Ref: R24013001
Date: 30th January 2024
Review of Design Report of the Proposed FRP pultruded Roof Structure
The report presents a design review and subsequent recommendations on the calculation report and
other data shared by the client as referred below.
1. References:
Input data received from the client:
a. Design report: UP004- FRP Roof Qatar - DESIGN REPORT.pdf
b. Connection design report: DETAIL 1,2, 3 and 4
c. Proposed connection details: 240119_UP004- FRP Roof Qatar
d. Requested clarifications from the designer.
2. Observations:
a. The material properties of FRP pultruded section considered in the design calculations are
inadequate. The given design seems to assume FRP as a ISOTROPIC material (i.e., properties
same in all directions). Whereas FRP, especially the pultruded section, is highly ANISOTROPIC
in nature, exhibits higher properties in fiber direction and relatively low properties in
transverse direction.
The properties of FRP pultruded section in longitudinal direction as considered in the design
are as follows:
Modulus of elasticity, E1 = 21.65 GPa, Ultimate strength, σ1 = 268.0 MPa
Whereas properties in transverse direction mainly governed by the type of resin system and
crosswise reinforcement mat used in pultrusion process. Typically, properties in transverse
direction would be in the range as followsModulus of elasticity, E2 = 5.50 GPa- 6.75 GPa, Ultimate strength, σ2 = 40.0 MPa- 80.0 MPa
Therefore, the design of FRP sections and their connections must duly consider an inherent
anisotropy of the FRP material system. The design philosophy considered in steel structure
cannot readily be applied in FRP design.
b. Typical check for connection design
Let’s consider the most critical purlin connections i.e. purlin spanning over continuous span
of 5.8 m length subjected to ultimate uplift wind load WL of 1.3 kN/m
Self-weight of purlin, DL = 0.071 kN/m
SDL = 0.15 x 1.65 = 0.25 kN/m
Maximum design load = 0.9 (DL+SDL) + 1.0WL
= 1.01 kN/m
5.8m
Ra
5.8m
Rb
Rc
Figure 1: Free body diagram
Maximum reaction force, Rb = -1.01 x 5.8 = - 5.86 kN
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Refer to the proposed connection design, FRP L-angle of 10 mm thickness is considered with
4-M8 bolts as shown in figure below-
Note: first, this type of connection between SHS 100x100x10 and L angle at the
continuous support is practically difficult to access the bolting inside the SHS.
Figure 2: Proposed connection details
To have proper access for bolting, either the continuity of purlin needs to be broken or
connection bolt should pass through the entire width of SHS section. In latter case, the
maximum shear force at the single bolt, V = 5.86 /2 = 2.93 kN =2930 N
Therefore, check for bearing resistance:
Please note that the connection design checks applicable for steel design as per AISC 360-16
cannot readily be applicable for FRP connection design.
Maximum bearing stress, σN = V/(dxt) = 2930 /(8 x 10) =36.625 MPa >22.85 MPa (i.e.
allowable transverse strength of FRP pultruded section considering partial safety factor of
3.50)_Hence, NOT OK.
All the Connection design must be revisited taking into consideration properties of FRP in
transverse direction too.
3. Comments and recommendations:
1. The given structural analysis assumes FRP as an isotropic material like steel. This is an
incorrect assumption with the FRP design. The given design calculations follow the steel
design philosophy as per AISC 360-16, which is irrelevant in FRP design.
2. Partial safety factors considered for the FRP material system must be properly verified in
reference to the applicable standards like EUROCOMP Design Code, etc.
3. The design of section SHS 100x 100 x 10 for purlin is derived for the longest span of end
bay only and the same is followed for all other short spans as well. This approach leads
to the overdesign of sections for short spans.
4. The connection designs in FRP are mainly governed by the properties in transverse
direction. Not considering the anisotropic nature of FRP material results in inadequate
connection design. Therefore, the design of all connections needs to be revisited.
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