STRUCTURES + BUILDINGS
can also contribute indirectly — e.g., by eliminating cold surfaces at exterior walls with a reduction in thermal conductivity or allowing large expanses of glazing for light and views through the use of central- ized lateral-resisting systems or thin floor plates. Construction type also has a significant impact on cost. Under the IBC, structural wood framing is permitted in Types IIIA, IIIB, IV, VA, and VB. The IBC specifies allowable height and area for each, and each has different requirements, largely related to fire protection. As shown in Tables 1, 2, and 3, which highlight information from the International Code Council (ICC) Building Valuation Data, February 2018, the aver- age cost for each construction type also varies widely. Table 2 highlights the difference in cost between two construction types commonly used for office buildings — Type IIA, which doesn’t allow structural wood framing in most applications, and Type IIIA, which is typically wood-frame. Both have similar allowable heights and building limitations (see table on page 31), but the average Type IIIA building costs $23 per square foot less. In Table 3, Type IIB construction is compared with Type VA — also commonly wood-frame — and shows an even larger savings of $34 per square foot for the wood building. Allowable heights and areas remain similar, except that slightly greater height is allowed for Type II. Conclusion Wood’s performance and design versatility create a wide range of opportunities for developers and building designers looking to create beautiful offices that are also cost effective. Light-frame, heavy timber, mass timber, and hybrid wood systems can all be used to create open structures that meet the need for space flexibility, with heights and areas that are comparable with mid-rise steel and concrete structures. Information provided by WoodWorks – Wood Products Council, which provides free technical support related to the design of commercial and multi-family wood buildings. To discuss the needs of a specific project, visit www.woodworks.org to contact a regional director or email help@woodworks.org. The hydraulically driven tables, programmed to mimic the forces of an earthquake, tested six different kinds of bridge connections integrated into a single bridge. Each connection had been previously tested on its own at the University of Nevada, Reno. “The individual connection tests had given us very good results for each connection,” said Saiid Saiidi, Ph.D., principal investigator of the project, professor in civil and environmental engineering at the university, and director of the Center for Advanced Technology in Bridges and Infrastructure. “And for the first time, our study combined these connections in a single bridge, which endured realistically strong earthquakes. We knew going into this that our individual positive tests
For a one- to five-story structure, using a light-frame bearing shear wall system with a code-defined flexible diaphragm is a common choice, and the most straightforward to analyze. This approach is compatible with custom designs and buildings with less glazing, since ample pe- rimeter walls are typically needed for lateral resistance in this type of system. For heavy timber-frame systems with more than three stories, a lateral- resisting core is a viable choice — whether comprised of mass timber or light-frame shear walls, concrete or CMU shear walls, or steel brace frames. Engineering analysis requires a rigid or semi-rigid diaphragm and stair or elevator shafts located centrally or somewhat symmetri- cally within the building. Another alternative is to use interior and/ or exterior steel moment frames. Exterior glazing and curtain walls should be checked for deflection compatibility with the lateral systems. Design considerations: Cost and value Facility costs and lease rates are always a consideration, but the single greatest cost to employers is the salaries of employees who occupy the space. If a building can be designed to improve productivity — for example, by providing better lighting or improving comfort — the pro- cess of optimizing building performance can improve the company’s bottom line. Wood systems can do this directly by creating warm and welcoming spaces that motivate a positive biophilic response. They
Proven connections Earthquake lab shakes two-span, 70-foot-long bridge in accelerated bridge construction method test.
Accelerated bridge construction methods were proved safe and ready for real-world application following tests on massive shake tables in the University of Nevada, Reno’s Earthquake Engineering Laboratory. The tests on April 24 subjected a 70-ton, two-span, 70-foot-long bridge to multiple earthquake simulations of approximately 7.5 magnitude.
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csengineermag.com
august 2018
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