Reinforced concrete is a composite material composed of a steel matrix encased within a dense concrete form. This material combination resists both crushing and bending loads. Spalling is the most common failure mode in South Florida observed during our Forensic Engineering inspections. Moisture and corrosive salt in the air permeate the concrete through small surface pores. Over time, this results in the reinforcing steel, or rebar, rusting, As the rebar progressively rusts, it slightly expands, separating the concrete and creating a visible crack.
Concrete edge spalling
Rusted rebar and collapsed concrete balcony
As cracks expand over extended time periods, concrete pieces may even break loose and fall. Extensively rusted rebar has a smaller area and will carry less bending load. When the weakened steel can no longer carry the imposed self-weight and applied loads, failures may occur. Concrete naturally cracks due to thermal expansion and contraction that occurs over multiple seasonal weather cycles. An expert inspector can distinguish between potentially harmful spalling and normal thermal cracks.
Modern soil compaction and deep foundation installation methods result in vibration waves that emanate from construction activities. Depending on the soil type and magnitude of the source, these waves may travel substantial distances. Adjacent foundations and structures may be directly impacted by vibration or indirectly affected by soil deformation which causes permanent settlement.
Vibration waves are defined by their frequency and speed, termed peak particle velocity (PPV). Frequency and peak particle velocity are plotted against each other to provide a range of values inside of which building damage is likely to occur. Different building materials may be damaged at varying ranges of vibration frequency and PPV. Florida Department of Transportation (FDOT) currently implements a 0.5 inch per second PPV limit for pile driving activities. A limit of 2 inches per second PPV as measured at windows and sills is recommended for multi-story buildings. Direct or indirect damage may still occur below prescribed limits.
Interior damage range of frequency and PPV
Permanent structural settlement
Potential damages range from superficial finish cracking to permanent building settlement. Given the potentially severe adverse effects, vibration mitigation methods are inherently necessary to mitigate damages. Mitigation techniques include limiting vibrations, vibration monitoring, equipment selection and setting optimization, foundation type selection, and following a prescribed installation pattern. Pre and post construction surveys are a useful tool to establish pre-construction conditions as a point of comparison to later conditions.
We perform all forms of structural inspections including Miami-Dade and Broward County 40 year inspections, in strategic partnerships with local engineering firms. This historic Coral Gables home dated from the early 1900's and exhibited radiating structural cracks in exterior walls in various places around the building perimeter. When the crawl space was accessed, large cracks in the foundation beams and improper patches were observed.
Structural cracks in wall from foundation settlement
Structural crack in foundation and improper patch
Over time, soils had shifted and the building settled, conforming to the new soil contour. Concrete block construction without intermediate reinforced concrete columns contributed to the wall cracks.
We were able to recommend underpinning the foundation to avoid further settlement. Proper foundation beam repair was performed with a structural patch and exterior walls cracks were filled with a structural grout.
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2787 East Oakland Park Blvd. Ft. Lauderdale, FL 33306
Serving All of South Florida Broward Miami-Dade Palm Beach County