Over the past 10 years, civil and structural engineers have complained loudly and often about building codes and their reference standards. The most common complaint is associated with the ever-increasing volume and complexity of design requirements. The second is the rapid and unceasing series of changes in the requirements, often without perceived benefit or improvement. The combined effect of these conditions is that engineers feel unable to remain abreast of code requirements and proficient at their application to design assignments, inevitably leading to errors and liability. The ASCE 7 Committee has heard these complaints and is endeavoring to respond to them.
The frequent changes to building codes and standards are driven by the International Code Council’s three-year update cycle for their I-Codes, which are adopted as the basis for codes enforced by most states and municipalities in the U.S. The three-year code update cycle has been in place for many years and even pre-dates the formation of the ICC, which merely maintained the tradition initiated by its predecessor organizations. The ICC maintains that this three-year cycle is necessary to assure that building codes don’t become outdated, that design requirements remain up to date and that important lessons on building safety are rapidly disseminated into practice. Traditionally, building codes changed relatively little between editions, making it easy for designers to understand what had changed and to remain abreast of the new requirements. But over the past 20 years, the triennial updates have encompassed more and more comprehensive change, made possible in part by the ease of submitting code change proposals in this era of the Internet and instant communications.
Ten years ago, the American Society of Civil Engineers, working with National Council of Structural Engineers Associations and other organizations, initiated a process of removing technical structural requirements from the body of the building code, instead adopting these requirements by reference to industry standards, such as ASCE 7. The purpose for this was two-fold. First, it removed important technical criteria from the political process associated with code change development and, second, it placed control of these requirements within the hands of the structural engineering community, through ASCE/SEI and other standards development organizations, as opposed to the ICC. It also provided the opportunity to slow down the endless cycle of changes. Starting in 2005, ASCE/SEI moved off the three-year standards update cycle, publishing the last edition in 2010. The next edition of the standard is planned for 2016, in time for adoption of the 2018 IBC. Thus, as a minimum, design loading criteria will remain stable and unchanged for much of this decade.
Early in the development cycle, the committee considered breaking the standard into several volumes.
It is still early in the development cycle for ASCE 7-16. Therefore, it is difficult to predict what changes are likely to occur in the standard. However, based on early discussions at the main committee, it appears that major changes or introduction of new design procedures is unlikely to occur. Rather, the cycle will likely focus on evolutionary improvement of the ASCE 7-10 requirements with a focus on simplification and clarification, and avoidance of over-prescription. The perception that the standard is overly complex can be traced to several things. First, in recent years, both the seismic and wind chapters have expanded substantially, driven by the desire to permit engineers to implement state-of-the-art tools such as wind tunnel testing and nonlinear dynamic analysis that provide economical and safe designs of complex structures, while maintaining relatively straightforward procedures that are applicable to the more routine construction to which the standard applies. Just figuring out which of the many procedures available for an engineer to use for a given loading adds considerable complexity. In a survey of structural engineers conducted by NCSEA, many indicated they prefer having fewer available procedures for a particular loading, such as wind or seismic, so that they need only learn one or perhaps a few sets of rules, rather than many. Further, when multiple procedures are available for a given loading, they will inevitably produce somewhat different results when applied to the same design, creating further confusion and lack of confidence in use of the standard.
Early in the development cycle, the committee considered breaking the standard into several volumes. One volume would contain a limited set of straightforward procedures that would be generally applicable to the design of most structures, such as the equivalent lateral force procedure for seismic loads and the simplified pressure coefficients procedure for wind loads. This volume would not necessarily contain requirements for ice loads, flood loads and other loads that do not affect the design of most structures. The second volume would contain the more complex procedures, such as the dynamic analysis methods for seismic design and the all-heights method for wind design, as well as the criteria for the less frequently used loading conditions. Many on the committee enthusiastically supported this approach. However, it failed to achieve consensus support of the committee because members feared the extra work associated with producing two volumes and also the difficulty of keeping the volumes consistent.
Instead of taking this two-volume approach, the committee is now focusing on several alternative approaches, including: continuing to ensure that requirements are written in a clear and easy to follow manner; moving alternative procedures out of the standard an into commentary or design guides; and, to the extent feasible, moving over-prescription out of the standard, relying instead on commentary, textbooks, design guides and other references to explain how to perform esoteric parts of the calculation process.
A major change in the 2010 edition of the standard was the introduction of performance-based design procedures and formal statement, within the commentary, of the target performance for structures of different risk categories. The 2016 edition will likely expand this approach, moving performance goals from the commentary into the body of the standard and adding additional goals associated with serviceability and post-loading function of critical facilities, concepts which have always been embedded within the standard, but never covered in any depth. Further, the standard may adopt the performance-based approach as the primary procedure for determining structural loading, with the present prescriptive procedures adopted as deemed-to-comply alternatives.
Several technical changes to the standard are also planned. Spurred by the recent tsunami disasters in Japan, Samoa and Indonesia, the committee has been hard at work developing a tsunami loads chapter, which will be related to but separate from the flood loads chapter in the present standard. The seismic community is at work on a new Simplified Static Procedure applicable to structures in zones of lower seismicity that omits many of the requirements of the present procedures. The seismic committees are also evaluating a design procedure for rigid-wall flexible-diaphragm buildings that better tracks the behavior of these structures in earthquakes. New site response coefficients are being introduced and it is possible that the standard will include new ground motion maps incorporating improved ground motion models for the eastern United States as well as Guam and the Marianna Islands.
As noted earlier in the article, there are several years left in the present standard development cycle and additional changes and improvements will likely be introduced. Interested engineers will be able to find updates on the progress of the standard in Structural Engineer and also in presentations at upcoming Structures Congresses.
Ronald O. Hamburger, S.E., is senior principal at Simpson Gumpertz & Heger, Inc. in San Francisco, Calif. He is also chair of the ASCE 7 Committee.