1,721,062 research outputs found
Discussion of “Prestress Force Effect on Vibration Frequency of Concrete Bridges”
No full textPaper without abstract
Creep analysis of continuous composite beams: effectiveness of simplified methods
No full textThe Effective Modulus and the Mean Stress methods are applied to perform the creep analysis of continuous composite beams with flexible shear connection. Static and geometrical actions, as well as, shrinkage and prestressing of the slab are considered. In the case of prestressing, both cast-in-situ slabs and post-connected precast slabs are analysed. These different actions are applied separately to evaluate the effectiveness of the simplified methods. Useful information on performing a simplified creep analysis by means of routine computer programs are given
Effetti della viscosità e del ritiro negli impalcati da ponte a sezione composta
No full textSi esamina il comportamento viscoso delle travi continue composte sottoposte alle principali azioni dipendenti dal tempo di interesse per gli impalcati da ponte: le azioni statiche e geometriche, il ritiro del calcestruzzo, la presollecitazione con cavi interni alla soletta gettata in opera o prefabbricata e post-connessa e la precompressione esterna. Do-po alcuni richiami sulle procedure numeriche di step by step e sui metodi algebrizzati, si presentano i metodi semplificati suggeriti dagli eurocodici. Infine si analizzano gli effetti connessi alle modalità di getto della soletta mostrando i vantaggi conseguenti alla ottimiz-zazione delle sequenze di getto
Time dependent behaviour of continuous composite beams: comparison between different prestressing techniques
No full textThe long-term behaviour of continuous steel-concrete composite beams is investigated to evaluate the effectiveness of the principal prestressing systems generally used to prevent concrete cracking in the regions of the internal supports. Four prestressing techniques are considered: the first with imposed support settlements, the second with internal cables in cast-in-situ slab, the third with internal cables in precast concrete slab and the fourth with external cables. The time-evolution of the compressive stress on the slab is studied evaluating the magnitude of the stress loss due to the concrete creep. The study is carried out on a composite beam model with flexible shear connection which permits taking into account the slip at the beam-slab interface and calculating the longitudinal shear force distribution which is particularly important at the cable anchorage sections
Seismic nonlinear behavior of steel-concrete composite bridges with dual load path
No full textThe paper analyzes the seismic transverse behavior of steel concrete composite (SCC) bridges with dissipative piers and continuous deck transversally restrained at the abutments, usually denoted as "dual load path" bridges. A simplified model is proposed in order to derive analytically the properties of an elasto-plastic SDOF system equivalent to the bridges, which can be used to perform a simplified seismic analysis or for design purposes. This permits to make explicit the non dimensional parameters controlling the elastic and post-elastic system behavior, and the failure modalities. The formulation is applied to the analysis of a set of 3-span SCC bridges with dual load path behavior and different piers height. The accuracy of the simplified model is tested by means of comparison with the results of incremental dynamic analysis
Casting sequences effects in continuous composite girders
No full textIn this paper, an analytical method for short and long term analysis of steel-concrete continuous composite girders with fractionated slab castings is proposed by taking into account the flexibility of the shear connection and the concrete behavior at early ages (concrete autogenous shrinkage and hydration thermal strain). The numerical solution is achieved by means of a finite element approach in conjunction with the step-by-step procedures. The proposed method is applied to a four span continuous composite deck by analyzing the tensile stresses in the slab produced by two different casting sequences
Effetti della viscosità nelle strutture miste acciaio-calcestruzzo con connessione flessibile
No full textL'articolo presenta i risultati di una ricerca svolta sugli effetti della viscosità del calcestruzzo in travi composte
Influenza del ritiro del calcestruzzo alle brevi stagionature e delle fasi di getto sulla fessurazione delle solette nei ponti a sezione composta
No full textIn questa memoria si affronta il problema della fessurazione delle solette nei ponti a sezione composta acciaio-calcestruzzo, valutando l’influenza delle modalità di getto e del ritiro del calcestruzzo alle brevi stagionature. L’analisi è condotta su un modello precedentemente proposto dagli autori, opportunamente riformulato per lo studio di impalcati composti con trave metallica a sezione variabile. La soluzione numerica è ottenuta con il metodo degli elementi finiti all’interno di una procedura step-by-step. L’applicazione ad un caso reale consente di evidenziare i vantaggi offerti da sequenze di getto ottimizzate rispetto al caso più semplice di esecuzione della soletta in avanzamento continuo
A beam finite element including shear-lag effect for the long-term analysis of steel-concrete composite decks
No full textThe paper presents a beam finite element for the long-term analysis of composite decks taking
into account the warping of the slab cross section and the partial shear interaction between the
slab and the girders. Slab shear-lag is taken into account by means of the product of a known
function, describing the shape of the slab cross section warping, and an intensity function
measuring the magnitude of warping along the beam axis. Time-dependent behaviour is
considered by means of an integral-type visco-elastic creep law for the concrete. The
numerical solution is obtained by means of the finite element method with a 13-dof beam
element and a step-by-step procedure for the evolution in time. The results of some
applications show the accuracy and the capability of the proposed element
Partially isolated bridges: simplified seismic assessment and design
No full textPartially restrained seismically isolated continuous (PRSI) bridges are a particular class of isolated bridges in which isolation bearings are placed only between the superstructure and the piers, while steel-plate stoppers or other devices restrain the transverse motion of the deck at the abutments.
This study illustrates a simplified model for the preliminary assessment and design of these systems. The dynamic problem of PRSI bridges is described in a variational form, in order to obtain a simplified solution based on a pre-fixed transverse deformed shape of the deck. Simple formula are derived for estimating the seismic response quantities of interest. Additional formula are also proposed to account for the contribution of higher modes of vibration, which are important for the verification of some bridge components, such as the abutment restraints.
Based on the simplified model, a procedure for the preliminary design of the isolation bearing properties is proposed. The objective of the design procedure is to control the internal actions on the piers by means of an appropriate configuration of the isolation bearings and this may be of interest both for the design of new bridges and the retrofit of existing bridges.
Validation studies are undertaken in order to assess the effectiveness of the simplified formulation in describing the bridge seismic response and the ability of the proposed design procedure to control the force demand on the piers
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