Abstract Civilian brick-concrete structure buildings generally have cracks, which have a certain impact on people's lives. This article makes a detailed analysis based on the characteristics of the masonry strength of the brick-concrete structure house, the structure is heavy, the bonding force between the mortar and the masonry is poor, the tensile, bending and shear strength is low, and the masonry is easy to crack. The causes and patterns of cracking in brick-concrete structure houses were clarified, and specific and practical solutions to prevent cracking in brick-concrete structure houses under different conditions were proposed.
Keywords brick-concrete structure; house cracking; analysis reasons; solutions
At present, civil buildings in our country are generally built with brick-concrete structures, because they It has certain thermal insulation and sound insulation effects, and the construction cost is relatively low. But it also has certain shortcomings. For example, cracks are prone to occur, which has a certain impact on people's lives. Slight impacts include affecting the appearance of the house, and it is prone to leakage and ventilation; serious impacts include major accidents such as house collapse, and even It will threaten people's lives. Therefore, actively analyzing its causes and proposing corresponding solutions is a major issue we face. Through the same analysis, we can understand that the main causes of cracking in brick-concrete structures are the following two points:
1. Temperature changes
First of all, we need to analyze the reasons for wall cracking due to temperature changes. Generally, materials will expand and contract due to temperature changes, so the materials that make up the various parts of the house Changes will occur to varying degrees, so there will be mutual repulsion and extrusion. Because the linear expansion coefficients of the roof concrete and the wall are inconsistent, the roof deforms greatly, causing overall deformation; when the structural processing between the roof and the wall Improper construction will cause the wall to be stretched. When the shear force and tensile stress are greater than the shear and tensile strength of the masonry, the wall will be pulled apart. This type of crack is generally found on the inner and outer longitudinal walls at both ends of the top floor of the building. Its shape is "eight" or "X" shaped, and it is symmetrical, but sometimes it is only on one end, and in minor cases it is only on both ends 1-2 If it appears in one bay, severe cases will develop to within 1/3 of the longitudinal length of both ends of the house, and develop from the top floor to the lower floors. This type of seam is more likely to occur in houses with rigid roofs, flat roofs, and no deformation seams or insulation layers. The severity of temperature difference cracks is related to the roof insulation condition, indoor and outdoor temperature difference and construction quality. In addition, when the house is taller, the deformation will be greater when the temperature changes, and the wall cracking will be more serious.
Secondly, through the analysis of the above reasons, we need to carry out corresponding preventive work on wall cracking caused by temperature changes, mainly introducing the following points:
1. Appropriate Adjust temperature expansion joint spacing. The design specification "Design Code for Masonry Structures" GB50003-2001 stipulates that roofs with insulation layers or insulation layers should have an expansion joint every 50 meters, and roofs without insulation layers or insulation layers should have one expansion joint every 40 meters. Expansion joints, this regulation is considered from the overall structure, but it does not apply to houses and structures in areas with large temperature differences and frequent temperature changes and severe cold areas, especially for areas with severe cold in winter and scorching heat in summer. The maximum spacing of expansion joints In addition to meeting the above requirements, the spacing between expansion joints should not be greater than 30m.
2. When the roof and floor of the house are not at the same elevation, such as a split-level house, reinforced concrete structural columns should be set up at the intersection of the vertical and horizontal walls at the staggered level and double-channel ring beams should be connected to the structural columns. , to help the wall resist tensile and shear stress.
3. Set sliding bearings at the bottom of the roof panels within 1-2 bays at both ends of the building or within 1/4 of the total length to allow them to expand and contract freely.
4. Appropriately increase the reinforcement of the roof ring beams and the four-corner structural columns of the house and increase the mortar grade of the top masonry.
5. The most important point is to do a good job in thermal insulation of the house. The traditional method is to set up an overhead heat insulation board, but the effect is not ideal. The author recommends using planting roofs and water storage roofs, or making the roof into a solar collector to convert solar energy into electricity or other energy, which is both sustainable and sustainable. development strategy, and can achieve very ideal thermal insulation effect.
2. Uneven settlement of foundation
First of all, we need to analyze the causes of wall cracking due to uneven settlement of foundation, which is the cause of cracking of civil brick-concrete structures. Another important reason. It is mainly due to the uneven foundation that causes irregular deformation of the building to develop laterally. The overall cracks in the wall will produce many crack effects due to uneven stress. The main crack effects are the straight eight-character structure and the inverted eight-character structure. These two structures are mainly caused by the uneven force use, which causes inconsistent force use. Such cracks will have a negative impact on the building, thereby reducing the service life of the building and causing quality problems and gaps. When the settlement of a long building is too large, a positive "eight" seam will be formed from bottom to top at both ends of the house, and will first break through at the diagonal side of the window. On the contrary, when the settlement of both ends is too large, the inverted "eight" seams formed from bottom to top at both ends will first break through at the diagonal side of the window, and may also break through at the window sill in the middle of the bottom floor to form a vertical seam from top to bottom. When a certain section of the building begins to sink, it is necessary to continuously strengthen the load-bearing pressure of the wall structure and the construction of load-bearing walls under the window sill, improve the angle composition between the wall structure and the interior of the wall, and improve the shortcomings and progress of the wall. Solve the problem of small force and improve the balance of force.
The causes of uneven settlement of foundations can be summarized as follows:
1. Uneven settlement caused by unstable foundations, obvious differences in soil quality and other geological reasons.
2. The construction area of ??the house is too large, the plane shape is complex, and the uneven settlement is caused by unreasonable construction.
3. The height, load and structural stiffness of adjacent parts of the house are greatly different and improper foundation treatment causes uneven settlement;
4. The house is built in some areas where the soil structure is unstable. In terms of soil quality, such as silt, mixed soil, etc., under the action of gravity over a period of time, uneven ground settlement will occur.
5. The emergence of uneven foundations due to substandard building quality.
Secondly, through the analysis of the above reasons, in the design process of brick-concrete structure buildings, it is necessary to strengthen the corresponding prevention of cracks caused by uneven settlement of the foundation, mainly including the following points:
1. When a house is built on a foundation with a large difference in soil quality, or there are significant differences in the height, load, structural stiffness, foundation treatment method, etc. of adjacent parts of the house, it should be installed at the different parts. Settlement joints are divided into several units with good stiffness and small length changes, which can reduce the stress caused by uneven settlement of the foundation in the sample body and avoid wall cracks. The code stipulates that the width of settlement joints in the "Code for Design of Building Foundations" GB50007-2002 should generally be greater than 5 cm. In order to prevent the upper structures from colliding with each other after the foundation settles, the width of the house should be widened when the house is high, up to a maximum of more than 12 cm.
2. Strengthen the rigidity outside the door and window openings. Connect the reinforced concrete lintels on the door and window openings with the steel bars of the interior walls to form a continuous lintel to enhance the overall rigidity of the house.
3. During the site selection process, you should try to avoid building on some soil with unstable soil structure. If it is unavoidable, you should use a raft foundation method to reduce settlement.
4. Due to the different penetration structures of the wall structure, there are many problems of weak walls and internal cracks in the walls.
5. The disadvantages of construction of buildings in caves caused by the problem of uneven foundation stress. Because of the uneven construction of local foundations, the foundation construction and stress points are different, resulting in foundation settlement.
6. During the design process, the beam structure drawings and architectural design drawings of the building should be strengthened in accordance with the design specifications to improve the rigidity of the building.
3. Conclusion
In summary, during the construction process of civil brick-concrete structure buildings, all influencing factors should be comprehensively considered, not only the relevant climate and environmental factors. , and standardized construction must be carried out in strict accordance with relevant procedures to ensure the quality of the house, so that the occurrence of house cracks can be effectively reduced or even avoided.
References
[1] Jiang Zhengrong. Concrete crack prevention manual[M]. Beijing: China Construction Industry Press, 1997.
[2] Li Feng. Use of building materials and new architectural design. Shanxi Jianzhou. 2010.2: 20-22