Figure 2 Schematic diagram of precast column grouting sleeve connection (note: please refer to the Key Process of Illustrated Assembled Building Construction – Sleeve Grouting for detailed understanding of sleeve grouting process characteristics) Lightning protection downlead design downlead is used to conduct lightning current from lightning arrester to grounding device.

It is easy to form the lightning electrical path through the form of reinforcement threaded sleeve or lap welding.

The first category is mostly used for public buildings, the second category is mostly used for residential buildings, and the third category is applicable to multi-storey residential buildings with seismic fortification category of C.

The precast building cancels most of the cast-in-place and cast-in-place construction work at the construction site, and puts forward different construction requirements for the electrical construction of the precast building, especially for the lightning protection construction.

The construction process is completed by the on-site electrical construction personnel and the structural construction personnel.

This paper introduces the structural process and construction characteristics of precast buildings, combines the relevant requirements of GB50057-2010 Code for Design of Lightning Protection of Buildings, and discusses the construction points and measures for the design of lightning protection downleads of precast buildings at this stage, and discusses different design ideas and construction methods of lightning protection downleads according to the characteristics of precast buildings, which is very worthy of your reference and study.

When the reinforcement in the concrete is used as the down lead, the design of the down lead shall be based on the provisions of Articles 4.3.5 and 4.4.5 of GB50057-2010 Code for Design of Lightning Protection of Buildings, and the location and quantity of the down lead shall be set according to the lightning protection category of buildings according to the requirements of Articles 4.3.3 and 4.4.3 of the code.

Short Waved Anchor

At present, two downlead connection nodes in the upper and lower precast columns are usually used in the design drawing Ф 10 Round steel is connected with two main reinforcements in the precast column and sufficient length is reserved outside the column as additional special conductor.
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Precast buildings refer to the buildings in traditional buildings, such as beams, floors, columns, walls, stairs, etc., which are precast in the factory and assembled on the site.

It can be seen from Figure 2 that the gap between the upper precast column grouting sleeve and the lower precast column head reinforcement has been filled with grouting material, so the reinforcement in the upper and lower precast columns does not form a continuous electrical path.

These precast components are produced by the precast component factory and transported to the construction site.

Taking the lightning protection down lead design of a precast building project as an example, this paper discusses the lightning protection design idea of the current precast building, and solves the construction problem of the lightning protection down lead of the precast building.

When the main reinforcement in the precast column is used as the lightning protection downlead, special measures need to be taken.

A project adopts the precast frame-shear wall structure+precast exterior wall panel structure system, which is composed of precast columns, precast composite beams, precast composite floors, precast exterior wall panels, precast stairs and other precast components.

Because the precast building is assembled by various modules, in the connection mode of precast components, the connection between beams and slabs is usually designed as precast plus cast-in-situ layer, while the connection between the longitudinal reinforcement between the upper and lower precast columns is connected by sleeve grouting technology.

The construction process is simple, time-saving and material-saving.

In the traditional cast-in-place concrete structure building, the lightning protection design of the building gives priority to the use of two diagonal main reinforcements in the structural column as the lightning protection downlead.

Compared with the traditional lightning protection design of the building, the lightning protection design of the precast building at this stage is still immature, and there are many problems in the construction process.

In the design of lightning protection downlead for precast buildings, in order to realize the electrical connection between components to meet the lightning protection requirements, it is necessary to design additional special conductors in precast components (mainly precast columns).

The advantages are fast construction speed, small restriction by climate conditions, labor saving and improved construction quality.

This article, “Discussion on the Design and Construction Points of Lightning Protection Downlead for Fabricated Buildings”, was published in the 10th issue of Fujian Building Materials, 2019, by He Zengping (Fuzhou Construction Engineering Quality Supervision Station).

Figure 1 The precast component split diagram of precast concrete structure building.

According to the requirements of the Technical Standard for Fabricated Concrete Buildings (GB/T51231-2016), precast concrete structure buildings are divided into three types: precast integral frame structure buildings, precast integral shear wall structure buildings, and precast wallboard structure buildings.

They are assembled by lifting equipment according to the lifting drawings, as shown in Figure 1.