Loading...
HomeMy WebLinkAboutBLD2008-00856 METAL DECK INSTALLATION.TIF6645 Goose Pointe Drive Denver, NC 28037 Metal Deck - Covered Rear Porch Structural Observations for Mr. Mark Battiste Valhalla Custom Homes Inc. 361 River Birch Circle Mooresville, NC 28115 by A. Wynn Yates, PE Yates /Starnes Engineering, PA 3300 Elstree Drive Charlotte, NC 28226 704 - 650 -5541 wyates @yseng.com September 16, 2008 Photo #2 This is the metal deck. It is reported to be Vulcraft, Type "B" wide rib, 1.5" deep, 22 gauge, painted metal deck. Type "B" deck is a roof deck and is non - composite. The equivalent Non - Composite Floor Deck would be the Vulcraft (Type "C ") (Conform)[1.5C], which will be referenced in this report. The supporting steel is either a L5x3.5x318" in the case of a 9' -9" clear span or back -to- back L5x3.5x318" in the case of a 13' -9" clear span. The maximum spacing between supports is 5'- 41/2 The metal deck spans left -to -right and is supported at the ends of a full wythe of brick masonry. The angles are oriented with the 3.5" wide leg horizontal and at the bottom of the angle, 4.625" from the underside of the metal deck. It is the intent to pour 4" of normal weight (145 pch, 3,000 psi concrete atop the metal deck so the total thickness of the concrete will be 5.5 ". See the following for additional comments. Photo #1 This is the front of the subject house. The scope of work, as defined by the general contractor is limited to an evaluation of the metal deck and angle supports to be used as forms for the covered rear deck of the house. The deck is located at the right/rear corner of the main Photo #4 The idealized bending capacity of the L5x3.5x3/8" angle is inadequate to carry the superimposed loads, due largely in part to the 5.5" total slab thickness and the use of normal weight concrete. In addition, the deflection from a 40 psf live load exceeds the allowing of U380. As noted above, there is no top flange on the angle upon which the metal deck can bear or attach. Photo #3 While orienting the angle so that its 3.5" wide leg is at the bottom increases the load carrying capacity, it causes the metal deck and concrete to be supported by a very thin edge of steel as seen in this picture. Vulcraft requires 3" of interior bearing surface as seen in the data that follows. Photo #5 At the left side of the deck, the clear span of the metal deck supports is 13' -9 ". The supports provided at back to back L5x3.5x318" with brick sitting atop the projecting horizontal bottom angle legs as barely seen in this picture. The double angles are inadequate to resist the applied loadings in the samc mariger a5 nnfod in the previous photo caption that applies for the 9' -9" clear span. -, 0`dJAEI.e'_'11"IFOW.1 LOAD !PSfi Photo #6 This table is reproduced from the Vulcraft 2001 ''Steel Roof and Floor Deck" catalog. This Table list the uniform allowable load the deck alone will carry. "WV is the maximum weight of concrete and deck that can be supported without composite action. "W1" can be interpolated between 55 and 72 pounds per square foot from the Table based on a 5'-4 -112" span between supports. The result is approximately 61 .5 psf., which happens to equal the 61 psi construction loads seen on the next page Note that this Table calls for a 3'' wide bearing surface to accommodate the support of the metal deck and concrete above. That is considerably wider than the 318" currently furnished There are additional reasons for considering this substitution as discussed in the following photo captions. 1.5 C CONFORM Photo #7 As noted in Photo Caption #2, "B" deck is intended to function as a roof deck. The Tables seen in this report are for Non - Composite, Conform, Floor Deck. The Conform is approximately 3% stronger than the "B" deck in resisting positive bending stresses, so the comparisons are valid. This Table shows that the clear span of 5' -3" can support the construction loads from workmen and wet concrete without mid -span shoring, but just barely. REINFORCED CONCRETE SLAB ALLOWABLE LOADS .. ._ '65 1 !si 1 W IM - 180 132 111 95 83 329 Z15 in t49 127 »0 . - 339 35 710 2fia f 267 :' 321 18 8 162 252 20] 284 z10 189 ts6 13s :i; -- 3P' 306 3� I, 321 212 332 20 174 .. .- :. _ 900 900 i 400 1 400 380 380 26] 233 33 0 313 2M" 2> _ t6o I 4x 35! 323 275 239 _,__ 4a 4CP i 400 400 )]0 310 3.39 368 758 298 249 1!3 183 .:. 400 39i 1 4W 1 Wp 3]0 315 272 x !00 I 400 400 )48 , c - 4x aPi ', 400 4W 400 4w Photo #8 This Table copied from the Vulcraft metal deck catalog shows that in order to meet ACI (American Concrete Institute) temperature and shrinkage (crack control criteria), 44- W29xW2.9 welded wire fabric is needed in the concrete. The W WF would be centered in the 4" vertical dimension from the top of the metal deck to the top of the concrete, i.e. 2" from the top of concrete. While it appears excessive in terms of load capacity, this is not the case when compared with the Table seen in Photo #6, where the capacity of the deck for total load is only 110 psf for a 5'- 4 -1/2" span. The total loading on this deck is 61 psf dead load and 40 psf live for a total of 101, which is less than 110.