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
- 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.
|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
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.
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.
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
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.
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.
188.8.131.52 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.
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.
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.
184.108.40.206 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.
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.
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.
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.
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.
220.127.116.11 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.
18.104.22.168 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.
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.
22.214.171.124 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.
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.
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.
ACI 318-99, Building Code Requirements for Structural Concrete and Commentary, American Concrete Institute, Farmington Hills, Michigan, 1999.
Aluminum Design Manual, The Aluminum Association Inc., Washington, D.C.
American Galvanizers Association, Centennial, CO.
American Society of Nondestructive Testing, Columbus, OH.
ANSI/ASME B 1.1, Unified Screw Threads, American National Standards Institute, New York, NY, 1989.
ASTM A36, Standard Specification for Carbon Structural Steel, American Society for Testing Materials, West Conshohocken, PA, 1996.
ASTM A153, Standard Specification for Zinc Coating (Hot-Dip) on Iron and Steel Hardware, American Society for Testing Materials, West Conshohocken, PA, 1995.
ASTM A193, Standard Specification for Alloy-Steel and Stain-less Steel Bolting Materials for High-Temperature Service, American Society for Testing Materials, West Conshohocken, PA, 1995.
ASTM A307, Standard Specification for Carbon Steel Bolts and Studs, 60,000 PSI Tensile Strength, American Society for Testing Materials, West Conshohocken, PA, 1994.
ASTM A325, Standard Specification for Structural Bolts, Steel, Heat Treated, 120/125 ksi Minimum Tensile Strength, American Society for Testing Materials, West Conshohocken, PA, 1996.
ASTM A490, Standard Specification for Heat-Treated Steel Structural Bolts, 150 ksi Minimum Tensile Strength, American Society for Testing Materials, West Conshohocken, PA, 1997.
ASTM A563, Standard Specification for Carbon and Alloy Steel Nuts, American Society for Testing Materials, West Con-shohocken, PA, 1996.
ASTM A615, Standard Specification for Deformed and Plain Billet-Steel Bars for Concrete Reinforcement, American Society for Testing Materials, West Conshohocken, PA, 1996.
ASTM A706, Standard Specification for Low-Alloy Steel Deformed and Plain Bars for Concrete Reinforcement, American Society for Testing Materials, West Conshohocken, PA, 1996.
ASTM A767, Standard Specification for Zinc-Coated (Galvanized) Steel Bars for Concrete Reinforcement, American Society for Testing Materials, West Conshohocken, PA, 2000.
ASTM A780-00 Standard Practice for Repair of Damaged and Uncoated Areas of Hot-Dip Galvanized Coatings, American Society for Testing Materials, West Conshohocken, PA, 2000.
ASTM B695, Standard Specification for Coatings of Zinc Mechanically Deposited on Iron and Steel, American Society for Testing Materials, West Conshohocken, PA, 1991.
ASTM F436, Standard Specification for Hardened Steel Washers, American Society for Testing Materials, West Conshohocken, PA, 1993.
ASTM F1554, Standard Specification for Anchor Bolts, Steel, 36,55, and 105-ksi Yield Strength, American Society for Testing Materials, West Conshohocken, PA, 1997.
AWS D1.1-2000, Structural Welding Code-Steel, American Welding Society, Miami, 2000.
AWA D1.4, Structural Welding Code-Reinforcing Steel, American Welding Society, Miami, 2000.
Building Code Requirements for Structural Concrete (ACI 318-02) and Commentary (ACI 318R-02), American Concrete Institute, Detroit, MI, 2002.
Code of Standard Practice for Steel Buildings and Bridges, American Institute of Steel Construction (AISC), Chicago, March 2000.
Cook, R. A., Behavior and Design of Ductile Multiple-Anchor Steel-to-Concrete Connections, Thesis Dissertation, The University of Texas at Austin, Austin, TX, 1989.
Cook, S.J., Till, R. D., and Pearson L., Fatigue Cracking of Horizontal Gusset Plates at Arm-to-Pole Connection of Cantilever Sign Structures, Michigan Department of Transportation, Lansing, 2000.
DeSantis, P.V. and Haig, P.E., "Unanticipated Loading Causes Highway Sign Failure," ANSYS Conference, 1996.
Dexter, R. J. and B. A. Kelly, "Research on Repair and Improvement Methods," International Conference on Performance of Dynamically Loaded Welded Structures, Proceedings of the IIW 50th Annual Assembly Conference, San Francisco, California, July 13-19, 1997, Welding Research Council, Inc., New York, pp. 273-285, 1997.
Dexter, R. J. and Ricker, M. J., Fatigue-Resistant Design of Cantilevered Signal, Sign, and Light Supports, National Cooperative Highway Research Program, Final Report-NCHRP Project 10-38(2), Transportation Research Board, Washington, D.C., June 2001.
Dexter, R.J. and Ricker, M. J., NCHRP Report 469: Fatigue-Resistant Design of Cantilevered Signal, Sign, and Light Supports, Transportation Research Board, National Research Council, Washington, D.C., 2002.
Draft of ACI 349 Code Requirements for Nuclear Safety Related Concrete Structures, American Concrete Institute, Farmington Hills, Michigan, 2000.
Esonix UIT Specification for Fillet Welds Associated with Traffic Signal Poles, Applied Ultrasonics, Birmingham, AL.
Federal Highway Administration, Manual for Uniform Traffic Control Devices, 2003.
Federal Highway Administration, "High-Strength Bolts for Bridges," FHWA Report No. FHWA-SA-91-031, Office of Technology Application, May, 1991.
FHWA Electronic Information System Survey on Sign Structure Failures, Spring, 1990.
Fisher, J.W., Barthelemy, B.M., Mertz, D.R., and Edinger, J.A., NCHRP Report 227: Fatigue Behavior of Full Scale Welded Bridge Attachments, Transportation Research Board, National Council, Washington, D.C., 1980.
Fisher, J.W., and Dexter, R.J., "Weld Improvement and Repair for Fatigue Life Extension, "Proceedings of the 12th International Conference on Offshore Mechanics and Arctic Engineering Conference (OMAE), 20-24 June 1993, Salama et al. Eds., ASME, Vol. III, Part B, Materials Engineering, pp. 875-882, 1993.
Fisher, J.W., Hausammann, H., Sullivan, M.D., and Pense, A.W., NCHRP Report 206: Detection and Repair of Fatigue Damage in Welded Highway Bridges, Transportation Research Board, National Research Council, Washington, D.C., June 1979.
Fisher, J.W. and R.J. Dexter, "Field Experience with Repair of Fatigue Cracks," AWS/WIC International Conference on Fatigue, Toronto, 9-10 May, pp. 45-52, 1994.
Fouad, F. H., Calvert, E. A., and Nunez, E., NCHRP Report 411: Structural Supports for Highway Signs, Luminaires, and Traffic Signals, Transportation Research Board, National Research Council, Washington, D.C., April 1997.
Garlich, Collins; 'Sign Structures under Watch' Roads and Bridges Magazine, July 1997.
Gilani, A., and Whitaker, A., "Fatigue-Life Evaluation of Steel Post Structures. I: Background and Analysis," Journal of Structural Engineering, March 2000.
Gregory, E. N., Slater, G., and Woodley, C.C., NCHRP Report 321: Welded Repair of Cracks in Steel Bridge Members, Transportation Research Board, National Research Council, Washington, D.C., October 1989.
Hartle, R. A. et al., Bridge Inspector's Training Manual, Report No, FHWA/PD-91/015, Federal Highway Administration, May 1995.
Holt, Thorkildsen; Publication for the 18th annual International Bridge Conference - 'Overhead Sign Structure Inspections in New York State', Pittsburgh, Pennsylvania, June 2001.
Illinois Department of Transportation, 'Sign Structure Inspection Manual', August 1985.
Jirsa, J. O., Cichy, N. T, Calzadilla, M. R., Smart, W. H., Pavluvcik, M. P, and Breen, J. E., Strength and Behavior of Bolt Installations in Concrete Piers, Research Report 305-1F, Center for Transportation Research, The University of Texas at Austin, Austin, Texas, November 1984.
Kaczinski, M. R., Dexter, R. J., and Van Dien, J. P., NCHRP Report 412: Fatigue-Resistant Design of Cantilevered Signal, Sign, and Light Supports. Transportation Research Board, National Research Council, Washington, D.C., 1996.
Kelly, B.A., Dexter, R.J., and Crompton, J., Weld Detail Fatigue Life Improvement Techniques, Report SR-1376, Ship Structure Committee, Washington, D.C., 1997.
Kulak, G.L., Fisher, J.W., and Struik, J.H.A., Guide to Design Criteria for Bolted and Riveted Joints, Section Edition, John Wiley and Sons, New York, 1987.
Manual of Steel Construction, Load and Resistance Factor Design, Second Edition, American Institute of Steel Construction, Inc., Chicago, IL, 1998.
McCrum, R., Brief Summary of Michigan's Research Work with Anchor Bolts on Cantilevered Sign Structures, Materials and Technology Division, Michigan Department of Transportation, Lansing, 1993.
National Cooperative Research Council Project 350, 2001.
New Jersey Department of Transportation Sign Structure Database, February, 2003.
New York State Department of Transportation, 'Overhead Sign Structure Inventory and Inspections Manual, 1996.
New York State Department of Transportation, 'Specification for Overhead Sign Structure Inspection,' October 2002.
Specification for Structural Joints Using ASTM A325 or A49O Bolts, Research Council For Structural Connections (RCSC), available from American Institute of Steel Construction (AISC), Chicago, 1999.
Standard Specifications for Structural Supports for Highway Signs, Luminaires and Traffic Signals, 4th Edition, American Association of State Highway and Transportation Officials, Washington, D.C., 2001.
Structural Bolting Handbook, Steel Structures Technology Center, Inc., Novi, MI, 2001.
Thorkildsen, 'Challenges to Hands On Inspection of Overhead Sign Structures', Structures Material Technology V, and NDT Conference, September 2002.
Thorkildsen; Development of Management System for New Jersey Overhead Signs' Highway Engineering Exchange Program (HEEP), June 2003.
Till, R.D., and Lefke, N.A., The Relationship Between Torque, Tension, and Nut Rotation of Large Diameter Anchor Bolts, Materials and Technology Division, Michigan Department of Transportation, Lansing, October 1994.
29 CFR Part 1926, Safety Standards for Steel Erection, Federal Register, Vol. 66, No. 12, Department of Labor, Occupational Safety and Health Administration (OSHA), 29 CFR Part 1926, Thursday, January 18, 2001.