Bohai Steel Structure Co., Ltd.

Bohai Steel Structure Co., Ltd.
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    Latest Code for Design of Steel Structures

    author:Bohai Steel Structure Co., Ltd.

    【Font size: big medium smail

    time:2019-10-09 09:46:32


    The force of the above-mentioned pillar support is in the ideal state, but in practical engineering, because of the errors in processing and installation, when the members of the support system do not adopt tensioning equipment or are initially installed under the action of dead weight, there will inevitably be initial deformation, which makes the member A in Fig. 2-3(a) in the case of the same question and height. The length of B is larger than that of member A and B in Figure 2-2(a), i.e. L2 > L1. In addition, for the inter-column support of the lower column of the crane beam, the circular steel support has a larger slenderness ratio, which makes the circular steel support more flexible and has a smaller compressive capacity, so its compressive effect can be ignored. However, the slenderness ratio of rolled section steel members is much smaller than that of circular steel supports, so the influence of bearing pressure can not be ignored. For example, the crane generates longitudinal horizontal force along the longitudinal operation of the factory building, which can be simulated as the vertical horizontal force P is applied to the right of the structure shown in Figure 2-3. At this time, the A-bar is compressed, while the B'bar should be pulled. Because of the processing and installation errors in practical engineering, the tensioned member B'does not immediately bear the tension that the compressive member A'should bear after unloading, but produces a lag phenomenon of force transmission (_=L2-L1 from the initial deformation of the member), which further increases the deformation of the compressive member A, and the transverse deformation also occurs. As the crane runs backward, the longitudinal horizontal force P is applied to the structure shown in Figure 3. Before the lateral deformation of the A-bar is restored, the bar can not bear the tension until the transverse deformation disappears completely and the initial deformation consumes completely, so the tension of the A'bar can continue to increase. 。

    In this process, when B's bar is unloaded under pressure, the deformation of A's bar has not disappeared and can not bear tension, so that the transverse deformation of B's bar increases and the axis of B's bar becomes S-shaped. In practical engineering, due to the processing and installation errors, the lag phenomenon of the force transmission of the supporting rod [2], under the action of reciprocating horizontal force, the stress difference of the same supporting rod becomes larger, the bearing capacity of the fatigue structural members and their connecting parts is more easily reduced, and the axis of the rod becomes S-shaped, even in support. When the support is designed according to the compressed member, the initial deformation caused by the initial processing and installation errors is assumed to be L. Hooke's law F*L/(EA) shows that the hysteresis of force transmission caused by initial deformation in Fig. 2-3 must make the compression bar A have the bearing capacity of not yielding under compression when the B bar reaches tension: P/A= L*E/L2 <(A*A)= fy.

    If Q235 steel is used, f = 215N/mm2, then L*E/L2 = 206x103x (AL/L) = 215, (AL/L) = 1/1000. When B reaches Cmax (bar tension is positive), if P is applied to the structure of Figure 2-3 (b), the stress in B bar will immediately change from Umax to 0 bar compression to negative, and the stress variation difference_=_max-_min is very large, so the reciprocating loading will greatly reduce the bearing capacity of the member. Therefore, in practical engineering, if the X-type support between columns is adopted, the initial processing and installation errors should be controlled so as to avoid the transverse deformation of the supporting rod when the rolled steel members with smaller slenderness are used. Some measures are taken to make the X-type supporting rods within the allowable error norm, so that the lag phenomenon of force transmission does not occur under the action of reciprocating horizontal forces, and the support between columns designed by tension can give full play to the role of supporting system, meet the requirements of stability and bearing capacity of the longitudinal structure of the factory building, and ensure the structure. Spatial performance.

    Because of the initial deformation of components such as processing and installation errors, and P/A=L*E/L2 < N/4_*A, it is suggested that the deformation of the former be 2.0 times larger and that the former be changed to 20*P/A=12*AL*E/L2=20*1/1000*206*103>1/A*103>1/A*21D>0521, which is better for A to be declared less than 100. 2) When the support is designed according to the tension member, the initial deformation is also caused by the error of initial processing and installation, and under the action of reciprocating load, the transverse deformation of the screw member increases, which leads to damage. Therefore, the support is designed according to the tension member, and the actual project must also be in tension 4. Summary 1) In the design process of the X-pillar support, according to the following conclusions: In the design of tension bar, when the slenderness ratio of the support between columns is not more than the allowable value of the code and is designed according to the compression bar, considering the processing, the installation error has initial deformation, and the slenderness ratio is better than less than 100.

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