This past Saturday August 12th, Nishkian Menninger employees gathered at a foggy Crissy Field in San Francisco for the summer company picnic. Having an opportunity to just relax with friends (whom you also just happen to work with) is invaluable. The Nishkian firms recognize how important this is – and we work hard to facilitate reconnection through events like these. We had a great turnout with many friends and family in attendance. Kevin and Kim Menninger orchestrated an outdoor cooking setup complete with a well-engineered wind screen. Everyone took turns stirring the pot in between games of ladder ball and frisbee.
The event also served as a baby shower for senior engineer Bethany Jones-Kent. She is expecting a baby boy in September. We wish her, and her husband Brandon, all the best!
Building codes require that buildings be classified based on the risk to human life, health, and welfare associated with their damage or failure. Minimum design loads, maximum allowable story drift criteria, and lateral force resisting system limitations are derived based on this classification. Building codes in the U.S. generally reference the ASCE 7 provisions for appropriate building classification criteria.
The idea of designing different types of buildings to different seismic force levels based on their “risk” is not new. The Building Code utilized increased Importance Factors for schools and hospitals for many years to provide a greater degree of resilience in certain structures. In the early 2000’s the first edition of ASCE 7 utilized the term “Occupancy Category” to define a buildings classification. However, the term “occupancy” is primarily used with fire/life safety issues and only implicitly defined risks associated with structural failure of a building. Consequently, the 2010 version of ASCE 7-10, introduced the term “Risk Category” in lieu of “Occupancy Category” to distinguish between the two considerations. Per commentary section C1.5.1 in the ASCE 7-10:
“The Risk Categories in Table 1.5-1 are used to relate the criteria for maximum environmental loads or distortions specified in the ASCE 7 to the consequence of the loads being exceeded for the structure and its occupants.”
Table 1.5-1 the ASCE 7 defines four distinct Risk Categories:
Risk Category I
Structures that are normally unoccupied and would result in negligible risk to the public should they fail. These include structures such as barns and storage shelters.
Risk Category II
This category contains all buildings and structures not specifically classified as conforming to another category. The majority of structures such as residential, commercial, and industrial buildings are included in this category.
Risk Category III
This category includes buildings and structures that could pose a substantial risk to human life in case of damage or failure. Structures under this category include:
Careful assessment of the Risk Category for a new project is required prior to design. Minimum design loads for snow, ice, and seismic considerations are greatly influenced by the importance factors defined in Table 1.5-2 of the ASCE 7 for different Risk Categories:
Additionally, buildings located in regions with high seismicity are particularly sensitive to Risk Category classifications. Per Chapters 11 and 12 of the ASCE 7 Risk Category selection has major impacts on:
For this reason it is important to note that changing a buildings occupancy can result in significant changes to gravity (in snowy/icy regions) and lateral designs. Careful consideration must be given to projects involving existing structures whose occupancy change triggers a bump from a lower Risk Category level to a higher one. The existing lateral and gravity systems may require retrofits to accommodate stricter structural system limitations, increased load demands and stricter allowable drift criteria.
In addition to ASCE 7, individual states have further defined and clarified Risk Categories for different buildings and each state’s Building Code should be considered and referenced when determining a buildings Risk Category. It is also helpful to work with a design professional such as an Architect when determining number of occupants in complex buildings made up of multiple occupancies and where total number of occupants may require different Risk Categories. In fact different Risk Categories can be specified within the same building structure in special conditions.
The Nishkian team has years of experience with thousands of projects across all Risk Category types. Should you have any questions on an upcoming or current project, please do not hesitate to contact any of our offices.
What once was a car wash and auto detail shop along El Camino Real off Shoreline Boulevard in the Silicon Valley is now turning into a luxury condominium community developed by Regis Homes Bay Area LLC. 1101 West, the new condominium building located at 1101 West El Camino Real in downtown Mountain View, is nearing completion and will hit the luxury property market this summer. The forthcoming 75,700-square-feet development is poised to bring 52 condominium units comprising of 6 studios, 18 one-bedroom, 17 two-bedroom, and 11 three-bedroom residences featuring spacious floor plans, refined finishes and sustainable design elements. Community amenities include an elegant lobby, landscaped courtyard with barbecues and fire pit, a bike pavilion with secure bike storage and workshop, a pet-friendly area and electrical vehicle charging stations available for every homeowner.
The structure includes a full story of below grade parking supported by continuous and spread footings with a concrete podium slab at grade creating a landscaped patio for the residents, and supporting four stories of traditional wood framing. The structure is set back from the street to promote foot and bike traffic. There is also a new bus stop in front of the building. With a Walk Score of 79 out of 100 in the Miramonte-Springer neighborhood in Mountain View, 1101 West’s location is very walkable so most errands can be accomplished on foot. Nearby parks include McKelvey Park, Eagle Park and Pioneer Park.
Regis Homes Bay Area with Van Tilburg, Banvard & Soderbergh (VTBS Architects), and Nishkian Monks of Bozeman worked together on this transit-oriented, urban-infill, luxury condominium building project to help with the Grand Boulevard Initiative, a collaboration of more than 30 different San Francisco Bay Area cities, agencies and other organizations working together to attract new development, retail, transit, employment, services and housing along the El Camino Real corridor which is one of the Bay Area’s major thoroughfares.
For availability announcements and more information about this project, visit http://www.1101w.com/
By Edwin T. Dean, PE, SE
Unreinforced masonry (URM), or the use of stone or brick masonry for structural walls, was a common approach in Portland building construction from the late 1800s to as recently as the 1950s. These buildings range in size from small one-story residences to large 10- or 12-story buildings, most with wood-framed floors with some structural steel or cast-iron components. Many of these buildings are historically registered and represent a valuable part of the City’s cultural heritage. Several are public buildings used for government operations or public schools. The characteristic of concern for this type of building construction is that they are extraordinarily vulnerable to earthquake damage, where even moderate ground shaking could result in partial collapse.
Earthquake occurrences in other West Coast cities, such as Loma Prieta in 1989 in the San Francisco Bay Area and Northridge in 1994 near Los Angeles, have demonstrated that this type of construction is susceptible to devastating collapse and associated loss of life and property damage. There were many URM buildings that were damaged in these events, including those that had been seismically strengthened. This damage represented a very significant economic cost, though fortunately not a large number of deaths and URMs did not represent the deadliest type of buildings. These cities now have URM mandates: in the Bay Area, this was largely put into place after the Loma Prieta event, and in Los Angeles it had been implemented prior to the Northridge event.
The Portland metro area has so far been spared from a major earthquake in recent history, though geoscientists believe that large damaging earthquakes are possible. Beginning in the 1980s, the building codes have progressively increased the seismic design requirements in recognition of the potential for such natural disasters. The rate at which URMs have been retrofitted to resist earthquakes on par with current code requirements has been slow.
The City of Portland’s Unreinforced Masonry (URM) Building Policy Committee (Committee) estimates that since 1995, roughly 8% of URMs have been demolished. Of those that remain, about 5% have been fully retrofitted and about 9% have been at least partially upgraded. At that rate, it could take almost another 100 years for the URM building inventory in Portland to be either strengthened or demolished. Based on the risks posed by URM buildings to public safety, the Committee is proposing a tiered retrofit approach, requiring URM upgrades to buildings over a defined period of time. See our prior blog article, Portland Poised to Mandate URM Building Seismic Strengthening, for more background information on this.
The Committee proposal to require seismic strengthening of URM buildings is a tiered approach based on the buildings’ use and occupancy. The only exceptions to these recommended requirements are for one- and two-family homes and URM buildings that were previously seismically strengthened to an acceptable defined standard.
The Committee has defined four categories or classes of URMs with differing levels of seismic strengthening requirements and time horizons to complete them. The classes range from 1 to 4 with Class 1 for Critical Buildings and Essential Facilities and Class 4 for Low-Occupancy structures. In between these, Class 2 is for Schools and High-Occupancy structures (Churches and Theaters), and Class 3 is for is the largest class of building (approximately 2/3 of all URMs) and covers every other URM building not in the other classes. The City has compiled a detailed inventory of the buildings and the classification that they would fall under. The timeframe for implementation of the seismic strengthening varies by Class, but generally requires a seismic assessment in 3 or 5 years and strengthening implementation in 10 to 20 years.
Step 1 – A seismic assessment (ASCE 41-13) with a schematic seismic upgrade strategy including detailed cost estimates must be completed within three or five years.
Step 2 – Parapets, cornices and chimneys must be braced, and the roof must be attached to walls within 10 years.
Step 3 – All floors must be attached to walls and the roof must be sheathed within 15 years.
Step 4 – A complete retrofit must be performed within 20 years.
Separately, the Portland Bureau of Emergency Management and Bureau of Development Services commissioned Goettel & Associates, Inc. to prepare a Benefit-Cost Analysis of the Proposed Seismic Retrofit Ordinance. The report was published on November 23, 2016, and concluded, “The benefit-cost results indicate that the benefits of the URM building seismic retrofits current under consideration exceed the retrofit costs for the defined “typical building” for each URM Class of buildings.” The Committee intends to present their codified recommendations for mandatory seismic strengthening of URM to City Council for adoption. The City Councils adoption of the mandatory ordinance will start the clock and require building owners to either strengthen their URM buildings, demolish them, or face growing fines and the eventual loss of the use of their buildings.
Cost to Implement
The implementation of this mandatory ordinance will have a significant financial impact on the building owner. The objective of such an ordinance from the City’s perspective would be to reduce the life-safety risk these buildings pose to the occupants and those people who may be nearby these buildings in the event of an earthquake. The benefit-cost analysis demonstrated that there was a net benefit to the seismic strengthening; however, those benefits are not directly correlated to the financial return of the building. The Committee in its recommendations were not able to identify anything more than $5M in available Urban Renewal Area (URA) capital funds to assist building owners with the high costs of implementing the seismic strengthening. There are also possible State and Federal tax exemptions or credits and funding from the State Seismic Rehabilitation Grant Program (SRGP) for schools and emergency service facilities and potentially the sale of Floor Area Ration (FAR) transfers to another site. Additionally, the current Committee recommendations do not provide any material relief to buildings with “special considerations,” meaning those with occupants needing affordable housing, schools, religious or non-profit users, or historic structures. The Committee report does not identify the total cost to implement the required mandate. The cost-benefit study identifies the current costs to seismically retrofit or strengthen the four classes of building types on a square-foot basis in Table 15 of their report. Combining these square foot costs with the building areas contained in the inventory list provides the following total costs:
Table 1: Estimated Total Retrofit Costs Based on BDS Inventory
|URM Class||UPGRADE||Cost per Square Foot||No. of Buildings||AREA in Square Foot||TOTAL||AVG per Building|
|Class 1||Immediate Occupancy||$111.45||10||49,329||$5,487,717||$549,772|
|Class 2||Damage Control||$82.62||92||3,253,423||$268,797.808||$2,921,715|
|Class 3||Life Safety||$68.77||220||8,379,527||$576,260,072||$2,619,364|
|Class 4||Modified Bolts Plus||$51.00||1,339||10,915,945||$556,713,195||$415,768|
This would indicate that the cost to implement this mandate, if all the buildings are strengthened, to be on the order of $1.4 billion. However, this amount is an oversimplification. Faced with these costs, which in many cases exceeds the economic value of the property, it is reasonable to assume that many building owners will either abandon the properties or opt to have the buildings torn down until market conditions favor the cost of rebuilding. This will particularly impact buildings at the lowest economic value, such as those being used for affordable housing. The mandate will also allow the seismic assessments to be performed and permit the seismic strengthening to be implemented over a period of up to 20 years, assuming that building owners will wait as long as possible to seismically strengthen their buildings. When this is factored in, and the time-value of the construction costs at a 4% annual escalation are accounted for in the total cost to implement this regulation, the total costs rises to approximately $4.6 billion. Again, this assumes that all the recommended buildings will be strengthened and the reality is that many will not due to the financial restraint.
“total cost to implement this regulation, rises to approximately $4.6 billion”
The URM Building Policy Committee will continue meetings and prepare final recommendations. These recommendations will be taken up by the Portland City Council, possibly as soon as the fall of 2017. At that point, the Council will need to decide if it will implement the recommendations, or some aspects of the recommendations, as an ordinance mandating seismic strengthening of URM buildings, or continue with the status quo as required by Title 24.85. Nishkian Dean will continue to monitor the development of this important issue that affects many of our clients.
Edwin T. Dean, PE, SE is Vice President and Managing Principal of Nishkian Dean a structural engineering consulting firm in Portland, Oregon.
 City of Portland Policy Committee, DRAFT Unreinforced Masonry (URM) Building, Policy Committee Report, dated October 2016, pg. 8
 Kenneth A. Goettel, Benefit-Cost Analysis of the Proposed Seismic Retrofit Ordinance, City of Portland, November 23, 2016, pg. iv
 Religious facilities would be provided relief from completing steps 3 & 4.
 Kenneth A. Goettel, Benefit-Cost Analysis of the Proposed Seismic Retrofit Ordinance, City of Portland, November 23, 2016, Table 15, pg. 31
1201 Tennessee is a new mixed-use residential development located in the heart of San Francisco’s Dogpatch neighborhood. Historically industrial, the Dogpatch district has experienced extensive residential and commercial growth since the 1990’s. 1201 Tennessee sits on land that was once a 1,500-foot long building used for production of rope by the Tubbs San Francisco Cordage Company. The industrial nature of the neighborhood is represented by a silo aesthetic along Third Street while San Francisco’s residential, Victorian architecture is represented along 23rd Street.
Developed by AGI Resmark the apartment complex offers 259 mixed-income units with ample parking and retail space on the ground floor. The project also includes 34 affordable units for families earning 55% or less of the area’s median income. The complex amenities include bicycle parking, shared work spaces, a roof deck, and a protected courtyard with green space. 1201 Tennessee is adjacent to both the MUNI rail system and Caltrain, making it accessible for people working in San Francisco or Silicon Valley. The structure of this project is five stories of wood construction over one level of concrete with a mezzanine level, all supported on a pile foundation system. Concrete and wood shear walls provide the lateral force resisting system.
Fougeron Architecture has designed the apartment complex collaborating with general contractor Devcon Construction, and structural engineers Nishkian Menninger in San Francisco and Nishkian Monks in Bozeman. Our San Francisco office designed the concrete substructure while our Bozeman office designed the wood superstructure.
For more information about the project and endorsement of the development, please visit: http://www.fougeron.com/project/tennessee and http://www.sfhac.org/project/1201-tennessee-street/
In our blog this week we will revisit the very important topic of the Structural Engineer during Construction. We discussed this subject in a previous blog The Structural Engineer’s role in Construction – From design through CA which highlighted several aspects of this step in a building’s evolution:
In this Part II Blog of the Structural Engineer’s role during construction, we examine several additional key pieces to a successful construction project. From setting up an initial kickoff meeting prior to the start of construction to providing an opportunity for younger engineers to see what they design to collaborative resolution of field issues to final visits and developing as-builts, construction is an important time for the Structural Engineer to be engaged and on site!
One item that’s extremely critical in the course of construction is getting off on the right foot. A kickoff meeting at the beginning of the project is critical to getting the entire team on the same page from the start. There should be a discussion of the RFI process and schedule of submittals and understanding of the expectation for response. And what is the process for responding? Will communication go through the Architect always? Should the General Contractor be copied on communication before official responses go out? Is there a tracking system in place where all the RFI, Submittal, meeting minutes, etc. are kept? These are often not always the same answers on each project and they should be thoroughly worked out at this kickoff meeting. Another good topic is discussing and confirming the steps at which site visits and Structural Observations are to be performed during the project. Establishing the process early with key team members involved issues is all to the benefit of the overall project and will go a long way to keeping things moving forward and on schedule.
Construction is a great learning opportunity for younger engineering staff to get on-site to “kick the tires” and see what we’re designing. As engineers, we often find ourselves behind a desk preparing calculations and running computer analysis without the opportunity to get a chance to see how things are physically built. A line drawn on a paper is often very different in appearance, shape, size, and relational context to the rest of what is being built in the field. Being able to go and see that on site is extremely important and a great time to get engineers out to interact with the elements we design and with the people who build it. It also gives us the very real understanding that drawing our plans, section, elevations and details to scale is extremely important. We’ve all seen in the field those times when the detail drawn on paper did not appear to be as intended when built in the field and this can, at times, be attributed to “not to scale” details. Site visits by younger engineers helps improve their skills for the next project!
Often times in construction there are elements that are not fully known until construction has begun. This can be site conditions after demolition, as-built plans that were relied upon, but ultimately did not match field conditions, or Owner direction changes during construction. Unforeseen conditions require a collaborative approach and typically rapid resolution process to make changes while construction is ongoing. In an unforeseen condition situation when an issue is identified as different than what was drawn on the drawings and the team needs to deal with it, collaborative coordination between Contractor, Architect, Owner, Structural Engineer and/or other disciplines, as required, is extremely important in the process of not only resolving the issue but resolving it as quickly as possible with as minimal design and cost impact to the overall project. Part of this process may involve a review of changes to the plans as well as changes to the contract where change orders are reviewed for the Owner from Contractor scope changes. A quick and collaborative approach to changing field conditions when they occur is critical to keeping projects on schedule and on budget.
And when construction is close to achieving substantial completion, the SE should have one last opportunity to visit the jobsite. Major structural work has likely been done for months. And while much of the building may be covered up at this time, this last visit provides one last look at the building for the design professional to confirm what was designed is what was built. Has anything changed since the last visit? Did any modifications happen in the field that were not communicated to the SE? Often everything is coming together as designed, but this is the last opportunity to confirm before the building goes into use.
And finally, developing a final as-built set that incorporates any updates during construction should be a part of every project. The as-built set allows Owners a snapshot of the actual construction of the building and a tool to rely on for future improvements to the building.
It should go without saying how important the Structural Engineer’s role is in construction and how important the construction period is for the Structural Engineer. The Nishkian firms nearly 100 years of Structural Engineering service includes significant achievements that could not have been realized without their critical involvement during construction. It’s an important part of the process we go through each and every time.
City of Bozeman officials recently invited the community to come out to Bogert Park and celebrate the newly restored Bozeman Creek and amenities. A ribbon cutting ceremony to dedicate the newly completed upgrades to Bogert Park was held on June 22, 2017.
In an effort to improve access and enhance the experience for visitors, the City of Bozeman has partnered with the State of Montana, Gallatin Valley Land Trust, Friends of Parks and other groups. As part of the enhancement project that totaled a $707,000 investment into the park, the Bozeman Creek channel was reconstructed to add a meander and a secondary channel for floodwater. A floodplain was re-established to slow velocities, filter runoff, and improve safety. Banks were re-graded to sustainable slopes. Existing vegetation was augmented, widening the riparian zone and improving diversity of species and age-classes. New park amenities include a stream access site, additional gravel trails, a wider and longer clear-span pedestrian bridge leading from East Koch Street into the park, and new swing sets—all adding to the value of the creek as a community amenity.
Design work for this project was done by several firms, including Confluence Consulting, TD&H Engineering, Vaughn Environmental, Design 5, Intrinsik Architecture, and Nishkian Monks PLLC. Highland Construction Services served as the general contractor.
Renderings courtesy of Intrinsik Architecture
By Nathan J. Hoesly, PE, SE
The use of engineered wood products is an essential component of nearly all wood-framed buildings. This article will focus on two specific types of engineered wood products, structural composite lumber (SCL) and glue laminated (Glulam) timber framing. Understanding the intended uses and differences between various SCL products and glulam framing is essential for design professionals.
Structural composite lumber (SCL) is a term used to describe a family of engineered wood products created by layering wood veneers or strands and bonding them with moisture-
Laminated Strand Lumber (LSL) is manufactured from flaked wood strands and resembles oriented strand board (OSB) in appearance, though the strands are arranged parallel to the longitudinal axis of the member. Members are commonly fabricated in 1 ¼”, 1 ½”, 1 ¾” and 3 ½” widths, and in 9 ¼”-16” depths to match common i-joists. Stud options are available in equivalent 2×4, 2×6, and 2×8 sizes that are stronger, straighter, and (as needed) longer than sawn lumber. LSL is typically less expensive than other engineered wood beams.
Due its high allowable shear strength, LSL beams have capacity for larger penetrations than other engineered wood beam options. While not as strong as LVL or PSL beams, LSL is generally cheaper and are ideal for short spans. LSL is also ideal for use in rim conditions due to minimal shrinkage, cupping, and high fastener holding strength when used in highly loaded diaphragms or for shear transfer at plywood shear walls.
Parallel Strand Lumber (PSL) is manufactured from veneers laid into long, parallel strands and bonded together. PSL beams are primarily used in beam and header applications where high strength is required. Common PSL beam sizes are available in widths of 3 ½, 5 ¼” and 7”, and depths matching I-joists from 9 1/2” – 24” deep. PSL columns are also available in sizes comparable with sawn wood members from 4×4 to 8×8 in size.
PSL beams are generally more expensive than glulam, LSL, or LVL beams. PSL beams can be stained or finished where an aesthetically pleasing exposed application is desired.
Laminated Veneer Lumber (LVL) is a commonly available engineered product that is manufactured similarly to PSL. Available sizes, strengths, and stiffnesses are similar to PSL but are generally cheaper, making it a commonly specified beam type. A benefit to LVL is that it can be fabricated in narrower beam widths (1 ½, 1 ¾”), and multiple plys can be nail-laminated together to form a larger beam. This is especially beneficial in retrofit options where lifting a wide, heavy beam into place is cumbersome or infeasible. LVL stud and columns are available as well from some manufacturers.
Glued Laminated Timber (Glulam) is manufactured by face-bonding layers of kiln-dried timber members, typically 2×4 or 2×6 in size, together with waterproof adhesives to form timber section. Glulams are popular due to their engineered strength, versatility, availability, and cost. Typical stock beams widths are available in 3 1/8”, 3 ½”, 5 1/8”, 5 ½”, 6 ¾” widths and depths exceeding SCL beams. However, custom glulams can be fabricated in almost limitless widths, depths and profiles, giving glulam beams a distinct advantage over SCL beams in their versatility and architectural appeal. Glulams have a long history of being used beautifully in exposed, large open areas such as vaulted ceilings, churches, theatres and a vast array of other public spaces. Manufacturing processes for glulams allow for members to be cambered, curved, and fabricated in unique shapes, such as arches or as bridge members. Different appearance grades for exposed conditions may also be specified to increase architectural appeal.
For exterior or weather-exposed conditions, glulam beams are generally preferred over SCL beams. Weyerhaeuser, one of the few manufacturers of PSL in the U.S., has a Wolmanized PSL product that is approved for weather-exposed framing beam applications, but it is relatively expensive. Few other SCL treatment options exist. Alternatively, pressure treated or preservative treated options exist for glulam members. Additionally, several naturally durable species of glulam beams are produced in the U.S., including Alaskan Yellow Cedar and Port Orford Cedar, which provide green alternatives to chemical treatments.
Both SCL and glulam beams may be used where a fire-rated exposed member is required, subject to meeting the provisions of Chapter 16 of AWC’s National Design Specification® (NDS®) for Wood Construction. Typically, only wider beam sections will meet the required fire rating due to the depth of charring of any exposed face. This often eliminates the use of LSL, and glulams are usually preferred over LVL and PSL due to cost, appearance, or available beam sizes.
Design professionals should be knowledgeable about specific product availability and costs in their areas during design as this can help drive which types of engineered wood beams are specified. Although SCL and glulam beams can be used interchangeably at times, they also have unique advantages and limitations to be aware of.
Nathan Hoesly, PE, SE is an Associate of Nishkian Dean, a structural engineering consulting firm in Portland, Oregon
Located in Oakland’s Lakeside neighborhood, 250 17th Street will be five levels of wood construction over two levels of concrete. The new apartment building will be comprised of a ground-level parking garage and 74 units of studio, one- and two-bedroom apartments. The building will offer tenants many amenities such as a gym, bicycle parking and repair, charging stations for electric vehicles, and a roof deck. The roof deck will feature a garden, a barbeque area, a trellis, and a water feature. The extra weight of planting and water drive the structural design of the roof.
The concrete podium at the second level will consist of a two-way post-tensioned structural slab. The slab is supported by bearing shearwalls and concrete columns. The floor framing of the timber superstructure will consist of ¾ ply supported by timber joists, LVL, and PSL beams. The beams will be supported by stud walls and wood columns. The lateral load resisting system will consist of concrete shearwalls beneath timber shearwalls. The ground floor slab will be a slab-on-grade over spread foundations at the columns, continuous wall foundations, and a partial mat foundation under the shearwall core.
Simeon Properties collaborated with San Francisco-based architecture firm Kotas/Pantaleoni Architects and Nishkian Menninger to construct the Class A, transit-oriented multi-housing development in Oakland, California. The transit-oriented site has a WalkScore© of 99 and is convenient to the 19th Street BART station, Interstates 880 and 980, Amtrak and ferry service, connecting residents to major employment centers in downtown Oakland, San Francisco, Emeryville and Silicon Valley. With Lake Merritt and Broadway Street within a few blocks, the live-work-play property will also provide residents with access to numerous dining, nightlife and recreational options.
Kotas/Pantaleoni Architects designed a façade that will incorporate seamlessly into the residential neighborhood between Oakland’s busy Broadway Street and Lake Merritt. Rendering can be seen at their website: http://kp-architects.com/work/alice-street/
Wood is often seen in multi-family mid-rise buildings as the most economical construction material. While the purpose of joists, beams, and wood stud walls are easily understood in their role carrying the gravity loads of a building, the lateral load resisting elements and how they work can be more confusing.
Lateral Load Resisting Shear Walls
When lateral loads due to wind forces or a seismic event hit a building, the loads travel through the floor, collecting into and being resisted by wood shear walls. The top and bottom plates of the shear walls act as continuous collectors, moving the lateral loads from the diaphragm into the shear wall. Plywood sheathing, the nailing of the plywood to wood studs, and anchor bolts at the sill plate resist the shear forces. As the lateral loads move from a horizontal plane (i.e. the floor) to a vertical plane (i.e. the wall), the lateral loads also create vertical tension and compression forces, which are resisted by end posts and a hold-down system located at each end of the shear wall.
Figure 1: Components of a Shear Wall
At the beginning of a project, as unit layouts and floor plans are being set, it is important to ensure that the building will have an appropriate shear wall layout. In multi-family buildings, corridors usually afford a sufficient length of interior shear walls, but exterior shear walls must be carefully coordinated between the client, architect, and structural engineer. Façade features, window sizes, and window locations can all critically affect exterior shear wall designs.
Stacking Shear Walls
Structurally, it is always more efficient to stack shear walls from the top of the building to the foundation (or podium). This allows the components that resist the compressive and uplift forces to be continuous. When shear walls do not stack, the building code requires that components be designed for an increased load, and extra framing members and connections are required to transfer the loads.
Figure 2: Stacked Shear Walls
The shear wall design is not just determined by the number of shear walls, but also the length of each shear wall. As shear walls get shorter, the hold-down system gets loaded more heavily. The minimum length of shear wall permitted on a project depends on the floor-to-floor height – the taller a floor, the longer a shear wall must be. This aspect ratio is determined by taking the height (h) and dividing it by the shear wall length (bs). Shear walls cannot have an aspect ratio greater than 3.5 but as a rule of thumb, aspect ratios should be less than 2. Where the aspect ratio exceeds 2, the wall’s shear capacity is penalized. In other words, shear wall lengths should always aim to be greater than half the floor height.
Nishkian Chamberlain has extensive experience with multi-family construction and would be happy to help you find cost-effective solutions to your construction and development needs. Please do not hesitate to contact us at NCInfo@Nishkian.com, or give us a call at (310) 853-7180. You can also go to our Contact page to connect with any one of our offices in your region.
Figure 3: Aspect Ratio