Reasonable layout and positioning of tower crane in engineering construction is a crucial link, and also a difficulty in construction organization design. The adverse consequences caused by improper arrangement and wrong positioning of tower crane in the project are very serious, which will lead to low production efficiency, delay construction period, difficult demolition and equipment exit, increase construction cost, and even cause potential safety hazards and safety accidents.
Unreasonable or wrong arrangement and positioning of tower crane in construction engineering can be divided into the following situations:
(1) In the construction organization design, only pay attention to the efficiency of the project and ignore the technical requirements of tower crane installation.
Most of the equipment for this type of users comes from rental channels. "Pay the rental fee should meet the use", transfer the loss caused by the layout or positioning to the third party or both parties to share, so that the lessor can formulate remedial measures for it. In the normal construction process, due to the lack of understanding of the technical performance of the tower crane before installation, the construction unit only pays attention to the maximum use of the tower crane in the project, considers the convenience and coverage of the surrounding residential building construction, and ignores the Attachment requirements of the tower crane after the tower crane is raised. As a result, the tower crane cannot be attached to the building after it exceeds the basic height. The distance between the tower crane and each residential building is greater than 10m It is necessary to design special wall attachment devices for reinforcement. Due to the wrong arrangement and positioning of tower crane, the construction period is delayed and the cost is increased.
In addition, in the construction of a high-rise residential building with arc strip blocks, if the construction unit lacks the reasonable selection and positioning demonstration for the tower crane installation foundation before installing a QTZ80 tower crane, the rail walking type can be adopted, so that the tower can be lowered through the tower crane walking to avoid the radian before dismantling, but it is made into a fixed foundation type, resulting in the front end of the boom and the balance arm when the tower crane is disassembled and lowered The tail end collides with the arc-shaped building, so it is impossible to lower the section. Therefore, a 150t truck crane is selected to directly dismantle from a height of nearly 50m, which not only increases the risk of high-altitude operation, but also increases the demolition cost. If the walking type is adopted, it is only necessary to lower the tower to a height of 19m, and a 25t truck crane can be used to dismantle the tower, which can reduce the cost by 70%. For example, in a residential community construction site in Jiangning, Nanjing, a QTZ40 tower crane was installed in the center of the corridor outside the residential building. Three sides of the tower crane were surrounded by buildings, and the section could not be lowered. Therefore, large tonnage truck crane was selected for high price demolition.
(2) In the construction organization design, the construction unit does not have the engineering geological survey report to carry on the construction in a hurry.
In order to speed up the construction period, the construction unit does not make a detailed study on the engineering basic data and geological report, and the tower crane is arranged hastily, and the positioning errors caused by the foundation problems often occur. In a construction site in Songjiang, Shanghai, due to the lack of detailed understanding of the foundation, the user unit randomly arranged the tower crane, made the foundation and installed the tower crane. After less than 5 days of installation, it was found that the foundation was seriously sinking and inclined, so the newly installed tower crane had to be removed immediately and remedial measures were implemented, which increased the construction cost. If not found and removed in time, it is likely to cause safety accidents.
(3) Although the layout and positioning of tower crane has been demonstrated repeatedly in the construction organization design, it has to be done due to the construction conditions.
The construction site of Wanda Plaza project, which is located in the prosperous section of Nanjing Xinjiekou, is a 5-storey building with a length of 120m and a width of 90m. The layout of tower crane has been verified by the construction unit and installed at 1 / 3 of the project center. Due to insufficient consideration of the dismantling scheme, the QTZ80 tower crane located in the engineering center should be dismantled after the completion of the construction. After the demonstration and screening of multiple schemes, the truck crane with a capacity of more than 200t must be used to meet the requirements of the demolition operation. When the working radius reaches 42m, the 54m main boom and 12m auxiliary boom of 200t truck crane are used for demolition. Because Nanjing Xinjiekou is located in a prosperous area, construction work is not allowed during the day, and all work must be carried out at night, which increases the risk of high-altitude operation and costs a lot. To sum up, the layout and positioning of tower crane is very important, and the determinants of tower crane layout and positioning in the project are also various.
In order to do a good job in the reasonable layout and positioning of tower crane in construction engineering, we can start from the following aspects:
(1) Select tower crane model. Firstly, according to the maximum working unit weight of the project, the tower crane lifting capacity, installation height and boom length are determined. Secondly, understand the technical performance and installation basic requirements of tower crane, whether its coverage can meet the use requirements, whether there is "dead angle" and "blind area" in the operation range, so as to provide the basis for reasonable layout and positioning of tower crane.
(2) Determine the number of tower cranes required. Sometimes, in order to reduce the blind area, a project needs more than one tower crane to work at the same time. In the construction organization design, the reasonable layout of multi tower operation is also one of the main focuses in the construction process.
(3) Determine the tower crane layout plan. After the model and quantity are determined, the tower crane layout scheme can be determined according to the engineering characteristics. The key point of multi tower operation in large-scale project is type selection and positioning, that is, how to arrange tower crane reasonably, we should not only understand the general situation of the project, know the progress of each node and the lifting and transportation requirements in each link, but also have scientific and economic calculation.
(4) Determine the tower crane positioning point and verify the tower crane foundation load. After the tower crane layout scheme is determined, the foundation positioning point can be determined. The reasonable selection of foundation positioning point depends on "up" and "down": the "upper" refers to whether the building corresponding to the tower crane foundation positioning point has attachment conditions; and "lower" refers to whether the foundation bearing capacity corresponding to the tower crane foundation positioning point can meet the requirements. The foundation of tower crane must meet the requirements of tower crane stability, foundation strength and foundation uniform settlement.
(5) Do a good job in site technical investigation and understand the surrounding environment of the project. Before the tower crane layout and positioning scheme is determined, the surrounding environment of the project shall be carefully investigated to see if there are obstacles affecting the tower crane operation, such as high-rise buildings and high-voltage lines, etc., and the environment during tower dismantling shall be estimated and understood. At the same time, they shall be familiar with the access roads and whether there are obstacles affecting the transportation of tower cranes, such as underground pipelines and cables.