Membrane Structure Design Is Generally Divided into Which Several Steps to Complete?

Membrane structure manufacturer introduces you to the three steps of membrane structure design:

(1) Find an initial equilibrium shape;

(2) Mechanical analysis under various load combinations to ensure safety;

(3) Cut and make.

Developed countries have proposed a variety of calculation methods since the 1960s. So far, the finite element method has been used as a more advanced and commonly used method. The element types are all triangular plane constant strain elements. This method is transplanted from the theory of large deformation of rigid plates and shells.

Membrane architecture as a softshell that can only withstand tension is not suitable for this type of flat unit, because, for a rigid shell, this flat unit can be regarded as a combination of flat stress unit and flat bending unit. The unit array can be formed by combining these two unit arrays. As a softshell, the membrane structure cannot resist bending, and can only rely on the curvature of the curved surface of the film, which causes the redistribution of the internal force in the membrane surface to resist the external load perpendicular to the curved surface.

If such a plate element with only in-plane stress is still used, the linear part of the strain will not reflect the effect of the out-of-plane z-direction displacement, which results in the element not containing the z-direction node reaction force. For each element, the static force is not Balanced. Fortunately, the non-linear part of the strain considers the effect of the z-direction displacement, so that the overall balance equation of the combined elements can be approximated by continuous iterations. The disadvantage is that too much in-plane displacement is required to meet the balance requirements. The actual situation is that only certain out-of-plane and in-plane displacement and curvature changes are required.

Taking these into consideration, membrane structure technicians have adopted curved membrane elements for the first time in the world. The linear part of the strain introduces the z-direction displacement and the curvature and torsion of the element. The nonlinear part still retains the influence of the z-direction displacement. In this way, the balance equation of each unit or the combined unit can be easily satisfied, the number of iterations is greatly reduced, and the deformation result is more in line with the real situation.

And because the stresses at different points in the element are different, it is more accurate to judge whether wrinkles appear. The curvature and torsion rate of each unit finally found can provide a lot of very useful information for judging the correctness and merits of the initial shape finding and cutting and cutting.

The shape-finding and internal force calculation method of the membrane structure established by the curved surface finite element has a very perfect surface shape and stress state, which is the most reasonable ideal initial state of the membrane structure. The so-called minimal surface refers to the surface with the smallest area under the given boundary conditions.

The stress at any point on this surface is equal. Since the 1960s, developed countries have proposed a variety of calculation methods for the shape finding of membrane structures, such as the physical model method, force density method, and dynamic relaxation method.

Not only the domestic but also the foreign calculation theories have so far used planar membrane units as the calculation model of the membrane structure. This method is transplanted from the theory of large deformation of rigid plates and shells.

Membrane structure as a softshell that can only be tensile is not suitable for the use of planar units. Its disadvantage is that it requires too much in-plane displacement to meet the balance requirements, while the actual situation is that only a certain out-of-plane and in-plane displacement And the curvature can be changed.

The consequence is that in the calculation of the internal force to be performed later, after substituting the real material constant, the difference between the minimal surface obtained by the previous shape finding and the actual possible membrane structure shape may not be visually significant, but it is for the calculation. It cannot be ignored, so the calculation is easily divergent or wrinkled.

This is also a common shortcoming of other previous methods. They often divide this coherent process into two stages of ideal shape-finding and actual checking, and there is no guarantee that the shapes found can be built with real membrane materials. Small surface.

Membrane architecture