Several structural structural problems should be noted in the reinforcement installation
Source: | Author:lichengcn | Publish time: 2017-08-09 | 23 Views | Share:
      Several structural structural problems should be noted in the reinforcement installation
      Introduction: rebar engineering is a very important project in housing construction, its construction is correct and the quality is directly affected the security of the structure.Currently, the main construction personnel according to the concrete structure construction drawing plane whole representation method for mapping rules and constructional detail "(03 g101-1, under the flat law) for the installation of the steel, if the site construction personnel, supervision of construction acceptance specifications and design specifications are not familiar with, total structure design specification is not clear;The designers did not make the technical disclosure of the specific features of the project;There will be some deviation in the installation of reinforcement.The following is an analysis of several problems that I found in engineering practice that are obvious and easy to ignore.
      Key words: reinforcement installation structure construction standard leveling method
1 column longitudinal bar
      In the pingfa, the frame beam, the frame beam and the frame column are detailed with the detailed structure of the reinforcement structure. The following aspects are to be noted in the following aspects:
      (1) the top node is easy to appear problem, should be the right choice of the connection structure detail drawing, one is a column longitudinal reinforcement into beams and the other is a beam longitudinal reinforcement stretch into the column, the former one way the upper column longitudinal reinforcement into beam and beam longitudinal reinforcement lap length acuity 1.5 LaE, and to ensure that at least 65% AS1 (AS1?The column longitudinal reinforcement of the lateral longitudinal area of the column can be extended into the beam, and the column longitudinal bars other than the beam width can be extended into the current casting.When the column of the lateral ratio of longitudinal reinforcement and depth of > 1.2%, also be two truncation, two breakpoints are 20 d apart, when using a way after vertical beam longitudinal reinforcement stretch into the column length acuity 1.7 LaE, when the upper beam ratio of longitudinal reinforcement and depth of > 1.2%, also should be truncated twice, breakpoint 20 d apart, adopt what kind of way, depending on this column construction joint position, usually the bottom of the beam or column construction joint in beam under 100 mm, with the first way, when the second option is used, must be left column construction joints on 1.7 or 1.7 LaE LaE + 20 d below.Top-level Liang Zhubian node plane such as a frame, frame column 400 x 400, bilateral symmetry with two Φ 25 + 3 Φ 22 column (the total area of 2122 was the lateral longitudinal reinforcement), 250 x 600, frame beam column anchor nodes using longitudinal reinforcement into beam, hidden inspection found that the Angle steel 2 Φ 25, not into 1 liang (250 by the beam width less than the column section 400), only 3 Φ 22 into beam 1 and its area percentage for only 3 x 380/2122 = 53.7% < 65%, does not meet the requirements, the Angle bar should be 2 Φ 25 into site casting, and due to the column of the lateral ratio of longitudinal reinforcement and depth of rho = 2 x 105 x 491 + 3 x 380/1.6 = 1.33% > 1.2%, should be dealt with according to the quadratic truncation.
      (2) the bottom frame - the upper part of the wall beam of the transfer layer in the seismic wall structure should be installed by frame support beam, and cannot be handled according to the general frame beam.The code of design for earthquake resistance (gb50011-2001) (hereinafter referred to as the "anti-regulation") 7.5.4 article 4: "...The anchorage length of the vertical steel bar at the upper part of the pedestal should meet the relevant requirements of the reinforced concrete frame beam.This one is mandatory and must be strictly enforced.In this case, the construction joints of the column must remain below the LaE of the outside longitudinal rib.Commerce-residence building project, a bottom box at the bottom of the layer 2 frame beam (supporting wall beam) reinforced installation error is seen, due to the construction unit to the bottom of the left column construction joint in beam, resulting in the effluent of longitudinal reinforcement anchorage length did not meet the requirements of LaE, finally had to put the column under the construction joints of concrete abort a welding and extended outside longitudinal reinforcement to solve.
2 reinforcement area
      Scope of frame beam, box beam stirrup encryption can be based on the constructional detail flat law according to different seismic grade is chosen, there is no much problem, but the frame column stirrup encryption range often there is a big problem, must pay attention to the following aspects:
      (1) the bottom column, the new rules, a: the bottom column root encryption area Hn / 3 or higher, Hn for column height, column root is refers to the top of the basement, the basement, should be at the top of the base (plinth top), the actual construction column root encryption area often didn't meet this requirement.A detailed description of the above requirements is described in 40 pages.
      (2) the frame pillar, Angle, frame shear wall structure in all columns stirrups should be along the whole high encryption, but not for all Angle along the whole high encryption stirrup, only when seismic grade for the first and second level should be encrypted, total structure design notes often only show aseismic levels, construction personnel generally do not understand design specifications have corresponding requirements.Between the main building and the podium in high-rise building is equipped with expansion joint, as a result of the main building and the podium seismic grade is determined respectively, the main part of the high Angle may need along the whole encryption stirrup, podium part of Angle may not need.
      (3) special parts of the column, usually occur in the staircase position and filler wall parts, due to the landing on the frame column, beam supporting often makes two adjacent frame column into a short column (Hn/h < 4), filler wall setting can also make the adjacent column to form short column, these parts of the column should be along the whole high encryption stirrup.
      In frame - shear wall structure, a small wall limbs (Lw 3 or less bw, bw for wall thickness, Lw a wall limb length), should be along the whole high encryption stirrup, strengthen at the bottom of the parts of the terminals of the aseismic walls, close to the hole wall at the end of column should be along the whole high encryption stirrup..
3 waist muscle
      The waist band actually consists of three kinds of conditions, the lateral structure of the beam, the anti-torsion bar and the waist of the frame support beam.In the construction drawing, the structural reinforcement symbol is G and the anti-torsion bar symbol is N. The two functions are not exactly the same, and the structural measures are different and should be noticed.
      The structural reinforcement is mainly to prevent the lateral fracture of the beam.Under "concrete structure design code" (hereinafter referred to as "mixed rules") (GB50010-2002) the provisions of article 10.2.16 stricter than the original specification requirements and reinforced dosage increased considerably, but must pay attention to only when hw 450 mm or more, just need to set up, each side waist muscle area of 0.1% or greater BHW.The spacing is 200 mm or less, hw emphasizes the web height, not beam section height h, strictly speaking, in the act of flat hw label is only a kind of approximate processing, does not conform to that stipulated in the specification, the mixing rules, hw = h0 of rectangular section (h0 for effective height), the       T section hw = ho - T for flange thickness (T).In addition, the anchorage length of the structural reinforcement into the column is 15d.
      The anti-torsion bars are determined by the torsion calculation, which is designed to resist the oblique cracks generated by torque, and the anchorage length of the reinforced concrete column shall be LaE (La).
      Because of box beam is eccentric tension, the waist of longitudinal reinforcement can have the effect of bear tension, diameter of not less than 16 Φ structural requirements, distance is not more than 200 mm, into column of the anchorage length of LaE (La).
      The cantilever beams are stiffened
      Problems found during the construction are: the upper beam longitudinal reinforcement, first cut off and the conditions of longitudinal reinforcement under end bending judgment is wrong, the design of cantilever beam, as long as meet the requirements of negative bending moment resistance, in addition to the two Angle of jin tong long arrangement, cantilever construction drawing in general will be the first row of longitudinal reinforcement is truncated at 0.75 l, but the mixing rules 10.2.4 stipulates, "in the reinforced concrete cantilever beam,...The rest of the steel should not be cut off at the top of the beam...The upper part of this area should be understood as the first row, because the cantilever beam has a negative bending moment and the tilt Angle of the critical oblique fracture is obviously small, which is not allowed to be truncated.Since the construction personnel are used to the past practice, when the upper part of the beam is only one row of longitudinal bars, the intermediate longitudinal bars of the first row will be truncated at 0.75 l, which must be corrected in the future.Should not be truncation of longitudinal reinforcement is to be bent in the end, depending on the relationship between l and hb, if l > 4 hb, bent in the end, if l < 4 hb, don't have to be bent, but at this time must be long set, such as the upper beam longitudinal reinforcement has two row, the second row of longitudinal reinforcement can be truncated at 0.75 l (see the flat act detail on page 66].
5 rebar joint
      Frame beam and column longitudinal reinforcement connection methods in "technical specification for concrete structures of tall building" (JGJ3-2002) article 6.5.3 fourth and fifth, six have a regulation, the link quality control in the concrete structure engineering construction quality acceptance specification "(GB50204-2002) in article 5.4 also have specific requirements, at present, the beam and column banding lap is used in the main reinforcement method has very few, welding, mechanical connections with most, concealment acceptance, it found that the main problems are:
      (1) the joint position is incorrect.The joint position should be located in the force less.Construction personnel should master a certain knowledge of mechanics, should know is bending beam span larger, near the negative bending moment, shear force is bigger, in a horizontal force under the action of bending moment is larger, at the end of the joint should try to avoid these positions, prior to good steel blanking length, upper beam longitudinal reinforcement joints as far as possible near the midspan, the lower longitudinal reinforcement (for welding) as far as possible away from across (Suggestions in beam stirrup encryption outside and away from the pedestal ln / 3).As far as possible away from the column end, all welding joints should avoid the beam and column hoop, which can't be avoided.
      (2) the number of joints does not meet the standard requirements.This is mainly to understand the concept of "the same connection section", it refers to the 35 d (d - large longitudinal reinforcement diameter) and not less than 500 mm in length range, every joint point located within the length of the joints are considered to be the same connection section of the joint, and longitudinal reinforcement welding joint area percentage should be less than or equal to 50%.Of mechanical connection joint, also should change the original approach, have been revised "regulations of technology of reinforced mechanical connection of general, it can be divided into three levels, the unlimited class I joint area percentage, class II joint area percentage is not more than 50%, level III sub area percentage is not greater than 25%.
      Through the analysis of the above problems, it is indicated that the rebar installation must be carried out in combination with drawing, plain, design specification and construction acceptance specification.Structure design work on the one hand, the designers should strengthen the sense of responsibility, always be specific, clear, targeted, important parts carefully so as not to rely solely on the flat law, on the other hand, construction, supervision personnel in addition to master the construction acceptance specifications, should also learn some requirements of the relevant provisions of structure design specification, only in this way, can improve the level of their work, to adapt to the needs of social development, to ensure the correctness of the steel bar installation and improve the quality of installation.