Development of projects is carried out in two stages: technical design and working drawings.
In the technical project, fundamental issues are solved: the place of transition, material, system, breakdown into spans, the design of spans and supports and the procedure for organizing construction. An estimate is drawn up for the technical project, which determines the cost of the structure.
After the approval of the technical design, working drawings are developed.
When developing working drawings, the solutions provided for by the technical project are specified and detailed to the extent necessary for the production of construction work.
Bridge design begins with locating the bridge crossing in plan and defining the bridge opening.
When crossing small watercourses, the location of the bridge crossing is usually subordinate to the main direction of the traced road.
The larger the watercourse, the more reasons to search for the most advantageous place of its intersection, in which the river crosses at right angles in the narrowest part of it: in a flood-free area or an area with a minimum width of floodplains. At the same time, they strive to ensure that the river bed is distinguished by straightness and constancy of position, and the geological structure favored the laying of foundations of supports.
To ensure these conditions, in some cases it is allowed to deviate the road from the main direction. The final decision is made after drawing up and analyzing various options for the location of the bridge.
For each of the bridge crossing options, in turn, the most economically profitable and technically feasible bridge scheme must be found.
The search for this scheme is carried out by developing several options and research, in the process of which the question of the size of spans, the system of spans and the appointment of their general dimensions, the choice of the type of supports and their foundations is being resolved. When developing bridge options, the conditions for the manufacture and installation of spans, methods of erecting supports, construction time and architectural advantages of the structure should be taken into account.
In an effort to best meet all the conditions, you can make several competing options. When drawing up options, the accumulated experience in the design of such structures, data from science and practice, and available standard solutions are used.
Choosing a bridge layout is a creative, do-it-yourself challenge that cannot be built from recipes.
Sometimes you have to subordinate the breakdown to the transition profile. For example, in steep slopes, high bridge heights, deep river beds and soft soils in the channel section of the crossing, a single span solution may be appropriate, eliminating the need for intermediate supports.
Spanning can be tailored to architectural requirements, which is typical for urban environments and when designing unique bridges. As a rule, when staking out, typical dimensions of the design spans should be assigned.
The designation of the span dimensions and their placement along the length of the hole cannot be made in isolation from the span system, and when using continuous and cantilever systems, the breakdown can be subordinated to certain ratios between spans, at which the best use of the span materials is achieved.
With regard to the purpose of superstructure systems, it is impossible to give a summary of the rules for their correct selection.
When assigning a superstructure system, it is imperative to take into account its operational qualities - rigidity, convenience of protection against corrosion, cost of current maintenance.
In modern conditions, it is impossible to choose the right structure scheme without considering comprehensively the issues of statics, manufacturing conditions, installation and operation.
New features of systems and structural forms, based on taking into account the spatial work, manufacturing and installation conditions, have been identified only in individual structures and therefore do not provide sufficient material for generalizations.
When choosing a system, the question of the type of connection of elements must also be resolved.
Welded spans can save up to 10-15% of metal. The complexity of their manufacture is reduced by 15-20%. The factories have mastered the technology of their manufacture. The operating experience of welded spans has shown that, with a good-quality manufacture, they have a number of advantages over riveted ones: they are less susceptible to corrosion, and are more convenient for cleaning and painting.
In structures with solid walls, assembly welding is also not particularly difficult. Up to now, assembly welding has not become widespread in end-to-end span structures. In most modern structures, the assembly connection is carried out on high-strength bolts.