4. Types of Formwork 4.1. Foundation Formwork Foundation formworks can be designed in various ways. Basically there is a difference between formwork for individual foundations, normally designed as socket foundations, and formwork for strip foundations. The type of design is dictated by the size, mainly by the height of the foundation formwork. The formwork for individual foundations is similar to column formwork and the formwork for strip foundations is similar to the formwork. Normally sheeting panels with formwork bearers in the form of walers are used for foundation formwork. Individual foundations are also secured by means of walers but of rim type. Bracing is by squared and round timbers as well as boards diagonally arranged. Tie wires as well as metal screws are used as formwork ties. Figure 7 Foundation formwork 1 formwork sheeting, 2 stull, 3 waler, 4 post, 5 thrust-board, 6 concrete bottom, 7 tie wire How is lifting of a foundation formwork prevented? ___________________________________________________ 4.2. Wall Formwork Wall formwork consists of vertically arranged upright timbers (formwork bearers) to which sheeting boards are nailed at the concrete side. The upright timbers are diagonally braced by means of boards at both sides. On cleats situated at every third upright timber, there are horizontally arranged walers. The opposite walers are tied at specified distances. Prefabricated sheeting panels may also be used instead of sheeting boards. Cleaning holes are to be provided at the foot of the formwork. Figure 8 Wall formwork (vertical section) 1 stull, 2 screw tie, 3 bracing, 4 waler 5 post, 6 cleaning hole, 7 thrust-board 4.3. Ceiling Formwork Ceiling formwork is the type of formwork mostly found in structures/buildings. The formwork sheeting may consist of sheeting boards or prefabricated sheeting panels. The formwork sheeting may consist of sheeting boards or prefabricated sheeting panels. The formwork sheeting lies on squared timber formwork bearers which are arranged on main bearers carrying off the forces to round timber columns. With smaller rooms, the main bearer together with two columns form a trestle. Diagonal board bracings are provided to take up horizontally acting forces. The round timber columns are placed on double wedges which serve as stripping aid and correction device. Figure 9 Ceiling formwork (vertical section) 1 formwork sheeting, 2 formwork bearer, 3 main bearer, 4 cleat, 5 column, 6 wall, 7 bracing, 8 support wedges Which auxiliary means is used to facilitate stripping of the columns? _____________________________________________________ 4.4. Beam Formwork Beam formwork has prefabricated formwork sheeting parts (sheeting bottom and side sheeting panels). Such individual parts are manufactured based on the beam dimensions specified in the project. For prefabrication of the formwork sheeting parts, a special preparation table must be manufactured on site. Figure 10 Preparation table 1 square strip, 2 post, 3 stop rail The sheeting bottom and the side panels consists of sheeting boards nailed together by means of cover straps. Depending on the size of the beam, the width of the sheeting bottom is dimensioned so as to accept, at both sides of the width of the reinforced concrete column, the thickness of the sheeting and cover straps and the width of a thrust-board (approximately 100 mm). The sheeting bottom can be placed on a pedestal support (a trestle formed by a waler connected with two columns by means of cleats) or on a round timber column also supporting a waler with cleat connection. In the latter case, the round timber column is located under the centre of the beam. By diagonal board bracing the round timber column and the waler above it, a composite triangle is formed. The side sheeting is erected on the sheeting bottom and held by a thrust-board. At the upper edge of the side sheeting a waler is mounted at both sides holding together the formwork by wire or spindle ties. A stull-batten is to be nailed on the formwork immediately above the ties to ensure that the projected beam width is kept when tieing the formwork. The waler and the columns are additionally braced by diagonal boards. Figure 11 Beam formwork 1 side panel, 2 cover strap, 3 waler, 4 thrust-board, 5 stull, 6 formwork bottom, 7 trestle, 8 tie wire What is the minimum width a sheeting bottom of beam formwork must have? _____________________________________________________ 4.5. Column Formwork Similar to beam formworks, the sheeting of column formworks is prefabricated according to the column dimensions from sheeting boards connected by cover straps. The sheeting panels are placed in a foot rim which is anchored in the soil by steel bolts. The foot rim consists of double-nailed boards. The foot rim must be exactly measured-in because it is decisive for the exact location of the column. It has the same functions as the thrust-board for foundation or beam formwork. When the sheeting panels have been inserted in the foot rim, vertical arch timbers are placed to take up the forces from the cover straps of the formwork sheeting. Around the arch timbers, which have the function of walers, column clamps of flat steel are clamped with wedges or a rim of boards is arranged similar to the foot rim. Additional formwork tieing by tie wires or steel screws is not necessary. The distances of the clamps are specified in the formwork project. Normally they are approximately 700 mm. The column in the formwork is laterally tied by diagonal board braces. Figure 12 Column formwork (horizontal section) 1 formwork sheeting, 2 cover strap, 3 clamp, 4 arch timber A lateral cleaning hole is to be provided at the foot of the formwork for removal of any impurities in the form-work before the concrete is placed. If a steel reinforcement is to be erected in the column formwork, two sides of the column only are to be provided with formwork first to permit easy erection of the reinforcement. After erection of the reinforcement, the remaining two sides of the column formwork can be mounted. The two sides mounted first are to be arranged cornerwise to ensure provisional stability. How can impurities in the column formwork be removed?