These Primary Load Bearing Steel Beams are the central components responsible for transferring vertical loads within the steel framework. Unlike secondary beams (such as standard I-beams or channel steel) that handle localized or distributed loads, these primary beams support the concentrated loads from the floor decking, secondary beams, equipment, and roofing, transferring them stably to the vertical steel columns. The product line comprises three main categories—welded H-beams, variable-section H-beams, and box-section beams—all fabricated from steel plates using submerged-arc welding and subjected to comprehensive non-destructive testing (NDT) as well as multi-stage anti-corrosion and fire-resistant treatments.
- Constant-section welded H-beams: The most widely used Primary Load Bearing Steel Beams on the market; uniform cross-section dimensions throughout; short fabrication cycles and moderate costs; suitable for standard floor spans of 6–24m and typical factory floor load requirements.
- Variable-section H-beams: Deeper sections at mid-span and tapered sections at supports; designed to align with roof bending moment distribution; specifically for portal rigid frame factory roofs to minimize inefficient steel usage.
- Welded box beams: Closed four-sided box cross-section with balanced bi-directional torsional rigidity; suitable for extra-large spans (24–36m), eccentric crane loads, and high-rise mega-frames; addresses the weak-axis rigidity limitations of H-beams.
- H-beam specification: H × B × tw × tf (representing beam depth, flange width, web thickness, and flange thickness, respectively); beam depth range: 300–2000mm.
- Box beam specification: B × H × t (representing section width, section depth, and box wall thickness, respectively); wall thickness range: 12–50mm.
- Factory-finished segment length: Standard lengths of 9m and 12m; lengths exceeding this are prefabricated in segments and spliced/assembled at height on-site.
- Q355B: Mainstream industry material; yield strength far exceeds ordinary carbon steel; meets requirements for 90% of heavy-load factories and high-rise intermediate floors.
- Q235B: Limited to low-rise, light-load indoor intermediate floors (spans under 6m); low load redundancy; outdoor use not recommended.
- Q355NL: For frigid regions with temperatures of -20°C or lower; possesses certified low-temperature impact toughness to prevent brittle fracture in cold conditions.
All main beams are fabricated via steel plate cutting, assembly, and welding; hot-rolled profiles are not used for modification. The extra-long main girder is cut into segments based on transport height limits, with weld bevels and butt-joint allowances pre-configured to avoid issues associated with oversized highway or marine transport; upon arrival at the site, high-altitude alignment and splicing can proceed immediately.
- Bolted End Plates: Plate thickness ranges from 18mm to 50mm (calculated based on maximum support reaction force); features pre-drilled holes for Grade 10.9 high-strength bolts. This is the most common connection method for primary floor beams, eliminating the need for on-site hot work (welding).
- Full-Penetration Groove Welds: Designed specifically for high-rise box-section primary beams; involves double-sided beveling of webs and flanges to achieve a butt joint with strength equal to the base metal, meeting seismic code requirements for high-rise structures.
- Support Stiffeners (Horizontal & Vertical): Mandatory structural components for primary beams; they prevent shear deformation of the web at the support and eliminate the risk of local crushing or collapse at the beam end, complying with national structural standards.
- Mid-span Transverse Stiffeners: Positioned at points of concentrated equipment loads or peak mid-span bending moments to suppress shear buckling deformation of the web.
- Secondary Beam Corbels/Brackets: Welded symmetrically on both sides of the primary beam to support secondary beams from various directions, accommodating cross-shaped, diagonal, and other connection configurations.
- Reinforcement Plates for Utility Openings: Annular reinforcement plates installed around web openings for MEP (mechanical, electrical, and plumbing) lines to ensure no reduction in cross-sectional load-bearing capacity.
- Shear Studs: Specifications include Φ16 and Φ19; used for primary beams in composite concrete floor systems to enable collaborative load-bearing between steel and concrete, thereby increasing the overall load-bearing capacity.
- Prefabricated Lifting Lugs: Symmetrically pre-installed at both ends of primary beams weighing over 5 tons; verified through lifting mechanics calculations and designed for vertical lifting of the entire beam unit.
- Temporary Connection Plates: Used for temporary alignment of segmented primary beams; controls joint misalignment to less than 2mm; removed by grinding after completion.
- Rust Removal Process: Primary Load Bearing Steel Beams undergo standardized Sa2.5 grade shot-blasting to remove rolling scale and loose welding rust, ensuring optimal paint film adhesion.
- Multi-layer coating system: Epoxy zinc-rich primer + epoxy micaceous iron oxide intermediate coat + polyurethane topcoat; total dry film thickness of 100–160 μm.
- Fire protection treatment: Application of thin-film or thick-film intumescent fire-retardant coatings based on the building's fire resistance rating, covering full fire resistance durations of 1, 2, or 3 hours.
- Coastal environment option: Hot-dip galvanizing (entire component); zinc coating thickness ≥85 μm to withstand long-term marine salt spray corrosion.
Standard supply includes Grade 10.9 high-strength bolts, nuts, flat washers, and tapered washers; all consumables comply with national standards for steel structure connections.
- Floor H-section primary beam: H-section body + thickened end plates at both ends + bearing stiffeners + secondary beam brackets + top flange shear studs + complete anti-corrosion and fire protection treatment.
- Portal frame variable-section roof primary beam: Variable-section H-beam + end plates + bearing stiffeners + flange purlin cleats + anti-corrosion treatment.
- Heavy-duty box-section primary beam: Box-section body + full-penetration groove welds at ends + internal and external stiffening rings + side brackets + thickened end closure plates.
Original material quality certificates, 100% ultrasonic testing (UT) reports for Grade I welds, dimensional inspection reports, and component coating/ID lists.
- High load-bearing capacity; resistant to sagging or plastic deformation under long-term stress in long-span applications.
- High overall frame rigidity with stable seismic and compressive performance; ensures ample safety margins for mezzanine levels.
- Fully prefabricated in the factory with controlled dimensional accuracy; requires only on-site bolting, resulting in a short construction cycle.
- Compact beam cross-section minimizes vertical space consumption, preserving interior usable space.
- Multi-layer anti-corrosion treatment combined with compliant fireproofing ensures a service life of over 50 years for both indoor and outdoor applications.
- Customizable span, section depth, and beam-column connection types; adaptable to irregular interior layouts.
- Main load-bearing steel beams: Customizable plate thickness; covers spans of 6–36m; adjustable bi-directional torsional resistance; supports concentrated loads across the entire floor.
- I-beams and channel steel: Fixed hot-rolled sections cannot be modified; insufficient lateral rigidity along the weak axis; supports only isolated point loads; maximum span limited to 6m.
- C-sections and circular hollow sections: Thin-walled, closed profiles with weak concentrated load capacity; suitable only for bracing or secondary framing; prohibited for use as primary vertical load-bearing beams.
- Main load-bearing steel beams: Supports dense welding of multiple brackets (stiffeners) on both sides; accommodates multi-angle secondary beam connections; suitable for complex beam-column joints.
- Hot-rolled sections: Flanges feature sloped surfaces, making extensive welding contact difficult; limits the density of secondary beam connection points.
- Main load-bearing steel beams: Variable-section designs allow plate thickness to decrease in line with bending moment reduction; precisely minimizes wasted steel and lowers overall costs.
- Hot-rolled structural steel: Fixed cross-sectional dimensions with a large load-bearing safety margin; efficient for short spans but extremely costly for long spans.
Primary Load Bearing Steel Beams handle the main load transfer for entire floors, roofs, and equipment platforms; other structural steel components serve as secondary beams, supports, or enclosure framing—the two categories are not interchangeable.
Verify original manufacturer material quality certificates; inspect for laminations or warping; flatten non-compliant plates using a plate leveling machine; simultaneously analyze drawings to generate cutting lists for flanges, webs, stiffeners, and connection plates.
Cut plates using CNC flame or plasma equipment; apply uniform beveling at primary beam splice locations; perform profile cutting for variable-section beam webs, allowing a 2–3 mm margin for weld shrinkage.
- H-shaped primary beams: Secure top and bottom flanges in assembly jigs; install webs vertically; use tack welding to position and align web centering and flange perpendicularity.
- Box-shaped primary beams: Enclose the four plates within an assembly jig; pre-install and tack-weld internal diaphragms; control plate misalignment (offset) at joints.
- H-shaped primary beams: Perform single-sided SAW, then flip the beam and use air-arc gouging to clean the root; complete full-penetration SAW on the reverse side to eliminate internal weld defects.
- Box-shaped primary beams: Weld internal diaphragm fillet joints first, then simultaneously weld the four main longitudinal seams of the box section.
- Quality requirements: All main beam seams must meet Grade I weld standards; 100% Ultrasonic Testing (UT) is required upon completion.
Use a hydraulic straightening machine to correct flange curvature and beam sweep (lateral bending); relieve residual welding stress; ensure beam straightness meets tolerance requirements.
Precisely mark locations according to drawings for stiffeners, corbels, and purlin cleats. Small components are welded to the beam using CO2 gas-shielded welding; finally, the end connection plates are assembled and fully welded.
CNC drilling machines are used for all end plates and bracket connection plates to ensure bolt hole coaxiality and eliminate the need for on-site reaming or rework.
For main beams supporting composite concrete floor slabs, specialized stud welding machines are used to weld Φ16 and Φ19 shear studs, with stud verticality deviation controlled within 1°.
Weld beads and spatter burrs are ground off the entire beam; web opening reinforcement zones and localized surface defects are repaired.
Overall shot blasting to Sa2.5 grade; sequential application of primer, intermediate coat, and topcoat with dry film thickness verification; application of fire-resistant coatings based on required fire ratings for specific zones.
Component ID numbers and axis/elevation markings are applied; dimensional accuracy, flaw detection reports, and material documentation are verified; upon passing inspection, components are waterproof-packaged for shipment.
- Beam straightness: ≤L/1000
- Flange verticality: ≤B/100
- Cross-sectional dimensional deviation: ±2 to 3 mm
- Standard finished segment lengths: 9m, 12m; extra-long components are prefabricated in segments.
|
Material Grade |
Yield Strength ReL |
Tensile Strength Rm |
Application Scenarios |
|
Q355B |
≥355MPa |
470～630MPa |
Main beam for factory and high-rise heavy load platform |
|
Q235B |
≥235MPa |
375～500MPa |
Low-rise light load main beam |
|
Q355NL |
≥355MPa |
470～630MPa |
Main beam used in severe cold areas |
- H-beam: Excellent flexural performance about the strong axis; lower lateral stiffness about the weak axis (relies on floor slabs and secondary beams for lateral restraint); load-bearing capacity increases by 35%–55% after steel-concrete composite retrofitting.
- Box beam: Balanced bidirectional flexural and torsional performance; suitable for eccentric loading and bridge crane main beam applications.
- Wind resistance coefficient: H-beam 1.35, Box beam 1.55.
- Transverse stiffeners must be added at concentrated load points to prevent local web buckling due to bearing stress.
- Main girder butt joints and critical bearing welds: Grade I welds, 100% Ultrasonic Testing (UT)
- Stiffener and bracket fillet welds: Grade II welds, 20% random Ultrasonic Testing (UT)
- Rust removal grade: Sa2.5
- Paint dry film thickness: 100–160 μm
- Fire resistance duration: 1h, 2h, 3h
- Hot-dip galvanizing zinc thickness: ≥85 μm
- Beam-to-column connection bolts: Grade 10.9 high-strength bolts
- End plate thickness: 18–50 mm
- Shear stud specifications: Φ16, Φ19; material: ML15
- Fully in-house processing: Proprietary production lines for steel plate cutting, submerged arc welding, and flaw detection; no outsourcing, ensuring controllable dimensions and weld quality.
- Compliant cross-border delivery: Simultaneous delivery of complete English inspection reports and customs clearance documentation to meet requirements for overseas engineering supervision and customs audits.
- Oversized transport solutions: Provision of complete construction drawings for sectional prefabrication and on-site splicing of extra-long main girders, overcoming cross-border transport limitations.
- Free technical verification: Pre-sales verification of main girder span, load, and connection selection to mitigate structural design risks.
Q1: How do I choose between H-section and box-section main girders?
A: Use H-section girders for spans under 24m with unidirectional vertical loads; use box-section girders for spans exceeding 24m, bidirectional eccentric loads, or reciprocating crane loads.
Q2: Does cutting openings in the main girder web affect structural safety?
A: Openings made at locations other than peak bending moment points—when reinforced with annular stiffening plates—do not compromise load-bearing capacity; however, arbitrary openings are prohibited in high-bending-moment zones at mid-span.
Q3: Can the fire-resistant coating for primary load bearing steel beams be applied on-site at a later stage?
A: Application can be done either via factory pre-coating or on-site coating; factory coating ensures uniform film thickness and generally aligns better with the scheduling requirements of overseas projects.
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