Commercial Structures
Structural Components Footing Piles Foundation Beams Joists Column Substructure Superstructure Reinforced concrete Re-bar Pre-cast concrete panel Deflection Cantilever
Footings A widening at the base of a foundation or column. Keep buildings from sinking Larger footings needed for heavier buildings or weaker soil.
Piles A long column hammered into the ground until it hits solid rock or cannot go any deeper due to friction. Used instead of footings Used primarily where soils are poor Expensive to install
Foundations Rest on footings Usually made of concrete Two functions: Support the weight of the building Act as a retaining wall to hold back the surrounding soil when there is a basement or underground parking garage.
Beams and Girders Different terms for the same object. Beams are large horizontal members that transfer floor loads, walls and roof loads to the columns and foundation walls.
Joists Transfer floor or roof loads to beams and walls. Usually steel in commercial buildings.
Columns Columns transfer loads vertically from beams to footings or to other beams.
Superstructure & Substructure Superstructure: The portion of the building structure starting above grade and up. Substructure: The portion of the building extending below the ground
Reinforced Concrete and Re-bar Reinforced concrete is a composite material usually consisting of concrete and steel bars (re-bar).
Pre-cast Concrete Panels Reinforced concrete building units manufactured in a shop and delivered, ready to use, to the building site.
Deflection The amount of sag in a joist or beam when a load is applied.
Cantilever Like a diving board. One end is rigidly secure, the other end is free to move. Example: A balcony (see next slide).
Structural Assemblies and Building Types Single-family residential vs. commercial structures Tilt-up buildings Cladding Open-web steel joist
Single Family Residential vs. Commercial Structures Commercial structures likely designed by an engineer. Residential homes are not. Commercial structures have more stringent design criteria. Commercial structures typically use concrete and steel; residential homes primarily use wood framing.
Tilt-up Building A method of construction, not a building type. Used primarily for single story buildings.
Cladding Materials Masonry Granite Pre-cast concrete Glazing panel Stone Marble Metal panel Stucco
Curtain Wall Cladding A general term, not a specific material. A cladding system that is entirely supported by the structural frame but is not loadbearing. The cladding is hung onto the building like curtains.
Spandrel The wall area between the top of a window on one floor level and the sill of a window on the floor level above.
Open-Web Steel Joist Also referred to as OWSJ One of the most common components used for commercial building structures Supports roof or floor loads and transfers loads to beams and columns or supporting walls.
OWSJ & Corrugated Metal Pan 1. The building frame is assembled. 2. Open-web steel joists span between the beams. 3. A corrugated metal pan is welded to the top of the joists. 4. The metal pan is filled with concrete for a floor structure.
Typical Problems and Concerns Settlement Foundation failure Suspended slab failure Buckling or damaged column Hostile environment Balcony damage
Building Settlement Tipping Settlement Uniform Settlement Differential Settlement
Settlement May affect the entire building. Could have no implications or could be a major problem. You will be asked to make some judgment calls.
Implications of Tipping Settlement The building may continue to settle. The floors may not be level, affecting building use. Substantial costs may be associated with stabilizing the building
Implications of Uniform Settlement The building may continue to settle. Services to the building may be affected.
Implications of Differential Settlement The building may continue to settle The floors may not be level, affecting building use. Substantial costs may be associated with stabilizing the building.
Foundation Failure Main type occurs when foundation can no longer hold back the surrounding soil. In this case, horizontal cracks develop near the mid-height. If the foundation is not reinforced at this point, the foundation will bulge and eventually fail completely.
Suspended Slab Failure A potential problem in parking garages especially. Pre-stressed and post-tensioned concrete subject to failure due to exposure to road salt. Failure can be catastrophic.
Preventing Suspended Slab Failure Epoxy-coated steel (in conventionally reinforced slabs, that is, re-bar) Protective membranes Concrete sealer
Buckling or Damaged Column Often caused by forklift collisions. Minor damage can be repaired. Major damage requires replacing the column
Hostile Environment The process conducted in an industrial building can affect the structure. Examples include: Arenas Metal plating facilities Dry cleaning facilities Frozen food storage
Balcony Damage Reinforced concrete, again, is at issue. When steel railings embedded in the concrete balconies corrodes, it expands and cracks the concrete. The concrete then falls off. In more severe cases, the balcony structure is compromised.
Inspection of the Structure Performance-based review Design analysis
Performance-Based Review A visual review of the visible components of the building. Works well for buildings that have some history time to settle, react to environment & seasons, reveal deficiencies. The trained observer can call for further investigation of specific areas and problems if warranted.
Design Analysis Structural engineer analyzes the as-built drawings of the building and verifies the design. Also reviews the actual construction. Time-consuming and expensive Useful if building is not very old and hasn t undergone changes, settling, seasons, etc.
Additional Testing Verify assertions made during a performance-based review. Investigate an area prone to problems that cannot be observed visually. Determine the extent of a problem that has been identified and defining the scope of the repair.
Destructive vs. Non-destructive Testing Non-destructive X-ray a weld on a structural steel component X-ray concrete Ultrasonic testing of concrete Destructive Removing finish surfaces to get a better look at a structural component Taking a core sample from concrete to test its compressive strength Taking a soil sample to verify the bearing capacity
Nondestructive Testing of Concrete Slab Chain Drag Test Schmidt Hammer Test Half-cell testing
Destructive Testing of Concrete Slab Compressive strength test Chloride ion test
Soil Testing Testing for structural characteristics of soil is common when developing raw land. May be warranted for an existing building that has settled substantially.