Design structure of soil-supported floor (Ⅱ)

Load transfer between floor joints

The actual free edges or corners of the floor that require load transfer are relatively rare, because these parts generally only appear on the circumference of the building

For the following types of floor joints, the load transfer must be considered separately

• Free expansion template joint: The floor joint device contains a round or square cross-section force transmission rod or a separate force transmission plate

  
  

• Freely retractable steel cutting key: Place the power transmission rod in the sleeve

  
  

• Restrict expansion and contraction template joints: use the method of setting force-transmitting steel bars to limit the free expansion and contraction of the joints.

  
  

• Limit the shrinkage of sawing seams (only for mesh reinforced concrete floor slabs): sawing will induce cracking chains to penetrate the entire floor slab vertically

  
  

1.

Aggregate occlusion refers to the ability of the aggregate particles exposed on both sides to contact each other when the narrow and irregular cracks are formed through the cracks to transfer the load from one side to the other

According to the research of Colley and Humphrey [54], in design applications, a crack with an opening width of 1.

Therefore, the design method is:

2.

The calculation method of the bending resistance, shear resistance and splitting force of the force-transmitting member and the steel bar can be found in Chapter 6.

Bearing capacity of punching and foundation support

1.

Since the main design load of the first floor of the industry is the point load generated by the racks and forklifts, its punching effect needs to be considered
.

The punching shear bearing capacity is determined by checking the shear stress at the circumference of the load action area and the shear stress at the critical section circumference at a distance of 2.
0d from the periphery of the load action area according to the method in Chapter 6.
4.
Here it refers to the concrete floor slab.
The effective height of the section
.
Refer to Figure 7.
8.

2.
Foundation support

Since it is assumed that the floor is in contact with the cushion layer, this part of the load within the perimeter of the punching critical section can be regarded as directly acting on the foundation, so the design force is reduced
.
The method of calculating the foundation reaction force is as follows:

Then, the reaction force can be subtracted from the acting force
.

Line load

The elasticity analysis method based on the research of Hetenyi [49] is used here
.
This analysis method uses the traditional comprehensive safety factor of 1.
5
.
Since a factor of 1.
5 has been used for material properties, no other factors should be used for loads
.
The equation used to determine the bending moment of the soil-supported floor uses the term λ, where:

Since this equation is based on the elastic distribution of the bending moment, Mun should use the cracking bending distance, which is the value obtained in Equation 2
.
The residual bending moment of fiber reinforced concrete slab or mesh reinforced concrete slab (calculated result of equation 4) should not be used
.

Equation 34 applies to linear loads far away from floor joints or floor slab edges
.
The bearing capacity of the floor slab against the linear load at the free edge is 3λMun, and it increases to 4λMun at the distance 3/λ from the free edge
.
If the floor joint can transmit at least 15% of the load, the bearing capacity of the floor slab at a distance of 1/λ from the floor joint can be increased to 4λMun
.
See Figure 7.
9 .

This situation can be explained by the fact that for the line load far from the edge of the floor slab, the distance between the position of zero bending moment and the load is about 1/λ.
This is the same as the case of floor joints with shear capacity but no rotational stiffness.
Similar
.

Uniform load

The elasticity analysis method based on Hetenyi [49]'s research is adopted here
.
This analysis method uses the traditional comprehensive safety factor of 1.
5
.
Since a factor of 1.
5 has been used for material properties, no other factors should be used for loads
.
As in the case of calculating the linear load above, the equation used to determine the bending moment of the soil-supported floor also uses the term λ (Equation 33)
.

The following equation does not consider the situation where the uniformly distributed load is close to the floor joint
.
Hetenyi [49] provided an analysis method for the uniformly distributed load near the floor joint, but it was extremely complicated
.
Traditionally, the factor of floor joints is ignored when calculating uniform load, and it is known that this will not cause damage to the floor
.
It is recommended to continue to use this method, although the designer can still refer to Hetenyi [49]'s method to analyze the floor slab more accurately
.

A common case of uniform load is heap load
.
Under normal circumstances, the floor slab will bear the uniform load of the random model, but it has been found that the maximum positive (downward) bending moment of the floor slab is caused by the uniform load with the acting width π/2λ, as shown in Figure 7.
10 (a) Shown
.

The maximum negative (upward convex) bending moment is generated at the position between a pair of uniformly distributed loads, and the action width of each uniformly distributed load is π/λ, and the uniformly distributed load spacing is π/2λ, as shown in Figure 7.
10(b) Shown
.
This distance is the critical roadway width that is usually said
.

The bearing capacity per unit area, q, is obtained by the following formula:

If the acting position of the uniform load is clear, Hetenyi[49] gives the equation of the positive bending moment caused by the uniform load with the acting width of 2c (as shown in Figure 7.
22(a)) as:

At the distance ɑ1 from the proximal end of the uniform load acting surface, that is, at the distance b1 from the distal end of the uniform load acting surface, see Figure 7.
11(b), the negative bending moment generated, Mn1, is obtained by the following formula:

If the location of the second uniform load is close to the first uniform load, an additional bending moment Mn2 will be generated, which is also determined by Equation 37, but the corresponding values ​​of ɑ and b must be used
.
Therefore, q can be determined by the maximum value of (Mn1+Mn2), which is equal to the negative moment bearing capacity Mn of the concrete slab
.