HomeMy WebLinkAboutFile Documents.1310 Red Butte Dr.0114.2018 (5).ARBK
Jeff Grinspoon & Jon Foley
Jeff@gomaven.net
Foley@gomaven.net
January 16, 2017
Regarding: 1310 Red Butte Bridge
Jeff and Jon:
We visited the site of your home located at 1310 Red Butte in Aspen Colorado in December 2015
and November 2016 to review the condition of your existing bridge. The bridge is a wooden structure
that spans approximately 30 feet. The wood in the bridge is currently in fair to poor condition and the
current structure is not sufficient to meet the current snow load requirements by the City of Aspen or
the suggested pedestrian live load per the National Cooperative Highway Research Program
(NCHRP).
While on site in November 2016, we tested the bridge by applying a 300 pound load to the center of
the bridge. With this load applied, the measured vertical deflection of the bridge was 3/16”. Since
deflections are linear with loading, we can extrapolate up to full live and snow loads. The required
flat roof snow load for your home is 75 PSF (pounds per square foot) which equates to a ground snow
load of 75 psf per ASCE7. The NCHRP suggests a live load of 90 psf for pedestrian bridges (see
attachment). The calculated deflection with full snow load is 5.6” and with full live load 6.75”. These
produce deflections of L/64 and L/53, which far exceeds the suggested L/500 by NCHRP or the
L/120 in the IBC.
Analyzing the existing bridge members for strength against snow load shows they are at
approximately 1/4th the strength required by code. This even assumes (3)2x8 per side when in reality
there are only two continuous 2x8 with a third member spliced in the middle of the span.
The current handrail is approximately 30” high instead of the code required 42”. Also it does not
appear that the handrail is in safe condition as it has excessive deflection with only a slight amount of
force applied to it. We could not measure this on site without more sophisticated testing equipment,
however, it does not appear to be able to resist a 200 lb concentrated load or 50 plf linear load
without excessive deflection.
In addition to being undersized, the wood members at the abutments are starting to show signs of rot
and some cracking. (see photos below) The members are cast directly into the concrete making
repair/replacement of the members difficult without completely replacing the bridge. The decking of
the bridge is also showing signs of rot with excessive algae growth on it. (see photo below)
04/24/2018
Due to all the conditions stated above, we are providing a plan to reinforce the wooden structure
without adjustment to the current configuration or foundation elements. To reinforce the bridge with
additional wood members would require significantly larger member sizes, therefore we are
suggesting to reinforce the bridge with a steel member, similar in color to the painted wood. Steel
also provides a more durable long term solution to avoid rot or water damage. Our design drawings
are attached.
If you have any questions, please do not hesitate to contact us.
Sincerely,
Dodson Harper, P.E., S.E.
04/24/2018
Figure 1: Rotten Wood at Abutment
04/24/2018
Figure 2: Cracked Wood at Abutment
Figure 3: Algae Growth and Rot on Decking
04/24/2018