Deck Lateral Loads the Truth Revealed

Dec lateral loads the truth is revealed the publishing of the permitted lateral load anchor detail in the 2009 international residential code has drawn question to whether lag screws alone can support deck lateral loads at the ledger recent testing reveals that indeed they can I'm Glen Mathewson former deck builder master code professional plans analyst for the City of Westminster Colorado technical adviser to the North American deck and railing Association and ICC author and approved education provider nhadra and I have submitted a public comment modification to proposal RB 263 in the development process of the 2015 IRC and are seeking approval at the final hearings this October currently we have a permitted connection to meet undefined loads with a blanket value proposal RB 263 gives an exception for this connection for decks that don't require guards an exception to something merely permitted is strange but regardless recent discoveries reveal Ledger's do just fine without lateral load anchors before we look into this we have to know our past to understand the present on July 14th 2006 a proposal for deck ledger fastening table was published for review in the development process for the 2007 supplement IRC it was based on testing performed by Virginia Tech researchers at the first of two hearings that year the committee approved the ledger table with comments that December the hearing results in committee comments were published the committee liked the table and thought it was a good starting point but they asked for additional study of the band joist connection to the framing this is where it all began as the committee approved a tested connection of the ledger to the banjoist the question arose as how well the banjoist is connected to the rest of the structure and would it be able to resist the lateral loads from the deck in response on April 6 2007 a public comment modification to the approved ledger table was published with no tested data available for banjoist performance at the time an anchor detail to bypass the banjoist altogether was proposed this was intended to address the committee's concerns from the first hearing the connection method is based on a detail from a FEMA document for earthquake resistant design but a few details were added to the IRC version such as nailing the floor sheathing at six inches on center and a load capacity for each anchor of 1500 pounds a best guess at the time the final action hearing the lateral load provisions were approved and lateral load resistance of deck Ledger's became permitted to be in accordance with the new detail in May the reasoning for the new provisions in the IRC were published as shown there was little to no justification case history or evidence supporting the provisions the deck failures referenced in the reasoning and prevalent in the US are decks that are not built with modern standards in the past mini decks were built without flashing and rotten band joists and framing resulted flashing at deck Ledger's is common industry practice today and required in the IRC prior to inspection there was no additional beam and this deck was supported by the cantilever alone many decks were built in the past with connections to unsupported band joist like this but this is no longer acceptable or standard practice nonetheless the lateral provisions were included in the IRC after only 46 days of review and they began to sculpt to the future of the decking industry this brings us to the present and the domino effect this new provision would have on the construction industry how would manufacturers respond to a 1500 pound design load how would building officials respond to a permitted detail how would it affect the decking industry for wood aye joists manufacturers it drove questions of how their floor systems will resist a 1500 pound concentrated load placed in the web of a single joist or two perpendicular joists their manufacturers Association designed and published details to answer these questions for perpendicular joists it would require six feet of blocking at the interior hold down and nails in the sheathing and blocking at four inches on center manufacturers also responded to this provision with technical bulletins but mistakenly understand it to be universally required in this quote it's reference to as a requirement quite contrary to its original inclusion in the IRC hardware manufacturers responded to the lateral load provisions with products to meet specific IRC figure and installation guidance for various applications such as concrete foundations however if we remember our past the first Domino was stood from a concern of the band joist connection to the floor framing in December of 2010 ICC es began work on a new acceptance criteria for a cable alternative to the hold-down anchor and threaded rod method permitted in the IRC ICC es staff provided an opinion regarding the nature of the lateral load detail in the IRC they state that without the hold down anchors installed engineered connections to the primary structure are required this implies the lag screws or bolts prescribed by the Leger fastening table don't provide any lateral restraint they further state that it's unknown whether the anchors are part of the primary structural system or a backup system regardless it's considered required based on its published 1500 pound load a value not derived from any science or engineering the industry responds to IRC lateral loads has misguide many designers to believe the two anchors are a universal requirement for decks this detail was provided on engineered house plans under the pretense it was required building code administrators have also responded to these unclear provisions in this interpretation from New Jersey to a builder it's understood to only apply to seismic regions this isn't based on any clear understanding of the provisions in the IRC but from vague ICC commentary ultimately the decking industry has had to make the biggest response builders are often required to install anchors on every deck regardless of design conditions homeowners are reluctant to the intrusive interior construction necessary for consist for installation and lateral load anchor provisions have driven up the cost of debt construction but without a justified return on investment the development of new code additions is what shapes the future today in 2013 the 2015 IRC is being created developing the code is looking ahead in time recent research from Washington State University has provided new and exciting insight into the nature of deck lateral loads and performance the study requested by the code Development Committee seven years ago has finally been provided and the results are dramatic researchers calculated wind and seismic lateral loads and tested live lateral load and ultimate lateral resistance on sample decks all research was based on a 12 foot by 12 foot deck for articles revealing the research results were published in the summer of 2013 after the first code development hearings concluded would design focus is a journal published by the Forest Products Society and is an excellent resource for wood engineering information from recognized researchers and their winds study they considered a 180 mile an hour wind in exposure see a wind force present at the tip of Florida about every seven hundred years under these conditions the ledger would only experience six hundred and fifty pounds of lateral load at its ends under the more prevalent 115 mile an hour design load across most of the u.s. it would be approximately 266 pounds the seismic study was based on soil Class D such as in California and the lateral load at each end of the ledger would be only 259 pounds bear in mind that both these studies assume there are no other connections along the ledger such as lag screws taking some of the load something never before done lateral live loads were tested with human subjects a sample deck was loaded 240 pounds per square foot with people swaying in unison perpendicular in angled deck and conditions were tested but no other means to brace the deck was provided again a 12 foot by 12 foot deck was the study subject loads parallel to the ledger provided the most force and displaced the deck by 7 inches at this point the researchers felt that deck inertia had overcome the force generated by the occupants and a maximum live load had been reached under the worst case tested and based on previous studies of bleacher seating researchers determined 12 pounds per square foot as an acceptable and conservative lateral live load design value for the 12 by 12 deck this would yield 1,750 pounds total and 875 pad pounds at the end of the ledger where hold down anchors are permitted the summary of worst-case lateral loading shows all sources are well below the 1500 pound value in the IRC but this doesn't answer the question that started at all does the lag screwed ledger and banjoist resist the lateral loads that's what this test answers to 12 by 12 decks connected to a mocked up floor assembly built according to IRC standards were pulled laterally at the center of the joists fan perpendicular decking was installed and the test was stopped at 7,000 pounds this was a comparative test two identical decks were built and connected with lag screws according to IRC provisions one was provided lateral load anchors one was not the decks were pulled laterally to see how the ledger and band joists would perform at 2,000 pounds of force there was 3.5 inches of displacement this is equivalent to the 7 inches of displacement measured here under the 750 pounds of force generated by the occupants in the previous test at this loads significant joists splitting has occurred from the decking fastener the test continued however and had a load of 3,500 pounds there was 17 inches of displacement at mid-span at this point the deck joists were well beyond failure testing continued - a load of approximately 7,000 pounds this is a force four times what could be generated by the occupants and the lag screws never failed according to the researchers furthermore even though the two outermost lag screws carried most of the forced these lag screws did not show any visible signs of withdrawal at the maximum load of approximately 7,000 pounds this performance is reiterated in the article a second time no visible signs of failure but we still we do not have the answer to the original question how did the banjoist handle the load this is the concern that brought the lateral load detail into the IRC according to the test results no damage was observed in the simulated house diaphragm further the researchers concluded these results point to the effectiveness of 0.5 inch diameter lag screws when selected and installed for the IRC deck ledger connection provisions with every new code developed this future soon becomes our present shouldn't it be based on all we have discovered ICC believes so and encourages on their website in regard to code development this process ensures that the international codes will reflect the latest technical advancements and address the concerns of those throughout the industry in a fair and equitable manner NADRA represents the concerns of the decking industry and has submitted a public comment modification to proposal RB 263 asking to remove the misleading and unnecessary lateral load connection from the 2015 IRC with the code representing our latest understanding of deck lateral loads deck structural performance can be appropriately accommodated and researched into the future blanket values and specific hardware details for deck lateral loads don't have a place in the IRC but this doesn't prohibit them from being installed by choice on a personal note when I'm not busy supporting NADRA in the decking industry I'm at work in Colorado administering code to my local community I wish only to enforce government regulation on my neighbor's that is proven fair and trustworthy I asked my fellow code officials to help me in that effort by protecting the validity and quality of the provisions of the International residential code and approving the modification proposed to RB 263 please share this video with those in the code and decking industry nad res code development proposals and public comments can be reviewed in entirety at nab Joerg forward slash code for more information concerns or questions regarding debt codes you are welcome to contact me or visit my websites thank you

Channel: Glenn Mathewson

Views: 19,299

Rating: 4.7979798 out of 5

Keywords: IRC, deck, decking, code, building code, lateral load, testing, rb263-13, rb263, Washington State University Tri-Cities (Organization), ledger

Id: nP6QzyxZgAw

Length: 13min 40sec (820 seconds)

Published: Wed Aug 28 2013