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Bridges & Structures

Guidelines for the Installation, Inspection, Maintenance and Repair of Structural Supports for Highway Signs, Luminaries, and Traffic Signals

15.0 Inspection Report

Reporting of deficiencies, condition ratings, and notification of any critical conditions can occur in a number of ways. Many agencies have opted for an electronic process, either using hand held devices or laptop computers to record information out in the field. It is important, whether using a paper reporting procedure or an electronic system, that all aspects of the report be finalized before leaving the site.

The inspection report should summarize many aspects of the inventory and inspection process but first and foremost identify deficiencies that may require maintenance or result in structural failure. The report is used as a tool to manage the ancillary structure inventory and must be complete, concise, and accurate. It should clearly call out any recommendations for further action. A recommended list of items to be included in a typical inspection report are listed below:

  • Inventory Information
  • Personnel / Firm / Inspector information
  • Inspector Ratings
  • Inspector Repair Recommendations (May include prioritization. See Section 16.1)
  • Inspector Recommendation on Inspection Frequency
  • General Photos
  • Deficiency Photos
  • Sketches
  • NDT Results (if applicable)

Inspection reports may take any number of forms. Most reports are submitted as electronic files, either as individual reports or part of a database management system. For documentation purposes, a paper copy, signed by the responsible party, is also normally required.

An example inspection report for a New Jersey Sign Structure utilizing an element based inspection system is located in Appendix C. An example inspection report in the PONTIS system is located in Appendix B.

16.0 MAINTENANCE AND REPAIR

16.1 Prioritization of Work

A protocol should be developed whereby deficiencies identified during the inspection can be addressed in a timely manner. The repair priority rating system given in Table 11 is one example. If Priority 1 repairs cannot be made within a reasonable timeframe, removal of the sign structure may be warranted.

Table 11 Repair Priority Rating
Condition Description Repair Timeframe
0 Not Applicable None
1 Items, if not corrected immediately, threaten the continued operation of the structure 3 days
2 Items that need to be corrected in a timely manner, above normal maintenance repairs. One Year
3 Items that can be corrected during normal maintenance operations. Three Years

For emergency situations, a Condition 'E' can be applied whereby the roadway may have to be immediately shut down. The inspection team should have a direct contact person to notify if any critical conditions are found. There have been cases where the inspection team and their traffic control remained on site while maintenance personnel and equipment mobilized to the site and removed structures found in critical condition. Many states have such procedures for bridge inspectors, and a similar protocol can be followed for ancillary structures.

Overhead sign structures can vary in cost from $10,000 to $150,000 depending on complexity. In comparison to other highway structures such as bridges, this is a relatively minor cost. For this reason many states that have found structurally deficient sign structures, decide on total removal and replacement rather than repair. If repairs are made it may be only a temporary measure. Some deficiencies like cracked welds, even if found on only one or two elements, are indicators that the structure has most likely reached its fatigue life and replacement is warranted.

Of course each sign structure should be evaluated on cost/benefit value when considering repair or replacement. Other factors such as traffic control could greatly add to the cost of total replacement.

16.2 Routine Maintenance

Ancillary structures, especially sign bridges, typically require lane closures and disruption of traffic flow, in order to access the structure for repairs and thus the inspector may be asked to perform routine maintenance at the time of the inspection. If not performed by the inspection team, this work should be completed by maintenance crews in a timely manner. Examples of deficiencies that require typical routine maintenance are:

  • Loose nuts
  • Loose or missing sign fasteners
  • Broken washers
  • Buried foundations
  • Clogged post drainage
  • Excessive vegetation
  • Rodent droppings
  • Spot loss of galvanization
  • Replacing pole caps, hand hole covers, anchor rod caps
16.2.1 Foundations

Routine Maintenance for foundations includes making sure that the foundation is visible to the inspector. If buried, this can accelerate corrosion and will not yield a full inspection. Many times not only are the foundations buried but the base plates and anchor rods are as well. This can be attributed to the widening of many highway shoulders where ancillary structures are positioned.

Drainage issues are very important for sign structures. Many structures are inspected and found to have standing water in the post. Drilling a small hole in the post to allow drainage or creating drain grooves in the top of the foundation can easily be done during routine maintenance. Blocked drain grooves are the most problematic maintenance item that can lead to catastrophic results. Inspectors and/or maintenance personnel should routinely clean the outlet simply using a screwdriver head or other probing tool.

Buried foundations should be uncovered and area around them regraded. Any buried foundations should be exposed to at least .3m (1 ft.) below the top of the foundation. Any excessive vegetation should be removed since it not only impedes inspections but harbors moisture and rodents.

Missing handhole covers can be a safety concern especially if electrical power is inside the post. Also, moisture, animals, birds and garbage can enter the handhole. It is recommended that all missing handhole covers be replaced. Missing post or truss end caps have the same potential problems and should be replaced. In addition to handholes sometimes there are conduit access holes, usually small holes 25mm to 50mm (1 inch to 2 inches) in diameter that allow small birds and insects to enter. An easy repair is to plug the hole with a plastic conduit end cap. A small hole may be drilled through the cap to allow airflow.

16.2.2 Connections

Missing or loose anchor rod nuts, both top nuts and leveling nuts, can be a serious problem since the load is then transferred to the adjacent rods. In many older cantilever structures there are only a total of four rods, so just one missing or loose nut can overload the remaining three rods. Damaged nuts should be replaced and loose nuts properly tightened.

Missing, broken, or loose bolts in member connections should be replaced. Consideration should be given to replacing aluminum bolts or black bolts used in structural connections with galvanized high strength bolts.

Many sign structures were constructed with steel towers/posts and an aluminum truss. The lighter aluminum helped to reduce structural loading. However, with these dissimilar metals it is important that the nonconductive materials, such as polymer pads, placed as barriers between the dissimilar materials remain so these materials do not touch and accelerate corrosion. Missing pads should be replaced in a timely manner.

The numerous fasteners that connect sign panels to the structure can loosen and fall off. Missing fasteners should be replaced unless it is determined that sufficient redundancy exists in the connection. A simple rule of thumb might be, fastener replacement is necessary if more than 20 percent of the connections are missing.

16.2.3 Coatings

Many steel structures have been galvanized to slow the corrosion process. Over time the galvanized layer may become ineffective and therefore lose its ability to slow the process of corrosion. Impact damage can also remove the protective coating. If there is minor loss of galvanization a touch up may be prudent. Total loss of galvanization may not be an immediate problem is there is no visible corrosion or section loss, but may result in a shorter structure service life.

Suggestions for routine maintenance of coatings include the following:

  • Clean debris from structure, remove or cut vegetation touching structure.
    • This is particularly important for weathering steel
    • Remove bird droppings that can accelerate corrosion

  • Touch up of galvanizing
    • Repair in accordance with ASTM A780 "Standard Practice for Repair of Damaged and Uncoated Areas of Hot-Dip Galvanized Coatings"
    • The surface should be ground to bright metal
    • A zinc rich paint or cold galvanizing compound should be applied

  • Painted structures
    • Paint must be removed to inspect suspected cracks
    • Repaint immediately after inspection (if OK) or after repair
    • Touch-up paint any scratches or locally defective areas

16.3 Repairs

In recent years many innovative repair methods have been researched and implemented for overhead sign structures. The most progress has been made regarding aluminum truss structures. These welded structures are very difficult to field repair. Even truss removal and repair is considered much more difficult than with a steel truss. The following paragraphs provide repair guidance for typical problems.

16.3.1 Foundations
16.3.1.1 Concrete

The foundations of ancillary structures are susceptible to deterioration due to their proximity to the traveled roadway and the influence of surrounding site conditions. Concrete, the most prevalent material type of foundation used, will deteriorate by cracking, delaminating and spalling. These types of deficiencies can be repaired so that the service life of the structure can be maintained.

Deterioration that includes cracking, spalling and delamination can be repaired as would be done with other concrete structures. The deteriorated or damaged concrete can be chipped away and replaced with mortar. Cracks can be sealed with epoxy or epoxy grout depending on their size. Large spall areas can be repaired with reinforcing that is drilled and bonded into the existing foundation for an integral connection.

A common deficiency that typically requires repair for an ancillary structure is the grout pad between the top of foundation and base plate. This mortar type mix is not the reinforced concrete used in other parts of the foundation, and usually serves only to support the steel base plate in compression. One easy repair is to completely remove the grout pad, if analysis can show that the base plate will meet existing buckling specifications without the pad. Once the grout pad is removed the gap area between the foundation and base plate should be closed off with wire mesh to prevent intrusion of debris or rodents into the post base.

If the grout pad is determined by analysis to be required to prevent the base plate from buckling, the grout should be completely removed and replaced using a prepackaged "non-shrink" grout placed in accordance with the manufacturer's requirements. The grout pad design should accommodate any drainage from the post and provide for adequate air circulation.

16.3.1.2 Anchor Rods

This critical connection between the post and foundation has been problematic. Many times the rod is not long enough and the anchor nut is not fully engaged. This in itself is not a serious deficiency as long as at least three quarters of the nut is engaged. If not, a coupler may have to be installed to lengthen the rod. This may involve complete foundation reconstruction. The first course of action is to see if the base plate can be lowered to fully engage the nuts.

A rod that is found to be fractured or does not meet required embedment lengths presents a serious condition. One method of adding anchor rods is to drill through the base plate and into the foundation so that new rods can be epoxy grouted into place, see Figure 35. Installation may be hindered by closely spaced base plate stiffener plates and may cut reinforcing steel in the foundation.

Base plate with Added Anchor Rods
Figure 35. Base plate with Added Anchor Rods.

In many states a new foundation is built adjacent to the old and the structure is relocated to the new foundation. For multi-tower sign structures or those with eight or more anchor rods with high redundancy a fractured anchor rod may not be critical. An analysis should be conducted to investigate the effects prior to determining repairs.

When replacing a nut or washer, wire brush and lubricate the anchor rods, use new top nuts and washers, lubricate the nuts, and tighten. Beeswax or toilet ring wax are good lubricants.

16.3.2 End Frames and Posts

End frames and posts connect ancillary structures to their foundations and are susceptible to damage from vehicles and maintenance operations. Common deficiencies covered here for repair include gouges, corrosion, impact damage and weld cracking.

16.3.2.1 Gouges

Gouges are common deficiencies in the end frame posts of ancillary structures since they can come in contact with machinery, vehicles and pedestrians. The size of the gouge in relationship to the size of the element will help determine the repair strategy. Gouges greater than 3 mm (1/8 inch) deep but less than half the member thickness may be ground with a transition slope to reduce the possibility of cracking. This repaired member will be more susceptible to fatigue and therefore should be inspected more frequently. Gouges greater than half of the member thickness can also be ground but the reduced structural capacity of the effected area should be investigated.

16.3.2.2 Impact Damage

Damage to end frames and posts due to impact are common. If gouges occur due to impact the proceeding paragraph provides repair guidance. Dents from impact need to be evaluated for reduced structural capacity due to local buckling. All welds in effected members need to be inspected for potential cracking from the impact force. Weld repairs should be made in conformance with the AWS Bridge Welding Code.

16.3.2.3 Corrosion

Where bases of end frames or posts exhibit corrosion, the source of moisture should be removed whenever possible by regrading and removing vegetation. Corroded areas should be properly cleaned and recoated. If corrosion has caused enough section loss to reduce the structural capacity of the member below required values, the area can be strengthened with steel collars or concrete encasement.

16.3.3 Trusses and Mast Arms

Many sign structure trusses are three dimensional space frames. In determining the need and type of repairs to these structures, consideration should be given to the significant redundancy many of them possess. In an unpublished load test of a four-chord bridge structure by the Iowa Highway Department, the structure was able to carry in excess of its design load even when numerous members were totally cut.

16.3.3.1 Connections

Sign structures arrive in sections for transportation and are erected at the site. Many times the connections do not always perfectly fit together. This may not be a serious problem if the gap created by the misalignment covers less than 25 percent of the total faying surface area. If the gap is greater, shims should be used to provide even contact. Shims should not be inserted into a tightened connection; rather, the connection must be loosened, shims inserted, and then retightened.

16.3.3.2 Cracks

Weld crack problems with steel structures are easier to repair than aluminum. The repair may be made 'in-situ' or that portion of the structure can be removed from service and repaired. Corrections to weld problems may include hammer peening, hole drilling to arrest the crack, vee-and-welding, or detail modification.

Hammer peening provides a compressive stress to the weld surface that helps to reduce the tendency to crack and to keep any crack from propagating. It has been useful for fatigue cracks up to 3 mm (1/8 inch) deep. Hammer peening followed by surface grinding can increase the strength of the connection by one fatigue strength category. Ultrasonic Impact Treatment (UIT), sometimes called ultrasonic peening, is a recently developed technique used to treat fillet welds to increase their fatigue strength. This has been used in Texas to treat welds in ancillary structures and is a patented process developed by Applied Ultrasonics.

A drilled hole is often used to arrest a crack that goes through the entire thickness of the weld material. For small cracks this may be enough to arrest the crack permanently, but offers only a temporary fix for larger cracks. The diameter of the hole to be drilled is often taken as 20mm (.75 inch); however, a more structure specific hole size can be calculated based on the stress range, edge distance and yield strength of the material. The inside of the drilled hole should be tested with dye penetrant to assure that the crack end was removed. Figure 36 illustrates actual crack repair details.

Repair Detail for Overhead Sign Truss Chord Crack
Figure 36. Repair Detail for Overhead Sign Truss Chord Crack.

16.3.4 Longitudinal Splits or Cracks

Longitudinal splits and cracks generally develop due to freezing of trapped water or build up of packout corrosion in slip joints. Longitudinal cracking at slip joints can also occur due to excessive bending stresses.

Slip joints, or telescoping splices that may develop packout corrosion, particularly a problem with weathering steel, should be sealed around their base with a weld, epoxy, or silicone sealant

If a longitudinal split or crack in a telescoping splice extends beyond the telescoping splice, the pole should be replaced.

If the longitudinal split or crack does not extend beyond the telescoping splice, the pole may be repaired by applying stressed steel bands around the perimeter. A 25 mm (1 inch) diameter hole should be drilled at the end of the split or crack, followed by applying steel bands around the post at the crack. The bands must be designed to replace the strength of the section area of the cracked length of the member. Poles prone to this splitting can be retrofitted with the bands as a preventive measure. Members with small splits (less than two times the diameter) due to freezing water inside them can also be repaired in this way. Where freezing has occurred, 25 mm (1 inch) holes should be drilled near the bottom of the member and similar members to drain any water. Members with larger splits should be considered for replacement.

16.3.5 Composites for Repairs

Research conducted at the University of Utah for the Utah State DOT and New York State DOT has resulted in a fiber composite wrap that surrounds the deficient weld area and helps transfer the load past the area of damage. It is an attractive repair option since it can be installed in-situ with materials that cost just a few hundred dollars.

16.3.5.1 Material Properties

The fiber composite wrap is actually a Fiber Reinforced Polymer (FRP). An approved installer that is thoroughly trained by the specific manufacturer should install the material. Surface preparation is critical and installation should only occur during weather deemed acceptable by the manufacturer. Surface preparation can include scrubbing, acid etching, water rinse and air-drying. The cure time for the applied repair resins is usually about one hour.

16.3.5.2 Repair Examples

A good example of such an application is repair to an aluminum sign truss bridge. During inspection it was found that the welds connecting the diagonals to the chord had cracked over a significant portion of their length. FRP was chosen as a repair technique. The application included member cleaning and application of the FRP material using strips wrapped around the members. Figure 37 below shows the completed application. These repairs, initially thought to be just temporary for one year or less, are now being considered as a permanent repair solution.

Truss repaired with FRP
Figure 37. Repair of Truss Members Using FRP.

16.3.6 Vibration Dampeners

Many ancillary structures, especially mast arm type, can visibly be seen vibrating under load. Though structurally sound, the excessive vibration may cause concern to the traveling public. The recommended repair is installation of a dampener to reduce the displacements.

16.3.6.1 Types of Dampeners

The most common type of dampener found on ancillary structures is the Stockbridge damper, also called a dog bone damper, see Figure 38. There are two weights on the end of a flexible shaft that can be tuned based on the natural frequency of the structure and thereby offer maximum effect. They are also very easy to install on existing structures as a retrofit.

Stockbridge Damper.
Figure 38. Stockbridge Damper.

To counteract galloping of signal arms a flat panel called a sign blank can be installed horizontally directly over the signal head acting as a drag against the up and down motion. The sign blank must be correctly placed over the signal head to break the airflow. This type of dampener has been used in Texas, see Figure 39. Other dampeners developed include the Florida impact damper and the Wyoming strand damper.

Texas Flat Panel Damper.
Figure 39. Texas Flat Panel Damper.

For natural horizontal wind gusts the Wyoming strand damper, Figure 40, is also helpful as is any kind of horizontal strut that can reduce out of plane bending.

Wyoming Strand Damper
Figure 40. Wyoming Strand Damper.

References

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