The level of bridge construction is gradually improving, and the sliding formwork construction of hollow thin-walled piers holds an important position. As an emerging technology, it has positive significance in creating a safe engineering environment and improving construction efficiency. The bridge construction industry has also achieved more significant development results due to the application of this technology.

Overview of the Sliding Formwork Technology for Hollow Thin-Walled Piers

In the substructure of bridges, the hollow thin-walled pier is a widely used structural form, which has multiple characteristics such as light weight, high strength, and good appearance. Reasonable setting of hollow thin-walled piers helps improve the overall stiffness of the bridge. The hydraulic sliding formwork system is an important support in construction, with the formwork system being the most critical. The formwork can bear the lateral pressure of concrete. Different from the inner formwork, the height of the outer formwork is controlled by increasing its height standard by 150mm. The surrounding ring is an important device to stabilize the planar shape of the formwork. Under its action, the surrounding ring can also connect the lifting frame and the formwork to form a stable whole. It is required that the surrounding ring has a high strength to ensure the geometric shape of the formwork. The lifting and bearing system mainly consists of two parts: the lifting frame and the supporting rod. The supporting rod that is suitable for the working performance of the jack is selected to effectively play the role of the bearing pillar and maintain the stability of the hydraulic sliding formwork system. The operating platform is the main construction site and should have sufficient strength and stiffness. In addition, the suspended scaffold can assist construction personnel in inspecting the quality of concrete and other related work, including components such as beams and suspenders.

Construction Technology of Sliding Formwork for Hollow Thin-Walled Piers

(1) Measurement and setting out. Using a total station as the main equipment, the specific positions of the four corners of the pier body are accurately measured and the ink line is marked, and the formwork erection work is completed based on this.

(2) Fabrication and installation of reinforcement. Cooperate with high-quality suppliers to purchase reinforcement raw materials that meet the quality standards. When the materials enter the site, the quality of each batch of materials is mastered through spot checks. The materials are classified and stacked with the bottom raised, and a rainproof cloth is laid to prevent the reinforcement from rusting due to factors such as rain. Prepare well before binding, and thoroughly clean all kinds of impurities such as oil stains on the surface of the reinforcement. The reinforcement scaffolding is set on the bearing platform, and the reinforcement is bound reasonably according to the requirements of the design drawings. The segmented pouring method is adopted, and the length of each section is set to 3m. When the wind is too strong, the reinforcement is prone to displacement. To avoid this problem, the length of the stressed main reinforcement in each section is required to be 4.5m. The position of the main reinforcement joints in the same section should be strictly controlled to ensure they are staggered from each other. The connection of the main reinforcement of the pier body should be stable, and it can be effectively connected by using the rolled straight thread sleeve, and the joint quality should be inspected.

(3) Formwork erection. A crane is arranged on site to achieve a rapid vertical lifting effect through the cooperation with the tower crane. The formwork is 3m high. In addition, adjustment sections with lengths of 1.5m and 1m should also be equipped. The pouring height of each section is 3m. When installing the first section of the formwork, it should be placed at the top of the foundation, and the second section of the formwork is installed on the basis of the first section. Referring to the actual construction situation, if the strength of the concrete in the second section increases significantly and meets the strength requirements for formwork removal, the pre-set first section of the formwork can be removed, and then this part is lifted to the second section of the formwork. Following the above method, all formwork turnover construction operations are completed in turn.

(4) Concrete pouring. After the formwork is installed in place, reinforcement measures are taken. The construction unit conducts self-inspection and then submits it to the supervision for inspection. Only after it is found to be correct can the concrete be poured. C40 concrete is selected here, and the quality requirement is a slump of 16-20cm. Based on the construction demand, the mixing station produces an appropriate amount of concrete that meets the quality requirements, and the concrete is transferred to the site by a tank truck and poured into the formwork through a delivery pump. The concrete pouring adopts a layered and sequential advancement method, and the thickness of each layer is preferably 30cm. The pouring time of each layer should be reasonably controlled and must be completed before the previous layer of concrete initial sets to avoid cold joints between layers. During the pouring process, concrete segregation is prone to occur. It is necessary to adjust the position of the concrete delivery pipe to ensure that the distance between the pipe mouth and the concrete surface is ≤2m. The vibrating device used for the vibrating operation is a φ50mm insertion type vibrator. In addition to the vibrating treatment of this layer, the insertion depth into the lower layer should reach 5-10cm to enhance the bonding effect of each layer of concrete. Over-vibration and under-vibration should be avoided, and the position of the vibrator should be controlled to avoid touching reinforcement and other components.

(5) Formwork removal and curing. The strength of the concrete is inspected, and the formwork can be removed after the requirements are met. Firstly, the outer formwork is removed, and then the inner formwork is removed step by step after it is found to be correct. During this period, a special person should inspect to determine the stability of the formwork. If displacement occurs, the construction must be suspended. The position of the drill rig should be flexibly adjusted according to the actual situation, and the formwork should be removed again. Strengthen the on-site protection to avoid on-site personnel being injured due to the falling of the formwork. All the removed formworks should be effectively cleaned and evenly coated with a release agent. After the concrete pouring is completed and after 6-8 hours, it can enter the curing stage. It is appropriate to cover it with geotextile and sprinkle water. A number of small-hole pipes are arranged at the pier to spray the concrete of the hollow thin-walled pier construction process appropriately. Under normal circumstances, the curing should last for at least 7 days.

Conclusion

In summary, based on the application of the sliding formwork construction technology, the construction quality can be improved, and the performance in terms of economic benefits is also better. The construction of each link of the sliding formwork construction technology for hollow thin-walled piers is safe and reliable, and the overall quality meets the expected requirements. Therefore, the proposed technology can be used as a reference for similar projects.