This is the Engineering Policy Guide Test Site. To view the current EPG click here

Difference between revisions of "903.21 Construction Inspection Guidelines for Sec 903"

From Engineering_Policy_Guide
Jump to navigation Jump to search
m ("ensure" correction)
m (Per TS, minor updates)
 
(8 intermediate revisions by the same user not shown)
Line 1: Line 1:
−
[[image:903.20 KC skyline.jpg|left|475px]]
+
[[image:903.20 KC skyline.jpg|right|475px]]
  
−
==General ([http://www.modot.mo.gov/business/standards_and_specs/Sec0903.pdf for Sec 903.1])==
+
==903.21.1 General ([http://www.modot.org/business/standards_and_specs/SpecbookEPG.pdf#page=13 for Sec 903.1])==
  
−
Responsibility for erection of signing and route marking on interstate and certain primary routes has been assigned to Construction & Materials.  
+
The contractor is responsible for erection of highway signing in accordance with the plans, specifications and provisions.  The construction inspector should provide quality assurance oversight to ensure proper installation.
  
−
Changes in standards and specifications have been rapid and numerous. Due to these changes, it is essential that all personnel assigned to inspection of signing projects, regardless of previous signing experience, make a detailed study of the plans, specifications and proposal before work commences.
+
==903.21.2 Staking, Layout and Hold Points==
  
−
The list of equipment and materials contained in proposals for erection of signs is to be submitted by the contractor soon after award of the contract.  The list serves a purpose similar to that outlined in [http://www.modot.mo.gov/business/standards_and_specs/Sec0901.pdf Sec 901].  
+
The contractor is responsible for all staking and layout.  The Resident Engineer should include “Verification of highway signing locations” on the list of contractor Hold Points. After the contractor stakes the sign locations, the inspector should review each location with the contractor and determine whether there are any conflicts with other signs or roadway items and adjust as necessary.  District Traffic personnel should be consulted before making any significant changes to the planned location.  For large signing projects, it is recommended to invite district Traffic staff to the hold point evaluation of sign locations.  Once grading of the slopes is complete, and the sign locations are approved by the engineer, the contractor will have the information needed to determine the post lengths.  To save time, some contractors prefer to pre-order extra length for posts and field cut to the required length. No payment should be made for excess cut-offs.
  
−
==Staking==
+
==903.21.3 Base Construction Inspection (for Sec 903.3)==
  
−
Check preliminary staking to determine whether the plan location of each sign conflicts with another sign or roadway item.  How this is done will later be explained in detail. The amount of staking done at this time depends on the grading of the roadway portion of the project. If signing is let after roadway completion, it is suggested that the sign number and station be painted on the pavement edge. Laths may be used temporarily to establish plan position of the footing or footings.  If signing is let in conjunction with grading, bridges and paving operations, it is important for the Resident Engineer to authorize the station location and offset distance as soon as possible.  From this information, the contractor will determine the post length required.
+
Excavating, forming, pouring and curing of concrete sign bases will be done in accordance with contract requirements. Inspection of these operations is similar to procedures set out in Division 700 of the ''Missouri Standard Specifications for Highway Construction'' for structures. Galvanized signposts are not to be stored on the ground. Storage on the ground for lengthy periods results in stained and unsightly posts. Ensure the base, post and sign installation details are in accordance with the standard plans. The inspector should check welds on cover plates and base plates of bolt-down posts for rust spots. These and other small areas where galvanizing has been chipped off due to rough handling should be cleaned and repaired. If a post shows considerable rust along welds, it should be rejected. The area around washers and bolts on breakaway features is to be free of beads and runs so a true value is obtained for torque requirements.   
−
[[image:903.20 snow.jpg|right|385px|thumb|<center>'''Signs are located so they will not be splattered by snow and ice'''</center>]]
 
−
Plan location of a sign is only approximate. The inspector is to check each plan location to determine that sight distance is ample, the sign will not conflict with any roadway or bridge feature and is positioned so that it will not be splattered by snow and ice removal from a nearby overhead bridge.  Also, if highway lighting is to be installed, carefully check to see that a pole or group of poles will not obscure sign face copy.  Avoid locating a large shoulder mount sign directly behind a lighting pole.  A light near a sign face will cause glare on a portion of the face and lessen its effectiveness.
 
  
−
After preliminary staking is completed, the entire signing project should be checked with the help of district traffic personnel. A general rule to follow in checking a sign location is that there should be an unobstructed view of the sign face for a distance of 50 ft. per in. of letter height for the silkscreen type of sign, and 60 ft. per in. of letter height for a reflectorized sign using cutout letters.  This ideal distance cannot be obtained in every case due to geometrics of certain interchanges, addition of lighting, number of signs involved in a particular area and many other factors.  However, an effort should be made to adjust signs to obtain the above sight distances whenever possible.  Avoid shifting a sign to a location where its effectiveness is lost or its message can be misunderstood.  Whenever possible, signs should be located behind guardrail installed for other purposes.  When this can be done, there is no need for a breakaway feature on the post.  Another point to be checked is the possibility of offsetting structural signs 30 ft. from edge of pavement.  This offset will also eliminate the need for the breakaway feature.  Even though a structural sign cannot be offset 30 ft. from edge of pavement, it is desirable to offset it as far as possible for added safety.  
+
==903.21.4 Sign Inspection==
  
−
To determine if proper sight distance will be available, place range poles or laths at horizontal limits of the sign.  An observer facing the sign location at the proper distance and in the approximate plane of an approaching driver may readily determine any conflicts.  Any necessary adjustments in sign location can then be made.  
+
The inspector is to make a careful inspection of signs when they arrive on the project site and that they are stored properly. Signs should be stored vertically and not in contact with the ground or vegetation. Moisture trapped between signs can damage the reflectivity.  When signs are unpacked, carefully inspect each sign for damage incurred in packaging or in transit and for errors in copy. Make spot checks of letter and numeral height and spacing using the original plan drawings as a guide.  
  
−
After sign locations have been correctly established, final staking may be done. The time of this staking depends upon whether signing is a separate project or is included in a general contract.  
+
Night inspections as well as daytime inspections should be made of all signs, delineators and mileposts. Make night inspections to check reflectivity of signs and delineators.
 +
Sign erection inspection consists not only of checking sign faces during erection but also of making certain the panel has minimum plan horizontal and vertical clearances. The sign is to be erected so that its top edge is horizontal and its vertical edges plumb.  Skew angle should be 93° from the roadway.  Refer to [https://www.modot.org/missouri-standard-plans-highway-construction Standard Drawings] for details.
  
−
Skew angle, shown on [http://www.modot.mo.gov/business/standards_and_specs/documents/90303.pdf  Standard Plan 903.03] for 2- and 3-post signs, is very important in the erection of shoulder mount signs.  If a sign is erected without proper skew angle, the sign will reflect too much light from vehicle headlights and sign copy will be unreadable due to glare.  The skew angle may be increased to give better nighttime readability when the panel is located on the inside of a short radius curve.  It is also good practice to skew all single-post, shoulder mount signs in the same manner.  Exceptions are “Stop” sign panels and structural signs located 30 ft. from edge of pavement.  These signs are normally more effective if they directly face approaching traffic.
+
==903.21.5 Truss Erection==
−
 
 
−
The number of stakes required to provide line and grade for sign footings varies, depending upon type of footing and the number of footings required for a particular sign.  It is not intended to set out an exact procedure and number of stakes to be employed for any particular footing.  Enough “red heads”, “tacked hubs” and grade stakes should be provided so the contractor will be able to establish correct line and grade using tools of the carpenter’s trade.
 
−
 
 
−
==Base Construction Inspection (for Sec 903.3)==
 
−
 
 
−
Excavating, forming, pouring and curing of concrete sign bases will be done in accordance with contract requirements.  Inspection of these operations is similar to procedures set out in [http://www.modot.mo.gov/business/standards_and_specs/DIV0700.pdf Division 700] for structures.  Galvanized signposts are not to be stored on the ground.  Storage on the ground for lengthy periods results in stained and unsightly posts.  Forewarn the contractor that there is practically no margin for error in setting the post since the safety program requires the breakaway feature to be properly located and the sign base to be flush with ground line. The inspector should check welds on cover plates and base plates of bolt-down posts for rust spots.  These and other small areas where galvanizing has been chipped off due to rough handling should be cleaned and repaired.  If a post shows considerable rust along welds, reject the post.  The area around washers and bolts on breakaway features is to be free of beads and runs so a true value is obtained for torque requirements.  The contractor should provide suitable bracing for each post set in concrete to ensure it will remain plumb during the concrete placement and curing period.  The contractor is required to clean concrete from the post immediately after placement is finished.
 
−
 
 
−
==Sign Inspection==
 
−
[[image:903.20 inspector.jpg|right|150px|thumb|<center>'''An inspector'''</center>]]
 
−
The inspector is to make a careful inspection of signs when they arrive on the project site.  Some contractors store signs on the project for a considerable time before erection.  Other contractors prefer to have all posts erected before ordering signs shipped from the fabricating plant.  If signs are to be stored, the inspector is to insist that the signs be stored so air can circulate around sign faces and so they are not in contact with the ground or vegetation.  When signs are unpacked, carefully inspect each sign for damage incurred in packaging or in transit and for errors in copy.  Make spot checks of letter and numeral height and spacing using the original plan drawings as a guide.
 
−
 
 
−
If the contractor erects sign panels directly from a delivery truck, be present to inspect each panel as it is erected.  If a sign is slightly damaged, the contractor should be allowed to make field repairs if he wishes to do so.  Forewarn the contractor that the state reserves the right to reject the panel if it is not suitably repaired.  All stud bolts should be checked before acceptance to be sure they have not been damaged or pulled loose from the sign back.
 
−
 
 
−
Repair of a [[:category:1042 Highway Sign Material|reflective sheeting]] covered panel should be so done that the repaired section is not noticeable either by day or night under car headlights, from a distance of approximately 15 to 20 ft.  If a reflective sheeting covered panel is dented, the dents should be hammered out or filled with a compound of powdered aluminum and epoxy, ground to a smooth, flat finish and covered with a piece of reflective sheeting of the same color and shade as the original.  After a reflective sheeting repair has been made, it should be given a finish of clearcoat plastic sealer.  The important thing to remember in repair of a reflective sheeting panel is to seal the edges of the repair so moisture cannot get behind the reflective sheeting. 
 
−
 
 
−
Repair of metal for baked enamel panels is to be done as set out above.  Repair of the painted surface is to be done with colors that exactly match the original color.  A wise contractor usually asks the fabricator to send with the signs a small quantity of air-dry enamel that will match the enamel used on the panels at the plant.  Carefully inspect all enameled signs for indications of peeling paint.  Usual indications are many small blisters on the surface and bare spots on the panel that show no signs of being chipped by careless handling.  Reject signs that show evidence of peeling or blistering of enamel.  This cannot be overstressed because peeling of enamel from signs previously erected has been a serious problem.
 
−
 
 
−
Reject any letter, numeral, arrow or border segment that has been dented or shows cracks in the enamel or reflective finish.  To date, satisfactory repairs of cutout letters have not been accomplished.  Most contractors will not attempt repair in the field.  It is very simple to replace a letter or figure of this type.
 
−
 
 
−
Each cutout letter, numeral, arrow or border is to have enough rivets to hold the reflectors securely in place.  If reflector buttons slip or become misplaced during sign erection, the inspector should require additional rivets to be placed in strategic locations to secure all reflectors in a letter, figure or symbol.
 
−
 
 
−
Night inspections as well as daytime inspections should be made of all signs, delineators and mileposts.  Make night inspections to check reflectivity of reflectorized sheeting, reflectors in cutout letters and delineators.  Remember that dew and frost collection on signs that have reflective sheeting tends to lessen the desired effect of the signs.  Inspections should be made before dew or frost collects to properly evaluate effectiveness of signing.
 
−
 
 
−
Sign erection inspection consists not only of checking sign faces during erection but also of making certain the panel has minimum plan horizontal and vertical clearances.  The sign is to be erected so that its top edge is horizontal and its vertical edges plumb.  On bolt-down posts, grouting of bases should not be permitted until the sign is fastened in final position. Check all aluminum nuts to see that they are tightened to a snug fit but are not so tight as to exceed yield strength of the material.  A rule to follow for obtaining a snug fit on a nut that utilizes a lock washer is to tighten the nut until the washer is flat plus an additional one-half turn.  Care should be taken in tightening the nut on hook bolt connections, as excessive tightening will distort the plane of the sign face or pull the hook bolt from its eye in the zee bar stringer.
 
−
 
 
−
All nuts on sign base anchor bolts are to be tightened snugly before the space between base plate and concrete base is filled with expansive grout.  The expansive grout should be an extremely stiff mix using as little water as possible.  When grout is packed into place there should be no excess water squeezing out of the mix.  Water added for final troweling and finishing should also be kept to the minimum necessary for a neat appearance.  The inspector should insist on either a membrane cure or a wet burlap curing period of the specified time.
 
−
 
 
−
==Truss Erection==
 
  
 
Normally, plan truss locations are carefully checked before the project is placed under contract.  There have been very few occasions when they have had to be moved to clear a roadway structure.  However, if a truss’s location needs to be changed, district Traffic and district Design should be consulted.  Features that should not be altered when moving a truss are:  
 
Normally, plan truss locations are carefully checked before the project is placed under contract.  There have been very few occasions when they have had to be moved to clear a roadway structure.  However, if a truss’s location needs to be changed, district Traffic and district Design should be consulted.  Features that should not be altered when moving a truss are:  
  
−
:(1) Maintain the 17 ft. minimum clearance from the highest point of pavement to the lowest member of the truss.  
+
:(1) Maintain the 17 ft. 6 in. minimum clearance from the highest point of pavement to the lowest member of the truss.  
  
−
:(2) Maintain a minimum of 2 ft. of backfill over the entire truss footings.
+
:(2) Check for possible conflicts with overhead power transmission lines. Refer to [http://www.modot.org/business/standards_and_specs/SpecbookEPG.pdf#page=13 Sec 901.1]. 
  
−
:(3) Where highway lighting is to be installed in conjunction with signing work or is to be let at a later date, take care to avoid locating a mercury vapor luminaire closer than 50 ft. ahead or behind the truss.  This is to prevent the luminaire from reflecting light from the sign face into the motorist’s eyes when located in front of the truss.  
+
Staking, excavating, forming and concreting of truss footings and pedestals are similar to operations performed when building a bridge footing.  Inspection procedure should follow, in general, instructions set out in [https://www.modot.org/missouri-standard-specifications-highway-construction Division 700] of the ''Missouri Standard Specifications for Highway Construction''.  In addition, conduit run through the truss pedestal is to be properly capped to prevent concrete from entering during placement.  
  
−
:(4) Check for possible conflicts with overhead power transmission lines.  Refer to [http://www.modot.mo.gov/business/standards_and_specs/Sec0901.pdf Sec 901.1]. 
+
When truss erection is done after the roadway is opened to traffic, the inspector will make certain the contractor takes necessary measures to ensure traffic protection. If traffic will have to be stopped for truss erection, the inspector is to require the contractor to have all pre-erection column adjustments made in advance. The contractor should have all necessary workers and erection materials at hand before traffic is stopped so the least possible delay occurs. The inspector should instruct the contractor to adjust the columns for the overhead truss to the proper spacing by use of the leveling nuts. Proper spacing depends on the material from which the truss is fabricated and the temperature of the truss material at time of erection.
  
−
Staking, excavating, forming and concreting of truss footings and pedestals are similar to operations performed when building a bridge footing.  Inspection procedure should follow, in general, instructions set out in [http://www.modot.mo.gov/business/standards_and_specs/DIV0700.pdf Division 700].  In addition, conduit run through the truss pedestal is to be properly capped to prevent concrete from entering during placement.
+
Plans for both aluminum and steel overhead trusses generally show one inch of collar space on each side of the column at a temperature of 55º F.  A temperature correction should be made by adjustment of the base leveling nuts. For example, if a 75 ft. steel truss is to be erected at a metal temperature of 110º F, the following calculations are to be made:   
−
 
 
−
When truss erection is done after the roadway is opened to traffic, the inspector will make certain the contractor takes necessary measures to ensure traffic protection.  If traffic will have to be stopped for truss erection, the inspector is to require the contractor to have all pre-erection column adjustments made in advance.  The contractor should have all necessary workers and erection materials at hand before traffic is stopped so the least possible delay occurs.  The inspector should instruct the contractor to adjust the columns for the overhead truss to the proper spacing by use of the leveling nuts.  Proper spacing depends on the material from which the truss is fabricated and the temperature of the truss material at time of erection.
 
−
 
 
−
Plans for both aluminum and steel overhead trusses generally show one in. of collar space on each side of the column at a temperature of 55º F.  A temperature correction should be made by adjustment of the base leveling nuts. For example, if a 75 ft. steel truss is to be erected at a metal temperature of 110º F, the following calculations are to be made:   
 
  
 
:Using a coefficient of expansion for steel of 0.0000065 per degree Fahrenheit, the correction would be:
 
:Using a coefficient of expansion for steel of 0.0000065 per degree Fahrenheit, the correction would be:
  
−
:: (110º -55º) x 75 x 0.0000065 = 0.027 ft. = 5/16 in.   
+
:: (110º - 55º) x 75 x 0.0000065 = 0.027 ft. = 5/16 in.   
  
−
Each space, nearest to the roadway, between the collar and the column should be reduced by 5/32 in.  If the same length truss is aluminum, the coefficient of expansion for aluminum is 0.000013 per degree Fahrenheit and the correction would be:
+
Each space, nearest to the roadway, between the collar and the column should be reduced by 5/32 inch.  If the same length truss is aluminum, the coefficient of expansion for aluminum is 0.000013 per degree Fahrenheit and the correction would be:
  
−
::(110º-55º) x 75 x 0.000013 = 0.054 ft. = 5/8 in.   
+
::(110º - 55º) x 75 x 0.000013 = 0.054 ft. = 5/8 in.   
  
−
Each space, nearest the roadway, between column and collar should then be reduced by 5/16 in.  Conversely, if metal temperature is below 55º F, column tops should be adjusted to increase the space by the amount calculated.  The foregoing calculations were made on the assumption that the truss columns were spaced plan distance apart and that the truss was fabricated to plan length.  Any variation from plan in either case will have to be taken into consideration and adjustments made accordingly.  
+
Each space, nearest the roadway, between column and collar should then be reduced by 5/16 inch.  Conversely, if metal temperature is below 55º F, column tops should be adjusted to increase the space by the amount calculated.  The foregoing calculations were made on the assumption that the truss columns were spaced plan distance apart and that the truss was fabricated to plan length.  Any variation from plan in either case will have to be taken into consideration and adjustments made accordingly.  
  
 
The foregoing instructions are given with the knowledge that most overhead trusses, over a period of time, gradually shift left or right and finally bear against the collar.  This is probably due to traffic vibration and to unequal coefficients of friction between column and truss bearing areas.  However, it is essential to set the truss on the columns with proper spacing, based on temperature, between each column and its respective collar during initial erection.  
 
The foregoing instructions are given with the knowledge that most overhead trusses, over a period of time, gradually shift left or right and finally bear against the collar.  This is probably due to traffic vibration and to unequal coefficients of friction between column and truss bearing areas.  However, it is essential to set the truss on the columns with proper spacing, based on temperature, between each column and its respective collar during initial erection.  
−
 
−
==Truss Lighting Systems==
 
−
 
−
Sign lighting placed on overhead trusses usually consists of a series of Mercury Vapor or Metal Halide luminaires wired in parallel and mounted forward of the catwalk.  Their placement angle or angle of longitudinal tilt should be such that sign face area is equally illuminated at all points.  Inspect each fixture for shipment damage and to ensure that proper bulbs and ballasts are installed.  Each fixture is to be wired to the No. 10 gauge power supply cables by use of tap splices and short lengths of No. 14 THW or THHW insulated wire, rather than by wiring power supply cables to the terminal in each fixture. 
 
−
 
−
Test cable-conduit between the power source and truss switch box in accordance with [http://www.modot.mo.gov/business/standards_and_specs/Sec0901.pdf Sec 901.4].  This is particularly important where the truss circuit is to be wired to an existing mercury vapor lighting circuit or to a mercury vapor lighting circuit that is to be placed by another contractor.  If truss circuits are checked in advance of final connections, the inspector can be reasonably sure that if trouble develops on the mercury vapor circuit, the sign lighting circuit will not be the cause.
 
  
  
 
[[Category:903 Highway Signing]]
 
[[Category:903 Highway Signing]]

Latest revision as of 08:52, 27 April 2021

903.20 KC skyline.jpg

903.21.1 General (for Sec 903.1)

The contractor is responsible for erection of highway signing in accordance with the plans, specifications and provisions. The construction inspector should provide quality assurance oversight to ensure proper installation.

903.21.2 Staking, Layout and Hold Points

The contractor is responsible for all staking and layout. The Resident Engineer should include “Verification of highway signing locations” on the list of contractor Hold Points. After the contractor stakes the sign locations, the inspector should review each location with the contractor and determine whether there are any conflicts with other signs or roadway items and adjust as necessary. District Traffic personnel should be consulted before making any significant changes to the planned location. For large signing projects, it is recommended to invite district Traffic staff to the hold point evaluation of sign locations. Once grading of the slopes is complete, and the sign locations are approved by the engineer, the contractor will have the information needed to determine the post lengths. To save time, some contractors prefer to pre-order extra length for posts and field cut to the required length. No payment should be made for excess cut-offs.

903.21.3 Base Construction Inspection (for Sec 903.3)

Excavating, forming, pouring and curing of concrete sign bases will be done in accordance with contract requirements. Inspection of these operations is similar to procedures set out in Division 700 of the Missouri Standard Specifications for Highway Construction for structures. Galvanized signposts are not to be stored on the ground. Storage on the ground for lengthy periods results in stained and unsightly posts. Ensure the base, post and sign installation details are in accordance with the standard plans. The inspector should check welds on cover plates and base plates of bolt-down posts for rust spots. These and other small areas where galvanizing has been chipped off due to rough handling should be cleaned and repaired. If a post shows considerable rust along welds, it should be rejected. The area around washers and bolts on breakaway features is to be free of beads and runs so a true value is obtained for torque requirements.

903.21.4 Sign Inspection

The inspector is to make a careful inspection of signs when they arrive on the project site and that they are stored properly. Signs should be stored vertically and not in contact with the ground or vegetation. Moisture trapped between signs can damage the reflectivity. When signs are unpacked, carefully inspect each sign for damage incurred in packaging or in transit and for errors in copy. Make spot checks of letter and numeral height and spacing using the original plan drawings as a guide.

Night inspections as well as daytime inspections should be made of all signs, delineators and mileposts. Make night inspections to check reflectivity of signs and delineators. Sign erection inspection consists not only of checking sign faces during erection but also of making certain the panel has minimum plan horizontal and vertical clearances. The sign is to be erected so that its top edge is horizontal and its vertical edges plumb. Skew angle should be 93° from the roadway. Refer to Standard Drawings for details.

903.21.5 Truss Erection

Normally, plan truss locations are carefully checked before the project is placed under contract. There have been very few occasions when they have had to be moved to clear a roadway structure. However, if a truss’s location needs to be changed, district Traffic and district Design should be consulted. Features that should not be altered when moving a truss are:

(1) Maintain the 17 ft. 6 in. minimum clearance from the highest point of pavement to the lowest member of the truss.
(2) Check for possible conflicts with overhead power transmission lines. Refer to Sec 901.1.

Staking, excavating, forming and concreting of truss footings and pedestals are similar to operations performed when building a bridge footing. Inspection procedure should follow, in general, instructions set out in Division 700 of the Missouri Standard Specifications for Highway Construction. In addition, conduit run through the truss pedestal is to be properly capped to prevent concrete from entering during placement.

When truss erection is done after the roadway is opened to traffic, the inspector will make certain the contractor takes necessary measures to ensure traffic protection. If traffic will have to be stopped for truss erection, the inspector is to require the contractor to have all pre-erection column adjustments made in advance. The contractor should have all necessary workers and erection materials at hand before traffic is stopped so the least possible delay occurs. The inspector should instruct the contractor to adjust the columns for the overhead truss to the proper spacing by use of the leveling nuts. Proper spacing depends on the material from which the truss is fabricated and the temperature of the truss material at time of erection.

Plans for both aluminum and steel overhead trusses generally show one inch of collar space on each side of the column at a temperature of 55º F. A temperature correction should be made by adjustment of the base leveling nuts. For example, if a 75 ft. steel truss is to be erected at a metal temperature of 110º F, the following calculations are to be made:

Using a coefficient of expansion for steel of 0.0000065 per degree Fahrenheit, the correction would be:
(110º - 55º) x 75 x 0.0000065 = 0.027 ft. = 5/16 in.

Each space, nearest to the roadway, between the collar and the column should be reduced by 5/32 inch. If the same length truss is aluminum, the coefficient of expansion for aluminum is 0.000013 per degree Fahrenheit and the correction would be:

(110º - 55º) x 75 x 0.000013 = 0.054 ft. = 5/8 in.

Each space, nearest the roadway, between column and collar should then be reduced by 5/16 inch. Conversely, if metal temperature is below 55º F, column tops should be adjusted to increase the space by the amount calculated. The foregoing calculations were made on the assumption that the truss columns were spaced plan distance apart and that the truss was fabricated to plan length. Any variation from plan in either case will have to be taken into consideration and adjustments made accordingly.

The foregoing instructions are given with the knowledge that most overhead trusses, over a period of time, gradually shift left or right and finally bear against the collar. This is probably due to traffic vibration and to unequal coefficients of friction between column and truss bearing areas. However, it is essential to set the truss on the columns with proper spacing, based on temperature, between each column and its respective collar during initial erection.

Retrieved from "https://epgtest.modot.org/index.php?title=903.21_Construction_Inspection_Guidelines_for_Sec_903&oldid=49309"