EVERGREEN UNITED
STRUCTURAL
CLASSROOM
BUILDING
GYMNASIUM
LAB
BUILDING
FRAMING
Structural design begins with creating a framing layout. To do that we worked with the architect to find a layout that doesn’t just satisfy building codes and local regulations, but that’s also structurally efficient, and we worked with the construction team to determine what materials satisfy the budget, the construction schedule, the ultimate goals of sustainability. This wasn’t a linear process. We went from a low-carbon cast-in-place concrete to mass timber, and we changed the framing layout of the buildings many times, but every change was in the spirit of trying to produce the best design that we could within the limited time that we have.
The frame of all three buildings in substantially mass timber, with some steel members in areas of particularly high load or where a cantilever support was needed. Mass Timber was utilized due to its low carbon footprint, fire resistance, renewable sourcing, aesthetic, speed of construction, structural strength, and positive effect on mental health (biophilic design). The use of mass timber also eases the acoustic burden to surrounding residential communities relative to other materials during construction.
The classroom and lab buildings have visually graded Western species 24F-1.8E glulam girders and purlins, with dimensional lumber DF-L No. 2 subpurlins. The columns are visually graded Western species DF grade L2D, combination 3. The subpurlins are not needed to support the gravity loads, but are present to support the limited sizes of the CLT panels that form the subfloor and diaphragm of the second floor and roof. Due to the long spans necessary in the gymnasium due to the courts, the second floor and roof are supported by top-bearing glulam trusses. The glulam beams utilized in framing are provided with a camber of 1.5 times the dead load deflection for roof beams and 1.0 times the dead load deflection for floor beams.
Structural calculations are available below for all framing members.
FOUNDATION
DESIGN
SLAB-ON-GRADE
Structural design begins with creating a framing layout. To do that we worked with the architect to find a layout that doesn’t just satisfy building codes and local regulations, but that’s also structurally efficient, and we worked with the construction team to determine what materials satisfy the budget, the construction schedule, the ultimate goals of sustainability. This wasn’t a linear process. We went from a low-carbon cast-in-place concrete to mass timber, and we changed the framing layout of the buildings many times, but every change was in the spirit of trying to produce the best design that we could within the limited time that we have.
The frame of all three buildings in substantially mass timber, with some steel members in areas of particularly high load or where a cantilever support was needed. Mass Timber was utilized due to its low carbon footprint, fire resistance, renewable sourcing, aesthetic, speed of construction, structural strength, and positive effect on mental health (biophilic design). The use of mass timber also eases the acoustic burden to surrounding residential communities relative to other materials during construction.
The classroom and lab buildings have visually graded Western species 24F-1.8E glulam girders and purlins, with dimensional lumber DF-L No. 2 subpurlins. The columns are visually graded Western species DF grade L2D, combination 3. The subpurlins are not needed to support the gravity loads, but are present to support the limited sizes of the CLT panels that form the subfloor and diaphragm of the second floor and roof. Due to the long spans necessary in the gymnasium due to the courts, the second floor and roof are supported by top-bearing glulam trusses. The glulam beams utilized in framing are provided with a camber of 1.5 times the dead load deflection for roof beams and 1.0 times the dead load deflection for floor beams.
Structural calculations are available below for all framing members.
FOOTINGS
Isolated footings were designed to resist both one-way and two-way shear, sliding, and to transfer gravity loads within the allowable bearing capacity of the soil as determined from the geotechnical report GPI No. 2958.I Columns are pin-connected to the footings and thus do not pass bending forces into the footing. This implies an even distribution of force, if the footings is modeled as flexible, over the base of the footing. Grade beams were utilized to connect the footings below the braced frames to adjacent footings to prevent them from sliding relative to one another during a seismic event. Where excavation of one footing would be so close to another that it is impractical to keep them separate, or the isolated footings would overlap, combined footings are utilized.
To determine the amount of reinforcement required for strength and by minimum code requirements, the square footings were "cut in half" and modeled as a cantilever beam with a uniform distributed load, assuming flexible contact, caused by the reaction of the soil against the footing surface. Combined footings are modeled as a multi-span beam with pin supports. In this instance, due to the moment changing signs closer to the supports reinforcement will also be required towards the top of the footing closer to the column-to-footing connections.
FOUNDATION PLAN FOR CLASSROOM
ISOLATED FOOTING
LATERAL LOAD RESISTING SYSTEM DESIGN
WIND LOADS
The directional procedure outlined in ASCE 7-16 Table 27.2-1 was followed in order to determine the wind forces that need to be considered when designing the lateral system and all components and cladding of the building. The ATC Hazards by Location website was referenced to find the basic wind speed of 102 mph for a Risk Category III building. All parameters utilized in the calculation of the wind forces are listed below, followed by a calculation of the wind forces. While seismic forces governed the lateral system of the building, wind forces still needed to be considered when design the curved architectural flourish and large diagonal staircase on the sides of the gymnasium, as well any other components and cladding like the hardware holding the living green walls.
SEISMIC LOADS
The California’s Office of Statewide Health Planning and Development's Seismic Design Map (available from www.seismicmaps.org) was utilized to find the seismic parameters for the 18605 Jamboree Rd. site. The Equivalent Lateral Force Procedure is then utilized to determine the design seismic forces on the classroom building as permitted by ASCE 7-16 Table 12.6-1. The dead loads as well as a 10 psf partition live load, per provision 12.7.2, are used to find the effective seismic weight.
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The classroom building has been designed with a 12" seismic joint to isolate the two rectangular sections of the building that, together, make up an L shape. Therefore, seismic forces will be determined for these two sections of the building separately, labeled buildings A and B in the design calculations below. Both sections have very different loading, building A having only solar panels on the roof, building B with a rooftop garden and occupancy on the roof. This naming convention is for the calculation of seismic forces only, the building is experienced by the occupant as one single building internally with continuous corridors. The gymnasium and lab do not require a seismic joint.
The story drift is then determined per section 12.8.6 of ASCE 7-16. Given the buckling-restrained brace, a deflection amplification factor of 5 and a seismic importance factor of 1.25 are used to determine the design story drift. For classroom A the design story drift is 3" at the roof, and 1.5" at the second floor. For classroom B the design story drift is 5.8" at the roof and 2.0" at the second floor. The allowable story drift per Table 12.12-1 for Risk Category III classroom building is 2% of the height. The story drift for Classroom A is only 0.8% of the height, and the story drift for Classroom B is 1.6% of the height. Therefore, the limits fall within the allowable limits, and the combination of 5.76" and 3", totaling 8.76", is less than the 12" seismic joint space. Collision between the two buildings should not occur.
BUCKLING RESTRAINED BRACES
All buildings utilize a Buckling -Restrained Brace Frame (BRBF) to transfer lateral loads from the diaphragm and collectors down to the foundation. Conventional braced frames rely on buckling of the brace for their ductility which results in degradation of brace capacity and stiffness. The addition of a concrete casing to restrain buckling allows for the BRBF to utilize the ductility of steel more effectively, and to rely instead on axial yielding of the core during large seismic events. The steel is assumed to fail in tension, and this failure state is used to determine the area of steel in the core. A brace was then selected from the CoreBrace Bolted Brace Design Guide.
SEISMIC LOAD SUMMARY
COREBRACE BUCKLING RESTRAINED BRACE
DEFLECTED SHAPE OF CLASSROOM A
LATERAL DEFLECTION
GRAVITY LOAD RESISTING SYSTEM DESIG
DEAD LOADS
The weight of all materials, and the self-weight of the structure itself, must be considered during design. For this project in particular, the large-scale installation of solar panels and green roofs created heavy dead loads. Through the proper determination of these loads and then the proper design of structural members, our team was able to achieve our environmental goals while maintaining the structural integrity of our buildings.
LIVE LOADS
In order to accurately assess the required structural capacity of the buildings, loadings from occupancy and furnishings during normal use were considered. It is important to reference and utilize industry standards and codes. For this reason, a comprehensive evaluation was conducted using best judgment to determine the most applicable live loads from ASCE 7-16 Table 4.3-1.
COLUMN DESIGN
The columns are visually graded Western species DF grade L2D, combination 3, with capacities determined from the NDS 2018 supplement. All columns were checked for compression, tension (due to any possible uplift), and bending due to any eccentricity in the loading.
GIRDER DESIGN
Most girders were specified as visually graded Western species 24F-1.8E glulam girders, with capacities determined from the NDS 2018 supplement. Girders were checked for bending, shear, and bearing. The dead load deflection was utilized to determine the camber as per American Wood Council's guidance at 1.5 times the dead load deflection for roof beams, and 1.0 times the dead load deflection. Collectors were also checked for compression, tension, combined bending and tension, and combined bending and compression. The collectors taking the largest amount of the load in the region of the braced frames are steel, due to the large loading present.
CONNECTIONS
Due to the small structural team on this project and large scope of this project, the structural design ( e.g. checking for bearing deformation, tearout, block shear, bolt or weld size and strength, etc.) of connections was not undertaken. Instead, we considered load path, selected appropriate connections, and produced detailed drawings of the connections in Revit. Connections considered were Column-to-footing connections, Column-to-column connections, Column-to-girder connections, Purlin and subpurlin to girder connections. CLT panel to steel member connections, and buckling-restrained brace frame to collector connection (bolted gusset plate).
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In the buckling-restrained brace bay, the collector is a steel W-section. Metal studs are to be welded to the top flange of the W section at regular intervals. These metal studs fit into holes drilled in the CLT panels, and they keep the diaphragm from slipping during high seismic loading. The shear force, determined from a load combination with an overstrength factor of 2.5, would be distributed over the number of metal studs that would need to designed to handle the shear force over the cross section of each stud.
HIDDEM COLUMN-TO-GIRDER CONNECTION
COLUMN-TO-FOOTING CONNECTION
STRUCTURAL
DESIGN
CALCULATIONS
Final documentation of calculations for the design of structural members was produced in Maple Flow and BlueBeam Revu. The following links can be used to view all structural design calculations. Note that due to the similarity of framing, loading, and scale of the Lab and Classroom A, the Lab Calculation report only contains the calculations for the framing members that are unique to the Lab. Classroom A and Laboratory calculations have a linked bookmark table on the second page for ease of navigation.
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Classroom A - Structural Design Calculations
Classroom B - Structural Design Calculations
Laboratory - Structural Design Calculations