Flexural Performance of Grouted Steel Tube Truss Concrete Composite Slabs

Literature Overview

The research by Hou Hetao, Lan Ruhai, Feng Mingyuan, Zhang Shuhui, and Zhang Bo, published in Industrial Construction (Vol. 47, No. 7, 2017, pp. 29-33), introduces and experimentally validates a novel grouted steel tube truss concrete composite slab designed to improve the flexural performance of existing composite floor systems for large-span applications. Funded by the National Natural Science Foundation (Project No. 51578324) and the Shandong Provincial Natural Science Foundation (Project No. ZR2016EEM07), this study combines experimental testing with theoretical analysis.

Structural Configuration and Design Rationale

The proposed composite slab integrates a grouted steel tube truss as the structural web element within a precast-overcast concrete floor system. The steel tube truss serves multiple functions: it acts as the primary load-bearing element during construction (scaffolding-free formwork), provides permanent structural reinforcement, and enhances the composite action between the precast and overcast layers. The grouting of the steel tubes with concrete further improves the local stability of the tube elements and enhances the overall section stiffness.

Experimental Setup and Results

Two simply supported composite slab specimens were tested under uniformly distributed loading to evaluate their flexural performance. The test results demonstrated the following characteristics:

Performance Parameter	Test Result	Assessment
Ductility	Good ductile behavior observed	Meets construction safety requirements
Crack pattern	Progressive crack development	Predictable failure mode
Ultimate load capacity	Satisfactory flexural strength	Adequate for designed span
Deflection	Within acceptable limits	Serviceability criteria met
Failure mode	Bending failure with yielding of truss elements	Ductile failure confirmed

Theoretical Analysis and Design Methodology

The authors developed theoretical models for predicting the flexural load-bearing capacity and deformation behavior of the grouted steel tube truss composite slab. The analysis accounts for the composite action between the precast concrete layer, the steel tube truss web, and the overcast concrete layer. The grouted steel tubes are modeled as composite column elements within the truss, with their contribution to the overall flexural stiffness calculated based on the transformed section properties.

Key Design Parameters

Parameter	Design Consideration	Typical Range
Steel tube diameter	Influences truss geometry and stiffness	60-120 mm
Tube wall thickness	Affects tube stability and load capacity	2.0-3.0 mm
Grout concrete strength	Contributes to tube composite action	C30-C40
Truss height	Primary determinant of section modulus	150-300 mm
Overcast layer thickness	Provides composite action and crack resistance	40-80 mm

Manufacturing and Construction Quality Considerations

From a steel pipe manufacturing perspective, the steel tubes used in this truss system are typically small-diameter ERW (Electric Resistance Welded) or cold-formed tubes conforming to GB/T 3091 or GB/T 13793. The manufacturing quality of these tubes—particularly the weld seam integrity, dimensional accuracy, and surface finish—is critical for ensuring the structural performance of the composite slab. Any defects in the tube manufacturing, such as incomplete weld fusion, wall thickness variation, or surface corrosion, can compromise the truss load-bearing capacity and the composite action with the surrounding concrete.

FMEA for Construction Quality

Potential Defect	Cause	Effect on Performance	Prevention Measure
Incomplete grouting	Insufficient grout flowability	Reduced tube composite action	Use high-flow grout with superplasticizer
Tube misalignment	Poor fabrication tolerances	Reduced truss efficiency	Implement tight dimensional control
Concrete layer delamination	Insufficient bond at interface	Loss of composite action	Surface roughening and shear connectors
Tube corrosion	Exposure during construction	Reduced long-term capacity	Apply protective coating or use galvanized tubes

Key Reflections

This research presents a practical solution to the challenge of achieving large-span floor systems with improved flexural performance. The grouted steel tube truss concept offers advantages over traditional rebar trusses in terms of construction speed, formwork elimination, and predictable structural behavior. The experimental confirmation of good ductility is particularly important for seismic applications, as it ensures that the slab can undergo significant deformation before failure. However, the study is limited to two specimens under monotonic loading, and further investigation into cyclic loading behavior, long-term creep effects, and fire resistance of the grouted tube truss system would strengthen the design basis. The theoretical models developed provide a foundation for design, but their validation against a broader range of geometric configurations and loading conditions is necessary before widespread adoption in structural design codes.