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B-43 Foundation Reports for Fire Damaged Structures

This guideline presents an evaluation methodology for fire exposed concrete members. The aim is to provide a uniform evaluation procedure while meeting applicable standards and applying forensic engineering principles.

Effective date: 02/15/2018

Technical Details

Prior to re-use, concrete supporting structural loads that have been subject to extreme heat shall be assessed by a competent licensed design professional to determine whether the concrete has been damaged or has deteriorated in structural integrity and durability. A competent professional may be a California licensed architect, civil engineer, structural engineer or geotechnical engineer experienced in concrete design. Construction permit submittals that include structural concrete that has been exposed to extreme heat shall include a Foundation Report as described herein.

The investigation procedure and apparatus shall be in accordance with generally accepted engineering practices. Concrete structural elements showing visual signs of deterioration or damage such as spalling, cracking and surface color changes shall be evaluated using visual and non-destructive testing techniques.

A detailed evaluation can provide the licensed design professional confidence in the remaining concrete and anchor bolts meeting requirements for the structural design. Additional destructive test studies may be performed to determine the extent and effect of deterioration or damage, and to determine the presence of non-visual distress such as concrete strength reduction, loss of bond between steel and concrete, and internal cracking.

  1. Visual inspection – Identify seismic-resisting system and potential exposure or damage. Identify locations of surface crazing, concrete cracking, surface erosion, and spalling. Provide measurements of crack widths/lengths and spalled area, and an analysis of the effect of these defects upon steel reinforcement, seismic elements, and vertical load capacity of the foundation. Identify surface color changes and quantify the surface area. Identify melted materials (plastic, glass, aluminum, steel) indicating exposure temperature.
  2. Non-destructive testing – Various methods exist to determine concrete hardness and strength. Use of investigative techniques such as the Schmidt Hammer Test (ASTM C905), Penetration test (ASTM C803) and Pullout Test (ASTM C900) may be incorporated into an overall investigation to help identify areas requiring additional studies. Other testing techniques include sonic methods such as impact-echo methods, ground penetrating radar, infrared thermography and radiography. Schmidt hammer readings may be correlated to the core strength test results first for the results to be acceptable. Integrity of the seismic resisting system may be justified using standard test methods. Pullout strength tests be performed on hold-down anchors and mudsill anchors that are being reused unless justified by engineer. Load applied on pullout strength tests shall be as prescribed by the engineer-of-record but shall not be less than the following:
    Anchor Diameter (inches) Test Load (pounds) Test Duration (seconds)
    1/24,10010
    5/86,50010
    3/49,60010
    7/813,30010
    117,40010
  3. Destructive testing – Questionable concrete strength suspected of non-visual deterioration or damage may be investigated through the use of destructive standard test methods. Concrete coring (ASTM C42) may be used to determine strength, density, depth of carbonation of concrete, chemical analysis, water/gas permeability and for petrographic analysis. The fidelity of Schmidt hammer test results shall be verified through correlation with results of compression testing on concrete core samples.

Required Foundation Report Contents

Title Page – Report title, property owner’s name, property address, APN; author’s name, title, professional engineering registration seal, signature and date.

Project Description – Purpose and scope.  Intent to re-use entire or partial foundation.  Type of foundation system.

Photographs, Findings and Test Results – Include visual inspection, non-destructive testing and results, destructive testing and results, laboratory testing and results and photographic documentation. State major findings of investigation.  Date(s) of site visit(s), testing, location of laboratory testing, etc.

Sketches/Drawings – A sketch of the foundation layout identifying locations of the damaged and discolored areas noted during visual observation.  Identify locations of testing (e.g. Schmidt hammer test, pull test, coring, etc.)

Evaluation of Findings and Test Results – Engineering assessment of results.

Conclusions – Clearly state if the structural integrity is compromised or not. Clearly state if durability is affected and how.

Recommendations – Provide clear recommendations for any necessary remedial work to address the defects identified in the report and reference specific corresponding remediation details provided in the engineered plans. Include a summary of structural observations and special inspection requirements.

Tables

Reference Documents

References

  • ACI 216, American Concrete Institute, Code Requirements for Determining Fire Resistance of Concrete and Masonry Construction Assemblies
  • ACI 301, American Concrete Institute, Specifications for Structural Concrete
  • ASTM C42, Standard Test Method for Obtaining and Testing Drilled Cores and Sawed Beams of Concrete