??May 2014
Codes and Standards
The History and Relevance of Codes
Think of the types of events that might have forced the creation or adoption of a national system of codes and standards. Probably the last thing that would ever come to mind is a flood of molasses cascading through the streets of Boston. But that’s exactly how engineering history was changed forever in the United States.
After several bridge and rail structural failures around the turn of the 20th Century highlighted a need for more monitored design, the molasses disaster got the engineering community on the same page.
On Jan. 15, 1919, at the Purity Distilling Co., a 50-foot container holding more than 2.5 million gallons of molasses exploded. Literally, the rivets blew out of the container, and molasses gushed through the streets of Boston at 35 mph – killing 21 people and injuring 150.
Following the tragedy, forensic experts tried to trace back through construction for a single person to target with the liability risk. There was no definitive person to take the blame. Thus, they created the first use for a professional engineer (PE). This and other building problems led to the advent of professional engineers. This created the need for engineering licensure in Massachusetts. The PE or architect of record stamps the plans, assuming all of the liability for the design of the building or device.
To prevent a massive amount of liability falling to a single person, and to create a set of good practices, codes and standards were created. The codes and standards act as the minimum acceptable design for engineering and architecture. The theory is that, if a design professional follows the codes and standards, he can have some mitigation of the risk and feel slightly protected from the close eye of an attorney following an accident.
Today, codes and standards are being re-visited, updated and changed constantly to keep the public safe. The creation of codes and standards allows designers to understand the minimum acceptable requirements for buildings. Codes help licensed and registered architects and engineers with their designs.
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Different societies were formed to address different topics. The American Society of Mechanical Engineers (ASME) created the standards for pressure vessel design, which would guide modern-day designs in the United States for molasses containers. The American Society of Civil Engineers (ASCE) creates ways for Civil Engineers to predict loads on structures. The overarching building code that cities cite in their individual building codes is known as the International Building Code (IBC). This document references to other codes like the ASCE 7 code, and the American Society for Testing and Materials (ASTM), which deals with all of the building trades.
The trades then further define themselves with more specialized codes, based on their individual areas. For instance, the American Institute for Steel Construction (AISC) publishes codes for steel construction, the American Concrete Institute (ACI) writes codes for concrete and reinforced concrete. The one with which people in masonry are familiar and hold near and dear is formerly known as the Masonry Standards Joint Committee (MSJC). The MSJC was a conglomerate of the ASCE, ACI and The Masonry Society (TMS).
Starting in 2013, after years of collaboration, TMS now is the sole namesake of the masonry building codes. Cities tend to adopt codes after the codes have been published for a while. For instance, some cities may say that IBC 2006 or newer codes may be used for design. This does not mean that once the city moves on to newer codes, the outdated code can be discarded. Regarding existing structures, the building was designed with a certain code, and that is the document to reference when dealing with rehabilitation. Also note that, sometimes, cities have their own building codes that govern design.
The 2006 IBC references earlier documents of AISC, ACI and MSJC (TMS) codes. When the 2015 IBC code is released, it will reference the MSJC 2013 code that was released last year. Some people still may be using the 2008 MSJC, which is acceptable in many areas. However, many changes have occurred to the code in the cycles between 2008 and 2013. The allowable stress of masonry has been increased from 0.33f’m to 0.45f’m (2013 MSJC Section 8.3.4.2.2). Notably, the Empirical Design of Masonry has been moved to the Appendix A, and Chapter 14 is now Masonry Partition Walls. The design of masonry walls can be governed by the Allowable Stress Design, the Strength Design, or with the prescriptive tables.
Hand calculations for masonry partition walls can get lengthy from the many scenarios of interior walls and from running through the whole design, only to find that the loading combination has failed. Masonry partition walls are strong, durable, fire resistant, energy efficient, sound absorbing and have positive attributes that have stood the test of time.
The design of interior partition walls have been cumbersome to the designer in the past, but have been made easier with the prescriptive tables. Prescriptive tables have been created for loadings of five pounds per square foot (5psf), and 10psf. In order to use these tables that give height (or length) of wall to thickness of wall, many assumptions must be met to boil down designs to a prescriptive table.
These assumptions restrict the design to risk category I, II and III structures, while neglecting category IV structures like hospitals, vital government buildings, egress stairways and meeting areas of 300 or more people.
To allow more flexibility to the design the International Masonry Institute (IMI) created an internet program available at http://imiweb.org/partitionwall to address more scenarios, including seismic areas and category IV buildings. The IMI Partition Wall Calculator is a fast, easy way to create plan- and specification-ready documents, allowing for more ease of design for quality masonry partition walls.
This program is intuitive and can be used by architects, engineers and contractors to design the size and reinforcement for concrete masonry block or clay brick partition walls in different support conditions.
The program produces fast results, allowing designers to save time and choose the most economical design, while contractors can use the program to change walls on the job to save money on the bid.
Joe Packhem is a staff engineer for the Masonry Advisory Council. For more information, call 847-297-6704.
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