What Is Negative Reinforcement?

Negative reinforcement ^[1] , also called negative moment reinforcement. In the design of reinforced concrete structures, the reinforcement used to resist negative bending moments is called negative bending moment reinforcement.

In simple terms: the concept of negative moment steel bars can be used in the reinforcement structure of the following components:

For the negative bending moment steel bars of cast-in-situ concrete slab members of general industrial and civil buildings, especially the negative bending moment steel bars of cantilever members, the control of the thickness of the concrete protective layer has always been a weak link. The method introduced in this article using a thick steel bar (or steel pipe) to suspend a negative bending steel bar has the advantages of low material cost, simple manual operation, and stable control effect.

In the construction of cast-in-situ reinforced concrete slabs, negative reinforcement tends to be stepped on and lowered artificially, thereby increasing the thickness of the concrete protective layer. In addition, there will also be the phenomenon that the negative ribs are bound and detached, the hooks are tilted, and even the hooks are upward, which results in a reduction in the effect of the negative ribs in the plate and a reduction in the bearing capacity of the cast-in-place plate. So how to prevent negative tendons from being displaced, loosened and tilted?

Preventing human trampling

During the construction, the various types of work should coordinate with each other, and work should be carried out in accordance with the order of woodwork supporting molds, main steel bars for binding hydropower pipes, and pipelines reserved for negative steel bars. The construction procedure is reasonable, which can avoid human stepping. It should be inspected and reorganized before the concrete is poured.

Controlling negative tendon displacement with a horse stool

General horse stools can be made of 6 rebar (or larger sizes such as 10, 12, etc. according to the approved construction organization design plan). The height should be based on the thickness of the cast-in-place slab minus the thickness of the reinforced concrete protective layer, the main reinforcement and the negative The diameter of the ribs is determined. The horse stool is staggered with not less than one negative rib per meter within the range of distributed ribs, and not less than two within 1 m2, and is tied firmly with a wire under the negative rib.

Concrete falls on grey tray

When pouring concrete, the concrete in the bucket should not directly fall on the upper part of the steel bar of the cast-in-place plate, but should fall on the ash tray. We use 30 × 3 angle steel welding to make an iron ash tray of 1.0 m × 1.5 m to withstand the weight of the concrete. Workers can stand on the left and right sides of the ash tray for work. When pouring the next bucket of concrete, the ash tray can be moved to the upper part of the cast-in-situ concrete and poured forward in turn. In this way, it can not only reduce the pressure of the concrete on the reinforcing steel, and play a buffering role; it can also prevent human stepping during construction.

1.Negative rib length = net length of negative rib + left bend + right bend;

2. The number of negative reinforcements = (reinforcement range-deduction value) / reinforcement spacing +1;

3.Distribution tendon length = length of negative tendon arrangement range-negative tendon deduction;

4.The number of negative reinforcement distribution bars = the length of the negative reinforcement in the input interface of the negative reinforcement / the distance between the distributed reinforcement +1;