Overview
Structures can be built in all shapes and sizes, underground and overhead. Underground structures are built to handle storm water and sewage. Overhead structures are built to handle all types of traffic, such as vehicle, railway as well as foot and bicycle.
Contract Documents
Review all contract & plan documents for type of structure to be constructed. Also review the contract addendums and special provisions for changes to the contract specifications.
Bridges:
The City utilizes MoDot Standard Specifications when constructing bridges with project specific provisions. Category:701 Drilled Shafts, Category:702 Load-Bearing Piles, and Category: 703 Concrete Masonry Construction, are referenced manuals on the MoDot Web Site.
Submittals
Review Contract Division 1 for list of items that require submittals. This section should show all items that need to be submitted, who reviews and approve the Contractors submittals. If the project has federal funding check for the Buy America clause of all steel to be used on the project.
Bridge Reinforcing Steel:
Changes in design footing elevations require splicing of reinforcing steel in footings or columns. Splice lengths are critical because of Missouri's location to possible earthquake zones. Therefore each splice length should be checked with the Bridge Designer Engineer.
Make sure the reinforcing steel submittals has been approved and on CIP Projects with Federal Funds, check for "Buy America" Certification. Check plans for clearance of re-steel from forms.
Field Observations
For storm & sewer drainage structures check structure size, location, Type of bedding material for structure placement and backfill. For box culverts check structure footing, reinforcement size and placement. Check quality of forms, QC testing of concrete for air, slump and cylinders. Check placement of concrete and rate of pour, then check cure and protection. Make sure all material to be installed has approved submittals prior to placement into the project.
Bridges Drilled Shafts(701):
The shaft portion of a drilled shaft is usually founded on limestone and occasionally hard shale, with a smaller diameter socket into limestone or shale. The inspector should carefully study all general specifications and special provisions pertaining to drilled shafts and become familiar with the designer's intent.
The integrity of the rock socket shall be verified by a foundation inspection hole.
Bridges Load-Bearing Piles(702):
Cast in place concrete piles consist of pre-driven shells of steel later filled with concrete. The most commonly used type of spirally welded stell, sometimes called pipe piles.
Structural Steel piles are rolled H-Sections which are used in certain types of pile installations. These piles extend into the ground and transmit loads from footing to bearing stratum as columns. Pile tip reinforcement is sometimes specified when driving steel pile through boulders or thin layers of rock to protect the pile tip. Pile points can be accepted by certification and should be checked to see that they meet the specification requirements.
When Pile Driving where pre-boring is required the hole shall be of a diameter not less than that of the pile and shall be large enough to avoid damage to the pile in driving through the hole into hard material.
The inspector should be familiar with power plant, hammer, cap, cushion block, leads, and other elements used in driving. The contractor should have bulletins available for equipment he is using.
A qualified inspector should be assigned continuously on pile driving work to see that each pile is driven to specified bearing, that all piles are properly located. The inspector must keep a detailed record of the data for each pile. He must also insure that all piles have been properly inspected.
Bridge Substructure(703):
See Section 703 of the Modot Engineering Guide Policy.
Plans should be reviewed, noting that footings are to be keyed 6 inches into rock or 18 inches into shale with the sides of the footing cast against the rough surface or neat lines of bearing material.
Test Holes should be drilled before any concrete is placed for footings other that those on piles.
Check the following items during excavation:
Suitable material is kept separated from unsuitable material.
All excavated material is stored in locations where it will not bear against any part of the structure.
Satisfactory arrangements bave been made to drain the excavation or to seal out water before concreting is started.
Backfill area has been inspected to make sure all embankment will be solidly supported.
After construction: Check all cavities are filled at once with backfill material and where required, arrangement has been made for density tests on backfill. Arrangements have been make for required drainage, and backfill is being place and compacted by specified methods and to required density.
Footings on Rock or Shale(703.19.2):
Never excavate below plan elevation until probable elevation of suitable material has been determined by probes or drilling.
Forms(703.1.11):
Before placing concrete, forms must be checked for conformance with plans and specification and all irregularities corrected. The contractor should be informed of any needed corrections far enough in advance of a scheduled pour. The contractor designs forms and is responsible for the completed work. All forms should be strong enough to hold plastic concrete in place until it has hardened, without bulging or sagging. Forms should be tight enough to prevent mortar leakage.
Oiling of forms or application of any form coating should be done before placing reinforcing steel. Form ties must be such that portions can be removed or broken back as required without damage to concrete.
Forms having interior right angles corners require a chamfer strip inserted if the corner will be exposed in the completed structure.
When forming pile cap end bents, the construction project manager should review for approval the method the contractor intends to use before permitting the end bent cap to be formed.
Deck Forms(703.2):
Deck forms must be mortar tight and constructed to produce a deck of proper thickness true to line and grade. The concrete surface wil be no better than the quality of the forms.
On steel structures, overhang forms outside exterior beams or girders are usually the area of greatest potential for problems with grade control, alignment, and mortar tightness. Again, the reinforcing steel shall have the clearance, from the forms, that is shown on the bridge plans.
Machine Finishing(703.2.7):
Except for irregular areas or for structures excepted by special provisions, all riding surfaces on bridges and surfaces to receive a wearing course must be finished by use of a mechanical finishing machine. Any machine proposed must meet the approval of the engineer. Pan vibrators on bridge deck finishing machines are not vibrating screeds.
The rails must be properly supported both vertically and laterally to maintain true grade. Rails and wheels of the machine must be clean. Proper crown and slope must be set. This can be checked from a taut string. Screeds normally are set in accordance with the manufacturer's recommendation.
After the finishing machine has been checked out, it should be moved over the entire portion where concrete is to be placed. This allows checking the clearance to reinforcing steel, required deck thickness over forms or concrete slab form panels, and conformity with headers or expansion plates. It is also a check on rigidity and alignment of rails.
During concrete placement, it is important that concrete be deposited uniformly and approximately to grade. Movement of large quantities of concrete with finishing screeds cause the machine to ride up and leads to surface irregularities. Screeds or rollers should be lowered to the surface with the machine in forward motion. The number of passes required will vary due to many factors but should be enough to provide a smooth surface meeting straight-edge requirements. The final pass should be delayed to cover as much length of deck as possible for best results.
Following the machine finishing operation, the surface must be checked with a straight edge. If irregularities are found, the area must be refinished and checked again until the irregularities have been eliminated.
The Special Provisions should be reviewed for conditions and degree of skew for skewing the machine.
"The concrete shall be covered with clean mats as soon as the interim curing compound has dried sufficiently to prevent adhesion, and the concrete surface will support the curing mat without marring or distorting the finish, but not more than 90 minutes after the concrete is floated or textured." The 90 minutes is a guidance. There may be situations where the concrete has not set sufficiently in 90 minutes. The concrete should be checked frequently in this situation. The wet burlap should then be placed as soon as marring or distortion of the finish will not occur.
Concrete Placement(703.2.8):
Concrete air and slump are to be within specification prior to any placement of the concrete in the structure.
Cylinders for compressive testing must also be cast as needed or required. Instructions for sampling and testing of concrete and frequency of tests are also found in the QC and QA section of the contract.
Concrete is usually placed in wall sections through tubes or chutes. These must extend far enough inside forms to restrict the drop to that permitted by specifications.
Concrete for riding surfaces may be conveyed or placed by mechanically applied pressure using approved concrete pumps.
When an approved concrete pump is used, the designated location for quality control sampling to determine air content and slump is the point of discharge from the mixing truck.
Vibration is an essential part of concrete placement. Its purpose should not, however, be confused with methods for distribution. Vibration is to densify, not move concrete.
Specified rates of concrete placement are minimum (not overall averages) and must be met for any one hour period during placement. These rates are often quite critical on steel structures where reversal of stresses is involved. If placement rate lags seriously on a steel structure, it may become necessary to require installation of a temporary header.
The backwall should be poured a minimum of 24 hours prior to the deck with the top of the construction joint to conform with the crown of the roadway.
After the concrete has been properly finished, the surface must be textured to provide a non-skid surface. A hand operated device producing a textured surface equivalent to that required for machine combing should be used. The time of texturing should be carefully chosen to avoid damage to the surface finish but should be early enough to assure adequate indentation. Overlapping of the comb or finned float should be avoided, small gaps are acceptable.
Curing(703.2.9):
The surface of all deck concrete and other surfaces to be surface sealed must be cured with continuously wet mats. The mats must be wet when placed so they will not absorb moisture from the fresh concrete. They should be placed at the earliest possible time at which surface marring will not occur.
Curing of such surfaces shall continue for not less than 7 days or as specified in the special provisions. This period may be extended if specified strengths given in the contract have not been attained.
Bridge Slab:
Review MoDot's Bridge Slab Bridge slab checklist
prior to pour.
Form Removal(703.2.13):
Forms and falsework must be left in place until strength specified in contracts plans has been attained. Removal of falsework requires care to prevent damage to the concrete.
Honeycomb and indentations left by form hardware such as snap ties must be carefully repaired by filling with mortar as specified. Particular attention must be given to color of the mortar. It may be necessary to add a small amount of white cement to match the color of the concrete to be repaired. Such patches must be carefully cured.
Review contract to see if surface sealing is required.
Documentation
Record location of structure in field book, footing conditions, reinforcement placement. Quantity of concrete poured, air, slump and cylinders made and time of pour. For pipe structures record date installed, location, length and size of pipe.
For bridge structures record all pay items included in the contract for the bridge.
Bridge Pile Driving(702.1.5):
The inspector should record in detail all important facts regarding driving of each pile. The field book notes should be organized in a sequence similar to that shown in the Pile Driving Worksheet.
See an illustration of field book data for driving structural steel pile. This can be found at:P:\ENGINEERING DIVISION\Construction Mgmt., Inspections\Tiki-Wiki-Pages_for_PWIPM\Examples for Field Book Documentation.pdf
Bridge Substructure(703):
Structure Excavation.
Record measurements for excavation computations directly in the field book. Where there is structural excavation, original and final sections must be taken.