S02 - Specifications - Structural - 506-22-502.pdf

June 22, 2023

Mike Duke AIA

Principal

RDC/JPA Architecture

3131 Newmark Drive Suite 200

Dayton, Ohio 45342

Subject: VAMC Ann Arbor SCIP-2 Recladding

THP # 20202.01

Dear Mike:

This letter summarizes my thoughts regarding the VAMC Ann Arbor SCIP-2 project.

The SCIP-2 building at the VAMC Ann Arbor is a two-story, steel framed structure with a basement. The building was constructed in 2017and the floor area is approximately 15,000 sf. The structure is surrounded on three sides by the original hospital structure, separated by expansion joints. The north face of the building is exposed and the existing façade on this elevation consists of an insulated metal panel (IMP) system.

Presently the existing façade is experiencing several issues including air and water infiltration. The current project intends to install a new membrane and rain screen over the existing IMP system.

Existing IMP Structural Backup Framing

The existing first-floor facade backup consists of an eight-inch reinforced CMU with 2” CFMF Z-purlins spaced at 16” on center vertically. The purlins are attached to the CMU with 1¾” Tapcon fasteners with unknown diameter, at 16” O.C. The 3-inch IMP is directly attached to the Z-purlin with (2) SS ¼” diameter x 3 ¼” long 14/17 TEK3 fasteners at an assumed spacing 16” O.C. Spacing is not specifically called out on the drawing.

The existing second floor backup framing consists of HSS 6x2x3/16 spaced vertically from approximately 3’-3” to 4’-4”. An adjustment angle consisting of a CFMF 16 ga angle is attached directly to the HSS framing via unknown screw attachment. The 3-inch IMP is attached to the adjustment angle with (2) SS ¼” diameter x 3 ¼” long 14/17 TEK3 fasteners at an assumed spacing 16” O.C. Spacing is not specifically called out on the drawing.

New Rain Screen Structural Backup Framing

The proposed new Rain Screen backup framing is to be attached outboard of the existing 3-inch IMP.

The framing consists of 2 inch-16 ga Z-purlins horizontal at 16” O.C. to accommodate 2 inches of

Letter

Mike Duke/ VAMC Ann Arbor SCIP-2 Recladding additional EPS insulation and 7/8”-16ga hat channels running vertical at 16” O.C. on the outside of the Z-purlins on which to attach the rain screen.

Existing First Floor CMU and Second Floor HSS Framing

The lateral loading on these two structural components is unchanged from the original construction.

The vertical loading of these elements has increased slightly with the new recladding system weight of approximately 2.5 pounds per square foot. Axial load in the HSS member is increased by less than

150#/ea. The vertical load in the CMU wall has increased approximately 30 plf.

The existing CMU and HSS framing members have adequate capacity to support the lateral and vertical loads from the new cladding.

Potential Construction Issues

• Existing Insulated Metal Panel (IMP)

The quality of the existing IMP façade installation is unknown, and the means of attachment

(number of fasteners and spacing) is not well documented. The existing IMP has an exterior skin of 24 gage or 22 gage sheet metal. New fasteners placed into the skin of this material will have very low capacity which is further complicated by the possibility of debonding of the insulated core from the metal panel due to tension forces in the fastener due to wind negative pressures (suction). It is recommended that the new Z-purlin sub-framing be directly anchored to the CMU wall or HSS framing behind the existing IMP. It may also be difficult to tighten the fasteners due to the compressibility of the panel.

• Attachment of New Sub-Framing to Existing CMU or HSS Framing

The attachment of new sub-framing back to the existing CMU or HSS requires a fastener of 5 to

6 inches long. Typically, screws attaching façade elements are loaded in shear. The load transfer in the proposed system is approximately 4 inches from the face of the backup resulting in a moment applied to the fasteners. The combination of shear and moment fastener loading reduces fastener capacity and may result in deflections within the façade system.

New fasteners need to be placed accurately to attach to the HSS 6x2 framing. The screw must engage a flat area on the face of the HSS approximately 1-1/4” wide otherwise the screw will not attach to the HSS and may engage the existing 16 GA IMP attachment angles adding to the potential for movement of the façade system.

• Condensation within Cavity

Rain screens by their nature are not watertight since some moisture is expected within the cavity where the cold form metal framing sub-framing resides. It is important to incorporate proper drainage from within the cavity. Corrosion of the sub-framing is a possibility; therefore, we recommend a minimum of 16 GA sub-frame materials.

Letter

Mike Duke/ VAMC Ann Arbor SCIP-2 Recladding

Minimum Fastener Recommendations

Z-girt (2”-16 gage)

• Attachment to HSS backup framing use ¼”ɸ -20 x 5” min. TEK Screw, the HSS are spaced from 3’-9” to 4’-3”. At 16” OC max install 10-16 x ¾” HWH TEK

• Attachment to CMU backup use ¼”ɸ x 6” Tapcon. If anchor is to existing hat channel use ¼”ɸ

-20 x 3-1/2”HWH TEK

Hat Channel to Z-girt (7/8-16 gage)

• Attachment to Z-girt use (2) 10-16 x ¾” HWH TEK

These fastener recommendations likely do not cover all the details for the façade recladding effort. I would suggest that the sub-framing work be performed as a delegated design. This will ensure that all areas of the façade attachment effort will be analyzed for the appropriate wind loads and attachment to the variable backup structure.

Please contact me if you have any questions or comments related to this letter.

Sincerely, THP Limited, Inc.

Frank J. Ellert PE

Principal