Steel-Structured Residential Buildings: Design & Systems Guide

1. Technical characteristics and challenges of steel-structured residential buildings

1.Building facade: Compared with traditional reinforced concrete residential buildings, steel-structured residential buildings require that the facade not be overly complex; otherwise, design and construction difficulty will increase, and costs will rise significantly.

2. Building fire protection: Steel columns generally use thick-applied fireproof coatings to meet the requirement of secondary fire resistance rating. Steel beams use thin-applied fireproof coatings, which do not affect aesthetics after plastering work is completed.

3. Interior space: The use of steel structures allows for more column-free or few-column spaces. Compared with traditional shear wall residential buildings, the interior space layout is relatively flexible, and the feasibility of later modifications is improved, which is beneficial for marketing.

4. Building sound insulation: New lightweight, thermal-insulating, heat-insulating, and high-strength wall materials are used as the enclosure structure for exterior walls.

2. Structural system of steel-structured residential buildings

Currently, the main structural forms of steel-structured building systems include the frame structural system, the framed-braced structural system, and the frame-shear wall structural system.

1.Frame structural system: A pure frame structural system is generally not more than 15 stories in seismic zones. The frame structure allows flexible layout and provides large interior spaces for the building, with relatively uniform stiffness among its parts. This structure has good ductility, a long natural vibration period, is not sensitive to seismic action, and exhibits good seismic performance. However, the lateral stiffness of a pure frame structure is small, and its large lateral displacement can easily cause damage to non-structural components; therefore, it should not be built too high.

2. Framed-braced structural system: When the lateral displacement of a pure frame under wind and seismic loads does not meet the requirements, a braced frame can be adopted—that is, a certain number of braces are arranged in both the longitudinal and transverse directions of the frame system. In such a system, the frame layout principles and column grid dimensions are basically the same as those of the frame system. Braces are mostly arranged around the service area at the center of the floor, and the longitudinal braces are connected with the transverse braces to form a braced core tube. Using vertical braces composed of axially loaded members to replace the frame structure composed of bending members can provide much greater lateral stiffness than a pure frame structure and significantly reduce inter-story drift.

3. Frame-shear wall structural system: Arranging a certain number of shear walls in a frame structure forms a frame-shear wall structural system. In this system, shear walls serve as the lateral load-resisting structure. It combines the flexible layout and convenient use of frame structures with greater stiffness, and can be used for high-rise steel structures of 40 to 60 stories. When reinforced concrete walls are placed around service areas (e.g., stairwells, elevator shafts, and bathrooms), a frame-multi-tube structural system is formed. This system has large lateral stiffness in all directions, becoming the main lateral load-resisting component that bears most of the horizontal loads, while the steel frame primarily carries vertical loads.

In the design process, the choice of which system to use should comprehensively consider multiple factors, such as the large column grid factor that highlights the advantages of steel structures, and the large bay, easily changeable layout factor that meets the needs of modern living. To make the structure economical and reasonable, multi-story steel residential buildings have some requirements for structural layout. Of course, these requirements are not absolute; under feasible conditions, doing so would be more economical and reasonable, mainly as follows:
① Adopt a rectangular plan or a building plan composed of rectangular plan units;
② Arrange frame columns in rows in the transverse direction of the building;
③ Place braces or truss webs in partition walls without openings;
④ When using a spaced truss system, the longitudinal corridor of the building should be located in the middle of the transverse trusses.

3. Design considerations

1.Joint design: In a steel structural system, joint design is as important as member design and therefore must be given sufficient attention. Joint design in steel structures includes beam-column joints, beam-beam joints, column-column joints, column base joints, column cap joints, etc. The design should ensure that the joints are safe and reliable, and should adopt simple, stable, and reliable construction techniques, reducing or avoiding field welding. Steel joints can be classified into three types according to their load transfer characteristics: hinged joints, semi-rigid joints, and rigid joints. Beam-column connections are typically rigid, while beam-beam connections are hinged. It is recommended to use conventional design methods and avoid having too many bolts on the web.

For beam-beam hinged joints, it is not recommended to use the extended gusset plate practice, as it increases the number of bolts. Special attention must be paid to this when reviewing the steel shop drawings (contractors prefer the extended gusset plate method because it is convenient for installation and material preparation), to avoid discrepancies between the shop drawings and the design, which could lead to insufficient bolt quantity and create safety hazards.

2. Selection of wall materials: Generally, to highlight the advantages of steel structures — light self-weight, flexible layout, and good modifiability — traditional masonry blocks or other materials with high self-weight are not suitable for steel-structured residential buildings. Lightweight materials are typically used, such as hollow concrete blocks, aerated concrete, composite walls composed of profiled steel sheets with lightweight insulation materials, OSB boards, CS boards, etc. Currently, autoclaved lightweight aerated concrete (ALC) panels are widely used. This material is lightweight, has good waterproof and anti-permeability properties, good thermal insulation, sound insulation comparable to ordinary concrete hollow blocks, high strength, and is easy to construct. It performs well both as exterior walls and interior partition walls.

In addition, when designing walls, the strength, material, and dimensions of connectors must be accurately specified. The connection method should fully consider the characteristics of the wall and the main structure, and adopt simple and fast connection methods wherever possible, to facilitate construction and improve work efficiency.

3. Staircase design: In industrial steel-structured buildings, steel stairs are mostly used, but they are generally not used in residential systems because of their poor sound insulation. Therefore, concrete stairs or profiled steel sheet-concrete composite stairs are often used in steel-structured residential buildings. During design, attention should be paid to the placement of stair stringers and joint treatment, because at these locations, beam-beam connections typically occur, which impose concentrated loads on the connected beam, making it more prone to local instability.

4. Floor system design: In industrial steel-structured buildings, the floor system mostly uses traditional metal decking or steel bar truss decking with a formwork-free system, but this is generally not used in residential design because the bottom steel plate affects later decoration, requiring a full suspended ceiling and reducing the clear room height. Generally, traditional cast-in-place slabs or precast composite slabs (PC composite slabs) are used. In recent years, detachable HS prefabricated steel bar truss decking has also appeared. After removing the plastic formwork, a completely cement-based surface is exposed, achieving an effect similar to aluminum formwork. No plastic or metal parts are left exposed; the bottom surface of the concrete slab is smooth and flat, the same as ordinary cast-in-place slabs, making it convenient for fine decoration.

Conclusion: Steel-structured residential buildings are a type of green, eco-friendly construction. They are light in weight, require lower foundation costs, take up less land, and can be highly industrialized. They also look good, have a short construction period, perform well in earthquakes, and offer fast returns on investment with less environmental impact. Overall, they not only make good economic sense but also point the way forward for residential construction.That said, there are still some limitations: high upfront costs and strict technical requirements for construction. But as supporting technologies improve and construction systems become more standardized, steel-structured residential buildings will gradually overcome these industry challenges and become a core option for green, low-carbon residential construction in the future.