1、 Structure Form of Cover Beam
Cap beam, also known as cap beam, is a cross beam set on the top of a column pier or thin-walled pier. The load on the upper structure of the bridge is transmitted to the lower structure through the cap beam. The height of the cover beam varies from 1000 mm to 2000mm, and the width varies from 1200 mm to 2000mm.
The general structure of_cap beams is shown in the following figure:
2、 Construction of cover beam formwork
The construction methods of cover beam formwork usually include hoop method, cross steel bar method and support method, among which hoop method is the most common one. A Bailey beam or I-beam is arranged on the bracket of the hoop, and a distribution beam is arranged on it. Hoist the bottom formwork to the distribution beam with a crane, set out the position of the cover beam and the position of the reinforcement framework on the installed bottom formwork, after applying the release agent, check the flatness of the formwork, retest the position of the formwork, and prevent the cover beam from shifting. After the bottom die is installed, the steel skeleton and the binding steel bar are installed. After the steel bar is tied up, the side die of the cover beam is finally installed. The template should remove the oil and contaminants on the surface of the template. The joint of the template should be clamped with double-sided rubber pads, and the bolts of the template should be tightened to ensure that the template is tight and does not leak slurry. When the thickness of the protective layer meets the design requirements, lay enough cable and wind rope or support to ensure that the formwork does not deform or move during the construction process.
The cover beam formwork can be demolished when the concrete strength 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 a crane and not thrown away.
3、 Design of cover beam formwork
The design of cap beams requires that the drawings provided by Party A are generally the general structural drawings of cap beams. If the cap beams are prestressing, the relevant drawings of the anchorage end and the tension end of the cap beams should also be provided.
_1. The design of cover beam formwork should meet the requirements of strength, stiffness and stability. The oblique cover beams should be laid out in three surroundings in order to accurately extract the geometric dimensions of the formwork components. When necessary, the angle protons should be set up to facilitate workshop welding.
_2. Cover beam formwork is usually bottom-wrapped side and end-wrapped side. Side die is usually divided into standard section and end section. The bracket design of the bottom die end joint should have sufficient stiffness and meet the requirements of stability. The bottom die should be designed to be disassembled first, and there should be a certain slope between the connecting edge of the first disassembly and the bottom die panel to facilitate the disassembly of the die. The dimension of the opening part of the bottom die cylinder or square column should be 10mm-20mm larger than the design dimension of the construction drawing, and the connecting edge of the opening part should be retracted by 5 mm welding of the panel edge.
_3. The main fixing form of the cover beam formwork is the top and bottom alignment. The top and bottom alignment are fixed on the double channel steel back rib of the side die. In the design, whether the bottom alignment bolt can pass through the bottom of the bottom die should be taken into account. In order to fix the position of the top and bottom alignment bolt, the welding of the connecting plate on the back rib should also be considered. If the scheme only takes the form of top-to-bottom pulling, measures should be taken to tighten the bottom of the side die.
_4. If the cover beam is a pre-stressed cover beam, it is necessary to draw the template section of the pre-stressed anchorage end and tension end accurately, and connect the end die with the side die in a reasonable way.
4、Standardization of Formwork Design for Cover Beam
It is suggested that standardized design should be adopted as far as possible in the future design of cover beam formwork to meet the standardized requirements of products.
_1. Cover beam panel is made of 5 mm steel plate, connecting edge-12*80 strip steel and L80*8 angle steel, back rib 8# channel steel (spacing 300 mm or so), cover beam height is generally 2.0 m, so back rib 12# channel steel (spacing 750 mm-1000mm). Bottom die setting rib does not exceed 10 # channel steel, so as to facilitate the site selection of distribution beam or square wood model. The connection bolt is M20*50 and the tension bolt is T24.
_2. 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 cover beam formwork construction