Steel Structure Construction: Verticality Correction – Correction of the Verticality of Steel Columns 1–3 2020.pptx

In Project 2 of the ‘Steel Structure Construction’ course, one of the tasks involved in the construction of a single-storey steel structure workshop is the correction of the verticality of steel columns. The course is taught by Associate Professor Zhang Guangjun, whose email address is: The relevant learning content covers provisions of the regulations; Clause 11.4.1 of the "Code for Construction of Steel Structures" stipulates that after the installation of the first section of steel columns, corrections to verticality, elevation and axis position must be carried out promptly, This includes the correction of the elevation and plan position of the steel columns, as well as the correction of their verticality. There are specific methods for correcting the verticality of steel columns. Method 1 involves using a theodolite and following its operating procedures to correct the verticality of the steel column; two theodolites are required for this correction, as shown in the diagram. First, place one theodolite on one side of the steel column, ensuring that the vertical sighting line is aligned with the baseline of the column base. Next, for the correction of steel column verticality, one method involves using a plumb bob weighing 1 to 2 kilograms when the column is at a considerable height, as illustrated in the diagram. The procedure is as follows: at a suitable height on the column, weld a steel bracket to the side of the column prior to measurement; a magnetic chuck is also required here. Next, secure the end of the plumb line to the plumb bob and measure the distance between the side of the column and the plumb line. If the measurements are consistent at both ends, this indicates that the column is vertical; if they are inconsistent, it indicates that the column is not vertical. Correct the verticality of the steel column as follows: when correcting the verticality of the steel column, after the column has been hoisted into position, use the rotation of the crane boom to carry out the initial alignment work. Generally, the verticality of the steel column is controlled within 20 millimetres. Only after the anchor bolts at the base of the column have been tightened may the crane release its hook. Another key operational point when correcting the verticality of steel columns is that, as there will always be a certain degree of vertical deviation after the column has been installed,⁠ for sections requiring a tight contact surface, tight contact must be achieved when the column is in its lowest position; other sections will exhibit a wedge-shaped gap. To ensure reliable force transmission at the contact surface, stainless steel shims of varying thicknesses can be inserted into the gaps. First, carry out the verticality correction of the steel columns. During the operation, note the following: firstly, when correcting the steel column, work should first be carried out on the side with the greater deviation, followed by the side with the smaller deviation; if the deviation figures for both sides are similar, the side with the smaller deviation should be corrected first, followed by the side with the greater deviation. Secondly, once the verticality of the steel column has been corrected in both directions, the horizontal axis and elevation should be rechecked. Thirdly, the correction of the steel column’s verticality must be carried out using two precision theodolites for observation; the observation point should be set at the top of the column, and the instrument must be positioned so that the plane of rotation of the telescope is as perpendicular as possible to the plane of observation—that is, the angle must be greater than 75°—to prevent measurement errors. Among the operational precautions for correcting the verticality of steel columns, wind pressure acts on the column surface; the wider the column, and the greater the column height, the greater the impact of wind, which in turn affects lateral deflection of the column. Therefore, during column alignment operations, if the column height exceeds 8 m and wind speeds exceed force 5, the work must not be carried out; deviations caused by sunlight striking the side of the column must be excluded. The Code stipulates in Clause 11.1.6 of the ‘Code for Construction of Steel Structures’ that during the installation and alignment of steel structures, factors such as temperature, solar radiation and welding deformation must be analysed for their impact on structural deformation. The contractor and the supervising body should carry out measurement and acceptance under the same weather conditions and at the same time of day. Once the crane has hoisted the steel columns onto the foundation, the columns are only temporarily secured to the foundation by anchor bolts, and their installation position is not precise; therefore, they must be aligned before final fixation. 33. Alignment of steel column verticality, Operational precautions: At Shenzhen Airport Terminal 3 (a structure 1,128 m long, featuring two temperature joints and movable hinged supports), the steel roof structure can undergo 60 mm of translational movement due to diurnal temperature variations, Correction of the verticality of 3 steel columns; deviations in verticality exist. Correction of the verticality of 3 steel columns – animated video. Correction of the verticality of steel columns, Thank you to the Steel Structure Construction Study Group. The lecturer is Associate Professor Zhang Guangjun. E-mail: Address: No. 552, North Gangtie Road, Qiaoxi District, Xingtai City. Postcode: . Next, I will introduce the process of correcting steel columns. Clause 11.4.1 of the ‘Code for Construction of Steel Structures’ stipulates that once the first section of steel columns has been installed, corrections to verticality, elevation and axis position must be carried out immediately. We have already covered the first two aspects; below, I will explain the correction of verticality. First, let us look at the correction methods. The first method involves using a theodolite. To correct the verticality of a steel column, two theodolites are required. as shown in the diagram. First, position one theodolite on one side of the steel column, aligning the vertical sighting line with the baseline of the column base. When measuring the centre line of the steel column, observations must be made from the bottom upwards. If the vertical centre line aligns, this indicates that the column is vertical; if it does not align, adjustments must be made to the column until it aligns with the theodolite’s centre line. Use the same method to measure the horizontal line, ensuring that the centre line on the other side of the column is perpendicular to the horizontal axis of the baseline. Once the positioning of the steel column is complete, temporary fixing of the column can be carried out. Next, I will introduce the second method, namely the plumb bob correction method. When the column is relatively tall, a plumb bob weighing 1 to 2 kilograms should be used for measurement, as shown in the diagram. Locate the column to be measured and determine a suitable height on its surface. At this point, before commencing the measurement, weld a steel bracket to the side of the column, securing it with a magnetic suction cup. Next, securely attach the upper end of the plumb bob, then measure the distance between the side of the column and the plumb line. If the measurement results show that the distances at the top and bottom are the same, this indicates that the column is vertical; however, if they differ, this indicates that the column is not vertical. Next, let’s discuss how to stabilise the plumb bob. Place the plumb bob in an empty bucket or one containing water, taking care to ensure there is a gap between the tip of the bob and the bottom of the bucket; this will ensure a highly accurate measurement. When it comes to aligning a column, in addition to the measurement method described above, you can also adjust the column’s verticality by adding, removing or replacing shims, to adjust the column’s verticality, as well as by using calculation methods to determine the inclination value for correction. When hoisting steel columns, once the column base has been inserted onto the foundation bolts, the column alignment phase begins. This stage primarily involves adjustments to the elevation and correction of verticality. The specific operational points for correcting the verticality of steel columns are as follows: Firstly, when correcting the verticality of the steel column, once the column has been hoisted into position, initial alignment can be carried out by rotating the crane’s jib. Typically, the verticality of the steel column must be controlled within a tolerance of 20 mm; only after the anchor bolts at the base of the column have been tightened may the crane release the lifting hook. (2) Given that a certain degree of vertical deviation will always remain after the steel column has been installed, for those sections requiring a tight contact surface, it is inevitable that the tight fit will occur at the lowest point, whilst other sections will exhibit a wedge-shaped gap. To ensure reliable force transmission at the contact surface, gaps can be addressed by inserting stainless steel shims of varying thicknesses. The following points should also be noted during alignment: (1) When aligning steel columns, the side with the greater deviation should be corrected first, followed by the side with the smaller deviation. If the deviation figures for both sides are roughly similar, the side with the smaller deviation should be corrected first, followed by the side with the larger deviation. (2) Once the perpendicularity of the steel column in both directions has been successfully corrected, the plane axis and elevation should be rechecked. If they meet the relevant requirements, the eight wedges around the column should be tightened, ensuring that the tightness is consistent; otherwise, under the influence of wind, the column will tilt towards the looser side. (3) For the operation of correcting the verticality of the steel column, it is essential to use two precision theodolites for observation. The upper observation point should be set at the top of the column, and the instrument must be positioned so that the plane of rotation of the telescope remains as vertical as possible to the plane of observation (the angle should be greater than 75°), in order to prevent measurement errors. (4) The effects of wind. Wind exerts pressure on the column surface; the wider the column and the greater its height, the greater the impact of wind forces, and consequently the greater the effect on lateral deflection of the column. Therefore, during column alignment operations, work cannot be carried out when the column height exceeds 8 m and wind speeds exceed force 5. Deviations caused by lateral sunlight should be eliminated, particularly during the intense sunlight of summer. Clause 11.1.6 of the ‘Code for Construction of Steel Structures’ stipulates that during the installation and alignment of steel structures, the effects of factors such as temperature, sunlight and welding deformation on structural deformation must be analysed. It is advisable for the contractor and the supervising unit to carry out measurement and acceptance under the same weather conditions and at the same time of day. Steel structures exhibit significant thermal expansion and contraction; therefore, during installation, it is essential to fully consider all factors affecting structural deformation, such as temperature, sunlight and welding deformation. These factors can typically be controlled through a series of measures, including construction simulation analysis and calculation, on-site monitoring, and optimisation of the construction sequence (which includes the welding sequence). Furthermore, the construction and supervision teams must carry out measurement and acceptance checks under broadly similar weather conditions and at similar times of day to avoid the impact of environmental conditions on the measurement results. The image shown depicts Shenzhen Airport’s Terminal 3. This structure is 1,128 metres long, features two thermal expansion joints and has sliding hinged supports. Under the influence of the temperature difference between day and night, its steel roof can undergo 60 mm of translational movement. Finally, let’s take a look at the requirements regarding deviations. The ‘Code for Acceptance of Construction Quality of Steel Structures’ sets out specific provisions regarding the deviation in the verticality of column axes. Right then, that concludes our discussion on the correction of steel column verticality. Take a moment to relax and watch the animated video I’ve created especially for you all, to reinforce what you’ve learnt in this lesson. Right then, that concludes our coverage of correction. Thank you all, and see you next time!