Rapid climate shifts in human history

We are currently witnessing the most rapid climate shifts in human history. Naturally, this has put immense pressure on engineers and scientists to develop solutions. This problem is wide-spread, and no industry is free from the burden of change. One industry that has seen widespread political debate is the construction of residential buildings. Shelter is one of the basic requirements for life. Moreover, an ever-growing population creates a constant demand for more buildings. Pair this with the environmental benefits of urban densification, there is an even larger demand for tall buildingsc A more popular trend emerging, especially in Scandinavian countries, is the utilization of mass-timber products in mid-sized residential construction. Originally spurred by the environmental benefits, engineers have begun to analyze timber in increasingly bigger projects. This paper will be an analysis of structural timber from a design and construction perspective. For timber to be adopted, regardless of the environmental benefits, it must have tangible benefits over steel or concrete.
Timber is a material that has been surrounded by stigma for centuries. As one of the oldest structural materials used by humans, timber has seen a transformation in applications over human history. The technological advancements in timber design have transformed wood buildings from glorified match boxes to sturdy, low impact structures. The most significant technology to emerge is the use of lamination. The two prominent laminated timber products used in large construction are glue-laminated timber (GLULAM) and cross laminated timber (CLT). Both members are made by applying a thin layer of glue between long cuts of timber. The strength of wood lies primarily in-line with the grains of the wood. GLULAM is laminated with the grains oriented in the same direction. This allows for strong tensile and compressive resistance. CLT is laminated with alternating, perpendicular grain directions between sheets. Although not as strong in tension or compression, CLT provides significantly higher bending strength than GLULAM [1]. Both materials allow engineers to optimize the material used in design.
From a structural standpoint, mass timber has minimal benefits over steel or concrete. Counterintuitively, fire resistance is one of the primary benefits of mass timber. Ignited timber members form an insulating layer of charcoal during the burn. This insulation prevents failure of the inner core. [2] Designers account for this by increasing the size of the member to allow for this charcoal threshold. These thresholds become significant when comparing member sizes between timber to concrete. Both materials use large cross-sectional areas for load resistance, with timber requiring larger members than concrete. Regardless, this is relatively insignificant because timber is approximately one third the weight per volume of normal reinforced concrete. This allows for significant weight savings in larger structures [3]. Not only does this allow designers to make reductions in support sizes, but it also allows for thinner foundations. Concrete foundations are standard practice and are virtually unavoidable during building design. Reducing concrete usage allows projects to have a lower environmental impact as well as significant cost savings. These cost savings can be extended further using prefabrication, a method in which members are constructed to exact dimensions. Like prefabricated steel, prefabricated timber allows for rapid construction and reduced on-site errors [3]. The added benefit of timber over steel is the ability to make modifications on-site, further reducing cost or schedule delays. A timber beam can be cut to size if the wrong size is received; a steel beam must be sent back for modifications.
There are significant drawbacks currently limiting the widespread use of mass-timber, particularly the market price of timber construction. Large scale timber construction is significantly more expensive than the cast concrete alternative. For a 10-story building utilizing CLT, the expected cost is 16-29% higher than using concrete. These values were obtained in the Pacific North West, where CLT manufacturing is abundant and the prices are the lowest [4]. This has deterred construction in favorable areas, and virtually eliminated any North American project outside of the Pacific North West. Furthermore, from a structural standpoint, the current limiting factor on design is the use of steel connections. Large timber structures are reliant on steel plates or nails due to the higher load resistance. Using mechanical tests, steel connections produce roughly 2.5 times the connection strength compared to the wooden dowel counterparts [2]. As discussed earlier, the primary benefit of utilizing timber is the charcoal insulation during fire. When steel connections are inserted into the timber, heat is rapidly conducted to the center of the member. The heat weakens the core of the member, decreasing the load capacity of the beam. This can be catastrophic as load is typically higher at connection points. Maximum load is also a significant factor in timber design. Currently the tallest mass timber building is 85.4m tall and contains 18 storeys, located in Brumunddal, Norway [5]. For reference, Stantec tower located in Edmonton is roughly triple the size. The significant limiting factor preventing timber megastructures is the absolute strength of timber. Timber members simply cannot compete with the strength characteristics of concrete or steel. This significantly limits large scale applications of timber; reducing the likeliness that designers will adopt the material in other applications.
It should be noted that the global move towards greener technology has been largely dependant on logistics and cost. Although the threat of climate change is imminent, the economic market still dictates most actions. In a privileged society such as North America, changes are slow to be adapted if they also cause inconvenience. When analyzing timber as structural material, it is important to analyze the material from a structural and logistical perspective. The primary benefit of utilizing timber is the carbon negative effects of the material. This is obviously beneficial from an environmental sense, but the material has encountered hurdles due to higher construction costs. Timber has minimal structural benefits over concrete or steel, especially in structures larger than twenty storeys. Most benefits of utilizing timber on a large scale come with significant costs that are not easily reduced by advancing technology. Financial incentive, such as government subsidized initiatives, could potentially narrow the gap in costs. Alternatively, there would need to be a large increase in concrete or steel prices. Until prices are settled, it is unlikely that timber will be adopted as a common building material in large scale applications.
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