The actual thickness of the composite slab after casting is calculated by measuring the thickness of the precast bottom slab on site and the height from the top of the precast bottom slab to the top of the reinforcement.

The space requirement for laying electrical pipelines has increased.

In the laminated plate area where the electrical trunk line passes through and intersects with ordinary pipelines, the space requirement for electrical pipeline laying is about 15mm larger than the intersection area between ordinary pipelines PC20 (including some gaps).

The conventional reinforcement arrangement principle here is that “radial reinforcement+erection reinforcement” (all linear reinforcement) is placed on the original two layers of upper iron reinforcement, and four layers of reinforcement are arranged on the upper part of the external corner area.

1.

3 Arrangement of radial reinforcement at external corners 2.

It can be seen from Table 1 that the measured thickness of the laminated plate is ＞ the theoretical thickness ＞ the design thickness.

There is a general problem of super thick construction pouring in projects using composite plates, which will bring a series of adverse effects.

2.

Therefore, 2~3 layers of reinforcement will be added to the reinforcement layout space, as shown in Figure 3.

Even some projects have unreasonable reinforcement binding sequence, Five layers of rebar are arranged in the upper part of the external corner area.

Cause analysis Through field investigation, the actual thickness of the laminated plate is mainly composed of the following parts: 1.

1.

As a result, there may be cross overlaps at the concentrated locations of pipelines, most of which are three pipes and two pipes.

Gap between reinforcement, pipeline and precast base plate; 5.

In this paper, the environmental category of the laminated plate is considered as Class I, and the thickness of its protective layer is taken as 15mm.

1.

1 The thickness composition profile of the laminated plate.

Fig.

The construction is inconsistent with the design intent of the drawing.

The specific composition is shown in Figure 1.

The calculation formula is: theoretical plate thickness=design value of precast base plate thickness 60mm+required height of pipeline laying and reinforcement arrangement+15mm of protective layer; Measured plate thickness=the average measured thickness of precast bottom plate (the average measured value is about 65mm)+the measured height from the top of precast bottom plate to the top of reinforcement+the thickness of protective layer is 15mm.

Two layers of connecting structural reinforcement are required at the top of the precast bottom slab.

Investigation: In the investigation of the super thick construction pouring of laminated slabs for some precast residential projects under construction and using laminated slabs, the investigation of three projects was combed.

Combined with the project practice, the causes of super thickness are explored, and specific control measures are proposed from design, production, construction and other aspects.

Fig.

Required thickness of reinforcement arrangement; 4.

The space requirement for pipeline laying in the intersection area of three pipelines is about 20mm larger than that in the intersection area between ordinary pipelines PC20, as shown in Figure 2.

Refer to 15G366-1 Truss Reinforced Concrete Laminated Slab (60mm thick base plate) and 15G310-1 Fabricated Concrete Connection Node Structure (floor and stair) for rebar binding.

Therefore, 2~3 layers of reinforcement will be added to the reinforcement layout space, as shown in Figure 3.

Although the construction drawing of electrical discipline clearly stipulates that “only two layers of pipes are allowed to cross at the same place, and the crossing of pipelines of three layers or more is not allowed, and the pipe crossing is staggered with the upper and lower layers of reinforcement”.

4.

Required thickness of electrical pipeline laying; 3.

Even some projects have unreasonable reinforcement binding sequence, Five layers of rebar are arranged in the upper part of the external corner area.

Figure 5 Design Node of Laminated Layer Reinforcement Arrangement 2.

2.

Most of the electrical pipelines in the houses where the strong current trunk line crosses the ordinary pipeline are PC20 (ordinary pipeline, diameter 20mm), but the strong current trunk line from the electric well to the strong current box is PC32 (trunk line, diameter 32mm).

Actual thickness of protective layer.

The one-way slab joints are constructed according to the connection of one-way slab joints.

This problem is most prominent in areas with concentrated pipelines such as strong and weak electric wells.

Due to the insufficient control of the production accuracy of the precast component factory and the inadequate acceptance of the components, the actual situation feedback from the survey shows that the measured value of the precast floor on site is 61~68mm.

Compared with other parts, two layers of reinforcement are required for the reinforcement layout space, as shown in Fig.

If the 130mm thick laminated slab cast-in-situ laminated layer rebar is truss rebar, only one layer of rebar is placed on the truss rebar, as shown in Figures 5 and 6, according to this arrangement, the height of truss rebar through the pipe can be fully improved..

The actual thickness of the precast bottom plate; 2.

Figure 4 The space requirement for the arrangement of reinforcement at the connection node of one-way slab joint is increased.

Among the research results of the above three projects, the application scope of laminated plates, the design thickness of typical parts, the measured thickness of typical parts, the theoretical thickness of typical parts, the difference between the measured and designed thickness, and the difference between the theoretical and designed thickness are shown in Table 1.

Figure 2 The space requirement for the layout of three pipelines and two crossing reinforcements for ordinary pipelines has increased.

The conventional reinforcement layout principle here is “radial reinforcements+erection reinforcements” (all linear reinforcements) placed on the original two layers of upper iron reinforcements, and the upper part of the external corner area is arranged with four layers of reinforcements.

The one-way slab joints are constructed according to the one-way slab joints.

In the design drawings of some projects, the top surface of the external corner of the special-shaped slab of the structure needs to be added with radial reinforcement.

As the current design drawings do not carry out refined layout of electrical pipelines, the pipe laying route is temporarily determined by electromechanical installation workers on site for pipeline construction.

The external corners of special-shaped plates are in some project design drawings, and the top surface of the external corners of structural special-shaped plates needs to be added with radial reinforcements.

The specification for the production of super thick precast floor requires that the production accuracy of the precast floor is ± 5mm.

1.

Loop Box

1.

Two layers of connecting structural reinforcement are required to be arranged on the top of the precast bottom slab.

Compared with other parts, two layers of reinforcement are required for the reinforcement arrangement space, as shown in Figure 4.

In addition, the height of truss reinforcement is not strictly controlled in the production process, leading to the truss reinforcement floating easily in individual projects, which will also have a negative impact on the floor thickness control.