Category:760 General Construction Inspection for Structures
|Bridge Clearance Report Form|
|Typical Computation for Haunch|
|Reporting of Changes to Bridge Clearance FAQs|
|Work crews build a new 670 ft. bridge deck alongside the existing westbound deck of the Gasconade River Bridge on I-44. Crews use a bridge-jacking technique to slide the 2000-ton new bridge into place.|
This article is intended as a guide to adequate and uniform administration of inspection during construction of structures. The specialized structures are not discussed. Sound engineering judgment must be applied to those situations which occur so seldom that it is impractical to consider them in this article.
Structures include: bridges built of steel, concrete or a combination of both; bridges or trestles built of timber; concrete retaining walls, concrete crib-type retaining walls, or metal bintype retaining walls, single to multiple box culverts of concrete, storm drains, and sewers, and structural plate pipe and structural plate pipe-arch culverts.
Inspection work on structures is a great responsibility. The public safety is often at stake. Substandard construction will often lead to excessive maintenance costs.
Specifications, plans, and special provisions contain many details which the engineer must check. Such provisions govern if they should conflict with instructions in this article since this article only supplements design and contract details in a general way.
- 1 760.1 Preparation For Inspection
- 2 760.2 Inspector's Diary
- 3 760.3 Staking Structures
- 4 760.4 Vertical Clearance
760.1 Preparation For Inspection
A good inspector will study plans, specifications and special provisions in great detail. If there are questions or an error has been made, immediately consult the resident engineer. The inspector should learn what materials will be used, what samples must be taken, and what on-site tests and measurements must be made. Prepare to answer questions relating to structural plans and specifications at the preconstruction conference. Obtain supplies and equipment needed for the job and check each item carefully to be sure it is in proper working order.
The inspector should carefully examine the site and compare the information on the plans with site conditions. Spot check for any errors. If the structure is a bridge, study physical features that may affect the work and its progress and check seasonal conditions, high water levels, or other conditions that could affect the order in which operations might be performed. For a culvert, the inspector should determine if the site will be properly drained to prevent flooding or damage to the structure during construction.
For all structures, particularly in urban work, the inspector should note the position of all utilities. Check all utility agreements and right-of-way plans to see if utility adjustments clear construction. The district office should be notified of any omission to avoid construction delays.
The inspector should promptly set up the necessary field books so that completed work can be measured and entries made promptly in the proper book or on forms furnished for this purpose.
Following is a list of equipment needed for typical structure inspection. Additional items necessary for project management are found in other sections of the article.
- l. All plans, specifications, special provisions, right of way plans and agreements, and utility data that apply to the structure.
- 2. Survey equipment appropriate to the job.
- 3. One or more 100 ft. steel tapes, extra plumb bobs, and other equipment necessary for staking the structure.
- 4. 50 ft. steel tape in case.
- 5. 6 ft. folding rule.
- 6. Bound field books for field notes and diaries.
- 7. Set of current standard drawings applicable to the contract.
- 8. All necessary standard forms for use on the structure.
- 9. Equipment for necessary field tests:
- a. Compaction test equipment where required.
- b. Slump cones and tamping rods.
- c. Concrete cylinder molds.
- d. Air meters for air-entrained concrete.
- e. Compressive test machine and capping set.
Bridge Work Over Traffic
Bridge work by contractor or MoDOT forces, including erection, rehabilitation, or demolition, should not be allowed over traffic unless a bridge platform protection system is installed below the work area except for work performed above a deck that is intact. The protection system is necessary to catch falling objects such as tools, overhang brackets or materials. Lifting of objects that are heavier than the capacity of the bridge protection system should not be allowed. For example, swinging or setting large objects such as girders and deck panels over traffic should not be allowed even with a bridge protection system in place.
760.2 Inspector's Diary
Structure inspectors should keep a daily diary covering all operations. The amount of information to be kept is at the discretion of the resident engineer who must decide how much of the detailed record will be kept in his own diary. The resident engineer has the ultimate responsibility for maintaining a complete written history of the project, even though delegating portions of the task to others.
On a large bridge, such as a major stream crossing, a well organized inspection team is needed. One or more inspectors should be assigned to each major work phase under general supervision of a chief inspector. Typical major work phases are pile driving, substructure inspection, falsework and grades, superstructure forming, painting, slab inspection, and related work. Many phases may be in progress at the same time. The inspectors assigned to any phase will be the best qualified to prepare a detailed record of events concerning their area of responsibility. Their diary should contain considerable detail such as records of all instructions to the contractor's representative, a detailed description of active work in their area of responsibility, and a complete record of any unusual occurrences on the job, such as methods which might affect job quality, unusual storms, abnormally high water, a list of all equipment and manpower, etc. The diary is a history. It should not be confused with field data books for items such as grades, moisture tests, slump, etc., nor should it duplicate this data. Keep entries neat and systematic.
760.3 Staking Structures
Recommended procedures for staking structures are outlined in Construction Surveying - Staking Structures. The responsible MoDOT personnel shall satisfy themselves by independent check that staking is complete and accurate. Sometimes the bridge survey will have been made so far in advance of construction that radical changes have occurred in stream meander and flow lines. Large changes could affect the position of the bridge relative to the stream bed and nullify information shown on the plans. During staking this should be checked by taking a profile across the stream along the roadway centerline and a stream bed profile approximately 300 feet up and downstream. If large changes are found in either of the above, it may be necessary to shift the structure or revise footing elevations. The data should be sent to the district office for review and for transmittal to the Bridge Division if a design review appears warranted. Once staking is complete and checked, the resident engineer or the chief inspector should review the staking in detail with the contractor's authorized representative to be sure the individual knows the location and purpose of each stake.
760.3.2 Control Points
"Control points" establishing centerline and elevations are responsibilities of MoDOT. Such points should be established by staking methods compatible with instructions in Construction Surveying.
Contractor's forces are responsible for establishing such items as pile position, placing of footing forms and column forms, etc. Once they have done this using control points established by project forces, their request for an independent check should be granted.
As work progresses, it may be necessary to shift control points closer to the work in progress. Typically such points are established on previously completed concrete work such as top of footings or centerline of caps.
Typical items to be checked after the contractor has established their positions are piles, footings, columns, caps, anchor bolt wells, and bearing devices.
The division of responsibility under which the engineer is responsible for control points (always set on permanently fixed objects) and the contractor for intermediate points (on forms or temporary objects) is established by Sec 105.8 of the Standard Specifications.
760.4 Vertical Clearance
The legal vehicle height in the state of Missouri ranges from 13 ft. 6 in. to 15 ft. 0 in. Any loads over the legal height limit require a permit.
In order to issue permits for over-height loads, it is important that the department maintain current, accurate records of vertical clearances over and under state marked routes.
District personnel shall be responsible for measuring vertical clearances on all bridges over state routes, county roads, city streets and railroads. This includes measuring clearances on new bridges and rehabilitations that are open to traffic and measuring any time the clearance changes due to construction or maintenance projects. All bridge clearances should be verified every five years. Transportation Planning is responsible for keeping the master records of vertical clearance measurements, which are used by the Motor Carrier Services Oversize/Overweight Permits office.
760.4.2 Notification Requirements
|Reporting of Changes to Bridge Clearance FAQs|
Clearances shall be submitted at the following times:
- 1. At least two weeks before any change in vertical clearance, district personnel should advise Transportation Planning and the Motor Carrier Services Permit Office, via the BridgeClearanceReport email group, of the projected change in clearance.
- 2. Actual clearances should be measured in the field after any structure is placed across the roadway (including phased construction elements such as girders) or any time the clearance has changed significantly during construction due to setting deck panels, pouring the decks, placing construction forms or falsework, etc. An email should be sent to the BridgeClearanceReport email group.
- 3. The final vertical clearance should be measured and reported when the vertical clearance is permanent. A Bridge Clearance Report form (C-239A) should be sent to the BridgeClearanceReport email group. (See Bridge Clearance Report Form).
- 4. Vertical Clearance data that is entered into TMS will be assigned a clearance measurement date, which will be either the actual date it was measured, if known, or the date that the measurement was entered into TMS. Clearances should be remeasured every five years to ensure that an accurate database of vertical clearance measurements is maintained for the structures.
760.4.3 Roadway Measurement Requirements
Vertical clearance shall be measured on every project. This includes rehabilitation and resurfacing work as well as new construction and any temporary restrictions. Minimum vertical clearance measurements for bridges over state routes, county roads, or city streets shall be taken and reported to Transportation Planning and the Motor Carrier Services Oversize/Overweight Permits office via the BridgeClearanceReport email group.
When measuring vertical clearance, the following should be kept in mind:
- 1. All measurements shall be taken on the roadway surfaces only and not on the shoulders, even though the minimum clearance may be less on the shoulders.
- 2. One bridge over multiple routes, including ramps, will require a vertical clearance measurement for each route and in each direction of travel.
- 3. Measurement shall be made from the bottom of the lowest obstruction (beam, concrete, light fixture, rivet or bolt head, through truss member, etc.). This clearance shall be measured and rounded down to the nearest inch and reported to Transportation Planning and the Motor Carrier Services Oversize/Overweight Permits office via the BridgeClearanceReport email group.
- 4. Measurement information shall include structure identification number, route, and county. Also identify the route and direction over which the structure spans. When several roadways are involved, identify all roadways and structures with the proper clearances. For clarity, a sketch of the structure with measurements shown can be included.
760.4.4 Railroad Vertical and Horizontal Clearances
When the rehabilitation or new construction involves a structure over a railroad not only should the vertical clearance be taken, but the horizontal clearances to the nearest obstacle should also be taken.
This horizontal measurement should be taken from a point half way between the two rails of the railroad track to the nearest obstacle. (See Bridge Standard Details - Horizontal and Vertical Clearance for more information on measurement.) If multiple tracks are located under a structure additional measurements should be taken. Vertical clearance measurements should be submitted to Transportation Planning on the Bridge Clearance Report form via the BridgeClearanceReport email group. Both vertical and horizontal clearance information should also be sent to the Railroad Projects Manager located in Multimodal Operations at Central Office, who will in turn submit this information to the respective railroad company for their records.
When measuring horizontal and vertical clearance, the following should be kept in mind:
- 1. One bridge over several tracks will require several vertical clearance measurements.
- 2. All measurements for railroads are to be taken above the top of the rails and for a width of 18 ft., centered on the rails. This provides the vertical clearance for the width of a standard rail car plus anything it may be hauling that would extend beyond the sides of the car. Report actual vertical clearances.
- 3. Measurements shall be made from the bottom of the lowest obstruction.
- 4. Measurement information shall include structure identification number, route, and county. When more than one railroad track is involved, identify each work track with the proper clearance. For clarity, a sketch of the structure with measurements shown can be included.
- 5. Horizontal clearances are measured from the center of the track to the nearest lateral obstruction (usually the closest pier). The minimum clearances are normally shown on the plans and this must be maintained upon completion of the project. The plans should indicate a minimum horizontal clearance for temporary construction. If this information is not indicated on the plans, contact the Rail Projects Manager in Multimodal Operation immediately.