Why did the Silver Spring Transit Center crack?
Why will it continue to crack?
The answers to these questions are really quite simple. They were known long, LONG before the SSTC was designed and built.
http://nrmca.org/aboutconcrete/cips/42p.pdf
"Thermal cracking occurs due to excessive temperature differences within a concrete structure or its surroundings. The temperature difference causes the cooler portion to contract more than the warmer portion (or the warmer portion to expand more than the cooler portion), which restrains the contraction (or expansion). Thermal cracks appear when the restraint results in tensile stresses that exceed the in-place concrete tensile strength."
"Concrete members will expand and contract when exposed to hot and cold temperatures, respectively. Cracking will occur if this bulk volume change resulting from temperature variations is restrained. This is sometimes called temperature cracking and is a later age and longer term issue."
"Expansion joints and spacing between joints have to be designed to withstand such temperature induced expansion and contraction to prevent cracking."
"The key to reducing thermal or temperature-related cracking is to recognize when it might occur and to take steps to minimize it. A thermal control plan that is tailored to the specific requirements of the project specification is recommended. ... A large part of the responsibility to minimize thermal cracking lies with the designer and contractor. Steps include establishing the concrete mixture, specification limits for temperature of concrete as delivered and in the structure, insulating the structure and termination of protective measures, and in critical conditions, post-cooling of structural members."
"The key to reducing thermal cracking is good communication between the designer, contractor, and concrete producer."WMATA design and construction standards, to which the SSTC was supposed to have been designed and constructed, require expansion/contraction joints to be located no farther than 100 feet apart. The 315 ft. by 580 ft. SSTC has NONE.
Montgomery County's "fixes" for the severely cracked SSTC are a latex concrete overlay and exterior reinforcement for under-designed beams. These "fixes" do not address the source of the cracking problem--the SSTC's complete lack of expansion/contraction joints.
The SSTC's severe cracking was made public in a report released by Montgomery County in March 2013. Since then hundreds of news media reports (print, TV, radio, internet) have failed to report that Montgomery County's "fixes" do not address the source of the cracking problem--that is, the SSTC's complete lack of expansion/contraction joints.
The SSTC will continue to crack in the future.
Do you find it ironic that the source of the document referenced above (http://nrmca.org/aboutconcrete/cips/42p.pdf) is the National Ready Mixed Concrete Association, 900 Spring Street, Silver Spring, MD? I do; particularly since my aunts' and grandfather's house, that I visited often as a boy, was located right across Colesville Road at the corner of Spring Street and Fairview Road. (Their house is gone now, replaced by a commercial building.)
When have you seen cracks like these in a brand new building that hasn't even opened yet? In this case, a glorified parking garage that hasn't seen its first car or fully loaded bus?
Since before 2012 when it first began, Montgomery County, WMATA, the Federal Transit Administration and the Maryland Transit Administration have known about the SSTC's severe cracking.
In their March 2013 report KCE Structural Engineers, the Washington DC firm that Montgomery County commissioned to investigate the SSTC's severe cracking, identified that the 315 ft. by 580 ft. SSTC has NO expansion/contraction joints. KCE notes in their report that the SSTC was supposed to have been designed and built according to WMATA specifications, which require expansion/contraction joints to be located no more than 100 ft. apart.
Nevertheless, Montgomery County proceeds with "repairs" that won't fix the source of the problem--the SSTC's complete lack of expansion/contraction joints. The SSTC will continue to crack in the future. At the least the SSTC will be expensive to maintain; and, at worst, the SSTC is a threat to public safety.
- Why haven't news media asked officials from Montgomery County (including Isiah Leggett and members of the County Council), from the Federal Transit Administration (53% federal funding) and from the Maryland Transit Administration (11% state) why they are "fixing" the lemon SSTC, when the public was promised a brand new, unflawed transit center?
- Why haven't news media asked Montgomery County officials why they chose Foulger Pratt to build the SSTC, instead of bidding it for construction (like most large public works projects)?
- Why haven't news media asked Montgomery County officials why they selected Parsons Brinkerhoff to design the SSTC and Balter Company to inspect and test concrete, instead of selecting a design engineering firm and a concrete inspection/testing firm and special quality inspector in open competition?
- Why haven't news media asked Montgomery County officials why they proceeded with repairs to the SSTC without briefing the public on what the County is doing, and why, and taking the public's questions and comments on the public record?
- Why haven't news media asked officials from Montgomery County, from the FTA and from the MTA if they consider the SSTC public-private partnership to be a good deal for the public, whose money they've spent designing, building and "fixing" the brand new, yet-to-be-opened, severely flawed, $130+ million, lemon SSTC?
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UPDATE
8/7/14
http://pileofsteamingbs.blogspot.com/2014/08/dont-worry-silver-spring-transit-center.html
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