Prof. Ing. Giuseppe Campione
Ph. D, Prof. Ordinario Tecnica delle Costruzioni – Dipartimento di Ingegneria – Università di Palermo
Questo articolo si riferisce a un caso di studio di danni permanenti prodotti in elementi strutturali di una gru portuale a causa di una pressione dell’aria eccessiva, utilizzata nei test di tenuta all’aria. Gambe e bracci a sezione quadrata o rettangolare sono stati danneggiati durante i test di tenuta all’aria, con frattura della saldatura, instabilità locale e complessiva di irrigidimenti e piastre e plasticizzazione diffusa delle pareti in acciaio. Sono state eseguite prove di trazione in laboratorio su provini estratti, ispezione visiva, stadia piana, laser scanner e test a ultrasuoni per individuare le zone fratturate e instabili e quantificare l’estensione e la percentuale di danno. Inoltre, sono state eseguite analisi numeriche dettagliate, che includono non linearità geometriche e meccaniche, con codice ANSYS. Infine, un modello meccanico semplificato basato sulla soluzione di un sistema a telaio piano ha permesso di ottenere semplici espressioni analitiche per calcolare la pressione dell’aria che produce la prima plasticizzazione in questo tipo di strutture. Le previsioni analitiche sono risultate in accordo con i risultati sperimentali e numerici.
1. INTRODUCTION
The case study here examined is that of port crane, such as those shown in Fig. 1, in which the arms, legs, diagonals and ties are steel box girders that can be hermetically sealed with welds to protect them from corrosion, thus reducing maintenance costs were damaged during air tightness tests. The crane is made of steel components, composedby a movable gantry frame supporting the arms made with a pair of box girders, articulated and cable-stayed (figure 1).
Several studies present in literature (Gang et al. 2013, Hwang et al..2018, Fasl and Larosche 2020, Wang et al. 2021, Tran et al.2021), were addressed to analyze both statically and dynamically the behavior under service and at ultimate limit state of port crane including second order, fatigue effects under service, wind or earthquake actions.
Major of the studies are based on structural analyses performed with non linear finite element models adopting beam or shell elements discretized with finer mesh size (Dzioba et al. 2024, Marpaung et al. 2024, Dönerkaya et al. 2025). Air tightness test is a maintenance test in which air is put inside the structural elements having closed boxes with rectangular or square section to verity that structure is stagnant.
Tests are conducted to verify the air-tightness of structures that, when exposed to aggressive environments (such as marine environments), has to be protected by making them watertight. The air tightness test is part of the durability test and therefore must be performed by keeping the structure elastic well below the yield point of the material. The test must therefore be carefully designed with regard to the optimal value of air pressure to be injected into the container and the injection method ensuring that the stresses induced in the structure during the test are elastic. One example of experimental research referred to Air tightness […]
Leggi l’articolo completo su Costruzioni Metalliche n. 2/2026