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19901 Quail Circle
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701-770-9118
michaelh@nsgia.com
Important Limitations of This Analysis
While we have attempted to model the composite action between the HSS tube and SIP panels,
our analysis still has significant limitations:
1. Simplified Composite Model: Our composite analysis uses basic mechanics of materials
principles and makes assumptions about effective width and composite efficiency that
may not fully capture the complex interaction between components.
2. Connection Behavior: We use simplified assumptions about the fastener efficiency based
on spacing, but don't model the actual mechanical behavior of specific fastener types or
their interaction with the MGO board material.
3. Load Distribution: Our analysis still treats the system as a beam with uniform loading,
whereas in reality, the SIP panels themselves would distribute loads more evenly
throughout the entire structural system.
4. System Integration: The integrated spline approach creates a fundamentally different
structural system than a traditional beam supporting panels from below, with
three-dimensional behaviors that are difficult to capture in a two-dimensional beam
analysis.
5. Time-Dependent Behavior: Our analysis does not account for potential long-term effects
such as creep, fastener loosening, or environmental factors that could affect the
composite action over time.# Preliminary Analysis: W-Beam vs. HSS Options for SIP Panel
Support
Summary Overview
This document presents our initial comparative analysis between standard W-shape steel beams
and HSS (Hollow Structural Section) square tubing for supporting Structural Insulated Panel (SIP)
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wall systems across 20-foot spans. Our preliminary calculations examine deflection performance,
structural capacity, cost considerations, and installation implications.
Based on our limited analysis using standard engineering formulas, it appears that while HSS
square tubing offers certain advantages in terms of installation simplicity and thermal
performance, our calculations suggest potential challenges with deflection performance
compared to the W14x43 I-beam for 20-foot spans.
Beam Options Analyzed
We evaluated three primary structural options to support SIP wall systems:
Section
Weight
(lb/ft)
Moment of Inertia
(in⁴)
Section Modulus
(in³)
Width
(in)
Depth
(in)
W14x43
I-beam
43.0
372.0
54.4
8.0
13.7
HSS6x6x3/8
32.6
54.1
18.0
6.0
6.0
HSS6x6x1/2
41.5
65.0
21.7
6.0
6.0
Analysis Methodology
We attempted to apply standard beam deflection formulas for simply supported beams under
uniform loading using the Python NumPy library. We performed two types of analysis:
1. Initial non-composite analysis treating the HSS tube as an isolated structural element
2. Follow-up composite analysis attempting to account for the stiffening effect when the
HSS tube is mechanically fastened to SIP panels
For both analyses, we used the following parameters:
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19901 Quail Circle
Fairhope AL 36532
701-770-9118
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● Uniform load: 1500 lb/ft (excluding beam self-weight)
● Span length: 20 feet
● L/360 deflection limit: 0.667 inches
● Steel modulus of elasticity: 29,000,000 psi
● Steel yield strength: 50,000 psi
It should be noted that these calculations represent our best understanding of standard structural
analysis principles but would require verification by a licensed structural engineer. Our composite
modeling uses simplified assumptions about connection behavior and effective widths that would
benefit from more sophisticated analysis techniques.
Deflection Performance Results
The deflection analysis across a 20-foot span yielded the following results:
Beam Type
Maximum Deflection (in)
% of Limit
Status
W14x43 I-Beam
0.515
77.2%
PASS
HSS6x6x3/8
3.517
527.5%
FAIL
HSS6x6x1/2
2.944
441.6%
FAIL
Bending Stress Analysis
The bending stress analysis shows:
Beam Type
Maximum Moment
(lb-in)
Bending Stress (psi)
% of Capacity
Status
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19901 Quail Circle
Fairhope AL 36532
701-770-9118
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W14x43
I-Beam
925,800
17,018
34.0%
PASS
HSS6x6x3/8
919,548
51,086
102.2%
FAIL
HSS6x6x1/2
924,906
42,622
85.2%
PASS
Cost and Weight Considerations
Beam Type
Weight (lb/ft)
Est. Cost ($/ft)
Cost Difference
W14x43
I-Beam
43.0
$38.59
Reference
HSS6x6x3/8
32.6
$35.84
-7.1%
HSS6x6x1/2
41.5
$43.59
+13.0%
Composite Action Analysis
To better understand the impact of the diaphragmic effect created by mechanically fastening SIP
panels to the HSS tubing, we conducted an additional analysis modeling the composite action.
This analysis considers how the connection between the MGO board facings and the HSS tube
increases the effective moment of inertia of the system.
Composite Beam Results
Fastener
Spacing
Composite
Efficiency
Effective I (in⁴)
Deflection (in)
% of L/360
Limit
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19901 Quail Circle
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24"
30%
76.3
2.442
366.3%
24"
50%
91.0
2.046
306.9%
24"
70%
105.8
1.760
264.0%
24"
90%
120.6
1.545
231.7%
12"
30%
76.3
2.442
366.3%
12"
50%
91.0
2.046
306.9%
12"
70%
105.8
1.760
264.0%
12"
90%
120.6
1.545
231.7%
6"
30%
76.3
2.442
366.3%
6"
50%
91.0
2.046
306.9%
6"
70%
105.8
1.760
264.0%
6"
90%
120.6
1.545
231.7%
3"
30%
76.3
2.442
366.3%
3"
50%
91.0
2.046
306.9%
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19901 Quail Circle
Fairhope AL 36532
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3"
70%
105.8
1.760
264.0%
3"
90%
120.6
1.545
231.7%
Key Findings from Composite Analysis
1. Significant Stiffness Improvement: The best-case scenario shows an effective moment
of inertia of 120.6 in⁴, which represents a 2.2x improvement over the non-composite HSS
tube alone (54.1 in⁴).
2. Typical Installation Configuration: With 12" fastener spacing and 50% composite
efficiency, the effective moment of inertia increases to 91.0 in⁴ (1.7x improvement),
resulting in a predicted deflection of 2.046 inches.
3. Comparison to Original Analysis: While the composite action significantly improves
performance, the analysis suggests that even with optimal fastening, the system may still
exceed the L/360 deflection limit at a 20-foot span.
4. Further Optimization Potential: The model indicates that increasing composite efficiency
through connection details and fastening methods could further enhance performance.
Additional system enhancements such as increased MGO board thickness at connection
points might provide further improvements.
Foundation/Support Point Considerations
Our preliminary analysis suggests pier/foundation considerations may vary with beam selection:
● Based on our calculations, the W14x43 I-beam appears to offer higher stiffness compared
to the analyzed HSS sections of similar weight
● If our deflection calculations are accurate, the HSS options might require additional
support points, which could affect overall project costs
Potential Approaches to Consider
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Fairhope AL 36532
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1. For 20-foot spans: Based solely on our preliminary calculations, the W14x43 I-beam might
be more suitable for the analyzed loading conditions.
2. For shorter spans: HSS square tubing might potentially be more viable for shorter spans,
as deflection is proportional to the span length raised to the fourth power.
3. Other possibilities that might warrant professional evaluation:
○ Larger HSS section sizes (e.g., HSS8x8 or HSS10x10) for longer spans
○ A hybrid approach using W-beams for primary structure and HSS tubes for shorter
connections
○ Custom reinforced HSS designs for specific applications
Summary
Our analysis suggests that while a non-composite HSS square tube would face significant
deflection challenges over 20-foot spans, the composite action created by the mechanical
fastening of SIP panels substantially improves performance. The diaphragmic effect from regular
fastening of the MGO board facings increases the effective moment of inertia by up to 2.2 times.
With optimal composite action, the calculated deflection of the HSS6x6x3/8 system improves
from 3.442 inches to 1.545 inches - still exceeding the L/360 limit but representing a significant
improvement. This suggests several possible approaches:
1. Enhanced Composite Action: Further optimization of the connection details and
fastening methods could potentially increase composite efficiency beyond what our
model predicts.
2. Hybrid Solutions: Combining the HSS tube approach with strategic intermediate supports
could create a viable system while maintaining most of the installation advantages.
3. Span Reduction: The composite HSS system may be viable for shorter spans
(approximately 12-14 feet) without modification.
4. Larger HSS Sections: Using larger HSS sections (such as HSS8x8 or HSS10x10) in
combination with the composite action could potentially meet deflection requirements for
20-foot spans.
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19901 Quail Circle
Fairhope AL 36532
701-770-9118
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We encourage professional engineering evaluation of the complete integrated system to
determine the optimal approach, as advanced modeling techniques may identify additional
composite behaviors not captured in our simplified analysis.
© North Star Group, Inc.
19901 Quail Circle
Fairhope AL 36532
701-770-9118
michaelh@nsgia.com
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