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  April 2008  
 
A Fire Resistance Dilemma
In ACI 318-02, load factors for reinforced concrete were reduced, but there was not an accompanying reduction in the ?-factor for calculation of flexural design strength of tension-controlled sections. The obvious result of this change was a reduction in the ratio of service load moment to design flexural strength for these types of members. The not so obvious result of this change was a reduction in the calculated fire endurance of these members. The magnitude of the reduction in calculated fire endurance and discrepancy between calculated fire endurance and tables for fire endurance found in ACI 216.1 are discussed.

Avoiding the Dead Zone
Constructibility issues don’t always arise because members are heavily reinforced—geometry can also be a culprit. The intersections between a beam and a circular column or a curved wall are common examples. The curvilinear layout of the vertical bars in the column or wall results in slight offsets that can create “dead zones” through which horizontal bars cannot pass. Methods of dealing with these situations are discussed.

ACI Bestows its Annual Awards
The Annual Awards of the American Concrete Institute were handed out March 30, 2008, at the ACI Spring 2008 Convention in Los Angeles, CA. During the convention’s Opening Session, ACI bestowed Honorary Membership to four of its most active members. ACI’s highest citation is given in recognition of “persons of eminence in the field of the Institute’s interest, or one who has performed extraordinary meritorious service to the Institute.”

ACI Reaches out to Partners in Asia
As part of ACI’s mission of international cooperation, ACI President David Darwin and senior ACI staff met in late 2007 with ACI’s International Partner associations in Japan, Korea, and Taiwan and participated in an International Chapter Roundtable.

ICRI 2007 Project Awards
The International Concrete Repair Institute (ICRI) named its Project of the Year for 2007. ICRI also handed out Awards of Excellence in nine categories and Awards of Merit were given to 15 projects in eight categories.

ACI Code Requirements for Repair of Buildings
In 2006, the ACI Technical Activities Committee approved formation of ACI Committee 562, Evaluation, Repair, and Rehabilitation of Concrete Buildings. The committee’s main goal is to develop a code and commentary for evaluation, repair, and rehabilitation of existing concrete buildings with a target completion date of 2012. With strong input from the ACI Strategic Development Council and the International Concrete Repair Institute (ICRI), the repair code is truly an industry-led effort that includes participation by design professionals, contractors, owners, academics, testing laboratory personnel, and materials suppliers.

Extending the Service Life of Parking Structures
Parking structures are subject to severe environments, but a well thought out plan can help owners efficiently manage the structure’s need for maintenance over the service life. The plan should be developed with an understanding of the importance of timely repair, identification of the root cause of deterioration, and repairs with an appropriate service life. Such a systematic approach will be useful for the restoration and maintenance of all structures.

Concrete Q & A: Was Fresh Concrete Frozen?
A cold-weather project of mine includes normalweight concrete slabs placed on metal decking supported by structural steel framing. Test results for fieldcured cylinders were low, with the highest 28-day test result at 1700 psi (12 MPa) for what was supposed to be a 3500 psi (24 MPa) design. I believe the fresh concrete in the slab may have frozen. How can I tell if the low strength is due to freezing? What strength loss is expected when fresh concrete is frozen? Also, if the concrete didn’t freeze, could strengthtest results this low be caused by slow strength gain because of low temperatures?

 


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