ABSTRACT: This is a sample file demonstrating the ...

52 downloads 0 Views 472KB Size Report
FBC TAS 102A. Redland. Static uplift capacity of mechanical tile attachments with clips. 1995. FBC TAS 108. Redland. Wind tunnel test for determining ...
1

A study of wind load interaction for roofing field tiles Daniel J. Smith1, Forrest J. Masters2 Cyclone Testing Station, James Cook University, Townsville, QLD 4811, Australia 2 Department of Civil and Coastal Engineering, University of Florida, 365 Weil Hall, Gainesville, FL 32611, USA email: [email protected], [email protected] 1

ABSTRACT: Roof cover loss is a leading cause of building performance issues during high wind events. Post-event damage assessment from the 2004 hurricane season in Florida suggested that in some cases roofing tiles did not perform as predicted by the Florida Building Code. Key objectives of the current research were to (a) develop a comprehensive understanding of the windinduced load interaction for field tiles and (b) assess the conservatism of design parameter tests for roofing tile systems. A series of three experiments were developed in order to accomplish (a) and (b). Preliminary results for each experiment are presented. Lift coefficients were computed using both low-resolution (i.e. method of standardized tests) and high-resolution surface pressure measurements. Wind-induced attachment reactions for mechanically fasted tiles were measured via load cell. Attachment capacities were measured via constant displacement uplift testing. The findings include: a) low-resolution surface pressure measurements provide a conservative estimation of lift coefficients, b) wind-induced reactions at mechanical fastenings are dominated by withdrawal forces and are dependent on wind direction, and c) attachment capacities are dependent on point of load application. These findings are discussed in the context of standardized testing methods for roofing tiles. KEY WORDS: ICWE14; Roofing Tiles; Roof Damage; Florida Building Code; Residential Buildings; Surface Pressure Measurements; Redland Technology; Uplift Capacity; Attachment Reactions. 1

INTRODUCTION

Annual hurricane-induced economic losses have increased steadily in the U.S. during the past 50 years, averaging $1.3 billion (in constant 2006 dollars) from 1949-1989, $10.1 billion from 1990-1995, and $35.8 billion from 2001-2006 [21]. Wind related damage on the East and Gulf coasts of the U.S. alone averages $5 billion in annual economic losses [22]. Florida is a particularly strong contributor to annual losses, largely due to the high likelihood of hurricane landfall in the Southeast U.S. [20]. Insured losses related to roof cover damage (i.e. shingles, roofing tiles, metal) accounted for over 50% of insured losses in Florida during the 2004-2005 hurricane seasons [1]. Although asphalt shingles are the most prevalent form of roof cover in Florida, roofing tile systems represent significant market share, particularly in the South Florida region due to their aesthetic appeal, ventilating characteristics, and durability. As of 2011, estimates for tile roofing market share were 56%, 36%, and 24% for Broward, Palm Beach, and Lee Counties respectively [13]. Insurance claim analysis post-2004 hurricane season in Florida suggests insured losses for tiled roofs were greater than asphalt shingles when wind speeds were greater than 54 m/s (120 mph). Replacement costs for roofing tiles are a key factor, exceeding those of asphalt shingles by more than 400% [1]. In addition to cladding replacement costs, damage to any roof covering system during hurricane events increases likelihood of water ingress related damages, making roof cover loss a leading cause of building performance issues during hurricanes [12]. Post-2004 hurricane damage assessments indicated that in several instances, tiles did not perform as predicted (i.e. failed at less than design level wind speeds) by the 2001 FBC and FRSA/TRI Concrete and Clay Tile Installation Manual [12]. In order to reduce hurricane related economic losses, it is imperative that roof cover design provisions are accurate and conservative. Several full-scale studies have examined wind loading on roofing field and ridge tiles [18, 19, 24, 26, 28-29] but few, if any, have examined the underlying assumptions employed by design equations. This paper discusses the Redland Technology study [23], which serves as the basis for current roofing tile design provisions in Florida. The study was based on several of the first published works to study wind loading mechanisms of roofing elements [1417]. A brief review of the current design provisions, including limitations, is presented to preclude an overview of three experiments recently conducted at the University of Florida to investigate wind load interactions for roofing field tiles. 2

CODES AND STANDARDS

In 1991, the Southern Building Code Congress International (SBCCI) commissioned an independent testing agency, Redland Technology, to investigate wind loads on roofing tile systems and develop a code consistent design methodology. Two

14th International Conference on Wind Engineering – Porto Alegre, Brazil – June 21-26, 2015

2

experiments were performed by Redland to develop their design method: (a) wind loads were estimated from wind tunnel tests where surface pressures on medium and high profile roofing tiles were measured as wind was blown across a mockup tile array and (b) wind uplift resistance was estimated from constant displacement rate uplift tests that quantified the uplift resistance of roofing tiles with various attachment methods. The resulting method was incorporated into the Standard Building Code (SBC), and eventually the Florida Building Code (FBC) [10] and International Building Code as Equation 16-33 and Equation 16-34 respectively, FBC Testing Application Standards (TAS) 101, 102, 102A, 108 [6-9], and FBC Roofing Application Standard (RAS) 127 [11]. The study was also the basis for SBCCI 11-99 [25] and ASTM International standards C1568, C1569, and C1570 [3-5]. Key limitations of the study include: (a) the approximated relationship between near-roof flow and approach flow conditions (e.g., using ASCE 7 [2] design pressures), (b) wind angle of attack perpendicular to the leading edge only, and (c) use of low-resolution surface pressure measurements to determine design parameters for roofing tiles. Smith et al. [27] discuss this study and related building code development for roofing tiles in detail. Table 1 summarizes the development of testing standards. Wardell [30] also summarized the progression of building codes and attachment techniques related to roofing tiles in the High Velocity Hurricane Zones (HVHZ) of Florida. Table 1. Progression of standardized test methods for roofing tiles in the U.S.

3

Publication Year

Test Method

Technical Basis

1993

SSTD 11

Redland

1995 1995 1995

FBC TAS 101 FBC TAS 102 FBC TAS 102A

Redland Redland Redland

1995

FBC TAS 108

Redland

1995

FBC TAS 116

BS5534/ Redland

Procedure for determining air permeability of rigid, discontinuous, roofing systems.

2003

ASTM C1568

SSTD 11/ Redland

Mechanical uplift resistance testing. Derived from SSTD 11, essentially a combination of TAS 101, 102, 102A.

2003

ASTM C1569

SSTD 11/ Redland

2003

ASTM C1570

SSTD 11/ Redland

Method Overview Includes methods for determining uplift capacity of mechanical, mortar, and adhesive attachments. Airpermeability method added in 1999 revision. Static uplift capacity of mortar or adhesive tile attachments. Static uplift capacity of mechanical tile attachments. Static uplift capacity of mechanical tile attachments with clips. Wind tunnel test for determining overturning moment coefficients and aerodynamic load multipliers for tiles.

Wind tunnel method for determining wind resistance. Derived from SSTD 11, similar to TAS 108. Test for determining air permeability of a roofing tile system. Derived from SSTD 11-99 update, similar to TAS 116.

EXPERIMENT ONE: CHARACTERIZATION OF THE PRESSURE FIELD ACTING ON THE ROOFING TILE

Experiment one objectives were to (a) characterize the wind pressure distribution on low-, medium-, and high-profile field tiles using rapid-prototype tile models with a high-resolution array of pressure taps and (b) investigate the validity of assumptions employed in design parameter tests (i.e. TAS 108). Methodology In order to execute (b), Experiment one was designed as a modified version of TAS 108. A key modification was the inclusion of a larger distribution of pressure taps (256 vs 27). Additional deviations from TAS 108 include: choice of underlayment (selfadhered vs. standard two-ply 30/90 system for TAS), absence of plenum chamber below test deck to simulate internal pressure per TAS, number of tile courses per specimen (5-6 vs 9 for TAS) and reference wind speed range (18-35 m/s vs 31-49 m/s for TAS). It was assumed that underlayment type would have negligible impact on wind-induced pressures along the tiles above. The effects of simulated internal pressure were found negligible by Redland Technology [23] for this type of experimental configuration. The dimensions of the testing apparatus allowed for installation of five or six tile courses as opposed to the nine courses required by TAS 108. Although this limits the length for flow development upwind of pressure measurements, data analysis for this experiment primarily emphasizes comparisons within the data set (i.e. varied wind angle, number of pressure taps) as opposed to comparisons with loads on in situ tiles. The reference wind velocity range was chosen primarily due to the fragile nature of the rapid-prototype tile models. All design parameters were normalized by the reference velocity. Wind loading took place in the University of Florida Dynamic Flow Simulator (DFS), which is capable of generating wind speeds up to 100 m/s (224 mph) across a partial mockup roofing system. Array specimens were attached to a rectangular roof deck mockup either directly or above battens.

14th International Conference on Wind Engineering – Porto Alegre, Brazil – June 21-26, 2015

3

Figure 1. Dynamic Flow Simulator and tile array specimen configuration for Experiments one and two. To characterize wind loading, the full-size model replicas of low-, medium- and high- profile tiles were used to measure surface pressures through 256 taps connected to a Scanivalve pressure scanning unit. Three-axis wind velocities were measured inside the DFS test section using a Turbulent Flow Instruments Cobra Probe mounted above the deck and upwind of specimens. Each of the six tile profile/attachment combinations were subjected to three different reference wind velocity levels. Exact velocity at each of the three levels varied by +/- 2 m/s depending on DFS engine conditions. Wind velocity levels 1, 2, and 3 correspond to 18-22 m/s (40-49 mph), 26-30 m/s (58-67 mph), 31-35 m/s (69-78 mph) respectively. Results Tile surface pressure data from Experiment one were analyzed to assess the sensitivity of roofing tile lift coefficients and aerodynamic multipliers to number of pressure taps (256 vs 27), installation configuration (direct vs battens), and wind angle of attack. TAS 108 provides specification for estimating lift coefficients (CL ) for roofing tiles. Lift coefficients are used in Equation 1633 of the FBC (Eq. 16-34 for IBC) to estimate design wind loads for roofing tile systems in areas outside of the Florida HVHZ. The methodology for computing the parameter assumes that spatial variation of wind induced surface pressure is negligible along the width of a tile and that wind perpendicular to the leading edge generates the strongest uplift. In accordance with the first assumption, TAS 108 requires 20 pressure taps along the centerline of the upper surface and seven pressure taps along the centerline of the bottom surface of the tile to be tested. Surface pressures were measured in Experiment one with model tiles and 256 pressure taps distributed across the full width and length of the upper and lower surfaces. The mean surface pressure for the sample period was computed at each tap and converted to a dimensionless pressure coefficient using the following equation:

CP =

P - P∞ q

(1)

where CP = coefficient of pressure, P = mean local pressure at the tap, P∞ = mean free stream static pressure at 16 cm reference height, q = mean velocity pressure at 16 cm reference height. The tile models were used for all Experiment one testing, however, the lift coefficient (CL ) for each tile configuration was computed using two different methods for comparison. The first method represents the design parameters as calculated per TAS 108 with 27 centerline surface pressure measurement locations. Since pressure taps on the models were not located at all 27 TAS 108 locations, in some cases surface pressures were interpolated for TAS 108 locations using actual centerline taps on the models. The second method incorporates all 256 taps on the upper and lower surfaces of the models. Measured pressures were used to fit gridded pressure surfaces for the upper and lower faces of the tile with dimensions extending to the edges of the tile. This was

14th International Conference on Wind Engineering – Porto Alegre, Brazil – June 21-26, 2015

4

achieved using a custom routine developed via Matlab R2011a. The fitting component of the routine uses a distance-based Greens’ function approach. A pressure coefficient was computed for each rectangular element in the grid by averaging pressures at the four nodes (Eq. 2) that make up the element and multiplying by the elemental area dxdy. C'pt = [C'pt +C'pt i

i11

'

i12

+ Cpt + C'pt ]/4 i21

(2)

i22

where C'pt = 4-node average pressure coefficient at an element on the top surface of the tile, C'pb = 4-node average pressure i

i

coefficient at an element on the bottom surface of the tile (note: lower surface equation is identical but not shown), and C'pt , i11

C'pt , C'pt , C'pt = pressure coefficients on the interpolated surface at the four nodes that make up element i. i12 i21 i22 In order to account for the curvature of tile profiles (i.e. when normal forces are not in the vertical direction), a set of threedimensional geometric points (1 cm resolution) for the outer shell of each tile were either provided by the manufacturer or manually recorded using a three-dimensional scanner. These points were imported to Matlab and used to compute the slope at each elemental location in the gridded pressure surfaces. Slope data were combined with pressure data at each element to calculate the lift coefficient using the following equation:

C'L =

∑i C'pb δi cos(φi )cos(θi ) ∑i C'pt δi cos(φi )cos(θi ) i i l*b l*b

(3)

where C'pb and C'pt are defined previously, δi = area dxdy of a single element, l = length of the tile, and b = exposed width of the i i tile, θi = slope dz/dx at an element in the direction parallel to the leading edge, φi = slope dz/dy at an element in the direction perpendicular to the leading edge. Lift coefficients were computed using 27 pressure locations along the centerline (i.e. the approach of standardized tests) and all 256 distributed pressure taps (Figure 2). In all testing configurations, lift coefficients computed using the 27 centerline locations were larger than those computed with the 256 tap data. High-, and medium-profile configurations show greater variation between the methods, likely due to the variation in profile (and vertical component of uplift force) from the centerline of the tile outward for those two profiles. The variation between methods was least significant for low-profile configurations. Attachment method (i.e. direct to deck vs. battens) did not appear to have significant effect on variation between the two methods. In order to use FBC design Eq. 16-33 (IBC Eq. 17-34), CL must be computed per TAS 108 (SSTD-11 for IBC) or 0.2 can be used as a default value. All configurations except medium-profile direct and low-profile with battens suggest 0.2 is a conservative estimate for design. However, future research should seek to verify these estimates for in situ roofing tile systems subjected to wind load. Lift coefficients showed slight dependence on the reference wind speed (an average of +/-10% from 18 to 35 m/s). In general, higher wind speeds (i.e. levels 2 and 3) resulted in larger lift coefficients. Longitudinal and vertical components of turbulence intensity in the test section were found to be inversely proportional to wind speed. The longitudinal and vertical turbulence intensities decreased from 2.7% to 1.0% and 1.8% to 1.0%, respectively, with an increase in mean wind speed from 19 m/s to 35 m/s. Turbulence is known to promote earlier reattachment (reducing effect) in negative pressure flow separation zones. Higher levels of turbulence at comparatively low wind speeds in the DFS test section indicate a less coherent flow pattern, which may have reduced the effect of negative pressure separation regions at the leading edge of tiles. This may have decreased the magnitude of uplift pressure in relation to reference velocity pressure. In comparison, the effect of turbulence was lessened at higher wind speeds which may explain why lift coefficients were slightly larger in those cases.

14th International Conference on Wind Engineering – Porto Alegre, Brazil – June 21-26, 2015

5

Figure 2. Lift coefficients for roofing tiles at three reference velocity levels. H, M, L indicate high-, medium-, or low-profile tile respectfully, B, D indicate battened or direct to deck installation respectfully, and 256, 027 indicate the number of pressure measurement locations used to compute 𝐶𝐶𝐿𝐿 respectively (Note: Velocity 3 wind speed data for M/D specimens were not available). 4

EXPERIMENT TWO: TILE ATTACHMENT REACTION MEASUREMENT

Research objectives of this experiment were to directly quantify the reaction forces of field tile mechanical fastener attachments and compare results to Experiment one findings. Concrete field tiles were affixed to a six-axis load cell at the mechanical fastening location and subjected to wind loading in the DFS test section (Figure 1). The load cell provided direct measurement of wind generated withdrawal and shear forces at the fastener. For each array specimen, a single load cell instrumented tile was installed in the center of the fifth (or fourth for 45° cases) course. Velocity measurement was as described for Experiment one. Methodology An ATI Industrial Automation model Nano25 (IP65) six-axis load cell measured wind induced reaction forces on roofing tile mechanical fasteners. The load cell is capable of resolving forces in the x- (shear), y- (shear), and z-axes (withdrawal) and consists of a 28 mm (1.1 in) diameter by 28 mm (1.1 in) steel cylinder with silicon strain gauges fixed on the interior face. A custommachined steel block, with threaded #8 screw hole in the center, was secured to the upper face of the load cell to allow mechanical fastener attachment. For each tile array, the top of the load cell arrangement was installed level with the test deck (or batten) and directly below the tile installation hole nearest to the under lapping edge (left side from leading edge view of the tile). Load readings were captured with 100 Hz sampling rate via National Instruments Labview 2010 and a DAQ analog-to-digital converter. Each specimen consisted of a low-, medium-, or high-profile array of concrete tiles attached either directly to the deck or over nominal 2.5 cm (1 in) x 5 cm (2 in) timber battens. A single tile in the center of the second to last course of each array was affixed to a load cell below using a single #8 machine screw of variable length depending on the configuration. All other tiles in the array were mechanically fastened using one #8 x 6.4 cm (2.5 in) Quik Drive tile roofing screw. In order to adjust wind angle of attack, tile arrays were installed with orientation of 0° (wind perpendicular to tile leading edge), 45°, or 90° (wind parallel to tile leading edge). Specimens were transported to the DFS test section by forklift. The cobra probe ambient reference pressure apparatus was located below the test section. For each test, data acquisition was initiated during an initial 0 m/s velocity period. After 10 s, velocity in the test section was increased to reference velocity level 1 (18-22 m/s) for 60 s (note: a sampling time of 60 s was chosen to expedite testing since load cell force readings were relatively constant once wind load was applied). Finally, velocity was reduced to 0 m/s and after an additional 10 s, data acquisition was terminated to complete the “step-up” and “step-down” time history sequence. The sequence was repeated for three trials at each of the three reference velocity levels. After testing an array configuration, the test deck was removed from the test section, tiles were removed, and a new array combination was installed. This process was repeated over non-consecutive days until all 18 combinations of tile profile (high-, medium-, low-), attachment (direct, battens), and wind angle of attack (0°, 45°, and 90°) were complete.

14th International Conference on Wind Engineering – Porto Alegre, Brazil – June 21-26, 2015

6

Results Mean withdrawal (z-direction) and shear forces (x- and y-directions) at the mechanical fastener were computed from the load cell data. Figure 3 shows the measured withdrawal forces. Shear forces (not shown) were, in general, of lower magnitude than withdrawal (z-direction) forces, suggesting the wind-induced reaction is dominated by vertical uplift at the fastener. The data indicate that withdrawal force is dependent on wind angle of attack. For high-profile configurations, there was an increase in withdrawal load with increasing wind angle. For medium-profile configurations, withdrawal forces were much greater for the 0° wind angle. Increase in withdrawal force during wind loading was not discernable from signal noise for two low-profile data sets (L/B/45 and L/D/90), which indicated relatively small withdrawal loads but did not allow computation of mean load increase. Low-profile data for battened attachments indicate that withdrawal loads were greater for a 0° wind angle than for a 90° wind angle while direct attachment configurations indicate higher loads for a 45° wind angle than for a 0° wind angle. Withdrawal loads were weakly dependent on installation configuration for both medium-, and low-profile cases. High-profile cases indicate slightly larger withdrawal forces at the highest wind speed level for directly attached configurations.

Figure 3. Measured z-direction withdrawal force (N) at a single screw fastener for roofing tiles at three reference velocity levels where H, M, L indicate high-, medium-, or low-profile tile respectfully, B, D indicate battened or direct to deck installation respectfully, and 00, 45, 90 indicate wind angle of attack. *(Note: data sets L/B/45 and L/D/90 are not shown). 5

EXPERIMENT THREE: CONSTANT DISPLACEMENT RATE UPLIFT TESTING

The research objective was to quantify the mechanical uplift resistance of standard field tile attachment configurations using the method prescribed by TAS 101/102 (FBC) and SSTD-11 (IBC) with modifications. Concrete roofing tiles were subjected to constant displacement rate mechanical uplift using a dual column tabletop Universal Testing Machine (UTM) and concrete anchors installed at one of five points along the centerline of the tiles. Specimens included high-, medium-, and low-profile tiles installed on plywood test decks with foam adhesive or mechanical attachments, and “direct to deck” or battened configuration. Ten replicates were completed for each profile/attachment/loading point combination. Significant modifications from TAS 101/102 include the use of five points of load application as opposed to one (at 0.76L), absence of underlayment, ten samples as opposed to 14, and load application perpendicular to the tile surface as opposed to the vertical direction. TAS 101/102 requires specimens to be loaded from a point 0.76L (where L is the length of tile) from the head of the tile. This point is meant to represent the center of pressure loading for the tile. The approach stems from aerodynamic theory for a flat inclined plate in a wind field. Five points of load application were used in Experiment three to assess attachment capacity sensitivities to this approach. Methodology The testing apparatus consisted of an Instron Universal Testing Machine Model 3367 and custom steel frame (Figure 4). The UTM has a 30 kN (6750 lbf) uniaxial load cell capacity, with rated accuracy of ± 0.5% of the indicated load. The system incorporates Bluehill 2 software that samples at 100 Hz. Load was transferred to the tiles using a steel chain, a steel jig, and a concrete anchor. The steel frame was constructed using 50.8 mm (2 in) square steel tubing with welded connections. The top portion of the frame has an 18.5° (4:12) pitch. A swivel joint fastened to the UTM load cell enabled the steel chain to be oriented such that loading was perpendicular to the surface of each tile. The steel jig and chain connected the swivel joint to the concrete anchor installed on each tile specimen.

14th International Conference on Wind Engineering – Porto Alegre, Brazil – June 21-26, 2015

7

Test decks consisted of 38 cm (15 in) by 244 cm (8 ft) 15/32 performance category APA rated plywood with 32/16 span rating, and exposure 1 bond classification attached to nominal 2 x 4 timber framing. A single Quik Drive #8 x 6.4 cm (2.5 in) WSCT Series Tile Roofing Screw (ASTM A641 Class 1) was used for attachment of each specimen tile (direct to deck and batten configurations). A self-adhered underlayment approved for roofing tiles in the State of Florida was installed on adhesive-set tile test decks prior to tile attachment. Underlayment was not used for mechanically attached configurations. Adhesive-set tiles were installed by licensed 3M representatives using 56-63 g (2.0-2.2 oz.) of 3M two component foam roof tile adhesive (AH-160). Six tile specimens were installed on each plywood test deck. Concrete anchors (0.64 x 3.2 cm) were installed at one of five points along the centerline located at 8, 16, 24, 32, and 40 cm respectively from the head of each tile. Ten replicates of each install/loading point were tested for each tile profile. The first tile (first course) on each test deck was present for proper orientation of the tiles above and was not subjected to loading. Tile head laps were 76.2 mm (3 in). A 2.5 x 5.1 x 38.1 cm (nominal 1 x 2 x 15 in) section of lumber was positioned below the interlocking edge of high-profile tiles during installation to simulate the effect of an adjacent tile. Battens were 2.5 x 5.1 x 38.1 cm (nominal 1 x 2 x 15 in) timber installed using #8 x 6.4 cm (2.5 in) galvanized screws.

Figure 4. Instron Universal Testing Apparatus (UTM) and steel tile loading frame for Experiment three mechanical uplift testing. A single test deck was fixed to the test frame using welded steel clamps. The test deck was positioned such that the specimen in the last course was tested first. Using the UTM, load was applied to the anchor of the tile at 50.8 mm/min (2 in/min) through the steel loading chain. The swivel joint system allowed load to be applied perpendicular to the tile surface. Upward deflection of the specimen was measured at the leading edge by hand during load application. The failure threshold corresponded to either ultimate failure (broken tile) or 50.8 mm (2 in) leading edge deflection per TAS 101/102. After failure, the loading jig was disconnected and the tile was removed. The clamps were released and the test deck was moved into position for the next specimen (in the course below). Five tiles on each test deck were tested before the entire test deck was removed and replaced with the next deck.

14th International Conference on Wind Engineering – Porto Alegre, Brazil – June 21-26, 2015

8

Results The minimum, maximum, and mean uplift resistance values were computed for each attachment/loading point combination for low-, medium-, and high-profile (Figure 5) tiles (Note: low- and medium-profile data are not shown, however, general trends are consistent with high-profile data). Tile uplift capacities were strongly dependent on attachment type. Adhesive-set configurations had larger uplift capacities than direct to deck and battened attachments for all three tile profiles. Magnitudes of direct to deck and battened attachment capacities were similar for all three profiles with high-profile configurations slightly smaller than the others. Uplift capacities were strongly dependent on point of load application as expected due to changes in the moment arm for each case. Uplift capacity was shown to decrease with increasing distance from the head of the tile for mechanically fastened attachments (direct and battens) for all three profiles. However, adhesive-set attachments did not follow this trend, likely due to the large area of adhesive contact towards the center of the tile. Uplift capacities for adhesive-set attachments were slightly lower at loading points farthest from the center (i.e. points 1 and 5). It should also be noted that varying the point of load application also changes the rate of load application to attachment locations, which may have impacted attachment resistances to uplift load. TAS 101/102 estimates the attachment resistance of roofing tiles for design. The angle of load application was a notable modification from the TAS method in Experiment three. Uplift testing is meant to simulate uplift load generated by wind. Windinduced pressure acts normal to the tile surface and so the application of load was applied perpendicular to the tile surface in Experiment three. TAS 101/102 requires load to be applied in the vertical direction. The difference between the two angles (i.e. a vertical plane and a plane normal to the testing surface) for the test slope used in the current study (18.5° relative to a horizontal plane) is 13.5°. The normal and shear components of a vertically applied load are 0.97 (cos 13.5 °) and 0.23 (sin 18.5°) respectively, meaning the TAS method introduces a shear loading mechanism that may not be present in typical wind loading conditions.

Figure 5. Minimum, maximum, and mean uplift resistance values for mechanical uplift testing data sets of 10 samples. High denotes high-profile tiles, DD, FM, and BT denote direct to deck, foam adhesive, and battened attachment configurations, and 15 represent the point of load application at 8, 16, 24, 32, and 40 cm respectively from the head of each tile. 6

CONCLUSIONS

The results of Experiment one confirm that low-resolution surface pressure measurements (i.e. TAS 108 methodology) can be used to compute lift coefficients that are conservative with respect to spatial variation of pressures on a roofing tile. However, the data from Experiment two indicate that loading from wind perpendicular to the leading edge (i.e. TAS 108 methodology) does not necessarily create the worst load case. Attachment configuration (i.e. direct to deck vs battens) was also shown to vary the effect of various wind angles on attachment reactions. Current testing provisions may be enhanced by considering multiple wind directions and the effect of battens. Experiment three findings indicate that foam adhesive-set configurations have higher uplift capacities than mechanical attachments (aging effects not considered). It was also shown that that direct to deck configurations have higher capacities than battened configurations. Attachment capacities were strongly dependent on the point of load application. Considering geometric differences among typical roofing tiles, the center of pressure for wind-loading is likely to vary with wind direction and tile profile. The use of a more tile-specific point of load application, rather than a “one size fits all” approach (based on aerodynamic theory) during mechanical uplift testing may provide a more conservative outcome for design.

14th International Conference on Wind Engineering – Porto Alegre, Brazil – June 21-26, 2015

9

ACKNOWLEDGEMENTS This paper was written through the support of the Florida Building Commission, the Florida Department of Emergency Management, and the International Hurricane Research Center (FIU). Special thanks to Joseph Esposito and Matthew Terza for their invaluable contributions in the laboratory. The authors also thank the following groups for additional support and guidance: Tile Roofing Institute, Eagle Roofing Company and Technical Representative Manual Oyola, Boral Roofing, 3M, and the American Plywood Association. Any opinions, findings, conclusions, or recommendations expressed in this paper are those of the authors and do not necessarily reflect the views of the sponsors, partners, or contributors. REFERENCES [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] [18] [19] [20] [21] [22] [23] [24] [25] [26] [27] [28] [29] [30]

ARA. (2008). 2008 Florida Residential Wind Loss Mitigation Study. Applied Research Associates Inc., Florida Office of Insurance Regulation, Tallahassee, FL. ASCE. (2010). ASCE 7-10: Minimum Design Loads for Buildings and Other Structures. American Society of Civil Engineers, Reston, VA. ASTM. (2003a). C1568-03 Test Method for Wind Resistance of Concrete and Clay Roof Tiles (Mechanical Uplift Resistance Method). C15 Committee, ASTM International. ASTM. (2003). C1569-03 Test Method for Wind Resistance of Concrete and Clay Roof Tiles (Wind Tunnel Method). C15 Committee, ASTM International. ASTM. (2003). C1570-03 Test Method for Wind Resistance of Concrete and Clay Roof Tiles (Air Permeability Method). C15 Committee, ASTM International. FBC. (2010). Testing Application Standard No. 101-95 Test Procedure for Static Uplift Resistance of Mortar or Adhesive Set Tile Systems. 2010 Florida Building Code. FBC. (2010). Testing Application Standard No. 102-95 Test Procedure for Static Uplift Resistance of Mechanically Attached, Rigid Roof Systems. 2010 Florida Building Code. FBC. (2010). Testing Application Standard No. 102A-95 Test Procedure for Static Uplift Resistance of Mechanically Attached, Clipped, Rigid, Roof Systems. 2010 Florida Building Code. FBC. (2010). Testing Application Standard No. 108-95 Test Procedure for Wind Tunnel Testing of Air Permeable, Rigid, Discontinuous Roof Systems. 2010 Florida Building Code. FBC. (2010e). 2010 Florida Building Code. Florida Building Commission, International Code Council, Inc. FBC. (2010f). Roofing Application Standard No. 127 Procedure for Determining the Moment of Resistance and Minimum Characteristic Load to Install a Tile System on a Building of a Specified Roof Slope and Height. 2010 Florida Building Code. FEMA. (2005). Hurricane Charley in Florida: Observations, Recommendations, and Technical Guidance. Mitigation Assessment Team Report, Federal Emergency Management Agency, Mitigation Assessment Team, U.S. Department of Homeland Security, Washington D.C. FPHLM. (2011). Survey of Single Family Residential Buildings in Florida. Florida Public Loss Model: Engineering Team Report. Hazelwood, R. A. (1980). “Principles of wind loading on tiled roofs and their application in the British standard BS5534.” Journal of Wind Engineering and Industrial Aerodynamics, 6(1–2), 113–124. Hazelwood, R. A. (1981). “The interaction of the two principal wind forces on roof tiles.” Journal of Wind Engineering and Industrial Aerodynamics, 8(1– 2), 39–48. Kramer, C., and Gerhardt, H. J. (1983). “Wind loads on permeable roofing systems.” Journal of wind engineering and industrial aerodynamics, 13(1), 347– 358. Kramer, C., Gerhardt, H. J., and Kuster, H.-W. (1979). “On the wind-loading mechanism of roofing elements.” Journal of Wind Engineering and Industrial Aerodynamics, 4(3–4), 415–427. Laboy-Rodriguez, S. T., Smith, D., Gurley, K. R., and Masters, F. J. (2013). “Roof tile frangibility and puncture of metal window shutters.” Wind and Structures, 17(2), 185–202. Li, R., Chowdury, A., Bitsuamlak, G., and Gurley, K. (2014). “Wind Effects on Roofs with High-Profile Tiles: Experimental Study.” Journal of Architectural Engineering, Housing and Residential Building Construction. Malmstadt, J., Scheitlin, K., and Elsner, J. (2009). “Florida Hurricanes and Damage Costs.” Southeastern Geographer, 49(2), 108–131. National Science Board. (2007). Hurricane Warning: The Critical Need for a National Hurricane Research Initiative. National Science Board. Pielke Jr, R. A., and Landsea, C. W. (1998). “Normalized hurricane damages in the United States: 1925-95.” Weather and Forecasting, 13(3), 621–631. Redland Technology. (1991). Fixing studies for MRTI normal weight tiles - SBCCI submission. Redland Technology. Robertson, A. P., Hoxey, R. P., Rideout, N. M., and Freathy, P. (2007). “Full-scale study of wind loads on roof tiles and felt underlay and comparisons with design data.” Wind and Structures, 10(6), 495–510. SBCCI. (1999). SSTD 11-99: Test Standard for Determining Wind Resistance of Concrete or Clay Roof Tiles. Southern Building Code Congress International. Shdid, C. A., Mirmiran, A., Wang, T.-L., Jimenez, D., and Huang, P. (2011). “Uplift Capacity and Impact Resistance of Roof Tiles.” Practice Periodical on Structural Design and Construction, 16(3), 121–129. Smith, D. J., Masters, F. J., and Gurley, K. R. (2014). “A historical perspective on the wind resistance of concrete and clay roofing tiles.” RCI Interface, Vol. 32, No. 10, 2014. Tecle, A., Bitsuamlak, G. T., and Chowdhury, A. G. (2013). “Wind Load on Ridge and Field Tiles on a Residential Building: a full scale study.” Advances in Hurricane Engineering@ sLearning from Our Past, 506–516. Tecle, A., Bitsuamlak, G. T., Suskawang, N., Chowdhury, A. G., and Fuez, S. (2013). “Ridge and field tile aerodynamics for a low-rise building: a full-scale study.” Wind and Structures, 16(4), 301–322. Wardell, C. (2006). “Tile Roofs for Hurricane Zones.” CoastalContractor.

14th International Conference on Wind Engineering – Porto Alegre, Brazil – June 21-26, 2015