Parametric Study on the Nonlinear Dynamic Response of Cold-Formed Steel Structure under Blast Loading

Abstract

Cold formed steel (CFS) framing systems are increasingly used in modern construction due to their lightweight nature, high strength-to-weight ratio, and construction efficiency. However, their thin-walled sections are particularly susceptible to damage under extreme loading conditions such as blast events or also accidental loads. This study presents a numerical investigation on the finite element modelling and response analysis of composite cold-formed steel frame structures subjected to blast loading. A multi-storey CFS frame building is modelled using a global finite element approach to evaluate its overall structural response under gravity and blast loads. Blast effects are represented through idealized pressure-time histories applied to exposed structural components. Critical members identified from global analysis are further examined using detailed finite element models to capture local buckling, stress concentration, and material non-linearity. Composite action is induced through localized strengthening to enhance energy absorption and delay failure. The response is calculated in terms of displacement, stress distribution, and damage progression. The proposed methodology framework offers a practical approach for assessing and improving the blast performance of cold-formed steel frame structures. This study also contributes to the development of efficient numerical methodologies for blast-resistant design of cold-formed steel structures

Introduction

Cold-Formed Steel (CFS) consists of thin steel sheets shaped at room temperature into sections such as C-sections, Z-sections, lipped channels, and built-up members. Due to their high strength-to-weight ratio, ease of fabrication, and versatility, CFS systems are widely used in light commercial buildings, wall and floor systems, secondary framing, and modular construction.

Blast Load Physics

A blast is the rapid release of a large amount of energy within a very short time, generating a shockwave that propagates in all directions. The resulting pressure-time history consists of a positive phase (high-pressure shock wave) followed by a negative phase (suction effect). The intensity of blast loads depends on the explosive charge weight, standoff distance, and structural geometry. Key blast parameters include reflected pressure and impulse, which significantly influence structural response.

Standards and Design Guidelines

Blast-resistant design of CFS structures is governed by:

• ASCE/SEI 59-11 for blast protection of buildings.
• AISI S100 and related technical guidance for CFS member design and buckling resistance.
• Eurocode EN 1993-1-3 for cold-formed steel members and sheeting.

Design Checks for Blast Resistance

Important design considerations include:

• Local Capacity: Resistance of plates, flanges, and connections against peak blast pressures.
• Global Stability: Prevention of progressive collapse and maintenance of overall structural integrity.
• Serviceability and Residual Capacity: Limitation of permanent deformations and preservation of post-blast functionality.

Significance of Blast Loads

Blast loads are among the most severe extreme loading conditions because they produce intense pressure waves within milliseconds. Considering blast effects is essential for:

• Protecting occupants and critical assets.
• Preventing progressive collapse.
• Ensuring resilience and operational continuity of infrastructure.
• Reducing economic losses due to damage and downtime.
• Enhancing the performance of lightweight systems such as CFS structures, which are susceptible to buckling and high-strain-rate effects.

Research Gap

Although extensive research exists on blast resistance, progressive collapse, and strengthening techniques, studies focusing on the blast behaviour of multi-storey cold-formed steel frame structures remain limited. Existing work mainly investigates individual components or gravity-load scenarios. The effects of nonlinear dynamic response, negative-phase blast loading, and damage propagation in composite CFS frames are not fully understood, creating a need for detailed finite element investigations.

Problem Statement

The study aims to develop a finite element model of a G+10 cold-formed steel moment-resisting frame and evaluate its nonlinear dynamic behaviour, damage mechanisms, and overall structural performance under blast loading.

Model Description

The proposed structure is an 11-storey (G+10) CFS moment-resisting frame with dimensions 34 m × 37.5 m × 38.5 m, comprising:

• 4 bays in the X-direction and 5 bays in the Y-direction.
• Story height of 3.5 m.
• Box-section beams and columns.
• Lightweight concrete slab (130 mm).
• CFS wall systems.
• Blast scenario: 50 kg TNT charge at 15 m standoff distance.

Blast parameters calculated include:

• Incident overpressure: 35.2 kPa
• Reflected overpressure: 275.95 kPa
• Positive phase duration: 0.1425 s
• Negative peak pressure: −55.19 kPa

Proposed Methodology

The research methodology includes:

1. Validation of the finite element model using published literature.
2. Selection and design of CFS members according to AISI, IS, and Eurocode provisions.
3. Development of a global 3D finite element model of the G+10 building.
4. Gravity load analysis to verify structural stability.
5. Blast load calculation and application based on IS 4991:1968.
6. Nonlinear dynamic blast analysis to study structural response and damage.
7. Extraction of key response parameters such as story drift, story shear, and member damage.
8. Identification of critical structural components and vulnerable regions requiring redesign.

Conclusion

This study investigated the structural and dynamic performance of a Cold-Formed Steel (CFS) structural system. Finite element modelling and dynamic analysis were carried out to evaluate key response parameters including absolute displacement, absolute velocity, absolute acceleration, kinetic energy, and potential energy components under the selected blast loading. The results are demonstrated in the above Table II. Evaluation of the energy response parameters provided additional insight into the structural behavior of Cold-Formed Steel Structural system. The obtained results provide a clear understanding of the deformation characteristics, dynamic response, and energy absorption behavior of the CFS model. The study demonstrates the capability of numerical analysis to evaluate the structural response under extreme blast loading conditions and offers a foundation for future research on improving blast-resistant structural systems through material optimization, structural modifications, and advanced design approaches like the provision of Functionally Graded Material Composites through material gradation.

References

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Copyright

Copyright © 2026 Prathamesh Ravikiran Lagad, V. M. Bogar. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.