1,721,058 research outputs found
Overall response of 2-ply laminated glass plates under out-of-plane loading
Full text linkThe results of an experimental and numerical investigation on the mechanical response of undamaged and damaged 2-ply Laminated Glass (LG) plates with different interlayers are presented in the paper. Three different interlayers, polyvinyl butyral (PVB), SentryGlas (SG) and Saflex DG41 (DG41) characterized by different rheological properties and fully tempered glass plates were considered. Simply supported plates under out of plane loads were tested in three different configurations: configuration 0, undamaged; configuration I, partially damaged, with a broken ply below (bottom ply) and configuration II, partially damaged, with a broken ply above (top ply). In the three configurations the top ply is always subjected to compression while the bottom one is in tension. The main aspects and the different response of each configuration were discussed and compared. Experimental results highlighted the influence of the interlayer properties on both the pre- and post-breakage behavior. Moreover, numerical models were developed to reproduce the experimental results. For the post-breakage response two different strategies were developed: a) the equivalent temperature variation and b) elastic-brittle constitutive law. Differences and advantages associated with both solutions are discussed. Finally, extensive parametric numerical analyses are proposed to underline the influence on the mechanical response of different parameters: i) plate geometry (size effect); ii) interlayer thickness; iii) glass thickness; iv) additional glass ply (3-ply LG plate). It is underlined that the size effect plays an important role on the mechanical response of LG plates and it should be always considered in the design. The numerical findings were used to define a critical length from which the plates behave as monolithic, independently of the stiffness of the interlayer
Advanced Seismic Design for Storage Pallet Rack Steel Frames
Full text linkIn the paper, a study on the design of braced and unbraced steel storage pallet racks in seismic zone is summarized. On the basis of a geometric layout of interest for routine design, rack performance has been evaluated via two alternative approaches: the well-established modal response spectrum analysis (MRSA) and an advanced strategy combining non-linear time-history analyses with the measurement of the damage in joints. Reference is made to two recent Italian earthquakes scaled by different values of the peak ground acceleration. Furthermore, cyclic joint behavior has been reproduced by means of a suitable model accounting for joint strength/stiffness degradation, whose excursions in plastic range has been considered to monitor the damage
Modal identification of storage racks for cheese wheels
Full text linkDuring the Emilia-Romagna earthquake (2012), a great number of steel racks used to store cheese wheels collapsed, causing a non-negligible damage to the Italian economy. Therefore, for similar structures that survived and are in service, a deep investigation towards the assessment of their effective safety is required. In the seismic analysis of these frames, the mechanical constraint acting onto the racks due to the reinforced concrete sidewalls, possible nonlinearities exhibited by the base-plate joints and the in-plane restraint provided by wooden boards that connects adjacent columns should be carefully modelled to ensure realistic design results. In the paper, an experimental activity, based on suitable modal identification techniques, is presented to capture the dynamic behaviour of these peculiar structures. The scope is to collect data useful to calibrate numerical finite element models in order to accurately define the aforementioned unknown parameters. Furthermore, a few numerical models based on ideal restraints are herein discussed stressing out non-negligible differences in terms of expected seismic and static response
Evaluation of European approaches applied to design of TWCF steel members
No full textThin-walled cold-formed (TWCF) steel members are widely used in aerospace, automobile and architecture industries. Among the various advantages, mainly associated with the relatively simple and very cheap techniques required for their production and shaping, it is important to mention the relevant high strength to weight ratio. Beside the benefits, it has to be pointed out that the TWCF member response is quite difficult to be predicted because of the significant influence of local, distortional and overall buckling phenomena, owing to the frequent presence of open mono-symmetric cross-sections. The present paper can be intended as a typical technical paper whose results are useful not only for research activities, but, especially, for the routine design. It summarises a study aimed at increasing the safety of two European approaches that should be potentially adoptable for designing TWCF steel members. The grade of reliability of these existing European procedures has been evaluated by predicting the performance of more than 240 TWCF members tested in laboratory, selected in the framework of 13 experimental studies, taken from the literature. Being the assessed load carrying capacity sometimes significantly greater than the characteristic-experimental one, suitable safety factors have been consequently calibrated and proposed for each cross-section type, to be directly adopted in routine design to match the requirements associated with the limit state philosophy. Finally, the strength of additional TWCF beam-column specimens has been predicted to assess the efficiency of the proposed coefficients for practical cases frequently encountered in routine design. A complete benchmark is proposed in Appendix A, where the application of the considered design procedures for one selected case is reported
Post-earthquake damage assessment of moment resisting steel frames
Full text linkThe assessment of damage in structures that have suffered one or more earthquakes is of paramount importance to better understand the post-earthquake effective behaviour, and eventually to define the more appropriate design strategies for retrofitting and repairing. The paper,which is focused on moment-resisting (MR) steel frames, deals with postearthquake assessment after one or more seismic events. A procedure combining non-linear time-history finite element analysis with the low-cyclic fatigue theory have been applied to appraise the damage level of each frame component and then the residual load carrying capacity have been evaluated via the incremental static analysis of the damaged frames. It is worth underlining that, onthe basis of the discussed numerical results, the damage measurement and the residual load carrying capacity, which are often neglected in routine design, appear very useful to increase the knowledge on the effective safety level of the frame after one or more earthquake
Recent development on the seismic devices for steel storage structures
No full textGoods and products are stored in framed systems, such as pallet racks, used for industrial and commercial activities. In the last years, pallet rack code provisions for seismic loads have been significantly improved, but there are still relevant aspects that need attention for guaranteeing a safer structural design. For example, in the current European and American standards, no indications are given about the seismic isolation systems applied to these structures. Only two ways to enhance the performance of racks in seismic zones are reported: rack netting and structural strengthening. Both methodologies present logistic and technical problems. For this reason, researchers are investigating more efficient solutions, like the base isolation systems. An accurate isolation system can bring benefits in terms of reduction of the structural damage and improving the safety of the stored items. Since the cost of the structural frame is often negligible, with respect to the cost of the stored products, avoiding the overturning of merchandise is an important challenge. Moreover, falling pallets can bring to the overall global collapse due to an impact given on beams or columns. In the paper, a critical overview of base isolation systems developed for different steel storage rack typologies is presented and discussed, highlighting the main characteristics and the advantages associated with their use in practical cases. Furthermore, four different applications of energy dissipation devices are briefly discussed, comparing these systems with the previously introduced devices
Characterization of existing steel racks via dynamic identification
Full text linkSteel storage racks are widely used in logistics for storing materials and goods. Rack design is carried out by adopting the so-called design-assisted-by-testing procedure. In particular, experimental analyses must be carried out by rack producers on the key structural components in order to adopt the design approach proposed for the more traditional carpentry frames. For existing racks, i.e., those in-service for decades, it is required to evaluate the load carrying capacity in accordance with the design provisions currently in use. The main problem in several cases should be the appraisal of the key component performance, owing to the impossibility to obtain specimens from in-service racks without reduction or interruption of the logistic flows. To overcome this problem, a quite innovative procedure for the identification of the structural unknowns of existing racks has been proposed in the paper. The method is based on in-situ modal identification tests combined with extensive numerical analyses. To develop the procedure, cheap measurement systems are required, and they could be immediately applied to existing racks. A real case study is discussed, showing the efficiency of the procedure in the evaluation of the effective elastic stiffness of beam-to-column joints and base plate connections, that are parameters which remarkably affect the rack performance. The structural unknowns have been determined based on four sets of modal tests (two configurations on the longitudinal direction and two in the transversal direction) plus 9079 iterative structural analyses. The results obtained were then directly compared with experimental component tests, showing differences lower than 9%
Post-failure behavior of 2-ply laminated glass plates with different interlayers
Full text linkModern design codes, such as the new Eurocode on the design of structural glass components, consider the prediction of the post-failure behavior of these elements of paramount importance for a proper and safe design. In this view, an experimental investigation is presented in the paper, on the mechanical response of undamaged and damaged 2-ply Laminated Glass (LG) under quasi-static loads, with different interlayers, namely polyvinyl butyral (PVB), SentryGlas (SG) and a plasticized version of PVB, Saflex DG41 (DG41). Firstly, undamaged specimens (UDLG) were tested in simply supported configuration (configuration 0) with a vertical load in the middle increased up to the failure of the bottom glass ply. damaged LG specimens (PDLG) were then tested into two different configurations: configuration I, with broken ply below (bottom ply) and configuration II, with broken ply above (top ply). All the presented tests were performed under displacement control. For both configurations, the interlayers influence on the post-breakage behavior was discussed. It is underlined that the global response of the two configurations was completely different: configuration II, which was characterized by a deformed shape opposite to the load direction, showed a good residual stiffness and reached high failure loads. On the contrary, in configuration I, the response was characterized by a low stiffness and load carrying capacity. In addition, also the influence of different glass types was discussed, focusing attention on tempered and toughened glass. The results showed that the contribution of the fractured layer cannot be disregarded in the evaluation of the global stiffness of a PDLG and its contribution is strictly related to the interlayer and glass typologies
Seismic devices for steel storage structures
No full textThe importance of the logistics sector has increased even more in the last year, due to the Pandemic event which lead to an increasing of the online purchases. Goods and products are generally located in steel frames known as steel racks or simply racks. Consequently also the safe design of these structures, i.e. preserve their fully functionality and avoid their collapse, is becoming of paramount importance, especially when they are located in strong and moderate seismic zones. Despite pallet rack provisions for seismic loads have been significantly improved in the recent years, only two classic ways to enhance the seismic performance are considered: rack netting and structural strengthening. Both of these suggested solutions are not fully effective to preserve the integrity of the stored products that, when subjected to strong accelerations, can topple and fall down. The only reliable and effective systems seem to be the introduction of seismic devices, such as base-isolation and energy dissipation systems. Since no indications about these techniques are reported in the standards, many researches worldwide are trying to fill this gap. Unfortunately, up to now, just theoretical studies and very limited applications are available in literature. In the present paper a short overview on the base isolation systems available on the market for different steel storage rack typologies is presented highlighting main advantages and defects of each solution
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