As a senior chartered professional engineer with decades of experience collaborating with architects across New Zealand, I've observed that even the most seasoned professionals can overlook critical structural considerations
These oversights can lead to project delays, increased costs, and compliance issues. To help you navigate these challenges, I've compiled the top five structural aspects you should always keep in mind before embarking on your next townhouse, residential, or commercial building project
Seismic Design & Earthquake Resilience
Why It Matters: New Zealand's unique geological setting makes it one of the most seismically active countries in the world. Earthquake resilience isn't just a regulatory requirement—it's a necessity for the safety and longevity of any structure.
Key Considerations:
Structural Systems Selection: Stiffer systems like concrete shear walls provide better damage resistance due to their low inter-storey drifts, meaning buildings can be up and running immediately after moderate size earthquakes. Flexible systems on the other hand, like steel portal frames, provide better overall safety resilience at higher, more extreme levels of shaking.
Architectural Configuration: Be mindful of building symmetry, mass distribution, and vertical irregularities, as these can significantly impact seismic performance. Symmetry in plan and consistency vertically makes a huge positive difference to the seismic performance.
Knowing when to consult an Engineer
Why It Matters: While architects are versed in structural basics, specialized engineering expertise is crucial for complex projects. Attempting to handle structural design without an engineer's input can lead to safety risks, code violations, and project cost increases due to re-design.
Recognizing the Limits of Architectural Expertise:
Complex Structural Challenges: Elements like large open spaces, unconventional shapes, innovative materials, or intricate details often require advanced structural analysis that goes beyond standard architectural training.
Regulatory Compliance: Structural engineers specialize in understanding and applying codes and standards, such as the New Zealand Building Code and NZS 1170 series. Architects are generally limited to specifying timber structures according to NZS3604.
Safety Assurance: Engineers conduct detailed calculations to assess load capacities, seismic resilience, and material performance, safeguarding the building's integrity under various conditions.
Risks of Omitting Engineering Input:
Design Flaws: Critical structural elements may be under-designed, leading to potential failures.
Increased Costs: Errors can result in costly redesigns and construction delays.
Liability Issues: Architects may face legal consequences if structural deficiencies cause accidents or non-compliance.
3. Load-Bearing Structures and Load Paths
Why It Matters: A clear understanding of how loads are transferred through a building is essential for safe and efficient design. Overlooking this can lead to structural inefficiencies, increased costs, and potential safety hazards.
Key Considerations:
Simplifying the Load Path Concept:
What Is a Load Path? Think of a load path as the route that weight (loads) takes from the point of origin (like the roof or upper floors) down to the foundation and into the ground.
How Loads Move: Loads are collected by floors and roofs, transferred to beams and joists, passed down to columns or load-bearing walls, and finally reach the foundation where it’s spread out into the ground.
The Goal: Ensure that this path is as direct and uninterrupted as possible to optimize structural performance and material use.
Designing with Load Paths in Mind:
Align Structural Elements: Place walls, columns, and supports directly over one another across different floors to create straight load paths.
Minimize Interruptions: Be cautious with design features like large openings or overhangs that can disrupt load paths. If they are necessary, plan for additional structural support like lintels or transfer beams.
Efficient Load Transfer: Direct load paths reduce the need for complex structural solutions, making the building easier and more cost-effective to construct.
Compliance with Building Codes and Standards
Why It Matters: Non-compliance can result in legal repercussions, project delays, and safety hazards. The New Zealand Building Code (NZBC) sets the minimum requirements for safety, health, and structural integrity.
Key Considerations:
NZBC Clause B1 (Structure): Familiarize yourself with the performance criteria related to structural stability under various loads, including seismic, wind, and live loads.
Documentation and Evidence: Maintain thorough documentation to demonstrate compliance, including calculations, specifications, and material certifications.
Updates and Amendments: Stay updated on changes to codes and standards, such as recent amendments to earthquake-prone building provisions.
Site-Specific Considerations
Why It Matters: Every site presents unique challenges and opportunities that can significantly influence structural design and overall project feasibility.
Key Considerations:
Geotechnical Investigations: Conduct comprehensive soil tests to identify issues like liquefaction potential, soil bearing capacity, and groundwater levels. These should be done early on by the engineer, during the architectural concept phase.
Wind Loads: Council and BRANZ wind maps are not accurate and Councils can simply choose not to accept their own maps. If the wind zone changes in the later stages of design, this can cause huge design costs and delays. Better to get the site wind speed finalised early on.
Environmental Factors: Consider flood zones, coastal erosion, and other environmental risks that may require special design measures. Council maps usually have information on these flooding and erosion risks (As well as liquefaction hazard maps).
About the Author
Marlo Bromley is a senior chartered professional engineer with over 15 years of experience in the New Zealand construction industry. He has collaborated with architects on numerous low and high-profile projects, specializing in structural engineering solutions that marry aesthetic ambition with practical execution.
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