Welcome to today’s video on a pivotal topic in structural engineering: “Why We Need Performance-Based Structural Design.” This topic is deeply rooted in my professional journey, sparked by a question I faced over 40 years ago. A client asked me, “Is my structure going to be safe after you design it?” At that time, I could only offer assurances based on adherence to design codes. This moment ignited a lifelong quest to enhance structural safety, leading me to explore why performance-based design is not just an option but a necessity.
[The Core Question: What Does “Safe” Mean?]
To address structural safety effectively, we must first define what “safe” means. Structures face various hazards throughout their lifespan, such as earthquakes, floods, hurricanes, and fires. Each of these presents different challenges. While we strive to model and account for these hazards, precise predictions are often elusive. Understanding safety means comprehending how structures respond to various events and the impact of these events on their performance.
[Historical Context: Evolution of Building Codes]
Building codes have historically evolved from prescriptive requirements to performance-based approaches. Ancient codes, like those mandating parapets, were designed to address specific safety concerns. Modern codes, while more advanced, still set rigid standards that may not fully adapt to real-world scenarios. For example, a railing height that feels secure on a lower floor might be perceived differently on a higher floor, illustrating that code compliance doesn’t always align with actual safety needs.
[The Limitations of Prescriptive Codes]
Prescriptive codes establish minimum safety standards but can be rigid and may not address all safety concerns. They are updated periodically, but this doesn’t automatically make older structures unsafe. A building designed under an older code might now be considered deficient by current standards, but does this mean it’s unsafe? Performance-based design addresses this by focusing on how a structure performs under various conditions rather than just meeting prescriptive rules.
[The Advantages of Performance-Based Design]
Performance-based design evaluates how a structure performs under specific scenarios, such as major earthquakes or severe weather events. This approach allows for more innovative solutions and precise safety measures tailored to each structure’s unique characteristics. For new buildings, it provides the flexibility to explore different design options based on performance criteria. For existing buildings, performance-based evaluation assesses how structures perform under current conditions and identifies areas needing improvement.
[The Importance for Existing Structures]
Performance-based design is particularly beneficial for existing structures. Instead of retrofitting buildings to meet outdated codes, performance-based evaluation focuses on current performance and identifies critical areas for improvement. For instance, a building designed with seismic reinforcement spaced at 150 millimeters may be reassessed under new codes with a 100-millimeter requirement, but performance-based evaluation allows us to determine if the existing reinforcement is adequate given current conditions.
[The Future of Structural Design]
Looking ahead, performance-based design should become the standard for new construction and a critical tool for evaluating existing buildings. It offers a more nuanced and effective approach to ensuring safety and resilience. Future developments in structural engineering will likely include consequence-based and resilience-based designs, which consider the broader impact of structural performance on communities and environments.
The shift from prescriptive codes to performance-based methodologies represents a fundamental change in how we approach safety and resilience in structural design. My journey, beginning with a simple yet profound question about safety, has highlighted the limitations of traditional design codes and illuminated the necessity for performance-based design. This approach emphasizes a structure’s ability to withstand specific threats and provides a more tailored and effective strategy for ensuring safety.
For new constructions, performance-based design offers innovative solutions and greater flexibility. For existing buildings, it provides a practical alternative to outdated retrofits, focusing on critical areas for improvement. As structural engineering continues to evolve, integrating performance-based design as a standard practice will enhance safety and resilience, contributing to the well-being of communities and the environment.
