Generally, the section of a column is determined according to experience, and then it is calculated in trial, or the section can be estimated according to the top force of the column.The section main beam of the beam is generally taken as about 1 / 10, and the secondary beam is taken as 1 / 15.These are preliminary estimates and can also be determined by experience.Finally, comprehensive adjustment should be made according to displacement, deflection and crack.

Relationship between main beam and secondary beam

In the frame beam structure, the main beam is placed on the frame column, and the secondary beam is placed on the main beam.At the intersection, carefully calculate the main beam, which is a main force bearing component, and should not be careless.

Key points of calculation and structural features:

1.In addition to bearing the dead weight, the main beam mainly bears the concentrated load from the secondary beam.In order to simplify the calculation, the dead weight of main beam can be converted into concentrated load calculation.

2.Similar to the secondary beam, the mid span section of the main beam is calculated as T-section, and the bearing section is calculated as a rectangular section.

3.At the main beam support, the secondary beam and the negative reinforcement of the main beam cross each other, so that the position of the negative reinforcement of the main beam moves down. When calculating the negative reinforcement of the main beam, the single row reinforcement H0 = H – (50-60) mm, and the double row reinforcement H0 = H – (70-80) mm.

4.The main beam is an important component, which is usually calculated according to the elastic theory without considering the plastic internal force redistribution.

5.In principle, the bending and cutting of the stressed reinforcement of the main beam should be determined according to the bending moment envelope diagram.

6.At the intersection of the secondary beam and the main beam, cracks occur at the top of the secondary beam under the action of negative bending moment, and the concentrated load can only be transmitted to the abdomen of the main beam through the compression zone of the secondary beam.This effect is about 0.5 ~ 0.6 times of the beam height on both sides of the concentrated load point, which can cause the main tensile failure inclined cracks.In order to prevent this kind of damage, additional transverse reinforcement should be set on both sides of the secondary beam. The concentrated load located in the lower part of the beam or within the height range of the beam section should be borne by the additional transverse reinforcement (hanging bar and stirrup).The additional transverse reinforcement should be arranged within the length of S = 2h1 + 3B.

How to determine the length of non through longitudinal reinforcement on the upper part of slab support

Support reinforcement generally refers to all reinforcement at the support, which is subdivided into bearing reinforcement (bending reinforcement), bearing lower reinforcement (longitudinal bottom reinforcement), support stirrup (reinforcement at support end).The bearing bar refers to the negative reinforcement (plate shoulder pole) of the plate at the support, and the upper reinforcement (beam shoulder pole) of the through beam at the support, and the shape is just like the shoulder pole.Non full length reinforcement refers to negative reinforcement or distributed reinforcement of slab, which is different from “full length setting” of stressed reinforcement.There is no other relationship between the three except that they are all steel bars.My understanding: they are all located at the support, but different structures, functions and shapes mean different ranges.03101, the longitudinal structure of the beam can be understood. 

What are the general reinforcement, bottom reinforcement, upper reinforcement and lower reinforcement

Full length reinforcement refers to the reinforcement that runs through the whole length of a member (such as a beam), which is neither bent nor interrupted. When the reinforcement is too long, it can be lapped or welded, but the diameter does not change.The through reinforcement can be either load-bearing reinforcement or frame reinforcement.

In addition, the reinforcement can be connected in the same length according to the length of the steel bar.The bottom plate reinforcement is usually the reinforcement at the bottom of the slab or foundation beam or foundation cap of the independent foundation.The upper reinforcement and the lower reinforcement are the upper or lower reinforcement of building components.The erection reinforcement is mainly the structural reinforcement with fixed spacing and load-bearing reinforcement position.The distributed reinforcement is used in roof slab and floor slab. It is vertically arranged with the stress bar of the slab to transmit the bearing weight evenly to the stress bar, fix the position of the stress bar, and resist the temperature deformation caused by thermal expansion and cold contraction. reinforcement is to set additional hanging bar at the concentrated force to prevent the beam from cracking, which looks like a treasure, so it is called.

When the lower raft reinforcement of beam slab raft foundation is in the same direction as the longitudinal reinforcement at the bottom of foundation beam and is directly under the foundation beam

The beam slab raft foundation is usually two-way equal sorghum under the column, especially for high-rise buildings, when the spacing between the two directions is similar, it is difficult to distinguish the primary and secondary; secondly, it is difficult to distinguish the stress direction of the foundation beam, so which direction should be lifted?In addition, there are a lot of steel bars here, and if the hanging bars are set (also two-way), the joints are full of steel bars, so it is difficult to ensure the compactness of concrete during construction.Therefore, it is recommended to place densified stirrups in this place (both beams are placed). Moreover, the stirrups of foundation beam are generally not small. 8 ~ 12 stirrups should be enough. The spacing of stirrups is @ 50, which is very important. It is difficult to construct small concrete.

Generally speaking, the erection reinforcement is used to erect stirrups in the beam. It almost appears in the beam with more than three stirrups, that is, the reinforcement on both sides has passed, and the middle reinforcement has only additional reinforcement (i.e. the pick-up reinforcement). If there is no erecting reinforcement, the stirrup in the middle cannot be bound, so the erection reinforcement appears

Through bar

1The through reinforcement is a kind of long reinforcement which has been passed through many spans. The intermediate joint needs to be bound or mechanically connected, and it can also be welded when the quality is guaranteed 

2The through reinforcement is the longitudinal reinforcement, which is the most important stress bar of the beam 

3The bearing of beam needs additional reinforcement and negative reinforcement, which often extend into one third of adjacent span and cut off, not through reinforcement 

4Non through bars should be marked in situ. Most of the time, they are stress bars 

5The stirrup of beam is multi limb. When the upper and lower reinforcement can not meet the requirement of the number of legs, the erection reinforcement shall be added. The force is not considered in the calculation of erection reinforcement, only to meet the requirements of stirrup limb number and ensure the integrity of beam, there is no need to mark on the drawing

6The side of the beam sometimes needs to add structural reinforcement, torsional reinforcement, etc 

The bottom elevation of independent column foundation is -6.00 m, and the elevation of ground beam top is -1.00 M. the ground is located at + – 0.00, and the upper part is frame structure. There is only one floor and the floor height is 7.5 M. when is the backfill?When are the bricks built (both underground and overground)?

Generally, 72 hours after the foundation is completed and the column has been poured to the ground, the foundation beam or the position close to the outdoor ground shall be backfilled, and then the foundation beam and upper structure shall be poured, and the brickwork shall be done after the completion of the frame part,

Reinforcement anchorage

1For the bending anchor of the beam tensile reinforcement at the end support, the straight section of the bending anchor is no less than 0.4lae, the hook section is 15d, and it should enter the “vertical anchorage belt” of the side column, and the reinforcement hook should not be in parallel contact with the longitudinal reinforcement of the column (the width of the “vertical anchorage belt” of the side column is: the width of the “vertical anchorage belt” of the side column is from the column center line beyond 5D to the inner side of the longitudinal bar of the column);

2When the concrete cover is used in the horizontal section, the hook section should be “tied into” the reinforced concrete inside the end corner bar;

3When the anti-seismic frame beam is directly anchored to the middle column support, the longitudinal reinforcement should cross the central line + 5D and ≥ Lae;

4The bending hook of longitudinal reinforcement in beam is 15d, the hook of longitudinal reinforcement with eccentric tension of column and the hook of reinforcement structure is 12D;

5The first vertical reinforcement of the wall body and the first steel bar of the slab are parallel to the nearest component, and the distribution distance between the vertical reinforcement of the wall and the slab is 1 / 2;

6When the reinforcement of two members overlaps, the principle of not repeatedly setting and taking the larger one is adopted;

7The principle that the anchorage of reinforcement in the joint should not be in parallel contact.

85 Lae 

9The longitudinal reinforcement of wall column is 1.6 Lae 

10The reinforcement anchorage of the upper column is 1.2lae than that of the lower column 

11The reinforcement anchorage of the lower column is 1.2lae than that of the upper column 

12When the diameter of the upper column is larger than that of the lower column, the connection position of the lower column should be moved to the upper end of the column, and the connection position of the upper column should be moved downward. 

13The reinforcement outside the top corner column is all extended into the beam and slab, and the length is 1.5lae above the beam bottom.12D (the bending length of the upper part of the roof beam must be 1.7lae to avoid the reinforcement crowding at the top of the joint) and 1.5lae + 20d (when the reinforcement ratio outside the column > 1.2%)

14When the length of the straight anchor is greater than the anchorage length, the straight anchor can be adopted. 

15Lae (from the bottom of slab) is used to anchor the top layer of concealed column and wall. 

16The longitudinal reinforcement of the frame column extends to the top of the upper shear wall floor, which can be used generally, and the bending anchor part extends into the beam or slab Lae 

17The length of the wall horizontal reinforcement extending into the end column: Lae when the straight anchor is satisfied, and 15d bending at the opposite side of the end column when the straight anchor cannot be satisfied, and the length of the straight section shall be > = 0.4lae

18The horizontal reinforcement of shear wall shall extend to the wall end and bend to the inner horizontal plane.

19The horizontal reinforcement outside the corner shear wall shall pass through continuously.

20When the steel bar end support of the floor frame beam adopts the straight anchor, it is > = Lae and > = 0.5 bearing width + 5D.

21When bending anchor is adopted for the end support of frame beam of floor, it is extended to the inner side of column longitudinal reinforcement + 15d bending.The length of straight section must be > = 0.4lae, which is the requirement of design. If this condition cannot be met, it must be replaced by smaller steel bars.

22The middle support of frame beam extends into the support > = Lae and > = 0.5 bearing width + 5D.

23The reinforcement of low span beam of high and low span beam of floor extending into high span beam is Lae, and that of low span beam of roof high and low span beam extending into high span beam is 1.6 Lae.

24The bending length of the upper reinforcement of the roof frame beam at the end support is: 1) extending to the bottom of the beam; 2) 1.7 Lae; 3) 1.7lae + 20d (longitudinal reinforcement of the upper part of the beam > 1.2%).

25The length of straight anchor is 15d when it is smooth steel bar. The lower reinforcement of arc-shaped secondary beam extending into the support is Lae.

26When the end of coupling beam is small wall limb, the value of upper and lower reinforcement of pure cantilever beam, well beam and secondary beam is the same as that of frame beam.

27When the coupling beam meets the requirements of straight anchorage, the length of the connecting beam extending into the wall is Lae and > = 600. The diagonal cross concealed bracing and diagonal cross structural reinforcement anchoring into the wall are Lae.

28The anchorage length and lap length of side structural bar are 15d. When the side of beam is anti torsion waist bar, the anchorage length and mode are the same as that of the lower part of frame beam.

29The lap length of beam erection reinforcement is 150.

30The bending length of reinforcement is 12D when the foundation beam is extended, 1 / 2 of the beam height when there is no extension, and the bending length of the extra part of the reinforcement is 15d.

31The low span reinforcement of high-low foundation beam extends into the high-span Lae.

32The length of the negative moment reinforcement at the bottom of the foundation beam from the column center line to the span is span / 3 and > = 1.2la + beam height + 0.5 column width.

33When the secondary beam of the foundation has no extension, the upper reinforcement extending into the support (main beam of Foundation) is > = 12D and > = 1 / 2 of the support width.The reinforcement of the lower part of the secondary beam of the foundation is greater than or equal to LA, and the upper and lower reinforcement is bent for 12D when it is overhanging.

34When the upper reinforcement of the slab extends into the support, it is La, and the bottom reinforcement extends into the support > = 5D and reaches the center line of the support.

35The upper reinforcement and middle reinforcement of the bottom plate of beam slab raft foundation are > = 12D and reach the beam center line, and the lower reinforcement extends to the inner side of beam stirrup + bending 15d.

36The length of U-shaped edge banding reinforcement: raft thickness – 2 * protective layer + 2 * 12D.The bending length of longitudinal reinforcement of staggered edge sealing: 1 / 2 plate thickness – protective layer + 75.

37The number of inclined longitudinal reinforcement at the lower part of beam haunch is – 1 and no less than 2.Lae is anchored into the beam.

Stirrup area densification

The reinforcement zone of stirrup is for seismic structure.According to the different seismic grade, the regulations of stirrup densification zone are also different.Generally speaking, the beam ends of reinforced concrete frame and the two ends of columns in each floor should be densified.The length of the densified zone at the end of the beam is generally 1.5 times of the beam height.The length of column densification area is generally 1 / 6 of the height of each layer of column.But the root of the bottom (first floor) column should be 1 / 3 high.