Analysis of the influence of the model on the large span space frame structure (Part 1）

The dynamic characteristics of the structure of the large span roof structure are obviously different from the dynamic characteristics of general multi-layer / high-rise structure. If artificial analysis is performed in the process of structure analysis, the upper large span roof and the lower multi-layer support structure are performed separately, and it will often lead to a large error in the analysis of the two parts of the structure. Especially when the span is large and the lower structure rigidity / overallness is poor, this error often brings unsafe analysis results to the structure. Therefore, at present, for the general large span roof structure, the overall analysis considering the action of the roof is often used. However, how to reasonably consider the dynamic characteristics/layer deformation characteristics of such a whole structure needs to be analyzed in detail.

1.Project Overview

The roof structure of the Tennis Pavilion of Dongli Sports Center uses 90M (main span) × 56m (side span) space frame structure as the cover support system, the lower part of the lower part is independent column support, and the other side is a multi-layer with a single span structure. The structure of the structure is used to design the structure of the double-layer oblique truss. The node forms a welding ball node.

2.Design analysis and comparison

2.1 Preliminary analysis results

For this structure, the design first carried out the design and optimization of the space frame for the upper structure. For the support point of the roof structure, the elastic support form of the sideline side of the structure column is used to simulate. In the above-mentioned layout, the diagonal size of the space frame shell is basically controlled at 4000mm× 4500mm, and the minimum angle of the abdominal rod is about 40 °. Through the preliminary optimization design, the structure is basically controlled at 40kg/m.

2.2 SAP2000 results

Adopting the same reticulated shell model, and at the same time, considering the actual function of the lower structure, and the design uses the SAP2000 for analysis of the overall characteristics of the structure.

The analysis results show that there are many differences in the internal force analysis results of the reticulated shell due to the consideration of the overall effect of the structure.

2.2.1 The vibration mode of the reticulated shell itself changes in order

1) In the separate analysis of the reticulated shell structure, the first vibration mode of the reticulated shell appears in vertical (0.24s), and in the overall analysis, although the first vibration mode of the space frame  shell also appears in the vertical direction, it also appears in the vertical direction, but Expressing weak vertical stiffness (R= -0.68s).

2) In a separate analysis, the emergence of the form of reticulated shell is in accordance with the rules: first-order positive symmetry / opposite; second-order positive symmetry / opponent and other order appears. Except for the first-order vertical vibration in the overall analysis, the space frame shell is basically coordinated with the horizontal deformation of the overall structure.

2.2.2 The stress ratio/deformation distribution of the reticulated shell itself changes

1) In a separate reticulated shell analysis, the stress distribution of reticulated shell rods has a certain regularity, but after considering the overall structure, the stress ratio of the rod is generally improved, especially near the support point and space frame shells. The stress of the corner is more increased than the stress.

2) Due to the changes in the supporting effect of the overall structure, the maximum vertical deformation capacity of the space frame shell has changed a lot. The maximum deformation of the vertical maximum deformation in a separate analysis is 120mm, and the maximum deformation in the overall analysis is 175mm.