3,752 research outputs found

    Improvement of the mathematical model of the diagram of deformation of the compressed composite steel and concrete structures

    Full text link
    The mathematical model of the stress-strain ratio of compressed concrete at elevated temperatures for composite structures described in Eurocode EN 1994-1-2:2005 Eurocode 4 divided in two stages: Stage 1 - represents the ascending branch and is defined by two parameters: compressive strength fc, θ and corresponding deformations εcu,θ, stage II - the descending branch which is accepted for numerical methods. The design practice showed deficiencies in the provisions on models of deformation diagrams given in Eurocode 2. Part 1-2 General provisions. Structural Fire Design. (EN 1992-1-2:2004), (ENV 1992-1-2:1995), which were reflected in the national standards in the process of harmonization. A technique for determining the refined diagrams “σc,θ – εc,θ” was developed for the design of composite reinforced concrete structures in case of fire. Diagram parameter values were adjusted for concretes based on silicate filler at high temperatures, the mathematical stress-strain model of the concrete under compression and high temperatures was specified

    Passing-through Tubular Column Joints for Steel and Composite Constructions made by Laser Cutting Technology

    Get PDF
    In steel moment-resisting frames, tubular columns have many structural and architectural advantages over open-section columns. Tubes are in fact particularly recommended for structural elements subjected to compression and bending forces in all directions, thanks to their higher radius of gyration and the axial-symmetric distribution of their mechanical properties. Therefore, the use of hollow profiles for the realization of columns can lead to a reduction of the total costs and furthermore to simplifications in the realization process of steel-concrete composite structures. However, the difficulties in realizing tubular column joints adopting open I-section beams, the most commonly used all around the world, severely reduce the use of tubular columns. Nowadays, beam-to-tubular-column steel and composite joints are commonly realized in two main ways: i) the connection is made by directly welding the beams or the beam stub to the wall of the steel tube; ii) supplemental plates are used to connect the beams to the circular column. Both ways have many disadvantages: the direct connection is the most convenient solution in terms of rapidity and easiness of fabrication but the performance of the joint is strongly limited by significant local distortions of the tube wall near the girder flanges; additional elements can assure a more effective transfer of the stresses from the beam flanges to the column wall or from the flanges of one beam directly to the beam placed on the opposite side, but their use implies a discontinuity in the column and requires extensive welding to reconnect the column pieces. To overcome these issues, innovative solutions with continuous passing-through elements inside the column were studied in the past years, highlighting several advantages from a mechanical point of view. Indeed, the continuous elements can pass by slots of limited size made on the column wall, without requiring the complete discontinuity of the column itself and the joint requires less cutting and welding operations, resulting in lower overall cost and better mechanical behavior. However, despite all the advantages, many problems arise from the fabrication and constructional points of view, limiting the effective performance of the joints. One of the solutions to overcome the difficulties in the fabrication and constructional processes of this joint typology lies in the application of modern Laser Cutting Technology to steel and composite structures. Several issues were studied in the present thesis, with both numerical and experimental tests, to define an appropriate fabrication process and to better characterize the mechanical behavior of the tubular column connections with passing-through elements, under vertical and horizontal loading conditions

    Compressive performance of AFRP reinforced laminated bamboo stub columns

    Get PDF
    Engineered bamboo construction can be affected by natural defects, insects, corrosion, etc., which will result in damaging the mechanical properties of structural components. However, traditional reinforcement methods such as setting steel supports and increasing the cross-sectional area of components may cost a lot and cause a negative influence on the appearance of building. Many engineering practices and research works show that applying FRP (Fiber Reinforced Polymer/Fiber) sheet is an economical and efficient method for reinforcing and retrofitting building structures. Therefore, the compressive performance of AFRP (Aramid Fiber Reinforced Polymer/Fiber) reinforced laminated bamboo lumber (LBL) stub columns was studied in this paper. Through six groups (three replicates for each group) of stub columns with six different cloth ratios, the influence of AFRP on the failure pattern and mechanical properties of bamboo columns was explored. The test results showed that AFRP could effectively restrain the lateral deformation and improve the mechanical behavior of LBL columns. With the increase in cloth ratio, the ultimate strength and elastic modulus increased linearly in general, while the Poisson’s ratio gradually decreased. The reduced modulus of reinforced columns in the elastoplastic stage increased up to 161.31% compared with normal columns. Although the ductility of LBL columns laterally wrapped by AFRP was greatly improved, the initial stiffness, yield point and turning points between elastoplastic stage and plastic stage basically remained unchanged in contrast to unreinforced columns. Based on the test results, an empirical equation considering the cloth ratio was proposed to calculate the ultimate strength of AFRP reinforced LBL columns, using ‘Lam and Teng’ model. In addition, a simplified equation was also proposed to calculate the compressive strength of reinforced LBL columns derived from Mises yield criterion. The results of this work can be a reference to promote the application of strengthening and retrofitting engineered bamboo structure with FRP

    Sustainability of Concrete With Synthetic and Recycled Aggregates

    Get PDF
    Concrete is a material used widely in building and construction applications worldwide; hence, it plays a significant role in the global construction sector. Cement is a major component of concrete and is used in construction applications, either on its own or as a composite with other materials, to improve workability, durability, strength, weight, and shrinkage. However, cement and concrete production and use have adverse environmental effects. Thus, great efforts have been made to produce eco-friendly concrete. This book examines several aspects of sustainable concrete technologies, including new forms of concrete as well as different approaches for creating sustainable cement

    Static and dynamic response of RC beams strengthened with NSM C/GFRP rods

    Get PDF
    openNegli ultimi anni è stato dimostrato che la tecnica di rinforzo Near Surface Mounted (NSM) rappresenta una valida alternativa ai metodi di rinforzo convenzionali, come le fasciature esterne (metodo Externally Bonded). Potenzialità, vantaggi ed applicazioni sono stati studiati negli ultimi 20 anni cercando di ottimizzare il sistema ed i parametri che lo influenzano. È interessante approfondire il tema sia dal punto di vista statico, evidenziando la non validità dell’ipotesi di conservazione delle sezioni piane, che si manifesta a causa dello scorrimento tra FRP e resina, che per semplicità non viene mai preso in considerazione dai modelli analitici proposti in letteratura, che dal punto di vista dinamico, che consente di analizzare l’andamento delle frequenze proprie di vibrazione, per monitorare l’efficacia del rinforzo e come agisce il grado di danneggiamento. Durante questo lavoro di ricerca sono state effettuate prove statiche e dinamiche su campioni di travi in cemento armato rinforzati con barre in CFRP e GFRP mediante tecnica NSM. Lo scopo del progetto è proprio quello di analizzare gli effetti delle differenti tipologie di rinforzo applicate. Le prove statiche a flessione sono consistite nell’applicazione di cicli di carico e scarico, questi test hanno consentito di definire il comportamento dei campioni di trave anche in presenza di fessurazione del calcestruzzo e di individuare diversi livelli di danno. Dopo ogni step di carico sono state effettuate le prove dinamiche in vibrazione libera che hanno consentito di osservare come agisce il rinforzo. Sono stati osservati anche i modi di rottura delle travi. Le risposte del campione non rinforzato sono quindi state confrontate con quelle dei campioni rinforzati, il comportamento è stato analizzato anche attraverso dei modelli teorici. Infine, è stato sviluppato un modello agli elementi finiti dei campioni di trave in modo da validare i risultati ottenuti sperimentalmente.The Near-Surface Mounted (NSM) strengthening technique has proven, in recent years, as a valid alternative to the conventional strengthening methods, like the externally bonded (EB) technique. In the last two decades its potential and its advantages, as well as its applications, has been studied, trying to optimize the construction system and the parameters that influence it. However, it is interesting to deepen the topic both in static, highlighting the non-conservation of the flat section, due to the bond-slip effect between FRP rod and resin, which, for simplification has never been taken into consideration by analytical models proposed in literature, both in dynamic key, which allows, by studying the trend of proper frequencies of vibration, to understand the effectiveness of the reinforcement and how different types of damage affect it. Therefore, in this research work, static and dynamic tests were performed on RC beams strengthened with NSM CFRP and GFRP rods, which still need to be investigated. The aim of the research is to analyze the effects of different types of strengthening. Bending tests with cycles of loading until failure are carried out, these tests allowed to define the behavior of beam specimens, even in presence of damage, and to generate different damage degrees, due to cracking of concrete. At each step of load, dynamic analysis, by free vibration test, allows monitoring the effectiveness of the reinforcement at different damage degrees. Failure modes of beam models are also analyzed. A comparison between the responses of the unreinforced and reinforced models is presented; the behavior of beam specimens was also analyzed by theoretical models. In the end, a finite element analysis of beam models has been developed, in order to validate the results obtained by the experimental research.INGEGNERIA CIVILE, EDILE E ARCHITETTURAopenVecchietti, MARIA VITTORI

    Repair of fire-exposed preloaded rectangular concrete columns by postcompressed steel plates

    Get PDF
    This paper describes an experimental study of axially loaded, fire-exposed, rectangular reinforced concrete (RC) columns repaired with post-compressed steel plates. Seven RC columns with identical section dimensions and reinforcement details were fabricated and tested. Six of them were exposed to a four-hour fire load according to the ISO 834 Standard. After one month of cooling, five of the fire-exposed columns were installed with precambered steel plates which were then post-compressed by a method newly developed by the authors. All columns were tested under axial compression to determine their ultimate load capacity, deformation and ductility. The effects of steel plate thickness, initial precamber displacements and preloading level on the ultimate load capacity of repaired RC columns were investigated. The test results show that up to 72% of the original capacity of the axial load-carrying capacity of fire exposed columns repaired with post-compressed steel plates can be restored. Furthermore, the repaired specimens show better ductility and post-peak deformability. An analytical model was adopted to predict the ultimate axial load capacity of fire exposed columns repaired with post-compressed steel plates. Comparison of the theoretical and experimental results reveals that the analytical model can accurately predict the ultimate axial load capacity of the repaired columns.postprin

    Reinforced Concrete Corbels – State of the Art.

    Get PDF
    This paper represents a historical review, state-of-the-art review, on the experimental researches carried out on corbels in general and strengthening of corbels in particular. The corbels discussed are made of normal, high-strength and self-compacting concrete and subjected to two types of loading, monotonic and repeated loadings. Moreover, a review on the techniques of strengthening used to enhance the load carrying capacities of reinforced concrete corbels is presented too. Finally, directions for future work are proposed and a comprehensive list of references is provided

    High strain-rate tests at high temperature in controlled atmosphere

    Get PDF
    • …
    corecore