9300 W MALL DR 2019-06-25 - Laserfiche WebLink

• DEl DIBBLE ENGINEERS INC required,such that any upgrades that are done are voluntary and are limited by the existing conditions to improvements that are"technically feasible,"as defined by Chapter 2 of the IEBC,and are intended to substantially improve the capacity of the lateral force resisting system,but are not intended to bring the building into compliance with the current code. Unfortunately,the options available for retrofit anchors into existing concrete stem walls,under current AC!Chapter 17 limitations and the existing technology do not provide tensile anchorage exceeding approximately 3.5 kips. In our professional opinion,these upgrades will improve the performance of the structure under lateral forces. To clarify this design intent and limitation, we have clarified the Scope of Structural Work in our Genera/Notes section. 3. On the permit structural calculations where the wood shear walls are checked against the design demands (for example,Bldg A 1st Floor Walls),exceed the Demand Capacity Ratio(OCR)by nearly 14%. It is unclear if the 75%of the IBC 2015 lateral forces is being used(for example,531 plf/533 plf=0.84, approximately a 15%reduction)to compare against the wood shear wall design values. Please clarify. DEI Response:Thank you for this question. t apologize for the confusion on this point. The wall areas that are"grayed out"on the spreadsheet calculations,such as Building A, 1st Floor, West Elevation,do not exist These are locations where The building steps. The wood framed portion of the building exists on only one half of the building,and the other half is a concrete garage structure at that level 4. Please provide calculations checking the redundancy factor,p,per ASCE 7-10 Sec 12.3.4.2. It appears to be unclear whether a redundancy factor of 1.0 or 1.3 is used for the design of the wood shear walls. DEl Response:The redundancy factor used for the calculated design is 1.0. This is conforming with the requirements of Section 12.3.4.2 based upon existing long interior walls at each level The existing corridor walls and unit party walls have an inherent stiffness due to their being long sheathed walls with few penetrations. The flexible diaphragm will contribute lateral forces to the interior walls. As a result,each of the perimeter shearwall lines is assumed to take no more than 25%of the story shear,and each shearwall line has multiple shearwails resisting that shear. The building plans are regular and generally symmetrical • 5, Please provide calculations indicating that the drift criteria for the structure with the structural repairs have been satisfied per ASCE 7-10 Sec. 12.12. DEI Response:The requirements of Drift do not apply for an existing structure. The IEBC as referenced by the!BC would allow the structure to be put back in similar kind to existing. in comparison with existing,the retrofits are only an improvement to that which currently exists. However,for comparison,and per your request,we have attached a set of calculations to demonstrate the story drift based upon the shearwa!l deflections,as contrasted with the allowable story drift per ASCE 7-10, Section 12.12. The calculations demonstrate that the drift criteria are generally met, with the exception of the ground level on buildings A and C. The shearwall deflection at these two locations is limited by the available capacity of retrofit hold down anchorage via the Delta(a)term in the deflection calculation. As stated above,current codes, technology,and existing building limitations do not provide technically feasib- •t4 fit anchors that can