Post on 30-Jul-2022
Dahlke Manor
Engineering Judgment Report
Fire Rating of 3-HR and 2-HR rated assemblies EJ#1
Client Name: Peter Meijer Architect, PC
Client Address: 605 NE 21st Avenue Portland, OR
Date: 3/3/2021
Dahlke Manor – Engineering Judgment Report
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Table of Contents 1 Project Overview ........................................................................................................................................ 3
2 Applicable Codes, Standards, and Guides ................................................................................................. 3
3 Discussion .................................................................................................................................................. 3
3.1 Approach ............................................................................................................................................. 3
4 Proposed Design ........................................................................................................................................ 3
5 Assembly Analysis ...................................................................................................................................... 7
5.1 W/D Comparison of C-Channel and W-Beam ...................................................................................... 7
6 Summary .................................................................................................................................................. 11
7 Conclusion ............................................................................................................................................... 11
8 Appendix .................................................................................................................................................. 12
Dahlke Manor – Engineering Judgment Report
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1 PROJECT OVERVIEW
Dahlke is a 9-story residential apartment tower of Type IA construction with a 1-story lower story attached
community space, located in Portland, Oregon serving low-income residents. It will be under the jurisdictional
review of the City of Portland. The proposed scope of work is a 1-story 700 SF addition for a kitchen and break
room associated with the Community Room.
New Structural channels are part of construction scope of work to create openings in existing masonry walls.
Existing walls are 8" hollow brick masonry or 8" hollow concrete block and meet 3-hour minimum rating for
Type 1A construction. The existing ceiling structure is 4 1/2" concrete slab above concrete pre-block and
beam system, providing a 2-hour rated assembly. See Appendix A for original permit drawings and photo of
existing ceiling structure for reference of the existing structure.
Code Unlimited has been asked to provide Engineering Judgment (EJ) letter for the 3-hour protection of
structural channels and 2-hour protection of angle sections supporting floor construction at the existing walls.
2 APPLICABLE CODES, STANDARDS, AND GUIDES
• 2019 Oregon Structural Specialty Code (OSSC)
• 2019 Oregon Fire Code (OFC)
3 DISCUSSION
3.1 Approach
• The proposed beam assembly has been analyzed in accordance with 2014 OSSC §703.3 Alternative
Methods for Determining Fire Resistance.
• The proposed design is compared to the 3-hour fire rated channels per ISOLATEK CAFCO IFRM.
• Portions of the tested assembly are modified to suit the unique design condition. The modification is analyzed
for equivalency using published fire test data and acceptable fire science principles.
4 PROPOSED DESIGN
The proposed assemblies of C12x30, C12x25, and L8x8x3/8 as well as the 1/2" plates & L6”x4"x5/16" (against
ceiling) members are being installed (see Fig 1, 2, 3, 3b, 4 and 5). For this EJ, all of the members will be
examined in detail and compared in a Table against the ISOLATEK designs and all steel members attached to
these C-Channel will be protected. The C-Channel members are considered primary structure. Per 2019
OSSC Table 601, are required to be minimum 3-HR. fire rated for the construction Type. The Angle sections
are roof support members and required to be 2-HR rated per 2019 OSSC Table 601. The L8x8x3/8 assembly
contains a L4x4x3/8 angle section. Protection will be consistently applied to the attached 1/2" plate projections
and L-angle attached to the horizontal beam (See EJ#2). As a conservative measure, the L4x4x3/8 weight will
not be added as part of the complete assembly evaluation. It is assumed that the proposed assembly will be
Dahlke Manor – Engineering Judgment Report
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exposed to fire on the left side and the assembly will require continuous protection from three sides with
shielding on the concealed side (against Concrete or CMU wall) not requiring protection.
Fig 1: C-Channel Locations.
Fig 2: C-Channel C12x30 -3Hr Rating
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Fig 3: C-Channel C12x25-3Hr Rating
Fig 4: Angle L8x8x3/8-2Hr Rating
See EJ#2
C12x25 and steel plate combined to be
heated on 4 sides
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Fig 4b: Proposed assembly of wall plate.-2Hr
Fig 5: Angle L6x4x5/16-2Hr Rating
See EJ#2 for
IFRM Protection
L6x4x5/16
Protected by 2 Hr
See EJ#2
for IFRM
Protection
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5 ASSEMBLY ANALYSIS
The proposed assembly of C-Channel C12X25 and C12x30 is intended as a primary structural member. The
proposed assembly of angles L8x8x3/8 and L6x4x5/16 are intended as a secondary structural member.
Compared to the C10x30 member in the ISOLATEK CAFCO assembly as shown in figure 6.
Figure 6: ISOLATEK CAFCO WB3-4 Protection
5.1 W/D Comparison of C-Channel and W-Beam
The proposed assembly has an inherent fire resistance greater than the tested beam, W/D comparison:
1.01>0.96. We have compared the beam as proposed along with the test configuration. See Fig. 6 and 7
below.
C10x30 ASTM
W/D Ratio = 0.96
Heated Perimeter of C12”x25
C-Channel Total Heated Perimeter = 23.0
Weight per foot from Figure 6
Calculated W/D Ratio = 1.08
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Heated Perimeter of C12”x30
C-Channel Total Heated Perimeter = 23.5”
Weight per foot from Figure 6
Calculated W/D Ratio = 1.28
Heated Perimeter of 1/2"x12"x2' plate against wall (Fig. 4b)
Steel Plate = 12+(2)1/2” =13
Total Heated Perimeter = 13”
Weight per foot =20.4 lb/ft
Calculated W/D Ratio = 1.56
Heated Perimeter of L8”x8”x3/8”
Angle Iron = 2*(8”+3/8”)
Total Heated Perimeter = 16.75”
Weight per foot (20.1lb/ft) from Figure 7
Calculated W/D Ratio = 1.2
Heated Perimeter of L6”x4”x5/16”
Angle Iron = 6+5/16”
Total Heated Perimeter = 6.3125”
Weight per foot (10.3lb/ft)
Calculated W/D Ratio = 1.63
Heated Perimeter of Combined C12x25 & 1/2"x16"x1'9” knife plate (Fig. 3)
Steel Plate = 16+1/2”+8=24.5
C12x25 (exposed) 35”-8=27
Total Heated Perimeter = 51.5”
Weight per foot (27.13 + 25) =52.13 lb/ft
Calculated W/D Ratio = 1.01
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Fig.7. C-Channel Dimensions
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Fig.8. Weight of L8x8x3/8”
Member Weight(lb/ft) Perimeter D (in) W/D Mils
C10x30 30 28.8 (3 Sides-Beam) 0.96 324
C12x25 25 23.0 (3 Sides) 1.08 324
C12X30 30 23.5 (3 sides) 1.28 324
C12x25 &
12x16x1/2”
Knife Plate
52.13 51.5 (4 sides) 1.01 324
12x12 1/2”
Wall Plate (2-Hr)
20.4 13 (3 sides) 1.56 157
L8x8x3/8 (2-Hr) 20.1 16.75 (2 sides) 1.2 157
L6x4x5/16 (2-Hr) 10.3 6.315 (1 side) 1.63 157
Table.1. W/D ratios
Evaluated against the Isolatek published rating table (Fig.6), the proposed steel assemblies have larger W/D
ratios than the C-channel in the tested configuration. Additionally, the members will be partially concealed and
most are attached directly to a concrete wall that will act as a heat sink, which will extend the time to heat the
member to failure per ASTM E119 criteria.
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6 SUMMARY
While evaluating fire resistance requirement of members, different sized beams are compared against each
other through a factor referred to as the W/D Ratio. The weight per unit length of a member is divided by the
length of exposed heated perimeter area to determine the inherent fire resistance of a member. Lower W/D
ratios correspond with thinner steel members that will be subject to earlier failure when heated.
During this evaluation, ISOLATEK CAFCO IFRM protection of miscellaneous shapes was included, where the
minimum required W/D ratio (0.96) of the C-Channel in the assembly is less than the proposed (calculated)
minimum member W/D ratio (1.08). The tested C-Channel requires 324 MILS (Fig. 6) of intumescent protection
to provide 3-hour fire-resistance (Figure 6). The proposed C-Channel has greater inherent fire-resistance
because of a large W/D ratio and is only heated from 3 sides as opposed to 4 in the compared design.
Protection thickness is provided for 3Hr. Also, the 1/2"x16"x1'9” knife plate connected to the C12x25 as a
combined assembly in Table 1.
The angle sections L8x8x3/8 & L6"x4"x5/16" are only required to be 2-HR rated, this requires 157 MILS (Fig. 6)
of intumescent protection.
Note: Any GWB provided in the field over the assembly will increase the overall rating of the assemblies.
HSS-4x4x5/16” Stongback protection to be prescriptively protected as a primary support member (3 hours per
Table 601. (No EJ Required) per X790. (See Appendix below)
7 CONCLUSION
When the steel ledger/beam assemblies are protected with Intumescent paint as listed in Table 1 above, the
assemblies evaluated in the letter will meet the 2 or 3 hour requirements for fire-resistance per the OSSC.
Franklin Callfas
Principal/Fire Protection Engineer
Code Unlimited
Dahlke Manor – Engineering Judgment Report
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8 APPENDIX
HSS-Post Protection
UL Design-SFRM for HSS Strong Backs