This paper takes up one of the cases, included in the audit reports on final accounts for fiscal 1984. By explaining the contents, we intend to give a typical example of the audit activities, conducted by the Board of Audit of Japan, on public works.
UNECONOMICAL DESIGNING COST FOR GIRDERS OF BRIDGES
Prestressed concrete bridge girders were designed in two phases-basic and detailed designs-but could have been designed at one time in the latter phase. If so, the designing cost could have been saved by ¥ 105 million.
Japan Highway Public Corporation (to be called JHPC hereafter) was established in 1956 to construct and operate expressways and other general toll roads in Japan. In 1963, it opened a part (71 km) of the Meishin Expressway, Japan's first expressway. About 20 years have passed, and there are now about 3,435 km of expressways (as of the end of 1983). With such expressway improvements, time required to travel through the Japanese Islands have been dramatically shortened and the expressways have played a most vital role in the nation's economy and people's life.
Expressway construction was carried out at a rate of about 150 km annually. As a result, roads which run North and South through the Japanese Islands have now mostly been improved, and today expressway construction is shifting its emphasis toward the preparation of traverse roads which connect the eastern and western areas of the Japanese Islands. These traverse roads pass through mountainous areas and require the construction of many bridges and tunnels, thereby considerably increasing construction expenses. With these points in mind, we decided to include the question whether expressway bridges are economically designed when we prepared an audit plan on JHPC.
Our audit began with a survey of JHPC's bridge design system.
The expressways have reinforced concrete bridges and prestressed concrete (PC) bridges, etc. We made a detailed study of the outline of design, specifications, and other matters concerning these bridges, and found the design process of a PC-structured bridge differs from that of reinforced concrete bridges.
In the case of reinforced concrete structures, both general design and planned design are initially prepared. Detailed design is then compiled by a design consultant and orders for construction are issued. On the other hand, in the case of PC-structured bridges, the design is divided into 'basic design' and 'detailed design', after the initial preparation of general design and planned design. The former is given to a design consultant as a design for the issue of construction orders, and the latter is conducted by the contractor after the conclusion of contract of the PC bridge construction.
The contractor may carry out the work without applying the PC method indicated in the contract drawing. In that case, detailed designs are to be prepared on both methods, one shown in the contract drawing, and the other as chosen by the contractor.
What is the reason for handling design processes of PC-structured bridge differently from those of other type bridges? Before investigating that point, we would like to introduce the development process of the PC bridge construction methods in Japan.
(note) Types of Design
General Design Preparation
This is the design and general concept of the structure, which is drawn on paper and compiles a general plan of structures in different types and is taken into study for comparison on the spot. Material requirements and construction expenses, on reference date, may be estimated from the existing data.
Planned Design
Planned design compiles data necessary for the comparison of structural types. It is to determine the height of girders and the framework of main girder arrangement, and to calculate dimension of main section, fundamental dimension and the number of piles. It then calculates the quantity of required materials. If these figures can be estimated from the existing data, design calculations may be deleted.
Basic Design
This concerns prestressed concrete structures and steel ones. It defines main frame of structure and forms of handrail, drainage appliance, expansion joints, supporting parts and other accessories, as well as main sectional dimensions, kinds and quantity of required materials, and construction methods. The design of unimportant minute parts can be deleted; or assumed figures are acceptable.
Detailed Design
This covers all the necessary designs required to carry out precise construction. The detailed design is intended for actual construction, so all necessary instructions should be stated in the construction planning paper, and the designer's intention should be fully conveyed to the construction staff.
As for the application of prestressed concrete to road bridges in Japan, the pretension system and the post tension system were introduced in 1951 and .1953, respectively. Earlier, company "K" had introduced technology based on an initial patent by Eugene Freyssinet, and promoted the development and expansion of PC bridges, using the Freyssinet method (see note below). With the expiration of the patent based on the Freyssinet principle in 1956, various anchoring methods of the post-tension system, besides the Freyssinet method, were introduced from abroad.
Since around 1955, the introduction of various techniques, regarding PC methods, has been attempted. The progress of PC road bridge technology, using these methods, owes a great deal to construction of expressways, starting with the Meishin Expressway. There are various types of PC bridges, constructed by JHPC, such as pre-tension girder, midair floor, simple T-girder, simple composite girder, connecting composite girder, continuous composite girder, and simple box girder types. In these constructions, major methods which were actually used by JHPC as anchoring methods under the post-tension system amount to over ten kinds including the "Freyssinet Method".
(note) Freyssinet Method
This is a kind of PC steel anchoring system used for the on-site construction of prestressed concrete structure, wherein highly tensioned PC steel wire or PC steel twist wire is passed through the male-cone and female-cone and anchored in wedge form. The system was invented by Eugene Freyssinet of France, and called the "Freyssinet Method".
As mentioned earlier, JHPC adopts a system to order; construction of PC bridges with the preparation of basic design, and requires the contractor to carry out the detailed design. Why follow such processes? According to the explanation by JHPC, there ?re various construction methods in the anchoring of PC steel materials, which is the most important factor in PC bridge technology. Therefore, JHPC believes that the contractor should feel free in selecting the construction method which can display the best technology, and along with the systematic process of design and construction good-quality work can be expected. This is the reason they allow the contractor to carry out detailed designing.
We wondered, however, if this explanation would be still acceptable under the current situation where they have stored a number of experiences through the construction of many PC bridges. The second stage of our audit was to probe this point.
In carrying out documentary and field audit, we decided to conduct a comparative study mainly on achievements, resulting from the basic design which JHPC prepared through the service of the design consultant and the detailed design which was compiled by the construction contractor. Also, in the field audit, we sought the opinion of the JHPC staff and listened to ideas expressed by the contractor concerning the design at the actual PC bridge construction site.
In the result, it became clear that continuous and connecting forms were used in the case of large and expansive PC bridges on the main track and that the cross section of many of them were box-type. For these cases, there are various PC steel material anchoring methods. In the case of continuous girders especially, the structure becomes a statically indeterminate, creating secondary stress. This requires a specific study including the working process on the location such as drying shrinkage and creeping deformation. Therefore, we concentrated our efforts mainly on the designing of T-type and I-type cross sectional PC simple girders.
The construction work of T-type and I-type cross sectional PC simple girders, under the yard manufacturing carried out by JHPC during fiscal 1982, amounts to 49 (construction expenses total 19.5 billion yen). The quantity of PC simple girder bridges included in such constructions records 94. These bridges have a span of about 35 meters with each constructed as main track or inter-bridges.
One of the fundamental differences between the basic design and detailed design is that, in the former, structure particulars (arrangement plan of PC steel materials, etc.) are not needed, while, in the detailed design, all the possible minute details for the work are required in the compilation of the plan. In comparing the two, however, we found out that there existed no big differences between the basic design and detailed design, on the points of girder sections, PC steel material standards, reinforcing bar arrangement, and quantity.
As for the reasons, it can be said that both in the basic and detailed designs all of the anchoring methods which are considered the most important part in the design of the PC girders are done using the Feyssinet method, and that in such PC simple girders JHPC and design consultants have accumulated a number of design experiences. That is, concerning the PC simple girders of T-type and I-type cross sections, the contents of design have already been standardized. It has been so generalized that no other methods can compete from the points of economy and reliability. Differing from the initial view of JHPC, there now seems to exist little benefit in allowing a contractor to prepare detailed design.
From the survey results, concerning the PC simple girders, it has been made clear that there was no necessity to prepare basic and detailed design separately. It was possible to have the design consultant prepare the detailed design from the beginning and to order the construction work based on that design. If this process was followed, JHPC could have reduced design expenses by about 105 million yen in fiscal 1982.
In reply to our viewpoint, JHPC immediately carried out studies on the past situation, concerning the PC bridge design methods. As a result, they realized that the Freyssinet method is generalized as the PC steel material anchoring method, and that, along with the accumulation of construction experiences and advancement of the designers' technological ability, there exists little necessity for the contractor to re-design the plan. In November, 1983, we received a reply from JHPC that they would conduct detailed design in the beginning, instead of the basic design, and would revise design procedures thereafter.
We have introduced a summary of the matter we handled concerning the PC bridge design methods. In looking at the recent execution system of projects, we notice that most design and construction operations, irrespective whether national or corporation projects, are specialized and sectionalized. Especially regarding design, actual design work is conducted by a design consultant upon the conclusion of the definite plan. Also, as for PC bridges, current technology owes much to the introduction of know-how from abroad, and the construction companies which initially introduced the technology used to play a large role in carrying out design. From now on, however, in the detailed design of PC simple girders, it is suggested that JHPC will fully utilize past design and construction experiences. We also expect that, moving ahead with the rapidly advancing technology and accumulating construction experiences, JHPC will take a fresh look at their project execution system and revise the old stagnated situation.