HomeMy WebLinkAboutFile Documents.121 E Hyman Ave.0149.2018 (84).ARBK WILSON STRUCTURAL ENGINEERING,
INC.
September 15th, 2020
Mr. Bob Horenn e
Durango, Colorado !'�
970-247-1601
<info@bhstair.com> 02/18/2021 ...O./
Re: Cayton Residence stairs to roof, Aspen, Colorado RcO(tGUM iIGE
WSE Proj. #: 10720 justinh
Dear Mr. Horenn:
At your request, we have analyzed the semi-circular stair stringer and glass guards of the
stairs to the roof for the Cayton residence. The following is a list of assumptions that were
made in our structural analysis:
Design Criteria (per Table R301.5 of the 2015 International Residential Code):
1. Concentrated Load = 2001bs any direction, any location along top
2. Uniform Load = 50p1f perpendicular to glass at top
3. Load of 501bs on 1 square foot at any location on glass
4. Height to top of glass or handrail = 44"
Stringer Assumptions:
• The full dead plus live loads on the treads and landing have been applied at a single point
with the greatest eccentricity such that the torsional effect is maximized.
• There is no torsional restraint for the stringer from above the lower bearing point to the
upper landing bearing point of the stringer.
• The LVL's have the following minimum design values:
► Bending Stress (flat use value) Fb = 2350psi
► Longitudinal Shear Stress Fv = 150psi
► Modulus of Elasticity E = 2,000,000psi
► Equivalent Specific Gravity SG = 0.50
• The LVL plys are connected such that they act as a single homogenous member.
• The stringer has adequate bearing/connection capacity at both upper and lower bearing
points.
• The treads, guardrails, landings, bearing assemblies and connections have not been
analyzed and are assumed to be adequate to support the applied loads.
• The LVL plys shall be assembled with adhesive and dowels as described in the stair
drawings provided by B&H Stair.
• The stringer connection to existing floor and wall framing shall be as described in the stair
drawings provided by B&H Stair.
Laminated Tempered Glass Guards and Connections Assumptions:
• The laminated tempered glass guards have the minimum design values:
► Modulus of Rupture Fr = 24,000psi
► Material complies with Category ll or CPSC 16 CFR Part 1201 or Class A of ANSI
Z97.1
48 County Rd. 250•Durango, CO 81301 • (970) 385-6774
• A 24" wide section of the laminated tempered glass guard is engaged when the point load
is applied at the top of the section.
• The lag screws for connecting the guards have the minimum design values:
► Tensile strength = 60,000psi
• The lag screws are installed into the side-grain (not edge or end) of the built-up LVL tread
assemblies.
• The lag screws meet the minimum size and spacing requirements shown in the attached
calculations.
• The lag screws and glass standoffs are located as described in the stair drawings provided
by B&H Stair.
• The glass standoffs (CRL #ACSB22BS) used for this design are adequate to resist the
minimum required applied loads (listed above).
Conclusion:
We found that the composite LVL stringer will have adequate strength and rigidity to carry the
applied loads and resist the torsional effect due to the curvature of the stringer, provided that
the connections to the landings are adequate. We found that the glass guards and
connections require the following criteria to meet the applied loading:
• Glass thickness shall have a minimum nominal thickness of 0.625".
• Lag screws shall have a minimum thread penetration (not including tip) into the built-up
LVL tread assembly of 4.0".
Please do not hesitate to call if you or others wish to discuss these findings.
Respectfully, S .P.41X• dad4)%_,
O j'•VO N kiii�p
David L. Wilson, P.E. c.)•
Principal -o:� 29350 Z;�
SS/ONAC••��
48 County Rd. 250•Durango, CO 81301 • (970) 385-6774
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