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RESEARCH PAPERS

Analysis of Sandwich Panels for an Energy Efficient and Self-Supporting Residential Roof

[+] Author and Article Information
Daniel Thomas, Susan C. Mantell, Jane H. Davidson

Department of Mechanical Engineering, University of Minnesota, 111 Church Street, S.E., Minneapolis, MN 55455

Louise F. Goldberg, John Carmody

College of Architecture and Landscape Architecture, University of Minnesota, 1425 University Avenue SE, Suite 220, Minneapolis, MN 55455

The units on R-value are not repeated in the remainder of the document.

Faces made of wood composites, such as OSB, have creep that can be significant when combined with a core having a relatively low creep (33).

J. Sol. Energy Eng 128(3), 338-348 (Nov 04, 2005) (11 pages) doi:10.1115/1.2210503 History: Received May 06, 2005; Revised November 04, 2005

The structural and thermal feasibility of a self-supporting sandwich panel for energy efficient residential roof applications is assessed. The assessment is limited to symmetric sandwich panels comprising two face sheets and an insulating core. Feasible panel designs are presented for loading conditions, corresponding to southern and northern climates in the United States. The base case panel is 5.5m long for a nominal 4.6m horizontal span and an 812 roof pitch. Face sheet materials considered are oriented strand board, steel, and fiber reinforced plastic. Core materials considered are expanded polystyrene, extruded polystyrene, polyurethane, and poly(vinyl-chloride) foams. A wide range of material options meet building code limits on deflection and weight and prevent face sheet fracture and buckling, and core shear failure. Panels are identified that have structural depths similar to conventional wood rafter construction. Shortening the overall panel length provides greater choice in the use of materials and decreases the required panel thickness. Suggestions for improved panel designs address uncertainty in the ability of the plastic core to withstand long term loading over the expected life of residential buildings.

Copyright © 2006 by American Society of Mechanical Engineers
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Figures

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Figure 1

Conceptual sketch of a cathedral panel roof/attic system. The panel shown is a symmetric sandwich structure comprised of two face sheets and an insulating core.

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Figure 2

Sandwich panel failure modes considered in the present analysis: (a) deflection, (b) core shear failure, (c) local buckling, and (d) face yield or fracture (adapted from (39))

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Figure 3

Deflection modes for thermal and transverse loading: (a) pure bending due to thermal expansion load, valid for thin, flat face sheets; (b) pure bending due to transverse load; (c) pure shear due to thermal expansion load, relevant for panels with thick or profiled face sheets and weak cores; and (d) pure shear due to transverse load

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Figure 4

Interpretation of the relevant code (4) limit on roof deflection, code requirements are shown on the left and the corresponding simply supported beam model is shown on the right

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Figure 5

The geometry and coordinate system used in the present analysis

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Figure 6

Required face sheet thickness with varying core thickness, for a 29kg∕m3 EPS core and a 1530N∕m2(32psf) total distributed load (climate I). Panel length is 5.5m.

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Figure 7

Required face sheet thickness with varying core thickness, for a 29kg∕m3 EPS core and a 3920N∕m2(82psf) total distributed load (climate II). Panel length is 5.5m.

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Figure 8

Required face sheet thickness with varying core thickness, for a 48kg∕m3 XPS core and a 1530N∕m2(32psf) total distributed load (climate I). Panel length is 5.5m.

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Figure 9

Required face sheet thickness with varying core thickness, for a 48kg∕m3 XPS core and a 3920N∕m2(82psf) total distributed load (climate II). Panel length is 5.5m.

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Figure 10

Required face sheet thickness with varying core thickness, for PUR cores (48kg∕m3, no feasible solutions, 112kg∕m3, and 240kg∕m3) and a 1530N∕m2(32psf) total distributed load (climate I). Panel length is 5.5m.

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Figure 11

Required face sheet thickness with varying core thickness, for PVC cores (48, 100, and 250kg∕m3) and a 1530N∕m2(32psf) total distributed load (climate I). Panel length is 5.5m.

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Figure 12

Required face sheet thickness with varying core thickness, for three PVC cores (48 and 100kg∕m3) and a 3920N∕m2(82psf) total distributed load (climate II). There are no solutions satisfying the dead load constraint for 250kg∕m3 PVC. Panel length is 5.5m.

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Figure 13

Required face thickness with varying core thickness, for a 96kg∕m3 PUR core, climate I loads. The top line for each material is for ϕLL=2.4, ϕDL=7.0; the bottom line is for ϕLL=1.0, ϕDL=2.0.

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Figure 14

Required face thickness with varying core thickness, for a 96kg∕m3 PUR core, climate II loads. The top line for each material is for ϕLL=2.4, ϕDL=7.0; the bottom line is for ϕLL=1.0, ϕDL=2.0.

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Figure 15

The surface represents the combinations of face sheet thickness, core thickness, and panel length which satisfy the structural and weight requirements for panels constructed from steel face sheets with 48kg∕m3 XPS core. The loading is 3920N∕m2(82psf) total distributed load (climate II). The shaded region represents panel designs which have less than R-7 (RUS-40).

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Figure 16

Failure mode map for panels with steel faces and a 48kg∕m3 XPS core, climate I loads. Dark regions indicate combinations of panel length and core thickness for which there are no feasible designs. R-value limit indicates R-7 (RUS-40) insulation level.

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Figure 17

Failure mode map for panels with steel faces and a 48kg∕m3 XPS core, climate II loads. Dark regions indicate combinations of panel length and core thickness for which there are no feasible designs. R-value limit indicates R-7 (RUS-40) insulation level.

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