Bridge Expansion Joint in Road Transition Curve: Effects Assessment on Heavy Vehicles

applied sciences

Article Bridge Expansion Joint in Road Transition Curve: Effects Assessment on Heavy Vehicles

Paola Di Mascio, Giuseppe Loprencipe *, Laura Moretti, Lorenzo Puzzo and Pablo Zoccali Department of Civil, Constructional and Environmental Engineering, Sapienza University of Rome, Via Eudossiana 18, 00184 Rome, Italy; [email protected] (P.D.M.); [email protected] (L.M.); [email protected] (L.P.); [email protected] (P.Z.) * Correspondence: [email protected]; Tel.: +39-064-458-5112

Academic Editor: Zhanping You Received: 11 May 2017; Accepted: 7 June 2017; Published: 9 June 2017

Abstract: Properly-designed road surfaces provide a durable surface on which traffic can pass smoothly and safely. In fact, the main causes that determine the structural decay of the pavement and its parts are the traffic loads. These repeated actions can create undesirable unevennesses on the road surface, which induce vertical accelerations on vehicles, up to hindering contact between pavement and tire, with dangerous consequences on traffic safety. The dynamic actions transmitted by the vehicles depend on these irregularities: often, a bridge expansion joint (BEJ), introducing a necessary discontinuity between different materials, determines from the beginning a geometric irregularity in the running surface. Besides, some structural conditions could emphasize the problem (e.g., local cracking due to the settlement of the subgrade near the abutment or the discontinuity of stiffness due to the presence of different materials). When the BEJ is located in a transition curve, an inevitable vertical irregularity between road and joint can reach values of some centimeters, with serious consequences for the road safety. This paper deals with the analysis of a case study of a BEJ. Several test surveys were performed in order to fully characterize the effects on both vehicles and pavement. The three-dimensional representation of the pavement surface and the acceleration measurements on a heavy test vehicle were performed to analyze the joint behavior under traffic. Finally, a finite element model was implemented to evaluate the stress contribution on vehicle components induced by the vertical irregularities.

Keywords: bridge joint; heavy vehicles; road unevenness; road safety

1. Introduction Highway bridge expansion joints (BEJ) allow vehicles to move between two uncoupled, but even, adjacent road sections. Generally, a road built on a structure needs a longitudinal break to reduce the effects of hygrothermal and/or seismic deformations and tangential stresses due to the traffic. Sometimes, complex structure configurations of a bridge (e.g., arch bridge) permit avoiding BEJs, in addition assuring aesthetic results for the artwork [1]. BEJ should absorb possible displacements of the two parts, ensure bending and shear transmission and guarantee safe traffic circulation in every condition (dry, wet, warm, freeze, etc.) during the service life [2]. Moreover, they should absorb all actions induced by the relative displacements of coupled structures: thermal variations, wheel dynamic vertical loads, braking and other horizontal forces [3]. BEJ presents a planarity problem when the joint is located in a transaction section of the road (transition curve-clothoid) between two consequent road elements with different curvatures. In fact, in this section, the road transversal slope is changing between the values necessary in two adjacent elements with different horizontal curvatures. Consequently, in this transitional area, the road pavement is characterized by a skew or slanted surface (Figure1) and, if the joint is large

Appl. Sci. 2017, 7, 599; doi:10.3390/app7060599 www.mdpi.com/journal/applsci Appl. Sci. 2017, 7, 599 2 of 21 Appl. Sci. 2017, 7, 599 2 of 20

(e.g.,is characterized a highway by seismic a skew joint), or slanted the vertical surface irregularity(Figure 1) and, between if the joint road is and larg jointe (e.g., can a highway reach values seismic of somejoint), centimeters.the vertical irregularity between road and joint can reach values of some centimeters. This undesirableundesirable local local irregularity irregularity in additionin addition to the to construction the construction unevenness unevenness can cause can important cause important dynamic actions on running vehicles, the bridge structure and joints [4,5]. dynamic actions on running vehicles, the bridge structure and joints [4,5].

CROSS SLOPE 2

CROSS SLOPE 1 BEJ

IRREGULARITY

BEJ DIMENSION

Figure 1. IrregularityIrregularity between bridge expansion joint (BEJ) and the road inin a transition curve.

In this case, dynamic actions induced by vehicle tires stress BEJ. Traffic Traffic runningrunning onon bridgesbridges produces a stressstress spectrum,spectrum, whichwhich maymay causecause fatigue.fatigue. The stress spectrum depends on various parameters: thethe geometry geometry of theof vehicles,the vehicles, the axle the loads, axle the loads, vehicle the spacing, vehicle superficial spacing, characteristics superficial ofcharacteristics the pavement of (unevenness)the pavement [ 6(unevenness)], the composition [6], the of composition the traffic and of itsthe dynamic traffic and effects. its dynamic Several repetitionseffects. Several of these repetitions dynamic of loads these during dynamic the loads design during life of the pavementdesign life can of the cause pavement a rapid andcan generalcause a decayrapid and of the general structure decay or localof the breaks structure in correspondence or local breaks with in correspondence the BEJ, although with well-constructed the BEJ, although [7]. Awell-constructed BEJ is anyhow [7]. a discontinuity A BEJ is anyhow of the a disconti pavement,nuity and of dynamicthe pavement, actions and caused dynamic by heavyactions vehicles caused runningby heavy on vehicles it cannot running be overlooked. on it cannot For be thisoverlooked. reason, inFor Eurocode this reason, 1 [8 in], whereEurocode traffic 1 [8], loads where on bridgestraffic loads are described, on bridges it isare specified described, that init theis specified proximity that of expansion in the proximity joints, an of additional expansion dynamic joints, amplificationan additional factordynamic should amplification be applied. factor In this should sense, be the applied. same Eurocode In this sense, also the suggests same aEurocode conservative also simplificationsuggests a conservative consisting simplification of adopting an consisting amplification of adopting factor of an 1.3 amplification for any cross factor section of within1.3 for 6any m fromcross thesection expansion within joint.6 m from the expansion joint. Following specificspecific recommendations for the fatigue de designsign of modular bridge expansion joints [7], [7], it is possible to to avoid avoid BEJs’ BEJs’ durability durability problems. problems. In In any any case, case, the the unevenness unevenness induced induced by by the the presence presence of ofa BEJ a BEJ still still remains, remains, and and in certain in certain conditions conditions (i.e., (i.e., BEJ BEJlocated located in road in road transition transition curve), curve), it can it worsen. can worsen. In particular, this paper focuses on the analysisanalysis of thethe detrimentaldetrimental effects induced by BEJ unevenness in terms of road safety, dynamicdynamic incrementincrement of wheelwheel loads transmitted to the pavement and vehicle components’ stress.

2. Heavy Vehicle-Bridge Interaction:Interaction: The Expansion JointJoint RoleRole Moving heavy vehicles apply to roads and bridgesbridges wheel (dynamic) loads, which are higher than nominal (static) loads. Static loads depend on the total weight of the vehicle and itsits geometricgeometric axle conﬁguration,configuration, whereas dynamic wheel forces depend on the road pavement proﬁle,profile, functional characteristics ofof thethe vehicle vehicle (e.g., (e.g., geometry, geometry, mass mass and and stiffness stiffness distribution, distribution, tire andtire suspensionand suspension type, operativetype, operative speed) speed) and structural and structural characteristics characteristics of the bridge of the superstructure bridge superstructure (i.e., span (i.e., length, span geometry, length, staticgeometry, scheme, static natural scheme, frequencies natural frequencies and damping). and damping). Unevennesses due to a road BEJ can produce importantimportant dynamic load increments:increments: this depends on thethe interaction interaction between between running running vehicles vehicles and thean bridged the superstructure,bridge superstruc as wellture, as as the well interactions as the betweeninteractions structural between components structural components and vehicles and [9]. vehi Figurecles2 [9].shows Figure the 2 dynamic shows the interaction dynamic (coupling)interaction between(coupling) vehicle between and vehi bridgecle and [10]. bridge [10]. Appl. Sci. 2017, 7, 599 3 of 21 Appl. Sci. 2017, 7, 599 3 of 20

Initial Surface Dynamic Surface Roughness Vehicle + Roughness + (Input to the vehicle) Dynamics Force

Dynamic Bridge Bridge Dynamic Tyre Deflection Dynamics

FigureFigure 2. Schematic 2. Schematic block block diagram diagram of of dynamic dynamic bridge-vehicle interaction. interaction.

The roughnessThe roughness input input to theto the vehicle vehicle is is the the sum sum of of thethe initial surface surface profile profile of ofthe the pavement pavement and and the dynamic deflection of the bridge. This input excites the vehicle and results in dynamic tire forces. the dynamic deflection of the bridge. This input excites the vehicle and results in dynamic tire forces. Finally, these forces are in turn applied to the bridge and cause larger dynamic displacements of Finally,the these bridge forces [11]. are in turn applied to the bridge and cause larger dynamic displacements of the bridge [11].The largest bridge vibration occurs when the bridge’s and vehicle’s natural frequencies are Thesimilar largest [12]. bridgeIt is notvibration clear, however, occurs if whenlarge bridge the bridge’s responses and are vehicle’smainly due natural to excitation frequencies of the are similarvehicle [12]. Itcaused is not by clear, the initial however, roughness if large profile, bridge or responses by the dynamic are mainly deflection due of to the excitation bridge. There of the was vehicle causedlittle by systematic the initial study roughness concerning profile, the orconditions by thedynamic when dynamic deflection interaction of the is bridge.important There and waswhen little systematicthe two study systems concerning may be regarded the conditions as essentially when uncoupled. dynamic interaction is important and when the two ≅ systems mayAccording be regarded to Cantieni as essentially [13], bridges uncoupled. with a fundamental natural frequency f 2.5–4 Hz ≅ According(maximum to span Cantieni L 25–40 [13], bridgesm) are more with asusceptible fundamental to the natural dynamic frequency actions fof=∼ heavy2.5–4 commercial Hz (maximum vehicles (equipped with steel leaf suspensions) than bridges with a fundamental frequency lying span L =∼ 25–40 m) are more susceptible to the dynamic actions of heavy commercial vehicles (equipped outside this range. This difference is because the wheel loads of such vehicles have a predominant with steelfrequency leaf suspensions)content in the same than range bridges [13]. with This aeffect fundamental is known as frequency “frequency-matching”: lying outside it leads this range.to This differencedynamic amplification is because the of the wheel corresponding loads of such strong vehicles dynamic have bridge a predominant response, a frequencyphenomenon content also in the sameknown range as “quasi-resonance”. [13]. This effect is known as “frequency-matching”: it leads to dynamic amplification of the correspondingThe DIVINE strong (Dynamic dynamic Interaction bridge response,between Vehicles a phenomenon and Infrastructure also known Experiment) as “quasi-resonance”. research The[14]DIVINE correlated (Dynamic the dynamic Interaction bridge response between under Vehicles traffic and to the Infrastructure length-span bridge: Experiment) research [14] correlated1. Long-span the dynamic element bridge of bridges response (L > under 100 m): traffic The type to the of vehicle length-span suspension bridge: is not very significant unless the road profile is poor. Furthermore, the fundamental frequency of bridges is less than 1. Long-spanthat of elementheavy vehicles, of bridges and (thus,L > 100 these m): bridges The type tend of to vehicle attenuate suspension the dynamic is not components very significant of unlesswheel the roadforces. profile is poor. Furthermore, the fundamental frequency of bridges is less than that2. ofMedium-span heavy vehicles, bridges and (L thus, ≅ 30–100 these m): bridges Frequency-matching tend to attenuate with the the dynamic truck body components bounce of wheelfrequencies forces. occurs in medium-span bridges. The experimental dynamic responses were well 2. Medium-spanwithin code bridges recommendations (L =∼ 30–100 for high-quality m): Frequency-matching road profiles. with the truck body bounce ≅ frequencies3. Short to occursmedium-span in medium-span bridges (L bridges. 15–30 m): The Bridges experimental with natural dynamic frequencies responses within the were range well 4–8 Hz tend not to dynamically couple with vehicles at either body bounce or axle-hop frequencies, within code recommendations for high-quality road profiles. respectively characterized by frequency∼ within the range of 1.5–4.0 and 8.0–15.0 Hz [15]. 3. Short4. Short-span to medium-span bridges (L bridges≅ 8–15 m): (L “Quasi-resonance”,= 15–30 m): Bridges but with with minimal natural amplification, frequencies occurs within the rangebetween 4–8 short-span Hz tend bridges not to and dynamically the axle-hop couplevibrations with of heavy vehicles vehicles. at either The effects body of bounce body or axle-hopbounce frequencies, are also transmitted respectively to short-span characterized bridges by with frequency minimal within amplification. the range The of dynamic 1.5–4.0 and 8.0–15.0response Hz [ 15of ].short span bridges can be much larger than expected for dynamic effects. ∼ 4. Short-spanThe DIVINE bridges research (L = 8–15 has m):shown “Quasi-resonance”, that road profile, butbridge with natural minimal frequency amplification, and bridge occurs betweendamping short-spanare important bridges elements and to the be axle-hopcontrolled. vibrations Road profile of measurement heavy vehicles. is now The routine, effects ofand body bouncesignal processing are also transmittedtechnologies are to relatively short-span stra bridgesightforward. with The minimal DIVINE amplification. project also demonstrated The dynamic responsethat dynamic of short vehicle span models bridges can accurately can be much repr largeroduce dynamic than expected wheel forces, for dynamic and many effects. researchers have demonstrated that the bridge/vehicle interaction problem can be analytically solved [12]. Some Thetools DIVINE permit researchdeveloping has and shown validating that road bridge profile, models bridge including natural both frequency road profile and bridge and bridge damping are importantnatural frequency elements [16]. to be controlled. Road profile measurement is now routine, and signal processing technologies are relatively straightforward. The DIVINE project also demonstrated that dynamic vehicle models can accurately reproduce dynamic wheel forces, and many researchers have demonstrated that the bridge/vehicle interaction problem can be analytically solved [12]. Some tools permit developing and validating bridge models including both road profile and bridge natural frequency [16]. Appl. Sci. 2017, 7, 599 4 of 21

The model proposed by Green and Cebon [10] consists of a single degree of freedom vehicle on a simply-supported bridge. It does not detail the nonlinearities of vehicle suspensions and the complexities of sprung mass motion, but it ensures a good representation of the problem. Cantieni [13] and Tan et al. [17] elaborated multiple-degree-of-freedom models to describe dynamic bridge-vehicle interaction and found good agreement with experiments carried out on highway bridges. In these approaches, road unevenness is modeled by artificial profiles that simulate the desired roughness level [18]. Green and Cebon [10] performed a parametric study based on previously literature works [19–21] and using the model proposed by Cantieni [13]. The results of this study permit ascertaining when coupling is important and when it can be ignored. For highway bridges, the most important parameters are speed, frequency and initial vehicle excitation. Moreover, vehicle suspensions are important in determining the dynamic response of bridges under a single vehicle, as demonstrated both by the DIVINE results and by Woodrooffe et al. [22]. Different suspension systems induce different dynamic loads on roads (i.e., amplitude and frequency content). For example, for roads in fair condition and at a speed of 80 km/h, the dynamic load induced by a truck fitted with airbag suspension is about 60% of the dynamic load induced by the same truck, but fitted with steel multi-leaf suspension [22]. This paper presents a case study of a highway BEJ with a big unevenness due to the torsion of the cross-section along a transition curve. After five years of service life, it had partial breaks and superficial cracks in the head cross beam where it was located. Asphalt pavement before and after the BEJ was affected by severe distresses (e.g., cracking and rutting). Indeed, the impulsive vibrating actions of the heaviest and quickest vehicles produced a surface wear of the joint so important that its service condition was very unsafe. The geometric configuration of the road section is such that the allowable vehicle speed is quite high, and the concomitant presence of the joint determined the cause of many accidents, even serious ones, which have affected both light and heavy vehicles [23]. The irregular circulation induced by the BEJ was causing hard braking and acceleration, which have environmental effects [24]. Moreover, the condition of the BEJ had required several maintenance works during its even short service life. The present work focuses on the geometric characterization of the BEJ and on the assessment of the effects on road traffic, with particular attention to heavy vehicles running on it. Specifically, safety and comfort analyses were carried out, evaluating also the dynamic increment of loads transmitted to the pavement (and then to the bridge) and the stress magnitude on vehicles’ mechanical components. The importance of these analyses is that the interpretation of their results is useful to identify strategies and procedures for policies to guarantee minimum safety levels at roads.

3. Methodology and Case of Study The study of the bridge-vehicle interaction requires measuring and analytical treatment of the road profile and the dynamic wheel forces applied to the investigated BEJ. The profile analysis allows evaluating general ride characteristics referring to standards, comfort and safety [25] and choosing pavement sections where the warning values of the previous evaluation are reached and maintenance works needed [26–29]. The evenness properties of the road pavement profile can be measured using three different methodologies:

• Topographic equipment: the rod and level are surveying tools used to represent the three-dimensional pavement surface. • Inclinometer-based proﬁling systems: they create a reference plan to measure the relative slope during the equipment movement (Dipstick developed by The Face Companies, USA, “CHLOE” proﬁlometer, a device developed at the road test for determination of the slope variance on pavements, USA) [30]. Appl. Sci. 2017, 7, 599 5 of 21

• Inertial proﬁlometer: this equipment uses an internal inertial reference system (e.g., Longitudinal Proﬁle Analyzer “APL” developed by French Road Research Laboratory, Automatic Road Analyzer “ARAN” developed by Fugro Roadware, Mississauga, Canada, etc.) [30].

TheAppl. Sci. acceleration 2017, 7, 599 analysis permits measuring dynamic tire forces and ride quality at5 differentof 20 speeds. Moreover, it permits determining the main vehicle oscillation and vibration components in the The acceleration analysis permits measuring dynamic tire forces and ride quality at different frequency domain and comparing them to the first bridge’s natural frequency. This kind of analysis speeds. Moreover, it permits determining the main vehicle oscillation and vibration components in can be performed by means of in situ measurements [31] and simulation models [32]: both approaches the frequency domain and comparing them to the first bridge’s natural frequency. This kind of wereanalysis used in can the be present performed study. by means of in situ measurements [31] and simulation models [32]: both approaches were used in the present study. 3.1. Case Study: An Unevenness Bridge Joint The3.1. Case case Study: study An refers Unevenness to a steel Bridge girder Joint bridge characterized by a 50 m-long span (medium-span bridge). AccordingThe case study to experimentalrefers to a steel resultsgirder bridge published characterized by Kim by et a al. 50 [ 12m-long] for aspan span (medium-span equal to 40.4 m, for thisbridge). type According of bridge, to the experimental fundamental results natural published frequencies by Kim ofet theal. [12] first for bending a span equal and torsionto 40.4 m, modes (respectivelyfor this type 2.33 of and bridge, 3.86 the Hz) fundamental are within natural the characteristic frequencies frequencyof the first bending range of and heavy torsion vehicles’ modes body bounce(respectively (1.5–4.0 Hz). 2.33 and For 3.86 this Hz) reason, are within it is important the characteristic to avoid frequency the presence range of of heavy localized vehicles’ irregularities body that couldbounce increase (1.5–4.0 theHz). loads For this transmitted reason, it tois importan the bridget to structure avoid the during presence the of passages localized ofirregularities heavy vehicles that could increase the loads transmitted to the bridge structure during the passages of heavy on the bridge structure. Furthermore, the examined highway carries a high percentage of daily vehicles on the bridge structure. Furthermore, the examined highway carries a high percentage of heavydaily vehicle heavy traffic vehicle (Table traffic1), (Table whose 1), effective whose effect travelingive traveling speed wasspeed found was found to be withinto be within the range the of 80–120range km/h. of 80–120 km/h.

TableTable 1. 1.Examined Examined road traffic trafﬁc features. features.

Type of RoadType of SpeedSpeed Range Range (km/h) Average Average Daily Daily Traffic Trafﬁc (ADT)% of % Heavy of Heavy Vehicles Road (km/h) (ADT) Vehicles Highway 80–120 20,500 20 Highway 80–120 20500 20

In theIn lastthe last ﬁve five years, years, an an accident accident rate rate higher higher than the the national national average average value value [33] [ 33was] wasfound found for for the examinedthe examined Italian Italian highway. highway. Many Many accidents were were localized localized in correspondence in correspondence to a bridge to a bridgeand, in and, particular, near one of the BEJs present in this area. After a brief in situ inspection, it was found that in particular, near one of the BEJs present in this area. After a brief in situ inspection, it was found that a reduction of the contact area between vehicles’ tires and pavement took place in many cases a reduction of the contact area between vehicles’ tires and pavement took place in many cases during during the passage on this BEJ, and sometimes, there was a complete loss of contact, as shown in the passageFigure 3. on this BEJ, and sometimes, there was a complete loss of contact, as shown in Figure3. As aAs consequence a consequence of theseof these issues, issues, additional additional in situ measurements measurements were were carried carried out outto evaluate to evaluate the detrimentalthe detrimental effects effects on on the the bridge bridge structure, structure, pavement,pavement, passengers passengers and and vehicles vehicles induced induced by the by the peculiarpeculiar geometry geometry of theof the BEJ. BEJ.

FigureFigure 3. Loss 3. Loss of of tire/pavement tire/pavement contact during during the the passage passage on onthe theBEJ. BEJ.

Appl. Sci. 2017, 7, 599 6 of 21 Appl. Sci. 2017, 7, 599 6 of 20

Furthermore, the surface pavement surrounding thethe BEJ presented several distresses, caused by the dynamic load increment ofof roadroad vehiclesvehicles (Figure(Figure4 4).).

Figure 4. Pavement condition of the area surrounding the BEJ.

3.2. In Situ Test and Equipment The following tests were performed on the highway section including the joint: The following tests were performed on the highway section including the joint: 1. Precision geometric-topographic measurements, along with about 500 m-long branch: The survey 1. wasPrecision made geometric-topographic using a precision theodolite measurements, (total station) along with and about a rod, 500 assuming m-long branch: the carriageway The survey markingswas made as using the edges a precision of the surveying theodolite area. (total The station) coordinate and reference a rod, assuming system was the carriagewayrelative; just themarkings elevations as the were edges linked of the to the surveying absolute area. system. The coordinateIn the area referenceclosest to systemthe joint, was a 1 relative; × 1 m mesh just × sizethe elevationswas considered, were linked while toin thethe absolute other distant system. zones, In the 3 m area × 3 closest m and to 10 the m joint,× 10 m a 1meshes1 m meshwere × × created.size was considered,This discretization while in theallowed other distantperforming zones, the 3 mglobal3 m layout and 10 mof the10 mplatform meshes wereand, particularly,created. This the discretization carriageway allowed markings performing and the theroad global edges. layout of the platform and, particularly, 2. Evaluationthe carriageway of dynamic markings action and due the to road the edges.joint, with accelerometers installed on a heavy vehicle 2. test:Evaluation The measured of dynamic accelerations action due were to theanalyzed joint, within the accelerometers time and frequency installed domains. on a heavy In particular, vehicle thetest: equipment The measured used accelerations was composed were of: analyzed in the time and frequency domains. In particular, the equipment used was composed of: • Three-axle heavy vehicle, with an overall empty load equal to 16.04 t (P1 = 3.208 t; • P2Three-axle = P3 = 6.416 heavy t; see vehicle, Figure 5); with an overall empty load equal to 16.04 t (P1 = 3.208 t; • ThreeP2 = P3 concrete = 6.416 blocks t; see Figurewhose5 weights); were, respectively, 1.82 (C1), 2.04 (C2) and 2.18 t (C3); • • SevenThree concretepiezoelectric blocks accelerometers: whose weights 4 were,accelero respectively,meters with 1.82 a (C1),bottom 2.04 scale (C2) ±50 and g 2.18 (Type t (C3); A) • andSeven 3 with piezoelectric a minimum accelerometers: full-scale range 4 accelerometers of ±20 g (Type with B). a The bottom Type scale B accelerometers±50 g (Type A) were and located3 with a on minimum the right full-scale end of the range axles of connected±20 g (Type to B). the The vehicle Type frame, B accelerometers while three were of the located four Typeon the A rightaccelerometers end of the were axles placed connected one toon the each vehicle vehicle frame, axle. whileThe last three Type of A the accelerometer four Type A wasaccelerometers located on werethe left placed side oneof the on eachfront vehicleaxle to axle. control The the last possible Type A accelerometerasymmetry of wasthe transversallocated on theacceleration left side of distribution. the front axle to control the possible asymmetry of the transversal acceleration distribution. Appl. Sci. 2017, 7, 599 7 of 21 Appl. Sci. 2017, 7, 599 7 of 20

FigureFigure 5. 5. GeometricGeometric (in (in cm) cm) and and load load characteristics characteristics of of the the test test vehicle. vehicle.

Inside the vehicle cab, a signal control exchange and a PC were located to record and verify Inside the vehicle cab, a signal control exchange and a PC were located to record and verify collected data and to re-calibrate the equipment if necessary. collected data and to re-calibrate the equipment if necessary. Four different loading conditions were considered to examine the phenomenon. They represent Four different loading conditions were considered to examine the phenomenon. They represent various heavy vehicle configurations (Table 2) and various dynamic increments, because the various heavy vehicle conﬁgurations (Table2) and various dynamic increments, because the phenomenon is sensitive to both the speed and load condition of heavy vehicles, as reported by phenomenon is sensitive to both the speed and load condition of heavy vehicles, as reported by Lu et al. [34]. The considered speed and load combinations gave to the BEJ energy values comparable Lu et al. [34]. The considered speed and load combinations gave to the BEJ energy values comparable to those reached on the structure under real service conditions. to those reached on the structure under real service conditions. Table 2. Considered load-speed combinations. Table 2. Considered load-speed combinations. Test Number Speed (km/h) Speed (m/s) Load Blocks Total Load (t) Test Number1 Speed 107 (km/h) Speed 29.72 (m/s) C1, C2 Load and Blocks C3 Total 22.08 Load (t) 21 84107 23.33 29.72 C1, C1,C2 C2and and C3 C3 22.08 22.08 32 103 84 28.61 23.33 C1,C3 C2 and C318.22 22.08 3 103 28.61 C3 18.22 44 85 85 23.61 23.61 C3 C318.22 18.22

3.3. 3D Finite Element Model 3.3. 3D Finite Element Model In addition to the in situ measurements, a simulation model was implemented. In particular, In addition to the in situ measurements, a simulation model was implemented. In particular, a 3D a 3D model of the asphalt concrete pavement and the seismic BEJ was developed using LS-DYNA. model of the asphalt concrete pavement and the seismic BEJ was developed using LS-DYNA. It allowed It allowed evaluating the stress magnitude on the test heavy vehicle mechanical components (Figure 6) evaluating the stress magnitude on the test heavy vehicle mechanical components (Figure6) due to due to the vertical irregularity that characterizes the BEJ. For this reason, the vehicle is modeled in the vertical irregularity that characterizes the BEJ. For this reason, the vehicle is modeled in detail, detail, while for the BEJ, a simple geometry, able to describe the unevenness, was considered. while for the BEJ, a simple geometry, able to describe the unevenness, was considered. In addition, In addition, only the concrete slab was modeled to reduce the computational burden, its bottom only the concrete slab was modeled to reduce the computational burden, its bottom surface being surface being fully constrained. fully constrained. Appl. Sci. 2017, 7, 599 8 of 20 Appl. Sci. 2017,, 7,, 599 599 8 of 20 21 Appl. Sci. 2017, 7, 599 8 of 20

Figure 6. LS-DYNA 3D model. Figure 6. LS-DYNA 3D model. The pavement is a three-layer (two asphalt concrete and one cement concrete) 22.4 m long and The pavement is a three-layer (two asphalt concrete and one cement concrete) 22.4 m long and 4 m-wideThe pavementmodel. The is BEJ a three-layer is located (twoat the asphalt middle concreteconcre of thete strip and (Figure one cement 7), where concrete) there 22.4 is a m 0.8-m long hole and 4 m-wide model. The BEJ is located at the middle of the strip (Figure 7), where there is a 0.8-m hole in4 m-wide the lower model.model. layer, TheThe while BEJBEJ istheis locatedlocated two upper atat the the layers middle middle are of of theinterrupted the strip strip (Figure (Figure by 7the), 7), where BEJ where (2.00 there there m is long). ais 0.8-m a 0.8-m The hole jointhole in in the lower layer, while the two upper layers are interrupted by the BEJ (2.00 m long). The joint surfacethein the lower lower is 3 layer, cm layer, lower while while than the twothethe two upperrolling upper layerssurface, layers are thus interrupted are the interrupted upper by pavement the by BEJ the (2.00 layersBEJ m (2.00 long).have m a The long).transition joint The surface zonejoint surface is 3 cm lower than the rolling surface, thus the upper pavement layers have a transition zone ofissurface 31.60 cm lowerism 3before cm than lower and the than rollingafter the the surface, rolling joint thussurface,to reach the upperthus the the appropriate pavement upper pavement layers height. have layers The a transition pavement/joint have a transition zone of model 1.60 zone m of 1.60 m before and after the joint to reach the appropriate height. The pavement/joint model consistsbeforeof 1.60 and mof afterbefore15540 the and8-node joint after to brick reach the joint the(solid) appropriate to elements.reach the height. Mechanicalappropriate The pavement/joint characteristics height. The modelpavement/joint of the consists materials of model 15,540 are consists of 15540 8-node brick (solid) elements. Mechanical characteristics of the materials are linear-elastic8-nodeconsists brickof 15540 for (solid) the 8-node bottom elements. brick layer Mechanical (solid)(concrete elements. slab-structure) characteristics Mechanical and of the viscoelasticcharacteristics materials for are theof linear-elastic twothe uppermaterials layers. for theare linear-elastic for the bottom layer (concrete slab-structure) and viscoelastic for the two upper layers. bottomlinear-elastic layer (concretefor the bottom slab-structure) layer (concrete and viscoelastic slab-structure) for the and two viscoelastic upper layers. for the two upper layers.

Figure 7. Pavement and BEJ model (detail of the BEJ zone). Figure 7. Pavement and BEJ model (detail of the BEJ zone). Figure 7. Pavement and BEJ model (detail of the BEJ zone). With respect to the boundary conditions adopted in the model, the horizontal displacements on the sidesWith ofrespect the model to to the the boundarywere boundary restrained conditions conditions to repres adopt adoptedented inthe in the theconfinement model, model, the the horizontaldue horizontal to the displacements presence displacements of the on surroundingtheon thesides sides of oftheportion the model model of pavement.were were restrained restrained toto repres representent the the confinement conﬁnement due due to to the the presence presence of the surroundingThe test portionvehicle ofmodel pavement. (Figure 8) was initially built to perform roadside hardware crash test simulationsThe test [35–37]. vehicle It model is the (FigureIVECO 8 8))FIAT waswas 180 initiallyinitially NC, builtIVECObuilt toto perform(Groupperform CNH roadsideroadside Industrial), hardwarehardware Torino, crashcrash Italy, testtest 4-axlesimulations heavy [ [35–37].35goods–37]. vehicle, ItIt is is the the with IVECO IVECO a net FIAT FIATmass 180 of180 NC, 10,560 NC IVECO, kgIVECO and (Group a (Group total CNH mass CNH Industrial), of aboutIndustrial), 30,000 Torino, Torino,kg. Italy, Its model 4-axleItaly, consists4-axleheavy heavy goods of about goods vehicle, 12,000 vehicle, with shell, with a net150 a mass solidnet mass and of 10,560 of100 10,560 beam kg andkg elements and a total a total (in mass total,mass of aboutof about about 15,000 30,000 30,000 elements). kg. kg. ItsIts modelmodel consists of about 12,000 shell, 150 solid andand 100100 beambeam elementselements (in(in total,total, aboutabout 15,00015,000 elements).elements).

Figure 8. FE model of the 30-ton truck. Figure 8. FE model of the 30-ton truck. Figure 8. FE model of the 30-ton truck. Appl. Sci. 2017, 7, 599 9 of 21 Appl.Appl. Sci. Sci. 2017 2017, ,7 7, ,599 599 99 of of 20 20

TheThe whole whole suspension suspension system system of of the the vehicle vehicle te testtestst was was modeled modeled to to reproduce reproduce the the dynamic dynamic effects effects andand the the vehicle vehicle behavior behavior during during the the test, test, as as shown shown in in Figure Figure 99. 9.. The The reference reference trucktruck hashas anan oldold typetype ofof suspensionsuspension (leaf (leaf(leaf springs), springs),springs), with withwith elastic elasticelastic steel steelsteel beam beamsbeamss packed packedpacked over overover each eacheach axle, axle,axle, and andand hydraulic hydraulic dampers. dampers.

FigureFigure 9. 9. Detail Detail of of the the rear rear suspension suspension system. system.

These elements were reproduced with a variable thickness shell beam, while the axles are steel These elements were reproduced with a variablevariable thickness shell beam, while the axles are steelsteel beams. The main parts of the vehicle’s structure have an elastic-plastic behavior. The loads are beams. The The main main parts of the vehicle’s structure havehave anan elastic-plasticelastic-plastic behavior.behavior. The loads are accurately transferred to the pavement because this vehicle is equipped with inflated tires and accurately transferredtransferred to to the the pavement pavement because because this this vehicle vehicle is equipped is equipped with inﬂatedwith inflated tires and tires rolling and rolling wheels, as shown in Figure 10. A contact surface with a Coulomb-like friction ensures the wheels,rolling wheels, as shown as inshown Figure in 10 Figure. A contact 10. A surfacecontact with surface a Coulomb-like with a Coulomb-like friction ensures friction the ensures interface the interface between the two bodies (tire-rubber and pavement). betweeninterface thebetween two bodies the two (tire-rubber bodies (tire-rubber and pavement). and pavement).

((aa)()(bb))

FigureFigure 10. 10.10. Pneumatic Pneumatic tire tire components components adopted adopted in in ( (aa)) the the vehicle vehicle model model and and ( (bb)) the thethe tire tiretire model modelmodel front frontfront sectionsection during duringduring a aa general generalgeneral time timetime step. step.step.

The model was validated and then used to calculate the stress, strain and acceleration of each The model was validatedvalidated and then used toto calculatecalculate the stress,stress, strainstrain andand accelerationacceleration of eacheach element of the pavement, joint and vehicle. These data are useful, for example, to verify the fatigue element of the pavement,pavement, joint and vehicle.vehicle. These datadata are useful, for example, to verify thethe fatiguefatigue damage of the vehicle structure, estimating the effects of an uneven surface as the BEJ examined. damage of thethe vehiclevehicle structure,structure, estimatingestimating thethe effectseffects ofof anan unevenuneven surfacesurface asas thethe BEJBEJ examined.examined. 3.4. Front and Rear Axle Quarter Car Model 3.4. Front and Rear Axle Quarter Car Model The linear quarter-truck model (Figure 11a) described in [32] was implemented in MATLAB to The linear quarter-truck model (Figure 1111a)a) describeddescribed in [[32]32] was implementedimplemented in MATLAB toto estimate the dynamic load increment induced by the BEJ at several speeds. The basic equations of estimate the dynamic load increment induced by thethe BEJBEJ atat severalseveral speeds.speeds. The basicbasic equationsequations of motion for the examined model are (1) and (2): motion for thethe examinedexamined modelmodel areare (1)(1) andand (2):(2):

.. . . mmuxxu ===ccs((xxs−−−xxu))−−−((kks +++kkt))xxu +++kksxxs +++kktuu,, (1) (1) muuxuu css (xss xuu ) (kss ktt )xuu kss xss kttu , (1) Appl. Sci. 2017, 7, 599 10 of 20

Appl. Sci. 2017, 7, 599 = − + − 10 of 21 ms xs cs (xu xs ) ks (xu xs ) . (2)

.. . . where mu is the unsprung mass, ms is the sprung mass, ks is the suspension spring constant, msxs = cs(xu − xs) + ks(xu − xs). (2)

kt is the tire spring constant, cs is the suspension viscous damping constant, xu is the vertical where mu is the unsprung mass, ms is the sprung mass, ks is the suspension spring constant, kt is the tiredisplacement spring constant, of the unsprungcs is the suspension mass, xs viscous is the vertical damping displacement constant, x ofu isthe the sprung vertical mass, displacement xs is the . of the unsprung mass, xs is the vertical displacement of the sprung mass, xs is the time derivative of time derivative of vertical displacement of the. sprung mass in m, xu is the time derivative of vertical displacement of the sprung mass in m, xu is the time derivative of vertical displacement of the ..  ..  unsprungvertical displacement mass, xs is the of accelerationthe unsprung of themass, sprung xs is mass, the accelerationxu is the acceleration of the sprung of the unsprungmass, xu is mass the andaccelerationu is the roadof the proﬁle unsprung elevations. mass and u is the road profile elevations. ThisThis mathematicalmathematical modelmodel waswas formulatedformulated inin thethe formform ofof statestate equations.equations. TheThe generalgeneral formform ofof thethe statestate modelmodel forfor aa linearlinear dynamicdynamic systemsystem isis reportedreported inin EquationsEquations (3)(3) andand (4):(4): .  = + x x= AxAx+ BuBu,, (3)(3)

y y==CxCx++DuDu,, (4)(4) wherewhere AAis is the the state state matrix, matrix,B theB the input input matrix, matrix,C the C output the output matrix, matrix,D the directD the transmissiondirect transmission matrix, xmatrix,is the statex is vectorthe state and vectoru and yandare, u respectively, and y are, therespectively, input (proﬁle the elevations)input (profile and elevations) the output (reactionand the forces)output vectors(reaction (Figure forces) 11 vectorsb). (Figure 11b).

 0 1 0 0  V − − x  ks cs ks cs  mS s =  ms ms ms ms  A   c 0 0 0 1 ks s  k c − ()k + k − c   s s s t s   mu mu mu mu 

m u xu = []  0  C 0 0 kt 0   k 0 = []− t   D k u B = t  0  = [] x xs xs xu xu y kt   m  u = []u  u  (a) (b)

FigureFigure 11.11. SchemeScheme ofof ((aa)) thethe quarter-truckquarter-truck modelmodel andand ((bb)) thethe matricesmatrices usedused inin thethe state-spacestate-space modelmodel inin MATLAB.MATLAB.

The mechanical parameters of the front and rear axles used in the model are consistent with the The mechanical parameters of the front and rear axles used in the model are consistent with the data provided in [30] (Table 3). data provided in [30] (Table3).

Table 3. Mechanical parameters of the quarter-truck model [32]. Table 3. Mechanical parameters of the quarter-truck model [32]. Parameter Value Parameter1350 Value kg (front) ms (sprung mass) 13501470 kgkg (front)(rear) m (sprung mass) s 1470335 kg kg (front) (rear) mu (unsprung mass) 335450 kgkg (front)(rear) m (unsprung mass) u 270450 kN/m kg (rear) (front) ks (suspension spring constant) 660 kN/m (rear, steel) 270 kN/m (front) k (suspension spring constant) s kt (tire spring constant) 760660 kN/m kN/m (standard (rear, steel) radial) 16.8 kN s/m (front) cs (suspensionkt (tire spring viscous constant) damping constant) 760 kN/m (standard radial) 89.0 kN s/m (rear) 16.8 kN s/m (front) cs (suspension viscous damping constant) 89.0 kN s/m (rear) Appl. Sci. 2017, 7, 599 11 of 21

Appl. Sci. 2017, 7, 599 11 of 20

Appl.According Sci. 2017, 7, 599 to Equation (5), the dynamic load coefﬁcient (DLC) was calculated to characterize11 of 20 the According to Equation (5), the dynamic load coefficient (DLC) was calculated to characterize magnitude of dynamic tire forces [9]: the magnitudeAccording of to dynamic Equation tire (5), forces the dynamic[9]: load coefficient (DLC) was calculated to characterize the magnitude of dynamic tire forces [9]: RMS dynamic tire force DLC = RMS dynamic tire force (5) DLC = Static tire force (5) RMSStatic dynamic tire force tire force where RMS is the root mean squareDLC of the= dynamic tire force signal calculated along the road proﬁle,(5) oftenwhere indicated RMS is usingthe root the meanσ notation. square of The theRMS dynamictireStatic force tire tire force (σ) force can signal be calculated calculated by along means the ofroad Equation profile, (6): oftenwhere indicated RMS is theusing root the mean σ notation. square The of theRMS dynamic tire force tire (σ )force can be signal calculated calculated by means along of the Equation road profile, (6): T ZT N often indicated using the σ notation. The2 RMS1 tire force2 (σ) 1can Nbe calculated2 by means of Equation (6): σ 2= 1 f (t) 2dt = 1 f ,2 (6) σ = f (t) dt = ∑ kf , (6) T T N k=1N k T10 N1 k=1 σ 2 = 0 f (t)2 dt = f 2   k , (6) T N k=1 wherewherefk fisk is the the dynamic dynamic tire tireforce forcef(t) f(t) atat timetime tt0 == k × Δ∆t,t ,Δ∆t tisis the the simulation simulation output output time time step step and and T isT is thethe total total simulation simulation time time ((TT == NN × Δ∆t).t). where fk is the dynamic tire force f(t) at time t = k × Δt, Δt is the simulation output time step and T is the total simulation time (T = N × Δt). 4.4. Test Test Results Results and and Discussion Discussion 4. TestTheThe Results geometric-topographic geometric-topographic and Discussion measurements permitte permittedd plotting plotting the the level level curves curves of ofthe the surveyed surveyed pavementpavementThe area,geometric-topographicarea, whichwhich isis characterizedcharacterized measurements by the the presencepermitte presence dof ofplotting three three BEJs the BEJs levelmarked marked curves as as BEJ1,of BEJ1, the BEJ2surveyed BEJ2 and and BEJ3BEJ3pavement (Figure (Figure area, 12 12).). which InIn particular,particular, is characterized three different by the longitudinal longitudinalpresence of alignments,three alignments, BEJs marked highlighted highlighted as BEJ1, in inFigure BEJ2 Figure and12, 12 , werewereBEJ3 examined. examined.(Figure 12). In particular, three different longitudinal alignments, highlighted in Figure 12, were examined. BEJ1 BEJ2 BEJ3 Alignment 1 BEJ1 BEJ2 BEJ3 Alignment 1 Alignment 2 Alignment 3 Alignment 2 Alignment 3

Figure 12. Level curves (in m) of the surveyed road. Figure 12. Level curves (in m) of the surveyed road. Figure 12. Level curves (in m) of the surveyed road. In Figure 13, the location of all three examined BEJs along the alignments is depicted. The most criticalInIn Figure BEJ, Figure close 13 13,, to the thewhich location location many of ofaccidents all all three three were examinedexamined localized, BEJsBEJs is alongBEJ1, whichthe alignments is in a sag issection is depicted. depicted. (Figure The The 13). most most criticalcritical BEJ, BEJ, close close to to whichwhich manymany accidents were were loca localized,lized, is isBEJ1, BEJ1, which which is in is a in sag a sagsection section (Figure (Figure 13). 13). Alignment 1 Alignment 2 Alignment 3 BEJ1 BEJ2 BEJ3 52.0 Alignment 1 Alignment 2 Alignment 3 BEJ1 BEJ2 BEJ3 52.0 51.5

51.5 51.0

51.0 50.5 Elevation (m) Elevation 50.5

Elevation (m) Elevation 50.0

50.0 49.5 0 50 100 150 200 250 300 350 400 450 500 49.5 0 50 100 150 200Distance 250 (m) 300 350 400 450 500 Distance (m) Figure 13. Road longitudinal profiles and the BEJs’ location.

FigureFigure 13. 13.Road Road longitudinallongitudinal profiles proﬁles and the the BEJs’ BEJs’ location. location. Appl. Sci. 2017, 7, 599 12 of 21 Appl. Sci. 2017, 7, 599 12 of 20

In thethe examinedexamined portion portion of of the the road, road, a rotation a rotation of the of carriagewaythe carriageway takes takes place, place, and BEJ1 and is BEJ1 placed is inplaced correspondence in correspondence with the with transition the transition curve, whilecurve, the while other the two other (i.e., two BEJ2 (i.e., and BEJ2 BEJ and 3) are BEJ located 3) are inlocated the circle in the arc. circle Applying arc. Applying a high-pass a high-pass Butterworth Butterworth filter filter with with cut-off cut-off spatial spatial frequency frequency equal equal to 0.05to 0.05 cycles/m cycles/m (wavelength (wavelength of of 20 20 m) m) to to the the three three 500 500 m-long m-long alignments, alignments, itit waswas foundfound thatthat the most significantsignificant irregularitiesirregularities werewere placed placed in in correspondence correspondence to to the the three three BEJs BEJs compared compared to to the the elevations elevations in thein the remaining remaining part part of theof the pavement pavement profiles profiles (Figure (Figure 14). 14).

BEJ1 BEJ2 BEJ3 0.03

0.02

0.01

0.00 0 100 200 300 400 500 Elevation (m) Elevation -0.01

-0.02

-0.03 Distance (m)

Figure 14. Filtered longitudinal proﬁle:profile: Alignment 2.

Moreover, FigureFigure 14 14 shows shows that that the unevennessthe unevenness caused caused by the by expansion the expansion joint in thejoint road in transitionthe road curvetransition (i.e., curve BEJ1) (i.e., is much BEJ1) greateris much than greater the than other the two other BEJs. two For BEJs. this For reason, this reason, further further analyses analyses were speciﬁcallywere specifically carried carried out for out BEJ1 for (FigureBEJ1 (Figure 13). 13). From the inspection survey, the largest pavement deformation was found 25 m after the joint location. Other Other pavement pavement unevenness unevenness characterize characterizedd by by wavelengths wavelengths of ofabout about 15 m 15 occurred m occurred after after the theBEJ1. BEJ1. They They are arelinked linked to the to the dynamic dynamic load load applied applied to tovehicles vehicles bumping bumping on on the the joint joint with with a a speed of 90–110 km/h and and the the principal principal oscillation oscillation frequency frequency of of about about 2 2 Hz Hz (body (body bounce). bounce). The roughness assessment of the survey road section was performedperformed calculating the most worldwide used roughness evaluationevaluation criteriacriteria [[38]:38]: the the International International Roughness Roughness Index Index (IRI). (IRI). This approachapproach [39[39]] is is based based on on a mathematicala mathematical model model (quarter-car), (quarter-car), whose whose mechanical mechanical parameters parameters (also known(also known as golden-car) as golden-car) are listed are listed in Table in 4Table. 4.

Table 4. Golden-car mechanical parameters for the IRI quarter-car model.model. Parameter Value Parameter Value ms (sprung mass) 9000 kg mmus (unsprung(sprung mass) mass) 9000 1350 kgkg ks (suspensionmu (unsprung spring mass) constant) 569.7 1350 kN/m kg ks (suspensionkt (tire spring spring constant) constant) 569.7 5877 kN/mkN/m kt (tire spring constant) 5877 kN/m cs (suspension viscous damping constant) 54 kN s/m cs (suspension viscous damping constant) 54 kN s/m Its calculation is performed using Equation (7): Its calculation is performed using Equation (7): l / v = 1 − ⋅ IRI l/v x x dt (7) Z  s u 1 l 0 . . IRI = xs − xu · dt (7) l 0 Appl. Sci. 2017, 7, 599 13 of 21

Appl. Sci. 2017, 7, 599 . 13 of 20 where l is the length of the profile in km, v is the simulated speed equal to 80 km/h, xs is the time . derivative of vertical displacement of the sprung mass in m and xu is the time derivative of vertical where l is the length of the profile in km, v is the simulated speed equal to 80 km/h, x is the time displacement of the unsprung mass in m. The final value is expressed in slope unitss (e.g., m/km  or mm/m).derivative of vertical displacement of the sprung mass in m and xu is the time derivative of vertical IRIdisplacement was developed of the unsprung in order tomass assess in m. not The only final the value ride qualityis expressed on road in slope pavements, units (e.g., but m/km also other detrimentalor mm/m). effects, such as dynamic load increment (on both vehicle and pavement) induced by road pavementIRI irregularities. was developed The in order algorithm to assess tobe not used only forthe itsride calculation quality on road is provided pavements, in [but40]. also other detrimental effects, such as dynamic load increment (on both vehicle and pavement) induced by The Italian highway road agency requires calculating IRI on a segment of 10 m, admitting in road pavement irregularities. The algorithm to be used for its calculation is provided in [40]. general values lower than 1.8 m/km [38]. In the case of short span bridges and when joints are present The Italian highway road agency requires calculating IRI on a segment of 10 m, admitting in on roadgeneral pavement values lower surface, than IRI 1.8 values m/km until[38]. In 2.5 the m/km case of are short tolerated span bridges [41]. Accordingand when joints to Figure are 15, all examinedpresent on alignments road pavement have IRIsurface, values IRI greater values than until the 2.5 threshold m/km are limit tolerated suggested [41]. byAccording [41] in theto area acrossFigure BEJ1, 15, while all examined close to alignments the other have two BEJsIRI values (i.e., greater BEJ2 and than BEJ3) the threshold and in thelimit remaining suggested by part [41] of the profiles,in the the area IRI across values BEJ1, are lowerwhile close than to the the threshold other two value.BEJs (i.e., The BEJ2 only and exception BEJ3) and is in Alignment the remaining 2 across BEJ3part (IRI =of 3.55the m/km).profiles, Consideringthe IRI values the are significant lower than difference the threshold found value. between The theonly three exception BEJs in is terms of IRIAlignment values, it 2 is across evident BEJ3 that (IRI BEJ1 = 3.55 has m/km). the most Consid criticalering the unevenness. significant difference found between the Severalthree BEJs in insitu terms measurements of IRI values, it is were eviden carriedt that BEJ1 out has to the evaluate most critical the dynamicunevenness. consequences on Several in situ measurements were carried out to evaluate the dynamic consequences on heavy heavy vehicles running on BEJ1. All of the recorded accelerometer signals were made uniform to vehicles running on BEJ1. All of the recorded accelerometer signals were made uniform to a a homogeneous time duration of T = 4.587 s and considering a time sampling equal to 5.6 × 10−4 s (∆t). homogeneous time duration of T = 4.587 s and considering a time sampling equal to 5.6 × 10-4 s (Δt). Thus,Thus, a whole a whole number number of Nof =N 8192= 8192 samples samples waswas registered for for each each signal. signal. In addition, In addition, for all for of all the of the verticalvertical acceleration acceleration measures, measures, the referencethe reference time ttime0 corresponds t0 corresponds to test to vehicle test vehicle transit transit on atransversal on a roadtransversal section located road section at about located 29 m at before about the29 m BEJ. before the BEJ.

Alignment 1 Alignment 2 Alignment 3 IRI threshold BEJ1 BEJ2 BEJ3 12

6 IRI (m/km) 4

0 0 50 100 150 200 250 300 350 400 450 500 Distance (m)

FigureFigure 15. International15. International roughness roughness index index (IRI)(IRI) values values calculated calculated on on a segment a segment of 10 of m. 10 m.

Table 5 shows the time of the three axles’ passages on the joint for each loading test, captured by Tablemeans5 ofshows a high the frame time rate of camera. the three axles’ passages on the joint for each loading test, captured by means of a high frame rate camera. Table 5. Time of bump between axles and joint. Table 5. Time of bump between axles and joint. Test Number t1 (s) t2 (s) t3 (s) 1 0.999 1.184 1.230 Test Number 2 t1 (s) 1.273 1.509t2 (s) 1.567 t3 (s) 13 0.999 1.038 1.231 1.184 1.278 1.230 24 1.273 1.258 1.491 1.509 1.549 1.567 3 1.038 1.231 1.278 4 1.258 1.491 1.549 Appl. Sci. 2017, 7, 599 14 of 21

Appl. Sci. 2017, 7, 599 14 of 20 FigureAppl. Sci. 162017 shows, 7, 599 the recorded accelerometer signals provided by the accelerometers on14 theof 20 front, Figure 16 shows the recorded accelerometer signals provided by the accelerometers on the medium and rear axles (number of tests = 1), with the indication of the three bump axle times. Positive front,Figure medium 16 andshows rear the axles recorded (number accelerometer of tests = 1), withsignals the providedindication by of the threeaccelerometers bump axle on times. the peakPositivefront, values medium peak higher values and than rear higher 1 axles g werethan (number 1 foundg were of tests forfound all= 1),for of with all the of the testthe indication test vehicle’s vehicle’s of axles,the axles, three conﬁrmingconfirming bump axle the thetimes. loss loss of tire/pavementofPositive tire/pavement peak contact values contact due higher todue thethan to passagethe 1 g passage were on found on BEJ1. BEJ1. for all of the test vehicle’s axles, confirming the loss of tire/pavement contact due to the passage on BEJ1. Test Number 1 Test Number 1 Front Axle Medium Axle Rear Axle t t t 2 Front Axle 1 Medium2 3 Axle Rear Axle t t t 2 1 2 3 1.5 1.5 1 1 0.5 0.5 0

Vertical Acceleration (g) 0

Vertical Acceleration (g) -0.5 -0.5 -1 -1 00.511.522.5 00.511.522.5Time (s) Time (s) Figure 16. An example of accelerometer signals (front, medium and rear axles: Test Number 1) and Figure 16. An example of accelerometer signals (front, medium and rear axles: Test Number 1) and axles’Figure bumps 16. An transiting example ofover accelerometer the bridge expansion signals (front, joint. medium and rear axles: Test Number 1) and axles’ bumps transiting over the bridge expansion joint. axles’ bumps transiting over the bridge expansion joint. Analyzing the maximum positive vertical accelerations obtained for each configuration test Analyzing(TableAnalyzing 2), it thewas the maximumfound maximum that positivethe positive medium verticalvertical axle was accelerations the most obtainedcritical obtained one for for(Figure each each configuration 17). conﬁguration In addition, test test (TableFigure(Table2), it was 172), highlightsit found was found that the the importancethat medium the medium of axle the wasmoving axle the was speed: most the critical mostincreasing critical one the (Figure one vehicle (Figure 17 velocity). In 17). addition, resultsIn addition, Figurein an 17 highlightsincrementFigure the 17 highlights importanceof vertical the accelerati of importance the movingon on of vehicles the speed: moving and increasing passengers. speed: increasing the vehicle the velocityvehicle velocity results results in an incrementin an of verticalincrement acceleration of vertical on accelerati vehicleson and on vehicles passengers. and passengers.

Front Axle Medium Axle Rear Axle Front Axle Medium Axle Rear Axle 2 1.82 1.61.8 1.41.6 1.21.4 1.21

(g) 0.81

(g) 0.60.8 0.40.6 0.20.4 0.20 0 1 (V=107 km/h) 2 (V=84 km/h) 3 (V=103 km/h) 4 (V=85 km/h) Vertical acceleration - acceleration Vertical value peak positive 1 (V=107 km/h) 2 (V=84 km/h)Test Number 3 (V=103 km/h) 4 (V=85 km/h) Vertical acceleration - acceleration Vertical value peak positive Test Number

Figure 17. Maximum positive vertical acceleration values recorded during each test. FigureFigure 17. 17.Maximum Maximum positive positive vertical vertical accelerationacceleration values values recorded recorded during during each each test. test. Appl. Sci. 2017, 7, 599 15 of 21 Appl. Sci. 2017, 7, 599 15 of 20

AllAll of of the the collected collected datadata werewere alsoalso analyzedanalyzed in in the the frequency frequency domain, domain, and and the the results results were were representedrepresented using using the the acceleration acceleration powerpower spectral density density (PSD) (PSD) function. function. Th Thisis procedure procedure permitted permitted studyingstudying the the principal principal oscillationoscillation and and vibration vibration comp componentsonents of ofthe the vehicle vehicle due due to the to bump the bump (Figure (Figure 18). 18).

0.02 Body bounce Pitching (~2 Hz) (~3 Hz) Body roll 0.018 front axle medium axle 0.016 rear axle

Body bounce 0.014

0.012 Body bounce (~2 Hz)

/Hz) Pitching 2 0.01 PSD (G 0.008

Axle hop 0.006

Body roll 0.004 (~1 Hz) Axle hop (~10-20 Hz) Tyre oscillation 0.002 (~40-60 Hz) Vibration (>100 Hz)

0 0.1 1 10 100 1000 Frequency (Hz) FigureFigure 18. 18.Power Powerspectral spectraldensity density (for(foreach each axle, axle, average average value value of of the the four four tests tests with with the the 20 g accelerometer).20 g accelerometer).

AccordingAccording to to Figure Figure 18 18,, the the mainmain oscillationoscillation components are: are: • ≅ ≅ • VehicleVehicle roll roll oscillation: oscillation: body body rollroll ff =∼ 1.0 1.0 Hz Hz ( T(T=∼ 1 s)1 s) (sprung (sprung mass); mass); • Primary vehicle oscillation: body bounce f ≅ 2.0 Hz (T ≅ 0.5 s) (sprung mass); • Primary vehicle oscillation: body bounce f =∼ 2.0 Hz (T =∼ 0.5 s) (sprung mass); • Vehicle pitching oscillation: pitching f ≅ 3.0 Hz (T ≅ 0.33 s) (sprung mass); • ∼ ∼ • VehiclePrimary pitching vehicle oscillation: axles oscillation: pitching axlef hop= 3.0 f ≅ Hz 10–20 (T = Hz0.33 (T s) ≅ (sprung 0.1–0.05 mass); s) (unsprung mass); ∼ ∼ • • PrimaryTire oscillation vehicle axlesand vibration: oscillation: f ≅ axle 40–60 hop Hzf =(T10–20 ≅ 0.025–0.017 Hz (T = 0.1–0.05s) (unsprung s) (unsprung mass); mass); • • TirePower oscillation and other and part vibration: in vibration:f =∼ 40–60 f > 100 Hz Hz ( T(T=∼ < 0.025–0.0170.001 s) (vibration). s) (unsprung mass); • Power and other part in vibration: f > 100 Hz (T < 0.001 s) (vibration). Lower frequency responses (1–4 Hz) characterize the vehicle’s body (sprung mass) bounces, or pitchesLower and frequency rolls. High-frequency responses (1–4responses Hz) characterize (10–50 Hz), instead, the vehicle’s correspond body to (sprung axle hop mass) vibrations. bounces, or pitchesAcceleration and rolls. High-frequencymeasurements an responsesd their (10–50processing Hz), instead,permitted correspond identifying to axleall hopvibrational vibrations. componentsAcceleration induced measurements in the vehicle and test their by processing the geomet permittedric irregularity identifying of BEJ1. all In vibrational particular,components the most inducedimportant in the ones, vehicle which test have by the a frequency geometric irregularityrange 1–4 Hz, of BEJ1.determine In particular, the complete the most lifting important from the ones, whichpavement have of a frequencythe rear axles range of th 1–4e running Hz, determine ordinary the heavy complete vehicles. lifting Consequently, from the pavement this phenomenon of the rear axlesreduces of the the running adherence ordinary of wheel-pavement, heavy vehicles. until Consequently, the complete this loss phenomenon of adherence. reducesFurthermore, the adherence in the paved areas adjacent to the joint, more accentuated irregularities appear, due to the considerable of wheel-pavement, until the complete loss of adherence. Furthermore, in the paved areas adjacent to dynamic increment of the loads transmitted to the pavement. the joint, more accentuated irregularities appear, due to the considerable dynamic increment of the In this sense, several simulation analyses were performed using the linear quarter-truck model loads transmitted to the pavement. described in [32] to estimate the dynamic load increment for the heavy vehicles’ characteristic speed In this sense, several simulation analyses were performed using the linear quarter-truck model range running on the examined road (i.e., 80–120 km/h). The results of the simulation analyses described in [32] to estimate the dynamic load increment for the heavy vehicles’ characteristic speed (Figure 19) show higher DLC values, increasing vehicle speed in analogy with literature rangestudies running [34,37]. on The the DLC examined calculation road was (i.e., performed 80–120 km/h). considering The resultsjust a limited of the segment simulation having analyses a (Figuretotal length 19) show of 100 higher m: 50 DLC m before values, and increasing 50 m after vehicle the BEJ1. speed in analogy with literature studies [34,37]. The DLCComparing calculation the wasDLC performed obtained for considering two different just alig a limitednments segment(i.e., 1 and having 3), the ahighest total length values of were 100 m: 50found m before for Alignment and 50 m after3, whose theBEJ1. unevenness (due to the BEJ presence) was greater than Alignment 1. Comparing the DLC obtained for two different alignments (i.e., 1 and 3), the highest values were found for Alignment 3, whose unevenness (due to the BEJ presence) was greater than Alignment 1. Appl. Sci. 2017, 7, 599 16 of 21 Appl. Sci. 2017, 7, 599 16 of 20

Appl. Sci. 2017, 7, 599 16 of 20 InIn fact, fact, the the rotation rotation of of the the carriageway carriageway alongalong thethe transitiontransition curve curve has has its its torsion torsion axis axis (inner (inner roadside) roadside) veryvery close close to to Alignment Alignment 1. 1. In fact, the rotation of the carriageway along the transition curve has its torsion axis (inner roadside) very close to Alignment 1. front-mean value rear-mean value front-alignment1 front-alignment 3 rear-alignment 1 rear-alignment 3 0.5 front-mean value rear-mean value front-alignment1 front-alignment 3 rear-alignment 1 rear-alignment 3 0.5 0.4

0.4 0.3

0.3 DLC 0.2 DLC 0.2 0.1

0.1 0 70 80 90 100 110 120 130 0 Speed (km/h) 70 80 90 100 110 120 130 Speed (km/h) FigureFigure 19. 19.Front Front and and rear rear axles axlesdynamic dynamic load coeffi coefficientcient (DLC) (DLC) values values at at different different speeds. speeds. Figure 19. Front and rear axles dynamic load coefficient (DLC) values at different speeds. Figure 19 also reports the DLC mean value for both front and rear axles calculated considering allFigure three alignments.19 also reports A major the DLC dispersion mean value (referred for both to the front DLC and mean rear value) axles calculatedwas found considering for the rear all Figure 19 also reports the DLC mean value for both front and rear axles calculated considering threeaxle, alignments. probably caused A major by the dispersion mechanical (referred parameters to the considered. DLC mean value) was found for the rear axle, all three alignments. A major dispersion (referred to the DLC mean value) was found for the rear probablyThe caused results by obtained the mechanical from the parameters DLC analysis, considered. in analogy to what was found through in situ axle, probably caused by the mechanical parameters considered. accelerationThe results measurements, obtained from highlighted the DLC that analysis, the rear in analogyaxle is the to most what critical was found one in through terms of in the situ The results obtained from the DLC analysis, in analogy to what was found through in situ accelerationdynamic load measurements, transmitted to highlighted the pavement that and the to the rear bridge axle isstructure. the most critical one in terms of the acceleration measurements, highlighted that the rear axle is the most critical one in terms of the dynamicDLC load values transmitted were also to calculated the pavement for the and first to 100 the m bridge of the structure. examined road branch, where no BEJs dynamic load transmitted to the pavement and to the bridge structure. are present, to better underline the effects caused by BEJ1. Figure 20 shows that the DLC of the first DLCDLC values values were were also also calculated calculated forfor thethe firstfirst 100 m of of the the examined examined road road branch, branch, where where no no BEJs BEJs 100 m-long road has values significantly lower than those calculated in the area surrounding BEJ1. areare present, present, to to better better underline underline the the effectseffects causedcaused by BEJ1. Figure Figure 20 20 shows shows that that the the DLC DLC of ofthe the first first 100100 m-long m-long road road has has values values significantly significantly lower lower thanthan thosethose calculated in in the the area area surrounding surrounding BEJ1. BEJ1. Rear axle

First 100 m Rear axle100 m surrounding the BEJ

0.5 First 100 m 100 m surrounding the BEJ

0.50.4

0.40.3

DLC 0.30.2 DLC 0.20.1

0.10 70 80 90 100 110 120 130 0 Speed (km/h) 70 80 90 100 110 120 130 Speed (km/h) Figure 20. Dynamic load coefficient (DLC) values at different speeds before the bridge expansion joint and across it (Alignment 3). FigureFigure 20. 20.Dynamic Dynamic load load coefﬁcient coefficient (DLC) (DLC) values values at differentat different speeds speeds before before the the bridge bridge expansion expansion joint joint and across it (Alignment 3). andFinally, across itthe (Alignment stress distribution 3). on heavy vehicle mechanical components due to the transit on BEJ1 was investigated by means of a 3D model. The obtained results are depicted in Figure 21: since Finally, the stress distribution on heavy vehicle mechanical components due to the transit on the maximum depth of the measured elevation is about 2.5 cm, the stress magnitude is not BEJ1Finally, was investigated the stress distribution by means of on a heavy3D model. vehicle The mechanical obtained results components are depicted due toin theFigure transit 21: onsince BEJ1 particularly burdensome for vehicle components. wasthe investigated maximum bydepth means of the of ameasured 3D model. elevation The obtained is about results 2.5 arecm, depictedthe stress in magnitude Figure 21: sinceis not the particularly burdensome for vehicle components. Appl.Appl. Sci. Sci.2017 2017, 7, 7 599, 599 17 of17 20 of 21

Thus, the location of a BEJ in a transition curve does not provide a significant increase in the maximummechanical depth components of the measured of road vehicles, elevation while is about it meaningfully 2.5 cm, the affects stress traffic magnitude safety is(due not to particularly the loss burdensomeof tire/pavement for vehicle contact) components. and dynamic load increment (i.e., higher forces transmitted to the road pavement and bridge structure).

(a)

(b)

(c)

FigureFigure 21. 21.Heavy Heavy vehicle vehicle stress stress (MPa) (MPa)at at90 90 km/h:km/h: ( (aa)) full full vehicle, vehicle, (b (b) )magnification magniﬁcation of ofmedium medium and and rearrear axles axles and and (c )(c magniﬁcation) magnification of of front front axles. axles. Appl. Sci. 2017, 7, 599 18 of 21

Thus, the location of a BEJ in a transition curve does not provide a signiﬁcant increase in the mechanical components of road vehicles, while it meaningfully affects trafﬁc safety (due to the loss of tire/pavement contact) and dynamic load increment (i.e., higher forces transmitted to the road pavement and bridge structure). For these reasons, the road agency planned:

• the reconstruction of the joint to permit a more regular and continuous variation of the planimetric geometry of the road platform; • measures for the reduction of the driving speed (i.e., speed cameras and speed enforcement) to ensure a better circulation.

The adopted strategies ensure that under ordinary conditions, the circulation is regular, and the accident risk for road users is reduced; moreover, the reduced number and frequency of the required maintenance works increase the trafﬁc safety.

5. Conclusions In road engineering, bridge expansion joints often cause troubles concerning evenness and skid resistance. Even if the joint is designed and built in accordance with the best practice, the discontinuity of the pavement may produce a dangerous unevenness. This irregularity could be very important if the joint is in a transition section (clothoid) of the road, as considered in the paper. In fact, in this section, the curvature and super-elevation of the road gradually change between two consequent elements with different planimetric curvature. Consequently, in this area, the road surface is “slanted”, and if the joint is large (for example in a highway seismic joint), the elevation difference from the points of the road can reach some centimeters. This difference could produce an additional, undesirable unevenness in addition to a possible construction unevenness. A heavy vehicle was instrumented with piezometric accelerometers to evaluate the effects of the irregular BEJ on a running vehicle. The results of the performed surveying and tests highlighted the unevenness on the surface profile caused by the presence of the BEJ along a transition curve. The analyses carried out in the present work underline how this kind of discontinuity may affect the response of truck suspensions and the dynamic response of the bridge. The measurements permitted also identifying the most representative frequencies of loads applied to the structure. The results also confirmed the possibility of a complete lifting of the vehicle’s rear axles with serious risks of grip loss on the road and, consequently, serious detrimental effects on road traffic safety. The road agency adopted two main actions to improve the level of service in the road section and to ensure a safe and efficient traffic flow: reduction of geometric irregularities resulting from the joint and reduction of the allowed speed. BEJs are localized irregularities that can have different severity levels according to many factors, such as if placed in the road transition curve. This study provides a guidance on the evaluation of the detrimental effects induced by BEJs, which may affect all of the road infrastructure components: vehicles, pavement, bridge and users, with attention to safety. The results can be used by road agencies to specify strategies and procedures for policies to guarantee minimum safety levels at roads.

Author Contributions: Giuseppe Loprencipe had the original idea for the study. Giuseppe Loprencipe and Paola Di Mascio carried out all in situ measurements. Giuseppe Loprencipe, Laura Moretti and Pablo Zoccali analyzed the data. Lorenzo Puzzo implemented the finite element model in LS-DYNA and performed the data post-processing analysis. Giuseppe Loprencipe and Pablo Zoccali wrote sections for the first draft of the manuscript. All authors contributed to further drafts and had full access to all of the data. Conflicts of Interest: The authors declare no conflict of interest. Appl. Sci. 2017, 7, 599 19 of 21

Abbreviations The following abbreviations are used in this manuscript:

BEJ Bridge expansion joint DIVINE Dynamic Interaction between Vehicles and Infrastructure Experiment DLC Dynamic load coefﬁcient IRI International Roughness Index PSD Power spectral density RMS Root mean square

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