Structural Steel Design – Everything you need to know

Technological advancements dominate the times we live in. From simple stone and wood buildings to massive metal towers, architecture has changed dramatically over the past century. Steel is considered a green product because it is completely recyclable. For a brand new residential or commercial building, the builder can purchase recycled steel. Some structures reach record heights, bridges span great rivers, and some sculptures unite countries.

Steel is essential to the creation of many of the world’s most recognizable buildings. For budding civil engineers, steel construction is an important subject. Steel is an alloy of iron and carbon. Because of its strength and tensile strength, it is used in construction and other applications. Steel is added to concrete because it has tensile strength; without it, concrete has high compressive strength.

What is a steel structure?

The term steel structure refers to the metal arrangement developed with steel structural members connected to support loads and provide complete rigidity. This construction is reliable and uses less raw materials than other forms of structures such as concrete and wood structures due to the high elasticity of steel.

Steel is a material used in almost every type of modern building structure, including airport terminals, large industrial plants, high-rise buildings, equipment support systems, bridges, buildings, heavy industrial structures and pipeline supports. Steel manufactured with suitable shape and chemical composition to meet the conditions of the construction is considered as structural steel.

Steel compartments can have various shapes, heights and meters, depending on the specifications of the respective project. Some shapes can be produced by hot or cold rolling, while others can be produced by joining flat or bent sheets together. Some common shapes are plates, I-beams, U-channels, and angles.

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Benefits of steel structure for residential construction

There are many benefits of using steel in residential construction. These include:

Strength and design freedom

In terms of color, texture and shape, steel allows architects to be more creative. Because it combines resilience, strength, beauty, precision and versatility, it gives architects more flexibility to experiment with concepts and develop new solutions. Large open areas without intermediate columns or load-bearing walls are possible because steel can be transported over long distances. It stands out for its flexibility when bent to a certain radius, forming segmental curves or free-form combinations for facades, domes or canopies. Steel is less affected by on-site variations because it is factory finished to the most stringent requirements under well-managed conditions.

Fast, efficient and resourceful

In any season, steel can be assembled quickly and efficiently. With little on-site labor, components are prefabricated off-site. Depending on the size of the project, the entire frame can be built in days rather than weeks, resulting in a construction time that is 20 to 40 percent shorter than on-site construction.

For single-family homes in more difficult locations, steel typically allows for fewer points of contact with the ground, minimizing the number of excavations required. Smaller, simpler foundations can be built due to the lower weight of structural steel compared to alternative framing materials such as concrete.

These performance improvements provide significant financial and resource efficiency benefits, such as faster project schedules, reduced site management costs and a faster return on investment. Below 150°C there is little change in the properties of steel. Therefore, in high temperature working places, steel structures are suitable but insulation panels should be used under well-controlled conditions.

Adaptable and accessible

The function of a building can change dramatically and quickly. Tenants may request modifications that significantly increase floor loads. Depending on the needs and capacity of the space, it may be necessary to move walls to create new interior layouts. Steel structures allow for such adjustments.

Non-composite steel beams can be combined with existing floor slabs, can add covers to the beams for increased strength, and can easily be reinforced, supplemented with additional framing, or even moved to different locations, beams and joists, support different loads.

All existing communications, computer networking and electrical wiring systems can be easily accessed and modified using the steel structure and floor system.

Endlessly recyclable

When a steel-framed building is dismantled, its components can be recycled or returned to the closed-loop recycling system used by the steel industry. Steel can be recycled indefinitely without losing any of its qualities. Nothing is wasted. Since about 30% of new steel today is made from recycled steel, steel reduces the need for raw natural resources.

Increased fire resistance

The industry now has a good understanding of how steel buildings react to fire through extensive testing of steel structures and whole steel structures. Modern design and analysis methods enable precise determination of the fire resistance requirements of steel frame structures, often resulting in a significant reduction in the required level of fire protection.

Earthquake Resistance

Earthquakes are unpredictable in their magnitude, frequency, duration, and location. Because of their ductile and flexible nature, steel is the material of choice for design. Under great stress, it bends rather than breaks or disintegrates. The primary purpose of many beam-to-column connections in steel buildings is to support gravity loads.

However, they can also withstand significant lateral loads caused by wind and earthquakes. They can withstand high winds, earthquakes, hurricanes, and heavy snowfalls, among other severe impacts and adverse weather conditions. Termites, insects, and mold do not affect them; unlike wooden frames, they are also resistant to corrosion.

Lighter and less environmental impact

The environmental impact of the construction is lessened by the fact that steel constructions can often be substantially lighter than concrete counterparts and need less extensive foundations. The utilisation of transportation and fuel is decreased because they use fewer and lighter materials. If necessary, steel piling foundations can be removed, recycled, or reused at the end of a building’s life, leaving no trash behind.

Steel is energy-efficient because heat quickly escapes from steel roofing, keeping homes cool in hotter climates. For better heat retention in cold areas, double steel panel walls can be adequately insulated.

Characteristics of steel structure

The following are some of the major properties of steel structures.

Steel structures are strong and have high load-bearing capacity

Steel is characterized by excellent earthquake resistance, good impact resistance and dynamic load resistance, and high structural reliability. Steel has a homogeneous internal structure, similar to the structure of an isotropic homogeneous object. The mathematical theory is more consistent with the actual working performance of steel structures. Therefore, steel structures are very reliable.

The ratio of density and yield strength is significantly lower than that of concrete and wood. As a result, considering the same stress parameters, the steel structure has small cross-section, is light, easy to transport and install, and is suitable for large spans and high heights.

Steel structures are heat resistant but not fire resistant. Protect the surface of the structure from temperatures above 150°C.

Steel loses most of its strength and modulus of elasticity between 300 and 400°C, and at about 600°C the strength of steel tends to zero. Refractory materials must protect steel structures in buildings with specific fire safety criteria to increase the level of fire resistance.

Steel structures have low corrosion resistance.

It is susceptible to rust, especially in high humidity and corrosive environments. Generally, rust removal, galvanizing, painting and periodic maintenance are required for steel structures. To prevent corrosion, specific precautions such as “zinc block anode protection” are required for offshore platform structures immersed in seawater.

Highly mechanized steel structure manufacturing and installation process

Steel structures are rapidly manufactured in the factory and assembled on site. High production efficiency, rapid on-site assembly and minimal construction time are all advantages of mechanized steel structure manufacturing plants. The most industrialized structures are made of steel.

High strength and seismic resistance

Steel structures have advantages over conventional reinforced concrete structures, including superior heterogeneity, high strength, fast construction, good seismic resilience and high recycling rate. The mass of steel elements is light under the same stress conditions because steel has many times greater strength and elastic modulus than masonry and concrete. Steel structures are flexible structures that make it possible to identify hazards at an early stage and prevent them due to their expected significant deformations from the point of view of destruction.

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Methods of steel structure design

Structural steel design can be done in three different ways: simple, continuous, or semi-continuous. To simplify design calculations, the joints of the structure are assumed to be either hinged or flexible.
Simple designs idealize their joints as perfect pins.

Regardless of the time they are applied, continuous innovation assumes that the joints are rigid and that the connected elements cannot rotate relative to each other. Most designs created today are based on one of these two assumptions, although a semi-continuous plan is now possible, a more practical option.

Below are the methods of designing steel structures:

Simple design of steel structure

The most common method is simple design, which is still used frequently. Bracing or, in some multi-storey buildings, concrete cores are often used to provide structural resilience to lateral and sway loads.

The designer should take into account the assumptions of the overall response and ensure that connections are detailed to prevent the occurrence of moments that could adversely affect the performance of the structure.

The types of details that meet this condition have been proven by many years of experience, the designer should take into account the typical connections at joints in simple structures.

Continuous design of steel structures

The moment transfer combinations between members are expected to be rigid in continuous design. The action of the frame is what keeps the frame from swaying. Frame analysis is usually performed using software because continuous design is more complex than basic design.

Continuous frames must be designed with realistic sample load combinations in mind. Depending on whether the frame is designed elastically or plastically, the connections between members must have different properties.

In flexible design, joints must have sufficient rotational stiffness to ensure that the forces and moments distributed throughout the frame do not deviate significantly from the calculated values. The assembly must be sufficiently rigid to withstand the moments, forces and shears generated by the frame analysis.

The strength of the assembly, not its stiffness, is the most important factor in plastics design for calculating the ultimate load capacity. The presence of plastic hinges in assemblies or components will depend on the strength of the assembly, which will have a significant impact on how the structure collapses.

If joints are designed to be hinged, the joints must be determined to have sufficient flexibility to support the rotational movements that occur. When calculating the sway stability, sway deflection and deflection of the beam, the stiffness of the joint will be very important.

Semi-continuous design of steel structure

Semi-continuous design is actually more complex than basic or continuous design because the actual response of the assembly is more accurately represented. Developing analysis procedures that closely follow actual assembly behavior is laborious and not suitable for routine design.

For braced and unbraced frames, there are two simplified procedures briefly described below. Unbraced frames provide lateral load resistance from bending moments in columns and beams, while braced frames use bracing or core systems to provide this resistance.

How to design a steel structure?

1. Determine whether steel structure is suitable for the building

Steel structures are often used for high-rise, large-span, complex frame, heavy load or crane requirements, high vibration, high tightness, movable or frequently assembled and dismantled buildings.

The buildings include permanent structures as well as stadiums, opera houses, bridges, television towers, factories, warehouses, garages and hangars. This corresponds to the characteristics of steel structures.

2. Structure selection and layout

With the variety of factors involved, the layout and selection of structures must be carried out with the help of professional engineers. It is necessary to highlight the “conceptual design” throughout the design of steel structures, because it is very important for the selection and layout of structures. The mechanical relationship between the main structural system and its subsystems, the failure mechanism, the earthquake damage, the experimental phenomena and the engineering experience can all be used to generate design ideas for problems that are difficult to perform precise rational analysis.

Using a broad perspective, decide on the specific configuration and measures of the control structure.
Conceptual design can support the rapid and efficient initial design, comparison and selection. During the selection process, many steel structure parameters must be considered. Where there is a lot of snow on the roof, the roof curvature must allow for snow sliding. Similar considerations must be made in areas with high rainfall.

A supporting frame will be more cost effective than a frame with only connected nodes if the construction is approved. The main components of a cable-stayed or membrane cable system with large roof spans may be selected for the structure. Steel-concrete composite structures are commonly used in the design of high-rise steel buildings.

Depending on the system characteristics, load distribution and properties, the structural arrangement must be carefully considered. In general, the mechanical model must be clear and the stiffness must be uniform. Reduce the area of ​​influence of heavy loads or moving loads as much as possible to ensure that they are transmitted to the foundation as quickly as possible.

Anti-skid backing must be evenly distributed between the columns. The center should be as close as possible to the line of action of the lateral force. Otherwise, the structure must be designed in a torsional manner. Some lines of defense are required on the opposite side of the structure. On the floor plan of a frame structure, the direction of load transfer of the secondary beam can sometimes be changed to meet different needs.

Secondary beams are often arranged in short aisles to reduce the cross-section, but this increases the cross-section of the main beam and reduces the clear floor height, sometimes overwhelming the side columns of the top floor. To support the main beam and piers at this stage, the secondary beam can be supported on a shorter main beam.

3. Structural analysis

At the moment, linear elastic analysis is typically used in the actual design of steel structures, with p-Δ, and p-δ being taken into account when the conditions permit. Recent finite element software may take steel’s elastic-plastic properties and geometric nonlinearity into consideration to some extent. This creates the necessary framework for a more detailed analysis structure.

Not all structures require software; typical structures can be discovered in reference books like mechanical manuals to get internal forces and deformations without using the software.

4. Engineering judgment

The output should include “engineering judgment” if the structural software is used properly. For example, calculating the overall shear force, the periodicity of each direction, the deformation properties, etc. Deciding whether to modify the model for a new analysis or the calculation results are based on “engineering decisions”. The conditions applicable to different software will be different.
Beginners must understand them perfectly.

The calculations used in engineering and mechanical calculations often differ in specific ways. However, existing conditions, concepts and structures will be applied to ensure the safety of the structure. Sometimes assumptions with serious errors will be used to achieve practical design methods.

Quantitative calculations are not as important in steel structure design as the concept of “relevant conditions, concepts and structures”. Engineers should not abuse the use of structural software. Engineering disasters of this type can be avoided by careful attention to conceptual design and engineering evaluation.

5. Component design

Material selection is essential when designing components. Q235, comparable to A3 and Q345 are commonly used. To simplify project management, a single grade of steel is often used for the main structure. A component made from a mixture of steels of different strengths may also be selected for financial reasons. Q345 may be selected when strength is the deciding factor. Q235 would be a better choice if it were stable.

Current theory uses elastic methods to evaluate cross sections during component design. The flexible approach to calculating internal forces of structures is not suitable for this. All current structural software has the function of post-processing section verification. Some software now has the ability to upgrade from the provided section library for components that fail the test due to advances in software technology. And automatically review and verify calculations until successful, just like SAP 2000. One of the goals of section optimization design is to achieve this. For architects, this significantly reduces work.

6. Drawing preparation

The steel structure design drawing is divided into two stages: is the detailed construction drawing and the design drawing company provides the design sketch. According to the design drawing, the steel structure manufacturing company usually makes detailed construction drawings; however, the design company sometimes does this. The preparation of detailed construction drawings is based on the design drawing.
The drawing and its content must be completed.

In order to facilitate the process of creating detailed construction drawings that accurately reflect the design intention, the design drawing must clearly show the design basis, loads, technical data, design requirements, structural layout, selection of component cross-sections and main node structures. A list should be used to show the main documents. Detailed construction drawings are often called layout drawings or shop drawings.

The design should be suitable for direct manufacture and processing in the shop. A complete list of materials should be attached and any additional non-identical component units should be drawn and described individually.

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