Stage Load Assessment & Accessible Handrail Installation
December 9th, 2016
Final Report, Rev. February 1, 2017
TABLE OF CONTENTS
Cover ...................................................................................................................................... 1
Table of Contents ................................................................................................................... 2
Executive Summary ................................................................................................................ 3
Report Overview ..................................................................................................................... 5
Project Background ................................................................................................................ 5
Existing Available Documents ................................................................................................ 5
Existing Conditions ................................................................................................................. 6
Stage .............................................................................................................................. 6
Pathway .......................................................................................................................... 8
Stage Load Analysis ............................................................................................................... 10
Pathway ABAAS / ADA Compliance ....................................................................................... 17
Conclusions and Recommendations ...................................................................................... 18
Stage .............................................................................................................................. 18
Pathway and Railings ..................................................................................................... 22
A. Existing Conditions – Topographic Worksheet
B. Lower Path Slope Calculations
C. Existing Stage Framing Plan and Details
D. Spall & Coring Locations, and Rebound Hammer Statistics
E. Structural Calculations
F. Test Reports
i. Concrete Compressive Strength
ii. Petrographic Analysis
EXECUTIVE SUMMARYJMT was tasked by the National Park Service (NPS) to perform the following work at the Carter Barron
Amphitheater in Rock Creek Park:
A structural load assessment of the existing stage floor.
Complete an earlier design for installation of accessible handrails along an existing pathway.
Verify compliance of the maximum pathway slope for complying with the Architectural Barriers Act
Accessibility Standard (ABAAS) and the American Disabilities Act (ADA) .
The stage floor, built in the 1950s, is constructed with a monolithically poured concrete frame consisting of
concrete beams, slabs and columns. The original stage floor was subsequently modified by filling in floor
openings with concrete. A painted, wood sleeper and plywood floor currently overlays the concrete slab of
the stage. Historical documentation indicates steel truss systems supporting fabric covers, curtains,
backgrounds and lighting systems were once in place. These truss systems have been removed.
A previous report completed in 2014 noted areas of considerable water penetration, cracking, spalling and
rusted reinforcing at the concrete stage. The report also noted chloride contaminated concrete at the front
of the stage. A structural load and stress analysis was not performed at that time.
JMT performed a structural load analysis using the original design loads from the historic documents. The
forces and stresses obtained from this analysis were compared and checked against the structure’s capacity
based on current Codes and Standards. Concrete strength was indicated on the historic documents and JMT
obtained core samples for testing to confirm the material properties of the concrete. Results of the core
testing show that the concrete strength is higher than the original design strength and that the concrete is in
generally good condition.
Based on current Codes, the structural load analysis indicates the structure is currently subjected to forces
and stresses above its allowable design capacity in shear strength solely with the dead load of the structure.
Therefore, subjecting the stage area to additional live loads for any type of Code defined or classified use is
not recommended. Use of the structure as a stage should be suspended as the current Code requires a 150
psf live load until at such time the structure can be replaced, or strengthened and repaired to allow for the
application of stage loads.
As further discussed in the conclusions and recommendations section of this report, it is recommended that
1. Suspend operations on the stage structure for use as a stage or other loadings as would be
defined by any of the IBC, Chapter 3, Use and Occupancy Classifications.
2. The NPS should consider implementing a temporary shoring systems as soon as possible,
until the structure could be replaced or strengthened and repaired.
3. The structure could be removed and replaced, or strengthened and repaired, to allow for the
application of stage loads. This would generally provide for the direct construction and account
of quantities and costs. This option results in a new stage structure with a 75 to 100-year use.
For comparison, a preliminary order of magnitude estimate for removal and replacement could
be $520,000 to $620,000.
4. Another option could be to strengthened and repair the structure by installing carbon fiber
systems with the conventional repair of damaged areas. This option may be considered as it
allows for the existing structure to remain in place. Complete strengthening and repair could
result in a fully rehabilitated stage structure with a 50 to 75-year use. Generally, repair projects
of this type have in-direct costs with cost changes during construction. For comparison, a
preliminary order of magnitude estimate for carbon fiber and repair could be $460,000 to
5. Planning for the future work is recommended to further define and detail project requirements,
direction, schedule, scope, costs, and funding.
The pathway from the promenade to mid-section of the amphitheater is currently designated as an accessible
route for disabled persons. As tasked by the NPS, JMT provided separate construction documents apart
from this report for a railing system which meets structural requirements based on a previous design. We
were asked to verify this existing pathway is in compliance with Architectural Barriers Act Accessibility
Standard (ABAAS). JMT performed a field survey and used this data to calculate the running and cross
slopes of the pathway. These calculations indicate that both the running slope and cross slope are steeper
than the maximum slopes as allowed, and therefore, do not comply with ABAAS. Providing an accessible
pathway meeting ABAAS requirements requires rework of the pathway itself and subsequent coordination of
the railing profile. Due to the non-compliant slope of the pathway the railings should not be installed without
correcting the pathway.
REPORT OVERVIEWJohnson, Mirmiran & Thompson (JMT), was tasked by the National Park Service (NPS), to perform a
structural load assessment of the stage floor, and to complete an earlier design for installation of accessible
handrails along an existing pathway. We were also asked to verify compliance of the maximum pathway
slope permitted for complying with the Architectural Barriers Act Accessibility Standard (ABAAS) and the
American Disabilities Act (ADA).
PROJECT BACKGROUNDThe Carter Barron Amphitheater stage floor structural system was constructed circa 1950s. The annual
attendance for performing arts attractions is approximately 70,000 patrons. The stage floor consists of a wood
sleeper and plywood finished floor over a reinforced concrete supporting structural system. Historic
documentation has shown stage truss framing systems supporting enveloping stage curtains, backgrounds
and lighting with sound systems. The truss framing system has since been removed.
Concern for the reinforced concrete supporting structural system was raised in a previous condition assessment
report completed in February 2014 by Protection Engineering Group. The report indicated areas of
compromised strength of the concrete, including evidence of excessive calcium chloride calcification,
particularly at the proscenium. Other damages resulting from calcification, such as rusting of reinforcing and
spalling, were noted. A structural load and stress analysis was not performed as part of this report.
Previous work, including new seating, lighting and approaches, along with the removal of the overhead stage
trusses, was completed under a contract in early 2004. (Reference Historic Photo on Page 1.
Funding limitations precluded the installation of handrails to a newly paved asphalt pathway at the
amphitheater leading from the promenade to the mid-section. NPS tasked JMT to finalize a structural design
for an Architectural Barriers Act Accessibility Standard (ABAAS) compliant handrail system along this
pathway, with the intent to match existing railings based on Rehabilitate Carter Barron Amphitheater, Phase I,
04-11-2003 drawings that were supplied by the NPS. New work includes the fabrication and installation of
approximately 512 linear feet of handrails from the promenade to the mid-section of the amphitheater to match
the existing bronze-colored anodized aluminum railings. Previous survey information of the pathway was not
available; therefore, survey work was required to verify existing pathway slopes for compliance to applicable
ABAAS/ADA Codes and Standards.
EXISTING AVAILABLE DOCUMENTSExisting documents reviewed included but not limited to:
Amphitheater, Revision A, 3/14/50, drawing no 55.9-41-S1A
Rehabilitate Carter Barron Amphitheater, 11-16-2001.
Rehabilitate Carter Barron Amphitheater, Phase I, 04-11-2003.
Rehabilitate Carter Barron Amphitheater, Phase II, 5-7-2003.
Structural Assessment of Cater Barron Amphitheater, Condition Assessment Report, Protection
Engineering Group, February 2014.
These documents and their contents are further referenced in the remainder of this report.
STAGEThe stage area (indicated by the red hatch in Figure 1) is approximately 72-feet wide by 78-feet deep,
and stands 12-feet tall above grade. It is constructed with a reinforced concrete one-way slab and beam
system, and bidirectional moment-resisting frames for lateral resistance. Columns appear to be bearing
on spread footings, though this could not be verified without exploratory excavation. Existing drawings
indicate that the structure was built in the 1950s; a reproduction of which can be referenced in Appendix
C. This framing plan indicates six floor openings framed between the concrete beams. These openings
likely allowed for stage production operations. Also, originally, a front portion of the stage floor appeared
to have been framed with sheathing over a lumber joist system.
Figure 1: Stage Area Location
On August 25, 2016, JMT traveled on-site to observe and document the existing condition of the structure,
which included items such as concrete damage (e.g. spalls, cracks, water damage), notable deflections,
general conformance to existing drawings, and to determine coring locations for subsequent concrete
sampling and testing for strength and petrographic analysis. Access to underneath the stage was readily
available, and the general condition of the underside of the stage structure can be seen in Figure 2.
The six original framed openings and the bay at the
front potion of the stage have been in-filled with
concrete. The in-fill slab is supported by thickened
slab ends bearing on top of steel angles (Figure 3).
Documentation for the construction of the in-fill slabs
was not available. Also, there were several
instances where spalls were observed at the in-fill
areas which appear to have been caused by rusted
rebar. Locations of spalls, cracks and other damage
can be found in Appendix D.
Figure 2: Picture at the Underground Entrance Looking Up at the Stage Structure
Figure 3: Concrete Fill at Trapdoor Opening w/ Spall Damage
At the northeast and northwest corners, the two staircase landings showed signs of undermining below
the elevated slabs (Figure 4). The landings were constructed without retaining walls. Continuance of
the undermining will eventually lead to instability or compromising of the landings and staircases.
PATHWAYThe pathway at the amphitheater leading from the promenade to the mid-section of the seating area is approximately 4-feet wide by 270 feet long with an elevation change of approximately 12 feet. It is primarily constructed with asphalt with a few segments being concrete. Existing handrails are provided at limited portions along the pathway (Figures 5 & 6). A field survey of the pathway was performed by JMT on August 25, 2016. Results of the survey is shown on the drawings titled Existing Conditions – Topographic Worksheet, which can be found in Appendix A.
Figure 4: Stair Landing at Northwest Corner with Soil Falling Out from Underneath Slab
Figure 5: Existing Railing
Figure 6: Existing Lower Path and Handrails
STAGE LOAD ANALYSISJMT’s load analysis was based on current standards, as well as a review of a historically based analysis that
would have been performed circa 1950s. The structure was modeled in RAM Elements software (by Bentley)
to ascertain the applied forces. The RAM Elements software was used to then check the applied structural
forces and stresses of the members against the members’ capacities that were calculated in accordance
with The Building Code Requirements for Structural Concrete, ACI 318-14, and Commentary on Building
Code Requirements for Structural Concrete, ACI 318R-14. Original design live load and material properties
were indicated on the existing drawings as follows:
Stage Floor Design Live Load = 100 psf.
Soil Bearing Capacity = 4000 psf.
Concrete (Class B) = 2500 psi.
Reinforcing Steel (Intermediate Grade) = 20 ksi allowable (40 ksi yield)
As a part of the scope of work, JMT hired ECS Mid-Atlantic (ECS) to obtain concrete cores for compressive
and petrographic sample testing. The purpose was to confirm the 2500 psi design concrete strength, and to
obtain a general condition of the concrete matrix through petrographic analysis. JMT and ECS performed
field sampling on September 28, 2016 to obtain five cores (three for compression testing and two for
petrographic analysis). To avoid damaging the exterior stage wood finish, cores where obtained by drilling
up from underneath the slab (Figure 7). Locations of the five cores can be found in Appendix D.
Figure 7: ECS Obtaining a Compression Core with an Underside Surface Mounted Drill Rig
After the cores where taken, holes were patched with dry-pack grout. A typical core sample is shown in
Figure 8: Core Sample
On October 6, 2016, JMT received the results of the three compressive break tests from ECS, which can be
referenced in Appendix F. Results are summarized in the table below:
A compressive strength of 4000 psi (lower bound) was used for member capacity calculations.
On October 30, 2016, JMT received the results of the two petrographic analysis, which can also be
referenced in Appendix F. Generally, the petrographic analysis showed that the concrete samples were in
good condition, but were of poor quality for modern exterior concrete due to the lack of an adequate air void
system to offer resistance to cyclic freezing and thawing while in a saturated condition. No evidence of
freeze-thaw related damage was observed in either sample – an indication that the samples were not, or
rarely, in a saturated condition when experiencing cycles of freezing and thawing. ACI recommends an
average air content of 5 to 6% (+/- 1.5%) for exterior concrete with 1” aggregate in moderate to severe
conditions. Sample P-1 indicated an air void content of 1.8% and sample P-2 indicated an air content of
2.0%. Both were below the recommended values of ACI. It is possible that the waterproofing membrane,
wood sleeper and plywood floor, or combination thereof, provide some protection from freezing and thawing
The waterproofing membrane as indicated on the top surface of each sample also has protected the top
surface of the concrete from exposure from atmospheric carbon dioxide. Over time, exposure to carbon
dioxide leads to carbonation on concrete surfaces and weakens the concrete by reducing the effective depth
of the concrete cross section. Carbonation levels were generally observed as:
Top surface: 1/8” to 1/32”
Bottom surface: 1-1/16“ to 1-1/4”
These levels would be expected for concrete of this age.
Figure 9: Isometric View of the Analytical Model
The coarse and fine aggregate in both samples were similar and generally appeared to be hard, sound and
durable. Each sample showed a water cement ratio between 0.45 and 0.50. Concrete Surface Profiles of
the concrete samples were a CSP3.
For the analytical model, a live load of 100 psf was first applied to the structure, as this was the original
design load indicated on Amphitheater, Revision A, 3/14/50, drawing no 55.9-41-S1A. According to the
International Building Code, IBC 2015, a stage floor is typically designed for 150 psf. An isometric graphic
of the analytical model can be seen in Figure 9.
The structural analysis calculations for the Structural Load Assessment of the Stage Floor are presented in
Appendix E, Structural Calculations. The concrete structure was analyzed following the Load and Resistance
Factored Design (LRFD) methodology, based on ACI 318-14.
Calculations indicate significant computational shear overstresses in the beams and girders with the original
design and applied live load of 100 psf. These results can be attributed to the following:
1. The additional dead and live load resulting from the trapdoor and bay in-fill areas has increased the
overall applied loads to the structure. This has produced higher bending and shear stress onto the
supporting concrete beams and girders which were not accounted for in the original design. Also,
when the in-fill areas were constructed, the beams and girders were not reinforced to allow for the
added loads. Furthermore, the in-fill areas do not offer any structural continuity of the existing slab.
2. Computer models more accurately distribute the applied loads to supporting members based on their
inherent stiffness and continuity of the structure, as opposed to hand analysis. The load analysis
originally performed in the 1950s would not have allowed for these applications, but would have been
based on more simplified hand analysis and design procedures.
3. Review of the existing documentation found that shear reinforcement (i.e. ties or stirrups) were, at
several instances, spaced too far apart to be included and accounted for in shear strength; therefore,
those instances could only consider concrete shear strength for un-reinforced shear sections. ACI
318-14 limits spacing to a maximum of d/2.
4. The current procedure to determine the shear capacity of a concrete beam without web reinforcement
is significantly different than the procedure used in the 1950s. In accordance with the current Code
of the American Concrete Institute, ACI 318-14, the allowable shear capacity is less than the
allowable shear capacity calculated from the 1950s. Research and testing has occurred since the
1950s and the industry has resulted in a better understanding of shear behavior in beams. Codes are
typically updated as new information (through testing or experience) becomes available. Limited
shear calculations following the Allowable Stress Design (ASD) methodology ACI 318-56, indicate
that the beams were designed appropriately for an unreinforced web section in shear for the historic
Furthermore, when reviewing the analysis, it appears that the structure’s shear overstresses are triggered
with an application of the dead load only, which means that the structure’s self-weight has been performing
within the red zone (i.e. above the allowable design limit). Diagram 1 illustrates this concept, using Beam G1
as an example:
Because the Load and Resistance Factor Design (LRFD) procedure is being used as required by ACI 318-
14, the shear strength inequality ϕVn ≥ Vu had to be rearranged to present the shear capacity in a Factor-of-
Safety (FOS) format. Therefore, the beam’s inherent FOS for shear following current design codes equates
to 3.733. Analysis shows that the applied shear due to un-factored dead load is 8.81 kips – greater than the
allowable capacity of 6.91 kips. However, this value is still relatively less than the nominal capacity of 25.8
kips. Approaching the nominal capacity would remove any strength factors as required by the ACI Code and
would increase the risk of inducing a structural overload on the members. Furthermore, applying loads
greater than the allowable capacity could result in permanent deformations being induced in the members.
The structural capacity of the member is deemed acceptable when the applied load in all its applied
combinations of dead, live, seismic, etc. is less than the allowable capacity as required by the applicable
design Code (i.e. Va > Vd).
Other beams that are operating in the red zone are indicated in the structural calculations (Appendix E).
Diagram 1: Beam G1 Shear Capacity vs. Applied Dead Load
Application of a 150 psf live load, as required by current codes, results in further theoretical shear
overstressing of the stage framing, since the current stage framing floor structure is not adequate to resist a
100 psf live load, nor even its own intrinsic self-weight.
A shear failure crack can be seen in Figure 10 (as was documented in the February 5, 2014 report). This is
evidence to support the fact that the structure is not adequately performing in shear.
The structure will perform adequately in flexure for the historical 100 psf live load. Beam G7 contains the
highest flexural stress ratio of 0.95 ≤ 1.0. The structure, however, will be overstressed and operating in the
red zone for flexure to support the currently required 150 psf live load.
Existing documents (Figure 11) show that the stage floor was originally designed with a 2-inch topping;
however, the core samples taken (Figure 12) indicate a topping is not present. Rather, a painted wood
sleeper and plywood system currently overlays the stage floor (Figure 13). Based on the 2001 rehabilitation
drawings, it appears that the wood system is constructed with ¾” treated tongue-and-groove plywood over
2x4 sleepers spaced at 24 inches on-center (Figure 14). The wood sleepers bear on top of 6” x 6” x ¾” thick
rubber isolation pads at 12 inches on-center. The grade and species of the plywood and wood sleepers was
not indicated on the drawings. The plywood appears to be, overall, in poor condition, showing signs of
delamination of the plywood plies and separation at the joints.
Figure 10: Shear Failure Crack Photo Structural Assessment of Carter Barron Amphitheater,
Protection Engineering Group, Feb. 5, 2014. (unavailable)
Figure 11: 1950s original drawings indicating a 2-inch topping over
the concrete stage floor.
Figure 12: Core sample does not contain a 2-inch topping over the waterproofing
Figure 11: Painted wood sleeper system at the back of the
Figure 14: Existing wood sleeper system installed during
2001 rehabilitation work. (unavailable)
PATHWAY ABAAS/ADA COMPLIANCEAs the pathway is presently marked as an ABAAS/ADA accessible route and leads to priority seating areas,
the pathway would be considered an accessible route (as defined by the 2010 ADA Standards for Accessible
Design). Therefore, the pathway can be considered as one of two possibilities; a ramp, or only a generic
walking surface. It seems the pathway most appropriately falls under a generic walking surface (a ramp is
essentially a steeper walking surface, with stricter requirements). The table below shows a basic side-byside
comparison of requirements between a ramp and a walking surface:
Accessible Routes §402 ADA
Walking Surface §403 Ramp §405
running slope ≤ 1:20 running slope ≤ 1:12
cross slope ≤ 1:48 cross slope ≤ 1:48
Handrails not required
Handrails required on both sides (§505 for handrail
Edge protection not required Edge protection required on both sides
Clear width ≥ 36” Clear width ≥ 36”
If clear width is ≤ 60”, a 60” x 60” passing zone must be
provided at every 200 feet*
Landings required at every 30” of rise, changes in
direction, and at the start and end of the ramp*
* For walking surfaces, no specific requirements at turns except at 180-degree turns; whereas a ramp requires a
landing at any change in direction.
On August 25, 2016, JMT performed a field topographic survey on the pathway (Appendix A) . The running
slopes and cross slopes were calculated using the rise and runs from survey point – to – survey point
(Appendix B). Any slope that did not meet the requirements is highlighted in yellow (Figure 15 is a picture
taken to depict the path’s cross slope). This cross slope is typical along the length of the pathway and more
pronounced at the switchback. Measured and surveyed conditions of the pathway indicate the following:
1. Running Slope(s) ranging from 1:5 to 1:43
a. Approximately 160 linear feet (60%) of the 270-foot pathway is sloping greater than the 1:20
requirement. (Reference Table 1016.7.1 Maximum Running Slope and Segment Length
2. Cross Slope(s) ranging from 1:11 to 1:45 (100%) not meeting the 1:48 requirement. (Reference
1016.7.2 Cross Slope ABAAS).
3. The turning (switchback) space slope is steeper than 1:48 (Reference ABAAS 304.2).
Stage Load Assessment & Accessible Handrail Installation
December 9th, 2016
Final Report, Rev. February 1, 2017
Based on the survey, the pathway currently does not meet the walking surface (and therefore ramp) slope
requirements per ABAAS/ADA. Furthermore, since the pathway has a clear width ≤ 60 inches (5 feet), and
runs longer than 200 feet, the pathway will need a passing zone at some location – preferably within the
middle third. Therefore, for the pathway to be considered as an accessible route, additional work
needs to be performed. This will most likely entail demolishing the existing asphalt surface, regrading, and
repaving. Adding railings alters the pathway, and therefore, if the railings are added, the pathway must be
brought into compliance with ABAAS/ADA Standards.
CONCLUSIONS AND RECOMMENDATIONS
STAGEThe previous report prepared by Protection Engineering Group, Chantilly, VA, February 2014, indicated that
there was a concern for the performance of the stage floor structure due to observed damage such as
spalling, cracking, and calcification which could result in internal corrosion of the reinforcing due to chloride
levels in the concrete, as high chloride levels were recorded. This report recommended the following for the
Figure 15: Depiction of cross slope at the bend. Clearance at the sticks is approximately 3 inches (a 1:48
cross slope for a 4-foot wide path equals 1 inch).
1. Full depth concrete replacement of the 6-inch south proscenium concrete slab and adjacent
2. Full depth concrete replacement of the chloride contaminated concrete at the front of the stage
including its front edge.
Structural calculations (Reference Appendix E, Structural Calculations) for the stage load assessment
indicate that the concrete floor structure is not able to support the current code required applied live load
based on the mechanical shear properties, and shear design strength of the stage floor structure itself.
Revisions, alterations, or certifications for the addition(s) of loads to the stage area for the use of stage
lighting, sound equipment, stage constructions, etc. would require analysis of the existing supporting
structure to determine if the structure could support the loads. The analysis would then show an immediate
overstress condition with the application of the revisions, alterations, or additions and would not be
incompliance with Chapter 34 of the IBC Code in which it defers to the International Existing Building Code
(IEBC). The International Existing Building Code applies to matters governing the repair, alterations, change
of occupancy, additions to and relocation of existing structures which include the application of or certification
for new loads.
As loads are applied and add to the current loads of the stage floor structure and alter its behavior, the IEBC
would consider this an “Alteration” and require the Owner to have a structural analysis of the existing building
made to determine the adequacy of the structural systems for the proposed alteration. Furthermore, the
IEBC requires the analysis be performed to the current Codes and Standards and may not be grandfathered
to previous Codes and Standards. The analysis must consider current Code seismic, live, and other loads
in combination with the applied dead loads. JMT’s analysis finds the following:
1. The structural analysis presented in Appendix E, Structural Calculations, is based on current Codes
and Standards (ACI 318-14), as is required by IBC/IEBC, and shows little to no available transient or
live load additional capacity. This is non-compliant with the 2015 IBC, Chapter 16, Table 1607.1 for
stage floors. Per our findings, any assignment of additional point loads or distributed loads, in any
form, is not recommended without implementing some regimen of strengthening.
2. The structure is, and has been operating, above the allowable design capacities as determined by
current ACI 318-14 and IBC 2015 Codes and Standards when subjected to current and/or any
additional transient live loads in any form. Therefore, it is recommended that no further point loads
or transient live loads be applied until action is taken to address the shear overstresses.
3. Structural analysis based on a historic Allowable Stress Design (ASD) procedure seems to indicate
that the concrete strength participating in shear may have been appropriately designed back in the
1950s. Some shear reinforcement seems to have been spaced to the limits at the time and by our
engineering judgement appears to be spaced too far apart in some instances to be effective.
4. It is recommended that carbon fiber wrap be installed to strengthen and harden the structure for shear
to allow for the application of additional loads and effectively support the code applied superimposed
transient stage live loads. An example can be seen in Figure 16 below. Other solutions are available,
such as installing new columns, increasing the beam cross sections, or removing and rebuilding
sections of the stage. These alternate solutions, however, may not be as cost effective as installing
a carbon fiber wrap system.
5. Any spalls should be repaired with typical concrete repair practices.
6. The undermining of the stair landings should be repaired. A concrete or masonry foundation wall
should be constructed, and the remaining voids grouted with a low-pressure system.
7. The recommendations presented in the Protection Engineering Group, Chantilly, VA, dated February
2014, should be implemented and the areas noted in this report should also be repaired, replaced
8. The slab in-fills show exposed and rusted reinforcing, as may be attributed to water infiltration, and do
not offer or provide for a continuous monolithic slab system due to their attachment system to the
existing beams. The in-fills also altered the original loads to the supporting beams and have increased
the overall applied loads to the existing structure. Therefore, the in-fills should be removed and
replaced with a new system integrated into the existing structure, strengthened to accommodate the
Figure 16: Carbon Fiber Wrap Example (unavailable)
Removing and replacing the infill areas with a lighter system without strengthening the surrounding
system would not reduce the applied load sufficiently enough to avoid strengthening the structural
system. This is due to the net difference in the reduction of about 10 psf to 15 psf would not be
enough to overcome the limiting state stress ratios for shear. Reference structural calculations page
9. Observations of the plywood floor system show signs of delamination of the plies and separations at
the joints. The wood floor system has been exposed to weather since it was installed circa early 2001,
which would make it approximately 15+ years old. The grades or species of the wood system could
not be determined as would be needed to define the strength properties of the system. However, it is
likely weaker than the supporting concrete structure, which as discussed, cannot be certified for any
live loads without strengthening the concrete system. Therefore, at the time of strengthening the
concrete, it is also recommended to remove and replace the plywood and wood sleeper system.
As discussed, and based on current Codes, the structural load analysis indicates the structure is currently
subjected to forces and stresses above its allowable design capacity in shear strength solely with the dead
load of the structure. Therefore, subjecting the stage area to additional live load for any type of Code defined
or classified use is not recommended. Further use of the structure as a stage, as the current Code requires
a 150 psf live load, should be suspended until at such time the structure can be, replaced, supplemented, or
strengthened and hardened to allow for the application of stage loads.
As the stage floor was constructed in the 1950s, it is approximately 65 to 70 years old and quickly
approaching the end of its use. Also, as demonstrated by structural calculations, it does not meet current
Codes and Standards for use or construction. Therefore, it is recommended that:
1. The structural load indicates the stage floor structure is currently subjected to forces and stresses
above its allowable design capacity, therefore, the NPS should suspend operations on the structure
as would be defined by any of the IBC, Chapter 3, Use and Occupancy Classifications until the
structure can be replaced, or strengthened and repaired.
2. The NPS should consider implementing a temporary shoring systems as soon as possible to
provide positive control of the structure and mitigate the uncertainly of the behavior of the structure.
3. The structure could be removed and replaced, or strengthened and repaired. While conceptual
design of these systems is beyond the scope of this report, general methods would include:
a. Complete replacement would first involve the demolition of the monolithically poured concrete
frame consisting of the concrete slab, beams, and columns and footings. Removal of the stage
area would also remove the damaged concrete that was noted in the form of spalling, cracking,
and calcification. A new structure could then be built.
i. This option should be considered as the complete removal and replacement of the stage
would warrant a new stage structure fully designed to current Codes and Standards and
provide for a new 75 to 100-year structure.
ii. This option allows for the un-imposed construction and direct account of quantities and costs.
These types of projects may be bid on a lump sum amount as the scope of construction may
be quantified based on the demolition and replacement construction documents.
iii. For comparison, a preliminary order of magnitude estimate for removal and replacement
could be $520,000 to $620,000.
b. As previously discussed, installing the carbon fiber wrap and repair of the damaged areas,
would strengthen and repair the structure to allow for the application of additional loads and
effectively support the Code applied superimposed transient stage live loads.
i. This option may be considered as it allows for the existing structure to remain in place.
Complete strengthening and repair could result in a fully rehabilitated stage with a 50 to 75-
ii. Repair projects of this type have in-direct costs and with cost changes during construction.
Normally, concrete repair projects are bid based on estimated quantities with individual bid
items extended from the contractor’s unit prices.
iii. For comparison, a preliminary order of magnitude estimate for carbon fiber and repair could
be $460,000 to $560,000.
4. Other solutions may be available, such as installing new columns, increasing the beam cross
sections, or removing and rebuilding sections of the stage to increase the available live load. These
alternate solutions, however, may not be as cost effective as installing a carbon fiber wrap system,
or provide for the same use full life as complete demolition and replacement.
5. Planning for the future work is recommended to further define and detail project requirements,
direction, schedule, scope, costs, and funding.
PATHWAY AND RAILINGS1. As shown in Appendix B, Lower Path Slope Calculations, the entire pathway does not meet
ABAAS/ADA requirements for the cross slope. Furthermore, about 60-percent of the pathway
exceeds the running slope requirements.
2. The existing pathway cannot be endorsed as ABAAS compliant or ADA accessible. For the pathway
to be endorsed as ABAAS/ADA compliant, it will need to be reworked, regraded, and repaved,
regardless if the pathway is to be considered a walking surface or a ramp.
3. Drawings, specifications, a Class A cost estimate, and a proposed schedule for construction for new
handrails have been supplied to the NPS. However, this design does not compensate for the noncompliance
of the pathway and should not be construed as voluntary assumption by JMT that the
pathway with the addition of the railings will meet ABAAS/ADA requirements. Adding railings without
correcting the pathway slope does not correct the noncompliant running and cross slope issues. Even
though the drawings supplied detail handrails able to resist the applied loads, as required by IBC,
they cannot be ABAAS/ADA compliant due to the non-compliant slope of the pathway and should not
be installed without correcting the pathway.
JMT reserves the right to amend this report as additional and/or new information becomes available.
Last updated: July 21, 2021