Engineered Wood Products
Glued laminated timber is manufactured by bonding multiple layers of dimension lumber together with structural adhesives. The laminating process produces members that are stronger and more dimensionally stable than solid-sawn timber. The glulam beams can be manufactured in curved shapes for architectural applications. The design values for glulam are determined by the combination grade of the laminations. Cross-laminated timber consists of layers of lumber stacked at right angles and bonded together. The cross-lamination provides dimensional stability and two-way spanning capability. CLT panels are used for walls, floors, and roofs in mass timber buildings up to 18 stories. The panels are prefabricated with openings for doors and windows. The fire resistance of CLT is provided by the char layer that forms on the surface during fire exposure, protecting the interior wood.
Heavy timber construction uses large cross-section wood members for columns, beams, and decking. The minimum dimensions for heavy timber are 8 by 8 inches for columns and 6 by 10 inches for beams. The heavy timber construction provides inherent fire resistance through the charring mechanism. The exposed wood interior provides aesthetic appeal in addition to structural function. The connections in heavy timber construction use steel plates, bolts, and timber connectors that are designed to resist the design loads. The timber frame construction with mortise and tenon joinery and wooden pegs provides traditional aesthetic for residential and commercial buildings. The structural design of timber follows the National Design Specification for Wood Construction.
Timber Connection Design
Connections in timber structures transfer forces between members through mechanical fasteners and connectors. The design of timber connections follows the National Design Specification for Wood Construction which provides reference design values for bolts, screws, nails, and other connectors. The bolt connection capacity depends on the bolt diameter, the member thickness, the wood species and grade, and the orientation of the load relative to the wood grain. The yield modes for bolted connections range from yielding of the bolt in bending to crushing of the wood under the bolt. The dowel-type fastener design accounts for the dowel bearing strength of the wood and the bending yield strength of the fastener. The multiple fastener connections in timber trusses and frames must account for the group action factor that reduces the capacity when multiple fasteners are aligned in a row along the grain direction.
The heavy timber connections using steel plates, bolts, and timber connectors provide the structural continuity needed for large timber frames. The slotted steel plate connections at beam-to-column joints transfer moment and shear through bolts in double shear. The timber connectors such as split rings and shear plates increase the bearing area of the connection and improve the load transfer between timber members. The glued-in rod connections use steel rods bonded into the timber with structural adhesives to transfer high forces in a concealed connection. The fire resistance of timber connections requires that the steel components be protected by the timber section or by fire-resistant materials to maintain the connection capacity during fire exposure.
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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.
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.