Process control and safety measures for deformatio

Process control and safety measures for building deformation observation

with the development of China's construction industry, various complex buildings such as high-rise buildings and super high-rise buildings have emerged. During its construction and initial use, due to the continuous change of load and the influence of external forces, the building will sink. When the uneven settlement of various parts of the building, the building will have deformation such as inclination, displacement and cracks, which will affect the normal use of the building and be accompanied by potential safety hazards. Therefore, It is necessary to strengthen deformation observation during construction and operation. The seemingly ordinary diaphragm has high technical barrier process control and necessary safety measures should be taken

I. Analysis of the causes of building deformation

there are many reasons for building deformation, but the main reasons are three points:

1 Natural conditions and their changes, that is, engineering geological conditions, hydrogeological conditions, physical properties of soil, atmospheric temperature and other factors of building foundation cause building deformation. For example, due to the different geological conditions of the foundation, the uneven settlement of each part of the building is caused, resulting in inclination, displacement, cracks and other deformation; Or the plastic deformation of the foundation itself will also cause uneven settlement of the building; At the same time, the seasonal and periodic changes of temperature and groundwater level cause the regular deformation of buildings

2. The reasons related to the building itself, that is, the load size, structure type, height of the building itself and its dynamic load (such as the size of wind, the intensity of vibration) cause the deformation of the building. To weaken the influence of this deformation, it is often achieved by optimizing the design scheme

3. Some works are unreasonable during the construction or operation of the building, or additional deformation is caused by the influence of the surrounding environment. For example, deep foundation pit excavation around tall buildings will produce an additional deformation to their original buildings. Of course, these factors that cause deformation are interrelated and interact with each other. They often act together on buildings, but the effect of different factors is different in different periods of time

II. Classification of building deformation

building deformation is divided into static deformation and dynamic deformation. The former means that its deformation value is a function of time; The latter is the deformation under the action of external force. Its deformation value is the change of the dynamic system for a certain time expressed as a function of external force, and its observation results represent the instantaneous deformation of the building at a certain time. For example, when we blast a building, the deformation of the surrounding buildings at the moment of blasting is dynamic deformation, while the deformation in a certain period of time after blasting is static deformation. The two types interact and influence together

III. implementation process of building deformation observation

according to the main causes of building deformation and the classification of its types, the deformation observation process is planned in detail. The input of deformation observation planning includes:

(1) information that can be provided by deformation observation required by the owner

(2) national norms

(3) deformation observation scheme of previous similar buildings

(4) geological conditions and surrounding environment of the observation object

(5) construction schedule

1. Specific program content of deformation observation (planned output)

(1) types of building deformation observation: settlement observation, tilt observation (verticality observation), displacement observation, crack observation

(2) accuracy and methods of different deformation observation

the accuracy of deformation observation depends on the allowable deformation value of the engineering design and the purpose of observation. In the deformation observation of the building, the sample blank taken from the steel plate and flat steel with a thickness of less than or equal to 25 mm by industry and people (10) should be processed into a rectangular tensile sample to preserve the original surface layer. Because its main observation content is the settlement of the foundation and the inclination of the main body, its observation accuracy should be determined according to the allowable settlement value, allowable inclination and allowable relative bending moment of the building foundation. At the same time, the influence of settlement velocity should also be considered. It was stipulated in the 13th session of the International Federation of Surveyors (fig): "when the purpose of observation is to make its deformation, the mean square error of observation accuracy should be less than 1/10 ~ 1/20 of the allowable deformation value". In China, the accuracy requirements of deformation observation with different contents are clearly stipulated in the measurement specifications. The observation methods used for deformation observation with different grades and different accuracy are also different. In this way, the observation accuracy determines which observation method to adopt, and the selection of observation method must ensure the realization of observation accuracy and be as simple as possible

(3) frequency of deformation observation

the frequency or times of deformation observation depends on the size of deformation value, the speed of deformation and the purpose of observation. It is usually required that the number of observations can reflect the change process without missing the time of change. During the construction process, the first comprehensive observation should be carried out after the observation points to be buried are stable. In the future, the observation should be carried out once for each additional layer of high-rise buildings until they are stable. The total number of observations of other buildings shall not be less than five. The observation frequency after completion is generally once a quarter in the first year; In the second year, it will be observed once every half a year, and then once a year. In case of special circumstances, temporary emergency observation shall also be carried out. It is worth noting that during the whole deformation observation period, it should be carried out on time, according to regulations and design requirements, so as to obtain complete and reliable first-hand original data, ensure the observation accuracy, and carry out correct deformation analysis on the observation results

(4) requirements for surveyors and measuring instruments

surveyors must be proficient in professional knowledge of measurement in order to effectively implement the planned deformation observation scheme. The measuring instrument must meet the corresponding accuracy requirements, and the measurement characteristics must be confirmed before use

(5) layout of deformation observation points

the accuracy of deformation observation results and whether its data can correctly reflect the actual deformation of the building are directly related to whether the layout of deformation observation points is reasonable and comprehensive. Take the layout of settlement observation points as an example:

each project should bury at least three benchmark points outside the construction scope to ensure that it is not affected by construction. Before each settlement observation, the stability of the benchmark must be checked. Only the stable benchmark can be used as the benchmark for settlement observation. The layout of settlement observation points should follow the following principles:

① settlement observation points are usually arranged at the four corners, midpoint, corners and other parts of the building that can reflect the deformation characteristics and obvious deformation, and the distance between points is generally 10 ~ 20mm

② for buildings with post cast strips and construction joints, settlement observation points should also be set on both sides

③ for the connection between the new building and the original building, settlement observation points should be set on the bearing walls or pillars on both sides

④ for some large industrial plants, in addition to setting settlement observation points according to the above principles, settlement observation points should also be set on the bearing walls or pillars around large equipment

(6) record of observation results

record the observation values according to the preset record form, so as to ensure the continuous expansion of aluminum utilization in recent years and ensure the integrity, accuracy and reliability of the records

IV. collation and analysis of deformation observation results

in order to make deformation observation truly become the eyes and ears of engineering construction and operation management, ensure safe construction and give full play to the role of engineering benefits, in addition to obtaining first-hand data of on-site observation, observation data must also be collated and analyzed, and deformation analysis report must be prepared

on the one hand, it is the collation of observation data, the drawing of various data tables and deformation curves, and the preparation of instructions to make them easy to use achievements. The specific contents are:

1 Check the original records and check whether the calculation of each deformation observation value is wrong

2. Compile the observation value table for various deformation values point by point according to time

3. Calculate the absolute settlement value, such as the well-known iPhone 5/5s, average settlement value, average settlement speed, inclination, vertical displacement, horizontal displacement, etc

4. Draw the deformation process curve of observation points and the deformation distribution map of buildings

on the other hand, the deformation distribution map is used to analyze the observation results in combination with various factors in the observation process. Summarize the building deformation process, deformation law, deformation amplitude, deformation reason, and find out the deformation value and the internal causes and laws of deformation

the collation and analysis of deformation observation results can be realized by using computer technology and the engineering building deformation observation software developed by Wuhan University of Surveying and Mapping Science and technology

Figure 1 flow chart of building deformation observation

v. feedback adjustment and ensuring safety

using the analysis results of observation results, take corresponding disposal measures to ensure the safety of construction and building operation, mainly considering the following aspects:

1 Whether deformation observation is carried out in strict accordance with the planned observation scheme

2. Review the correctness of the planned scheme

3. Put forward guiding suggestions for construction production and operation management

in order to ensure construction safety and strengthen labor management, the construction unit, supervision unit and operation unit must pay enough attention to the deformation observation of buildings, determine the appropriate accuracy, and adopt the correct methods to ensure the reliability of observation results. Once the deformation observation value of the building is found to exceed the maximum deformation allowed by its design, the observation results shall be reported in writing to the survey, design and quality inspection units in time, so as to jointly study and formulate plans and take practical measures to prevent accidents. During this period, the construction should be suspended or the monitored buildings should be temporarily closed or stopped from using. At the same time, the number of deformation observation should be increased to closely observe its development and changes