Steel Design Guide: Design of Blast Resistant Structures

# How to Apply Steel Design Guide: Design of Blast Resistant Structures

Mastering the principles outlined in the AISC Steel Design Guide: Design of Blast Resistant Structures is crucial for engineers tasked with ensuring the safety and resilience of critical infrastructure. By understanding and applying its methodologies, you elevate your design capabilities, offering clients robust solutions that protect against extreme events and contribute to a safer built environment. This guide equips you to navigate the complexities of blast loading and progressive collapse mitigation, enhancing your professional value and career prospects.

Before You Begin

Prerequisites:

• • Knowledge: A strong foundation in structural analysis, steel design principles (including AISC Steel Construction Manual), understanding of dynamic loads, and familiarity with fundamental mechanics of materials.
• • Tools/Resources: Access to the AISC Steel Design Guide: Design of Blast Resistant Structures, relevant industry standards (e.g., ASCE 7), structural analysis software capable of dynamic analysis, and blast load estimation tools or consultation with blast specialists.
• • Time Required: 1-2 days for initial review and understanding, with ongoing application requiring project-specific time for analysis and design.

Step-by-Step Implementation

Step 1: Define the Threat and Performance Objectives

Begin by clearly defining the potential blast threat, including the type of explosive, standoff distance, and expected blast parameters (peak pressure, impulse). This information is critical for establishing the design basis. Concurrently, ascertain the required performance objectives for the structure – what level of damage is acceptable, and what are the critical life safety requirements? Failure to accurately define the threat and objectives leads to either over-design or under-design, both posing significant risks.

Step 2: Characterize Blast Loads on the Structure

Utilize the principles outlined in Chapter 2 to translate the defined threat into quantifiable blast loads acting on the structure. This involves understanding phenomena like pressure, impulse, reflection, and diffraction. Employ empirical relationships, analytical methods, or specialized software to predict external, internal, and net lateral loads. Common mistakes include oversimplifying load calculations or neglecting the transient nature of blast pressures.

Step 3: Select Appropriate Structural Analysis Methods

Determine the most suitable analysis approach based on the structure's complexity and the blast load characteristics. For simpler scenarios, Single Degree of Freedom (SDOF) systems (Chapter 4) can provide efficient estimations of peak dynamic force and displacement. For more complex structures, Multiple Degree of Freedom (MDOF) analysis may be necessary. Ensure your chosen method accurately captures the dynamic response, considering both elastic and nonlinear behavior where applicable.

Step 4: Evaluate Material Behavior Under Dynamic Loading

Recognize that steel properties change under high strain rates. Chapter 6 details the importance of considering the Strength Increase Factor (SIF) and Dynamic Increase Factor (DIF) for steel. These factors adjust material strengths to account for the rapid loading conditions. Incorrectly applying static material properties can lead to inaccurate strength predictions and potential failure.

Step 5: Design Structural Systems and Members

Apply the design methodologies presented in Chapters 5 and 6. For systems, consider the energy method to assess overall resistance. For individual members and connections (Chapter 7), verify that they can withstand the calculated blast forces and meet deformation criteria. This involves checking for failure modes such as breaching, tension, compression, shear, and flexure.

Step 6: Design Connections for Blast Loads

Pay close attention to connection design, as highlighted in Chapter 7. Blast loads can impose significant forces and demands on connections, often requiring enhanced ductility and strength beyond typical static design. Ensure connections can accommodate the expected deformations without catastrophic failure and confirm their required strength against the available strength under dynamic conditions.

Step 7: Incorporate Progressive Collapse Mitigation Strategies

While focusing on direct blast resistance, integrate progressive collapse mitigation as described in the guide.