Maurizio Froli

A Mechanical Model for the Elastic-Plastic Behavior of Metallic Bars

Abstract A simple mechanical model, which consists of a particular assemblage of elementary units composed of elastic springs and frictional sliding blocks, appears suitable for describing the various aspects of the elastic–plastic behavior of steel bars in standard tensile tests: oscillations in the average stress–strain curve, the distinction between local and global responses, instability due to the transition from an upper to a lower yield point, the spread of plastic deformation, strain-hardening behavior, elastic unloading and the influence of loading-device stiffness.

Statics Aware Grid Shells

We introduce a framework for the generation of polygonal gridshell architectural structures, whose topology is designed in order to excel in static performances. We start from the analysis of stress on the input surface and we use the resulting tensor field to induce an anisotropic nonEuclidean metric over it. This metric is derived by studying the relation between the stress tensor over a continuous shell and the optimal shape of polygons in a corresponding gridshell. Polygonal meshes with uniform density and isotropic cells under this metric exhibit variable density and anisotropy in Euclidean space, thus achieving a better distribution of the strain energy over their elements. Meshes are further optimized taking into account symmetry and regularity of cells to improve aesthetics. We experiment with quad meshes and hexdominant meshes, demonstrating that our gridshells achieve better static performances than stateoftheart gridshells.

STATISTICAL ANALYSIS OF THERMAL ACTIONS ON A CONCRETE SEGMENTAL BOX-GIRDER BRIDGE

A method is presented for statistical treatment of thermal actions measured on concrete bridges during long-term monitoring. The method is based on recognising that thermal actions are not entirely random, but contain deterministic components due to the Earth’s rotation and revolution. Greater precision and reliability could be attained in calculating frequent, quasi-permanent and 50-year return-period values for thermal actions by applying separate statistical analyses to these random and deterministic parts. The procedure is used to check the validity of the empirical relationships in Eurocode 1 between the effective mean temperature of a bridge and the shade air temperature.

LONGITUDINAL THERMAL BEHAVIOUR OF A CONCRETE BOX GIRDER BRIDGE

This paper analyzes the thermal behaviour of the prestressed, box girder Casilina Bridge over a motorway near Rome, Italy, based on a three-year monitoring program. A finite element model for trans...

Glass Tensegrity Trusses

High transparency and modularity, retarded first cracking, non-brittle collapse and fail-safe design were the basic requirements that inspired and guided the development of a new kind of glass beams. The two basic conceptual design goals were to avoid any cracking at service and to get a ductile behaviour at failure. These objectives were reached by a preliminary subdivision of the beam into many small triangular laminated panes and by assembling them together by means of prestressed steel cables. Two prototypes have been constructed at the University of Pisa, tested in the elastic domain under dynamics loads and successively brought to collapse under quasi-static, increasing load cycles. In order to investigate the decay process of residual mechanical resources, the second prototype has been repaired twice by substituting just the damaged triangular panes and then tested again each time up to failure. Experimental results resulted in a good agreement with non-linear numerical simulations performed by appropriate finite element modelling.

Static Concept for Long-Span and High-Rise Glass Structures

AbstractLightweight, transparent, long-spanned, and high-rise constructions characterize the vision of many architects. Glass is at present the best-performing material where high transparency and ...

A Proposal for the Consolidation of a R.C. Social Housing by Means of External Hybrid Steel-Glass Frameworks

A proposal for the seismic consolidation of an existing r. c. social housing complex is presented. The intervention is thought to concern just the external facades in order to minimize costs and discomfort of inhabitants. Two external hybrid steel-glass bracing frameworks have been designed, with the aim to reach both seismic and energetic advantages. The mechanics of the framework system takes advantages from the compressive strength of the glass panels and the tension strength of steel braces and columns. A hypothetical application on a typical r. c. building dating back to the ‘60s in the city of Leghorn (Italy) is illustrated.

Conception And Parametric Design Workflow For A Timber Large-Spanned Reversible Grid Shell To Shelter The Archaeological Site Of The Roman Shipwrecks In Pisa

Reciprocal structures, or nexorade, are composed by the assembling of groups of three or more beams mutually connected by mono-lateral T joints in a way that any relative movement is suppressed. This kind of structures can be easily built in relatively unprepared sites, dismantled, transported and re-used even by not specialized handcraft. For these reasons, reciprocal structures have been widely used in the past for military purposes, and nowadays they seem to satisfy very well the different requirements of a quick and temporary shelter of a large archaeological area when they are shaped as grid shells. This paper proposes the design of a reversible, reciprocal framed grid shell to shelter the archaeological site of the Roman Shipwrecks in Pisa. The structure must protect excavations and archaeologists from the weather and provide an easy access to visitors. Additionally, it must allow for easy disassembling and moving to another site. The design choices aim at optimizing both structural efficiency and esthetical qualities. A parametric workflow for both the form finding and the digital fabrication processes has been developed, and a prototype of accommodative steel T-joint for timber reciprocal beams has been realized. Finally, a model using CNCcutting tested the structural feasibility of such a design approach.