Design and Construction of Steel Plate Shear Walls - Eatherton ...

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esisting elements.How to use intermediate HBE’s between floors is notwell defined in the AISC Seismic Provisions. The commentarymentions that additional horizontal intermediate boundaryelements can be used to adjust the aspect ratio of a SPSWpanel, but the main body of the code requires that all HBE toVBE connections be moment connections and that all HBE toVBE intersections be laterally braced. It is the author’sinterpretation that these provisions do not apply to intermediateHBE’s. This should be addressed, however, in future editionsof the code.With the use of intermediate HBE’s, the slendernessand capacity of a wall is perfectly adjustable. Walls as slenderas the one shown in Fig 2 have been designed and constructed.A nonlinear pushover analysis was done on this wall to ensurethat the boundary elements will remain elastic while the webplate yields.Web Plate Thickness and MaterialWhen sizing the web plate there a few things to keep inmind. It is ideal to size the plate at each level to just satisfy thedesign shear force. This will make it more likely that the platewill yield at multiple floors and it will make for a moreeconomical design of the columns.At upper floors of a mid-rise or all floors of a low-risebuilding it becomes clear that even 3/16” to 1/8” plate can havemore capacity than is needed. The question quickly becomes: Figure 2 – Steel plate shearhow thin of plate should be used? AISC Seismic Provisions wall used in a high-enddo not limit plate slenderness, instead, the commentary states residence in Atherton, CA.that story drift limitations will indirectly limit the plateslenderness. For designs such as the ones shown in Fig 1 and Fig 2 the material andconstructability may control instead.As the web plate gets thinner the connection to boundary members becomes moredifficult. The connection shown in Fig 3 is from a SPSW used for a high-end residence in SanMateo County, California. 14 gage plate was specified with continuous welds on both sides tothe boundary members. Inadvertently, the steel fabricator shipped some of the panels to sitewith only intermittent welds around the panel perimeter. It was discovered that, while thehorizontal welds were fairly easy to complete in the field, the welds along the VBE’s requiredspecial attention. Initial attempts at vertical welding presented some difficulty, when uphandwelding (starting at the bottom and going up) began burning through the light gage plate. Aspecial downhand (starting from the top and going down) procedure was developed by thefabricator and qualified by the special inspector. The resulting welds were found to be adequate,but this demonstrates some of the challenges when using light gage web plate.Another factor to consider when using thin web plate is the shear that causes the plate tobuckle. Plate buckling is expected to occur as the tension field develops, but it is not desirable
for service loads, e.g. a stout wind.Researchers who have run tests onSPSW’s report extremely loudbanging as the loading reverses.Even though there haven’t beenany documented cases of SPSWbuildings making loud bangingsounds in wind storms, SPSW arerelatively new and it may yetbecome an issue. Theory ofelasticity texts give formulas forcalculating plate buckling and it isworthwhile to understand the loadat which an SPSW will buckle.Introducing intermediate HBE’swith shorter panel lengths willincrease the buckling load.The third consideration when choosing plate thickness is the material specification.Section 6.1 of the AISC Seismic Provisions limits the materials that can be used in the seismicload resisting system. Acceptable plate material includes A36 or A1011 Grade 55 (in either SSor HSLAS). A1011 is hot rolled sheet steel and as such should have more pronounced yieldingand more ductility than cold rolled sheet metal. It would be much more preferable, however, touse A1011 grade 30 or 33 sheet steel as it has a lower yield and more elongation. While thecommentary discusses low yield point plate material, it is suggested that future editions of theAISC Seismic Provisions explicitly allow these materials.Whenever light gage plate is used for the web plate it is the author’s opinion that it isworthwhile to require coupon tests to measure actual yield strength and percent elongation.Since the performance of the building is so directly tied to the plate material, the greaterunderstanding of the primary energy dissipating element will easily justify the slight additionalcost.Column DesignFigure 3 – Field welding of gage plate that requiredspecial procedure.The main body of the 2005 AISC Seismic Provisions states that the required strength ofVBE’s shall be based upon the forces corresponding to the expected yield strength, in tension, ofthe web calculated at an angle, α. To reach this level of force the beams are required to developplastic hinges. The commentary describes three methods that can be used to design the VBE.The first, nonlinear pushover analysis, will give the most accurate understanding of the SPSWresponse. Axial loads and moments in the columns caused by web plate yielding and plastichinging of the HBE can be used to design the columns to remain elastic. It is important to notethat elastic modeling of SPSW will not capture the intent of the design process: to size VBE’s toremain elastic while the web plate yields. To design the VBE for yielded plate and plastichinging of HBE’s requires consideration of the nonlinear response of the elements. Nonlinearpushover analyses, however, are not that common in most design offices.The second method called combined linear elastic computer programs and capacitydesign concept (LE+CD) uses an elastic model of the wall, considering moment connections and
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