engstruct.2019.109681S11120

Gridshell as Formwork: Proof of Concept for a New Technique for Constructing Thin Concrete Shells Supported by Gridshell as Formwork

This paper documents an empirical experiment conducted in August 2014 as proof of concept for a new method of constructing concrete shells. An idea initially presented by the first author in 2012, it uses redeployable gridshells onto which fabric is midstressed and concrete applied. Primarily, this system addresses key issues that led to their decline in use: construction methods/formwork systems were not reusable, nor were they easily customizable to create different shapes. Employing 27 man-hours over seven days, two concrete shells were achieved using the same reusable and reconfigurable formwork. Lightweight (0.6 kg) PVC gridshell formwork supported 106.92 kg of concrete to create a concrete shell that covered 1.11 m2 (floor area). The construction verifies a low-cost (£6.06/m2) efficiency and material utilization in the construction of very strong wide-spanning thin concrete structures. Detailed analysis of formwork behavior during construction and detailed measurements of resultant shell results prove this new method of deployable gridshells as a reusable and reconfigurable formwork to construct very strong concrete shells very quickly. Whilst the emphasis of the research focused on the construction process, the vaults were tested and sustained a failure load of 4.2 kN (4.32 times their deadweight), applied as a point load at the crown

Marionette Mesh: from descriptive geometry to fabrication-aware design

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