1,721,020 research outputs found
Risk of failure in existing RC balcony and strength verification under degradation phenomena
No full textIn the present paper, the safety conditions of reinforced concrete (RC) balconies subject to degradation phenomena caused by carbonation, presence of chlorides or water infiltration were examined. After a brief review of the typical damages of balconies occurring with detachments of plaster and bricks expulsion, some cases of collapses of balconies recently occurred were presented. Therefore, a calculation model was proposed for a hand verification of the flexural and shear strength of existing corroded T beams cast in place of lightened RC orthotropic slabs forming the balcony and for the calculus of deflection including slippage of steel bars. Diffused and pitting corrosion on steel bars, compressive concrete strength degradation, and concrete bond strength degradation are included in the model. This approach is simple and can be applied based on the experimental information available (carbonation test, chloride content, measurement of the pitting in the bar, a gravimetric method for general corrosion) or by utilizing analytical expressions calibrated on knowledge of the corrosion current intensity determined by linear polarization resistance measurement (LPR)
Modellazione integrata di un robot industriale ad architettura cartesiana
No full textI robot industriali hanno migliorato significativamente le prestazioni degli impianti manifatturieri automatizzati nel corso degli ultimi decenni. Tuttavia, la competizione internazionale crea una crescente necessità di diminuire ulteriormente i tempi ciclo e di aumentare l’accuratezza dei processi produttivi e dei prodotti finali. Per raggiungere questi obiettivi, i costruttori di robot stanno attualmente proponendo una nuova generazione di manipolatori leggeri ad elevate prestazioni: in certi casi vengono effettivamente progettate nuove strutture robotiche, talvolta basate su meccanismi a cinematica parallela, ma spesso si tratta semplicemente della ri-ingegnerizzazione di modelli di punta, che vengono modificati per soddisfare a requisiti più stringenti. In entrambi i casi, non è semplice riuscire a soddisfare le elevate prestazioni operative che sono attese senza la disponibilità di buoni modelli dinamici, poiché l’impatto di alcune scelte progettuali è difficilmente valutabile a priori, per mezzo della sola esperienza. Nella presente memoria si descrive in dettaglio lo sviluppo del modello dinamico di un robot industriale per l’asservimento di presse ad iniezione: la semplicità dell’architettura meccanica ha facilitato la completezza del modello, che è stato implementato tramite l’integrazione di alcuni pacchetti commerciali a basso costo. Lo studio condotto mostra che, anche basandosi sull’utilizzo di strutture robotiche già disponibili, esistono spesso ampi margini per il miglioramento delle prestazioni, purché si sia caratterizzato sufficientemente il comportamento del robot per mezzo di adeguati modelli dinamici
Proposta di un sistema meccatronico per la riduzione delle forze di contatto nel varo delle condotte sottomarine
No full textref. abstract: SP-ME-1
PV Large Utility Visual Inspection via Unmanned Vehicles
No full textThe robotics for Inspection and Maintenance (I&M) was introduced decades ago. Increasing their technologies, they were more and more used in more complex scenarios, thanks also to the legged robots able to move on uneven terrain as well as drones always more autonomous. Energy production plants were investigated in this paper, to evaluate how is the suitability for autonomous I&M; that’s matter of facts, that, until now, robotic based inspection of photovoltaic systems was considered only as one of the possible I&M strategies feasible for this category of energy systems. In this work, the advantages of autonomous inspection systems for large photovoltaic systems are discussed by connecting them to the specific characteristics of a large photovoltaic utility plant. The objective is to highlight that, based on a large investigation, in the case of photovoltaic energy, robotic inspection is a necessity rather than an option
Flexural Test on a Full-Scale 60-kW Wind Turbine-Tower Telescopic Steel Pipe
No full textA full-scale static test to failure was conducted on 6-m (236.22 in.)-long steel pipes constituting a segment of a telescopic wind tower with a 60-kW wind turbine. The diameter of the circular cross section of the steel pipes was 900 mm (35.43 in.), and the nominal thickness was 10 mm (0.39 in.). The steel grade was 355 MPa (51,488 psi). The tests were conducted in a force-controlled mode in a four-point bending test with a shear-to-span ratio of 2.05. The flexural limit states developed in the form of ovalization of the cross section and of local buckling. The buckling occurred in the plastic range because of the diameter-to-thickness ratio of the section. Although local buckling caused slight strength degradation, the reduction due to the shear-to-moment interaction and ovalization of the cross section was very significant (58%), while the recorded response revealed a good amount of postbuckling ductility (2.42). A finite-element analysis with ABAQUS code was also conducted for comparison with the experimental results and for validation of the simplified proposed model. By properly modeling the imperfection effects due to the roundness of the steel tube, good correlation of the structural response and failure mode, and with the analytical model, were also achieved
Practical calculus methods for flexural response of shallow beam foundation
No full textIn this work, the behavior of reinforced concrete (RC) beams on a soil foundation subjected to concentrated vertical loads and bending moments in both the elastic and the plastic phases was examined. Some of the simplified methods for hand calculations available in the literature, which are useful for the preliminary design of the foundation structures, are reviewed. A simplified plastic calculation method was developed. The method examines the limit cases of partial or full plasticization of soil and the formation of plastic hinges in the beam with elastic or plasticized soil. The proposed method showed good agreement with others in the literature. The purpose of the proposed method was to provide a simple calculation tool useful for calculating the foundation’s bearing capacity and for verifying the overstrength of the soil-foundation complex compared to that of the beam alone. The method highlights that the plastic resources of the soil-foundation complex depend not only on the characteristics of the soil such as cohesion, friction angle, and constant back soil, but also on the geometrical and mechanical characteristics of the foundation beam and on the characteristics of the vertical load (intensity, eccentricity). It was also shown that the maximum ratio of longitudinal steel bars should be determined to ensure the strength hierarchy with the plasticization of RC beams before soil plasticizatio
Multibody dynamics of a flexible legged robot with wheeled feet
No full textThe objective of this paper is to analyze the multibody dynamic model of biped flexible robots with wheeled feet. The following two points underline the novelty of this paper: 1) a novel physical and analytical model of a biped wheeled robot with flexible legs; 2) a biped locomotion composed by a combination of flexible links and wheeled feet. The validation of the model with the real robot gives to the scientific community a key reference to design future biped wheeled and flexible robots
Flexural Behavior for External Beam–Column SFRC Joints: Experimental Investigation and Design Suggestions
No full textExperimental research was carried out on the flexural behavior of full-scale external beam–column concrete joints cast with plain and steel fibrous reinforced concrete (SFRC) with hooked steel fibers, subjected to cyclic reversal loading. Four beam–column sub-assemblages were cast. Two of them, denoted as control specimens, were made of plain concrete (RC) and were reinforced with longitudinal bars and transverse stirrups, and two were made of hooked steel fiber-reinforced concrete (SFRC) with same longitudinal steel reinforcements of control specimens but with higher spacing of stirrups in the beam. The experimental results show that it is possible to avoid brittle failure of external beam to column joint assigning, as it is well-known, high percentage of transverse steel in joint region or utilizing less stirrups in all critical regions and replacing plain concrete with SFRC. In this case, it is possible also a more efficient control in the opening of the cracks. From the analytical point of view, experimental results were reproduced numerically by using a non-linear finite-element program (ABAQUS). With ABAQUS constitutive laws in compression and in tension able to include post-cracking resistance of material were adopted. In addition, utilizing a simplified closed-form softened strut-and-tie macro-model, it was possible reproduce the load-deflection curves of beam to column sub-assemblages. Analytical results were in a good agreement with monotonic response observed experimentally. Finally, design guides for ductile behavior of SFRC beam to column joints are give
Engineering failure analysis of corroded R.C. beams in flexure and shear
No full textIn the present paper, a simple model to reproduce the load-deflection response of corroded beams failing in flexure and shear is presented and discussed. Effects of diffused and pitting corrosion on steel bars, compressive concrete strength degradation and concrete bond strength degradation due to rust formation are included in the model. Engineering approach based on limit state theory was here adopted to predict the peak and the residual flexural and shear strength of corroded beams with corresponding deflections and ductility estimation. Calculation of deflection at cracking taking into account of rust formation and deflection at yielding and the ultimate state taking into account also of slippage of steel bars due to rust formation were made. The model was also widely verified against tests available in the literature referred to crack opening, pit depth, attach corrosion penetration, load-deflection curves
- …
