Design and Construction of Light Steel Structure Enclosure Systems

In recent years, light steel structure has been widely used in Steel Structure Warehouses, small Steel Structure Exhibition Halls ,Container Homes and office buildings due to its low steel consumption, short design and installation time and high industrialized production degree. This has promoted the development of steel structure enclosure system from unitary to diversified, which in turn has triggered the change of new design ideas and new construction methods.

The enclosure system of lightweight steel structure mainly includes wall system, roof system, lighting belt, edge wrapping and flashing, gutter and heat preservation cotton, etc. The enclosure system is the most important part of lightweight steel structure. The enclosure system is one of the most important components of lightweight steel structure, which determines the ornamental appearance of the building, waterproofing and heat preservation effect of the building.

1、Design and Construction of Roof and Wall Systems

1.1 Classification of color plate enclosure system

Color plate enclosure is divided into: single-layer plate, EPS sandwich panel, BHP color steel plate, GRC wall panel, polyurethane sandwich panel, glass wool on-site composite sandwich panel, rock wool sandwich panel according to the composition.

According to the construction mode is divided into: finished composite panels, site composite panels. Field composite board connection mode is divided into: lap board, bite board, dark buckle board.

According to the material is divided into: galvanized color steel plate, titanium plate, aluminum zinc color steel plate, aluminum alloy plate pressure plate, stainless steel plate pressure plate, copper plate.

1.2 Design considerations

Field composite plate because of its low processing cost and construction technology is more mature, so in the light steel structure is widely used. Roof color plate with 0.376t and 0.5t thick galvanized baking paint color plate.

Roof slope affects the discharge of rainwater on the roof, in the design of the roof slope should be taken 1/8-1/20, in the area of more rainwater should be taken the larger value (see CECS102:98), in addition to the roof slope and the use of the roof board type related to the general use of exposed nail plate slope requirements are larger, the hidden requirements are smaller.

Large-span steel structure roof panel should be used concealed buckle type color steel plate. In a large number of engineering applications, concealed fastening type color steel plate shows the following advantages: (1) Avoid temperature difference caused by excessive deformation of the roof panel, self-tapping screws are cut off. (2) In the rainy area, typhoon area exposed self-tapping screws in the temperature deformation, wind load vibration, rubber mat aging, it is very easy to cause corrosion and water leakage, the use of concealed fastening type of color steel plate can be avoided the above situation. For the single slope length greater than 60 meters of the roof needs to be processed into two boards, the formation of expansion joints between the boards, with the TETA cover sheet connection, TETA cover sheet can be sliding with the color plate each other, can solve the problem of temperature deformation.

1.3 Construction precautions

In the construction, for the large span of the roof, the color plate needs the whole piece of molding plate, because the crane lifting plate is easy to cause deformation of the plate, so the installation generally do not use the crane, more color to take the winch semi-slope lifting.

2、Lighting strip bead design and construction

Lighting board according to the material is divided into glass fiber reinforced polyester light board, polycarbonate made of honeycomb or solid plate, etc., according to the shape can be divided into the same waveform with the roof panel of glass fiber reinforced polyester light board (referred to as fiberglass fiber reinforced plastic light tiles) and other flat or curved surface of the light board.

Different lighting panels have different fixing methods, polycarbonate lighting panels using aluminum profile fasteners, waveform lighting panels using lighting panel bracket and self-tapping screws to connect and fix, and then glue sealing. The position of the light-reflecting plate is generally set in the middle of the span. Lighting board and self-tapping screws connected, there must be a cover. Sunshine plate hot and cold deformation is large, easy to be self-tapping nails cut, so the sunshine plate in the self-tapping nails should be opened at a larger hole. In the installation of light panels to consider the expansion and contraction of light panels.

Lighting board in 12m or less without lap, more than 12m need to lap, lap length of 200-400mm, lap at the application of two sealant, transverse lap does not need to edge, longitudinal color plate lap depends on the type of plate, ordinary compression molded steel plate, generally do not test false edge, directly with the color plate and the color plate with self-tapping nails, and the application of sealing sealant, the bite of the board need to do edge.

Lighting board longitudinal length direction lap should be set in the sandalwood strip near the roof waterproofing treatment shall be used sealant coating, sealant surface is easy to aging; lap using two water cement in the middle of a white or colorless sealant.

Lighting board lateral color plate lap: open type screw roof panel or dark type buckle roof panel, light board should be reserved board effective width, in the light board crest with long self-tapping screws fixed, taking into account the thermal expansion and contraction of the light board is not the same, should be used to pre-punched light board processing (8mm holes appropriate), self-tapping screws need to be placed under the strengthened waterproof washer, to prevent the light board thermal expansion and contraction of the screws after the cracking.

3、insulation wool

Insulation cotton has rock wool, glass fiber and other materials, insulation cotton has excellent thermal insulation properties, construction and installation convenience, energy saving effect is remarkable, low thermal conductivity and other characteristics. At present, the roofing system of domestic steel structure workshop adopts: (1) steel wire mesh+aluminum foil insulation cotton+single color plate; (2) double color plate+insulation cotton and other two ways.

The following is mainly introduced wire mesh + aluminum foil insulation cotton + single color plate roof construction methods.

Stainless steel wire or galvanized wire cross pull out diamond or rectangular shape, with 215 cm long self-tapping nails fixed in purlin, laying glass wool rolled felt, aluminum foil face to the indoor side, perpendicular to the purlin, in the eaves of the two sides of the more left about 20 cm of the rolled felt, with double-sided tape will be fixed in the outermost guillotine on the purlin. Use the reserved 20 centimeters of veneer for glass wool edging. Pay attention to the tension of the glass wool rolled felt, alignment, tight joints between the rolls, longitudinal need to lap, lap joints should be arranged in the purlin. According to the needs of the project, in order to avoid the generation of cold bridge, can be considered in the purlin pad rigid insulation material.

4、Gutters and soffits

Eaves can be divided into external drainage gutter eaves, internal drainage gutter eaves and free-fall gutter three forms according to the structure. Priority can be given to the use of free-fall and external drainage gutter eaves form. According to the material points have stainless steel gutter, steel plate gutter, color plate gutter. Gutter as the main roof drainage system, determines the rain and snow discharge, building roof normal use of function.

Figure 2 Exterior Drainage Gutter Eave Practice

Outside the drainage gutter gable due to leakage prevention, low cost, in the project can also be widely used. Outside the drainage gutter gutter is mostly taken with the color plate gutter. Construction of color plate gutter does not need to support its structural components, the gutter wall can be directly close to the external wall plate, set up on the wall support, in the roof panels on the outstretched connectors picked on the outer wall of the gutter, the sections of the gutter overlap each other, the use of rivets to connect and sealant sealing. Works can be used in the practice shown in Figure 2.

Figure 3 Edging and flashing practices

5、Edging and Flashing

Edging and flashing not only outline the lines of the building, affecting the aesthetic degree of the building, while structurally linking the building into a whole, windproof, rainproof, so that the building is more durable. See Figure 3 for details.

6、Summary and conclusions

Light steel structure has been widely used in factory buildings, small exhibition halls and office buildings because of its low steel consumption, short installation and design time, and high degree of industrialized production. Its enclosure system often use color steel plate, research summarize color steel plate maintenance system design and construction experience, put forward economic and reasonable node structure and construction program has important practical significance.

For the outer floor type level plate, should give priority to the use of dark buckle type color steel plate structure processing, can avoid the temperature difference deformation caused by the self-tapping screw is sheared, at the same time can avoid in the rainy area, typhoon area exposed self-tapping screw in the temperature deformation, wind load vibration, rubber mat aging caused by the plate corrosion and water leakage phenomenon.

Lighting board design and construction should pay attention to its thermal expansion and contraction, lighting board and self-tapping nail connection must have a cover. At the same time, pay attention to its differences with the color steel plate. Lighting board should be pre-punched processing (8mm hole is appropriate).

In order to avoid the generation of cold bridge, you can consider padding rigid insulation composite board on the purlin.

In the northern region with little rain and the project does not require a high level of eaves, it is recommended to use free-fall eaves. Its leakage is good, the cost is low, in the project has been widely used.

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