土木工程专业大跨度FRP网架结构英文文献和翻译 第3页

The strips can be curved and circumvoluted due to their small thickness. A typical CFRP strip with properties similar to those shown in Table 1 is able to resist a tensile force of 400kN or more, while the weight of a 300m long strip is less than 70kg. In comparison, the self weight of a 300m long high strength steel cable which can resist the same load is more than 500kg. The strips are arranged into a plane surface of a suitable pattern by some pre-defined rules. In the simplest weaving pattern, each strip passes over one crossing strip and under the next to form a web like a woven fabric. A part of such web is shown in Figure 2 (Pong et al. 2004). In a more general case, the number of strips meeting at a joint and the angles between these strips are the basic parameters of a weaving pattern: two strips at 90° to each other are shown in Fig. 3(a), three strips at 60° shown in Fig. 3(b), and four strips at 45° shown in Fig. 3(c). At the joints, strips can be fully inter-connected by adhesive bonding after complete shape formation or left unbonded so that sliding between strips is allowed. In the latter case, the static friction between strips can contribute to the stiffness under static loading while the sliding friction can consume the kinetic energy of the structure under dynamic loading.数字地形图测量实习总结

3 CONSTRUCTION OF SIMPLE FRPWWS

Following the five construction steps as shown in Figure 4, a simplest FRPWWS can be completed.
First, the outer and inner ring beams on temporary supports are constructed. In general, the outer  ring beam is in compression and the inner one is in tension when the web is in place. The outer ring beam is made of reinforced concrete while the inner ring beam is made of steel. The web which is woven with FRP strips is next fixed onto the ring beams with hinge joints and provided with some initial tension to form a plane surface. A tentative hinge joint scheme between the strip and the ring beam is shown in Figure 5, where the strip is tightly clamped between two stiff plates. The weaving of the strips should follow the rules of a specified weaving pattern which should have been designed by the structural engineer and the architect together. Weaving can be carried out easily due to the light weight and small thickness of FRP strips. The temporary supports to the inner ring beam are now withdrawn and the inner ring beam moves in the out-of-plane direction by its self-weight plus an additional weight where necessary. This out-of-plane displacement of the inner ring beam can also be effected by a set of high strength tendons. The installation of these prestressed tendons completes the construction process. According to force decomposition, a small out-of-plane force causes a large in-plane component and enables the web to be tensioned, leading to a web of sufficient stiffness to resist various loads.

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