Membrane structure is one of the representative forms of architectural structures in the 21st century, providing significant development space for modern spatial structural systems and architectural design. Excellent membrane structures have high strength, good flexibility, small thickness, light weight, strong fire resistance, durability, and airtightness [1]. They can be used in single layer, multi-layer, or inflatable applications, and can maintain curved structures well. In the field of architecture, it can be used as both a structural material and a template material, fully leveraging its high tensile strength. Its permeable and impermeable properties can improve the strength of concrete when used as a template, and it is suitable for large-scale or narrow construction sites. The excellent physical and chemical properties of membrane materials support the design of membrane structures, and the development of new membrane materials with excellent performance is driving the increasingly widespread application of membrane structures in concrete formwork.

1 Membrane structure

Membrane structure is different from traditional rigid structure, which is composed of flexible membrane materials as the main body. Membrane material is a coated fabric composed of a combination of substrate and coating. The substrate woven from reinforced fiber material determines whether it has excellent mechanical properties. The coating ensures the airtightness and self-cleaning of the material, protects and supports the fibers within a certain range, and evenly transfers the load attached to it. With the continuous development of membrane materials, membrane structures have become an important branch of today's structures, integrating construction technology, material technology, equipment management technology, and more.

The early membrane structures evolved from tent structures [4]. In the early stages of development, the most obvious advantage of this structure is that it does not use any hard rods such as metal or plastic, which can minimize the damage or destruction of internal materials caused by rod damage. Up to now, due to its small volume after packaging and relatively regular shape after packaging, it is easy to store and transport; There are fewer requirements for construction space, and the required equipment and instruments are simple; Part of the membrane structure adopts filling and exhaust equipment, which does not require supporting structures or requires a small amount of supporting structures, making construction convenient and space utilization high; It has advantages such as relatively low cost per unit area and is gradually being applied in concrete formwork.

Application and advantages of 2-membrane structure in concrete formwork

In the early stages of development, membrane structures were used to construct temporary military buildings [5,6], and with the continuous deepening of research, they were gradually used for the construction of various temporary exhibition halls and warehouses. Until today, membrane structures have been widely used in various fields, including the construction of various sports venues in daily life [7], temporary emergency stations, medical warehouses, and temporary command centers in military fields [8]. With the continuous development of aerospace technology, scholars are also studying how to use membrane structures to construct large lunar residential structures [8].

Nowadays, membrane structures are gradually being used in concrete formwork due to their advantages such as low cost, variable shape, easy construction, and easy transportation. Multiple experts and scholars have studied them with the aim of applying them to more fields of cast-in-place concrete engineering. As a new type of composite structure, flexible formwork concrete has incomparable advantages compared to ordinary concrete. It can be applied in soil slope excavation, foundation pit support, slope reinforcement and other engineering projects, as well as railway reinforcement, building soft foundation reinforcement, retaining wall reinforcement [9], bridge concrete columns and underground engineering. On the slope treatment side