Comprehensive Introduction to Two-Way and One-Way Waffle Formwork
Waffle Formwork In today’s construction industry, the use of modern structural systems to reduce costs, improve the quality of architectural plans, and enhance the seismic performance of buildings has become more important than ever. To select a suitable structural system, it is initially necessary to have a structural floor with diaphragm performance according to Standard 2800, among which one can consider beam-slab floors, two-way waffle slabs, and one-way waffle slabs. Of course, with proper implementation of joist-light form floors and the ability to model this type of floor in relevant software, it is possible to achieve a floor with appropriate performance. When did Beton Baspar Sanat Company start producing waffle formwork? Accordingly, Beton Baspar Sanat Company, considering the country’s needs and the increasing progress of construction engineering in our beloved country, initiated the production of two-way and one-way waffle formwork. Around the year 2011 (1390 in the Iranian calendar), when the first waffle floors were designed and constructed in Tehran, Beton Baspar Sanat, in collaboration with structural and architectural designers, including Mr. Farzad Deliri, began producing two-way waffle formwork measuring 60×60 cm with a height of 30 cm, and 90×90 cm waffle formwork with heights of 30 and 40 cm. In Chapter 9 of the National Building Regulations, a section is dedicated to slabs and floors with two-way joist performance, which must be considered when producing two-way waffle formwork. The most important point in this regulation is that the free distance between two waffle joists should not exceed 75 cm, which has not been observed in some types of waffle formwork produced in the market. Why should waffle slabs be used? What is the role of waffle formwork in waffle slabs? Waffle slabs, as a modern and efficient system with two-way load distribution and two-way performance, have gained a special place in construction projects. Due to their grid-like and honeycomb appearance, two-way load transfer capability, and reduction of dead load, waffle slabs have become an attractive and widely used option among structural designers. According to various international codes such as ACI 318 and Eurocode 2, waffle slabs, in addition to increasing structural stiffness, significantly save concrete and steel compared to beam-slab systems of the same thickness. This feature has made the waffle slab system, together with appropriate waffle formwork, applicable in large international projects as well as in various medium- and small-scale urban buildings. Top view of 90×90 cm waffle formwork with 40 cm height and 20 cm joist width before placing rebarTop view of 90×90 cm waffle formwork with 40 cm height Bottom view of 80×80 cm waffle formwork with 28 cm height for a 12-meter spanThe price of each 80×80 cm waffle formwork with 28 cm height is approximately 580,000 Toman.Execution detail of 80×80 cm waffle formwork with 28 cm heightExecution detail of 80×80 cm waffle formwork with 28 cm height History of Waffle Slabs The idea of designing grid slabs (waffle slabs) first emerged in the 1950s in Europe and the United States. The main goal was to achieve a system capable of covering longer spans (column-to-column distances of around 10 meters or more) without the need for heavy beams. The first projects using waffle formwork and waffle slabs included multi-story parking structures and commercial buildings, which faced limitations with traditional beam sizes defined by regulations. With the advancement of formwork technology and the introduction of lightweight plastic and fiberglass forms, various waffle formworks such as 60×60, 75×75, 80×80, and 90×90 cm with different heights for various span lengths were rapidly adopted in large projects such as airports, shopping centers, sports halls, and high-rise buildings. In Iran, waffle slabs have been introduced over the past two decades and are now widely used in modern construction projects, including office complexes, cultural centers, and luxury residential buildings. What is a Waffle Slab? (Waffle Slab Definition) A waffle slab, or two-way ribbed slab, consists of a series of intersecting joists arranged regularly in two perpendicular directions. The voids between the joists are formed by temporary waffle formwork, which can have various dimensions. Today in Iran, there is high demand for 80×80 cm waffle formwork with a height of 28 cm and 60×60 cm waffle formwork with heights of 25 and 30 cm. The spacing between waffle forms usually ranges from 10 to 20 cm and is selected based on the span and column-to-column distances in the architectural plan. Designing waffle slabs using waffle formwork allows: Reduction of slab weight Transfer of loads in two directions Increased flexural stiffness and overall system strength Easier passage for mechanical and electrical installations Advantages of Waffle Slabs Material Savings:By removing concrete in non-essential areas (tensile regions of the waffle slab), the volume of concrete used is reduced, and construction costs are approximately 20–30% lower than flat slabs. This feature not only contributes to economic savings but also results in a lighter slab with a lighter foundation. Long Span Coverage:This system can cover spans of up to 15 meters or more without large suspended beams, while flat slabs typically cover only 6–8 meters. This capability is crucial for commercial and industrial projects requiring open, column-free spaces. Dead Load Reduction:Removing excess concrete lightens the slab and improves the building’s seismic performance, which is particularly important in earthquake-prone areas. Architectural Beauty and Exposed Ceilings:The underside of the slab is a regular grid, which in many projects serves as the final ceiling without additional finishing. This feature is highly valued in the design of auditoriums, cultural centers, and modern commercial buildings. Ease of Installation for Services:The voids between joists provide a suitable path for pipes, cables, and other utilities, reducing the need for separate channels or additional openings. Durability and Longevity:With proper design and execution, waffle slabs can remain functional for decades with minimal maintenance. Disadvantages of Waffle Slabs and Waffle Formwork Requires precise formwork and substructure Relatively longer construction time compared to flat slabs Needs skilled personnel for correct reinforcement placement between waffle forms and proper positioning of shear studs Initial cost of waffle formwork is […]