Design principle of steel structure
(1) Clean the embedded steel dowel, and adjust its protective layer thickness according to 1: 6 to meet the specification requirements. First, tie 2 ~ 4 vertical bars and draw a horizontal bar grading mark, then tie two horizontal bars at the lower part and chest level and draw a vertical bar grading mark. Generally, the transverse reinforcement is on the outside and the vertical reinforcement is on the inside, so the vertical reinforcement should be tied first and then the transverse reinforcement, and the spacing and position of the transverse reinforcement should meet the design requirements.
(2) The wall reinforcement is bidirectional reinforcement, and all intersections of reinforcement shall be bound point by point. Within the overlapping range of vertical steel bars, there shall be no less than three horizontal steel bars. The lap length and lap position of transverse and longitudinal steel bars meet the requirements of design drawings and construction specifications.
(3) Double-row steel bars are bound with limit supports and lacing bars to determine the spacing of steel bars and the thickness of protective layer. Is there a support or tie? 6 and? 8 steel production, spacing of about 600mm, to ensure the distance between the double row of steel.
(4) On the outside of the wall reinforcement, a cushion block shall be bound or installed to ensure the thickness of the protective layer of the reinforcement.
(5) In order to ensure the correct elevation position of doors and windows, draw elevation lines on the vertical line of the hole. Doors and windows openings shall be bound with lintel reinforcement according to the design requirements, and the length of anchorage into the wall shall meet the design and specification requirements.
(6) The seismic structural reinforcement and anchorage length of each connection point shall be bound according to the design requirements.
(7) Cooperate with other projects to install embedded pipe fittings and reserved holes, and their positions and elevations should meet the design requirements.
2, roof steel binding
(1) Clean up the sundries on the template, use Mo Dou to pop up the main reinforcement, and allocate the reinforcement spacing.
(2) According to the design requirements, put the main reinforcement first, and then put the distribution reinforcement. Generally, steel bars at the bottom of the plate are bound with straight buttons or splayed buttons. In addition to the intersection of two steel bars at the periphery, other points can be staggered (the intersection of two-way slabs must be fully bound). If the floor is a double-layer reinforced bar, a reinforced horse stool should be added between the two layers of reinforced bars to ensure the position of the upper reinforcement.
(3) After the steel bar binding at the bottom of the slab is completed, the laying of water and electricity pipelines and the embedding of various embedded parts shall be carried out in time.
(4) After the water and electricity embedded work is completed, the protective layer of reinforcement shall be bound in time. When binding, hang up the thread to ensure that both ends of the cover iron are aligned. The intersection of protective layer reinforcement and reinforcement must be completely bound.
(5) After the steel binding is completed, the installation of steel protective layer pad and iron horse stool shall be carried out in time. The thickness of the pad is equal to the thickness of the protective layer, or 15mm if there is no design requirement. The anchorage length of reinforcement should meet the design requirements.
Common wrong practices are summarized as follows:
1. The concealed beam is used as a floor beam. This is the most common mistake. The reason why the concealed beam can't be a floor beam is because its rigidity is not enough and the load can't be transmitted in its own way, that is, the floor load? Board of directors? Dark beam? The transmission mode of columns is almost impossible. This will greatly underestimate the internal force of the plate. Personally, I think that according to the principle of the shortest internal force transmission distance, only when the slab is subjected to concentrated force, the hidden beam is set along the shortest direction of the slab (the two-way slab is in two vertical directions), so that the concentrated force can be assumed by the hidden beam and meet the requirements of bending strength and cracks. At this time, the calculated span of the slab can never be regarded as supported by the hidden beam. But in many cases, it is not necessary to do this, and the reinforcement of the plate can be directly increased, unless a hidden beam is used, because stirrups are needed for shearing (punching).
2. Corresponding to the previous question, the place where the stiffness suddenly changes (increases) should be regarded as a beam. The typical problem is the dislocation between plates with different elevations. The out-of-plane stiffness of staggered platform itself is relatively large, while the out-of-plane stiffness of plate is relatively small. Whether you like it or not, the load on the slab will be transferred to the staggered platform, so it should be designed according to the beam, especially the shear reinforcement should meet the requirements. This situation is more common in underground passages and stations, and the load is relatively heavy, but most people are sloppy in handling the wrong platform, which is very worrying.
3. The frame structure forms a de facto hinge. The most common thing is that the stiffness of the beam is much greater than that of the column, which makes the constraint of the column on the beam weak and forms a de facto hinge. This reduces the number of statically indeterminate, which is not conducive to earthquake resistance and difficult to form? Strong column and weak beam? . During the Sakamoto earthquake, the column of the subway station was seriously damaged, which also reminded us that we can't ignore this problem. The roof and floor of subway station can be regarded as a raft, and the stiffness of its beam is of course greater than that of its column, but it is not appropriate to make the beam stiffness larger at the middle plate. In addition, underground engineering, such as tunnels, culverts, subway stations, etc. Sometimes, it is easy to make the top plate, bottom plate and side wall with larger stiffness form a hinged quadrilateral, which is easy to lose stability when the earth pressure on both sides is quite different, which is not conducive to earthquake resistance.
4. The reinforced concrete slab wall is located in the distributed reinforced concrete. Many people always think that the distributed steel bars are similar to the stirrups of beams, so the steel bars are reversed carelessly. The role of distributed reinforcement is to fix the position of reinforcement, transfer stress and prevent temperature shrinkage cracks. It doesn't need to be wrapped like beam-column stirrups to prevent steel bars from bulging under pressure. More importantly, the section height of the slab wall is small. In order to increase the effective height and give play to the role of steel bars, steel bars should be placed outside in general. In some special cases, such as the underground continuous wall, for the convenience of construction, the effective height of the slab can be sacrificed and reinforced bars can be built in.
5. Put the beam on the frame beam near the column. Because the position is close to the column support, the rotation of the frame beam is constrained, and when the load of the beam on it is large, it will produce great torque, which makes it difficult to strengthen the frame beam. Some designers regard the connection between the frame beam and the lap beam here as a hinge, which is very unsafe because the plastic deformation capacity of the beam is limited.
6. The plate reinforcement does not extend into the reinforcement of the upturned beam. This is not easy to appear in the ground structure, but in underground engineering, because the structural form is not intuitive enough, a slight negligence will make mistakes. The most common thing is that there is a convergent beam on the top plate at the entrance of the passage, and its bottom inclines downward along the plate to form an irregular beam. Most people will arrange the reinforcement of this beam along the horizontal direction, and the longitudinal reinforcement of the plate will be anchored into the beam from the lower side. The distribution of steel bars in underground engineering is incomplete. At this beam, the longitudinal reinforcement of the plate is actually reinforcement, which should not only be anchored by reinforcement, but also be above the reinforcement of the beam. In addition, many people think that this beam is weak, so the reinforcement is sloppy. In fact, this beam has a certain torque due to unilateral stress, so it should be considered to transfer the plate load to this beam when strengthening.
7. The subway station does not count as the opening of the medium board. Because the influence of openings is difficult to calculate, and because some people don't take the influence of openings seriously, they are ignored in the calculation. When the hole is small, it may have little influence, but sometimes the middle plate of subway station is arranged in parallel with three rows of buildings and escalators, which seriously weakens the stiffness of the floor. Although there is a reinforcing beam near the entrance, the height of the beam is limited, and the thickness of the middle plate is usually 400 ~ 500, which is not enough to make up for the loss of stiffness. As for adding concealed beams to strengthen the entrance, it can't make up for the deficiency that the calculation model is inconsistent with the reality.