Traffic dynamic effect on road bridge joint

In road engineering, also a well realized bridge expansion joints always creates a discontinuity in the road surface. This unevenness produce very important dynamic load increase due to the moving heavy vehicles. The dynamic component of wheel forces depends on the road pavement profile, the functional characteristics of the vehicle (geometry, mass and stiffness distribution, tire and suspension type, operative speed, etc.) and structural characteristics of the bridge superstructure (span length, geometry, static scheme, natural frequencies and damping). The dynamic actions can produce a general decay of the structure and local breaks near the biggest pavement unevenness for example near the Highway Bridge Expansion Joints (BEJ) and could decrease or cancel the skid resistance between road and tire, with dangerous consequences on traffic safety. Generally, it is recommended to consider the dynamic actions between the vehicle and the road. The definition of these actions is possible by means of the analysis of vertical accelerations measured, for example, on a heavy vehicle axle running on the joint. An innovative approach for solving the problem of dynamic interaction between heavy vehicle and BEJ is presented, taking advantage of the all purpose explicit finite element code LSDyna. The proposed model allows to determine, varying the parameters of the test vehicle (load, geometric dimensions and speed), of the JOINT unevenness dimensions (amplitude and wavelength) and of pavement modulus, the stresses and deformations on JOINT and of each pavement layer due to dynamic actions generated by vehicle motion. The model allows to also determine the accelerations on the vehicle, to verify the Ride Quality of a uneven pavement

Finite Element Modeling of Aircraft Gear Interaction with Cement Concrete Pavement

Computational mechanics applied to dynamic impact/interaction problems is nowadays possible. This approach can be used to Jet the gear and pavement interact in a more complex and realistic way; the FE analysis evaluates either the contact forces and the stresses on the pavement and aircraft gear. This paper describes the development of a 30 Finite Element Model of a cement concrete pavement/joint system and an Airbus 300 gear. The code used to perform all the analysis was LS-DYNA v.950d, a nonlinear explicit Finite Element Analysis code. In order to examine the effects of the joint bump height and aircraft speed, two different pavement models were used, with and without dowels, running a total of 16+16 simulations (4 different speeds, 4 different bump heights for each model). The doweled joint model has been used to evaluate the joint Load Transfer Efficiency, the non-doweled model results have been compared to the values calculated using the Westergaard's theory

Dimensione del margine interno e modalità di funzionamento delle barriere da spartitraffico

La rete stradale italiana, a causa delle modalità con cui si è determinato il suo sviluppo, che ha seguito con relativo ritardo gli incrementi sempre crescenti del traffico veicolare, presenta oggi – obiettivamente – alcune incompletezze funzionali, specialmente riguardo alla sicurezza attiva e passiva degli utenti. Tali carenze possono emergere con evidenza come risultati di analisi tecniche razionali, che si avvalgano di un’ampia base di informazioni e delle necessarie competenze scientifiche. In questa ottica, dunque, il progettista ed il gestore stradale debbono considerare ogni aspetto relativo alle condizioni di esercizio delle carreggiate stradali, al fine di poter effettuare il dimensionamento di ciascun elemento in maniera coerente e nel rispetto delle prescrizioni normative. Un fattore specifico e rilevante riguarda gli spazi marginali stradali, interni ed esterni, per il cui progetto occorre sempre considerare anche la tipologia e le caratteristiche dei dispositivi di ritenuta da installare, poiché le loro modalità di funzionamento impongono di prevedere e garantire la disponibilità di adeguati spazi “operativi”. Queste avvertenze sono anche contenute nelle vigenti Norme tecniche, riguardanti sia il progetto delle strade, sia il progetto delle installazioni dei dispositivi di sicurezza, e sono rigorosamente valide per le nuove costruzioni stradali. Negli adeguamenti o nelle installazioni su strade esistenti, d’altro canto, il problema è ancor più significativo, poiché a seguito dei recenti provvedimenti del Ministro delle Infrastrutture e dei Trasporti (D.M. 22.4.2004 e D.M. 21.6.2004), le Norme stradali sono da considerare “di riferimento”, e gli spazi di lavoro delle barriere possono essere valutati su basi teoriche; la responsabilità di garantire corrette condizioni operative ricade perciò maggiormente sul progettista o sul gestore stradale, e deve comportare la necessità di riferirsi a rigorose analisi tecniche, fondate sull’esame dei dati che è possibile reperire e conoscere con certezza. Nell’articolo si tratta, in dettaglio, il problema del corretto dimensionamento del margine interno nelle strade a carreggiate separate, in relazione alla possibilità di installare le barriere di sicurezza da spartitraffico, scegliendole tra quelle attualmente omologate in Italia, ed a partire dall’esame delle caratteristiche prestazionali dei dispositivi risultanti dai certificati di omologazione

Bridge joint as pavement surface unevenness

Road bridge joint faulting is due to progressive structural decay under the stress produced by heavy vehicles. This faulting creates an unevenness on road surface that is undesirable for two reasons: − the generation of vertical accelerations on the vehicle. These accelerations decrease or cancel the skid resistance between road and tyre, with dangerous consequences on traffic safety; − the generation of impact actions on the joint, due to the punctual unevenness. These actions increase the speed of faulting process. Besides, there are some particular structural conditions that often emphasise the problem, for example: local cracking due to the settlement of subgrade near the shoulder; the discontinuity due to the change of elastic moduli of the different material on the road (asphalt concrete, cement concrete, iron, etc.); the possible differential settlements near the beam heads, even if they are well connected with the ceiling. The vehicle-bridge interaction can be studied by means of numerical models using the pavement profile data. The moving vehicle can be represented with an array of rigid bodies characterised by masses and suspensions. These are represented with simple or combined rheologyc schemes. The application of the models strongly depends on the exact knowledge of road surface including the bridge joint. The coming vehicle already has vertical oscillation motions that can be amplified when it pass through the joint. As the speed increase, as an elevation change in a short length produces a bump action. The valued displacements and stresses are much greater than the equivalent static values. Therefore even if there are not specific standards about this topic, the design of a joint without considering the traffic loads dynamic effects underestimates the real service condition and the fatigue resistance. These dynamic effect must be considered also in the bridge structural design. The definition of the dynamic actions between vehicle and bridge is possible also by means of the analysis of the vertical accelerations measured on a heavy vehicle axle running on the joint. This paper deals with the analysis of a case history of a bridge expansion joint. The three- dimensional representation of the pavement surface and the acceleration measurements on a heavy test vehicle were performed to analyze the joint behaviour under traffic

Dynamic effects in concrete airport pavement joints

The use of computational mechanics in the analysis of dynamic-interaction phenomena is going to be very widespread, and constitutes too a sound opportunity to deal with problems of an application nature. In particular, this approach can be used to study, in innovatory fashion, the dynamic interaction between aircraft landing gears and airport pavements, since, relative to the methods traditionally adopted, it is more suited to representing the real conditions of the problem. Finite-element analysis can be used to evaluate the contact forces and the stresses in the landing gear and in the pavement, due account being taken of the dynamic effects. This paper describes the development of a three-dimensional finite-element model that represents an aircraft landing gear and a concrete airport pavement with joints between adjacent slabs outfitted with, or devoid of, load-sharing dowels. The model was developed to evaluate the level of the dynamic effects in airport concrete-pavement joints, in particular when stepping comes about between adjacent slabs, i.e. differences in their surface elevations. A parametric analysis was carried out, elevation differences and aircraft speeds being varied, and using dowelled and undowelled pavements. Thirty-two simulations were then carried out (four different speeds, four different elevation differences, and two types of pavement). The results of the tests made with undowelled pavement, expressed in terms of relative displacements between adjacent slabs, were used to evaluate the efficiency of the joint during load transfer (LTE, Load Transfer Efficiency). The results of tests carried out with dowelled pavement, expressed in terms of stress state, were compared with the corresponding values taken from Westergaard’s theory and with those obtained by applying another finite-element model, published by the FAA (Federal Aviation Agency), which takes no account of the described dynamic effects

Rumore indotto dalle irregolarità puntuali della superficie stradale

Lo scopo del presente lavoro consiste nella quantificazione del rumore indotto dal passaggio dei veicoli sulle discontinuità puntuali della superficie stradale, mediante l’esecuzione di rilievi fonometrici. In alcuni siti di misura, opportunamente prescelti, sono state individuate dieci diverse irregolarità superficiali macroscopiche, considerate rappresentative delle situazioni più usuali (buche, caditoie, rotaie tranviarie, ecc); per queste discontinuità, sono state anche misurate le dimensioni geometriche, mediante una semplice strumentazione di misura. Le prove fonometriche sono state eseguite tutte con lo stesso veicolo, seguendo lo schema proposto dalla norma UNI 11819/1: “Statistical Pass by Method”. Per ciascuna irregolarità, sono stati effettuati due passaggi a 3 diverse velocità: (40, 50 e 60 km/h); inoltre, per valutare comparativamente l’incremento di rumore determinato dall’irregolarità, sono stati eseguiti ulteriori due passaggi alle stesse velocità su un tratto di pavimentazione non ammalorata adiacente alla buca. Per tutte le prove sono state esaminate le grandezze acustiche caratteristiche nel dominio del tempo (il valore massimo raggiunto dal livello di pressione e la storia temporale del livello di pressione sonora ponderato A). I risultati ottenuti consentono di sviluppare interessanti considerazioni in merito agli incrementi di rumore, in funzione della velocità del veicolo, della tipologia e delle caratteristiche di ciascuna irregolarità esaminata