8 basic knowledge of steel structure-Part One
Characteristics of steel structure
- Lighter weight.
- Higher reliability.
- Good vibration (shock) and impact resistance.
- Relatively highdegree of industrialization of steel structure manufacturing.
- The steel structure can be assembled accurately and quickly.
- Easy to be made as a sealed structure.
- Easy to be corrode
- Poor fire resistance
Steel grades and properties of commonly used steel structures
- Carbon structural steel：Q195、Q215、Q235, etc.
- Low-alloy high-strength structural steel.
- High-quality carbon structural steel and alloy structural steel
- Steel for special purpose.
The principle of material selection for steel structure
The principle of material selection for steel structures is to ensure the bearing capacity of the load-bearing structure and prevent brittle failure under certain conditions. It is considered comprehensively according to the importance of the structure, load characteristics, structural form, stress state, connection method, steel thickness and working environment, etc.
The four steel models proposed in the "Code for Design of Steel Structures" GB50017-2003 are the models that are "suitable" for use. They are the first choice when conditions permit. The use of other models is not prohibited, as long as the steel used meets the requirements of the specification.
Main steel structure technical content
High-rise steel structure technology
According to the building height and design requirements, the frame, frame support, tube and giant frame structure are respectively adopted, and its components can be steel, rigid reinforced concrete or steel tube concrete. Steel components are light and have good ductility, and can be welded or rolled, suitable for ultra-high-rise buildings. Rigid reinforced concrete components have high rigidity and good fire resistance, suitable for middle and high-rise buildings or bottom structures. Steel tube concrete construction is simple, only used for column structure.
Space steel structure technology
The space steel structure has light weight, high rigidity, beautiful appearance and fast construction speed. Spherical joint flat grids, multi-layer variable cross-section grids and reticulated shells with steel pipes as members are the structural types with the largest amount of space steel structures. It has the advantages of large space rigidity and low steel consumption. It can provide complete CAD in design, construction and inspection procedures. In addition to the grid structure, the space structure also includes a large-span suspension cable structure, a cable-membrane structure, and so on.
Light steel structure technology
A new structural form composed of light-weight colored steel plates and roof enclosure structures. A light steel structure system composed of large section thin-walled H-shaped steel wall beams and roof purlins welded or rolled by steel plates of more than 5mm, round steel made of flexible support system and high-strength bolt connection, the column distance can be from 6m to 9m, and the span can be up to 30m or more, the height can reach more than ten meters, and can be equipped with light cranes. The steel consumption is 20-30kg/m2. Now there are standardized design procedures and specialized production enterprises, with good product quality, fast installation speed, light weight, low investment, construction is not restricted by seasons, and it is suitable for all kinds of light industrial plants.
Steel-concrete composite structure technology
The load-bearing structure of beams and columns composed of section steel or steel management and concrete components is a steel-concrete composite structure, and its application scope has been expanding in recent years. The combined structure has the advantages of both steel and concrete, with high overall strength, good rigidity, and good seismic performance. When the outer concrete structure is used, it has good fire resistance and corrosion resistance. Combined structural members can generally reduce the amount of steel used by 15-20%. The combined floor and concrete-filled steel tube components also have the advantages of convenient and fast construction, and great potential for promotion. It is suitable for frame beams, columns and floors of multi-storey or high-rise buildings with larger loads, as well as industrial building columns and floors, etc.
High-strength bolt connection and welding technology
High-strength bolts transmit stress through friction and are composed of bolts, nuts and washers. High-strength bolt connection has the advantages of simple construction, flexible removal, high bearing capacity, good fatigue resistance, good self-locking performance, and high safety. The project has replaced riveting and partial welding, and has become the main connection method in the production and installation of steel structures. For steel components made in the workshop, automatic multi-wire arc submerged welding shall be used for thick plates. During on-site installation and construction, semi-automatic welding technology, gas shielded flux cored wire and self-shielded flux cored wire technology should be used.
Steel structure protection technology
Steel structure protection includes fire protection, anti-corrosion, and anti-rust. Generally, anti-rust treatment is not required after the treatment of fire-resistant paint, but anti-corrosion treatment is still required in buildings with corrosive gas. There are many types of domestic fireproof coatings, such as TN series, MC-10, etc. Among them, MC-10 fireproof coatings include alkyd enamel, chlorinated rubber paint, fluororubber paint and chlorosulfonated paint. During construction, appropriate paint and coating thickness should be selected according to the steel structure type, fire resistance grade requirements and environmental requirements.
Goals and measures of steel structure
Steel structure projects involve a wide range of areas and are technically difficult. National and industry standards must be followed in the promotion and application. Local construction administrative departments should pay attention to the construction of the specialization stage of steel structure engineering, organize the training of quality inspection teams, and summarize work practices and new technology applications in a timely manner. Mass academic groups should cooperate with the development of steel structure technology, extensively carry out domestic and foreign academic exchanges and training activities, and actively improve the overall level of steel structure design, production, construction and installation technology, and rewards can be improved in the near future.
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In this article; we explain about steel structure, why it is the best choice for residential construction, the characteristics of steel structure, the methods of design, and how to design a steel structure.
The advances in technology rule the era in which we live. From simple stone and wood buildings to enormous metal towers, architecture has changed considerably in the last century. Steel is considered a green product because it is entirely recyclable. For a brand-new home or business structure, the builder can purchase recycled steel. Some structures reach record heights, bridges cross the most significant rivers, and some sculptures bring together nations. Steel was essential to creating many of the world’s most recognisable buildings.
For aspiring civil engineers, steel structures are a crucial topic. Steel is an alloy of iron and carbon. Due to its hardness and tensile strength, it is utilised in construction and other applications. Steel is added to concrete because it has tensile strength; without it, concrete has a great deal of compression strength.
See also: Modulus of elasticity formulaWhat is a steel structure?
The term steel structure refers to a metal layout developed with structural steel pieces connected to support loads and provide comprehensive stiffness. This construction is reliable and employs fewer raw materials than different forms of structure like concrete and timber structures because of the high resilience degree of steel.
Steel is a material that is employed in almost every kind of structure in a contemporary building, including airport terminals, big industrial factories, high-rise constructions, equipment support systems, bridges, buildings, heavy industrial constructions, and pipe stands.
Steel fabricated with a proper form and chemical composition to satisfy the conditions of a project is understood as structural steel.
The steel compartments may be available in various shapes, heights, and meters, depending on the relevant project specifications. Some may be constructed by hot or cold rolling, while others may be built by joining flat or bent plates. Some common shapes are Plate, I-beam, Channels, and Angles.
See also: About structure designBenefits 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 colour, texture, and shape, steel gives architects a more creative look. Because it combines resilience, durability, beauty, accuracy, and malleability, it offers architects more flexibility to experiment with concepts and develop new solutions. Large open expanses without intermediate columns or load-bearing walls result from steel’s long-spanning capacity. It stands out for having the flexibility to bend to a certain radius, forming segmented curves or free-form combinations for facades, arches, or domes. Steel is less susceptible to on-site variability since it is factory-finished to the tightest requirements under well-regulated conditions.
Fast, efficient and resourceful
In any season, steel can be assembled fast and effectively. With little on-site labour, components are pre-manufactured off-site. Depending on the size of a project, an entire frame can be constructed in days instead of weeks, which results in a 20% to 40% shorter construction period than on-site construction.
For single homes in more challenging locations, steel frequently permits fewer contact points with the land, minimising the amount of excavation needed. A smaller, more straightforward foundation is possible due to structural steel’s lesser weight than alternative framing materials like concrete. These executional efficiency improvements translate to significant resource efficiencies and financial advantages, such as quicker project schedules, lower site management expenses, and an earlier return on investment.
Less than 150 °C causes little change in the steel’s characteristics. In hot workplaces, steel structures are therefore appropriate, but heat insulation panels should be used to
Adaptable and accessible
A building’s function can alter drastically and quickly today. A tenant can request modifications that considerably raise the floor load. Depending on the needs and space consumption, walls may need to be moved to create new interior layouts. Steel construction allows for such adjustments.
Non-composite steel beams can be combined with the floor slab already in place, cover plates can be added to the beams to boost strength, and beams and girders can easily be reinforced, supplemented with more framework, or even moved to handle different loads. Existing communication, computer networking, and electrical wiring may all be easily accessed and modified because of steel framing and floor systems.
When a steel-framed building is taken down, its parts can either be recycled or sent back into the closed-loop recycling system utilised by the steel industry. Steel may be recycled indefinitely without losing any of its qualities. Nothing goes to waste. Because about 30% of today’s new steel is made from recycled steel, steel reduces the need for natural raw resource use.
Added fire resistance
The industry now has a solid grasp of how steel buildings react to fire because of extensive testing of structural steelwork and whole steel structures. Modern design and analytical methods enable exact specification of fire protection needs for steel-framed structures, frequently leading to significant reductions in the amount of fire protection needed.
In terms of size, frequency, length of time, and location, earthquakes are unexpected. Because it is malleable and flexible by nature, steel is the material of choice for design. Under heavy pressures, it flexes as opposed to breaking or disintegrating. The primary purpose of many beam-to-column connections in steel buildings is to support gravity loads. They can, however, also withstand substantial lateral loads caused by wind and earthquakes.
It can withstand severe winds, earthquakes, hurricanes, and heavy snowfall, among other extreme forces and adverse weather conditions. Termites, bugs, mildew, mould, and fungi do not affect them; unlike wood 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
Excellent seismic performance, suitability for bearing impact and dynamic loads, and high structural reliability are all attributes of steel.
Steel has a consistent internal structure that is similar to that of an isotropic homogeneous body. The mathematical theory more closely matches the steel structure’s actual working performance. The steel structure is, therefore, very reliable. The ratio of density to yield strength is considerably lower than that of concrete and wood. Accordingly, given the same stress parameters, the steel structure has a small section, is lightweight, is simple to carry and install, and is appropriate for wide spans and high heights.
The steel structure is heat-resistant but not fire-resistant shield the structure’s surface from temperatures above 150°C
Steel loses a substantial amount of its strength and elastic modulus between the temperatures of 300 and 400 °C, and at about 600 °C, steel strength tends to zero. Refractory materials must shield the steel structure in buildings with specific fire safety criteria to increase the fire resistance level.
Steel structures have weak resistance to corrosion
It easily rusts, especially in an atmosphere with high humidity and corrosion. Typically, de-rusting, galvanising, painting, and routine maintenance are required for steel structures. To stop corrosion, specific precautions like “zinc block anode protection” are needed for offshore platform structures submerged in seawater.
Steel structure installation and manufacturing processes are highly mechanised
Steel structural components are quickly produced in factories and put together on site. High production efficiency, quick site assembly and minimal building time are all benefits of factory mechanised manufacturing of steel structural components. The most industrialised structure is made of steel.
High strength and seismic resistance
Steel structures have advantages over typical reinforced concrete structures, including superior inhomogeneity, high strength, quick construction, good seismic resilience, and a high recycling rate. The mass of steel members is light under the same stress conditions because steel has strength and elastic modulus that are several times higher than those of masonry and concrete. The steel structure is a flexible damage construction that can identify danger early on and prevent it due to its substantial predicted deformation from the viewpoint of being destroyed.
Methods of steel structure design
The design of a steel structure can be done in one of three ways: simple, continuous, or semi-continuous. To simplify design calculations, joints in structures have been considered to behave as either pinned or flexible.
Simple designs idealise their joints as flawless pins. Regardless of the applied moment, continuous innovation presumes that joints are rigid and that connected elements cannot rotate relative to one another. Majority of designs created today rely on one of these two presumptions, although a semi-continuous plan, a more practical option, is now feasible.
Following are the methods of design of steel structure:
Simple design of steel structure
The most conventional method is a simple design, which is still used frequently. Bracing or, in some multi-story buildings, concrete cores are typically used to ensure a structure’s resilience to lateral loads and sway.
The designer must be aware of the joint response presumptions and make sure that the connections are detailed in a manner that prevents any moments from arising that can negatively impact the structure’s performance.
The types of details that meet this condition have been demonstrated through many years of experience, and the designer should take note of the typical connections on joints in uncomplicated construction.
Continuous design of steel structures
Joints that transfer moments between parts are supposed to be stiff in continuous design. Frame action is what keeps the frame from swaying.
The frame analysis is frequently done using the software since the continuous design is more sophisticated than the basic design. Continuous frames must be designed with realistic pattern loading combinations in mind.
Depending on whether the frame is designed using an elastic or a plastic method, the connections between the members must have differing properties.
In a flexible design, the joints must have enough rotational stiffness to ensure that the forces and moments distributed throughout the frame don’t diverge noticeably from the calculated values.
The joint needs to be strong enough to support the moments, forces, and shears that result from the frame analysis.
The strength of the joint, not its stiffness, is the most crucial factor in plastic design for calculating the maximum load capacity. Whether plastic hinges are found in the joints or the members will depend on how strong the joint is, which will significantly impact how the structure collapses.
If joints are intended to have hinges, the joint must be specified with enough ductility to support the ensuing rotations. When computing sway stability, sway deflections, and beam deflections, the stiffness of the joints will be crucial.
Semi-continuous design of steel structure
True semi-continuous design is more complicated than basic or continuous design because the actual joint response is more accurately represented. The development of analytical routines that closely track the actual connection behaviour is extremely labour-intensive and not suitable for routine design.
For both braced and unbraced frames, there are two streamlined processes, which are briefly discussed below. Unbraced frames produce lateral load resistance from the bending moments in the columns and beams, whereas braced frames use a bracing system or a core to generate this resistance.
How to design a steel structure?
1. Determine whether steel structure is suitable for the building
Steel structures are typically utilised for high-rise, large-span, complicated frames, heavy load or crane lifting, huge vibration, high tightness requirements, moveable, or frequently put together and taken apart buildings.
Buildings include permanent structures as well as stadiums, opera houses, bridges, TV towers, factories, warehouses, garages, and hangars. This fits in with the steel structure’s characteristics.
2. Structure selection and layout
Given the variety of factors involved, the layout and selection of the structure should be made with the help of professional engineers. It is necessary to highlight “conceptual design” throughout the entire steel structure design process since it is crucial for the selection and layout of the structure.
The mechanical relationship between the primary structural system and its subsystems, failure mechanisms, earthquake damage, experimental phenomena, and engineering experience can all be used to generate design ideas for issues for which it is difficult to conduct a precise rational analysis. Using a broad perspective, decide the configuration and specific measurements of the control structure. Conceptual design can help quick and efficient early conception, comparison, and selection.
During the selection process, many steel structure parameters should be considered. When there is a lot of snow on the roof, the roof curvature should encourage snow sliding. Areas with high rainfall are given similar considerations. A support frame will be more cost-effective than one with only connected nodes if the construction is approved. The major components of a suspension cable or cable-membrane structure system with wide roof spans can be chosen for structures. Steel-concrete composite structures are frequently used in the design of high-rise steel buildings.
According to the system’s characteristics, load distribution, and nature, the structure’s layout should be carefully studied. Generally speaking, the mechanical model should be unambiguous, and the stiffness should be uniform. Reduce the influence range of heavy loads or moving loads as much as you can to ensure that they are transmitted to the foundation as quickly as feasible. Anti-slide support should be distributed equally among columns. The centre should be as near to the lateral force’s action line as possible. If not, the structure should be thought about in torsion. There should be several defence lines on the structure’s opposite side.
On the frame structure’s floor plan, the load transfer direction of the secondary beams can occasionally be changed to accommodate various needs. The subsidiary beams are typically organised in a short path to decrease the cross-section, but this increases the section of the main beam and lowers the net floor height, which can occasionally overwhelm the side columns on the top floor. To conserve the main beam and pillars at this point, 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.
The output result should include “engineered judgement” if the structural software is used correctly. For instance, calculating the overall shear force, the period of each direction, the deformation properties, etc. Decide whether to change the model for new analysis or the calculation result based on the “engineering decision.” The conditions that apply to various software vary. The novice should comprehend completely. The calculations used in engineering and mechanical calculations frequently diverge in specific ways.
However, applicable conditions, concepts, and structures will be adopted to ensure the structure’s safety. Sometimes assumptions with significant errors will be used to obtain practical design methods. Quantitative computation is not as crucial in the design of steel structures as the notion of “relevant conditions, concept, and structure”. Engineers should not overuse the use of structural software. Engineering disasters of this nature can be prevented by paying close attention to conceptual design and engineering judgment.
5. Component design
The selection of materials comes first when designing components. Q235, comparable to an A3, and Q345 are frequently used. To simplify project administration, the primary structure often uses a single steel grade. It is also feasible to select a part that is a blend of steel with various strengths for financial reasons. Q345 can be chosen when the intensity controls the situation. Q235 will be a better option if it is steady. The current theory uses the elastic-plastic approach to assess the section when designing components. The flexible approach to structural internal force computation does not match this.
All of the structural software programs available today have cross-section verification post-processing features. Some software now has the option to move up one level from the provided cross-section library for components that failed the test due to advancements in program technology. And automatically re-examine and verify the calculation till it is successful, like sap2000. One of the purposes of cross-section optimisation design is to achieve this. For architects, it significantly decreases work.
6. Drawing preparation
The design drawing for a steel structure is split into two stages: the construction detail drawing, and the design drawing company provides the design sketch. According to the design drawing, the steel structure manufacturing firm typically prepares the construction detail drawing; however, the design company occasionally does so.
The creation of detailed construction drawings is based on design drawings. The drawing and its contents must be finished. To make the process of creating detailed construction drawings that accurately reflect the design intent easier, the design drawing should clearly express the design basis, load data, technical data, design requirements, structural arrangement, component cross-section selection, and main node structure. A list should be used to display the primary materials.
Detailed construction drawings are often known as stakeout drawings or processing drawings. The drawing must be adequate for direct manufacture and workshop processing. A complete list of materials must be attached, and any additional component units that are not the same must be drawn and described individually.
Steel structure design: Software
In earlier times, steel structure design creation was done manually by drawing hundreds of sketches on paper. It used to be a tedious and time-consuming process. The advancements in technology have led to the introduction of various PC steel structure design software. Designers these days used these specialised software to get the designs ready quickly and efficiently. These engineering design software help in creating the most descriptive and detailed 3D models of steel structures. In fact, these software are so advanced that anyone with design capabilities can use them to create complex steel structure designs easily. Some of the best steel structure design software you can use include Advance Steel – Autodesk, Autodesk Revit, RAM Steel, and Edilus Steel.
Steel structures are highly suitable for residential buildings, towers, bridges, terminals, etc. It also benefits the house owners as it has fire and earthquake resistance. Additionally, it’s cost-effective and recommended for the construction of heavy industrial buildings.
Why is steel used in structural design?
Steel frame structures are very flexible. This offers complete design flexibility. Consequently, it is feasible to create a distinctive building. One of the main reasons structural steel is a good option in civil engineering is that this freedom cannot be attained with any other building material.
Which code is used for the design of steel structures?
The basic code for general steel structure building, known as IS 800, serves as the foundation for all structural designs and influences many other regulations controlling the design of other unique steel structures, including towers, chimneys, silos, bridges, etc.
What is the basic principle of structural design?
It is a fundamental principle of structures that they are built to resist external loads while remaining stable. Statics is the study of stationary forces acting on stiff objects and their causes and effects. A structure is referred to as a 'static body' when it is still or in balance.
What are the basics of structural design?
For the design of any structure, there are primarily 5 steps that must be taken. Modeling comes first, followed by load analysis, structural analysis, structural design, and detailing.
What is the importance of steel design?
It is used mainly because of its adaptability, sustainability, and flexibility. It is also a very affordable material. Steel frequently offers a solution when other materials are inadequate because of its high strength-to-weight ratio.
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