Columns

Category Archives: Columns

Seeing Through Glass Cracks

patterson slatonItleFAILURES
David Patterson, AIA, Deborah Slaton, and Kenneth Itle, AIA

 

Cracking was observed in the exterior curtain wall glass on an early-1970s mid-rise building in the Midwest. As originally constructed, the curtain wall included single-glazed 5.5-mm (7/32-in.) thick bronze-tinted glass at all floors—except the uppermost level, which featured single-glazed 9.5-mm (3/8-in.) thick clear polished plate glass.

The glass units ranged from 2184 to 3454 mm (86 to 136 in.) in height, and in width from 838 mm (33 in.) adjacent to the projecting building structural columns, to 1372 mm (54 in.). The original specifications for the glass were not available for review. However, several decades ago, a film was added to the interior face of the tinted glass as an additional sunlight-control measure.

During a recent maintenance program, the existing film was removed from the tinted glass, and a new film was applied. This film was also used on the clear glass at the topmost floor, on the south and west elevations. It was applied in the late fall, followed by sealant work in early winter. Within a month of the installation’s completion, cracking of clear (untinted) glass units in the narrower lights on the south elevation occurred, followed by cracking of both clear and tinted glass at several other locations.

Research into the film used in the retrofit installation revealed it was anticipated to result in a significant decrease in solar heat gain coefficient (SHGC) of the single-glazing (from 0.82 to 0.39). Retrofit films of this type both reflect and absorb energy from the sun’s rays; the absorbed heat energy can cause higher edge stresses in the glass than existed before film application. Glass cracking related to thermal stresses typically originates at, and perpendicular to, the edge of the glass, as seen in the photo.

Further, thermal stresses in a glass lite are increased by differential shading. For example, solar heat gain varies between shaded and unshaded areas of the glazing. Glass that cracked adjacent to the exterior projecting columns is in full shade during the early morning and full sun by the afternoon.

In contemporary construction, it is common to use heat-strengthened glass when films or tinted glass are specified. Although documentation is not available to confirm the glass type used here, the glazing appears to be plain annealed glass due to the lack of any markings indicating heat-strengthening.

Based on the likelihood the observed cracking is attributed to thermal stresses related to the application of the new film, removal of the film will be necessary to prevent the risk of further cracking over the next few years. Also, because the cracked glass presents a safety hazard, protection is required until remediation is completed. Among the lessons learned from this example: When improving any performance attribute of a building enclosure, care must be taken to understand the effect on the entire assembly’s behavior.

Deborah Slaton is an architectural conservator and principal with Wiss, Janney, Elstner Associates (WJE) in Northbrook, Illinois, specializing in historic preservation and materials conservation. She can be reached at dslaton@wje.com.
David S. Patterson, AIA, is an architect and senior principal with the Princeton, New Jersey, office of WJE, specializing in investigation and repair of the building envelope. He can be reached at dpatterson@wje.com.
Kenneth M. Itle, AIA, is an architect with the Northbrook, Illinois, office of WJE, specializing in investigation and preservation. He can be reached at kitle@wje.com.

Updating MasterFormat

KeithINSIDE CSI
Keith Robinson, RSW, CSI, FCSC, LEED AP

 

The MasterFormat 2014 Update includes hundreds of revisions from the previous 2012 update. Among the key revisions were changes to agreements contained in Division 00–Procurement and Contracting Requirements to account for evolving contract delivery processes in the construction industry as a whole.

There are also numerous updates, additions, and revisions to numbers and titles throughout. Some of the highlights include:
● rationalized content in Division 11−Specialties by changing several higher-level titles to give a more consistent organization of equipment work results;
● new parallel content in Divisions 12−Furnishings and 32−Exterior Improvements to improve understanding of locations for often similar interior public space furnishings and exterior site furnishings;
● revisions to Divisions 32−Exterior Improvements and 34−Transportation that captured key work results relating to airport infrastructure construction that aligns specification content with Federal Aviation Administration (FAA) and Transport Canada requirements; and
● extensive work with members of the Environmental Engineering Coalition on revision of Division 40, including a change in title to ‘Process Interconnections,’ and expansion of industrial scale pump classifications in Division 43−Process Gas and Liquid Handling, Purification, and Storage Equipment to help better meet user needs for work on process and heavy engineering projects.

There were additional changes throughout the document, including addition of numbers and titles relating to historical preservation and renovation, and improvements to “See Also” and “Includes” statements throughout to help users and make coordination of subject matter easier.

Many of the changes, such as those associated with Divisions 40 and 43, are the culmination of up to six years of effort by the MasterFormat Maintenance Task Team (MFMTT) and associated corresponding members to arrive at the best resolution.

A ‘living’ document, MasterFormat is maintained with the intent of being easily adapted to communicate project-specific requirements to the consumers of construction specifications. In comparison with the 16-division pre-2004 editions, the current 50-division format allows for more consistent placement of work results and expansion to meet the needs of the high degree of specialization now present in the construction industry. MasterFormat has been on a regular update cycle since 2010; currently updated every two years, its next update is scheduled for the first quarter of 2016.

MasterFormat allows for a range of flexibility in the specifying community by permitting specifiers to introduce user-defined numbers and titles into their project-specific work. This is a good approach to ‘test-fit’ a new or unknown work result; one that permits a specifier to group similar work results or products, and maintain clarity of the documentation process.

As a result, it is user-driven document—specifiers can submit user-defined numbers and titles at the MasterFormat.com website to propose their introduction as standardized content in the next update. Available to all CSI members, the site provides a master list of numbers and titles including the latest revisions, and a transition guide to assist in updating out-of-date content. (The MFMTT decision-making process and criteria is also available on the website to help increase the likelihood of acceptance for proposals.)

The 50-division MasterFormat has gained unprecedented industry-wide acceptance over the last couple of years. It is used at all phases of project delivery through organization of project information, assembly of project manuals, preparation of detailed costing information, and building relationships between drawing notations or building information model (BIM) content to the specification.

The revisions in the 2014 update to MasterFormat are organic and evolutionary in nature—this is in contrast to the wholesale reorganizations and significant changes that used to accompany new editions prior to 2004. The carefully planned updating process is clearly working.

MasterFormat 2014 Update will be available through the online bookstore at www.csinet.org/store.

Keith Robinson, RSW, CSI, FCSC, LEED AP, is a specifications writer with the Edmonton, Alberta, office of DIALOG. He has spent several years updating his firm’s library and master specifications to reflect the various challenges of identifying building materials and techniques relating to environmentally sustainable construction. Chair of the CSI-CSC MasterFormat Maintenance Task Team, Robinson has also provided contract documents and technical solutions for major projects in Canada, Egypt, Japan, and Costa Rica. He is Construction Specification Canada’s (CSC’s) 1st vice-president. Robinson can be reached at krobinson@designdialog.ca.

The Psychology of Professionalism

HORIZONS
Doug Schneider, CDT

Most people associate professional construction or engineering jobs with tangible objects such as wood, steel, concrete, and brick. However, there is also another important aspect of professional construction management or engineering that is sometimes overlooked, even by experienced building and design professionals. Continue reading