Construction Simulation Analysis and Optimization of Super High-Rise CFST Frame-Tube Structure

Literature Overview

Mao Shiyang et al. (2016), published in Construction Technology, present a construction simulation analysis of a super high-rise concrete-filled steel tube (CFST) frame-tube structure using the SAP2000 finite element program. The research was conducted jointly by Beijing University of Technology and China Railway Construction Corporation, combining academic rigor with practical engineering experience. The study addresses the complex interaction between time-varying material properties, boundary conditions, and load application sequences during the construction of tall CFST structures, ultimately proposing an optimized construction sequence and elevation pre-adjustment strategy.

Methodology and Simulation Approach

The simulation employed the element birth-death method to accurately represent the progressive construction process. This approach models each structural element as it is erected, activated, and loaded in sequence, capturing the true construction-stage behavior rather than assuming a fully assembled structure subjected to all loads simultaneously. The key time-varying factors considered include:

• Time-dependent material properties such as concrete strength gain, elastic modulus development, and shrinkage
• Boundary condition evolution as foundation settlement progresses and lower stories accumulate dead loads
• Load application sequence including dead weight, construction loads, and environmental loads

Key Findings on Vertical Deformation

The analysis revealed significant vertical deformation differences among the various load-bearing components of the CFST frame-tube structure during construction. This differential shortening arises from the differing stiffness and load paths of steel tubes, concrete cores, and the composite action between them. In a frame-tube configuration, the perimeter CFST columns typically carry larger axial loads than interior columns, leading to greater shortening and potential tilt or distortion of the structure if not properly managed.

The study demonstrates that the construction sequence directly influences the final内力 distribution and deformation pattern. Different construction schemes result in different stress histories for the steel tubes, which in turn affects the residual stress state and the long-term fatigue performance of welded connections. From a welding engineering perspective, this means that the welding schedule must be coordinated with the construction sequence to minimize the accumulation of residual stresses at critical weld locations.

Elevation Pre-Adjustment Strategy

Based on the vertical deformation analysis, the authors propose pre-adjustment values for the construction elevations of load-bearing components. This is a critical practical recommendation because uncontrolled differential shortening can lead to:

• Misalignment of floor slabs and connection plates
• Excessive bending moments at beam-column connections due to eccentricity
• Distortion of the overall structural geometry affecting architectural finishes
• Accelerated fatigue damage at welded joints due to out-of-plane bending

The pre-adjustment strategy essentially involves building components slightly higher than their final design elevation to compensate for predicted shortening. The magnitude of pre-adjustment depends on the predicted shortening of each component, which varies with the axial load, material properties, and construction sequence.

Welding Quality Considerations in Construction Sequencing

The construction simulation findings have direct implications for welding quality control in CFST super high-rise structures. When steel tubes are erected in sequence, the weld joints at tube splices experience different stress states depending on when in the construction sequence they are welded. Joints welded early in construction experience more subsequent loading cycles and thermal cycling, potentially leading to higher residual stress accumulation and fatigue damage.

The following welding quality control measures should be considered in the context of the construction sequence:

• Pre-weld heat treatment or controlled cooling for critical joints to reduce residual stresses
• Sequential welding of joint welds in a pattern that minimizes warping and distortion
• Post-weld magnetic particle testing (MT) or penetrant testing (PT) at every splice joint, with particular attention to the weld toes where fatigue cracking initiates
• Documentation of welding parameters and inspection results correlated with construction sequence for traceability

Integration with Engineering Practice

In practical engineering, the findings of this study should be integrated into the construction methodology statement. The optimization of construction schemes must consider not only structural performance but also welding logistics, quality control scheduling, and inspection requirements. For instance, if a construction sequence requires welding at heights where access is limited, the welding procedure qualification and inspection protocols must be adapted accordingly.

The study also highlights the importance of monitoring actual construction-stage deformations against predicted values. Real-time monitoring using total stations or inclinometers at critical locations allows for verification of the simulation predictions and adjustment of the pre-adjustment strategy if necessary. This closed-loop approach to construction management ensures that the final structure achieves its designed geometry and performance.

Reflections and Further Considerations

This research exemplifies the increasing sophistication of construction simulation in modern structural engineering. However, the study could benefit from incorporating more detailed modeling of the steel tube weld joints, including their reduced stiffness and strength relative to the parent material. The heat-affected zone at each splice joint represents a localized weakness that can affect the overall structural behavior, particularly under seismic loading. Future research should integrate welding metallurgy considerations into construction simulation, providing a more holistic approach to the design and construction of CFST super high-rise structures. The coordination between structural engineers and welding engineers during the planning phase is essential to ensure that construction sequences are both structurally sound and practically feasible from a welding quality perspective.