Dapeng Town Industrial Park, Tongshan District, Xuzhou City, Jiangsu Province, China
In the field of architecture, space structure is widely used in all kinds of large-scale buildings for its excellent spatial performance and diverse modelling adaptability. However, accurate design of mesh frame structure cannot be separated from the in-depth understanding and control of a series of key parameters.
(1) Constant Load: Constant load is the gravitational force borne by the space structure from the beginning to the end, including the weight of the net frame’s own rods, nodes and roof materials. Accurate calculation of the self-weight of the net frame members should be based on the selected steel type, cross-section size and length. The weight of roofing materials is relatively light if lightweight colour steel sheets are used, and significantly heavier if reinforced concrete panels are used. Accurate accounting of constant load is the basis for ensuring the stability of the net frame structure in the initial state.
(2) Live load: live load is the variable load that may appear in the process of using, such as roof maintenance load, snow load, wind load, etc.. Roof maintenance load should consider the weight of maintenance personnel and tools. The snow load value depends on the snow conditions in the region where the building is located, and the snow load value is larger in cold and snowy regions. Wind load and the building location of the landform, topography and height related, coastal areas or high-rise buildings, wind loads have a significant impact. These live loads in different working conditions may act individually or in combination on the network frame, the design must be fully considered.
(1) Span: span is a key geometrical parameter for space structure design, referring to the distance between the supports at both ends of the frame. The size of span directly determines the force pattern of the rack and the size of the bars. Large-span racks require stronger load-bearing capacity, and the cross-section of rods may be larger, and the requirements for node structure are also higher. For example, stadiums, exhibition halls and other large-span building network frame design, need to adopt a more reasonable structural form and rod arrangement, in order to cope with the challenges posed by the large span.
(2) Height: The height of the rack is the vertical distance between the upper and lower strings of the rack. Reasonable height of the rack can optimise the structural stress performance and reduce the internal force of the rods. If the height is too small, the structural rigidity is insufficient, and it is easy to produce excessive deformation; if the height is too large, although the rigidity is increased, the amount of material increases and the cost rises. Usually, the height of the grid according to the span by a certain ratio to determine, such as the span of 20 – 30 metres, the height can be taken as the span of 1/14 – 1/18.
(3) Grid size: Grid size refers to the grid size of the upper or lower strings of the grid frame bars enclosed by the grid size. Appropriate grid size affects the distribution of internal force and construction convenience. Grid is too large, uneven force on the rods, part of the rod internal force is too large; grid is too small, the number of rods increases, the node is complex, the construction difficulty and cost increases. The general grid size is between 1.5 – 4 metres, depending on the span, load and construction technology adjustment.
(1) Steel Strength: Steel is commonly used in space structure, and its strength indexes, such as yield strength and tensile strength, play a decisive role in the structural carrying capacity. Design according to the load and structural requirements to choose the appropriate strength level of steel, Q345 steel strength is higher than Q235 steel, suitable for large loads, large span Steel Grid Frame.
(2) modulus of elasticity: the modulus of elasticity reflects the elastic deformation capacity of steel when subjected to force. Modulus of elasticity of steel is basically stable, but there are slight differences between different types of steel. The accurate value is helpful to calculate the deformation of the frame under load and ensure that the structure meets the usage requirements.
4.Node parameters
(1) Node form: node is the intersection point of net frame, common node forms are welded ball node, bolt ball node and so on. Welded ball nodes have good integrity and high load carrying capacity, which are suitable for large span and large load net frame; bolted ball nodes are easy to install and fast in construction, which are commonly used in small and medium span net frames. Selection of node form need to consider the structural stress, construction conditions and cost.
(2) Node stiffness: node stiffness affects the overall force performance of the frame. Rigid nodes can better transfer the internal force of the bars, so that the net frame work well together; semi-rigid or flexible nodes will reduce the overall stiffness of the structure, the design needs to accurately consider the node stiffness of the structure of the internal force and deformation of the impact.
Space structure design, load, geometry, materials and nodes and other parameters are interrelated and affect each other. Only by comprehensively and accurately grasping these parameters and carrying out scientific analyses and calculations can we design a safe, reliable, economically rational and aesthetically pleasing mesh frame structure to provide a solid space guarantee for all kinds of buildings.
