Abstract: With the vigorous development of China's social economy, building science and technology have also developed rapidly. Especially in cities, with the shortage of land and the further utilization of land, high-rise buildings are increasingly becoming the main body of urban construction. From the perspective of strengthening quality and ensuring safety, combined with some experiences in practice, the author talks about some personal views.
1 Introduction
Generally speaking, floors 9 ~ 16 (
2 High-rise building strength control
Strength mainly refers to the strength of concrete. Because of the large amount of concrete, long construction period and many factors affecting climate and working conditions, sometimes the concrete strength of high-rise buildings is discrete or even unqualified. So how to overcome and control the strength of concrete?
2. 1 proportion selection
Before the project starts, the concrete with different strength grades shall be prepared according to the design requirements, and the grading test shall be conducted by the statutory testing institution. After the grading report comes out, the mixture ratio test (laboratory mixture ratio) should be done according to the grading, and it should be carried out in actual construction. But the question is whether the gradation is consistent with the site construction technology. According to statistics, when the water content of sand increases, the sand ratio decreases by 2% ~ 3%, the strength of concrete decreases by 15% ~ 20%, the cement dosage affects by 5% ~ 20%, and the gradation of stones and sand affects by 5% ~ 20%. The effect of water-cement ratio is to increase L% and decrease strength by 5% ~ 10%. Since the impact is so great, we should take corresponding measures to control it.
According to the situation of raw materials in the local market, carry out tests in different proportions to ensure timely adjustment of proportions during construction, such as 5 ~ 40 mm stones, M.
In order to ensure the practical universality of laboratory proportioning, the laboratory proportioning should be adjusted according to the water content and mud content of raw materials. In actual construction, it is necessary to strengthen the control of raw materials and take corresponding measures to adjust when the gradation of sand and gravel is poor, such as adding 0.5? L~ 10？ L sand and stone, etc.
2.2 Strict maintenance system
Pumped concrete is often used in high-rise buildings. Pumping concrete can not only shorten the construction period but also improve the construction performance of concrete. However, the application in some projects shows that the strength of concrete is still insufficient under the condition of strict control of mix proportion, raw materials and vibration. Analysis of the reasons, mostly for the serious shortage of construction period and maintenance time. According to the test results of relevant experts, the strength is 2: 1.5: 1 respectively, which is compared with the total wet curing for 28 days, the total wet curing for 3 days and the air curing for 28 days, thus showing the importance of maintenance.
There should be a maintenance plan for pouring mass concrete, and a special person should be responsible for it from the beginning to the end, and there should be enough understanding of maintenance from the subjective consciousness. Measures such as personnel, water source, day and night, coverage, etc. should be considered in the maintenance plan, and major key details should not be omitted.
Strengthen the supervision of maintenance period. Track and record maintenance measures and on-site maintenance, find problems in time, and ensure the effectiveness of maintenance.
2.3 Strengthen the concrete strength evaluation
Eliminate irregularities in the production of test blocks. When the strength test of concrete block is greater than the design strength, is it qualified in the strength evaluation? Not exactly. The Standard for Inspection and Evaluation of Concrete Strength (GBJ 107) stipulates that concrete strength should be inspected and evaluated in batches. An acceptance batch of concrete should be composed of concrete with the same strength grade, same age, same production process conditions and mixture ratio.
Choose one according to the corresponding conditions, which involves the problem of standard deviation. High-rise buildings have great differences in climatic conditions such as construction period, concrete pouring and maintenance, and the discreteness of concrete test values is also great, that is, the standard deviation is too large. If the overall evaluation is based on a batch, it is likely to be unqualified. Therefore, the evaluation should be carried out in batches, and the classification should be based on a batch with basically the same conditions, which not only conforms to the requirements of national specifications, but also conforms to the actual situation on site.
3 High-rise building "three lines" control
Axis, elevation and verticality are similar to the meridian of the building. For high-rise buildings, because of its wide coverage and difficult operation, displacement or inaccuracy often occurs. "Three-wire" control is a major difficulty in high-rise buildings.
3. 1 verticality control
Controlling verticality is one of the foundation and key links to ensure the quality of high-rise buildings. In order to control the verticality of the building, the positions of the four corner columns of the building should be determined according to the column network layout of the building. When installing the four-corner column formwork, the thickness line will pop up along the outer layer of the column, and the vertical formwork will be supported, and the verticality of the column will be measured by hanging the line: after the verticality is guaranteed to be 100%, the formwork will be aligned with the outer line for reinforcement and support, and concrete will be poured. After the four-corner column is removed, other columns take the four-corner column as the baseline, and pull steel wires to control the flatness and verticality of the front.
In the process of verticality control, double checking with laser instrument weight hammer can increase the verticality accuracy, and at the same time increase the internal and external double control, which can minimize the vertical measurement error of high-rise buildings.
3.2 Axis control
Axis transmission. In the process of high-rise building construction, scaffolding and construction layer move up synchronously, which leads to some surrounding datum points unable to be measured. Therefore, after the structural construction inspection axis is 0.00, several 200*200*8mm steel plates are embedded in the longest vertical and horizontal direction based on the-floor, and the control axis or main axis control points are marked on the steel plates: when the second floor and above are constructed, 200*200mm square holes are left in the corresponding positions of each floor based on the first floor, and the lower control points are measured with a big line hammer, and then the theodolite and steel tape measure are used. Control of hydrograph. Hanging two lines and pouring shear wall are the keys to process line control. When pouring shear wall, high-quality plywood with a thickness of 18mm should be adopted, the periphery of external wall should be fixed with large formwork combination, and the internal wall should be numbered in bulk. This ensures the flatness of the wall, but more attention should be paid to the verticality of the wall. Therefore: ① When shuttering, the four corners of the shear wall should be strictly controlled to ensure that the verticality deviation of the four corners is within the minimum range; (2) when pouring concrete, double lines shall be hung at the waist and top of the outer plane of the shear wall to ensure that the lines are always consistent with the formwork, and the problems shall be adjusted in time to achieve the purpose of linear control.
3.3 Control of elevation lines
Use at least four holes on the precontrol axis of each floor (generally at least three high-rise buildings are measured upwards) to locate the elevation, at the same time, recheck the elevation sum of multi-storey buildings, and then level to check whether these four points are on the same horizontal plane, so as to ensure the accuracy of the elevation.
Among them, the elevation accuracy of the four holes needs to be improved, and the elevation of the holes may lose its benchmark function due to formwork, pouring and loading during construction. Therefore, it is necessary to ensure the reliability of the putright point, strengthen the formwork support at the mouth of the cave, and control the floor thickness of this part with steel bars with a diameter of 12 to ensure the accuracy of elevation.
In the four corners of the building, where conditions permit, check points of storey height and cumulative storey height should be set up, and this position should be posted on each floor for checking to prevent excessive cumulative error. In the process of checking the elevation at all levels, it is necessary to realize that the four-hole control points at all levels and the external height check points are above the same level to confirm the accuracy of the elevation, so as to achieve the purpose of elevation control.
4 high-rise building safety management
Due to the long construction period of high-rise buildings, many outdoor operations and poor working conditions, a large number of people work intensively in a limited space, and the safety problem is more prominent. The following main control points of safety management are summarized here:
4. 1 foundation pit support
Before foundation pit excavation, the supporting scheme should be determined according to soil conditions, foundation pit depth and environment. Safety protection measures should be taken around the deep foundation pit (h≥2m), and no heavy objects should be piled up within the range of 1.2m from the pit edge. Drainage measures should be taken at the edge and inside of foundation pit. Strengthen the monitoring of the pit wall during the construction process, and handle it in time if any abnormality is found.
4.2 scaffolding
Scaffolding in high-rise buildings should be fully calculated, and the scaffold scheme compiled according to the engineering characteristics and construction technology should be accompanied by a calculation book. Frame and building structure system: two steps and three spans, rigid connection or flexible hard top. Scaffolding and protective railings: the construction ground should be fully paved and the dense mesh safety net should be fully enclosed. Material: steel pipe Q235(3# steel), with an outer diameter of 48mm and an inner diameter of 35mm. Welded steel pipes and fasteners are made of malleable cast iron. Unloading platform: there should be a calculation book and installation plan, and an independent support system.
4.3 template engineering
Construction scheme: It should include the design, manufacture, installation and formwork removal of formwork and support, and at the same time, it should formulate targeted measures for pumping concrete and seasonal construction. Supporting system: After full calculation, draw the construction details. The installation of formwork shall conform to the construction scheme, and measures shall be taken to keep the formwork temporarily stable during the installation. Demolition of formwork shall be carried out according to the procedures specified in the scheme, and the non-bearing part shall be demolished first. When dismantling, a cordon should be set up and supervised by a special person.
4.4 Construction electricity consumption
It is necessary to set up an electrical room with two-level protection and three-level power distribution to realize "four ones" for construction machinery; The center of the power line power supply system adopts TN-S system, that is, three-phase five-wire power cable, and its center point is directly grounded at the construction site. Grounding and neutral protection system: ensure that the resistance value is less than the specification value. Distribution box and switch box: three-level distribution and two-level protection are adopted, and two-level leakage protectors are matched.
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With the further development of social production and science and technology, a large number of advanced instruments and construction technologies are more and more widely used in the construction of modern high-rise buildings, which also puts forward higher and higher requirements for design, construction and supervision. Strength, three lines, cracks and safety are all kinds of sciences, which deserve in-depth study and discussion. The above is just my humble opinion on the control of high-rise buildings from a practical point of view, and I hope my colleagues will give more valuable opinions on the shortcomings of this paper.