Better Buildings by Design
What does it really take to design a good building?
Maryann T. Phipps, S.E., President, Estructure
Designing a building can be relatively easy based on available building codes and standards and a team of professionals with applicable knowledgeable and experience. On the other hand, designing a Good building, in this case from the standpoint of earthquake performance, can be a daunting task. Good buildings are designed for people: owners with financial investments, and occupants living, working, learning, teaching, and curing diseases in them. Good buildings are designed not only to meet prescriptive standards that a consensus process has determined to be suitable for most buildings, but also designed to achieve performance that is desired by the ownership considering the occupancy and use of the building. In most cases, Good buildings are designed and constructed to have a high degree of reliability to be functional for conditions that are likely to occur during the building’s life. In rarer natural events that a building might see once or twice in its life, a good building can be repaired and reoccupied. Under extreme events, a good building will protect the lives of everyone inside.
Recent earthquakes across the globe have demonstrated that most modern building codes are capable of protecting life loss in earthquakes. It is equally clear that buildings designed to satisfy minimum code requirements may not meet owners’ expectations or occupants’ needs. Additional tools are needed to address the disparity between the minimum code requirements of life safety and the desire for post-earthquake repairability and reoccupancy.
Designing a Good building requires a commitment throughout all stages of design and construction, and by all parties involved. It starts by establishing a set of objectives and expressing them in metrics meaningful to the owner and/or occupants, ranging from meet minimum applicable code requirements to controlling the response. The metrics may be related to recovery time or cost of repairs, or they might relate to protection of selected contents. These may be ultimately translated to engineering parameters as probability of exceedance, median, or average statistics. It is the designer’s responsibility to inform and educate owners about performance options to enable them to make informed decisions. This task is more daunting because quantitative data relative to earthquake damage to modern buildings and building systems in strong earthquakes is often lacking. Results of laboratory testing or engineering analysis may not be considered to have the same weight when measured against increased cost of construction.
Once a set of objectives is defined, structural systems can be explored and evaluated for their ability to achieve the desired objectives. For each structural system being considered, the designer must determine the probable range of damage states for selected hazard levels and evaluate them in light of the desired objectives. Empirical evidence, laboratory research and analytical studies demonstrate that all systems are not created equal and do not provide comparable performance. System selection and configuration play important roles in determining performance. Additionally, both structural and nonstructural systems must be considered together to reliably achieve performance objectives.
Predicting performance is an essential part of achieving performance goals. Probable yielding mechanisms, weak links and concentrations of nonlinear response must be identified in order to understand likely damage states and their consequences. Nonlinear response history analysis can be used as a tool to understand the range of performance that can be expected and avoid unacceptable designs. However, despite advancements in analytical tools, limitations of computer simulations should be recognized. First there is our evolving understanding of seismicity and inability to predict the ground motions that designs will be subjected to. Second, there is wide dispersion in performance predictions, even among experts employing some of the most sophisticated seismic prediction software available. In order to achieve reliable performance with high confidence, systems verified by analysis and with a proven track record of acceptable performance in past earthquakes should be used.
For most buildings, the value of the structural system represents 20 percent or less of the total value of the building. Eighty percent or more is comprised of nonstructural components, such as cladding, interior partitions, suspended ceilings, mechanical, electrical and plumbing equipment, utility distribution systems, and specialty components. Earthquake damage to these elements can cause injury, block egress, impact life safety systems, disrupt operations, delay reoccupancy and result in substantial property loss. Despite their importance to building to function, many nonstructural systems are commonly designed by third party specialty engineers outside of the traditional project design team. While design of nonstructural items may be delegated to others, their performance can be significant to the overall building performance. To ensure that delegated designs satisfy the goals and expectations established for a project, the performance requirements must be communicated, designs must be properly reviewed and construction must be inspected.
Finally, despite thoughtful designs and well-inspected construction, something can and often does go wrong during an earthquake. While it may not be possible to prevent all damage, it is possible to employ measures to limit the consequences of damage after an earthquake. This is always useful, but particularly so, when considering the consequences of damage to pressurized piping systems. For example, in order to limit the consequences of an unintended water release, additional shut-off valves may be installed in readily accessible locations to enable the water to be quickly turned off if there is a breech, and to allow the balance of the system to remain operational.
Lastly, independent, knowledgeable peer review has proven useful in discovering issues in design before an earthquake discovers them. Structural engineering is not a science, it is a profession underlain by science that is incomplete and occasionally contradictory. Peer review can bolster confidence in a good design, and prevent construction of a bad one.
Designing a Good building requires the collaborative efforts of an owner, design team, and contractor. In order to create a reliable structural system with predictable performance, and have confidence in the systems and contents inside, careful attention is required during planning, design and construction.
Maryann Phipps is a Structural Engineer with over 35 years of experience evaluating, designing and renovating buildings for earthquake resistance. She has served as Structural Engineer of Record for hundreds of renovation projects designed to enable buildings to remain operational following large earthquakes. She is presently serving as lead peer reviewer for multiple institutional buildings being designed for enhanced structural performance and will share insights from these projects in her address.
Maryann’s hands-on experience designing seismic protection for nonstructural components has helped make her a recognized expert in the field. She was the lead technical consultant for FEMA P-74 Reducing the Risks of Nonstructural Earthquake Damage, which received an Award of Excellence from the Structural Engineers Association of California. Maryann was co-leader of FEMA’s reconnaissance team for the South Napa Earthquake and co-authored FEMA P-1024 Performance of Buildings and Nonstructural Components in the 2014 South Napa Earthquake. Maryann was technical lead for a NIST-sponsored project Seismic Analysis and Design of Nonstructural Components and Systems intended to advance the state of practice in this field. Maryann is a current member of the California Hospital Building Safety Board, California State University Seismic Review Board, and UCSF Seismic Review Committee. She is also a Past President and Fellow of the Structural Engineers Association of California, and served as Director of the Applied Technology Council. Maryann is President of Estructure, a small structural engineering firm in Oakland, California.