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Steel trusses are structural frameworks constructed from steel, mainly triangular in shape. They are generally used to support roofs, bridges, and towers. The triangle is the preferred geometric form since it evenly distributes weight and provides stability. Steel trusses are known for their strength, durability, and ability to span long distances.
There are several key types of steel trusses, all having unique characteristics and applications. These include:
The Howe truss consists of diagonal members that slope down from the top chords to the bottom chords, forming a triangular pattern. The vertical members stress the structure's load-carrying capacity. Howe trusses are widely used in floor systems, bridges, and roofing applications, as they effectively distribute loads and offer good structural stability.
The Queen Anne truss is distinguished by its unique configuration, which involves vertical and diagonal members. The diagonal members, which are proud of the bottom chord, create a series of triangular shapes along the truss. On the other hand, the vertical members enhance the structure's load-carrying capacity. Queen Anne trusses are commonly used in historical buildings and decorative roofs due to their architectural appeal.
The Fink truss has a distinctive zigzag pattern of diagonal members. The diagonals create smaller triangular sections within the truss, efficiently distributing the roof's weight to the supporting walls or columns. Fink trusses are commonly used in prefabricated buildings, agricultural structures, and residential roofs because they provide good load distribution over long spans.
A fan truss is characterized by diagonal members that radiate from a central point or "joint," resembling a fan's structure. The horizontal ties keep the structure stable. Fan trusses are mainly used in bridge construction and support systems, as they effectively handle dynamic loads and are visually appealing.
Material Properties
Structural steel used in making steel trusses has a high tensile strength and stiffness. Therefore, it can withstand large forces without deforming. In addition, it is ductile, meaning it can stretch or change shape without breaking. This property allows trusses to absorb energy from loads, enhancing the overall structure's safety during extreme weather conditions. Usually, steel grades like ASTM A36 or A992 are common for truss construction due to their balance of strength and weldability.
Load-carrying capacity
Steel trusses are generally designed to hold specific loads, including dead loads (permanent weights such as the building's own weight) and live loads (temporary weights like people or furniture). In addition, other considerations are wind and seismic loads in regions prone to these forces. When sourcing steel trusses, it is crucial to consider the intended use and span length since these factors influence the required load capacity.
Corrosion Resistance
Steel is naturally prone to rust when exposed to moisture. However, protective measures such as galvanization, powder coating, or paint application significantly improve the truss's lifespan. Galvanization involves coating the steel with a thin layer of zinc, which acts as a barrier between the moisture and the steel. In addition, trusses in coastal areas or environments with high humidity require enhanced corrosion protection due to the increased risk of rust.
Connection Details
Steel trusses mainly make joints and connections using welds, bolts, or rivets. These connections significantly influence the structure's integrity and load-carrying capacity. For instance, welded connections provide a continuous strength, while bolted connections allow for easier assembly and potential disassembly. The selection of connection type depends on the design requirements and the truss's intended use.
Regular Inspections
It is critical to regularly inspect steel trusses for signs of wear, rust, or structural damage. Common signs to watch out for include cracks, bent members, and loose bolts or rivets. Inspections are usually carried out after extreme weather conditions or heavy usage. Moreover, periodic inspections at predetermined intervals (e.g., quarterly or annually) based on industry standards are crucial for long-term maintenance.
Corrosion Protection
Steel trusses are commonly known to be prone to rust and corrosion, especially in outdoor applications. The application of protective coatings such as paint, galvanization, or powder coating is indispensable in prolonging the life of steel trusses. Coatings act as barriers to moisture and environmental elements that lead to corrosion. In addition, protective coatings should be reapplied whenever they begin showing signs of wear, peeling, or cracking.
Drainage and Moisture Control
Moisture accumulation on trusses can lead to corrosion. Therefore, it is critical to ensure adequate drainage and moisture control on and around trusses. Water ponds should be drained and any debris removed from truss surfaces or roofs that may impede water flow. Moreover, it is good practice to regularly check for leaks in roofing systems that may contribute to moisture accumulation.
Structural Support
Steel trusses are fabricated to support specified loads. Therefore, it is necessary to ensure that trusses do not carry more weight than they can support. This means avoiding the accumulation of snow, debris, or vegetation on truss surfaces. In construction and building applications, planned preventive maintenance checks are necessary for identifying and addressing issues that may lead to overloading or undermining the structure's support system.
repair and Replacement of Damaged Elements
Any signs of fatigue or structural damage occurring in truss members should be addressed immediately. Early intervention helps to avoid the need to completely replace a truss. In cases where damage is extensive or beyond repair, consider replacing individual members or the entire truss with a new one. Standardized steel grades are widely used for replacement to maintain structural integrity.
Steel trusses are widely used in bridge construction, as they offer strength and rigidity while supporting large spans over water and valleys conveniently. Truss bridges distribute loads efficiently; therefore, they are ideal for heavy vehicular traffic and railroad usage. Some common types of truss bridges include Howe, Queen Anne, Fink, and Pratt. Each type is adapted to specific application requirements and aesthetic values.
Large-span structures commonly found in warehouses, factories, and power plants use steel trusses to make the roofs. The open interior space made possible by trusses allows for flexible usage, equipment installation, and unobstructed workspace. Steel trusses also provide the required structural stability to support heavy loads, including machinery and stored products.
Trusses have also become popular in agricultural buildings like barns and livestock shelters because of their ability to span wide openings, accommodating equipment and animals. They are equally well-suited for constructing greenhouse roofs, as they provide a lightweight yet sturdy framework that supports the structure while allowing ample sunlight.
Multipurpose arenas, stadiums, and exhibition centres use trusses to construct large, open roofs that support the structures' architectural appeal and functional requirements. These trusses allow such spaces to host grand events, sporting occasions, and exhibitions without the need for numerous internal columns that may impede movement. In addition, the truss designs enable them to hold up lighting, scoreboard systems, and audio-visual installations, enhancing the overall user experience.
Steel trusses are developed as well to construct multi-storey parking garages. They provide the required support for the floors and transfer loads easily throughout the structure. The open framework of the trusses equally permits ventilation and natural lighting, creating a safer and more pleasant environment for parked vehicles and users.
Truss type
This depends on specific requirements. For instance, a Pratt truss would be more suited for a bridge since it is good at bearing loads. On the other hand, a Howe truss would be more appropriate in constructions where the support of heavy materials is required.
Material
Trusses are often made from mild steel. Its tensile strength makes it easily malleable to complex shapes without breaking. Other metallurgical options available are carbon steel for enhanced strength against heavy loads and high-strength low-alloy steel, which is known for increased resistance to corrosion.
Galvanized steel trusses
Consider galvanized steel trusses for use in humid or corrosive environments. Zinc-coated steel acts as a barrier against moisture and rust to significantly boost the lifespan of the trusses. Moreover, they require minimal maintenance compared to paint-applied steel trusses.
Span and Load requirements
Spans refer to the distance supported by a truss, while load requirements are simply the total weight the structure will bear. Generally, larger spans and heavier loads require more complex or thicker steel trusses. Such details are crucial to the engineer, as they would determine the best truss design to adopt to equally provide the necessary support and stability.
Cross-sectional design
The choice of cross-section affects the truss's performance. Common options are I-shaped sections, which deliver remarkable bending resistance, and tubular sections, which reduce wind loads. Select a cross-section that balances aerodynamic requirements and structural efficiency depending on the project environment.
Connection details
Connected steel trusses help transfer loads between members, affecting the overall stability. Choose between welded connections, which are internally strong but less flexible, and bolted connections, which allow for coordination during construction in case of damage. The selection mainly depends on whether the application is permanent or would allow for possible modification later.
Costs
While galvanized and high-strength steels are pricier, they significantly prolong the lifespan of steel trusses and reduce the long-term costs of maintenance and replacement often incurred. At the same time, carbon steel is more economical since it is commonly manufactured. Always consider the total project cost, as the selected truss design, material, and finish will dramatically affect the final budget.
Strong and lightweight steel trusses can span large distances without support. This makes them suitable for large constructions and bridges. Also, they can tolerate extreme weather elements without warping, unlike wooden trusses. Steel trusses are equally cost-effective in the long run since they do not require regular maintenance, painting, or repairs commonly associated with wooden trusses.
The most popular steel used in steel trusses is structural carbon steel. It is strong and can be welded, making it perfect for holding heavy loads and spanning long distances. Other commonly used alloys are high-strength low-alloy steels. These are weathering types that provide excellent resistance against corrosion without having to add paint or any other form of protective coating.
Steel trusses have the advantage of being lighter than concrete trusses. Concrete can be extremely heavy, making it more challenging to support itself, especially in high-rise buildings. Also, steel trusses are easier and faster to put in place due to their prefabrication attribute. On the other hand, concrete is cast at the construction site, making it heavier to handle.
Gusset plates are key connective elements that reinforce steel trusses by properly distributing the loads among the members. They are usually placed at the joints where members meet to reduce the concentration of stress at that point. In addition, they transfer forces between the involved members, enhancing stability and allowing the truss to work as a unit.
