There is an essential difference between truss and grid frame in steel structure, that is, grid frame is a space structure while truss is a plane structure. grid frame is a grid structure composed of several rods according to certain requirements, there are two kinds of flat and curved grid structure, which is a kind of space structure more stable than truss; truss is also a structural system composed of rods, and the rods with smaller cross-section are composed of larger cross-section members. Our common advertising frame is the truss structure. Specifically, the development and evolution of truss types have experienced the following:
As early as more than 2,000 years ago, our ancestors have discovered the principle of triangle stability and invented the triangle truss, only the trusses then were made of different materials than now, but the principle was the same. Triangle trusses, like beams and arches, were the main method of realizing spanning in ancient buildings.
The beam truss, also known as the parallel chord truss, is a form of truss that appeared in the mid-19th century. At that time, the technology was not too developed, and timber bridges were the main form of bridges, adopting the technology of traditional arch bridges originated from Europe. Arch bridges have a high load carrying capacity but are prone to deformation, so the timber arch bridge utilized a combination of an arch and a reinforced steel frame. It is under the application of this form that the new type of truss began to appear one after another, which opened the era of beam truss.
The hollow truss appeared a little later than the girder truss and was proposed by a Belgian engineer. It is a structure which removes the diagonal web of parallel chord truss and utilizes the vertical web and chord. Although the overall effect of hollow truss is not as good as the whole truss, it is better in appearance and shape, and has its uniqueness and practicability in architecture. Early Yale University Library utilized multi-story hollow truss.
Trusses have continued to evolve, and in modern times, space trusses have become a universally popular truss style, suitable for use in large-span space structures. Most of the early trusses were in planar form and utilized horizontal bracing to solve stability problems. In contrast, the members of space joist are in three-dimensional position, and the cross-section is mostly in the shape of triangle or rectangle, which makes the overall stability of joist greatly improved.
In conclusion, trusses have a long evolutionary cycle, from the early days, and with the development of the times and society, the truss structure has been developing and evolving to meet the needs of use.