Application of Falling Method of Column Bottom Reinforcement in Space Frame Engineering ( Part 1 )

一、Project Overview

Space frame  with orthogonal and vertical pyramids. node type: bolt ball. support type: point support of lower chord opposite side columns. space frame size 38.5m×46.5 m. the horizontal projected area is 1790.3m2. the total length of the canopy is 38.5m. the total width is 46.5m. The column distance is 14.4 meters, the span is 32 meters, and the column height is 10.05 meters. The steel columns are welded H-shaped steel, the specification is H600×400×12×16, the drop height is 40cm, and the number of falling steel columns is 6. The steel columns are arranged symmetrically. 3 each on the east and west sides. The falling method adopts the falling method of strengthening the bottom of the column, and cuts off the steel column by 40cm.

二、Construction plan (specific steps)

1、Demolition

（1）In order to weaken the influence of lateral wind pressure during the construction process on the horizontal stability of the overall space frame, the fascia boards around the canopy are removed first.

（2）Remove the 200mm thick fine stone concrete wrapping table at the bottom of the existing steel column.

2、Work platform installation

（1）The basic operation platform is set at the position of the existing fine stone concrete wrapping platform on the station platform, and 40mm thick steel plates with a length and width of 1400mm*1000mm are welded around the bottom of the column. Both are welded to the steel columns, and the platform directly transmits the load borne by the upper steel columns to the original foundation. Except for the welding part, the other parts of the foundation platform are firmly lined with steel plates or wooden squares and the hard surface of the platform, and anti-slip expansion bolts are set as auxiliary fulcrums of the steel platform.

（2）40mm thick steel plates are welded along the steel column close to the upper part of the first-floor operating platform, and the outer skin of the steel column is laid out 700mm-1000mm wide along the width, and welded to the first-floor platform. The opening position is welded with a full thread bolt with a diameter of 36mm and a bolt length of 1125mm. Weld the reinforcement plate (upper base plate) at the upper 600mm of the lower base plate, and the welding position and method are consistent with the base plate. Bottom plan view of the operating platform, the position of the bolt hole corresponds to the vertical, and the hole diameter is 38mm.

3、Limit platform installation

Weld the limiting plate at 360mm above the upper bottom plate (to control the horizontal displacement of the steel column). A total of 2 limiting plates are stacked and placed between the plates and welded between the plates. The welding position and method of other parts are consistent with the bottom platform plate. The position of the bolt hole is corresponding to the vertical, and the hole diameter is 38mm.

4、Equipment installation and positioning

After the welding operation is completed, pass the full-thread bolts from the bolt holes of the limit plate to the lower bottom holes. During the bolt piercing process, install the upper and lower nuts in place, and weld the lower bottom plate with the bolts. The four bolts of each steel column are With this operation method, in order to ensure the accuracy of the position, the bottom can also be drilled on site to adjust the position and then welded. Tighten the upper and lower nuts of the bolts, use pads on both sides of the web to lift the jack up with steel pads, take reinforcement measures for the jack, and spot weld the bottom with the pads to prevent the jack from slipping and tilting. Four 25T jacks are used for each column. After on-site investigation and measurement, the total weight of the roof is 65 tons, which is divided into 6 steel columns. Each steel column (including the self-weight of the column) bears about 11 tons of pressure on the upper part, so the 25T jack Four already have sufficient safety reserves.

5、Fixing measures to prevent horizontal displacement of steel columns

During the overall lifting and lowering process, in order to ensure that the entire building only moves in the vertical direction and does not allow horizontal displacement, a limit device is used to control the horizontal displacement. First, fix the steel column at a height of 2 meters with a cable wind device. The function of the cable wind device is to fix and adjust the upper steel column after cutting and adjust the displacement deviation. The bottom of the cable wind device must be reliably connected to the hard surface of the platform. The existing concrete floor , Drive in a number of expansion bolts or connect them in a firm position, and adjust the tightening with the falling process of the steel column to ensure that there is no deviation during the falling process of the steel column. (Attention, pay attention to listening to the weather forecast before falling, and choose construction when there is no wind or less wind)

6、Steel Column Cutting

The first step is to cut the steel column flange: use oxygen acetylene to cut the steel column flange. Two 25-ton jacks are pre-stressed on each side of the two sides, and the jack at the web position is removed after the jack is tightened. The second step, steel column web cutting: use oxyacetylene to cut the web, and the lower position is 10cm from the top of the column bottom plate, and the upper position is 50cm from the top of the column bottom plate. After the web is cut off, remove the cut part of the 40cm steel column. By analogy, take the same method to cut off the remaining five steel columns. Cutting treatment: Correct the flange plate and web plate of the steel column at the cutting place, grind according to the steel column butt welding specification, and process the groove, and start the steel column falling construction after the trimming is completed.