the building structure pays attention to reliability in construction. The reliability of building structure is given on the premise that the construction quality of building structure meets the requirements. In the calculation of reliability, the uncertainty of various component materials, cross-section geometric dimensions and calculation mode is given. However, the uncertainty of component materials and cross-section geometry size is influenced by construction factors. Of course, the uncertainty of component materials is also related to the quality control of manufacturers, such as the performance of reinforced concrete and other materials. But quite a few material properties are also related to the construction quality, such as concrete strength, mortar strength, compressive strength of masonry, welding strength of steel structure members and so on. These are common problems in the structural construction of buildings.
1. The influence of the construction quality level of building structures on the safety performance of building structures
In the Unified Standard for Acceptance of Construction Quality of Building Projects and its corresponding specifications for acceptance of construction quality of professional projects, there are requirements for quality control of building materials, and acceptance of construction quality of building structural members and connectors from inspection lots, sub-projects, divisional (sub-divisional) projects and unit projects, as well as handling of unqualified ones. The construction quality of these entities has attracted the attention of construction enterprises, supervisors and other parties, but the influence of construction quality level on the safety performance of building structures has not been paid enough attention. The so-called construction quality level of building engineering should be reflected in the uniformity of construction quality, that is, the deviation of section size of components and the deviation of spacing between steel bars and stirrups are within the allowable range; The strength and discreteness of component concrete meet the requirements of relevant standards; Masonry mortar is full, mortar strength and its discreteness meet the requirements.
1. the influence of the construction quality level of the section size of structural members on the safety performance of building structures.
in the construction of reinforced concrete structure, the necking phenomenon of beam-column joints will occur due to the influence of formwork support operation. Because the shear bearing capacity of the joint is composed of concrete shear, stirrup and axial pressure in the joint area, the reduction of the section of the joint area will directly affect the shear bearing capacity of the joint.
2. The influence of reinforcement arrangement uniformity of structural members on structural safety performance.
the uniform and symmetrical spacing of the main bars of structural members is the basic condition for making the reinforced bars in the section of the members bear uniform and reasonable force, and it is also the basis for the assumption of flat section. If the main reinforcement configuration is biased to one side, the reinforcement on the side with less reinforcement will yield first, which will affect the actual bearing capacity of the component. Stirrups not only restrain concrete, but also support the main reinforcement. Uneven spacing is not conducive to the restraint of concrete, and too large spacing will weaken its support for the main reinforcement. Under the strong earthquake, the concrete spalling stirrups are exposed, and when the stirrup spacing is too large, the main reinforcement will buckle.
3. Influence of material strength and construction quality level of structural members on structural safety performance.
Whether the concrete strength construction quality of reinforced concrete structural members meets the design requirements is judged by the concrete test blocks cured under certain standard conditions. Masonry mortar in masonry wall is based on mortar test blocks with certain standard maintenance. The influence of component material strength on structural safety performance is very obvious. Because there is a certain difference between the strength of standard curing test blocks and the strength of structural components, the internal defects of concrete components and the fullness of mortar during construction also have a great influence on the bearing capacity of structural components.
4. the influence of the appearance and internal quality of the building structure on the safety and durability of the structure.
the external appearance and internal quality of the structure have obvious influence on the safety and durability of the structure. Exposed rebar in wet environment will cause rebar corrosion, and internal non-compactness will directly affect the strength of concrete and the bonding and binding force of concrete to rebar.
5. Influence of axis deviation of building components on structural safety performance.
in the construction process, the axis deviation of building components will be caused by loose setting-out, which will affect the stress of structural components. In the project we contacted, the tie rod of the grid structure was changed into a compression rod due to the installation error, and the axis of the wall was moved 2% outward, so that the wall moved 2% outward was placed directly on the cast-in-place slab. Of course, some examples have exceeded the requirements of the construction quality acceptance specification, and they should be treated before they can pass the acceptance. For the axis deviation that meets the quality requirements of the acceptance specification, it will also bring additional bending moment or torque caused by the axis deviation.
second, the common problems in brick-concrete structure
there are two main phenomena in the earthquake damage of multi-storey brick houses. One is the shear failure of masonry, that is, the wall is damaged by oblique cracks under the action of horizontal seismic force, and the other is the tilting failure; This kind of damage is caused by poor connection of the wall, and the wall is subjected to the earthquake force perpendicular to the wall surface, and it collapses. In the seismic design, the mortar label is determined by calculation, and reinforced alkali ring beams and structural columns are set according to the requirements of the code to ensure that the masonry has sufficient shear strength and prevent shear-type damage. At the junction of vertical and horizontal walls, Rachel reinforcement shall be set, and it is required to bite and rub masonry or leave oblique rubbing during construction to prevent tilting damage of masonry. The following are some main technical links in the construction of brick-concrete structure.
1. Masonry mortar shall ensure the mortar label required by the design. The code for construction and acceptance of masonry engineering not only has specific requirements for the composition materials of masonry mortar, but also improves the mortar label by 15% according to the design requirements for trial matching. The ingredients should be accurately measured and stirred evenly, and the consistency and water retention of mortar should also conform to the regulations. However, in many projects, some construction units are too troublesome to copy the mortar mixture ratio in some books regardless of the sand used internationally, mixing mortar, resulting in insufficient strength or high label, wasting cement.
2. The brick pouring experiment proves that the shear strength of clay brick masonry increases with the increase of brick moisture content; Using thousands of bricks, the shear radian of masonry is particularly reduced. Therefore, dry bricks should be resolutely banned.
3. Leave a rub at the temporary break and its form. Brick masonry of multi-storey brick houses should be built at the corner and the internal and external transition (T-shaped wall) and cross-shaped wall at the same time for integrity and seismic requirements, but in fact, considering the convenience of construction and the need of horizontal transportation, it is often necessary to temporarily break. To this end, the code has made corresponding provisions, and the temporary breaks that cannot be laid at the same time and must be retained should be laid into oblique rubs (step rubs). If it is really difficult to leave oblique rubs at the temporary breaks, straight rubs can be left except at the corners, but they must be made into male rubs (male rubs) and Rachel bars should be set. Some construction units often leave straight rubs at will regardless of the situation and position, and keep negative rubs) or do not add or add less Gallas, and mortar is not filled, which greatly weakens the interconnection of walls and the strength of masonry, so we should make up our minds to put an end to this form of rubbing.
4. The setting of reinforced alkali ring beam plays a great role in strengthening the overall stiffness of the floor, strengthening the connection between internal and external walls, strengthening the integrity of the structure and improving its shear strength. The ring beam construction should not only ensure the section size, reinforcement and alkali strength required by the design, but also pay attention to the connection and structure of node reinforcement during the construction. Especially for the corners of brick walls, the steel bars of ring beam joints should not be placed cross-wise. The outer ring steel bars should overlap the inner corner of the wall by 1m, and the inner ring steel bars should not overlap each other (the anchorage length of steel bars), but also add splayed steel bars. Nodes of internal and external transition (T-shaped) walls shall ensure the anchorage length of reinforcement) 3Sd(d is the main diameter of ring beam reinforcement). In addition, the steel bars along the ring beam should be overlapped, and they should be staggered from each other, instead of being connected on the same section.
III. Common problems in cast-in-place reinforced structure
Cast-in-place reinforced structure is easily damaged by earthquake. The earthquake damage of reinforced silicon frame structure is mainly due to insufficient silicon strength or insufficient attention to connection structure, and the ductility is reduced, resulting in cracks, silicon peeling and dislocation at the beam end of the shoe-made frame column; Or the silicon in the core area of frame joints is brittle and cracked, and the longitudinal bars are bent and bulged, or broken along the inclined section. The key point is that the quality of silicon directly affects the seismic performance and safety of the structure. Especially the ratio and strength of concrete.
the quality of steel bars and piles is the life of the whole structural system, and the strength of silicon is the key to the quality of silicon. The guarantee of strength depends not only on the quality of materials (cement variety and stability, aggregate strength, silt content and water quality, etc.), but also on scientific proportion and measurement and strict control of water-cement ratio. According to the selected sand and gravel aggregate, through calculation and trial matching, the required alkali grade ratio is obtained. If you don't weigh according to the proportion in the construction, you can mix the materials according to the volume at will, and the aggregate proportion is inaccurate, which will lead to insufficient concrete strength or high strength and waste cement. Practice shows that the alkali strength of sand and gravel aggregate will fluctuate by one level when the difference is only a few shovel. Therefore, aggregate must be weighed.
for more information about the engineering/service/procurement bidding, and to improve the winning rate, you can click on the bottom of official website Customer Service for free consultation:/#/? source=bdzd