Innovation Case

Technological innovation in bridge expansion joint—Pre-stressed multidirectional shifting retractor

Date: 2015-09-21
View Count: 378

 Technological innovation in bridge expansion joint—Pre-stressed multidirectional shifting retractor



I.     Background of innovation


It is learned that bridge expansion joints of the project companies affiliated to our company are mostly modulus-type Molor expansion joints. When they are damaged, they have to be cut to chip away concrete before replacement. It usually takes 2-3 days to chip away an expansion joint; and 7 days for place concrete or two days for fast setting concrete to cure after placement. Half-closed construction would impose great pressure on pavement traffic. In case of construction on a single lane, different pieces of an expansion joint will be welded, its overall stressing property will be impaired, and vehicular traffic on the neighboring lanes will affect the durability of newly placed concrete greatly.


In order to solve many problems in the retractor itself, and its repair and replacement, relieve the traffic pressure during repair, improve road improvement, and save maintenance costs, we have introduced the pre-stressed multidirectional shifting retractor.



II.    Pre-stressed multidirectional shifting retractor


1.    Product overview: Developed by Liuzhou OVM Machinery Co., Ltd., this product is composed mainly of a multidirectional shifting system, comb plates, waterproof rubber plates, anti-wear stainless steel plates, anchor bolts, etc. The comb plates are supplied in single pieces with a standard length of 1m each, which are spliced and installed on site, and placed by steel fiber concrete of over C40 at a time. With a stroke of 80~960mm, this product is suitable for multidirectional shifting bridges.


2.    Technical advantages: The tooth plate of the pre-stressed multidirectional shifting retractor is stressed as a whole with an excellent stressing property, and can turn 1.4º horizontally and vertically. The reactor features comfortable and quiet driving, and excellent longitudinal and transversal slip resistance. Since the waterproofing structure is in the lower part of the retractor and is almost invisible on the pavement, it is longer-lived. The retractor has a small mounting depth, so that when it is damaged, it is possible to remove and replace the damaged module alone, thereby reducing both maintenance costs and traffic impacts.


3.    Retractor construction process: The multidirectional shifting comb plate bridge retractor has stringent process requirements during construction, where the cutting width must be accurate and the former concrete must be chipped away thoroughly. The main construction process is as follows: inspection and application for commencement before staging à preparation, cutting, slotting and old joint removal after staging à positioning of the retractor multidirectional shifting system, screws and waterproof section steel à reinforcement and welding à embedding of rubber sealing strips à form mounting, concrete placement and comb plate mounting à concrete maintenance à site cleanup à nut tightening à hole sealing with epoxy resin à final inspection.



III.   Application of new technologies


1.    Cooperative framework: Through many rounds of negotiations with Liuzhou OVM Machinery Co., Ltd., a cooperative framework agreement was entered into, specifying the warranty period, reference price, etc. According to the demand of the project companies for bridge retractor replacement in this year, it was finally determined to conduct a pilot study on the Liuyang River Bridge on the Changsha-Zhuzhou Expressway in Hunan Province. Changsha-Zhuzhou Expressway Company entered into a construction contract with Liuzhou OVM Machinery Co., Ltd. under the direction of the framework agreement.


2.    Technology application: The Liuyang River Bridge formerly used modulus-type Molor expansion joints. In 2014, Changsha-Zhuzhou Expressway Company found central girder breaking, concrete crushing, significant vehicle jumping at the bridgehead and high noise, implying that there were potential safety hazards and impacts on nearby residents, and a sound solution was needed urgently. Since both parties entered into a construction contract, Changsha-Zhuzhou Expressway Company started retractor replacement and installation. However, in view of the high and fast vehicular traffic on the Changsha-Zhuzhou Expressway, the long construction period of expansion joint replacement for four lanes, and the difficulty of keeping the road unobstructed while ensuring safety, the headquarters proposed five requirements through close coordination with the project company, careful planning and scientific organization in order to learn construction progress, and identify and solve issues arising from construction timely: 1) performing quality management strictly, and asking the contractor to coordinate all operations rationally and ensure that the construction quality of each operation was acceptable; 2) asking the contractor to further optimize construction organization planning to ensure that the project was completed on schedule; 3) strengthening the management of the construction site to ensure safe and orderly construction, and minimize interference to vehicles; 4) making construction security arrangements and developing a meticulous contingency plan together with the traffic police, highway administration authority, etc.; and 5) compiling construction information and submitting it for inspection synchronously to ensure steady and efficient project progress. Through the close coordination between the headquarters and the project company, the continual optimization of the construction program and the traffic organization program, and rational arrangement and ongoing communication during construction, retractor replacement and installation was completed successfully within 30 days for the Liuyang River Bridge, and potential bridge and vehicle safety hazards eliminated quickly, providing a favorable and safe operating environment for the Changsha-Zhuzhou Expressway.



IV.   Conclusion


This innovation in bridge retractor was reflected in both management pattern and technology application. In this management pattern, the headquarters entered into a framework agreement, and the project company negotiated implementation details with the contractor, allowing for flexibility in cooperation and reducing maintenance costs. On the other hand, the pre-stressed multidirectional shifting retractor features comfortable driving, low noise, good durability, long service life, etc. itself, and may be replaced and repaired per linear meter subsequently, with minimal impact on pavement driving. In particular, with the traffic growth of the expressways managed by us, this will minimize construction impacts on toll collection, further reducing maintenance costs indirectly. This innovation in bridge retractor can be used as a reference for other projects.


Technological innovation in bridge expansion joint—Pre-stressed multidirectional shifting retractor

Modulus-type Molor expansion joints on the former bridge


Technological innovation in bridge expansion joint—Pre-stressed multidirectional shifting retractor

Multi-position pre-stressed multidirectional shifting retractor during construction

Technological innovation in bridge expansion joint—Pre-stressed multidirectional shifting retractor

Multi-position pre-stressed multidirectional shifting retractor after the completion of construction


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