What element is NOT typically part of the structural engineering services in DD?

The serviceability of HVAC systems is not typically part of the structural engineering services during the Design Development (DD) phase. Structural engineering primarily focuses on ensuring that the structural elements of a project—such as beams, columns, floor systems, and foundations—are designed to support loads, maintain stability, and meet safety standards. While HVAC systems are crucial for building functionality and comfort, their design and serviceability usually fall under mechanical engineering rather than structural engineering.

In contrast, the other elements listed are integral to structural engineering's role during the DD phase. The location of openings is important for ensuring that structural integrity is maintained while accommodating building utilities and architectural designs. Fire ratings and separations are critical for compliance with safety codes and regulations, which structural engineers must consider when designing elements like walls and floors. Foundation design flexibility relates to the adaptability of foundations based on site conditions and structural requirements, which is a key aspect of structural engineering responsibilities. Thus, focusing on serviceability issues related to HVAC systems aligns more closely with the mechanical aspects of building design rather than the structural considerations.