1、 Structural forms of piers and columns
Pier column is the lower structure which bears the load of the upper structure and transfers the load to the foundation. Pier column is divided into column pier, thin-walled hollow pier, solid pier, etc. Its cross-section forms are circular, square, rectangular round end, variable cross-section and so on.
The general structure of transition piers and columns for railway continuous beams is shown in the following figure:
2、Construction of Pier Formwork
The construction methods of Pier Formwork are usually divided into four types: Pier Casting method, sliding form construction method, climbing form construction method and turning form construction method, among which the more common method is sectional construction method.
When_sublevel or integral casting method is used, the gap between the cap and the pier formwork is first leveled by mortar, and the sponge strip is bonded. During construction, the formwork is assembled on the ground and connected with connecting bolts to form an integral whole. Adhesive strips are attached at the joints of the formwork to prevent sand lines on the concrete surface caused by leakage of grout. After the surface of the template is polished, the release agent is coated, and then the template is lifted and connected into a whole by a crane. After the template is in place, oblique branching is set to control the verticality of the template and stabilize the template. The piers with higher height are installed in segments. When assembling, the short section is used at the lower end and the long section is used at the upper end to ensure the appearance of the piers.
If the pier cap and the pier column need to be poured as a whole, after the reinforcement of the pier cap is tied up, the pier cap formwork is hoisted in blocks and assembled on the upper part. The lower part is re-positioned by the surveyor, and the upper part is temporarily fixed with scaffolding.
The construction sketch of_pier formwork is shown as follows:
The Pier Formwork can be demolished when the strength of concrete blocks reaches 2.5 MPa. The formwork should follow the sequence of first supporting and then disassembling. When demolishing the formwork, it should be assisted by crane and not thrown away.
3、 Design of Pier Formwork
The design of Pier Formwork requires that the drawings provided by Party A are generally the general structural drawings of piers. If there are other embedded parts or other structures on piers, Party A also needs to provide relevant detailed structural drawings or large drawings.
_1. The design of Pier Formwork should meet the requirements of strength, stiffness and stability. Special-shaped piers or caps should be lofted by three-dimensional lofting software, and template panels should be taken from the lofting entity.
_2. The Pier Formwork should first meet the construction requirements of Party A. If Party A has no special requirements for section, it should consider the requirements of plate sizing and other aspects. The lifting capacity of the field construction crane should be considered when the formwork is lifted in blocks.
_3. The tension forms of Pier Formwork are mainly divided into two types: one is through-concrete tension, the other is non-through-concrete tension (that is, we often say four-corner tension). The stiffness of the two kinds of double-tension ribs should meet the requirements of the code.
4. The large ribs of Pier Formwork are mainly divided into two types: one is large section steel, the other is truss type. When the section length of pier column is large and Party A does not adopt concrete to pull, large section steel or truss type to pull large ribs should be adopted to pull large ribs. The joint form of truss should be calculated and arranged according to the requirements of steel structure code. After the completion of the truss, some measures should be taken to eliminate the elastic deformation of the truss so as to prevent the large deformation of the middle part of the formwork truss span caused by the elastic deformation during the first use of the truss.
_5. Large concrete structures with catenary supports at the top of piers should be supported under the formwork of structures, and the support should meet the requirements of stiffness and stability.
4、Standardization of Pier Formwork Design
It is suggested that the standardized design should be adopted in the future Pier Formwork Design to meet the standardized requirements of products.
_1. Cover beam slab is made of 6mm steel plate, connecting edge-12*100 strip steel and L100*10 angle steel, back rib 10_channel steel (spacing 300 mm or so), and pier column rib is calculated in the form of concrete piercing and quadrangular tension. The connection bolt is M20*50, and the pull bolt is T30 pair (if the section is large, the calculation of the pull bolt does not meet the requirements can be replaced by 25 mm precision rolling thread steel).
_2. The construction protection of Pier Formwork and the construction operation platform can be used as the promotion and development direction of the standardization of pier design in the future. The construction platform can be simply designed to support and guardrail crossbars, which are connected with the vertical ribs of the template.
_3. Template should be pre-assembled in the factory after processing. After pre-assembled and qualified, the number should be marked at the prominent position of the template. The numbering method that can only distinguish each template should be specified. The numbering of workshop should be in accordance with the numbering of the assembly drawing.
5、 Picture reference of Pier Formwork Construction