Bolted Composite Joint Parameter Analysis of Square Steel Tube Concrete Column-H Steel Beam

Literature Overview

The paper by Zhang Ailin, Sun Yong, Liu Xuechun, Jiang Ziqin, Zhou Xiaojun, and Wang Qi from Beijing University of Technology and Beijing Engineering Technology Research Center for High-Rise and Long-Span Prestressed Steel Structures presents a parametric analysis of bolted composite joints connecting square steel tube concrete (SRC) columns to H-steel beams. Published in Industrial Construction (Vol. 46, No. 9, 2016, pp. 144-151), this research was funded by the National Natural Science Foundation of China (51278010).

Core Technical Content

The study uses ABAQUS software to establish three-dimensional finite element models of bolted composite joints between SRC columns and H-steel beams. Three groups of seven specimens were designed with varying joint parameters to investigate the influence of floor slab composite action on joint behavior under positive and negative bending moments.

Parametric Study Design

Key Parameters Investigated

• Profiled steel-concrete composite slab thickness
• Slab reinforcement ratio
• Shear stud quantity and arrangement
• Joint ultimate load capacity
• Ductility (displacement at peak load to yield displacement)
• Initial rotational stiffness

Key Findings

1. Ultimate load capacity, ductility, and initial rotational stiffness increase with increasing composite slab thickness and reinforcement ratio
2. These parameters decrease with reducing shear stud quantity
3. Positive and negative bending moments exhibit different sensitivity to slab composite action
4. The composite slab significantly enhances joint performance under positive bending

Technical Analysis from a Steel Pipe and Welding Perspective

Square Steel Tube Concrete Column

The SRC column in this joint configuration typically uses:

• Steel tube: Square hollow section (SHS) per GB/T 6728, with typical dimensions of 400×400 mm to 800×800 mm and wall thickness of 10-25 mm
• Steel grade: Q345B or Q355B with yield strength of 345-355 MPa
• Concrete: C40-C60 grade, filled through top openings with vibration assistance
• Steel tube fabrication: Cold-formed or hot-rolled SHS, with longitudinal welds conforming to GB/T 3091

Bolted Joint Design

The bolted composite joint connects the H-beam to the SRC column through:

1. End plate connection: Welded to the H-beam end, bolted to column flange plates
2. Shear studs: Connecting the composite slab to the top flange of the H-beam
3. Column stiffeners: Internal or external stiffeners to prevent local buckling of the steel tube

Bolt Specifications

The bolts used in the joint should conform to:

• Grade 10.9 high-strength bolts: For the primary load-bearing connection
• Diameter: M24 to M30 depending on design loads
• Number: Typically 8-12 bolts per connection face
• Tightening: Controlled tightening to 70-80% of proof load per GB 50205

Engineering Practice Integration

Welding Quality Requirements

The welded components of this joint require strict quality control:

Influence of Slab Composite Action

The parametric study reveals that the composite slab significantly influences joint behavior. From a fabrication standpoint:

1. Shear stud welding: Must be performed before concrete placement, with proper spacing (typically 150-300 mm) and embedment depth
2. Slab concrete quality: The concrete in the composite slab must achieve adequate bond with both the profiled steel sheet and the shear studs
3. Construction sequence: The relative timing of bolt tightening, concrete placement, and load application affects the final joint performance

Ductility and Energy Dissipation

The ductility of the joint is a critical seismic design parameter. The following factors influence ductility:

• Steel tube wall thickness: Thicker walls provide more confinement to concrete but may reduce overall ductility
• End plate thickness: Must be thick enough to develop full plastic moment without excessive deformation
• Bolt grade: Higher grade bolts (10.9) provide higher capacity but may reduce ductility compared to grade 8.8
• Slab reinforcement: Higher reinforcement ratio increases ductility by providing additional deformation capacity

Study Insights and Reflections

This parametric study provides valuable quantitative data on the influence of composite slab parameters on joint behavior. The findings have direct implications for the design and fabrication of bolted composite joints in SRC buildings.

From a welding engineering perspective, the study highlights the importance of the end plate-to-beam weld and the flange plate-to-tube weld as the most critical welded connections in the joint. These welds must be designed, fabricated, and inspected to the highest quality standards because their failure would result in immediate joint failure with minimal warning.

The finding that shear stud quantity significantly influences joint performance underscores the importance of proper stud welding practice. Each stud must be welded with adequate penetration, proper alignment, and sufficient weld metal volume to develop the designed shear capacity. Inadequate stud welding represents a hidden weakness that may not be detected by visual inspection alone.

The parametric approach adopted in this study—varying one parameter at a time while holding others constant—provides clear cause-effect relationships that are directly usable in design. However, engineers should recognize that in practice, multiple parameters vary simultaneously, and interaction effects may modify the individual parameter influences identified in this study.

This research contributes to the growing body of knowledge on composite steel-concrete connections and provides a solid basis for the development of simplified design methods that account for composite slab action in bolted SRC joints. The findings should be incorporated into future revisions of relevant design codes and specifications.

The practical significance of this work extends beyond the specific joint configuration studied. The methodology and insights are applicable to a wide range of composite steel-concrete connections in buildings, bridges, and industrial structures where SRC columns are used with steel beam connections.