Overhead Sign Structures Research Articles

Wind Loads on Overhead Sign Structures: A Comparative Study

Road signs are prone to extreme winds that cause significant damage. Overhead sign structures can disrupt traffic and cause harm to the traveling public if a failure occurs under extreme wind conditions. In this paper, we employ Computational Fluid Dynamics (CFD) in a comparative study to understand the aerodynamics of standard, porous, and curved signs. The study shows the viability of porous and curved overhead boards for lessening aerodynamic loads, which can mini-mize damage and enhance safety on roadways. Porous overhead signs can decrease the drag forces; however, the size of the openings is a vital parameter in reducing wind loads. Small and uniform perforations lead to higher drag forces, compared to larger ones, under the same porosity ratio. Introducing porosity to a solid panel moves the vorticity region further downstream, reducing the magnitude of pressures on the leeward side and decreasing the drag force. However, curved panels further enhanced the force reduction.

Behavior of Cross Arms Inserted in Concrete-Filled Circular GFRP Tubular Columns.

Fiber-reinforced polymer (FRP) materials nowadays have attracted much attention in both retrofitting of aged infrastructure and developing of new structural systems attributed to the outstanding mechanical properties. Extensive studies have been performed on concrete-filled glass FRP (GFRP) tubes for the potential application in piling, poles, highways overhead sign structures and bridge components. The new hybrid member also provides an alternative solution for traditional transmission structures. However, the connection between concrete-filled GFRP tubes and cross arms has not been fully understood. In this paper, an experimental study and theoretical analysis were conducted on the behavior of cross arms inserted in concrete-filled circular GFRP tubular columns. Steel bars with a larger stiffness in comparison with GFRP tubes were selected here for the cross arm to simulate a more severe scenario. The structural responses of the system when the cross arms were subjected to concentrated loads were carefully recorded. Experimental results showed that the concrete-filled GFRP tubes could offer a sufficient restraint to the deformation of the cross arm. No visible cracks were found on the GFRP tube at the corner of the cross arm where the stress and strain concentrated. Theoretical solutions based on available theories and equations were adopted to predict the displacement of the cross arms and a good agreement was achieved between the prediction results and experimental findings.

Condition Assessment of Ground-Mount Cantilever Weathering-Steel Overhead Sign Structures

AbstractThis paper is a part of an expansive research work aimed at assessing 82 weathering steel overhead sign structures (WSOSSs) in the Charleston Interstate System in West Virginia. A total of ...

Unified model for hollow columns externally confined by FRP

Nowadays, the employment of Fibre Reinforced Polymer (FRP) composites in civil engineering field has been successfully experienced. Different potential applications of solid concrete-filled FRP tubes are exploitable in marine piles, overhead sign structures, poles and posts, bridge columns and piers, girders, large pipes and tunnels (mainly circular cross-section). This technique is also used for the confinement of masonry columns, typically encountered in monuments and historical buildings (both rectangular and circular cross-section); hence the need of providing formulas for the design of an appropriate strengthening. Several analytical models are available in the scientific literature for assessing the increase of strength and ductility of concrete or stone solid elements externally confined with FRP or for hollow columns internally steal enclosed and externally FRP-confined but, there is still a lack of research about hollow columns only externally confined. The presence of an empty core implies a different stress state in the inner cylindrical surface with respect to the outer one. Inwards deformations are more significant and this behaviour is not taken into account by available models.The present study aims to illustrate a detailed summary of the existing analytical models and to provide a unified procedure for concrete and masonry hollow columns valid for both circular and square cross-sections. An iterative method that updates the geometrical parameters according to step-by-step uniaxial compressed column is shown in order to capture the real deforming behaviour of the compressed solid. This analytical approach has two important implications: the first is the ability of calculating the stress state of the column and of the external FRP reinforcement at each step; the second is that of theorizing a procedure, which is independent on the type of material used for the column. The outputs of the proposed method are then compared with experimental results currently available in the scientific literature. A good matching is obtained between the available experimental results and the analytical predictions in term of axial stress–strain curves.

Effects of traffic-induced vibrations on bridge-mounted overhead sign structures

Large-amplitude vibration of overhead sign structures can cause unfavorable psychological responses in motorists, interfere with readability of the signs, and lead to fatigue cracking in the sign structures. Field experience in Texas suggests that an overhead sign structure can vibrate excessively when supported within the span of a highway bridge instead of at a bent. This study used finite element modeling to analyze the dynamic displacement response of three hypothetical sign structures subjected to truck-passage-induced vertical oscillations recorded for the girders from four actual bridges. The modeled sign bridge structures included several span lengths based on standard design practices in Texas and were mounted on precast concrete I-girder bridges. Results revealed that resonance with bridge girder vertical vibrations can amplify the dynamic displacement of sign structures, and a specific range of frequency ratios subject to undesirable amplification was identified. Based on these findings, it is suggested that this type of sign structure be located at a bridge bent if its vertical motion frequency is within the identified range of bridge structure excitation frequencies. Several alternatives are investigated for cases where this is not possible, including increasing sign structure stiffness, reducing sign mass, and installing mechanical dampers.

Mitigating Fatigue in Cantilevered Overhead Sign Structures

Cantilevered overhead sign structures (COSSs) are widely used across highways in the United States. Several cases of excessive vibrations and failures caused by fatigue wind loads from natural and truck-induced wind gusts have been reported. Not enough research has included the effect of making structural design modifications on the fatigue performance of COSSs. Under fatigue wind-induced loads, the dynamic characteristics (frequency and damping) of COSSs are important parameters affecting their structural behavior. When frequencies of wind load and the structure match, resonance may occur, causing excessive vibrations, depending on the frequency value. If accompanied fatigue stresses exceed the fatigue endurance limit, failure occurs after a certain number of loading cycles. The objective of this study was to investigate stiffness and mass distribution of COSSs to control the structural frequency, thus mitigating fatigue caused by wind-induced gusts. For this purpose, modifications in the members' shape, arrangement, size, and layout of structure were examined. Three layouts were compared: four-chord, two-chord, and monotube COSSs. These layouts were designed according to the 2013 AASHTO Standard Specifications for Structural Supports for Highway Signs, Luminaires, and Traffic Signals and modeled with SAP2000. Wind pressure power spectral density and time history loading functions were applied to these structures to simulate natural and truck-induced wind gusts, respectively. Results showed that the vertical mono-tube COSS design with curved end post had the least mass, but fatigue stresses were comparable with the four-chord COSS. The two-chord COSS design had the largest mass and exhibited the highest fatigue stresses.

Examination of repair effect of fatigue crack occurs in the base of overhead sign structures

Examination of repair effect of fatigue crack occurs in the base of overhead sign structures

Vibration factors of overhead sign structures mounted on highway bridges

AbstractVibration due to traffic and wind causes fatigue damage to overhead sign structures mounted on highway bridges. Fatigue damage due to traffic vibration depends on the type and dimensions of the bridge, type of bearings, volume of traffic, location of overhead sign structures, etc. Factors influencing vibration are investigated in this study by carrying out frequency response analyses, with the parameters being the bridge, bridge pier and bearing types, the location of the sign structures and the weight of the electronic information panels. It can be seen that the damage increased after replacing the steel bearings by elastomeric bearings. These factors were verified through frequency response analyses. The results obtained in this study can be applied to the development of measures to prevent fatigue damage in overhead sign structures due to traffic vibration.

Rehabilitation of Cracked Aluminum Connections with GFRP Composites for Fatigue Stresses

The original design of existing aluminum overhead sign structures (OSS) did not consider fatigue as a limit state. Cracks propagate in the welds of the connection between the main chord and branches of OSS due to fatigue stresses caused by wind-induced vibration, which occasionally lead to complete fracture of the welds. A rehabilitation method for cracked aluminum welded connections using glass fiber-reinforced Polymer (GFRP) composites is investigated for its effectiveness under fatigue stresses. The results of constant amplitude fatigue tests for three types of aluminum connections from actual OSS are presented: (1) connections with no known cracks; (2) cracked connections rehabilitated with GFRP composites; and (3) connections with 90% of the weld removed and subsequently repaired with GFRP composites. The fatigue limits of the three connection types are established for four stress ranges including the constant amplitude fatigue limit threshold. The rehabilitated connections from OSS exceeded the fati...

Repair of damaged aluminum truss joints of highway overhead sign structures using FRP

An innovative repair technique is introduced for aluminum truss-type highway overhead sign structures, using fibre-reinforced polymer (FRP) sheets. The welded k-joints are typically subjected to excessive fatigue-induced cracking under the effects of wind and moving traffic. The repair technique proposed in this paper utilizes longitudinal FRP layers bonded to the diagonals and wrapped around the main chord to form alternating v-patterns, followed by additional circumferential layers for anchorage. Eight tests were conducted on four full-scale specimens. Weld lines at the junction between diagonals and main chord were ground to simulate a 90% loss of joint strength. After repair, diagonals were loaded to failure in tension. The study showed that full strength of the welded joints was restored using carbon-FRP sheets. Only 70% of joint strength was restored when using glass-FRP. The strengthening technique is particularly sensitive to quality control during installation. A field application using the proposed technique was successfully completed by the New York State Department of Transportation for a cracked aluminum truss over Route 88 in NY State.

Large scale testing and analysis of hybrid concrete/composite tubes for circular beam-column applications

Concrete-filled fiber reinforced polymer (FRP) circular tubes provide an effective structural system for a variety of applications such as piles, columns, overhead sign structures and utility poles. This paper discusses the behavior of concrete-filled Glass-FRP tubes ranging in diameter from 90 to 942 mm, using test results of eight beams, five columns and ten beam-column specimens. The effects of concrete fill, laminate structure of the tube, reinforcement ratio based on the wall thickness, as well as different failure modes are examined. Analytical models have been established and used in a parametric study to examine the effects of fiber orientation within the FRP tubes, thickness of the FRP tube, and the diameter of a central hole, which could be used to reduce the self-weight of the member. The benefits of concrete fill as well as the confinement effects have been demonstrated experimentally and analytically.

Repair of Cracked Aluminum Overhead Sign Structures with Glass Fiber Reinforced Polymer Composites

Transportation departments have been using aluminum overhead sign structures since the 1950s. It is well documented that cracks develop in the welds between diagonal and chord members due to fatigue stresses from wind-induced vibration of the slender members. The cracks propagate to complete failure of the members, which can cause collapse of the truss and inflict injuries. The original design of overhead sign structures did not consider fatigue as a limit state. In addition, field welding of aluminum structures for any possible repairs is prohibited. A repair method for the cracked aluminum welded connections between diagonals and chord members using glass fiber reinforced polymer composites (GFRPs) is proposed. The static load carrying capacity of the welded connection, and the cracked connection repaired with GFRP composites are established. The paper describes the surface preparation of the aluminum tubular members, and the architecture and application sequence of the GFRP composite to retrofit the connection. Experimental results are presented from static tests of welded aluminum connections, welded aluminum connections retrofitted with GFRP composites, and new aluminum connections that depend only on GFRP composite elements for their strength. The results from monotonic static tests carried out on cracked welded specimens from actual sign structures show that the retrofitted connection with GFRP reinforcement achieved 1.17 to 1.25 times the capacity of the welded aluminum connection without any visible cracks. This result, and the minimal traffic disruption anticipated in the actual field application, makes this retrofit method a good candidate for implementation.