by Comparative analysis of calculation of normal section bearing capacity of steel reinforced concrete members The steel reinforced concrete column and steel reinforced concrete beam take the steel as the skeleton, and configure the reinforcement and pour the concrete around the steel.
Their bearing capacity and ductility have been improved.
They have the respective advantages of steel and concrete, and make up for the defects when they are used alone.
Their good mechanical performance promotes the wide engineering application of steel reinforced concrete members, And the medium-sized steel members can be used to bear the construction load during the construction process.
Taking steel reinforced concrete beams and steel reinforced concrete columns as examples, using the method [1] of code for design of composite structures jgj138-2016, this paper compiles corresponding tables to calculate the normal section bearing capacity of steel reinforced concrete members, and compares them with the results of self-developed software cisdesigner and the third-party software xtract, At the same time, the accuracy and reliability of the algorithm results of cisdesigner program are verified.
2.
Calculation method of normal section bearing capacity of steel reinforced concrete members converted stiffness method: Based on the calculation method of steel structure, considering the converted stiffness of outsourcing concrete, it is suitable for the case with large amount of steel, and this method is relatively rough.
Limit equilibrium theory method: jgj138-2016 code for design of composite structures uses this method.
The section composed of section steel and concrete conforms to the assumption of plane section.
After considering the influence of section steel stress distribution, it is calculated according to the design method of reinforced concrete.
Superposition method: Based on the lower limit theorem of plastic theory, the lower limit of bearing capacity of steel reinforced concrete column is the superposition of bearing capacity under the condition that the steel and concrete meet the stress balance respectively.
Technical specification for steel reinforced concrete structures yb9082-2006 uses this method to calculate and superimpose the bearing capacity of section steel and concrete respectively.
Limit equilibrium theory method and superposition method are widely used in engineering practice.
This paper only compares the former method.
The premise assumptions of limit equilibrium theory method are as follows: section strain maintains plane; The tensile strength of concrete is not considered; The ultimate compressive strain of concrete at the edge of the compression zone is 0.0033, and the corresponding maximum compressive stress is the design value of concrete axial compressive strength FC multiplied by the influence coefficient A1 of concrete compressive stress in the compression zone; The stress graph of the concrete in the compression area is simplified into an equivalent rectangle, and its height is taken as the height of the neutral axis determined by the plane section assumption multiplied by the influence coefficient B1 of the concrete stress graph in the compression area.
The tensile and compressive stress figures of the section steel web are trapezoidal, which is simplified to the equivalent rectangular stress figure in the design and calculation; The stress of reinforcement is equal to the product of its strain and elastic modulus, but not greater than its strength design value.
The ultimate tensile strain of tensile reinforcement and section steel tensile flange is taken as 0.01.
The code for design of composite structures adopts the structural theory of concrete to check the section bearing capacity of composite structures.
The section steel flange is regarded as a part of the longitudinal load-bearing reinforcement.
It is assumed that the strain of concrete, reinforcement and section steel in the section of composite structure remains flat, the extreme compression deformation is close to 0.0033, and the tensile strength of concrete is not considered, The calculation formula of section bearing capacity of steel reinforced concrete members is derived.
Cisdesigner implements an algorithm to quickly generate p-m-m correlation surface of section of steel reinforced concrete members.
Without loading, the stress of each fiber unit can be known directly from the limit state strain control line of the section, according to the constitutive of the section fiber material and based on the plane section assumption.
In this way, a series of bearing capacity points of the section strain state with the same center of gravity axis can be obtained, which can be connected into an original PM curve, and the whole process does not involve any iteration and cycle.
A closed and complete PMM envelope can be obtained by gradually rotating the strain surface 360 ° around the local 1 axis of the section, as shown in Figure 1.
For the specific principle, please refer to the software technical description document [2].
Figure 1 ， rotation angle of strain surface along the section ， figure 2pmm related surface 3 The normal section bearing capacity of steel reinforced concrete beam takes two I-shaped steel reinforced concrete beams as an example.
The section size of beam 1 is 300mmx600mm, and C30 concrete, Q345 grade section steel and HRB400 grade longitudinal reinforcement are adopted.
The section size of the section steel is 200mmx400mmx6mmx10mm, the number of reinforcement in the upper and lower sections of the beam is 3 and 6 respectively, the diameter of the reinforcement is 14mm, and the distance from the resultant force point of the tensile reinforcement to the tensile edge of the section is as = 35.
The section of beam 2 is only modified on the basis of beam 1, and the reinforcement in the tensile area is double row 6 bars with a diameter of 20mm, and the others remain unchanged.
As shown in Figure 3.
Figure 3 ， section of steel reinforced concrete beam (beam 1 left and beam 2 right) 3.1 ， normal section bearing capacity of steel reinforced concrete beam [3] calculate the normal section bearing capacity of steel reinforced concrete beam according to the bearing capacity formula in 5.2 of code for design of composite structures.
The equivalent compression zone height of section steel beam 1 is x = 145.2mm, and the actual compression zone height xn = 145.2 / 0.8 = 181.5mm.
The calculation results of flexural bearing capacity of normal section are shown in Figure 4.
Fig.
4 calculation table of flexural capacity of normal section of steel reinforced concrete beam 1 (mu = 552.36kn-m) the equivalent compression zone height of steel beam 2 is x = 259.8mm, and the actual compression zone height xn = 259.8 / 0.8 = 324.7mm.
The calculation results of flexural capacity of normal section are shown in Fig.
5.
Fig.
5 calculation table of flexural bearing capacity of normal section of steel reinforced concrete beam 2 (mu = 896.61kn-m) 3.2 normal section bearing capacity of steel reinforced concrete beam of cisdesigner enter the section information of steel reinforced concrete beam 1 into the software cisdesigner, and the flexural bearing capacity of normal section is 544.42kn-m..
