Bridge maintenance strengthening technology programme i, project background and status analysis
1. 1 overview of the status of bridge operations
Our nation has achieved the highest level of bridge construction in the world, with a total of 906,000 road bridges, with a total length of 8868. 1 kilometres, of which more than 90 per cent are small and medium-sized. These bridges play a key nodal role in the integrated transport system, but with the growth of service, increased traffic loads and increased environmental erosion, a large number of them enter the peak phase of maintenance. According to the ministry of transport and communications, about 15 per cent of the existing bridges in the country have varying degrees of structural damage, of which 3. 2 per cent are at risk, mainly concentrated on the early construction of concrete and arch bridges. Some of the bridges, owing to low design standards (e. G., primary 15 load levels are difficult to meet current requirements for steam-20 and above), construction quality deficiencies (e. G., lack of concrete density and uneven thickness of steel-wire protection) and long-term overloading operations, have led to reduced carrying capacity and poor durability, posing a potential threat to vehicle safety。
1. 2 major disease types and causes
Bridge diseases are characterized by diversity and complexity and can be divided into three broad categories of disease, by structural area, in the upper, lower and ancillary structures. In the upper structure, concrete sorghum cracks are most common, including curved cracks (crossing the bottom of the center zone, due to overloading or inadequate bands), cut cracks (near the abdomen, mainly due to inadequate corrosive band configuration or deterioration of the concrete strength), and temperature condensation cracks (on the side of the beams, caused by the hot and dissension of concrete with water or seasonal temperatures). Corrosion of steel bands is another core disease, mainly due to the carbonation of concrete (a decrease in ph as a result of co2 infiltration) or the erosion of chlorine ion (an ice-saltering environment in coastal areas), which results in the fragmentation and stripping of the concrete protection layer, resulting in more than 20 per cent loss of steel bands in severe cases. In the lower structure, the bridge is often convected to the cracks (the foundations are not evenly sunk or concrete shrinks), concrete is stripped down (the thawing cycle), while the bridge is prone to back-filled depositions and the migration of front walls. The aging of the bench is manifested in the cracking of the rubber turtle, the cutting of the deformation or the emptiness, resulting in an abnormal charge transfer. Auxiliary facilities, such as bridge-painted lacunas, pit tanks, condensing devices or damage, also accelerate damage to the main structure。
1. 3 need and urgency for maintenance reinforcement
Bridges as traffic lifeline worksStructural securitySex is directly related to public safety and regional economic development. At present, the failure to deal with the disease of the bridge in a timely manner will result in a sustained decline in carrying capacity and even in structural collapse (e. G., the collapse of the bridge in a province in 2021, with direct economic losses exceeding $20 million). From an economic point of view, the cost of early maintenance reinforcement is only 30-50 per cent of reconstruction and indirect losses (e. G. By-pass transportation costs, regional economic stagnation) can be avoided. In addition, as the “high-traffic countries” strategy advances, the upgrading of existing bridges is an important initiative to improve infrastructure networks, and the goal of “functional upgrading, longer life expectancy and controllability” needs to be achieved through enhanced maintenance. Industry projects that the size of our strengthened market for bridge maintenance will grow by an average of 12 per cent annually over the next five years, and there is an urgent need for systematic technology programmes to support high-quality industry development。
Ii. Maintenance strengthening technology programme
2. 1 technical classification and selection
2. 1. 1 structural reinforcement techniques
The structural reinforcement method is designed to increase the carrying capacity and stability of bridges within the bridge maintenance consolidation technology. Such technologies are aimed primarily at defects in the main structure of the bridge, such as sorghum cracks, rusty steel or the ageing of feeder structures, which are restored or increased by physical reinforcement measures. Sticky steel reinforcement is a common method by which high-strength steel plates are adhesived on concrete surfaces with special glues. For example, the sticking of steel plates in the strips of concrete beams can significantly increase resistance to more severe cracks. The method is easy to construct, has little transportation impact and is relatively low cost, provided that the quality and surface treatment of the glue are ensured and the risk of separation is avoided. Carbon fibre consolidation is the use of carbon fibre sheet or plate wrapping structures to compensate for the lack of concrete through their high tensile strength. This technology is particularly relevant for bridges in a corrosive environment, such as salt fog erosion in coastal areas, as it is resistant to corrosive and light quality. Accurate control of fibre direction and layer numbers is required during construction to optimize the effect of stress. By adding new concrete layers to the original concrete structure, with steel bars, greater cross-section dimensions and band ratios. This approach applies to the overall reinforcement of old bridges, but the construction cycle is longer, and the combination of old and new concrete needs to be considered to avoid a slide of interfaces。
2. 1. 2 non-structural reinforcement technologies
Non-structural reinforcement technologies focus on improving the durability and use of bridges rather than directly enhancing structural carrying. Surface containment is the basic method, using epoxy resin or polymer cement coating on concrete surfaces, closing cracks and holes to prevent water infiltration and carbonization. For example, the application of a sealant on the surface of the bridge will slow the process of erosion of the steel and extend its useful life. The method is simple economic, but only for shallow diseases, with limited effect on deep cracks. Fragmentation slurries are injected at high pressure into low viscosity slurries (e. G. Polyurethane or epoxy resins) to fill gaps and bind both sides. This technique effectively restores structural integrity, especially for the repair of cracks cut or constricted temperature. The choice of aluminum material needs to be adjusted to the width of the crack and environmental conditions to ensure that the plasma is fully permeable without destroying the structure. Preservative coatings are coated on the surface of steel structures or bars, such as zinc-based coatings or fluorocarbon paints, to isolate corrosive media. In the application of a bridge or beam, coatings prevent oxidation and wear, provided they are periodically inspected and maintained to avoid the loss of the coatings resulting in the failure of protection。
2. 1. 3 principles of technology selection
The selection of appropriate reinforcement technologies requires a combination of the disease characteristics of the bridge, environmental factors and economics. The type of disease is the primary basis, such as the preferential use of glued steel or carbon fibre reinforced by curved cracks, while the problem of erosion requires a combination of containment and preservation measures. Environmental conditions, such as temperature, humidity or chemical corrosion, affect the durability of materials, for example, in the northern region where freezing cycles are considered and highly resistant materials are selected. Economic assessments include direct costs (materials, labour) and indirect costs (traffic losses), lower but narrow-applicability costs for sticky steel, and high and long-term benefits for carbon fibre sequestration. The feasibility of construction is equally critical, and a busy bridge should choose rapid construction techniques, such as slurry, to avoid completely closed traffic. In addition, technical compatibility needs to ensure that old and new structures work together, such as increased cross-sections, to validate the base load and avoid uneven deposition。
2. 2 common enhancements
2. 2. 1 consolidation of concrete structures
2. 2. 1. 1 sticky steel reinforcement
The implementation of the sticky steel consolidation process began with surface treatment, which required the removal of oil stains and loose layers from the concrete surface and the use of grinding machines to roughen the surface and boost the use of glue. The steel plate is then cut to the design size and drilled to install anchors to ensure its reliability. When the adhesive coating is even, the steel plate is put in place to pressure it to be in close contact and disturbance is strictly prohibited during solidification. The method has had a significant effect in the reinforcement of the bridge beams, such as a bridge with a crack across the middle base, a 30 per cent increase in the carrying capacity after the pasting of the steel plate, and a three-day construction effort to minimize the traffic impact. It should be noted, however, that steel plates are usually 3-10 mm thick, which may lead to increased self-esteem and affect structural balance。
2. 2. 1. 2 carbon fibre reinforcement
Carbon fibre consolidation is dominated by carbon fibre sheeting, with concrete surfaces being cleaned and bottom resin painted for permeability. The fabric is then cut and impregnated with specially designed resins, with layers attached to the structure surface, each layer being pressured to remove bubbles. Finally, coating of protective layers to prevent ultraviolet damage. The technological advantage lies in the light quality and strength, which is five times the strength of steel per unit weight and is suitable for high stress areas such as bridges. For example, a saline-infested bridge has increased the durability of carbon fibres by 50 per cent and reduced construction disruption without heavy equipment. However, the direction of fibres must be consistent with the primary stress, otherwise the effect would be reduced and the cost would be higher at approximately $800-1200 per square metre。
2. 2. 1. 3 increased cross-section
By adding new concrete to the outer layer of the original concrete, the larger cross-section forms a combination of cross-sections with a steel grid. The construction steps included the cutting of old concrete surfaces, the implantation of attached steel bands, the binding of new steel bands, the emulation of concrete and its maintenance to design strength. This approach is applied to fully reinforced bridges, such as those with insufficient beryllium heights, where additional concrete can increase resistance to bends and shears. For example, a 30-year-old liang bridge has increased its carrying capacity by 40 per cent, but attention needs to be paid to the treatment of new and old concrete surfaces, the use of interfaces to enhance glue and avoid cracking. The longer construction cycle, which takes approximately two to four weeks and requires temporary support, may affect transportation。
2. 2. 2 steel structural reinforcement
2. 2. 2. 1 weld reinforcement
Welding is strengthened by the addition of welding stitches, such as an angular welding or welding stitches, where the steel structure is connected or damaged, to enhance the crosssection. Prior to construction, rust and paint are to be removed and preheated to 150-200°c to prevent heat cracks. The current and voltage are controlled during welding to ensure the mass of the welding, and no damage detection is performed upon completion. The method is efficient and reliable and applies to local repair of beams or bridge towers, such as a welding of a steel bridge with a welding strength of 90 per cent. However, welding thermal impact areas may reduce material resilience by choosing low hydrogen welds and reducing welding deformations。
2. 2. 2. 2 stabilizing bolt links
A bolt connection is reinforced by replacing or adding a connection with a high strength bolt, such as a friction or pressure bolt. At the time of construction, drills, perforations, the removal of stabbings, the coating of stainproof oils, and the installation of bolts and pre-heating. This approach applies to the rapid reinforcement of the site, such as the loose bolt of the steel bridge panel, with a 25 per cent increase in connectivity after installation. The advantage is that welding is not required and heat damage is avoided, but precise control of the twist is required to ensure consistency of pre-heat pressure, otherwise slides may occur。
2. 2. 3 reinforcement of ancillary facilities
2. 2. 3. 1 repair of bridge pavement
The repair of the surface of the bridge consists of an old coating floor, the cleaning of the ground floors, the laying of a waterproof layer, and the distribution of asphalt concrete or epoxy sand. For example, the heavy surface of the bridge, which is then re-painted, can increase the level and drainage performance and extend its useful life by three to five years. Construction needs to be carried out during the cold season to avoid high-temperature deformation and to establish temporary lanes to reduce traffic disruptions。
2. 2. 3. 2 replacement of compressors
The replacement of the stretcher involves the removal of the old device, the cleaning of the slots, the installation of new stretch stitches (e. G. Model numeric or combo) and the filling of seals. The method addresses problems of congestion or damage, such as the failure of a bridge to extend a bridge leading to the transfer of beams and the improved comfort of replacement vehicles. Installation requires precise control gaps, adaptation to temperature changes, and regular cleaning of miscellaneous items to prevent card death。
2. 3 emerging strengthening technologies
2. 3. 1 self-rehabilitating concrete technology
Self-rehabilitating concrete technology automatically restores concrete upon the occurrence of cracks by adding microcapsulations or bacterial-based restorations. For example, microcapsule break-ups release restorations that fill cracks up to 0. 5 mm wide. This technology applies to the early crack control of bridges, such as the constricting cracks of the bridges, which reduces manual intervention. However, the costs are higher, with an increase of $200-300 per cubic metre, and restorations are limited by the width of the cracks and need to be reinforced in combination with tradition。
2. 3. 2 smart monitoring and reinforcement
Intelligent monitoring and consolidation technology integration sensors (e. G. Fibre-optic or voltage sensors) monitor the state of the structure in real time, transfer data to system analysis and trigger reinforcement measures. For example, sensors are installed at key parts of the bridge to monitor adaptations and cracks, and the slurry device is automatically activated when data are above the threshold. The method increases the speed of response, such as when a bridge is reinforced in real time during overload and avoids accidents. However, the system is complex and requires professional maintenance, initial investment is significant and suitable for important bridges or pilot projects。
Construction organization and management
3. 1 construction readiness phase
3. 1. 1 prior research and programme refinement
Systematic on-site research is required prior to the launch of the bridge maintenance reinforcement project. The technicians carry specialized detection equipment to conduct a comprehensive survey of the bridge structure, focusing on key data such as the distribution of cracks, the extent of steel rust and the strength of concrete. For example, the use of uav combined manual tests by a bridge across the river prior to consolidation revealed 15 cracks of more than 0. 3 mm width at the bottom of the main beam, providing an accurate basis for subsequent programming. Upon completion of the study, and in conjunction with the technical programme identified in chapter ii, a detailed construction organizational design was developed, defining the technical parameters, quality standards and acceptance requirements for the various processes. The programme needs to consider the surrounding environment of the bridge, such as traffic, hydrological conditions, etc., to ensure that the measures are practical。
3. 1. 2 preparation of materials and equipment
A system of on-site inspection is strictly enforced for the procurement of materials, and all reinforced materials are required to provide exit certificates and third-party testing reports. In the case of carbon fibre sheets, the tensile strength and elasticity modulus should be sampled to ensure compliance with the design requirements. In terms of equipment preparation, special machinery, such as high-pressure slurry machines, for crack repair under the technical programme, and specialized glue mixing equipment for steel reinforcements require early commissioning. In a project, errors in the pressure table of the slurry was detected during the preparatory phase, and the timely replacement of the equipment avoided deficiencies. Waterproofing, collision-proofing measures during the transport of materials and equipment, stacking and marking the duration of use to prevent poor performance。
3. 1. 3 construction team organization
Establishment of a professional construction team with clear division of labour and responsibilities. Each team is staffed by technical officers, security guards and quality examiners, forming a three-tier management network. Construction personnel are required to acquire operational specifications and safety elements through specialized training. For example, a sticker reinforcement group is required to undergo hands-on training in glue matching, steel pasting, etc. To qualify for induction. Establishment of a system of pre-shifting, with technical officers providing daily briefings on tasks, risk points and response measures. At the same time, emergency medical teams are deployed to ensure rapid response to emergencies。
3. 2 on-site construction management
3. 2. 1 optimization of business processes
The construction area is divided by streaming operations to avoid cross-interference. In the case of a continuous reinforcement of the liang bridge, the bridge was divided into three construction segments, followed by cracking ale, carbon fibre pasting and bridge pavement, each of which was completed and handed over to the lower steps. A “three-inspection” system, consisting of self-inspection, cross-checking and professional inspection, is in place for key processes to ensure that each process is completed before entering the next step. Dynamic adjustment processes during the construction process, such as the suspension of outdoor operations during rainy days, which resulted in pre-treatment of indoor materials and increased time utilization。
3. 2. 2 transport facilitation and contingency planning
Develop a phased closure programme for busy traffic sections. (c) set up temporary guidance routes with traffic wardens to channel traffic. During the consolidation of a bridge in a city, construction was selected from 22:00 to 18:00, to reduce the impact on daytime traffic. Emergency response plans include scenes such as storm surges, equipment malfunctions and emergency supplies such as pumps and backup generators. Blocks and alarm lights were installed in the construction area and reflect marks were added at night to prevent accidents。
3. 2. 3 environmental protection measures
Dust and noise-reduction measures, such as the spraying of water and dust in cutting areas and the use of low-noise equipment, are used in the construction. Construction waste is sorted, retrievable materials such as steel, wood are collected and concrete blocks are used for road-based construction. During the construction of a project near the river channel, a sediment tank was installed to treat the construction wastewater to avoid contamination of the water body. Upon completion, the site was cleared in time for the restoration of surrounding vegetation and for civilized construction。
3. 3 quality and security management
3. 3. 1 quality control system
Quality management teams, headed by project managers, are established to perform “process, staff” quality control. A 100 per cent acceptance and acceptance rate for raw materials is required and the construction process is well documented, including key parameters such as the time of adhesion of glue and the number of carbon fibre coatings. Use of non-destructive detection techniques, such as ultrasound detection of concrete density to ensure reinforcement. A project, which was reinforced with sticky steel, examined the plate's level of detail by knocking and found three empty drums and returned to work in time。
3. 3. 2 safety operating codes
High-altitude operating safety protocols are strictly enforced, and bridge builders must wear seat belts and helmets and have a solid operating platform. Temporary electricity is provided through a level-iii distribution system, and cable frames are empty to avoid crushing. Fireworks conduct fire proofs with fire extinguishers. In a project where welding is strengthened, fire-fighting equipment inspection systems were subsequently reinforced by sparks that ignited the flammable material below and small-scale fires that resulted from the failure of fire extinguishers at the site。
3. 3. 3 monitoring and inspection mechanisms
The supervisory unit operates by-site supervision and supervises all critical processes. Quality analysis sessions are held weekly to inform and correct problems. Following the completion of the sub-project, the inspection data will be uploaded to the bridge health monitoring system, organized by the construction unit. SomeBridges strengthenedWhen the project replaced the compressor with the acceptance, it found that the gap in the stretcher had exceeded the 2 mm mark and that the construction unit had immediately adjusted to the design requirements to pass the acceptance。
Iv. Quality assurance and acceptance standards
4. 1 quality control system
4. 1. 1 standard implementation
Bridge maintenance enhancements are subject to strict national and industry technical regulations. Prior to construction, a technical team system was organized to learn from standard documents such as road bridge strengthening design guidelines (jttg/tj22-2008) and concrete structure strengthening design guidelines (gb50367-2013) to ensure that all process parameters conform to mandatory provisions. For example, the bonding process for carbon fibre consolidation needs to control the duct thickness between 2 and 3 mm, which may result in a concentration of stress; pressure values for crack-up plume need to be adjusted to the dynamics of the width of the crack, generally at 0. 2-0. 4 mpa to avoid excessive pressure leading to secondary damage to concrete。
4. 1. 2 quality control of materials
Establishment of a double-check system for material entry, i. E. Supplier qualification review in parallel with third-party testing. All reinforced materials will be required to provide plant certification, model testing reports and environmental certification. In the case of epoxy resin glue, for example, emphasis is placed on detection of tensile strength (3030mpa), elastic mode (≥3000mpa) and dry fever aging performance (60°c water immersion after 500 hours) (90%). In material sampling, a project found that the extension of a batch of carbon fibre sheets was below the standard value of 2. 1 per cent and immediately initiated a process of re-exchange to avoid structural delays。
4. 1. 3 construction process monitoring
Quality control modalities combined with “first acceptance” are implemented. Once each process has been completed, the final inspection is performed by a team of self-inspects, by a special examining officer and by a supervisory engineer. For example, visceral steel reinforcement processes require the completion of triple checks of steel plate rust-grade sa2. 5, the timing of adhesive solidification, and the testing of solid hammers (5% empty drum rate). During a continuous construction of the liang bridge, an empty 0. 8 mm drum was found to be attached to a steel plate, which was immediately reducted to ensure the integrity of the transmission path。
4. 2 detection and monitoring techniques
4. 2. 1 non-destructive detection applications
A variety of non-destructive tests were used to verify the quality of hidden engineering. The ultrasound method is used to detect internal defects in concrete and to determine the depth and density of the cracks through the analysis of the acoustic parameters; the infrared thermal imager is able to identify temperature anomalies in the carbon-fibre paste area and locate the detaching area; and the shock echo method is used to assess the strength of the reinforced concrete, the value of which needs to be modified by the regional curve. In a cross-sea bridge test, ultrasounds revealed cellular defects inside the bridge site and prompt pressure-plug repair was performed。
4. 2. 2 structural health monitoring
Set up long-term monitoring systems in key areas. Installation of oscillometers in the main beams to monitor stress changes in the load function in real time; placement of transducing sensors at the substations to record sedimentation and deformation data; installation of temperature sensors in the floors of the bridge to alert the heat swelling and cooling risks. A high-speed bridge monitoring system has detected the loss of the substations through data anomaly, replacing them three months in advance to avoid sorghum fractures。
4. 2. 3 validation of the transport test
Following the completion of the hardening, a propulsion test is conducted to assess the structural power response properties. Using a bridge at 20 km/h velocity, 30 tons of heavy vehicles were used to measure cross-medial scratches, vibration accelerations, etc. The norm calls for a 10 per cent increase in the self-enhancement frequency of the reinforced bridge and a 15 per cent reduction in the resistance to nieby. In one of the tests, the base frequency of the reinforced pre-bridge was 3. 2hz, which was reinforced and raised to 3. 6hz to achieve the desired effect。
4. 3 acceptance standards and processes
4. 3. 1 sub-project acceptance
7 sub-engineering sets acceptance and inspection criteria:
- concrete defects: 95% crack closed depth, 3 mm/m surface flatness deviation
-stick steel reinforcement: an anti-gravity design value of 1. 5 times that of the anchor area, and a platinum thickness success rate 90%
-culture of carbon fibre: fibre direction deviation 5°, effective connection length 150 mm
-welding of steel structures: 100 per cent welding of ultrasound injury i
- bridge pavement: iri≤2. 0m/km flat, seepage factor 120ml/min
-foundation devices: installation of 2 mm flat and 10% variance in condensation
- waterproof layer: low-temperature 20°c non-fissile, glued strength 0. 4 mpa
4. 3. 2 receiving and inspection of hidden works
Image retention and acceptance of hidden processes, such as ground-based treatment, steel band connections, etc. Welding of steel bars by 500 sets for stretching tests with a 100 per cent pass rate, and the extraction test is used to test the anchor strength of the rods, which is resistant to the design values and development without cracks. A project found that three steel anchors were less than 80 per cent of the design value and that all of them were re-drilled。
4. 3. 3 completion of acceptance and inspection procedures
Use of the “three-stage acceptance” mechanism:
- pre-receipt and acceptance: completion report submitted by the construction unit after certification and pre-receipt and acceptance by the supervising unit
- formal acceptance and inspection: the construction unit organizes joint inspection and inspection by design, construction and testing units
- specialized acceptance: technical evaluation by industry experts for special structures
Receiving and inspection requires the submission of complete technical files, including material detection reports, construction records, monitoring data, etc. At the time of the acceptance of a large bridge, the group confirmed that the carrying capacity had increased by 35 per cent to meet the design objective by comparing static test data before and after consolidation。
VCost controlAnalysis of benefits
5. 1 composition of reinforced engineering costs
5. 1. 1 direct cost factor
The direct costs of improved bridge maintenance consist mainly of three main categories of materials, labour and mechanical usage. Material costs account for 45-60 per cent of the total cost of the project, with high price volatility for structural reinforced materials such as carbon fibre sheeting, glue and epoxy resin. In the case of a simple beam bridge with a distance of 30 metres, the cost of material purchases was approximately $1. 2 million, of which high-intensity carbon fibre fabrics were valued at $800 per square metre and specialized structural glues at 180 per kilogram. The labour cost is 25 to 35 per cent, the average daily wage of skilled workers is approximately 280 to 350 yuan, and that of ordinary workers is 200 to 250 yuan, and the level of professional skills in the construction workforce directly affects labour efficiency. Mechanical usage rates range from 10-15 per cent and include rental and operating costs for special machines such as high-pressure slurryers and hydraulic tractors, with rental costs for large equipment usually ranging from $8000 to $15,000 per shift。
5. 1. 2 composition of indirect costs
Indirect costs cover project management fees, testing and monitoring fees, transport handling fees, etc. Project management costs include supervision fees, design change costs, office costs, etc., representing approximately 8-12 per cent of direct costs. The supervision of a project is charged 1. 5 per cent of the total construction cost, and monitoring costs vary according to the size of the bridge, with a health monitoring system for large bridges amounting to $500,000 to $0. 8 million. Transport handling fees are particularly prominent in the municipal bridge project, and the construction of transit roads and the deployment of traffic wardens may exceed 20 per cent of direct costs. In addition, environmental protection measures such as dust protection nets, the acquisition and installation of sound barriers, and waste disposal costs constitute indirect expenses that cannot be ignored。
5. 1. 3 implicit cost recognition
Implicit costs include, inter alia, the cost of the risk of delay and the cost of re-entry for quality deficiencies. Delays in working terms not only involve default payments (usually 0. 1-0. 3 per cent/day of the contract amount), but may also result in subsequent operational losses, such as a 15-day delay in the consolidation of a highway bridge due to heavy rainfall, resulting in an increase in fuel consumption of about $300,000 for bypass vehicles. Quality defects are more costly to return to work, and a project requires a partial return to work due to the failure of the carbon fibre pasting process, resulting in a direct loss of $180,000 and a 22-day extension. In addition, social costs, such as disruptions to the surrounding business activities during construction and the handling of complaints by residents, need to be taken into account in a comprehensive manner。
5. 2 economic efficiency assessment methodology
5. 2. 1 full-life cost analysis
Using a life-cycle cost analysis (lcca) to assess the economics of the hardening programme, elements such as initial investment, operational maintenance costs, residual value, etc. Need to be calculated. In the case of a 25-year-old concrete bridge, an initial investment of $1. 8 million was made under the sticker reinforcement programme, while the reconstruction programme required $6. 5 million. Through a 20-year cycle, the operational maintenance costs (including regular testing, minor repairs) of the stick steel reinforcement programme are estimated at approximately $1. 2 million, compared with $0. 8 million for the reconstruction programme, but taking into account the residual value difference (30 per cent of the original value after consolidation and 50 per cent after reconstruction), the full life-cycle cost of the bond reinforcement is $2. 7 million, which is $3. 8 million less than the reconstruction programme. When the discount rate was 6 per cent, the net present value (npv) advantage of the reinforced programme was even more significant。
5. 2. 2 cost-benefit ratio calculations
The cost-effectiveness ratio (bcr) is the core indicator for measuring the economicity of the project, and decisions are made by quantifying the ratio of benefits to costs. The cost of the bridging project in a city is 3. 2 million yuan. The benefits include avoidance of collapse losses (estimated at 5 million yuan), extension of the life expectancy for 15 years (equivalent to 4. 2 million yuan), reduction of traffic congestion losses (average of 800,000 yuan per year and a total of 12 million yuan over 15 years), with a total benefit of 21. 2 million yuan and bcr value of 6. 63. According to industry standards, bcr > 1. 5 is economically viable and the programme is well above the benchmark. Sensitivity analysis shows that changes in traffic have the greatest impact on bcrs, which can still remain above 3. 2 when they fall by 30 per cent。
5. 2. 3 quantification of social benefits
Social benefits, although difficult to monetize directly, could be estimated through alternative methods. The social benefits of the strengthening of bridges include: safeguarding public safety (avoiding compensation for casualties), promoting regional economic development (improving logistics efficiency) and improving the quality of life of the population (reducing detour time). The strengthening of a national road bridge has resulted in a 20 per cent increase in access, a 15 per cent reduction in the time spent transporting agricultural products in the surrounding three townships and an annual increase in economic benefits of approximately $1. 5 million. In terms of environmental benefits, a reduction in the bypass could reduce carbon emissions by about 800 tons per year, equivalent to an environmental cost of $240,000. Integrated social and economic benefits can be achieved at a cost of up to 8. 2 for the hardening project。
5. 3 cost optimization strategy
5. 3. 1 optimization of procurement of materials
Establish centralized procurement mechanisms and a system of dynamic evaluation of suppliers to reduce the cost of procurement of materials. Three-to-five suppliers are selected through open tendering, and annual framework agreements are signed to target the risk of price volatility. A project has reduced the unit price from $850/m2 to $720/m2 through centralized procurement of carbon fibre materials, saving 13 per cent of the cost of materials. At the same time, a material substitution strategy has been introduced to introduce basalt fibres (at a cost of 40 per cent of carbon fibres) in non-critical areas, meeting performance requirements and reducing inputs. Establish a material loss rate assessment mechanism to keep the tape loss rate below 3 per cent and reduce waste。
5. 3. 2 organization optimization of construction
Reduced indirect costs by compressing the construction period with running water operations and parallel construction models. Bridges were divided into construction units to achieve multi-shift synchronization. A continuous liang bridge project has been carried out in parallel by reducing the duration of work from 90 to 65 days by three processes, namely, crack repair, carbon fibre pasting, and front-laying of the bridge, resulting in savings of approximately $450,000 in management costs and traffic handling costs. Introduction of bim technology to optimize the construction path, reduce mechanical idle time and increase equipment utilization by 25 per cent. Development of dynamic progress management mechanisms, key nodes early warning and avoidance of overall time lags due to partial delays。
5. 3. 3 process cost control
Implementation of target cost accountability, with total costs broken down into sub-projects. Establish a cost early warning mechanism to initiate correction procedures when 5 per cent of a sub-cost is exceeded. A project found that the use of glue was over-budgeted by 8 per cent during the consolidation phase of the glue, and would be reduced by 6 per cent through the optimization of matching technology, at a cost of $120,000. The introduction of value engineering analysis to simplify non-essential processes, subject to structural security, such as the adjustment of the thickness of the floors to 6 cm from 8 cm to save $280,000 for materials. Establish a cost database to provide historical cost references for follow-up projects and to develop mechanisms for continuous optimization。
Vi. Late maintenance and life-long strategy
6. 1 maintenance system design
6. 1. 1 sublevel maintenance system
Establishment of a three-tier maintenance management system for bridges, with maintenance cycles based on differences in structural importance and disease levels. The first level of maintenance provides comprehensive quarterly testing of key stressor components, such as the main beam and the bridge, focusing on the monitoring of crack development, steel erosion and deformation data. Secondary maintenance covers sub-critical structures, such as bridge-painting, stretching devices, and semi-annual special inspections to record indicators such as levelling, drainage, etc. Level iii maintenance involves ancillary facilities, such as railings and lighting systems, which are overhauled annually to ensure functional integrity. Following the tiered maintenance of a bridge, the rate of expansion of the main beam was reduced from 0. 15 mm to 0. 05 mm per month, reducing structural degradation by 70 per cent。
6. 1. 2 preventive maintenance measures
Active maintenance strategies are being pursued, and interventions are being made before the disease occurs. The bridge waterproof layer is re-painted every five years, using permeable silane impregnation to effectively prevent chlorinated ion infiltration; the branch is equipped with high-density polytetrafluoroethylene skateboards, regularly replenishing silicate lubrication and reducing friction factors to below 0. 05; and the drainage system is cleaned quarterly to ensure that leaks are not blocked and to avoid water erosion of concrete. A coastal bridge is protected by salt mist every spring, and the erosion rate of the bars is maintained at 0. 2 per cent for the fifth consecutive year。
6. 1. 3 maintenance of archives management
Build a health archive of electronic bridges that includes all-life data such as design drawings, testing reports, maintenance records, etc. The two-dimensional marking technique is used to link each component to the only archive, and the scan allows access to historical maintenance records. A project discovered three consecutive years of sunking exceeding the 0. 3 mm mark on a bridge by means of an archive system to adjust the base reinforcement programme in a timely manner to avoid the risk of uneven deposition. Archival data are updated in real time to support subsequent maintenance decisions。
6. 2 monitoring of technology applications
6. 2. 1 sensory system deployment
Multi-source sensor networks are installed at key locations to achieve real-time perception of structural state. ♪ the main beams in the middle ♪
