In the formwork of concrete structure, for the purpose of expediting the work and having a high repetition factor, larger-sized panels are used.
In this method, the concrete formwork is supported horizontally by scaffolding pipes and vertically by soldiers (vertical supports). The use of soldiers is aimed at increasing the panel’s resistance to lateral forces from concrete and facilitating the movement of panels.
The walls are usually adjusted in place using double-threaded jacks after installation at the desired location. In cases where the concrete formwork cannot be moved integrally and the wall thickness is minimal, vertical pipe struts and double pipe spacers are used instead of a soldier.
Retaining walls are mainly formworked in two forms: double-sided and single-sided. The formwork design for concrete walls depends on three critical factors: The formwork design for concrete walls depends on three critical factors: the wall’s height, lateral pressure resistance of concrete, and the stability of the formwork assembly.
Double-sided wall formwork system
This system is used where access to both sides of the wall is possible. For the double-sided formwork of walls, modular forms are installed on both sides of the enclosed reinforcement using pins, dowels, and intermediate clamps. Full-length bolts, spaced at one meter horizontally and 50 centimeters vertically, prevent the deformation and separation of two rows of concrete forms from each other due to lateral concrete pressures. Profiles or pipes are used as horizontal backers, and solgers are used as vertical backers, placed at 1-meter intervals from each other, to resist hydrostatic forces in the formwork of the wall. Using pipe backers and solgers not only strengthens the formwork due to its integration but also facilitates the movement of the formwork for the wall. Therefore, the components forming the composition of the wall formwork consist of: Modular formwork (with holes and without holes, usually large-sized panels), soldier, pin and wedge, full-threaded bolt, bolt nut (wing nut), wedge bolt (for connecting the soldier to the concrete formwork), clamp (clip), and pipe waler.
One-sided wall formwork system
One-sided or retaining wall formwork system is used in cases where it’s not possible to have formwork on the back of the wall (such as on the mountain side of roads) or when there’s no need for formwork on the back of the wall. Since it’s not possible to use bolts in one-sided walls, anchor bolts should be used instead of bolts. Unlike bolts that connect two-sided forms, anchor bolts are placed inside the concrete formwork and can be used to withstand lateral pressure on the upper portions of the concrete after the previous stage has hardened. For the lowest part of the wall, anchor bolts are typically installed in the foundation. To stabilize and support the formwork system in one-sided walls up to a height of 4 meters, double jacks (shoring jacks) are used, with their arms being adjustable telescopically. For one-sided walls that exceed a height of 4 meters, supportive columns are used, which consist of a combination of soldiers and adjustable screws in two types: left-hand and right-hand (double-threaded), connected to the beginning and end of the soldier. Moreover, for the formwork of concrete walls at greater heights, brackets and their related components are used. Double jacks (shoring jacks), brackets, and vertical anchor feet are among the other components of the single-sided wall formwork system.
Sloped Wall Formwork:
Variable Thickness Wall Formwork depicts a wall formwork where its thickness varies with height. As evident, to restrain the formwork for these types of walls due to lateral pressures from concrete, anchoring bolts of various lengths must be used. The holes of the anchoring bolts on the two-sided formworks of the wall should be aligned with each other.
Concrete formwork system for upward sloping walls: (With modular panels)
If the height of concrete structures is significant and concrete pouring operations need to be carried out extensively, concrete pouring should be done in multiple stages. Initially, it is placed in position using a crane, and in the next stage, it is positioned on the brackets. After installing the concrete formwork, the next stage of concrete pouring takes place. In the case of a double-sided concrete formwork, anchor bolts are typically used to withstand the lateral pressure of concrete. And if the formwork is one-sided, brackets and anchor bolts are used to resist the lateral pressure of concrete. In these formworks, brackets play a crucial role in stabilizing the formwork and the concrete pouring process.
Wall Jump Formwork System:
In various types of climbing formwork for concrete, the crane performs two functions: Lifting the concrete formwork and holding it in a new position until it is installed and securely fixed in place . For various types of elevated concrete formworks, it takes approximately 15 to 20 minutes for the concrete formwork to advance to the next stage, be transported, and installed. The jump form concrete formwork system significantly reduces the crane utilization time. The jump form concrete formwork system is used as a rising formwork system for bridge piers, retaining walls, core walls, breakwater walls, and care towers. In this wall formwork system, the process of connecting the concrete formwork to the wall is eliminated after lifting it, which reduces the crane usage time. (about a 5-minute reduction) After the self-compaction of the first concrete pouring phase, the climbing formwork is automatically retracted backward using a predetermined tool, allowing its detachment from the wall. In the next stage, it is positioned on the previously connected anchor bolts on the wall. This formwork system is known for its high safety standards due to the automatic nature of the concrete formwork attachment and detachment operations, eliminating the need for personnel involvement. Additionally, the installation and disassembly stages are advanced compared to other methods of top-down formwork. In contrast to other techniques where the forms need to be completely detached from the wall by a crane before lifting the brackets, this method has an advantage.
Self-raising concrete formwork system for walls:
For the construction of the core walls of tall buildings with various dimensions and complexities, self-raising concrete formwork systems are used. This formwork system does not require the use of a crane. The support of the formwork inside the core is entirely mechanized. The above formwork system is raised one floor (one stage) at a time by hydraulic jacks controlled from a central control panel. In this system, all formwork elements advance to the next concrete pouring stage in a relatively short time, often taking less than 30 minutes. Preparation for the next concrete pouring stage commences rapidly. In contrast, the aforementioned stage in previous formwork systems is lifted by a crane, which takes a significant amount of time, possibly one or several days. However, the self-raising concrete formwork system is cost-effective for buildings of 15 to 20 floors or more. .
In the self-raising concrete formwork system, both sides of the wall formwork are connected to the lifting system, and formwork personnel can easily detach the formwork from the wall. Leveling and aligning of the formwork are carried out using the adjustment screws embedded in the brackets.