INCREASE OF DURABILITY AND LIFETIME OF EXISTING BRIDGES. PIARC TC 4.4 EXPERIENCE. M.Sc. Gediminas Viršilas Head of Bridge Division, Lithuanian Road Administration Working group 2 of PIARC Technical Committee TC 4.4 Bridges and Related Structures presented the study Increase of Durability and Lifetime of the Existing Bridges at the end of the period 2004-2007 in PIARC 23th conference in Paris. Based on a questionnaire to members of PIARC technical committee TC 4.4, the scope of this topic was to present an inventory or a library of examples on how to increase the durability or lifetime of existing bridges and other highway structures or structure components with the intention of minimizing the agency's costs and/or traffic restrictions. How to increase the durability and/or minimizing the traffic restrictions were presented by evaluating and comparison of the traditional methods of solving the detected problems with the new, alternative, less established methods of solving the same problem. Definition of the traditional method and the new method is up to the person answering the questionnaire. The examples of solving the problems are completed with recommendation for the future design or detailing of bridges or other structures on how to avoid the detected damage/problems in the future. For easy access and to give overview, the examples are classified into four groups of examples dealing with: Group 1. Whole structures (bridges/culverts); Group 2. Superstructure: slabs and beams; Group 3. Substructure: piers and foundation; Group 4. Bridge components or furniture. The working group has received 49 examples from 20 countries or from approx. 60% of the countries asked to fill in the questionnaire. GROUP 1. WHOLE STRUCTURES (BRIDGES/CULVERTS) Group 1. Whole bridge/culverts include the following deficiencies/subgroups: 4.1.1 Insufficient load carrying capacity; 4.1.2 Deterioration; 4.1.3 Serviceability. Example 1. Belgium, Flanders Short description: Reinforced concrete 3 span bridge with mixed road and tramway traffic, the total length is 60m. Due to new tramway vehicles the load capacity is insufficient. So the bridge has to be strengthened. Traditional method: Replacement of the existing bridge (the cost is not calculated).
New/Alternative method: Rehabilitation of the existing bridge followed by strengthening the bridge deck slab with carbon fibre sheets. The agency's costs will attain 700'000 including bridge rehabilitation with new waterproofing layer and pavement. Conclusion: The reinforcement with carbon fibre sheets allows the preservation of the existing structure. The agency avoids an expensive new bridge construction and allows reduced use by road-users and tramways during execution time. With this strengthening method the appearance of the bridge doesn't change. Recommendation: Taking into consideration new materials, in this case carbon fibre sheets, allows cheaper solutions with the same load capacity and even with the same appearance of the bridge. Photo 1,2: Insufficient load carrying capacity of an existing bridge is remedied by strengthening with carbon fibre sheets. (Example from Belgium, Flanders). Example 2. Finland Short description: Due to leaking waters, the protecting zinc layer is consumed and the corrosion of the steel culvert is progressing. The steel loses its resistance. Traditional method: Replacing the old culvert by a new one. The traffic uses an alternative longer way or the culvert could be built in two stages. New/Alternative method: Slipping through a new culvert with smaller width and height into the old corroding culvert. The free space between the two culverts was filled with concrete. Conclusion: The example shows a simple method to replace a steel culvert without pulling down the existing one. Agency cost reduction: 40%. Execution time: The same for both methods, but almost no traffic disturbances at the new method. Expected life time: The same for both methods. Recommendation: The agency has chosen the same solution for an existing steel culvert as for a brick vault culvert.
Photo 3: Relining of a new culvert with a smaller width into an old corroded culvert and in that way avoiding traffic disturbance during replacement. (Example from Finland). Example 3. Finland Short description: A new pedestrian bridge was constructed through the opening of the old watercourse bridge. In this way the construction of a new pedestrian underpass was avoided. Traditional method: Building a new underpass generating considerable costs for the users and the agency. The need for a safe road crossing is due to the neighbourhood of a school. New/Alternative method: Using the clearance of the existing bridge for building a light and safe pedestrian bridge. To avoid heavy steel girders, the bridge is put on the abutments and suspended on a hanging system anchored on the repaired edge girders of the existing watercourse bridge. There are nearly no additional user costs. Conclusion: The multiple use of the space under an existing bridge makes good sense. It also allows avoiding traffic disturbances involved by a construction in the traditional way. Agency cost reduction: 40%. Recommendation: The use of the free space under bridges is often neglected and should be taken into consideration. Photo 4,5: Construction of a new pedestrian bridge inside an existing bridge. (Example from Finland).
GROUP 2. SUPERSTRUCTURE: SLABS AND BEAMS Group 2. Superstructure include the following deficiencies/subgroups: 2.1 Insufficient load carrying capacity; 2.2 Deterioration: 1. on slabs, and 2. on beams; 2.3 Serviceability. Example 1. Spain Short description: Strengthening of prestressed concrete beam due to impact from a heavy truck. Traditional method: Replacement of concrete and reinforcement with steel plates. New/Alternative method: Replacement of concrete and reinforcement with carbon Fibre Reinforced Polymer laminates. Conclusion: Agency cost reduction: 50 %. Execution time reduction: 73 %. Traffic user cost reduction: 20 %. Recommendation: Respect the decided clearance under the bridges to avoid impact from trucks. Photo 6,7: Impact on prestressed beams strengthened with carbon fibre material. (Example from Spain). GROUP 3. SUBSTRUCTURE: PIERS AND FOUNDATION Group 3. Substructure, includes the following sub-groups: 3.1. Insufficient load carrying capacity; 3.2. Deterioration; 3.3. Serviceability/settlement. Example 1. Italy Short description: Some columns exhibited deterioration. The concrete reinforcement cover had worn off in some places and the reinforcement was exposed. In addition, the detachment of the cladding represented a serious risk for the underlying urban areas. Traditional Method: The removal of 3 cm of the top layer by hydrodemolition in order to remove deteriorated concrete and expose the iron reinforcement. The preparation of reinforcement in the shape of an electro-welded 10x10 cm mesh using 10 mm rods, anchored by hooks fixed to the pre-existing structure by rheoplastic mortar. Casting of concrete
cladding to a depth of 0,10 m using rheoplastic, shrinkage-compensated repair concrete with Rck 50 MPa. New/Alternative method: Same measures as the traditional method, but different working conditions: Creation of a special multi-functional structure, which makes possible comfortable working conditions and ease of movement for the workers inside it. The structure allows comprehensive arrangements for hydrodemolition equipment, reinforcement, formwork, grouting and the isolating the work from the surrounding environment and, making it possible to move easily up and down the pier. This workshop may be regarded as 4m high 11 8 m box mounted coaxially to the pier that can move up and down through a hydraulic system. The workshop is totally enclosed with rigid panelling on its outer side and sliding seals where the box comes into contact with the pier. The workshop also has two working floors: 1. 2 m upper floor for hydrodemolition, perforating and the preparation of the reinforcement and casting; 2. 2 m lower floor for formwork assembly and disassembly operations. Conclusion: Time reduction: 30%. Agency cost reduction: 33%. Execution time: the same for both methods. Traffic user cost reduction: 100%. Expected life time: the same for both methods. Recommendation: Make provision of a special equipment to permit easy checking of the piers. Photo 8,9: Working platform on the pier and from inside. (Example from Italy). GROUP 4. BRIDGE COMPONENTS OR FURNITURE Group 4. Bridge component or furniture group includes the following subgroups: 4.1. Leaking of deck joints; 4.2. Inadequate or damaged parapets; 4.3. Wearing/deteriorated pavement; 4.4. Wearing of painting. Example 1. Norway Short description: Expansion joints are functionally damaged and concrete anchoring areas are severely deteriorated. Traditional method: Step-by-step replacement of expansion joint and reconstruction of part of bridges deck during night work. To minimize traffic interruption the working area is covered by steel plates during daytime.
New/Alternative method: The working areas are prepared below a bridge-over-bridge (a 120 meter long 2-lane flyover) and the replacement of expansion joints and reconstruction of part of bridges are carried out all day without interruption of the traffic. Conclusion: Agency cost increase: First year +5%. Execution time period reduction: 55%. Recommendation: Carry out expansion joints of highest quality including increased concrete cover or use of stainless steel and make the joints suitable for inspection and replacement. Photo 10: Replacement of expansion joints below a bridge-over-bridge (temporary flyover). (Example from Norway). Example 2. Japan Short description: Deteriorated pavement and expansion joint due to heavy traffic. Traditional method: Lane-by-lane repair of asphalt and expansion joints in off-peak hours. New/Alternative method: Closing the route in a short period for carrying out all repair works. Conclusion: Agency cost reduction: First year 10% and 50% over 50 years. Execution time period reduction: 97%. Extension of time until next intervention: 0%. Recommendation: Close a route 100% for a short repair period instead of closing lane-bylane in off-peak hours for a long period but make a very clear announcement of the work/traffic restrictions!
Photo 11: Instead of lane-by-lane repair outside peak hours, the entire route is closed 100% for short repair period and the agency have saved a lot of money. (Example from Japan). CONCLUSION AND RECOMMENDATIONS. 49 examples have been received from approx. 60% of TC4.4 member and corresponding member countries. The examples are coming from North America, Japan, Europe, South Africa and New Zealand. The examples cover all essential structural components (bridge decks, slabs, supports, nonstructural elements etc.). They also present traditional and new, alternative repair solutions for different causes of damage due to insufficient design, inappropriate detailing, construction and maintenance and due to impacts from traffic, fire, environment etc. or social and political changes. It is the working group s impression that the forwarded examples are representative and that it is reasonable to anticipate that each country has forwarded their best ideas or examples on how to, on one hand extent the life time of highway structures and, on the other hand, minimize agency costs, working period and traffic restrictions. All examples were divided into four categories defining the entire structure or its components and, for each category the defects are specified. The examples demonstrate that considerations about the free traffic flow and reduction of repair costs have been the most common reasons for proposing new alternative methods of carrying out repair works. Many examples are about reduction of working time and on avoiding traffic restrictions, for example replacement of a culvert by relining a new culvert inside the old one instead of digging up the road for replacement. Other typical examples are about using new materials, such as strengthening of concrete beams or slabs with carbon-fibre sheets instead of replacement. Several examples are about immediate cost reductions by postponing the repair works or by reducing the rate of corrosion, for example by applying the cathodic protection of reinforcement. One example show how considerable costs were saved by implementing modern, probabilistic calculation methods to demonstrate sufficient load-carrying capacity.
Further examples focus on cost reductions using new materials in order to extend the life-time of structure, for example by repairing a corroded steel culvert with fibre reinforced shootcrete. Most examples include recommendation to avoid similar damage or problem occurring in the future. Essential recommendations are: Use jointless bridges; Halving joints (hinges at mid span) should be avoided; Rebars in decks should be more resistant to corrosion; Make every part of a structure accessible for maintenance, repair or replacement; It is TC 4.4 s hope that the examples in this inventory will inspire agencies, consultants and contractors in similar situations to select the optimal maintenance or repair strategy. All this issue and the others, related to bridge topics you can find in PIARC web site www.piarc.com