Issues in Steel Structure Design and Construction Standards

Partial Issues and Solutions in Steel Structure Construction

1. Component Manufacturing Issues

The plates used in portal frames are very thin, sometimes as thin as 4 millimeters. For cutting multiple thin plates, shearing should be selected over flame cutting. Flame cutting causes significant wave-like deformation along the plate edges. Currently, most manufacturers use submerged arc automatic welding or semi-automatic welding for H-beam welding. If not properly controlled, welding deformation may occur, causing components to bend or twist.

2. Column Base Installation Issues

(1) Embedded Parts (Anchor Bolts)

Problems: Overall or layout misalignment, incorrect elevation, lack of thread protection. Directly causes misalignment of steel column base plate bolt holes, resulting in insufficient thread length.

Measures: Structural steel contractors must coordinate with civil engineering teams to complete embedded part installation before concrete pouring. Relevant dimensions must be verified, and parts must be securely fixed.

(2) Non-vertical Anchor Bolts: Poor levelness of frame column base plates causes anchor bolts to be non-vertical. Significant horizontal errors in embedded anchor bolts after foundation construction. Installed columns fail to align in a straight line, resulting in crooked structures that compromise building aesthetics, introduce installation errors, affect structural load-bearing capacity, and violate construction acceptance standards.

Countermeasures: Anchor bolt installation should adhere to the international practice of first leveling the base plate using lower adjustment bolts, followed by secondary grouting with non-shrink mortar to fill voids. During anchor bolt installation, use reinforcing bars or angle steel to secure the bolts. Weld them into a cage-like structure for enhanced support, or implement other effective measures to prevent anchor bolt displacement during foundation concrete pouring.

(3) Anchor Bolt Connection Issues

Symptoms: Column base anchor bolts not fully tightened, washers not welded to base plate; some anchor bolts lacking 2–3 exposed threaded sections.

Measures: Weld anchor rods to nuts, apply thickened fireproof coating and thermal insulation to chemical anchors to prevent loss of anchoring performance during fire, supplement foundation settlement observation data.

3. Connection Issues

(1) High-Strength Bolt Connections

1) Bolt mounting surfaces fail to meet requirements, resulting in difficult installation or tightening that does not satisfy design specifications.

Cause Analysis:

① Surface contaminants such as surface rust or oil residue, along with burrs or weld spatter on bolt hole walls.

② Defects remain on bolt mounting surfaces despite prior treatment.

Solution:

① Thoroughly clean surface rust, oil contamination, and bolt hole defects individually. Apply rust prevention treatment before use, bolts intended for assembly must not be used during formal assembly. Bolts should be managed and issued by designated personnel.

② Consider construction sequence when preparing assembly surfaces to avoid redundant work, and perform preparation whenever possible before lifting operations.

2) Damaged bolt threads prevent free insertion into nuts, hindering assembly.

Cause Analysis: Severe thread corrosion.

Solutions:

① Pre-select bolts before use; clean, derust, and pre-assemble them.

② Do not use damaged bolts as temporary fasteners, never force them into holes.

③ Pre-matched bolt assemblies must be stored as sets and not interchanged during use.

(2) On-site Weld Defects

Quality assurance is compromised; ultrasonic testing was not performed on Grade 1 and 2 welds requiring full penetration as per design requirements, main floor beams and columns remain unwelded, arc starter plates were not used during welding.

Solution: Prior to steel structure welding, inspect welding rod certificates. Select rods per design specifications and use them according to manuals and operating procedures. Weld surfaces must be free of cracks and slag inclusions. Grade 1 and 2 welds must not exhibit porosity, slag inclusions, or crater cracks. Welds must not exhibit defects such as undercut or incomplete fusion. Non-destructive testing must be performed on Class I and II welds as required. Welder stamps must be verified on specified welds and locations. Non-conforming welds must not be arbitrarily modified, corrective procedures must be established before any intervention. Repairs to welds in the same location should not exceed two attempts.

(3) Component Deformation Issues

1) Components may deform during transportation, developing permanent or gradual bends that render them uninstallable.

Cause Analysis:

① Deformation from welding during fabrication, typically manifesting as gradual bends.

② Improper support points during storage (e.g., non-vertical wooden blocks) or subsidence at storage sites, causing permanent or gradual deformation.

③ Deformation from collisions during transport, typically manifesting as permanent bends.

Preventive Measures:

① Implement measures to minimize welding deformation during fabrication.

② During assembly welding, employ counter-deformation techniques. Assembly sequence should follow welding sequence. Use assembly jigs and sufficient supports to prevent deformation.

③ During pre-transport and transportation, ensure rational placement of support points.

Solutions:

① Permanent bending in components is generally corrected mechanically. This involves straightening with jacks or other tools, or supplemented by correction after heating with an oxyacetylene flame.

② For gradual bending deformation in structures, correction is achieved through oxyacetylene flame heating.

2) Post-assembly full-length twist of steel beam components exceeds allowable limits, compromising installation quality.

Cause Analysis:

① Unreasonable splicing techniques.

② Assembly node dimensions fail to meet design requirements.

Solutions:

① Establish dedicated assembly workbenches for components. During tack welding, level the component base to prevent warping. Ensure all support points of the assembly table are level. Prevent welding distortion during assembly welding. Particularly for beam segments or ramp assemblies, adjust deformation after tack welding. Ensure node dimensions comply with design specifications to prevent component distortion.

② Reinforce components with low inherent rigidity before flipping for welding. Level components after flipping to enable post-weld correction.