The stay cable form traveler, also known as the front-pivot form traveler, is a piece of equipment used for the cantilever casting construction of the main girder of a concrete cable-stayed bridge.

1. Process Principle

Utilize the stay cable as the traction cable for the front pivot of the form traveler. The rear anchor point is anchored on the bottom slab of the already-cast girder segment, and the middle pivot is supported on the top surface of the already-cast main girder with a C-shaped hook. This changes the cantilever stress state of the form traveler at the rear anchor point into a simply supported stress state at the front and rear pivots, thus reducing the deflection and bending moment of the form traveler, improving its load-bearing capacity, and enabling the one-time casting of the entire segment of the main girder.

2. Characteristics of the Process and Construction Method

It adopts a steel box structure, which features a compact structure, strong integrity, high stiffness, large load-bearing capacity, and high safety. By combining the force transmission of hanging and pulling by the stay cable, it increases the construction length of the segment. It has a high degree of construction standardization, fast construction speed, good construction quality, but it is heavy and has high processing costs.

3. Scope of Application

It is applicable to the cantilever casting construction of the main girder of a large-span and long-segment concrete cable-stayed bridge.

4. Quality Control

4.1 Possible Quality Problems

4.1.1 Alignment Control

In the alignment control of the main girder, the form setting elevation of the form traveler given by the monitoring unit may lead to a mismatch between the construction alignment of the main girder and the theoretical alignment due to the difference between the actual construction and the theoretical calculation. If the construction errors of each link are not adjusted in a timely manner and strictly controlled during the construction, the construction alignment of the main girder will not be able to meet the requirements of the specifications.

4.1.2 Appearance

The flatness, color, and joint misalignment of the exposed concrete surface; problems such as exposed reinforcement, holes, honeycombs, pitted surfaces, and cracks in the girder body are likely to occur.

4.2 Assurance Measures

4.2.1 Large-area steel formwork should be used. In addition to meeting all the requirements for casting concrete in terms of strength, the design should mainly be controlled by stiffness to ensure its surface flatness.

4.2.2 For the splicing joints of the formwork, strive for a reasonable design and fine processing and manufacturing to reduce or avoid the occurrence of grout leakage.

4.2.3 Minimize the number of tie bolts as much as possible to reduce the holes in the concrete, and promptly seal and repair the holes left after the construction of the main girder is completed. Use cement mortar of the same grade as that of the main girder, strive to make the color consistent with that of the concrete of the main girder, and assign a dedicated person to be in charge.

4.2.4 Optimize and select the concrete mix proportion, ensure uniform mixing of the concrete, guarantee its workability, and ensure consistent color as a whole. At the same time, protect the already-cast girder surface from oil stains.

4.2.5 Take effective measures to strengthen the control of the accurate installation and positioning of the formwork, as well as the technological processes such as the mixing, pumping, vibration, and curing of the concrete. Carry out quality awareness education for the on-site management personnel and operators, and do a good job in the technical disclosure of each key process. Ensure the quality of the project by guaranteeing the work quality of each technological link.

4.2.6 Strengthen the measurement and recheck of the plane position and elevation of the main girder, especially the positioning of the reserved holes for the anchor rods of the form traveler, embedded parts, and the anchor backing plates for the stay cable tensioning must be accurate. The elevation changes of the main girder should be measured before and after the form traveler slides, before and after casting, and before and after the stay cable is tensioned to guide the elevation control of the next segment.

5. Safety Measures

5.1 Analysis of Main Safety Risks

The construction of the stay cable form traveler is high-altitude operation. During the construction process, the operators must earnestly do a good job in safety protection to prevent high-altitude falls and object strikes. In addition, during the construction operation, prevent the occurrence of electric shock accidents. During the use of the form traveler, prevent the form traveler from falling.

5.2 Assurance Measures

5.2.1 Formulate the safety operation procedures for the main sub-projects, and earnestly conduct safety technical disclosure and safety education and training before the operation.

5.2.2 During the assembly process of the form traveler, the stability of the assembly platform of the universal members must be frequently checked. A closed safety railing should be set up on the platform, wrapped with a safety net, and the pedestrian walkway should be fully paved with scaffold planks or iron sheets. Double-layer cross operation up and down is prohibited. If it is necessary to adopt it, the operation layer must be fully closed to prevent falling objects from hurting people.

5.2.3 The hoisting operation should be commanded by a dedicated person. The whistle and signals given by the commander must be clear and accurate according to the regulations. The commander should stand in a position where all the construction personnel can see, and at the same time, the commander himself should clearly see the entire hoisting process of the heavy object. The hoisting operation must be carried out in accordance with the requirements of the safety technical specifications.

5.2.4 During the cantilever construction of the form traveler, operations such as the forward movement, lifting, and anchoring of the form traveler must be carried out in accordance with the safety technical disclosure. In case of any abnormality, the operation should be stopped in a timely manner, and the operation can be continued only after the cause is found out and the safety hazards are eliminated.

5.2.5 When the wind force is above level 6, operations such as the form traveler's lowering, jacking, and sliding are not allowed, and at the same time, the anchor points of the form traveler should be reinforced. When the form traveler is in the working state, first check the anchoring condition of each anchor rod group and the connection quality at the connection between the stay cable and the form traveler, and further carry out corresponding reinforcement. During this period, no one should stay on the form traveler; when it is in the non-working state, the operation must be stopped immediately, take protective measures to prevent the form traveler formwork from sliding automatically under the action of the wind, and fasten the form traveler to the main girder with a steel rope.

5.2.6 The construction power lines must be standardized, and it is not allowed to randomly pull and connect them. The joints of the lines should not be exposed.

To Wrap Up

Only by strictly controlling these key points can the advantages of the stay cable form traveler in the construction of large-span concrete cable-stayed bridges be fully realized. In the follow-up, we will deeply explore the construction process of the stay cable form traveler.