- Detail

Application of simple unloading method in high-rise building construction

first, the problem is raised

with the continuous development of urban construction, a batch of high-rise buildings and super high-rise buildings have been allocated land. Fastener type steel pipe scaffold has the characteristics of convenient assembly and disassembly, flexible erection, and can adapt to the changes of the plane and elevation of buildings. Fastener type steel pipe scaffold is widely used in high-rise buildings. In order to meet the height requirements of buildings and limited by the performance of steel pipes, most super high scaffolds should adopt the method of sectional unloading

II. Comparison of common unloading methods

common unloading methods include cantilever steel beam, cable-stayed steel wire rope, upper and lower bracing, triangular steel pipe frame, etc. (see Table 1)

advantages and disadvantages of common unloading methods Table 1

III. Project Overview

the building of Shantou Rongxing international trade building is two and fifteen floors high (including five floors of the podium), the total height of the building is 86.55m, and the standard floor height is 3.15m. The total erection height of the scaffold is 92.00m, and the podium and tower scaffolding can be erected separately, that is, the tower scaffolding can be erected from the roof slab of the podium

IV. scaffold erection method

(I) the horizontal distance between the pole and the diagonal bracing

pole is 1.05M, and the longitudinal distance is 1.5m; The distance between the inner bent and the wall is 0.35m; The step distance of the longitudinal cross bar is 1.8m for the inner row and 0.9m for the outer row (that is, a full-length protective railing is set between each step frame of the outer row); The cross bridging step distance is 9.0m, and the cross setting

(II) unloading method and the connection between the frame and the building structure

1. Break through a batch of common key technologies. Because the height of the outer frame tower is too high, triangular steel pipe unloading frames are set around the 10th, 14th, 18th, 22nd and 22nd floors. The spacing of the unloading frames is the same as the longitudinal spacing of the upright (1.5m). See Figure 1 for the practice

2. The wall connecting rod should be set along the height of each floor, every 4.5m along the horizontal and at the corner point. The spacing of the wall connecting rod on the floor where the unloading frame is set is 1.5m. See Figure 2 for the practice

.

(III) scaffold board and protective railing

1. Lay four layers of bamboo scaffold board

2. Protective railings and 18cm high scaffold boards are set outside the construction layer frame

v. checking calculation of the overall stability of the unloading rack

the unloading rack is set every four layers from the straight section to the clamping true transition radius, and the erection height of each section is 3.15 × 4 = 12.6m, 12.6/1.8 = 7-step frame. The horizontal distance b (frame width) =1.05m, the longitudinal distance l=1.5m, and the step distance h=1.8m of the longitudinal horizontal bar. Four layers of bamboo scaffold boards are paved, and two layers are constructed at the same time. The working load qk=2kn/m2 (decoration frame)

(I) calculate the axial force n

1, ng1k (one-step longitudinal self weight) transmitted from the upper scaffold to the unloading frame × Full height)

φ forty-eight × 3.5 the standard value of the dead weight of the structure borne by the vertical pole of the steel pipe scaffold per meter is found in table A-1 of the technical code for safety of steel pipe scaffold with couplers in construction (JGJ) (hereinafter referred to as the code)

gk=0.1248kn/m

ng1k=0.1248 × seven × 1.8=1.572kn (calculated according to the average stress of the inner and outer upright)

2, ng2k (components and fittings - longitudinal self weight)

ng2k=2.950kn

3, nqk (construction load)

Σ Qk=2k/m2 × 2=4kN/m2

Σ k=(1.5 × one point zero five × 4)/2=3.150kn

4 values are substituted into the formula to calculate n

n=1.2 (ng1k+ ng1k) + 1.4 Σ k

=1.2 × (1.572+2.950)+1.4 × 3.150

=9.836kn

(II) diagonal stability checking calculation

1. The calculation diagram is shown in Figure 3

Figure 3 diagonal calculation diagram

2. The load borne by the outer diagonal bar (AO):

the load borne by the inner diagonal bar (Bo):

3. A horizontal crossbar with inferior accessories is added in the middle of the diagonal bar of the load frame to reduce the production cost of the equipment, The calculated length of the outer inclined rod is:

check Appendix B of the specification, i=1.58cm

λ= L0/i=298.7/1.58=189

check Appendix C of the specification φ= 0.201

4. Stability checking calculation of outer inclined rod

n/φ A=10.764 × 103/0.201 × 489=110n/mm214.164kn

(safety)

VI. actual application

when erecting the outer scaffold, the triangular steel pipe unloading frame can break through the limitation of the erection height of the outer scaffold, solve the limitation of the outer scaffold

, and solve the problem of superelevation erection of the outer scaffold. The method is simple, practical, economical and safe

VII. Some experience

1. The load of the upper double row outer scaffold is transmitted to the triangular steel pipe unloading frame through the fasteners. Generally, the anti slip design value of the fasteners is 8kN. For safety reasons, it is appropriate to add safety fasteners to the outer frame poles and unloading frames, and the outer inclined poles

2. The inner and outer inclined rods are not perpendicular to the floor. In order to ensure good contact between the inclined rod and the floor, the end of the inclined rod should be cut into an inclined mouth

3. The diagonal bar should be erected with straight steel pipe in full length, and lap joint is not allowed

4. When dismantling the scaffold, it must be carried out layer by layer from top to bottom. First dismantle the vertical double row outer frame, and then dismantle the triangular unloading frame

5. Compared with other unloading methods, the triangular unloading frame used in the construction of high-rise buildings does not require a large amount of one-time investment, and is not limited by the floor height and site, which can greatly reduce the construction cost

(Wang Jianzhong)

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