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Wave Forces on Cladding

Physical model testing in the Large Wave Flume for characterization of tsunami wave impact forces and structural response of metal building envelopes (cladding)

Wave impact tests were conducted in April/May 2016 on two metal building envelope subassemblies. The primary objectives for the tests were to:

  • To begin to characterize tsunami wave impact on typical metal building envelope subassemblies
  • To inform our methodology for capturing the effects of tsunami wave impact on the building envelope (i.e., cladding and secondary members), and the resulting demands on the structure
  • To investigate the demands of tsunami wave impact on components that are designed primarily for wind loading

To achieve these objectives, two full-scale test specimens were designed and detailed by NCI Building Systems in collaboration with the Metal Building Manufacturers Association (MBMA). These specimens represented the bottom 8 ft of a 36 ft tall, 10,000 sq. ft prototype building, square in plan and located in Seaside, OR. Designs followed the 2014 Oregon Structural Specialty Code, based on the 2012 International Building Code (IBC). Both specimens were designed for wind loads for Exposure Category C; one represented cladding for an essential facility, Risk Category IV, and the other was designed for a Risk Category II building. The 12 ft wide specimens were identical aside from an additional girt at 3 ft 6 in. from the base of the Cat. IV specimen (Figure 1 left, middle). 3 ft wide, 24 gage corrugated panels were fastened to each other and to a 16 gage, 8 in. ‘Z’ girt at 7 ft 6 in. and a 16 gage base angle anchored to the flume floor. Light gage flashing, attached to the panels and in contact with the flume walls, formed the side trim detail. All fasteners, including those for girt connections to flume wall support brackets, were typical sizes and patterns for the prototype. For the short, 12 ft girt span, the most liberal girt and panel design deflection limits were used so that the specimen would mimic the flexibility that would be observed on the prototype 25 ft span.



Figure 1. (Left) Cat. IV Specimen; (Middle) Cat. II Specimen; (Right) Failed Cat. II Specimen

The specimens were installed 1.753 m (5.75 ft) above the bottom of the wave flume; on the offshore side, the slope was set at 1:24. The specimens were subjected to solitary waves with initial water depths at the wavemaker ranging from 1.60 m (5.25 ft) to 2.00 m (6.56 ft), or a ‘dry’ condition to a 24.7 cm (9.72 in.) water depth at the test specimen. Wave heights ranged from 0.16 m (0.52 ft) to 1.40 m (4.59 ft), creating estimated net pressures from 0.77 kPa (16 psf) to over 9.58 kPa (200 psf) at the base of the specimen. The Cat. IV specimen resisted all wave loadings without damage until the trial with the initial water depth of 2.00 m (6.56 ft) and wave height of 0.80 m (2.62 ft), and an estimated net pressure of 7.20 kPa (150 psf). Local buckling was observed in two of the cladding ribs at 0.46 m (18 in.) from the floor. The Cat. II specimen experienced significant deformations and damage in the cladding by the trial with the initial water depth of 1.888m (6.19 ft) and wave height of 1.038 m (3.41 ft) (estimated net pressure at the base of 7.57 kPa (158 psf)), and the anchors at the base angle failed for a water depth of 2.00 m (6.56 ft) and wave height of 1.40 m (4.59 ft) (Figure 1 right).

Preliminary analysis of test results showed that the measured pressures were fairly uniform across the width for both specimens. Figures 2 to 6 show selected measurements for both specimens at an initial water depth of 1.753 m (5.75 ft) and wave height of 1.139 m (3.74 ft). Distributions of deformations and pressures varied over the height (Figures 2 and 3) and by specimen (Figure 4). Maximum pressures were observed at the P1 gage (located 1 ft from the base) for both specimens, but pressures were generally lower for the Cat. II specimen for the same initial water depth and wave height. Differences in measured pressures were more significant for other gage locations. Maximum deformations were measured at SP2 (located 2 ft from the base) for both specimens, but were an order of magnitude larger for the Cat. II specimen (Figures 5 and 6).


Figure 2. Pressure Gage Values, Cat. II, 1.753 m Initial Water Depth, 1.139 m Wave Height


Figure 3. Pressure Gage Values, Cat. IV, 1.753 m Initial Water Depth, 1.139 m Wave Height


Figure 4. Pressure Gage Values, Both Specimens, 1.753 m Water Depth, 1.139 m Wave Height


Figure 5. Displacement Values, Cat. II, 1.753 m Initial Water Depth, 1.139 m Wave Height


Figure 6. Displacement Values, Cat. IV, 1.753 m Initial Water Depth, 1.139 m Wave Height

Development of post-processing tool and data analysis by Saghy Saeidtehrani, Visiting Researcher, O.H. Hinsdale Wave Research Laboratory, Oregon State University; Ph.D. candidate from the School of Civil and Construction Engineering, Università degli Studi Roma Tre, Italy.

NCI Group, Inc. provided the metal building cladding designs, and Garco Building Systems provided the materials for the test specimens.

Physical Model Tests in the Large Wave Flume were conducted under the 2016 Lab-Days Program, supported by the OSU College of Engineering.