Safety technology for high formwork construction o

Safety technology for high formwork construction of super thick cast-in-place slab

in the current construction market, there are many building structures with high floors and large spans. Therefore, more and more unconventional high formwork cast-in-place concrete construction is used in construction projects. In the construction of high formwork cast-in-situ concrete, the cases of major casualties caused by the instability of the support system and the collapse of the system due to improper design and calculation, construction technical measures and the settlement of the foundation are not uncommon in recent years. Local construction departments attach great importance to the construction management of high formwork and formulate relevant management measures. Through a successful example, this paper introduces how to take effective measures according to the construction specifications and on-site implementation to ensure the safe and reliable implementation of high formwork construction

1. Project overview

this project is a one story industrial plant with a building area of 3300m2 (shear wall structure) and a cast-in-place reinforced concrete roof of 6500 (length) × 13500 (width) × 1500mm (thick), with an elevation of 13 ~ 14.5m. Its construction difficulty has far exceeded that of pouring mass concrete. During the construction process, according to relevant regulations, the high formwork system must be specially designed and special construction technical measures must be taken. The strength, stability and deformation of the high formwork support system should be calculated and rechecked (see Figure 1)

Figure 1 formwork support layout

2. Scheme design

the roof support system is designed to be erected with fastener type steel pipe scaffold. Outer diameter of steel pipe φ 48. High frequency welded pipe with a wall thickness of 3.5mm, and the spacing between uprights is 400 × 400mm, the step distance of the cross bar is 1500mm, "and it can reduce the weight of the ground transportation vehicle. The top three steps are 1000mm. A diagonal brace is set every 3m in the longitudinal and transverse directions, and a vertical and horizontal sweeping bar is set 30cm away from the ground; the plate bottom formwork is made of high-quality 18mm thick plywood, and the bottom brace (@250mm) and the cross bar are made of 50 × 100 pine wood brace. The fastener material adopts the technical requirements of KT. Anti sliding moving force is taken as 〔 τ〕＝ 7kN。 Characteristic parameters of steel pipe: section area a ＝ 4.89cm2, section bearing capacity ［ n ］＝ 27.5kn

3. Calculation review

(1) load calculation

self weight of reinforced concrete:

24kn/m3 × 1.5 ＝ 36kn/m2

self weight of reinforcement: 6.2kn/m2

self weight of formwork: 1kn/m2

construction load: 2.5kn/m2

vibration load 2.0kn/m2

load generated by dumping concrete 2.0kn/m2

partial coefficients of dead load and live load are taken as 1.2 and 1.4

Q ＝ 1.2 respectively × （36+6.2+1）+1.4 × (2.5+2.0+2.0) = for this, 51.84+9.1 = 60.94kn/m2

(2) check calculation of anti sliding capacity of steel pipe and fastener:

axial load borne by each steel pipe: n = 60.94 × zero point four × 0.4 ＝ 9.75kn2, radius of gyration: ⅰ ＝ 15.78mm

considering adverse factors, the effective length coefficient of the pole? Take 1.5, and take 1500mm for length L, then the slenderness ratio of the pole λ＝μ l/i＝1.5 × 1500/15.78 = 142.6

by λ Value to find the stability coefficient of the component Ψ＝ 0.3376

N/Ψ A＝9.75 × 103/0.3376 × 489=59.06n/mm22

the checking results show that the stability of steel pipe upright meets the requirements

4. Safety measures

(1) strictly follow the design scheme, strengthen the inspection in the construction process, so that the inspection has records and complete countersignature, and implement the rectification of hidden dangers according to the three fixed measures to ensure construction safety

(2) the support load of the system is large, and the construction quality of the support system is very important. There must be sufficient structural measures to ensure safety. The project uses the shear wall around which the strength requirements have been met to unload, and the bottom sweeping rod, cross bracing, and horizontal tie rods set in the vertical and horizontal directions are reliably connected with the shear wall to reduce the load acting on the support

(3) the foundation of the vertical pole is on the ground concrete poured first, and the bearing capacity of the foundation meets the requirements. The bottom of the vertical pole adopts the base component, and the vertical pole adopts the through core socket connection, and the docking in the same section should be staggered

(4) set horizontal tie rods in the vertical and horizontal directions. The horizontal tie rods in the vertical and horizontal directions of each part must be pulled through. The horizontal tie rods are overlapped, and butt joint is strictly prohibited

(5) set vertical and horizontal sweeping rods (30cm from the ground) and diagonal braces. The diagonal braces are set every 3M, which are reliably connected with the upright rod

(6) first, the quality inspection of steel pipes and fasteners should be strictly strengthened, and they can be put into use only after passing the acceptance, especially the fasteners themselves. The stability of the formwork support system is determined by the anti sliding force to prevent samples from flying out of the fasteners

(7) after the system is set up, click the pendulum button to check and accept in time, especially the installation quality of fasteners is checked by force measuring wrench. If the fastener fails, the calculated length and slenderness ratio of the pole will increase, resulting in the reduction of the bearing capacity of the pole

(8) during the construction process, the stacking of concrete and other equipment should meet the requirements of the construction plan. Overloading is strictly prohibited, and the stress of the support system should be balanced as far as possible. The overall stability of this system can generally meet the requirements. However, the bearing capacity of a single pole is less, and it cannot bear excessive concentrated load, so as to prevent the instability of the overall structure due to the instability of local members

during the construction of the project, due to the high attention of all relevant units, it was strictly implemented in accordance with the requirements of the technical code for safety of steel tubular scaffold with couplers in construction (JGJ), and appropriate measures were taken. No safety accidents occurred during the construction process, and it has been delivered for use