There are multiple factors that will affect the ABC costs and its progress. These will include the financial issues, ABC linked influential engineering operations, demolition, construction inventory like bridge lighting and traffic signs, mobilization and the site accessibility. Many construction activities in the conventional construction and the accelerated bridge construction are found to be similar. But certain minor differences between both the methods as well as in their management structure will make their completion rapid.
|Fig.1. Bridge Construction Using ABC Method|
Certain parameters that are highlighted in the ABC management structure are:
- The unfamiliarity of the process: The modular design will undergo a test before the first use. This makes it more reliable. As per the saying " Practice makes perfect", which is best guided by technical experience.
- The cost of training for the staffs: With the development of new technologies, it is necessary to train the staff to make the system more updated. The cost raised for the same is a good investment.
- Fabrication Timeline: For new factory products, a realistic duration is necessary
- Repetition of a continued work on similar projects by the same labors: For similar projects, no training is necessary. This would result in cost saving and timely completion.
Factors Affecting the Progress and Benefits of ABC
The factors affecting the progress of ABC construction are as follows:
1. Constraints Affecting The Timely Completion of ABC
2. Inventory and the Construction Sequence
3. Engineering Tasks that precedes the Accelerated Bridge Construction
4. Engineering Operations that are linked to ABC
5. The Construction Equipment used in ABC
Constraints Affecting Timely Completion
There are independently linked activities that are administrative and technical in nature , on any million-dollar project. These activities occur before starting the construction or during post-construction stage which tends to slow down ABC. These activities are summarized below:
- Final Approval of Millions of Dollar: The demand for increased funding because of the rising costs, inflation, and the unforeseen circumstances is always the biggest problem. The highway trust fund and the state budget are the usual sources. There are chances for delaying the project even if it is compensated by ABC.
- Preparing Bid Documents for a design -build contract: Accurate documents will contribute to the success of any project. This documentation will help in the proper calculation of the cost of the project. The contract documents are very important for the project implementation and their completion.
- Contractor and the consultant team selection: It is not easy to change the core contractor or the consultant in the midstream of a project. So it is advised to acquire the right people for the right job.
- Structural planning and design: Prefabricated, lightweight and durable structures are more preferred, in order to have speedy construction.
- Feasibility of the construction schedule: The construction schedule is best controlled and monitored with the help of computer software like the program evaluation and review technique (PERT), CPM. These would identify the activities in the critical path.
- Value Engineering: A detail study and comparison of merits of alternative solutions will help to identify expensive items for the design modifications before the project has been started.
- Environmental Permits and Approval: Any kind of undesirable or adverse effect on the environment like loss of fauna and flora have to be examined. The project completion should solve a single solution but must not create other problems.
Construction Sequence and Inventory
The factors relating to the inventory and the construction sequence are:
- Relocation of utilities for water, gas and other pipes: In order to have utility pipes which are supported by cross beams under the bridge to provide water, gas, telephone and cable facilities it is necessary to have good coordination with the agencies during the course of construction.
- Ease of Access to the site: The progress of the project is affected if there is a lack of easy accessibility to the construction site.
- Preparation of the site: In the site preparation it is necessary to provide easy access for the labours and the equipment for the construction of foundation at the level below the bridge. This must be also provided at the deck level. Space must be arranged for the storage of materials. A yard has to be prepared for the assembling of the girders closer to the site.
- Mobilization: A temporary office to carry out computing, telephone, parking and other necessary facilities are set up. It is used by 4 to 12 engineers and inspectors. This range is dependent on the size of the project. In order to monitor the daily progress, the quality and cost control full-time engineers will be resident. In order to support them, a backup team exists in the main office. Storage depots near to the bridge approaches is set up to facilitate mobilization.
- Demolition: An existing superstructure can be removed in a single go or by stages. The demolition waste is recycled to meet the environmental regulations.
- Entry and Exit Ramps: These ramps are located at a longer distance from the site.
- Bridges Approach: The access to the site is either provided at the beginning of the bridge or at the ending of the bridge. For this, one or more lanes can be closed. In order to meet the completion milestone both day and night time will be required.
- The Use of Grouting Methods or Soil Injections: This method helps in improving the foundation soil including the problems with liquefaction. This will help to protect the foundation in the salt water against corrosion, resistance to earthquakes, liquefaction, and erosion of soil under the footing. This will also help in fender damage from vessel collision.
- Foundations: This is considered as a geotechnical discipline. In order to have soil reports, the borings must be made preferably at the approaches and behind the wing wall that is proposed. The geotechnical engineer having good expertise will recommend the soil report and the type of foundation. The ABC construction method will make superstructure to be lighter and hence reduce the weight on the foundation. Thus the ABC will make a foundation which is lighter.
- Improving the performance of the bearing: In order to improve the performance of bearing during seismic effects multi-rotational and isolation bearings.
- Staged Construction: During the replacement of projects, it is desirable to reconstruct one travel lane at a time so that the lane is cut and removed making the bridge usable. This will help in minimizing the traffic disruption.
- Acceleration and Deceleration Lanes: During the planning of a new bridge, It becomes necessary to have an acceleration and a deceleration lane when the decks are placed closer to the exit or the entry ramps.
- Bridge Lighting: For undergoing the night work, temporary generators will be required. An electrical engineer will ensure coordination with the utility company to permit long term deck and overhead lighting. The locations for having the overhead lighting poles near to the approaches and the deck have to be identified. For saving energy, the solar panels are encouraged. The electrical engineer will install the solar panel at the approaches for the bridge lighting and the signage.
- Deck Drainages: For the rapid drainage of rain water, longitudinal and cross slopes will be provided. By planning for maximum intensity of rainfall, the size of the scuppers and inlet and the outlet pipes are computed. The scupper sizes and space is dictated by the maximum rainfall intensity. The deck drainage system will be connected to the public sewer system. There will be meeting with the utility company for obtaining advance approval.
- Bio-retention ponds: The construction of bio-retention ponds will help to collect and filter runoff from the bridge deck.
- The timely construction of approaches: The approaches are made using concrete slabs on grade with the retaining walls.
Engineering Tasks that precedes the Accelerated Bridge Construction
The acceleration construction is a method that is not successful and possible without demolition and mobilization. The Accelerated Bridge planning (ABP) and the staged construction(SC) are preceded by them for replacement. The replacement may be only for a bridge component, like the bearings or for the entire bridge. The requirements of the owner are made clear. Which includes:
- Wider Decks
- Reduced effect of earthquakes
- Reduction in the schedule
- Longer service life
- Lower maintenance
- Cost Saving
- Increased bridge ratings
The accelerated bridge planning must promote the environmental or the preservation laws along with the durability factors. During the planning stage an evaluation matrix for the life cycle cost, the construction cost, constructability, social and environmental impact, future maintenance, inspection details and the aesthetic factors have to be prepared. The difference in accelerated bridge construction for small, medium as well as the long span is addressed in the planning stage. The constraints raised in meeting the accelerated construction target, like erection during extreme weather can be avoided or minimized by undergoing an efficient structural planning. The following factors are considered:
- Improvement of aesthetics: The construction of an exterior arched beam can be carried out to hide the fascia girders. This would improve the appearance.
- Installation of interactive touch screens: This would feature bridge information for motorists
- Rider Comfort is increased: The deck cracking can be prevented by using a durable deck overlay. This is a protective system to keep the deck rid of cracks. This would also prevent post-tensioning that causes cracks in concrete. This helps in having a non-corrosive reinforcement. The layer would improve the crash worthiness of parapets and the barriers. One such application is the latex modified concrete.
Engineering Operations That are Linked to ABC
The important practical aspects related to this are mentioned below:
- Employing prefabricated deck panels and the composite girders like Inverse.
- The action of avoiding splices in long-span girders; Designation of highway route or the planning of the river navigation in order to make the delivery of heavy girders and the precast units from the yards where the fabrication is carried out at a rapid rate.
- Rapid construction is boosted by the use of special construction cranes and the modern equipment.
- The achievement of high strength concrete by improving the cold weather concrete methods
- Reducing all possibilities of construction accidents by improving the safety throughout the project implementation.
The use of temporary signs is necessary during the construction. These involve the traffic signs, warning signs and variable message signs (VMS). When compared to fixed sign boards the electronic VMS signs are more preferred. The warning signs, as well as the exit and directional signs, must be displayed and has to be located conveniently.
In the case of location the site, it is necessary that it is in an area to where the delivery of materials and the transport is easily accessible. This must also allow for a lane closure and temporary ramp construction.
The Construction Equipment Used in ABC
The warranty provided by the manufacturer is desirable against the undesirable and inefficient performance of the construction equipment. In order to facilitate improved performance, it is necessary to have specialized equipment. The modern construction equipment will boost and help in speedy construction. Such efficient equipment is:
- Mobile cranes
- Truck-mounted cranes
- Waste handlers
- Jib Cranes
- Fork Lifts
- Winches and Cable Pullers
For ABC, the modern construction equipment must be timely available and must have an experienced erection team also. For different structural elements like girders, box beams, arches, trusses, suspension cable bridges and cable-stayed ones different erection equipment is necessary.
An erection contractor must be equipped with the following requirements:
- Lattice boom crawler cranes
- Mobile Lattice boom cranes
- Mobile Hydraulic Cranes
- Tower Cranes
- Lattice Ringer Cranes
The tower cranes that have a maximum lightweight pickup of 20tons and a height greater than 400 feet is necessary. The lattice ringer is used for heavy weight pick up to 1400 tons and 400 feet. The Mobile lattice boom cranes are used for lightweight to medium pickups up to 300 tons. The Mobile Hydraulic cranes are used for lightweight to medium with a pick up to 650 tons. The Lattice boom crawler cranes are used for lightweight to medium pickup to 400 feet.
Along with the above-mentioned accessories like separate foundations, temporary bents, hydraulic jacks, crane mats and temporary pier brackets are also necessary.