PKPM's experience in making steel structure

PKPM's experience in making steel structure

  • 06 Jul 2020
  • steel structure

PKPM's experience in making steel structure

1. The optimized design of the steel structure is not to take over the design of others, according to the original design ideas, the amount of steel used for dead buckle, because this usually reduces the safety of the original design greatly, "load optimization" is to select the appropriate load, and the owner should be considered Possibility of minor changes to the structure, such as hanging lamps and re-arrangement of functional partitions. The constant load is made very small, the amount of steel used has not been reduced too much, and the functional limit is too restrictive. The optimization first considers the change plan, simplifies the steel structure force transmission mode and force transmission path, and saves a lot, and it should be relaxed when it comes to the joints of the members. If the safety reserve of each component of the original structure differs seriously, you can choose an appropriate safety reserve standard to adjust the model of each component, the increase of the increase, the decrease of the decrease. Structural safety is overall safety, and the use of strong individual members is useless.

2. Article 5.0.6 of the "Uniform Standards for Construction Quality Acceptance of Construction Engineering" (GB50300-2001): When the identification of the testing unit fails to meet the requirements, it can be accepted when the original design unit calculates that it meets the safety requirements. The "Project Management" of the first-level construction engineer said: When the inspection unit fails to meet the requirements, it can be accepted when the original design unit calculates that it meets the safety requirements. Take "liability for breach of contract" for actions that fail to meet the requirements.

3. If the welded ball of the grid is made of pressed steel plate, the thickness tolerance of the steel plate is close to ±2.5mm, and the deviation of the "strong rule" stipulates that it is not greater than 13% and 1.5mm. How to do it? When manufacturing, you can thicken the steel plate by 1mm to avoid the trouble of quality inspection.

4. The factory building with a crane of more than 20 tons is not allowed to be designed in accordance with the "Portal Rigid Frame Regulations" in China. The main reason is that the domestic crane beam installation deviation and crane track installation deviation cause card gauges, which increase the horizontal force by 4-5 times, resulting in The plant shakes violently and cannot be used normally. In short, any advanced design method can not be achieved beyond the actual construction level, and the requirements are in line with national conditions (or "company processing strength"). For example, the mast displacement of a 20-ton crane is controlled by the U.S. standard to control the displacement of the column head to H/240 (domestic H/400), so that no one is willing to drive, and the saving of a little steel is compared with the suitability of the plant.

It was so ridiculous to show that "design buckles home".

5. What kind of maintenance system needs to consider the gust coefficient?

(1) For brittle materials. For glass curtain walls, the gust coefficient must be used.

(2) Under the action of wind gusts, for temporarily increasing the load of steel materials that can withstand, there is no need to consider the wind gust coefficient.

(3) The maintenance system should not consider the gust coefficient. The gust coefficient is considered, and the safety is twice as high as the main structure, which is not conducive to the safety of the main body.

6. There are three kinds of deflection: (1), safety-related control standards. (2) Control standards reflecting the quality of installation. (3) Control standard with beautiful appearance. For example, single-layer reticulated shells only account for 1/300 of the stability defects, and the large deflection affects the structural safety. But the double-layer reticulated shell is only the control of the construction quality.

7. In the "Net Frame Regulations": "Temperature Stress Calculation" is limited to four-sided support grid.

8. The engineering principles of the biological world are the engineering design principles we pursue: (1) Saving. Use the least consumption to achieve the maximum effect. (2) Safety. Doing can overload organisms (buildings), even if partly damaged, it does not endanger the overall survival. (3). Simple and fast.

9. When the wind load of the grid frame and the grid shell is not large, when the permanent load accounts for less than 50% of the total load, it does not need to be considered according to "1.35*constant load".

10. The value of live load of the grid should not be less than 0.5KN/M2.

11. If the additional load exceeds 25Kg/M2, it should be considered whether there is a concentrated load on the purlin.

12. Chinese"Load Code" compares the wind load requirements with the US code: the US code has higher upward wind suction, greater horizontal wind at both ends, and less wind in the middle. The approximate calculation method of lateral movement in the "Gate Steel Frame Regulations" is only suitable for preliminary estimation. The formal lateral movement calculation uses the elastic integral calculation method.

13. The value of the wind load of the portal steel frame is stipulated in the "Technical Measures for the Design of Civil Building Engineering in the Country" for wind load: when L/H≤4, the "Load Regulations" should be used; when L/H>4, the portal steel frame regulations should be followed.

14. Open type: refers to the wall area with an opening area ≥80%. Partially closed: A. The openings are concentrated on a wall. B. The area of the wall opening is greater than the sum of the area of other wall openings. C. The opening is larger than 5% of the wall. D. Large uneven openings, the internal wind pressure increases to +0.6, -0.3 (no longer ±0.2).

15. When "end zone width" <"column distance", the half is used as the boundary, and the purlin wall beams are counted as more sides.

16. The wind pressure combination regulations in the "Gate Frame Rules" are based on "а <100". At this time, the wind pressure on the wall is reduced by 10%. Therefore, if "а >100", the wall pressure should be increased by 10% according to the door regulations.

17. The wind tunnel experiments of "rigid model" and "aeroelastic model" when the doors and windows of the wall facing the wind suddenly open show that the wind pressure on the inner surface of the roof is 5 times the average wind pressure, and the displacement is 5-10 times the average.

18. Wind vibration coefficient:

(1) high-rise buildings with H/B>1.5 need to consider the wind vibration coefficient (there is a calculation method).

(2) Large-span roof structure with T>0.25S (no calculation method).

(3) The relatively flexible stand canopy structure with a maximum wind vibration coefficient of 1.9.

(4) For general large-span grid frames or steel structures, the maximum wind vibration factor is 1.5.

19. The snow load on the roof is different from the snow load on the ground: (1) The weight of the snow on the roof is greater than that on the ground. Because the snow is absorbed into the snow-covered sponge body and then re-frozen. (2) The snow in the roof area is usually thinner than the snow on the ground. Because part of the snow is blown away by the wind. "Load Code" stipulates: Snow distribution coefficient, where: Sk is the roof snow pressure; S0 is the ground snow pressure.

20. Heating coefficient: Chinese codes do not distinguish between heating zones and non-heating zones; American codes distinguish between non-heating zones and the snow load is increased by 1.2 times.

21. ASTM A653 Grade33(37,40,50) is equivalent to China's Q235(Q255/Q275/Q340), which is mostly used to make color plates and thin-walled steel series. Look at it when calculating CFS. 1KSI=69N/mm2 is not a small unit.

22. The bending radius of cold-formed thin-walled steel can be calculated according to Rmax≤min(2t, 2.38mm). Therefore, when t<1.2mm, Rmax≤2t; when t≥1.2, R=2.4mm. It can be used to calculate the expanded width of special-shaped thin-walled steel or color plates. CFS modeling also uses the bending radius, which is stronger than a blindness!

23. Thin-walled steel anti-corrosion metal coating, harsh environment ≥ G90, general environmental conditions ≥ G40 or G60. The opening of the thin-walled steel web is not greater than 38*102mm, and it should be centered, otherwise reinforced. Reinforcement method: hole edge is 25.4mm outward, #8 screw @25.4mm connection. Hh≤0.5H, Lh max (00.5H, 102mm). From "Residential Steel Structure Design and Construction"

24. Screws for cold-formed thin-walled steel structures shall be no less than #8, and shall pass through at least 3 threads of steel members.

25. Comparison of wind load between portal frame and ordinary frame: see "Portal Frame Regulation" "Load Code"

Therefore, it is concluded that for the column, "GB50009-2001" is 1.63 times that of "CECS102:2002", the former tends to be safe. For Liang, "CECS102:2002" is 1.5 times that of "GB50009-2001", the former is safe. The light structure calculation is applicable to the portal frame, but not necessarily the portal frame; the structure that adopts the wind load according to the "Portal Frame Regulations" can be an ordinary steel structure, as long as it is a low-rise house, L/H<4 can use. The wind pressure combination regulations in the "Framework Regulations" are based on the premise of "а <100". At this time, the wind pressure on the wall is reduced by 10%. Therefore, if "а >100", the wall pressure should be increased by 10% according to the door regulations.

26. When the height of the light structure roof is greater than 18m, the shape factor of the wind carrier must be taken according to the "Load Code", and the structural measures can be adopted in accordance with the "Technical Regulations for Steel Structures of Portal Rigid Frame Light Houses" (CECS 102:2002). For the articulated column foot, L/H>2.3 and the column foot just connected, when L/H>3.0, the value of wind load according to "door stiffness regulations" is adopted. If the value is taken according to "Load Code", the structure is safe.

27. Seismic design principles of portal frame:

(1)adopt bottom shear method. Because the gantry is mainly of low-shear type, the mass stiffness is evenly distributed, the difference between the two modes is too large, and the first mode is mainly used, so the bottom shear method is used for calculation. (2), 7 degrees and below does not require seismic calculation (8 degrees and above are only required to calculate earthquake). But it does not mean that it is not necessary to take seismic measures. (3) The anti-seismic measures of the portal frame are mainly to strengthen the nodes: A. Bolt connection is used between the members as much as possible; B. The beam-column node, the tuck plate is added to the lower wing of the beam; C. The width-thickness ratio at the beam-column connection point is appropriately reduced; D, between columns

The joints between the supports and the members are designed according to 1.2 times the load-bearing capacity of the rods; E. The anchors at the foot of the supports between the columns and the joints of the columns are to be subjected to a pull-out check, and to prevent the anchors from shearing, set shearing keys.

28. The connection between the masonry maintenance part and the steel column needs to have a certain flexibility, and an appropriate gap is required, and the gap should be greater than the side shift value.

29. Daylighting panels are not suitable for areas with frequent snowfall.

30. Roofing panel materials and coatings: StE280-2Z and StE345-2Z should be used for hot dip galvanized substrates. Coating:

(1)Stainless steel plates and aluminum-magnesium alloy plates are suitable for high-rise buildings.

(2) The primary color plate of aluminum-zinc coating and coating 165g/m2 should be used in buildings with long service life.

(3) The coating of galvanized sheet is 275g/m2, suitable for tall buildings.

(4) 180g/m2 of galvanized sheet coating, non-important buildings should be used.

(5) Color-coated board. The coating adopts polyvinylidene chloride, which is suitable for higher buildings.

(6) The coating adopts silicon modified steel plate or high durability polyester, which is used in general construction.

31. Generally, the thickness of the end plate is not less than 1.0 times the diameter of the connecting bolt obtained by "theoretical calculation", and not less than 16 thick. Especially high-strength pressure-bearing bolts. Not "thickness not less than bolt diameter"!

32. In addition to satisfying the calculation, the thickness of the column base plate shall not be less than 16 thickness and not less than 1.5 times the thickness of the column flange. In addition, when the span (single span) is greater than 30 meters, the anchor bolt shall not be smaller than M30.

33. The damping ratio of the portal frame can be 0.05, and the multi-layer steel structure depends on the specific situation.

34. The welding stud (shear nail) is that the magnetic ring should be welded with heat-resistant and stable arc; when bent steel bar is used, Q235 steel is generally used, and when channel steel is used, 4# channel steel is generally used.

35. Composite beam: It is not allowed to directly bear the dynamic load. The internal force is calculated by the elastic method, and the strength of the section and the strength of the connector are calculated by the plastic method. Deflection cracks are elastic. In the construction stage, strength, stability and deflection need to be calculated. Before the concrete strength is increased to 75%, the construction live load can be taken as 1.0. When the lower part is provided with a support (and the support distance is less than or equal to 3m), it may not be checked. be=b0+min(6he1, )+min(6he2, ), where he1 and he2 refer to "total thickness of the plate-Wave height of profiled steel plate".

36. Partial shear connection composite beams can be used for equal-section composite beams that only bear static loads, have little concentrated force, and have a span of ≤20 meters. When calculating the internal force of the composite beam according to the elastic method, the internal force adjustment factor considering plastic development is ≤15%.

37. In the negative bending moment section of the composite beam, the lower flange is compressed, and the secondary beam can be a lateral support point. If the height difference between the secondary beam and the main beam is too large, the lower flange is supported by the corner brace. Pressure flange width). Aspect ratio: ≤9(Q235) and 7.4(Q345).

38. Deflection limit of composite beam: construction stage≤L/200. Use stage:

(1)when L≤7M, deflection≤min(200,L/250);

(2) when 7M < L≤9M, deflection≤min(250,L/300);

(3)L >9M, deflection ≤ min(300,L/400);

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