Progressive Collapse Resistance of Steel Tube Concrete Column-Composite Beam Frame Under Corner Column Failure

Literature Overview

This study by Wang Jingxuan, Yang Yong, Zhou Kan, and Li Qiuying from Lanzhou University of Technology and the University of Leeds investigates the progressive collapse resistance of steel tube concrete (STC) column-composite beam frames when subjected to corner column failure. Funded by the National Natural Science Foundation of China (Grants 52068047 and 51708270) and the Gansu Provincial Youth Science and Technology Fund (20JR5RA437), the research involved 1/4 scale model testing of a two-story, two-bay planar frame with corner column removal. Published in Engineering Mechanics in 2022, the study provides valuable insights into the structural behavior and progressive collapse mechanisms of STC composite frames.

Test Configuration and Loading Protocol

The experimental program involved a carefully designed scale model:

Parameter	Specification
Scale ratio	1/4
Frame configuration	Two-story, two-bay
Column type	Steel tube concrete (STC)
Beam type	Composite beam with profiled steel deck
Loading condition	Corner column removal followed by monotonic static loading
Measurement	Load-displacement curves, strain gauges, full-field deformation

The corner column removal scenario represents one of the most critical progressive collapse initiation conditions, as corner columns typically provide critical lateral support and moment resistance at frame boundaries.

Structural Response Stages

The test revealed four distinct stages in the structural response:

Stage	Description	Key Characteristics
Stage 1: Elastic	Linear elastic response	Proportional load-displacement relationship
Stage 2: Elastic-plastic	Initial yielding	Steel beam flanges begin yielding
Stage 3: Internal force redistribution	Load path reorganization	Forces transfer through adjacent columns to lower beam
Stage 4: Failure	Progressive failure	Steel beam fracture and torsional deformation

Failure Mode Analysis

The overall failure was concentrated in the failed bay, with the following characteristics:

Steel beam fracture: The primary failure mode was fracture of the steel beam, particularly at the web-flange junction where stress concentrations develop.
Torsional deformation: Significant torsional deformation of the steel beams was observed, indicating that the composite action between the steel beam and profiled steel deck was compromised during large deformations.
Sequential failure: The second-floor steel beam failed before the first-floor steel beam, which is consistent with the force redistribution mechanism where the second-floor beam carries the initial load and transfers it to the first-floor beam through the adjacent columns.
Composite deck separation: Partial separation between the profiled steel deck and steel beam occurred during loading, with some shear connectors (studs) being pulled out.

Energy-Based Assessment Method

The authors employed the energy equivalence principle to analyze the dynamic effects of progressive collapse and assess the residual progressive collapse resistance. The key finding was that the structure retained 15.3% progressive collapse resistance under the corner column failure scenario.

This energy-based approach provides a practical method for evaluating progressive collapse resistance without requiring full dynamic analysis, making it suitable for preliminary design assessments. The method considers:

Kinetic energy of the collapsing mass
Strain energy absorbed by the remaining structure
Energy dissipated through plastic deformation
Energy dissipated through friction and separation

Welding and Connection Considerations

The progressive collapse behavior is significantly influenced by the quality of welded connections:

Connection Type	Role in Progressive Collapse	Welding Requirement
Column-beam moment connection	Primary load path for force redistribution	Full-penetration groove weld, high toughness
Shear connector welds	Composite action between beam and deck	Full penetration, controlled heat input
Column splice welds	Continuity of load path through height	Full-penetration, qualified WPS
Deck-to-beam welds	Secondary load path during separation	Controlled weld geometry

The observation of steel beam fracture indicates that the connection welds were sufficiently strong to transfer forces, but the beam itself became the weak link. This is generally a desirable failure mode from a progressive collapse perspective, as beam fracture provides a more ductile failure mechanism than connection failure.

Strain Distribution and Force Redistribution

The strain measurements at critical locations revealed the force redistribution mechanism:

Initial phase: Strains develop uniformly in the failed bay beams as the load increases.
Yielding phase: Strains concentrate at the beam ends near the column connections, indicating plastic hinge formation.
Redistribution phase: As the second-floor beam yields extensively, strains in the first-floor beam increase significantly, indicating force transfer through the adjacent columns.
Failure phase: Strains reach fracture levels in the second-floor beam, followed by rapid strain increase in the first-floor beam.

FMEA Analysis of Progressive Collapse Vulnerabilities

Applying Failure Mode and Effects Analysis to the observed failure mechanisms:

Failure Mode	Severity	Occurrence	Detection	RPN	Mitigation Strategy
Steel beam web fracture	9	3	2	54	Web stiffeners, thicker web plates
Shear connector pull-out	6	4	3	72	Increased stud diameter, additional studs
Deck-beam separation	5	5	2	50	Continuous weld along full length
Column local buckling	7	2	3	42	Internal confinement, thicker walls
Connection weld fracture	9	2	2	36	High-toughness weld metal, NDT verification

Key Questions and Reflections

The study raises an important question about the representativeness of monotonic static loading in simulating progressive collapse dynamics. While the energy equivalence method provides a practical assessment tool, the actual dynamic effects of progressive collapse—including inertial forces, impact effects, and rate-dependent material behavior—may differ significantly from the static test results. The 15.3% residual resistance finding should be interpreted with this limitation in mind.

Another significant observation is the role of the profiled steel deck in progressive collapse resistance. The observed separation between the deck and beam suggests that the composite action is not reliable during large deformations. This has implications for the design of composite floor systems in progressive collapse-critical structures, where the deck may need to be designed as a catenary action element rather than relying on composite action.

Study Insights and Implications

This research provides valuable experimental data on the progressive collapse behavior of STC column-composite beam frames under corner column failure. The identification of four distinct response stages and the quantification of 15.3% residual progressive collapse resistance offer practical benchmarks for design verification. For steel pipe manufacturers, the key implication is that column wall thickness and local buckling resistance are critical for maintaining the load path during progressive collapse, as the columns must redistribute forces from the failed bay to adjacent bays. The study also highlights the importance of beam ductility and the need for adequate web stiffening to prevent premature web fracture. The energy-based assessment method proposed by the authors provides a practical tool for preliminary progressive collapse evaluation that can be incorporated into design workflows without requiring extensive dynamic analysis. The finding that the second-floor beam fails before the first-floor beam provides insight into the expected failure sequence that can be used to prioritize protective measures in critical structures.