Performance-based Engineering and the Building Code
A Comparative Study
Created with support from the Thornton Tomasetti Foundation. See here for acknowledgements.
We live in a world of increasing levels of risk. Natural hazards are increasing in frequency, and structural failures are becoming more common. Increasing globalization and interconnectivity between communities implies that the effects of such failures are no longer localized. To achieve a resilient infrastructure, nontechnical professionals who make important decisions about technical projects must have a basic understanding of structural design. Therefore, this project aims to clarify common misunderstandings about structural building design by contrasting traditional code methods against newer performance-based methods.
Design Using Building Codes
Building code design is the traditional and most widely used paradigm for designing buildings. Code design evaluates structures based on strength, as well as other serviceability factors such as deflection and vibration. A strength-based design means that the designer evaluates the theoretical maximum loading demand on a structure as well as the capacity of the structure to resist loads.
For example, for steel structures, the governing building code is the Specification for Steel Buildings as published by the American Institute of Steel Construction, referred to as AISC 360. One example provision in AISC 360 is paragraph C3 – Calculation of Available Strengths. This provision directs the designer to the appropriate chapters in order to design steel members using a method called direct analysis to account for the tendency of buildings to become unstable.
Performance-based design is an approach that changes the goal of design from strength-based (capacity greater than demand) to performance-based, whereby the building is evaluated based on its ability to achieve performance targets. Performance is measured in terms of damage caused by major events (storms, earthquakes, floods, etc.), and performance targets are given in terms of quantifiable entities called Decision Variables, or DVs, such as cost of repair.