Successful application in the process. For the main factors that should be considered in the design of similar projects, I have proposed my own solutions. 1 Overview In the past ten years, the application of self-supporting steel tube tower structures in engineering has been increasing. This type of structure is mostly used for lighting poles in stations and squares, and its height is generally between 25-40 m. In recent years, in the construction of a tower structure for high-voltage transmission line engineering, there has been a contradiction between the connection structure of the flange of the steel tube tower and the foundation and the construction process. The author has carefully analyzed and verified the engineering problems, put forward his own opinions and adopted by peer experts, effectively promoted the smooth implementation of the project, and has long been engaged in the design of civil structures.
2Engineering design features The project is a steel pipe tower of a high-voltage transmission line in a certain area. The design adopts a tower-one scheme. The foundation is a large-diameter borehole borehole. The representative diameters are 1 01400mm. They are 32M42, 16M42, and 32M56, respectively, and the anchor top positioning auxiliary steel plate top surface is 300mm above the ground. The design requires the base to be continuously poured and the top design elevation is considered. The above requirements are difficult to consider from the in-situ drilling process. From the perspective of engineering quality, the top position will have quality defects such as slurry leakage and excessive dog scum in the future. Even the positioning of the anchor bolt may be too large to meet the requirements of the construction acceptance specification. The top cap is to solve the problem. One of the effective methods. The quality of the project is easy to control, and the construction process is relatively reasonable is the main factor to consider this approach. The bearing capacity and reliability between the cap and the base are the most worrying problems of the original design unit. This requires the use of data to check and judge the ultimate bearing capacity of the joint between the 3 pile cap and the pile body. 3.1 Design parameters submitted by the owner Typical design data for check calculation are shown in Table 1. Table 1 Base diameter mm Top anchor bolt Specification Design length m Main rib configuration specification Main rib area mm2 ç ¼ Strength level Tower bottom function Standard value Horizontal shear force Vk/kN shaft pressure Nk/kN 3.2 Pile cap The basic assumptions of the ultimate bearing capacity of the joint with the pile body and the value of the important parameters are larger than 800mm, which belongs to the large-diameter short-thick pile according to the "Technical Specifications for Building Base" (JGJ94~94) and detailed survey of engineering geology Data, when calculating the eccentric compression member, the large coefficient of eccentricity can be taken as Z=1; 10.8N/mm2. Check the "Concrete Structure Design Specification" (GBJ10-89) Table 2.1.4, C20 grade 弯曲 bending compressive strength The design value = 11N/mm21d8N/mm2, so it can be pressed according to C20 level. /. "=11N/mm2 for checking; 1.1.1, and considering the seriousness of the social hazard of the high-voltage overhead line tower failure, the safety level of the base should be one level, and the importance coefficient of the base at one time is V= Reinforcement; the cross-section is taken at the bottom of the cap, the height from the bottom of the tower flange is H=1.5m; the influence of the latter; (7) It is considered that the single bearing capacity and the top displacement calculated by the original design unit meet the requirements of the relevant specifications. Applicable calculation formulas and cross-sectional dimensions of the test results and the area of ​​the reinforcing bars of the main ribs uniformly distributed along the periphery are known. They can be carried out in accordance with the formula 4.1.19-Bu 4.1.19-5 of the Code for Concrete Structure Design (GBJ10-89). The ultimate load carrying capacity of the eccentric compression members is checked, or the design value of the ultimate load capacity of the eccentric compression members of the cross section is designed.
According to the above design parameters and formulas, the ultimate bearing capacity of the eccentrically compressed positive section of the base cap can be calculated. The design value of the bending moment of the cap and the base joint (M) and the positive sectional limit of the actual energy contribution of the base can be calculated. The ratio of the bearing capacity design value (Mu) is as follows: the bending moment design value; Mu is the ultimate bending moment resistance design value contributed by the top energy.
Most of the ç ¼ structures in the project are allowed to work with cracks, although there are some differences between the assumed rigid nodes and the actual working state of the structure during structural analysis, but this difference is permitted in general civil engineering. The experimental results show that the joint connection between the cap and the base has a bending moment transmission capacity of 70% to 80%. The ratio of the action and the resistance between the cap and the base calculated in this paper is within the range of the bending moment transmission capability of the experimental study. In addition to the corresponding construction measures, it is considered that the top setting cap is safe and effective in determining the pile top 锶 effect. The method of converting the pile JbHshi is safe and effective // ​​and has been approved by the original design unit experts. Its characteristics are that the quality of the project is easy to control, the construction process is relatively reasonable and detailed. See the structure of the connection structure of the 01200 pile cap and the pile foundation. The importance level of such a project should be taken as the first level, correspondingly, one tower at a time. The structural importance coefficient should be taken as 1.2 because the steel tube tower is mainly subjected to lateral action, and the effect on the foundation is mainly shearing force and bending moment, so the length of the longitudinal reinforcement of the base into the cap should not be less than 40 times the diameter of the main rib. The lower elongation of the longitudinal ribs of the foundation should not be less than 4/T (the horizontal deformation coefficient of T). The diameter of the cap should be 200~300mm larger than the diameter of the base. The length of the top insert cap should not be less than 100mm. One level higher than the base.
For the joint of the cap and the top of a tower-one scheme, the design of the base section is recommended by dividing the bending moment design value of the base top by an adjustment factor of 0. >0.8.
6 Conclusions In this paper, combined with the engineering example, the ultimate bearing capacity of the base of the self-supporting steel tube tower structure and the bottom of the transition between the caps was checked and successfully applied in practical engineering. Relevant suggestions for major factors that should be considered in similar engineering design
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