2023 02 03 Structural Narrative.pdf

100 PERCENT SUBMISSION STRUCTURAL NARRATIVE

February 3, 2023

Overview of Structural Approach

1. Existing Building Description

The Levin Courthouse is a ten-story building with a basement level and two roof penthouse levels. The building was constructed in 1932 atop an existing concrete grade beam and caisson foundation system for a building previously located on the site. The footprint of the building is square, encompassing a full city block, and has a center courtyard above the second-floor level. Modifications to the interior spaces have occurred over the years, but the structural system appears to have been minimally modified. A vertical access addition was designed and constructed in 2015 in the courtyard space (2015 Prospectus

Project). The building is actively used and is planned to remain in use during this construction effort.

2. Basis of Knowledge on Existing Building

Our structural design is based upon a review of available documents provided to us and limited visual assessment of exposed structural elements to confirm drawing information and the general condition of these elements. Of the documents provided, two 1932 foundation drawings (D400 Basement Framing Plan and D401 Basement Sections & Details), miscellaneous 1932 architectural drawings, the 1932 steel erection drawings, and the 2015 Prospectus Project documents provide the greatest amount of information of the existing structural framing. It should be recognized that the available structural information provided to us is incomplete; further documentation and investigation as the project continues are recommended.

3. Existing Building Structural System Description

The gravity support system consists of a concrete encased steel frame supporting formed concrete tee-joists. Based on the limited document review completed, the lateral force resisting system most likely consists of the masonry perimeter and interior walls of the building working with the concrete floor diaphragms. The project specifications for the original 1932 construction provide detailed information regarding the materials used in the building construction.

4. Proposed Structural Design Modifications

There are four general areas of proposed structural modifications: 1) Lafayette Boulevard entrance, including installation of an exterior ramp and stair; 2) Fort Street entrance interior finish modifications; 3) addition of a vehicle sallyport at the basement level garage space; and 4) modification of second floor space to accommodate pedestrian sallyport and cell rooms. The effect on the structural systems for each proposed modification is described further below. All new work will occur within the footprint of the building with the exception of the proposed access ramps at the exterior of the Lafayette Boulevard entrance.

5. Code Review

For the proposed structural design modifications, the Facilities Standards for the Public Buildings Service

(P-100), 2018 edition with the 2019 Addendum applies. The 2021 editions of the International Existing

Building Code (IEBC) and International Building Code (IBC) are referenced by the P-100 and are applicable to this project. These standards and codes reference the following, which are also applicable to this project:

� American Society of Civil Engineers Minimum Design Loads for Buildings and Other Structures (ASCE 7)

2016 Edition with Supplement 1

� USMS Publication 64, Requirements and Specifications for Special Purpose and Support Space Manual, Volumes I and II, 2014 edition

� American Institute of Steel Construction Design Guide 11 Vibrations of Steel-Framed Structural Systems

Due to Human Activity, Second Edition

� American Society of Civil Engineers Seismic Evaluation of Existing Buildings (ASCE 31), 2003 edition

� American Society of Civil Engineers Seismic Evaluation and Retrofit of Existing Buildings (ASCE 41), 2017 edition

� National Institute of Standards and Technology Standards of Seismic Safety for Existing Federally

Owned and Leased Buildings, ICSSC Recommended Practice 8 (NIST GCD 11-917-12)

� Secretary of Interior’s Standards for the Treatment of Historic Properties (36 CFR 67)

6. Risk Category

All structural design is to the baseline design requirements of P-100.

7. Lateral Force Resisting System Design

The masonry wall assemblies are assumed to comprise the lateral force resisting system of the structure based on a limited review of the partial set of the April 21, 1932, and revised May 9, 1932, steel erection drawings (original steel drawings) provided. Proposed changes to the masonry walls affect less than 10 percent of the total system with the addition of a new door opening. The proposed changes do not warrant a review of the lateral force resisting system of the building for either wind or seismic forces per the IEBC.

Using an assumed Site D and Risk Category II per ASCE 7, non-structural components of the building impacted by the proposed design modifications are to be designed to meet Seismic Design Category B requirements. Per NIST GCD 11-917-12, seismic upgrades are not required due to the building use and location.

8. Flood Mitigation

The building is not located in a flood zone per the FEMA National Flood Hazard Layer (NFHL) Viewer.

From the Flood Insurance Study: FEMA, Volume 1 of 5, Wayne County, Michigan, October 21, 2021, revision, the historic flood elevation of the nearby Detroit River is 574.16 feet. Per the original D3 Basement Plan, the garage floor elevation is 598.25 feet at a floor drain. The lowest point of the basement floor is more than 24 feet greater than the historic flood elevation. Thus, flood resistant design and construction is not applicable to this project.

9. Physical Security Performance

Blast, progressive collapse, and vehicle ramming are beyond the scope for this project.

10. Live Loads

P-100 allows for 15 pounds per square foot (psf) of the 100 psf minimum floor live load for public spaces to be attributed to partition loads. Considering the nature of the entry spaces in this project, the new floor at the north entrance is designed for 100 psf public live and 15 psf “build out” loads.

IBC requires a minimum of 5 psf be applied to all interior partition walls.

11. Planned Design Methods

Conventional construction materials are planned to be used in this project.

Concrete designs are in accordance with American Concrete Institute Reinforced Concrete Design (ACI

318), 2019 edition.

Concrete Masonry design is in accordance with The Masonry Society Building Code Requirements and

Specification for Masonry Structures (TMS 402/602), 2016 edition.

Structural Steel is in accordance with American Institute of Steel Construction Steel Construction Manual

(AISC), Fifteenth edition. Both allowable stress design (ASD) and load and resistance factor design (LRFD) methods were employed. Where LRFD is used, floor vibration is reviewed. General serviceability

(deflection) limits are per IBC maximum limits.

Historic Preservation is considered in the structural design to minimize any effect on the historically significant features.

Lafayette Boulevard Entrance

Exterior Ramps and Stair

1. Geotechnical Investigation

G2 Consulting Engineers completed a geotechnical investigation, and their report and boring logs were provided to us.

At three locations in the sidewalk along Lafayette Boulevard, borings extended 5 foot below existing grade and were completed with a hand auger. The soils are described as silty clays and sandy clays at the depth of the ramp and stair foundations. Gravel, brick and wood debris is present within the bearing soils of the centermost boring. Organic soils (maximum content of 1.8%) are present in the anticipated bearing soils in the eastern and centermost borings. Water was reported at the 4.5-foot depth at the westernmost boring.

The unconfined compression strength of the soils is stated to be 1500 psf to 2500 psf, depending upon location. The completed soil borings extend to the bottom of footing elevations due to hand auger limitations.

The provided minimum 1500 psf allowable soil bearing pressure may allow for conventional, reinforced concrete foundations. However, the organic content and use of uncontrolled fill material observed at the centermost boring are generally considered unsuitable bearing materials and may cause greater settlement than desired for the access ramp and stairs. Removal and replacement of these materials or the installation of deep foundations (e.g., helical piers, micro-piles) would be necessary to ensure long-term performance of grade-supported foundations, however, each of these options are anticipated to be cost-prohibitive. Although there is risk that the new ramp and stair may settle due to the presence of the organic and fill materials, the geotechnical engineer advises the likely settlement will be minimal because the new, additional loading is minimal. This risk can also be mitigated by using a mat foundation system to distribute the load over a wider area.

2. Structural Systems

The new structural slab system is a supported slab system with a void space located below the slabs. The slabs consist of elevated, reinforced, cast-in-place concrete slabs that will require forming. A metal deck form/profile is provided in the current design with a wood-formed profile provided as an alternate. The slab is designed to support an additional 5-inch normal weight concrete topping slab to accommodate a wearing surface, snow-melt system, and waterproofing system. The slab is proposed to span in the direction of the ramp slope between intermittent beams. The intermittent beams are proposed to be supported at a stem wall at the exterior and at a column line nearer the building exterior wall. As a long-term maintenance concern, the long-term use of de-icing chemicals on the slab can eventually migrate through the waterproofing and slab system and cause corrosion of the embedded steel. The underside of the slab will not be easily accessible for inspection/observation/repairs.

The existing stairs at the entrance are to be modified to accommodate the intersection of the existing stairs with the new ramp wall and slab system. Document review efforts revealed that the stair support consists of concrete brackets extending outward from the basement wall/grade beam of the building. A thin structural slab spans between the brackets and supports the stepped concrete infill and granite treads. Portions of this existing support will be removed to allow for the new construction to occur.

Temporary shoring of the existing structural slab will be required to allow for bearing of the existing structural slab on the new ramp foundation wall.

The proposed foundation of the ramp consists of a new mat foundation bearing on the existing soils and located below minimum frost depth. The foundation design assumes an allowable bearing pressure no greater than 1500 psf based upon the geotechnical engineer’s recommendations. Based upon document review, the grade beam of the north wall of the building extends an estimated 9-feet below the basement floor elevation. Additional surcharge loading on this grade beam is incidental and not a structural concern.

Construction or control joints are used along the length of the ramps and stairs and at slab transitions between existing structure, landings, stairs, and ramps. Unbalanced grade conditions on either side of the stem walls are minimal. Guardrail loads per ASCE 7 are considered where applicable. Rail anchorage to the concrete stem wall is coordinated with Architectural.

Interior Modifications

1. First Floor Modification

New structural steel lintels at proposed masonry wall openings in the vestibule are provided. Temporary shoring to install these lintels and the upper-level stair well wall(s) above Closet 128-C (per original drawing D213) may be required prior to demolition.

Approximately 155 square feet of the floor of Closet 128-C will be demolished. The existing concrete floors in this area consist of a reinforced concrete tee-joist/slab with non-structural clay tile infill. The existing concrete floor is supported on concrete encased steel beams. In the area of demolition, the structural steel is mainly secondary framing for the stair above. The partial removal of the existing slab does not affect the remaining structural members.

A new floor structure will be provided at the -4’-6” finish floor elevation of the vestibule and loggia floor.

The new structure consists of a composite metal deck with reinforced concrete infill bearing on a new structural steel grillage supported on two new columns and foundations and the existing steel. We considered supporting the new slab on the existing concrete-encased steel beams, however, our structural review showed that the demand-to-capacity ratios of the existing beams with the additional load were in excess of 1.0; meaning that strengthening of the existing steel beams would be required. To avoid the complexity and expense of exposing and strengthening the existing beams, a nearly independent structural steel grillage support system was provided to support the new slab.

The steel grillage system at the –4’-6” finish floor elevation consists of three W12 beams spanning east-west: north, center and south. These beams will be supported on new W12 beams at the east and west ends of the subject area. At the south end, the new beams will connect into existing steel framing; at the north end, new steel columns on new isolated pad foundations will support the northeast and northwest corners of the subject area. The column installation also provides some flexibility in the field to locate the new structural members. The design intent is for the north beam to be as tight to the interior surface of the north wall in the basement space as possible to allow a new masonry wall to replace the existing

I18x18.4 beam located at the first-floor structure level above. The center beam is to be located at the north end of the lift/edge of where the existing clay tile walls below the stair are to be removed. The south beam can be adjusted within reason to meet existing conditions. Removal of the concrete encasement will be required for direct connection to the structural steel at the two southern corners of the subject area.

The concrete slab will span north-south between the new steel grillage beams and is comprised of 3-inch concrete atop a 2-inch composite metal deck, for a total of 5-inches in new slab thickness. The northern bay of the new floor infill is designed to support a 3-inch topping slab to create the “pit” for the new lift installation in the southern bay.

From this steel grillage, three columns extend up to support the existing first-floor structure, stair framing and perimeter walls to remain. One column will support the west existing W10 that is to be partially demolished for the new corridor; and two columns will support a new W8 beam that will support the remaining floor structure, wall, and stair system above the 0’-0” finish floor level.

The design attempts to consider constructability concerns including temporary shoring and the feasibility of installing the steel-to-steel connections, however, modifications may be required to accommodate actual field conditions encountered during construction.

All new steel and existing steel exposed for this work is to be fire protected. Architectural scope of work specifies new fire protection and UL rated assemblies.

2. Glass Partition Walls

Structural support for the glass partition walls, including those for the queue and the guard booth, consist of steel moment frames anchored to the existing floor system. Moment frames consist of continuous horizontal hollow structural steel (HSS) members welded to the columns with complete penetration welds.

The new HSS steel columns are either 2-1/2 inch square sections or 5x2-1/2 inch rectangular sections, depending upon location. The vertical profile of the horizontal member will maintain the 2-1/2 inch dimension on the elevation of the glass walls. Field welding of the moment frame structure will be required for assembly. The glass will span vertically between the first floor and the top horizontal member at the queue location. At the guard booth, the horizontal members are located below the planned counter space, slightly less than three-foot above the finish floor surface.

The column baseplates will be anchored to the existing first-floor topping slab. At the vestibule framing, the top of the new glass wall column will extend above the top of the original steel column. Brace or strut members securing the new column will bear on an existing checkered steel plate diaphragm located above the vestibule ceiling. The location of these braces will require field coordination and design review.

At select locations, the columns are to be braced to interior corridor partition walls. Connections of the interior corridor wall cladding systems are unknown; thus, the design assumes the cladding will be removed at anchorage locations for the installation of new structural connections. If, during construction, the existing cladding connections can be verified, they may prove suitable to support the new brace loads as the design loads are less than 400 pounds in all locations.

In the vestibule, the new glass elements are to be secured to the vestibule floor and a new steel channel spanning between the existing steel columns to accept the top of the glass partitions.

Fort Street Entrance

Structural support for the glass partition walls, including those for the queue and the guard booth, consists of steel moment frames anchored to the existing floor system. Moment frames consist of continuous horizontal HSS members welded to the columns with complete penetration welds. The new

HSS steel columns are 2-1/2 inch square sections. Field welding of the moment frame structure will be required for assembly. The glass will span vertically between the first floor and the top horizontal member at the queue location. At the guard booth, the horizontal members are located below the planned counter space, slightly less than three-foot above the finish floor surface.

The column baseplates will be anchored to the existing first-floor topping slab. At the vestibule framing, the top of the new glass wall column will extend above the top of the original steel column. Brace or strut members securing the new column will bear on an existing checkered steel plate diaphragm located above the vestibule ceiling. The location of these braces will require field coordination and design review.

At select locations, the columns are to be braced to interior corridor partition walls. Connections of the interior corridor wall cladding systems are unknown; thus, the design assumes the cladding will be removed at anchorage locations for the installation of new structural connections. If, during construction, the existing cladding connections can be verified, they may prove suitable to support the new brace loads as the design loads are less than 400 pounds in all locations.

In the vestibule, the new glass elements are to be secured to the vestibule floor and a new steel channel spanning between the existing steel columns to accept the top of the glass partitions.

Vehicle Sallyport

1. Geotechnical Investigation

G2 Consulting Engineers completed a geotechnical investigation, and their report and boring logs were provided to us.

At three locations at the basement level, borings extended 1.5 feet below the top of the basement slab and were completed with a hand auger. The auger was refused at each location at the 18-inch depth. At the westernmost boring, a 10 1/2-inch deep, reinforced concrete slab was discovered over mixed debris of sand, wood, and rubble. At the newer concrete ramp near Elevator 9, the slab depth was determined to be

8 1/2-inches over vapor barrier and 4-inches of pea gravel. At the third location, east of Elevator 9, two concrete slabs were identified; the upper slab is of 4-inch depth and the lower slab is at least of 9-inch depth (the bottom of the concrete was not recorded). A 1/4-inch void is present between the two slabs at the third boring location.

The soil borings show evidence of previous alterations to this space with multiple layers of concrete slabs and varying construction assemblies. The slabs of greater depth accommodate loading of the current parking and utility space uses of the building. The top slab of the double slab system east of Elevator 9 is likely a replacement for the original wood block flooring system.

2. Masonry Wall Construction

The new masonry partition walls are to be grouted solid and reinforced with reinforcing steel at no more than 24-inches on-center in both directions. The new walls are to be anchored into the first-floor structural slab and the slab-on-ground of the basement level. The anchorage of the new walls to the first-floor structure will allow for deflection of the first-floor structure without loading the new masonry walls. A concrete curb is provided to improve constructability of the glazed CMU at the existing sloped floor locations. Header beams will be provided at the west wall of vehicle sallyport to support the masonry wall above the garage door opening and in the smaller, man-door openings. Openings in the masonry walls will be provided to accommodate the existing utilities hung from the underside of the first-floor structure.

The connections of the walls to the floor slabs are designed for interior wind and live load forces. Due to the minimum construction requirements listed in Publication 64, the walls as constructed will resist the lateral wind loading if adequate anchorage is provided at the top and bottom of the wall.

3. Masonry Wall Foundation Support Options

The new masonry walls are to be supported on the existing concrete slabs-on-ground. Control joints are required where the new walls extend over edges of existing foundations.

As discussed above, east of Elevator 9, the soil boring discovered a ¼ inch void space between two concrete slabs. WJE suspects the lower slab is the original concrete slab-on-ground of the loading dock in this area and the upper slab is a newer infill slab to replace the wood block flooring system observed elsewhere in this basement space. WJE sounded the concrete slab-on-ground in this area by chain dragging and observed no discernable difference in the sound created. The void may continue throughout this area. The cause of the void space is undetermined. If the new CMU walls are to bear on the existing concrete slabs, there is a possibility the walls will settle due to the presence of this void space. WJE is recommending the top slab be removed and replaced for the lengths of the new CMU walls, thereby eliminating the void space. Pressure grouting the void is not recommended as the extent of the void is unknown.

The 1932 construction documents indicate the original masonry partition walls at the basement level are supported on conventional strip foundations. No significant distress in these masonry walls was observed during WJE’s site visits, indicating that conventional foundations should be adequate to support the masonry walls.

Second Floor Addition of Sally Port and Cell Rooms

The original architectural and steel construction drawings generally depict a steel beam located below the masonry partition walls throughout the building. In the original architectural drawings, the subject area of the second floor was labeled “work room” and is a large open space encompassing nearly the footprint of the second-floor level. The original design live load is unknown. Based on the original architectural drawings, many of the existing second-floor level partition walls were added after the original construction.

Based on review of the Prospectus Design Project calculations (Final Concept Design Calculations by Ruby and Associates, Inc., 2015), the existing second floor structure would require strengthening to support proposed solid grouted concrete masonry walls reinforced in each direction at 24-inches on-center. An alternative “truss” wall system (17 psf) was proposed which weighs significantly less than the fully grouted, heavily reinforced concrete masonry walls (70 to 93 psf). Proprietary ceiling systems are also proposed over the cell rooms and corridor between the cell rooms. Over the cell rooms, the proposed ceiling has a

3.53 psf self-weight, and over the corridor between the cell rooms, the proposed ceiling has a 7.73 psf self-weight. The ceiling over the corridor is an accessible ceiling; up to two persons may access the area at one time.

1. Structural Steel Review

In comparing the existing loads to the proposed loads, the summation of the new partition loads in the subject column bays are less than the summation of the existing partition loads which are to be demolished. Specifically, we reviewed the steel beam, labeled 131 on the original structural steel erection drawings, by comparing the proposed new demand loads with the existing demand loads of the approximately 16’-2” tall existing masonry and granite clad partition wall to be removed. Installation of the new “truss” partitions and ceilings results in a lower demand on Beam 131 than what is currently present.

By inspection, the remaining beams supporting this cell room and sallyport area will have less demand required of them than they have currently. Thus, the existing structural steel of the second-floor structure can support the “truss” wall and ceiling systems.

2. Concrete Slab Review

There is conflicting available information concerning the existing dimensions and reinforcement of the concrete tee-joist system in this area of the building. The Prospectus Design Project calculations considered a 16’-8” long joist that was field measured as 8-inches in depth, with 20-inches clear space between the joists and two No.4 reinforcing bars at the bottom of the tee. The narrative associated with these calculations, however, describes the depth as 10-inches. WJE field verified the second-floor framing in an area of the building and found the joists to be board-formed, 5-inches in width, 9-inches in depth and spaced at 25-inch intervals. WJE did not verify embedded reinforcement. WJE also found that the first-floor framing in other areas of the building varied. The clay-tile formed first-floor joist depth was measured to be 6-inches, with a 12-inch clear spacing between the joists and a single, smooth No.6 bar at the bottom of the tee in one area; in another area, a No.5 bar was exposed in the bottom edge of a clay-tile formed, 8-inch wide by 8-inch deep joist spaced at 22.5-inches on center. The capacity of the second-floor concrete tee-joist and slab in the subject area cannot be determined without specific information on the dimensions of the framing and the size of the reinforcement in the area under review.

The specific joist spans reviewed are 18’-0” long spans located within the existing second-floor level conference room located south of Elevator 9 and the column bay directly north of the conference room.

There is a significant amount of conduit suspended from the underside of the floor structure in this general area. The existing loading on the subject joist is limited to the second-floor live load, the equipment suspended from the floor structure, architectural finishes, and the self-weight of the structural member. Adding the new partition loads along approximately half the span of the joists increases the demand on the individual joists approximately 16 percent, depending on the magnitudes assumed for live load and equipment loading, and noting that the calculated demand is more than double that of the calculated capacity assuming two No.4 bars are located within each joist.

Local considerations, which may not be able to be fully determined until construction, relate to the placement of the wall in relation to the stem of the tee-slab as constructed. If the existing joists are spaced with 20-inches clear between the stems as noted in the Prospectus Design Project calculations and field measured in another area, the wall will be supported by the 2-inch structural slab spanning between the stems and strengthening will be required. To strengthen for this localized concern, without damaging the historic ceiling finish or altering the conduit below, the existing 5-inch thick topping slab will be removed on either side of the wall and replaced with a new reinforced concrete slab of the same thickness to transfer the weight of the partition wall to the stems of the adjacent tees.

Consideration was given in the analysis to sharing of the load with the adjacent joists, accounting for the partition load in lieu of the floor live load (people cannot stand and objects cannot be placed where the wall is located), and the use of the spaces the partition walls define as cell rooms (P100 requires 100 psf live and partition loads on all floors, but ASCE 7-16 requires only 40 psf live load in the cell rooms). Based on the most conservative available information, we recommend sharing the load among a minimum of three joists where the new walls which are parallel to the span of the tee-joist floor structure. This recommendation could possibly be reduced if the geometry of the concrete slab system and size of the steel reinforcement in an accessible location of the subject area is verified during construction. Testing for the yield strength of the reinforcement steel which is to be removed for the new access and lift framing at the LaFayette entrance; and testing for the compressive strength of the concrete through petrography of concrete cores may also provide increased calculated capacities of the existing structure without further reinforcing or strengthening.