Tension String Structure System

The output of steel in China has grown by leaps and bounds, and the application scope of building steel structures has been expanding. The steel structure system has exerted its advantages in the field of construction with its inherent characteristics of lightness, speed, goodness and economy. Arches, shells and reticulated shells, which are suitable for building large spaces and mainly under compression, when spanning a large span, there is a large horizontal thrust of the support and a large degree of sensitivity of the stability to the initial defects of the structure, and the strength of the member material is large problems such as low utilization. Solving the horizontal thrust and the stability of the arch shell structure has become a key point of structural technology.

As a branch of the prestressed steel structure, the tension string structure introduces flexible prestressed cables on the basis of the traditional rigid structure, thereby optimizing the structural performance, and has significant advantages in structural design, construction, material selection, and innovation. widely used in engineering. The essence of the tension string structure is to connect the upper compression-bending member and the lower tension member with struts. By applying to prestress to the tension member, the upper structure can be deflected, thereby reducing the final deflection under load and improving the upper member. And by adjusting the prestress of the tension member, the horizontal thrust generated by the structure on the support is reduced, making it a self-balancing system.

(1) Plane string structure

The plane string structure mainly includes string beams and string trusses (Figure 1-a). The plane string structure can be divided into a straight beam, arch and herringbone arch string structures according to the shape of the upper string member (Figure 1-b). The number of support rods is different, and the form can also be divided into single vertical rods and a V-shaped rod. The plane chord structure is arranged in parallel and then connected in the longitudinal direction by connecting members, that is, the overall structural system of the actual project is formed.

FIG.1 a（Schematic diagram of the plane stretched string structure） and b (Schematic diagram of the plane stretched string structure)

(2) Decomposable space string structure

The decomposable space string structure is also called the plane combination string structure, which refers to the structure combination with the characteristics of space force and can be divided into multiple plane string support members. According to the combination of the various members, they can be divided into three categories: bidirectional stretched string structure (Fig. 2-a), multi-directional stretched string structure (Fig. 2-b) and radial stretched string structure (Fig. 2-c)

FIG.2 a(Two-way stretched string structure)、b(Multidirectional stretched string structure) and c （Radial string structure）

（3）Non-decomposable space string structure As the name suggests, the indecomposable space string structure refers to the string structure that cannot be split into various plane string members. It forms an overall stress system in space, improves overall stiffness, and has better stress performance. The main types are chord dome, chord space frame, chord shell, and other structures.

(4) Introduction to engineering application of Zhang string structure

String beam (truss) structure

The main building of Shanghai Pudong International Airport (Phase II) is the first string beam structure in my country (Fig. 3). The upper portion of the string beam is in the form of rigid double arches and the lower portion is a cable-rod system. The span is 89 meters, the elevated span is 64 meters, the length is 414 meters, and the ridge height is 40 meters. It is supported by Y-shaped inclined columns.

FIG. 3 Main Building of Shanghai Pudong International Airport (Phase II)

The Gymnasium of the New Campus of Hebei Normal University (Figure 4) has a basketball court on the first floor and a volleyball court on the second floor. The roof adopts the chord-supported truss structure system with the upper chord as the arch. The distance between the inverted triangular three-dimensional trusses is 8 meters, the span is 41 meters, and the truss height is 1 meter. Compared with the general chord-supported truss, it is flatter and thicker. It is small and meets the requirement that the height from the highest point of the truss to the lower edge of the cable should not exceed 2.4 meters. The floor on second floor is divided into two areas. The floor in the area of 48m×40m on the west side adopts the composite beam floor structure, and the floor in the area of 56m×40m on the east side adopts the structure of the beam (string-branch) beam. It is 4 meters long, with a span of 40 meters. The building requires that the height from the top of the steel beam to the lower edge of the cable should not exceed 3 meters, and the steel beam should be a 150mm thick cast-in-place concrete floor.

FIG.4 Model diagram of the new campus gymnasium of Hebei Normal University

(5)String dome structure

The chord-supported dome in the lobby of Tianjin Free Trade Zone Business Exchange Center (Fig. 5) is the first chord-supported dome building in my country, with a span of 35.4 meters and a single-layer reticulated shell on the upper part. To a total of five cables.

FIG.5 Model diagram of the new campus gymnasium of Hebei Normal UniversityTianjin Free Trade Zone Business Exchange Center

The roof of the main hall of Henan Qinyang Gymnasium has a long axis of about 99.5m, a short axis of about 70.7m, and a vertical height of 7.2m, which is an elliptical surface. The rise-span ratio in the long-axis direction is 7.2%, and the rise-span ratio in the short-axis direction is 10.2%. After scheme optimization and comparison, compared with the double-layer reticulated shell structure, the chord-supported dome system has been simplified in terms of design process, construction technology and joint structure; Therefore, the overall stability of the structure is improved; the introduction of high-strength prestressed cables makes the strength of steel more fully utilized, reducing the amount of steel used and improving the span of the structure. Therefore, the main pavilion finally adopts the string-supported dome structure system (Fig.6).

FIG.6 Henan Qinyang Gymnasium Main Hall

(6)String support space frame structure

The 61m×148.6m and 61m×143m areas of the Shandong Guangrao International Expo Center are double-sloped roofs, and the chord support space frame structure system is adopted (FIG.7). The thickness of the frame is 3.8 meters, and prestressed cables are set in a certain range in the grid area, and the sag of the cables is 3.6 meters.

FIG.7 Guangrao International Expo Center

(6)String branch shell structure

Guangxi Liuzhou Kistler Museum (Fig. 8) The entire roof structure is composed of 12 single-layer reticulated shells. The height difference between the adjacent two reticulated shells is connected by vertical trusses, except that the middle reticulated shell is supported on the frame. Outside the column, all the rest of the reticulated shells land on both ends along the length. The front gate of the Kistler Pavilion has a large span, so prestressed cables and struts are set at the lower part of the single-layer shell to form a partial string-supported shell structure system, which achieves a greater span in the span. Safety and aesthetics also meet the requirements.

FIG.8 Guangxi Liuzhou Rare Stone Museum