Fire Resistance of Building Materials
The fire resistance of building materials and assemblies is determined by standard fire tests that measure the time the assembly can withstand exposure to a standard fire without failing. The ASTM E119 fire test exposes the assembly to temperatures that reach 1,000 degrees Fahrenheit within 5 minutes and 2,000 degrees within 60 minutes. The assembly passes the test if it does not allow the passage of flame or hot gases, does not exceed the temperature rise limits on the unexposed surface, and maintains its structural load capacity. The fire resistance rating is expressed in hours, with common ratings of 1, 2, 3, and 4 hours. The fire resistance of concrete depends on the aggregate type, with carbonate aggregates providing the best fire resistance and siliceous aggregates providing the lowest. The fire resistance of steel is improved by applying spray-applied fire-resistive materials, intumescent coatings, or gypsum board enclosures that insulate the steel from the fire heat.
The fire resistance of wood members is enhanced by the charring behavior of wood that creates an insulating layer on the surface. The char layer protects the interior wood from the fire and maintains the structural capacity of the remaining section. The heavy timber construction with large cross-section members provides inherent fire resistance through the charring mechanism. The fire-retardant treatments that impregnate wood with chemicals reduce the flammability and the flame spread rate. The fire resistance ratings for various wall, floor, and column assemblies are published in the building codes and in manufacturer listings. The designer selects the fire-resistive assembly that meets the code-required rating for the building occupancy and type of construction. The fire resistance of the structure is a critical component of the building fire protection system.
Fire-Resistive Construction Assemblies
The fire resistance of building assemblies is determined by standardized fire tests that expose the assembly to a controlled fire following the ASTM E119 time-temperature curve. The fire test measures the time until the assembly fails by one of several criteria: the temperature rise on the unexposed surface exceeds 250 degrees Fahrenheit average or 325 degrees at any point, flames or hot gases pass through the assembly, or the assembly cannot support the required structural load. The fire resistance rating of 1, 2, 3, or 4 hours indicates the duration that the assembly can withstand the fire exposure before failure. The hourly ratings are specified by the building code based on the occupancy type, the building height, and the type of construction.
Spray-applied fire-resistive materials are the most common method for protecting structural steel framing. The SFRM is applied directly to the steel surface by spraying, providing thermal insulation that delays the temperature rise of the steel. The thickness of the SFRM is determined by the required fire resistance rating and the section factor of the steel member. The bond strength and density of the SFRM must meet the standard specifications to ensure that the material remains in place during the fire and during the building life. The intumescent coatings expand when heated to form a thick insulating char layer that protects the steel beneath. The intumescent coatings provide a more finished appearance than SFRM and are used where the steel is exposed to view. The gypsum board enclosures around steel columns and beams provide fire resistance through the gypsum dehydration that absorbs heat and the paper reinforcement that holds the assembly together.
Learn more about understanding the strength design method for concrete structures for detailed guidance on this topic.
Quality Control and Inspection
The quality control program for any construction activity includes the inspection of materials upon delivery, the observation of work in progress, and the testing of completed work. The inspector verifies that the materials meet the specifications and are stored properly to prevent damage before installation. The observation of the work during installation identifies any deviations from the contract documents that must be corrected before the work is concealed by subsequent construction. The testing of the completed work verifies that the installed materials achieve the specified performance requirements for strength, durability, and function. The documentation of the inspection and testing results provides the permanent record of quality for the project that is used for future maintenance and renovation. The non-conformance report documents any work that fails to meet the specifications and tracks the corrective action through to completion and verification.
steel frame structure. structural steel. concrete house construction.
The quality assurance program provides confidence that the quality control activities are being performed effectively. The QA program includes audits of the QC processes, review of the documentation, and independent verification of the test results. The QA manager reports to senior management independently of the project management to ensure objective evaluation of quality. The QA program also includes the training and qualification of the inspection and testing personnel. The corrective action process identifies the root cause of quality problems and implements changes to prevent recurrence. The continuous improvement of the quality program uses the feedback from the QC and QA activities to improve the processes and procedures for future projects.
Codes and Standards Compliance
The building code requirements for each type of construction are established by the International Codes and the applicable local amendments. The designer must review the code requirements for the specific occupancy and type of construction to ensure that the design complies with all applicable provisions. The fire resistance requirements, structural loading criteria, energy efficiency standards, and accessibility provisions must all be addressed in the design. The special inspections required by the building code for seismic and wind resistance must be performed by qualified inspectors. The documentation of code compliance includes the plans, specifications, calculations, and test reports that demonstrate that the construction meets the code requirements. The permit application review by the building department verifies that the design complies with the code before construction begins.
The industry standards published by ASTM, ANSI, ACI, AISC, and other organizations provide the material specifications and test methods referenced by the building codes. The ASTM standards cover the testing and specification of construction materials including concrete, steel, masonry, and wood. The ACI standards provide the code requirements and design guidance for concrete structures. The AISC specification governs the design of steel structures. The MSJC code provides the requirements for masonry structures. The reference to these standards in the contract documents ensures that the materials and workmanship meet the established industry benchmarks for quality and performance.
Environmental Considerations
The environmental impact of construction activities must be managed to comply with regulations and to minimize the effect on the surrounding community. The stormwater pollution prevention plan for construction sites controls erosion and sediment runoff during the construction period. The dust control measures including water spraying, wind barriers, and stabilizing exposed soils prevent air quality impacts. The noise control measures limit construction activities to permitted hours and use quieter equipment where feasible. The waste management plan diverts construction and demolition waste from landfills through recycling and reuse. The material storage and handling procedures prevent spills of fuels, oils, and other hazardous materials that could contaminate the soil and groundwater. The site restoration after construction includes revegetation, landscaping, and the removal of temporary facilities to return the site to its intended final condition.
The sustainable construction practices reduce the environmental footprint of the project through material selection, waste reduction, and energy-efficient construction methods. The use of locally sourced materials reduces transportation energy. The recycling of construction waste including concrete, steel, wood, and cardboard reduces landfill disposal. The construction of energy-efficient buildings reduces the operational energy consumption and greenhouse gas emissions over the building life. The indoor air quality during construction is protected by sequencing the work to avoid contamination and by ventilating the building before occupancy.