Based on the problems in engineering practice, this paper first expounds the common problems in high-rise structure reinforcement engineering, and analyzes and summarizes the causes of the problems in detail, and finally puts forward the corresponding preventive measures.

Keywords:: high-rise structure quality common fault measures

Introduction to 0

Whether the installation position of steel bars in beams, slabs, columns and shear walls in high-rise structures is correct directly affects the stress situation of the structure. In addition to observing the construction regulations, it is particularly important to strengthen the joint review of design drawings, so as to solve some problems of steel binding before construction and ensure that the steel bars are not offset. Combined with engineering examples, the problems encountered in the construction process are analyzed and summarized, and the corresponding preventive measures are put forward.

1 project overview

A project, the structure type is frame-shear wall structure, and the foundation form is hand-dug cast-in-place pile, with two floors underground and 32 floors above ground, with a construction area of 18520 square meters. One of the difficulties in this project is the decomposition of steel bars, with large amount of steel bars, dense steel bars in beam-column joints and complex structure.

2 common reinforcement engineering quality problems

2. 1 column longitudinal reinforcement deviation

2. 1. 1 Phenomenon The foundation reinforcement of reinforced concrete frame column often deviates from the longitudinal reinforcement of floor column, which seriously affects the structural mechanical properties. Therefore, rectification must be carried out in time during the construction process.

2. 1.2 Cause analysis ① The formwork is not firmly fixed, and sometimes the formwork collides during construction, resulting in the dislocation of the relative position between the total reinforcement of the column and the formwork; (2) Due to the large error in stirrup manufacture, the size of the inner package does not meet the requirements, resulting in the column longitudinal reinforcement deviation, and even the entire column reinforcement skeleton distortion; (3) Do not pay attention to the role of concrete protective layer. For example, the cushion block is crushed due to low strength, uneven cushion block, small quantity, inconsistent cushion block thickness, and weak bond with longitudinal reinforcement, which affects the deviation of longitudinal reinforcement. (4) The constructors shake, trample and climb the bound steel skeleton at will, so that the binding points are relaxed and the longitudinal steel bars are offset; ⑤ When pouring concrete, the vibrating rod is easy to touch the stirrups and longitudinal bars, so that the bars are dislocated due to vibration; ⑥ The beam-column joints are densely reinforced, and the column reinforcement is often biased by the beam reinforcement; ⑦ During construction, sometimes the foundation column rebar and the bottom column rebar are bundled and installed together. As a result, the steel bar is too long, the upper part lacks stirrup constraint, the whole skeleton shakes, and the stiffness is poor, resulting in deviation.

2. 1.3 Precautions ① During design, the dimensional relationship among beams, columns and walls should be reasonably coordinated. If the column wall is 50- 100mm wider than the beam edge, that is, the big bag is small to avoid the situation of equal width from top to bottom; (2) According to the design requirements, mark the dimension line of the column wall section on each floor, and then fix the longitudinal reinforcement of the column wall protruding from the lower floor with two stirrups, or spot weld the horizontal reinforcement with column stirrups at the floor elevation of this floor and above 500mm; (3) Short steel bars should be inserted in the steel dowel of the foundation part, and reinforced step by step, and fixed by spot welding with positioning stirrups that make the steel dowel frame not deform; (4) Make stirrups correctly according to the design requirements, and bind them firmly with the longitudinal reinforcement of the column, and the binding points shall not be missed; (5) Between the side of the column wall reinforcement skeleton and the formwork, the wire embedded in the concrete pad must be firmly bound with the longitudinal reinforcement, and the thickness of all pads should be consistent, and the protective layer thickness of the longitudinal reinforcement should be the same; ⑥ Spot weld the longitudinal reinforcement of the fixed column with two stirrups at the beam-column joint, and bind the upper reinforcement at the same time.

2.2 omission of column stirrups at the core of frame joints

2.2. 1 Phenomenon Frame joints are important parts of the frame structure, but the beam-column reinforcement of the joints is cross-concentrated, which makes it difficult to bind the column stirrups in this part. Therefore, there are often omissions in binding stirrups on site.

2.2.2 Cause analysis Because the design unit generally does not design the arrangement sequence of column beam reinforcement and column stirrup binding of frame joints in detail, the phenomenon of node reinforcement congestion is quite common, which makes it difficult to bind the reinforcement at the core, so the column stirrup leakage phenomenon occurs.

2.2.3 Precautions ① Before construction, the steel binding sequence of frame joints should be reasonably determined according to the design drawings and the actual situation of the project; (2) After the bottom formwork support of the frame beam is completed, the reinforcement under the beam can be placed. If the beam is higher than the longitudinal beam, firstly, put the stirrup on the steel bar at the lower part of the beam and put it on the bottom die of the beam, and put the stirrup on the steel bar at the lower part of the longitudinal beam and put it on the bottom die of their respective beams. Then put a group of column stirrups that meet the design requirements into the column longitudinal bars at the joints. Then insert the longitudinal bars on the upper part of the cross beam and the longitudinal beam into their stirrups respectively, and finally pull the stirrups of each beam apart and tie them according to the designed spacing. If the cross-sectional height of the longitudinal beam is the same as that of the cross-beam, the insertion order of the above-mentioned transverse longitudinal beam reinforcement should be changed, that is, "longitudinal first and then transverse". (3) When the height of the beam at the beam-column joint is high or it is really difficult to bind the column hoop of the joint in some parts in actual operation, this part of the column hoop can be made into two identical L-shaped hoops with 135-degree hooks at both ends, which are inserted laterally from the column and hooked on the four-corner column rebar, or two identical open half hoops are adopted, and the joints of the hoops are welded by electric welding after insertion.

2.3 There are too many joints in the same connection section.

2.3. 1 phenomenon When binding or installing the steel skeleton, it is found that there are too many steel joints in the same connection section (for binding joints, the existing joints are regarded as non-staggered in the section from any joint center to 1.3 times the specified lap length, that is, they are located in the same connection section), and the percentage of the cross-sectional area of steel bars with joints in the total cross-sectional area exceeds the specified value in the specification.

2.3.2 Cause analysis ① The steel bar ingredients were neglected, and the reasonable collocation of the blanking length of raw materials was not carefully arranged; (2) Ignoring the stipulation that some components are not allowed to adopt binding joints; (3) Improper use of the percentage value of the cross-sectional area of the joint reinforcement to the total cross-sectional area; (4) It is not clear whether the reinforcement is located in the tension zone or the compression zone.

2.3.3 Prevention and control measures ① When batching, draw a few semicolons according to the reinforcement number of the bill of materials, indicating which semicolon is matched, and the installation method of the same group is different (the installation order of the same group number is downward). Add a text description; (2) Remember that the steel bar joints in axial tension and small eccentric tension bars should be welded, and binding is not allowed; (3) If it is unclear whether the reinforcement is in the tension zone or the compression zone, the joint position shall be handled according to the provisions of the tension zone.

2.4 beam stirrup hook collision longitudinal reinforcement.

2.4. 1 phenomenon At the bearing of the beam, the hook of the stirrup collides with the longitudinal reinforcement.

2.4.2 Cause analysis The hook of beam stirrup should be placed in the compression zone, which is reasonable from the stress point of view and the overall structure point of view. However, under special circumstances, such as in the practice beam support, the compression zone is at the lower part of the section, and if the stirrup bends below, it may be pressed open by the steel bar. In this case, it is unreasonable to put the stirrup hook in the tension zone, but in order to strengthen the firmness of the steel skeleton, it is customary to do so. In addition, there will be another contradiction in practice: in the current high-rise buildings, most projects in the form of frame or frame-shear structure need seismic design, so the stirrup hook should be 135 degrees, and the length of the straight part is longer than other types of hooks, so the stirrup hook will inevitably collide with the two rows of steel bars on the upper part of the beam.

2.4.3 Before binding reinforcement, the position of stirrup hook should be planned (placed on the upper or lower part of the beam). If there is only one layer of steel bar on the upper part of the beam, the stirrup hook will not conflict with the longitudinal steel bar. In order to avoid the stirrup joint being pressed open, the hook can be placed on the upper part of the beam (the tensile area of the component), but it should be specially fastened and spot-welded by electric welding if necessary. For two or more layers of longitudinal reinforcement, the hook should be placed at the lower part of the beam.

2.5 limb stirrup width is not allowed.

2.5. 1 Phenomenon The beam steel skeleton with combined stirrups on the limbs is bound and installed in the formwork. It is found that the width is not suitable for the requirements of the formwork, and the concrete protective layer is too large or too small, which seriously leads to the skeleton not being placed in the formwork.

2.5.2 Cause analysis ① Before binding the skeleton, the total width of stirrups is not positioned or positioned incorrectly; (2) The total width of the positioning stirrups has been taken into account, but the operation is not paid attention to, so that the two stirrups move inward or outward.

2.5.3 Precautions ① When binding the skeleton, first bind several pairs of stirrups to make the stirrup width of limbs meet the requirements of the drawings, then wear longitudinal reinforcement and bind other stirrups; (2) according to the cross-section width of the beam, determine a kind of double-limb hoop reinforcement (that is, the cross-section width minus the thickness of concrete protective layers on both sides), and when binding, place several such hoops along the length of the skeleton for positioning; (3) In the process of skeleton binding, the accuracy of the width of the four-limb hoop should be checked at any time, and the deviation should be corrected in time.

3 Conclusion

These common quality problems occurred in the construction process of this project, mainly because the construction managers were weak in quality consciousness, and did not summarize and analyze the quality problems in previous projects, and did not attract enough attention and sum up experiences and lessons in future engineering practice. I believe that the above problems can be overcome and avoided. As long as we can effectively improve quality awareness, strengthen quality management, improve the professional level of construction personnel, carefully construct and manage in place, these quality problems will naturally be eliminated.

References:

[1] Wang. Several problems that should be paid attention to in the construction of high-rise building reinforcement project. Engineering construction. 2006。

[2] Gu, Yi Libo. Problems needing attention in the construction of high-rise building reinforcement project. Heilongjiang science and technology information. 2004。

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