On the framework of the common quality problems and control measures

[Abstract] the current trend of high-rise housing construction, high-rise development, and its structure to use more frames (frame-wall structure but the design and construction quality problems caused by negligence is also not uncommon. In this paper, frame the causes of quality problems and hazards analysis, and the corresponding pre-control and approach.

[Keywords] concrete, framework, issues, control

1 Department of nodes Liangrui closely spaced steel bars
Requirements due to structural calculations, beam frame structure node through the end of the bars close, steel banding and vibrated concrete problems, prone to the following quality issues:
1.1 bar spacing is too small, does not meet the construction requirements, and even more reinforced side by side, affecting the bond between steel and concrete strength, steel can give full play to the tensile strength;
Reinforced criss-cross at 1.2 Core nodes, concrete vibrator difficult, easy to form in the cellular area and holes Core
1.3 beam negative moment reinforcement upper dense, easily formed in the upper beam is usually cracks.

Can take the following precautions:
1.4 pairs of beam cross-section of rational design, to ensure that the upper longitudinal beam reinforcement spacing not less than 30 mm and 1.5d (maximum diameter for the steel, the lower the minimum vertical spacing of not less than 25mm steel and d. When the reinforcement for the two row of the design, two rows of the upper and lower cross bars should be avoided,
1.5 In accordance with specification framework rely mainly on the coupling of shear and concrete commitment to the arrow, usually with no negative bent steel, which also reduces the node number and Liangrui parts of the steel,
1.6 In the steel banding process, the reinforced as evenly arranged, to ensure the reinforcement spacing to meet the construction requirements, especially in multi-limb coupling in the beam, we must first determine the location of reinforcement, under the correct position to determine the reinforcement stirrups geometry.

2 mishandling of the reinforced joints
As the eccentric axial tension and the steel tension member in connection with the seismic requirements and the mishandling of the reinforced joints, prone to the following questions:
Axial tension and eccentric tension member after the force will cause the joints opened, the component cracks, serious cause structural instability.

Can take the following precautions:
2.1 forms must strictly adhere to steel joints <<Concrete Construction Quality Acceptance>> (GB50204 one of the 2002 regulations,
2.2 axial tension and migraine. Has been reinforced by the tension member in the joints should be welded,
2.3 ordinary concrete of a diameter greater than 22mm steel, and greater than 25 mm in diameter Ⅱ, pan-class steel fittings are welded should be adopted,
Eccentric axial compression and compression of the compression steel column joints, when more than 32mm in diameter should be used when welding,
2.4 pairs with the seismic requirements of the reinforced joints, should give priority to the use of welding or mechanical connection, when using welding should meet the following requirements:
2.4.1 Longitudinal steel joints, should be used for a seismic rating of welded joints, the two seismic level, should adopt the welded joints,
2.4.2 to the bottom frame, shear wall strengthening the position of the vertical steel joints, the first and second seismic rating of welded joints should be used, should be adopted for the three seismic rating of welded joints.

2.5 required to control the location of steel joints, shall meet the following requirements:
2.5.1 either welding or steel banding from bending at the joints at the end, not less than 10 times the bar diameter, and should not be located the maximum bending moment at the components,
2.5.2 steel joints should not be located in Liangrui, encrypted end-column area of ​​stirrups within the
2.5.3 location of the reinforced joints in the same component to be staggered.

2.6 required to control the length of the steel joints,
2.7 required to control the spacing of stirrups,
Welded joints of the skeleton in the banding within the length of Africa:
2.7.1 When the lap steel in tension, its stirrups spaced not more than 5 d, and not more than 100mm.

2.7.2 When the lap bar pressure, its stirrups spaced not more than 10d, and not more than 200mm.

3 actual thickness is greater than the design thickness of the slab
Designers during the design process is not considered a variety of steel and embedded parts, the intersection between pipes, resulting in the actual thickness is greater than the design thickness of the slab, resulting in the following diseases:
3.1 unnecessary thick floor, resulting in material waste,
3.2 thick slab, the structure of the actual load exceeds the design load, and other aspects of the structure of the foundation caused problems,
Raise the floor elevation of 3.3, resulting in the upper part of the component size or position deviation, industrial buildings resulting in equipment installation difficulties. Links to free download http://www.hi138.com can take the following precautions:
3.3.1 Component design drawings should pay attention to the cross-section design, component design based on steel cross-sections and determine the relationship between various types of steel in the correct location to be specified in the drawings,
3.3.2 Design with the unit should pay attention to the professional handling of embedded steel pipe and the relationship between
3.3.3 should be carefully verified before pouring concrete template elevation and flatness, the floor started to set flags, so that the correct basis for concrete pouring.

4 beams, columns and panels are inconsistent in-situ concrete strength grade frame structure, prone to quality problems
Cast frame structure, due to structural design requirements, the concrete beams and plates often take a different intensity level from the importance of structural elements and force attributes of such an approach is more reasonable, but from the actual situation is often more harm than good, prone to the following questions:
4.1 With three plane a pouring of concrete strength grade, increasing the difficulty of construction, to extend the construction period, and probably because of mismanagement, often there will be low-intensity low-level board with high-strength concrete pouring, and high strength grade beam or a low-intensity node at the pouring of concrete, resulting in quality problems,
4.2 often result in a floor set on four weeks of construction joints, construction joints beam ends, which do not set the correct construction techniques, improper handling, not only increase the difficulty of construction, but also result in quality problems.

Pre-control can take the following measures:
4.3 Structural design of a uniform intensity level best to simplify the construction process and ensure the quality of construction, but with some more construction materials,
4.4 uses a strength grade of concrete columns, beams and plates using a different concrete strength, at the nodes to take special measures, such as using steel mesh segmentation method, to ensure that the node at the concrete strength grade of concrete with strength grade of the same column. During the construction process, the nodes should be specifically responsible for the concrete mixing, pouring and vibrating.

5 reinforced concrete protective layer thickness values ​​errors
Reinforced concrete protective layer is to protect the steel does not rust, and to ensure the reinforcement of the adhesive anchor performance, it should be taken seriously enough. However, due to the uncertainty requirements or design, construction workers do not pay attention, often the following issues:
5.1 beam or column, only the reinforcement of the protective layer thickness noted, while ignoring the stirrups of the protective layer, resulting in stirrups exposed or less than the thickness of the protective layer.

5.2 at the intersection of primary and secondary beam, main beam, secondary beam and plate steel deal with the relationship is not clear, resulting in negative reinforcement plates or protective layer thickness less than the effective cross-section height of the loss components, directly affecting the safety of components.

5.3 aboveground and underground parts of the columns due to different environmental conditions in which, according to regulatory requirements, should take a different protective layer thickness designers often overlook this difference, without special treatment, the construction of two things occur: a are all handled by normal environmental conditions, resulting in the underground sections of concrete cover thickness less than the second is based on underground environmental conditions Part of the deal, part of the normal environment, ground handling, as part of the underground part of the protective layer of protection than the ground layer thickness, The result after the reinforcement of the ground outside support, the underground part of the column height decreases the effective cross-section to form a security risk.

Can take the following precautions:
5.3.1 properly handle various types of steel components within the inter-relationship, then the correct position to determine the components of reinforced steel bars inside the protective layer and a high degree of effective cross-section components, and the components of the cross-sectional design, first determine the beam according to specifications within the stirrup protective layer thickness, which determine the correct stirrup position, reinforcement of the protective layer can be a + d1 (a minimum thickness of protective layer for the stirrups, d1 is the diameter steel stirrups, and greater than the minimum thickness specification, in order to determine the reinforcement the correct position, cross-site reinforcement of the correct position, according to the above approach to determine, according to various bars in the correct location to determine the relevant components of the effective cross-section height and the reinforcement calculation, in the construction of related components in the successful reinforcement of the correct position .

5.3.2 correctly distinguish between the environmental conditions in which the same components, distinguished between the different environments of concrete cover thickness of the underground part of the cross-section columns can be increased to meet the requirements of its protective layer thickness, while ensuring that the location of the upper and lower steel columns consistency, the force to meet the steel requirements.

6 exposed reinforcement and cracks Central Act
6.1 As the vertical structure of the pouring highly inappropriate, but also failed to take appropriate measures, reinforced protective layer pad assembly is not set, or set up a small number of pads, and reinforcement banding is not solid, loose, causing loss of the protective layer of concrete reinforcement, concrete After people die because vibrated operational errors, produce steel displacement prone to forming the structural elements of concrete exposed reinforcement.

6.2 As the second node when pouring concrete, Zhu stay clean mouth or not seriously clean up the second node without first pouring of laying mortar with strength grade of concrete will be poured directly, and the vibrator is not dense, concrete segregation, coarse bone concentrated material, construction joints folder with debris. prone to beam-column nodes there is no gap slag layer. Links to free download http://www.hi138.com