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Reinforced concrete
Structure refers to the use of equipped
rebar
enhanced
concrete
Made of structure. The main load-bearing elements are constructed of reinforced concrete. include
Shell structure
,
Large formwork
Cast-in-place structure
And use
Sliding form
,
Lift plate
Such as the construction of reinforced concrete structure of the building. A structure made of steel and concrete. Rebar withstands tension, concrete withstands stress. It has strong, durable, good fire performance and comparison
Steel structure
Advantages of saving steel and low cost.
- Chinese name
- Reinforced concrete structure
- Foreign name
- reinforced concrete structure; reinforced framing; RC structure;
- Group into
- Steel bar, cement, coarse aggregate, water, etc
- Advantage point
- Strong, durable, fireproof, seismic, corrosion resistant
- lacuna
- Self-weight, poor crack resistance
- should
- Construction project
Concrete is made of
Cementitious material
Cement, sand, stone and water, and mixed materials, admixtures, etc., are mixed in a certain proportion. After solidification, it is hard as stone, good compression ability, but poor tensile ability, easy to break due to tension. In order to solve this contradiction and give full play to the compression capacity of concrete, a certain number of steel bars are often added in the concrete tension area or the corresponding part, so that the two materials bond into a whole and jointly withstand external forces. This reinforced concrete is called reinforced concrete. The bonding and anchoring capacity of reinforced concrete can be obtained in four ways:
③ Mechanical occlusion between the uneven surface of the steel bar and the concrete, also known as
Bite force
.
④ The end of the steel bar is bent, bent or in
Anchorage zone
Welding short steel bar, welding Angle steel to provide
Anchoring force
.
Reinforced concrete structure
Reinforced concrete by country
Structural design
The design methods adopted by the specification are
Allowable stress design method
,
Failure strength design method
and
Limit state design method
. In the early stage of the emergence of reinforced concrete, most of the use of
Elastic theory
based
Allowable stress
Design method. In the late 2030s,
The Soviet Union
The failure strength design method considering plasticity in failure stage of reinforced concrete is adopted. In 1950, it was further improved to the limit state design method, which integrated the advantages of the previous two design methods, both to check the allowable stress, allowable crack width and deflection in the use stage, but also to check the bearing capacity in the failure stage, the concept is more clear, the consideration is more comprehensive, has been adopted by many countries and international organizations design specifications.
Reinforced concrete structure
Steel bar and concrete two different properties of materials can effectively
Work together
It is due to the bonding force between the concrete and the steel bar after the concrete is hardened. It consists of
Molecular force
(adhesive force), friction resistance and machinery
Bite force
Three parts. The mechanical bite force plays a decisive role, accounting for more than half of the total bonding force. will
Plain reinforcement
The end is made into a curved hook, and will
Reinforcement welding
into
Steel skeleton
And the mesh can be reinforced between the steel bar and the concrete
Adhesive force
. In order to ensure the reliable adhesion between the steel bar and the concrete and prevent the steel bar from being corroded, the steel bar must have a certain thickness around it
Concrete protective coating
[1-2]
. If the structure is exposed to an aggressive medium,
Thickness of protective layer
It needs to be bigger.
Beams and plates, etc
Flexural member
Medium tensile steel bar, according to
Bending moment diagram
The changes are configured along the vertical
Structural member
The pulled side. In structures such as columns and arches, steel bars are also used to strengthen the structure
Resistance to pressure
. It has two configuration methods: one is the pressure direction configuration
Longitudinal reinforcement
To withstand pressure with concrete; The other is configured horizontally perpendicular to the pressure direction
Reinforcement mesh
And screw
stirrup
To prevent the lateral expansion of concrete under pressure, so that the concrete is under three-way pressure
Stress state
Thereby enhancing the compressive strength and deformation ability of concrete. Because the steel bar configured in this way does not directly bear pressure, it is also called indirect reinforcement. In a bending member
Longitudinal reinforcement
The vertical direction must also be configured
Distributing bar
And stirrups to better hold the structure
wholeness
Bear the cause
Shrinkage of concrete
And temperature changes cause stress, and bear transverse
Shearing force
.
Reinforced concrete structure
Due to the low ultimate tensile strain value of concrete (about 0.15 mm/m) and the shrinkage of concrete, cracks are easy to appear in the tensile zone of the member under the conditions of service load. To avoid concrete cracking and reduce
Crack width
The method of pre-stressing can be used; Pre-apply pressure to the concrete (see
Prestressed concrete structure
).
Practice proves
Under normal conditions, cracks within 0.3 mm in width will not be reduced
Reinforced concrete
the
Carrying capacity
and
durability
.
In the temperature range from -40 to 60°C, concrete and steel bar physics
Mechanical property
There will be no significant change. Therefore, reinforced concrete structures can be used in various
Climatic condition
Next application. When the temperature is higher than 60°C, the internal structure of the concrete material will be damaged, and its strength will be significantly reduced. When the temperature reaches 200°C, the strength of concrete is reduced by 30-40%. Therefore, reinforced concrete structures should not be applied at temperatures higher than 200°C: When the temperature exceeds 200°C, it must be used
Heat-resistant concrete
.
1.
Steel frame construction
It is mainly made of steel structure, is the main
Type of building structure
One of them. Has the following characteristics: light weight, high reliability of work, vibration (shock) resistance,
Impact resistance
Well, it's highly industrialized,
Reinforced concrete structure
2, reinforced concrete structure is a structure built with steel and concrete, steel withstand tension, concrete withstand pressure. It has the advantages of firmness, durability, good fire resistance, saving steel and low cost compared with steel structure.
Due to the good plasticity and toughness of the steel, it can have a large deformation and can withstand the dynamic load well, followed by the homogeneity of the steel
isotropy
Good, genus
An ideal elastomer
, most in line with the general
Engineering mechanics
Therefore, the seismic performance of steel structure is better than that of reinforced concrete structure.
Reinforced concrete structure
3. Good integrity.
4, good modelability.
5, save steel than steel structure.
1. Self-importance.
4, the construction is affected by the season.
5, reinforcing repair difficulties.
Reinforced concrete is of course mainly related to its material: that is, steel and concrete, of which steel is reinforced
Tensile strength
concrete
Compressive strength
The most important thing. In addition, the construction is also related to the temperature and humidity of the weather, because it will affect the condensation speed of concrete.
Reinforced concrete structure
Reinforced concrete structure
1. When concrete continues to be injected at the construction joint, such as
Intermittent time
If you exceed the rules, press
Construction joint
Processing in concrete
Compressive strength
When it is not less than 1.2Mpa, it is allowed to continue perfusion.
Reinforced concrete structure
Treatment method: When the surface gap is thin, the cracks can be washed with clean water, and then wiped after fully wetting
Cement paste
. The mezzanine is handled with care. Before reinforcing, first build
Temporary support
Only after reinforcement can you chisel. Remove the debris and soft concrete in the interlayer, rinse it with clean water, fully wet, reperfusion, and use fine stone concrete to improve the strength level and carefully maintain.
The design and construction of reinforced concrete structures revolve around industrial standards and practical considerations, both of which have slowly developed with the experience and research accumulated during industrialization. As new methods, manufacturing processes, and construction techniques continue to emerge, building materials are steadily evolving. In some ways, industrial standards generally reflect accepted ideas and practices in accordance with construction norms. However, specifications usually talk about some minimum requirements, not the highest requirements. If you expect more than the minimum requirements, then meeting the most basic requirements is not your ideal goal.
[4]
Because designing and building concrete structures is a practical matter, many designers focus more on effective industry standards than on printed specifications. Therefore,
Industrial production
Standards affect the following about
Structural design
And several aspects of construction:
[4]
(1) Design methods and criteria.
[4]
(2) Production and construction process.
[4]
(3) Required tests and proofs.
[4]
(5) Special regulatory requirements (e.g. fire prevention).
[4]
Designers are usually not directly involved in the construction work, but they must consider the following practical problems.
[4]
1. The maximum amount poured at one time
The size of the pouring is subject to time (e.g. 8 hours
Working hours
), the size of the workload, the condition of the site, the number of vehicles transporting the concrete, the method of pouring, and the impact of the structural form (e.g. in the actual pouring)
Multi-storey building
Can only be poured one layer at a time).
[4]
For large structures, the maximum amount of pouring is usually a part of the total amount of pouring. When pouring has stopped for a period of time, the concrete that has been poured will harden before the next pouring. The joint between old and new concrete is called a cold joint or
Construction joint
. Designers must consider this up front - for example, because
Cast-in-place structure
Considered to be a single continuous structure, designers must carefully consider the impact of this construction joint.
[4]
2. Design strength on concrete (fc)
In the early stages of the design process, the designer must first determine the design strength of the concrete. Undoubtedly, this key value is related to the performance of the structure. Designers must also consider the technologies that are used today,
contractor
Ability and budget of the project. As a result, there are designs that continue to push the limits of today's construction technology, requiring the use of the best possible concrete (e.g
High-rise building
While other designs only require the use of low-strength concrete.
[4]
3. constructed
accuracy
Pouring in situ is a very rough job that rarely achieves precise geometry or smoothness
Surface course
. Experience has taught designers what errors are permissible and what errors can be corrected - they have learned to carefully write design instructions, deliberately select certain materials or do some supervision on site.
[4]
However, in general, the quality of factory precast concrete is higher
Cast-in-place concrete
. These components are precisely sized and can be modified. Although precise dimensions are required and smooth surfaces are matched
Basic structure
The formation is not critical, but they can make the building in
Surface treatment
And other architectural techniques are superior. Of course, if the concrete is covered or covered by something else after completion, then the effect of this shortcoming is not much. However, the designer must understand what is required of the more finely connected components of the structure
precision
To recognize the minimum requirements for accuracy in the construction of concrete structures.
[4]
4. Minimum size of concrete member
Because of the actual construction reasons, for the factory to meet
Protective layer
And the different requirements of steel bar spacing, some reinforced concrete structures must have a specific size.
When a slab, wall or beam is equipped with a bending bar, its size is mainly determined by the distance between the tensile bar and the outer edge of the compressed concrete. Therefore, in very thin beams, sheets, and walls, the bent steel bar is of little use.
[4]
In general, steel bars are arranged in two directions in the plates and walls. Even if the bending action occurs in only one direction, the specification requires a certain number of steel bars in the other direction to control cracks due to shrinkage and temperature changes. Even with the smallest
Thickness of protective layer
Sum minimum
Cross area
The rebar, the plate
Minimum thickness
It should also be approximately 2in, but except for joists or well structures, the thickness of the plate is usually larger to improve the bending resistance of the plant. The general rebar arrangement on the top or bottom is mainly determined
Bending moment
The positive and negative decisions.
[4]
Building code
Additional protective layer thickness is often required, and the protective layer thickness of the minimum thickness plate is 4in or larger, so as to ensure a high level of protection
Fire rating
.
[4]
Tips
The thickness of the board is determined by the size of the aggregate used.
[4]
l0in thick walls or thicker walls often have two layers of steel. Each layer is on the wall as permitted
The outer surface
It's very close. Walls with criss-crossing rebar (e.g., horizontal and vertical rebar) are rarely less than 6in thick.
[5]
