HMSG ENVELOPE BOD-100CD FINAL BACKCHECK-1821115.pdf

SMITHSONIAN FACILITIES

PROJECT NO. 1821115

MARCH 12, 2020

HMSG ENVELOPE REPAIRS

BASIS OF DESIGN

7TH ST & INDEPENDENCE AVE SW

WASHINGTON, DC

CallisonRTKL

PROJECT TEAM DIRECTORY

SMITHSONIAN INSTITUTION

Office of Planning, Design & Construction 600 Maryland Avenue SW Suite 5001 Washington, DC 20560

ARCHITECT

CallisonRTKL Inc.

2101 L Street NW Suite 200 Washington, DC 20037

STRUCTURAL ENGINEER

Silman 1053 31st Street NW Washington, DC 20007

BUILDING ENCLOSURE CONSUTANTS

Simpson Gumpertz & Heger Inc.

1625 Eye Street NW Suite 900 Washington, DC 20006

MEP ENGINEER

James Posey Associates, Inc.

3112 Lord Baltimore Dr.

Windsor Mill, MD 21244

SECURITY DESIGNER

M2H Protection 5100 Buckeystown Pike Suite 250 Frederick, MD 21704

CallisonRTKL

CONTENTS

I. Executive Summary

II. Physical Building Condition A. Building Enclosure

B. Structure

C. Mechanical

D. Electrical

III. Building Enclosure A. Applicable Codes and Design Criteria

B. Proposed Enclosure Systems

IV. Structural Systems A. Applicable Codes and Design Criteria

B. Proposed Systems

V. Mechanical Systems A. Applicable Codes and Design Criteria

B. Calculations

C. Proposed Systems

VI. Electrical Systems A. Applicable Codes and Design Criteria

B. Proposed Systems

VII. Security Systems A. Applicable Codes and Design Criteria

B. Proposed Systems

VIII. Appendix List of Applicable Codes, Standards, & Guidelines

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I. EXECUTIVE SUMMARY

The Hirshhorn Museum and Sculpture Garden (HMSG) Design for Building Envelope Repairs project includes the following scope:

• In-kind replacement of the precast façade panels along the outer face of the cylindrical building form,

• In -kind replacement of the balcony glazing system, and

• Replacement of the roof assembly.

PROJECT CONTEXT

The Hirshhorn Museum and Sculpture Garden (HMSG) serves as the Smithsonian Institution’s (SI) museum of modern and contemporary art. The iconic museum structure is located on the National Mall at the northwest corner of 7th Street and Independence Avenue, SW, and the Sculpture Garden is north of the museum across Jefferson Drive.

The museum was designed by Gordon Bunshaft of Skidmore, Owings, and Merrill and opened to the public in 1974. The museum has been determined eligible for individual listing in the National Register of Historic Places. The HMSG is a contributing resource to the National Mall Historic District, listed in the National Register.

The building is a three-story, cylindrical volume, 231 feet in diameter, floating14 feet above a paved plaza on four concrete piers and minimally connected at grade by a small fully glazed lobby with escalators to upper and lower levels. The building’s cylindrical volume is open to a central courtyard which is slightly offset from the center of the drum. Within the courtyard, a large, shallow, bronze fountain is similarly offset from the center of the courtyard. The main museum cylinder is elevated above a pedestrian plaza, located over a larger below-grade space. The building is clad in precast concrete panels with a pink granite aggregate (originally intended to be travertine but modified during the design phase). The featureless outer shell, punctuated only on the north by a viewing balcony, is contrasted by the walls of the inner courtyard, which are divided into equal, glazed cells, lighting the interior ambulatory galleries.

Now forty-five years old, the Hirshhorn Museum is in urgent need of enclosure repairs due to the effects of aging, the weather and the design deficiencies of the original enclosure systems.

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EXECUTIVE SUMMARY

BUILDING ENVELOPE TESTING AND FINDINGS

Recently, SI undertook a phased multi-year testing project from 2016 to 2019 to assess the conditions of HMSG. The HMSG Envelope Investigations and Temporary Repairs Scope included the following:

• Exterior Panel Investigation,

• Exterior Panel Monitoring,

• Fenestration Investigation,

• Balcony Leakage Investigation and Temporary Repairs,

• Plaza Assembly and Waterproofing Investigation,

• Roof Assembly Investigation,

• Testing of the Sculpture Garden Walls,

• Testing of the Museum Plaza Walls,

• Level 2 Floor Slab Condition Assessment,

• Structural Post Tension Tendon Testing, and

• Art Lab Temporary Leak Mitigation.

These investigations revealed several issues:

• The precast façade panels along the outer face of the building cylindrical form have compromised lateral attachments at many locations. The Design Team observed backside cracking and spalling on a number of the façade concrete panels adjacent to the bearing surface on the relieving angle. In 2018, SI initiated a façade monitoring effort to address life safety concerns prior to the building enclosure repair. Field observations also revealed the following installation deficiencies:

› Field chipping and cutting along the backs of the precast panels during construction.

› Small bearing areas at the relieving angles of the large panels.

› A defect in an out-of-plane load resisting wedge insert, likely a result of a manufacturing defect.

• The existing enclosure system completely lacks a vapor, air, and water resistive barrier and insulation. This condition results in ongoing water infiltration around balcony cold joints and severe condensation during cold months of the year along the interior side of the solid concrete structural exterior wall. During the Level 2 floor slab condition assessment, the Design Team determined that due to the significant seasonal condensation and balcony water infiltration, approximately 15 – 20% of the Level 2 insulation is wet. Moisture is trapped inside the insulation layer between the structural and topping slab with limited ways to drain or evaporate.

The trapped moisture is causing blistering of the epoxy paint flooring finish, seepage through the structural slab, and ongoing staining and paint blistering

CallisonRTKL | 3 on the underside of the exposed Level 2 floor slab above the museum plaza. The Design Team conducted extensive studies, including performance simulations of the wall assembly, and confirmed that insulation should be located inside the cavity between the precast facade panel and structural concrete wall.

• Condensation and water infiltration are causing constant deterioration of the gallery plaster walls and the Level 2 gallery floor assembly. These conditions negatively affect HMSG programs and exhibits. Furthermore, these conditions present a potential long-term concern for the Level 2 structural system.

• The complete lack of insulation results in poor building energy performance. In fact, HMSG is the most inefficient of the Smithsonian museum buildings for energy consumption (based on BTU/SP).

• The roof assembly of the building is at the very end of its useful life and requires replacement.

PROJECT GOALS

This project will address public and collection safety, energy conservation, and structural deterioration due to water infiltration and condensation. All component improvements are to protect a world class museum collection.

• Improve building envelope performance to reduce energy consumption and protect museum collections with a stable environment. Improvements to the envelope to meet prescriptive energy codes requirements.

• Prevent water infiltration and condensation on the interior of the building.

Improvements to the envelope to protect the core building structure.

• Closely match the character and appearance of the existing precast concrete panels.

• Closely replicate the existing profiles of balcony glazing. New glazing to have improved thermal performance and improve museum lighting conditions.

• Improve safety with upgraded precast and glazing attachments to meet blast requirements. New attachments to resolve installation deficiencies and provide improved access for repairs at the balcony.

• Improve balcony doors to meet accessibility requirements.

PROPOSED CONCEPT

The Design Team worked closely with HMSG, Smithsonian Facilities Office of Planning Design and Construction staff and preservation experts to define the most appropriate enclosure repair approach. A range of design options were developed. The study concluded that the problematic original design and installation of the anchor attachments, including shimming of the panels and other field modifications, has resulted in cracking, spalling, deterioration of the concrete along the relieving angles and rusting of the anchors. Reuse of the existing panels would present a significant risk

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EXECUTIVE SUMMARY

in the extensive conservation treatments for crack repair, and risk in damaging the very large (up to 14’ -3” by 7’6”) panels upon removal and reattachment to a more robust structural attachment system to meet blast requirements.

Proposed design concept includes the following:

• In-kind replacement of the existing outer façade panels with new precast panels to match the existing material. The face of the new façade will be offset 3 inches to allow installation of the waterproofing and insulation to resolve enclosure deficiencies. Design of the joints will be consistent with the existing design.

• In-kind replacement of the balcony glazing system. The proposed new glazing system will closely match the existing glazing system profiles. Balcony repair will include balcony waterproofing repair and replacement of the balcony concrete pavers (installed in 2017 during temporary a leak repair project).

• Replacement of the roof assembly system. The roof assembly is not visible from the street level and the roof replacement project will not result in any changes of the non-visible rooftop equipment profiles.

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A. Building Enclosure

WALL ASSEMBLY

The exterior facade consists of a cast-in-place concrete cylinder which is architecturally exposed at the Level 2 and roof parapet levels, with architectural precast concrete panels in between. The outward- facing elevations of the cylinder include a small area of glazed curtain wall overlooking a concrete balcony that cantilevers from Level 3 of the north elevation. The interior-facing facade of the cylinder consists of floor-to-ceiling curtain wall and precast spandrel panels. The Phase 1 exterior wall scope of work pertains to the outward-facing elevations of the cylinder clad with precast panels, the north- facing balcony, and adjacent glazed curtain wall (Photo 1).

PHOTO 1: OVERALL VIEW OF HIRSHHORN MUSEUM’S NORTH FACADE

II. PHYSICAL BUILDING CONDITION

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PHYSICAL BUILDING CONDITION

The existing exterior wall construction consists of a 2 ft -8 in. thick cast-in-place cylinder-shaped cast-in-place reinforced concrete backup wall that is supported by a ring beam on Level 2 and four concrete piers on the plaza level, referred to as Level 1. The exterior walls consist of, from interior to exterior:

• Existing concrete backup wall, 2 ft-8 in. thick;

• Existing air cavity, thickness varies ( min field verified dimension is 3/4”)

• Precast concrete panels, thickness varies, approximately 4 in. thick.

The precast panels have an exposed aggregate finish and are approximately 7 ft-6 in.

wide, with alternating small (4 ft-0 in. tall) and large (14 ft-3 in. tall) panels. In plan, the panels have a flat back surface and curved face. The joints of the panels are filled with sealant, and the panels are arranged in a running bond pattern. The exterior face appears cylindrical in shape, but after analysis of a point cloud generated from a 3D laser-scan of the building, the exposed facade surfaces of the building are neither circular in plan nor completely vertical in section. Prior investigation by Simpson Gumpertz & Heger (SGH) also determined that the cast-in-place concrete backup wall has an irregular geometry that, combined with the geometry of the precast panels, creates a cavity that varies in depth between at least 4-1/2 in. to less than 1 in. (Photo 2).

PHOTO 2: VIEW OF EXTERIOR WALL ASSEMBLY WITH REMOVED PRECAST PANEL

The exterior wall assembly does not have a weather barrier membrane and does not have insulation. Prior investigation by SGH determined that the lack of insulation contributes to wintertime condensation on the interior surfaces of the exterior walls.

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The cladding anchors on the exterior of the drum consist of galvanized steel strap anchors for lateral support and relieving angles at the bottom of the large panels for gravity support. The small panels are interlocked with the large panels with stainless steel pins and utilize strap anchors for both their lateral and gravity supports. The relieving angle bolts are supported by wedge inserts cast into the concrete backup wall.

The bottoms of the large panels are laterally supported by rebar welded to the toe of the relieving angle and pocketed into the panel. Prior investigation by SGH found that some of the panels lack competent lateral attachment to the building structure because they have limited bearing and/or spalled concrete heels at the relieving angles. Some of the panels have evident lippage in which one panel protrudes, often up to a 1/2 in. or more, relative to the adjacent panel. Refer to Section 4.4.1 - Building Envelope (pp. 65 to

106) of the Building Envelope Study dated 07 November 2016 for the Hirshhorn Museum and Sculpture Garden Restoration and Repair of Building Envelope and Plaza project (SF Project No. 1421111) for further information.

BALCONY GLAZED CURTAIN WALL

A cast-in-place concrete balcony cantilevers from Level 3 at the north facade of the museum. The concrete balcony structure and concrete railing have an exposed aggregate finish similar to the precast panel cladding. Precast concrete pavers cover the top surface of the balcony, which is separated from the interior space by floor-to-ceiling curtain wall. The balcony curtain wall system is recessed approximately 3 ft from the exterior face of the precast panel cladding on the main elevation, which creates return walls at the ends of the balcony and a soffit above the curtain wall, both which are also clad with precast panels.

The balcony curtain wall separates the balcony from the interior and is a stick-built curtain wall set in a window-wall configuration (Photo 3). The curtain wall is faceted to mimic the curve of the building and extends slab-to-slab with aluminum mullions and exposed structural neoprene glazing gaskets (SNGG). Electric heaters span between the vertical mullions of the balcony curtain wall and are clad with curtain wall trim.

PHOTO 3: OVERALL VIEW FROM THE INTERIOR OF THE BALCONY AND CURTAIL WALL

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BALCONY WATERPROOFING

The balcony waterproofing terminates on the face of the metal sill flashing, which is integrated with the curtain wall sill SNGG (Photo 4). The balcony waterproofing is a fluid-applied waterproofing membrane which turns up the concrete curb around the perimeter of the balcony but is not integrated with the base of the return wall. The waterproofing membrane is covered with a protection sheet and concrete pavers supported on pedestals sit atop of the waterproofing assembly.

PHOTO 4: VIEW OF BALCONY WATERPROOFING BELOW CONCRETE PAVERS

ROOFING ASSEMBLY

The museum is covered by a low-slope roof that is supported by the coffered concrete roof slab. The roof is internally drained with four area drains on the main roof surface and one drain on the elevator overrun, which extends above the elevation of the main roof. The roof slab is slightly sloped toward an interior concentric valley that connects the four main drains and has kite-shaped crickets between each drain. The roof is covered with a gravel-surfaced built-up roofing system and the tapered insulation below the roofing membrane follows the same sloping pattern of the roof slab and adds to the roof surface slope. The roof is surrounded by short concrete parapets along the exterior and courtyard perimeters. The parapets are integral with the cast-in-place concrete band of the exterior walls, and the roofing membrane terminates on the vertical face of the parapets (Photo 5). A post-installed safety tie-off system is fastened to the interior parapet, but it is currently not a certified or functioning system and therefore not in use

CallisonRTKL | 9 by SI. There is access to the roof from Level 4 with a ladder and a roof hatch. Rooftop mechanical equipment is limited to one air-handling unit and two exhaust fans. Level 4 has no interior ceiling finishes and the concrete coffers are exposed in the offices and collections storage spaces below.

The existing roof assembly consist of the following components, from interior to exterior:

• Existing concrete roof deck, 5 to 7 in. thick;

• Two-ply asphalt built-up membrane vapor retarder, unknown thickness;

• Flat polyisocyanurate insulation, approximately 2 in. thick;

• Tapered polyisocyanurate insulation, thickness varies;

• Perlite cover board, 1 in. thick;

• Four-ply asphalt built-up roofing with gravel surfacing, unknown thickness.

PHOTO 5: ROOFING TERMINATION ON EXTERIOR CAST-IN-PLACE CONCRETE PARAPET

B. Structure The structure consists of a 3 story ‘O’-shaped structure with solid exterior perimeter wall and a curtain wall enclosure facing an interior courtyard. The exterior of the building is uniform with the exception of a balcony facing north on Level 3 (Photo 6).

The site is bounded by tall concrete walls creating a square enclosure concentric with the building’s circular plan. Level 1 is an open rectangular plaza with the exception of four sculptured structural cores spaced equally around the radius. The soffit below Level 2 expresses the structure where the loads transfer to the sculptural cores. The Lower Level is non-concentric with the structure above and extends to the south east significantly beyond the footprint of the cylinder above. Where no Lower Level exists below the Level 1 plaza, a framed slab cast against grade and supported on caissons supports the plaza. A portion of this slab appears to have been removed during the 1991 Plaza Resurfacing project.

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A characteristic feature of the design is the use of exposed aggregate concrete in the exposed cores as well as the precast exterior panels and site walls.

PHOTO 6: EXTERIOR BALCONY

FOUNDATIONS

The building foundations consist of a mix of shallow spread footings within the footprint of the Lower Level and belled caissons at the framed Level 1 plaza slab outside of the footprint of the Lower Level. Large pile caps support the columns coming down at the four cores. Foundation walls measuring 1-ft thick surround the Lower Level footprint.

The perimeter concrete walls are supported by wall footings or caissons. Based on the notes in the original building construction drawings, the design bearing value for the spread footings and caissons was 6 ksf.

SUPERSTRUCTURE

The plaza, referred to as Level 1, is supported on columns typically spaced at approximately 20 feet by 24 feet. The Level 1 floor framing consists of concrete pan joists spanning east west. The joists are supported by girders spanning north south between concrete columns. In order to accommodate a column free space in the Lower Level between grids 8 and 5, a one-way concrete slab spanning between post tensioned beams was used in place of the pan joist system (Figure 1). At the south side of the plaza, an opening is framed out for the escalator. Additionally, the slab is thickened in an area spanning diagonally from opposite cores and has reinforcing tie bars. In the original design there was a framed opening in the plaza just north of the foot print from which a set of stairs came up to the Level 1 plaza. These stairs ran underneath Jefferson

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Ave and provided access to the sunken sculpture garden from the plaza. During the 1991 Plaza Resurfacing project the opening was infilled and a sculpture was placed over the former opening. The stairs remain in place but can only be accessed from the sculpture garden.

FIGURE 1: ONE-WAY SLAB SPANNING BETWEEN POST-TENSION BEAMS

The Level 2 framing is a large structurally expressed concrete transfer grid supported by four stair core wall systems located at northeast, south-east, south-west and north-west corners of the building. The transfer framing consists of a set of reinforced concrete circumferential and radial beams and two-way reinforced concrete slabs between the beams (Figure 2). The beams span between a ring girder at the inner diameter perimeter and a full height concrete building wall at the outside diameter perimeter. The inner ring beams and the outer exterior walls are centered around different foci creating unsymmetrical floor plans.

The Level 2 structural system transfers the loads from the higher levels to the four core wall frames below. Each core consists of two fin walls which are tapered vertically and in plan. The core walls bear on concrete walls at Level 1 and a pile cap below the Lower Level.

The upper levels are supported by the reinforced concrete columns resting on the innermost ring of the Level 2 framing and a 2-ft 8-in thick continuous reinforced concrete wall resting on the outermost ring of the Level 2 framing. Level 3, Level

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4 and the roof level consist of radially oriented, grouted post-tensioned concrete beams spanning between the innermost reinforced concrete ring beam and the outer continuous wall. A one-way concrete slab spans between the rectangular post tensioned joists. It appears that the post tensioned beams are detailed with a horizontal sliding support at the inner ring beam end and doweled in with heavy rebar at the outer perimeter concrete wall. There are also intermediate ring distribution beams for torsional stability (Figure 2). At Level 3 and Level 4 there are framed openings for the escalators. All other access to the upper floors occurs through stairs and elevators in the four cores.

Special detailing measures were taken to assure proper distribution of post-tensioning forces within the floor system. Neoprene pads were installed at the end of the beams framing into the inner and at the roof and Level 3 beams there are Teflon bearings on every second beam. This is presumed to allow for the compressive posttensioning forces to be accommodated by the beams and not the rings.

FIGURE 2: FRAMING PLANS

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While there is indication of a defined lateral system on the original structural drawings, it is assumed that the Hirshhorn employs concrete shear walls stiffened by the circular shape as Level 3 through roof level have slip connections or are not doweled into the walls. The continuous outer concrete wall acts as a shear wall and is the main lateral force resisting system above Level 2. Below Level 2, the lateral forces are transferred to the core walls and down to the grade level slab and foundation. The Teflon bearings described above also allow for lateral movement in the case of high lateral forces.

EXTERIOR FACADE

The façade of the museum is composed of precast panels along the outer diameter.

These panels have lateral and gravity attachments back to the 2-ft 8-in thick exterior concrete wall. The panels cover the entire façade except for the where the balcony extends out on the north side of the building overlooking the mall. The interior courtyard is primarily glazed with continuous ribbon windows floor to ceiling and precast panel cladding at floor levels and cladding columns that are fully exterior of the glazing system.

The building was designed with different foci for the inner and outer radii. Previous investigations have identified a number of issues with the original panel installation resulting in some existing panels not being adequately supported in their current conditions. Reference 2017 Building Envelope Study for documentation of the existing condition. Large panels are supported for gravity with two clip angles at the base.

These same clip angles provided the lateral support at the bottom of panels by way of a rebar welded to the clip angle and a groove in the panel. Large panels are supported for lateral loads with two strap anchors at the top of panels. Small panels are supported for gravity and lateral at the base from the top of the large panel below by way of shims and a dowel from the small to large panel below. Previous investigations show localized chipping of the substrate wall to allow for panel connections. Original details do not indicate the exact locations of embedded connections, therefore some anchorage locations are unknown.

C. Mechanical

EXISTING SYSTEMS

The existing air handlings units (AHUs) are located in the Lower Level East and West main mechanical rooms. They are multizone, constant volume units with duct mounted reheat coils that serve specific zones throughout the building. For now, the existing units are remaining, but in the future they will most likely be replaced since the current mechanical systems are so energy intensive. There have also been reported temperature and humidity issues, which we believe to largely be due to the fact that all of the AHUs pull air from a common return. Because of these issues and inefficiencies, the existing mechanical systems will likely be replaced in the future.

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D. Electrical

DISTRIBUTION

The existing switchgear date to the original construction of the building in the early 1970’s. They are well-maintained but are approaching obsolescence. They feed two main switchboards, which were manufactured in 1997. The switchboards are also well-maintained and can be expected to operate for at least fifteen more years. Feeder conduits and conductors do not show any sign of damage; however, there are no electrical test records. The electrical closets are crowded; in many closets the working space is less than the safe minimums required by the National Electrical Code. The panels, switches, and transformers in the closets are in good condition, and many have been replaced in recent years.

BRANCH WIRING

Most of the galleries are unfinished spaces, with the ceilings being the exposed structure of the coffer slab above. Much of the wiring for the gallery runs in raceways embedded in the structural slab, e.g. the circuits supplying the receptacles in the Lerner Room and the Level 3 balcony. The conditions of the raceways is unknown.

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III. BUILDING ENCLOSURE

A. Applicable Codes and Design Criteria

• 2018 International Building Code (IBC)

• 2018 International Existing Building Code (IEBC)

• 2018 International Energy Conservation Code (IECC)

• 2018 International Code Council Performance Code for Buildings and Facilities

(ICCPC)

• American National Standards Institute (ANSI) and Single Ply Roofing Industry (SPRI)

› 2013 ANSI/SPRI RP-4, Wind Design Standard for Ballasted Single-ply Roofing Systems

• American Society of Heating, Refrigerating & Air Conditioning Engineers (ASHRAE)

› ASHRAE 90.1, Energy Standard for Buildings Except Low-Rise Residential Buildings

› ASHRAE 55, Thermal Environmental Conditions for Human Occupancy

• American Society of Civil Engineers (ASCE)

› ASCE 7-16, Minimum Design Loads and Associated Criteria for Buildings and Other Structures

A full list of applicable codes and standards for the project is provided in the Appendix.

B. Proposed Enclosure Systems

WALL ASSEMBLY

The original wall assembly functioned as a barrier wall that repelled all water at the face of the precast concrete panel cladding and provided sealant joints to limit water penetration at panel joints. In addition, the solid concrete backup wall, where continuous, provides significant inherent water penetration resistance. As sealant joints between panels have deteriorated, the present-day wall system behaves as a transitional wall system (transitional between a barrier and a rainscreen), where partially deteriorated sealant joints between panels allow an increasing amount of water to

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BUILDING ENCLOSURE

enter the cavity between the cladding and the backup wall. In the current assembly, the water penetration resistance of the wall relies on the thickness and mass of the concrete backup wall to prevent absorption to the interior.

The proposed assembly would alter the behavior of the wall to function as a contemporary rainscreen. In this configuration, the new precast panels and sealant joints deflect bulk water while a new dedicated air and water barrier applied to the backup wall functions as the primary prevention of water penetration. Contemporary rainscreens include flashings to direct water from the wall cavity back to the exterior, and the current design incorporates this philosophy with concealed cavity flashings. The proposed wall assembly (WL-01) will consist of, from interior to exterior:

• Existing interior finishes;

• Existing concrete backup wall, 2 ft-8 in. thick;

• Fluid-applied air, water, vapor barrier, 40 mils dry thickness;

• Semi-rigid mineral wool insulation board, thickness varies, 2 in. to 4 in. thick;

• Air cavity, thickness varies, minimum 1 in. thick;

• Traditional precast concrete panel, typically 4 in. thick.

WL-01: TYPICAL EXTERIOR WALL ASSEMBLY

While not necessary from a performance standpoint, the current exterior wall design will reproduce the location, geometry, and width of the existing panel-to-panel joints to preserve the historic appearance of the facade. The joints will be filled with sealant to match the existing appearance and to limit bulk water entry into the exterior wall cavity. The proposed air and water barrier is vapor-impermeable and, relative to insulation in the wall assembly, will be on the winter-warm side to limit the potential for condensation. The project team confirmed that the hygrothermal performance of the proposed wall assembly is acceptable using computer simulation tools (e.g., WUFI and

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THERM). Due to the large uninterrupted wall areas, the proposed air and water barrier is fluid-applied which can either be spray- or roll-applied to increase the efficiency in application. The air and water barrier should be removed locally around precast panel anchor locations prior to setting the panels to prevent panel rotation. To re-establish the continuity of the membrane, sealant must be applied around the perimeter of the precast panel anchors and over the bolt heads.

Because the existing wall is thermally massive, it takes a relatively long period of time for the exterior wall to either heat up or cool down. During long periods of cold weather, the current wall experiences condensation on the inside surface of the concrete backup wall. The proposed addition of cavity insulation will both limit the potential for condensation and contribute to the overall energy efficiency of the building enclosure.

The proposed semi-rigid mineral wool insulation board is intended for use in a rainscreen application and will be secured to the backup wall with a combination of stick-pins and retaining clips.

To accommodate the addition of prescriptive-level amounts of insulation, the wall cavity grew in thickness, and the overall wall dimension increased outwards by 3 in.

Maintaining existing wall thickness while adding a consistent insulation thickness is not practical, as the project team measured the cavity dimension to be less than 1 in.

in some locations. The 3 in. wall offset will be measured from the current face of the exterior panels, which are slightly skewed in plan and section, as is documented using laser scanning techniques. The proposed precast panels will maintain the appearance of the building’s existing cladding and feature a typical series of staggered smaller and larger panels, with unique panels around the balcony. The exposed aggregate finish and matrix color will match the existing panels and the surrounding exposed cast-in-place concrete, which will be cleaned to restore its original appearance.

BALCONY GLAZED CURTAIN WALL

The existing balcony curtain wall is arranged in a slab-to-slab configuration and utilizes a structural neoprene glazing gasket (SNGG) to capture the four sides of the glazing and fit into the aluminum mullions. The existing curtain wall includes a replacement of glazing (SF project 8345105) and a recent addition of blast film. Thus, the current mullions are T-shaped due to the trim added to the original profile during the blast film project and do not match the original architectural drawings. The frames include split vertical mullions and solid horizontal mullions to approximate the building’s curve with facets. Access to the balcony is through two sets of bronze double-doors. Electric heaters are fit between the vertical mullions and line the interior sill of the curtain wall units. The proposed balcony curtain wall assembly would largely restore the appearance back to the original architectural drawings, which had thinner rectangular horizontal and vertical mullions. In order to match the appearance of the original curtain wall, meet contemporary criteria for blast loading, and provide a practical method of construction, the curtain wall will be a field- assembled, blast-resistant, field-glazed four-sided structural silicone custom steel curtain wall with aluminum trim.

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The proposed balcony curtain wall assembly (CW-02) consists of the following components:

• High-strength stainless steel mullions;

• Aluminum interior trim covers, painted white to match existing;

• Aluminum exterior trim covers, painted bronze to match existing;

• Electric heater and enclosure between vertical mullions;

• Glazed-in metal panel at curtain wall head;

• Glazing assembly GL-01 (see below) adhered with structural silicone.

The bite of the structural silicone glazing required to resist blast loading is 3/8 in. min.

The glazing bite and installation geometry of the structural silicone will require the vertical and intermediate horizontal mullion faces to be 1-1/4 in. wide. A traditional mechanically fastened trim cap is not feasible, as the mullion is not wide enough to accommodate a screw spline or receiver. The proposed system includes a structurally-adhered aluminum trim cap to match the appearance of the profile of the original glazing gasket. A sloped sealant wash or sealant joint should be provided between the glass, behind the trim cover and both should be periodically wept to the exterior.

The basis-of-design for the curtain wall includes welded setting chairs at glass quarter points at the horizontal mullions, and edge blocking at the vertical mullions.

The existing curtain wall experiences condensation on interior glazing surfaces during cold winter months. In order to reduce condensation, the new curtain wall assembly will include double glazing and more powerful heaters to keep near-glass temperatures above the dew point to the greatest extent feasible given the need to fit heating units within existing mullion geometry. Upgrading to a curtain wall with triple-glazing could have further increased the thermal performance of the assembly but would alter the thickness or plane of the existing glass. The project team analyzed the hygrothermal performance of the proposed balcony curtain wall assembly using computer simulation tools (e.g., THERM) and determined under typical assumed operating conditions, the performance is acceptable, but the prevention of all condensation under all conditions cannot be guaranteed.

Two doors provide access to the existing balcony, and the new curtain wall will reproduce the position, size, and appearance of these doors. The door frames will be fastened to the mullions of the surrounding curtain wall. The door, frame, and any other door components will be bronze or covered with bronze cladding. The door finish will be seamless bronze sheet metal. In order to reduce condensation formation on door components, the new assembly consists of a custom bronze door with stiles that are thermally improved. In addition, the doors will include a heat trace cable set within the door stops at the head and jambs to locally raise surface temperatures and reduce the condensation risk. Provision of heat trace is not practical at the sill and consequently the sill will remain susceptible to wintertime condensation.

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The proposed balcony double door assembly consists of the following components:

• Custom thermally-improved bronze door and door frame;

› With C280 Muntz Metal;

› With Statuary Bronze finish;

• Custom bronze ADA door threshold;

• Offset in-ground floor closer for one door leaf;

• Overhead operator for one door leaf;

• Heat trace system clad in bronze at head and jambs;

• Glazing assembly GL-01 (see below) adhered with structural silicone.

The new curtain wall glazing will be improved from the existing glazing to meet blast loads, improve thermal performance, block ultra-violet light passage into gallery space, and meet other envelope performance criteria. The basis-of-design glazing will be an insulating glass unit (IGU) approximately 1- 3/8 in. thick. Although, the new glazing will be slightly thicker than the existing glazing, the location of the exterior plane of the glass will be held constant to closely maintain its appearance.

In order for the museum to utilize the Lerner Room space as exhibit space, the proposed balcony curtain wall assembly, including the doors, must block 100% of UV light to protect the artifacts within the museum. The proposed design includes a special interlayer within the laminated pane that blocks a broad- spectrum of UV-light frequencies. Use of a broad-spectrum UV-blocking interlayer prevents the need for shading devices to prevent UV exposure and preserves the view out to the National Mall.

The proposed balcony glazing assembly (GL-01) consists of the following, from interior to exterior:

• Laminated glass consisting of:

› 1/4 in. Heat-strengthened, low-iron glass;

› 0.06 in. Polyvinyl butyral (PVB) 100% UV-blocking interlayer;

› 1/4 in. Heat-strengthened, low-iron glass;

• 1/2 in. Argon with stainless steel spacer;

• 5/16 in. Fully tempered, heat-soak tested, low-iron glass;

› With Low-E coating on #2 surface.

BALCONY WATERPROOFING ASSEMBLY

The museum has experienced significant leakage through the concrete cold joint between the projecting balcony slab and the concrete backup wall. To address chronic water leakage, replacement of the pavers and fluid-applied waterproofing system occurred between approximately 2008 and 2010; these repairs reduced, but did not eliminate, the leakage. Additional remedial waterproofing repairs were completed in 2017 at limited locations around the cold joint. The Phase 1 scope of work includes

20 | HMSG ENVELOPE REPAIR - BASIS OF DESIGN

removal and replacement of the existing balcony waterproofing membrane.

The proposed balcony waterproofing assembly (BL-01) consists of the following, from bottom to top:

• Existing concrete balcony deck, cleaned and abraded to receive new waterproofing;

• Cold fluid-applied fleece-reinforced waterproofing membrane, 80 mils thick;

• Corner reinforcing at all inside and outside corners and cracks;

• Loose-laid protection board, 1/4 in. thick;

• Pedestals for pavers, thickness varies;

• Custom concrete pavers, 2 in. thick.

The new balcony waterproofing membrane will be continuous and will be integrated with the adjacent wall water barrier and curtain wall perimeter flashings. The balcony waterproofing membrane will extend up the backup wall, behind the precast at the returns and at the corners near the exterior wall a minimum of 8 in. above the paver surface. At the balcony railing, the waterproofing membrane will terminate below the elevation of the paver to keep it concealed from view and maintain historic appearance.

The selected waterproofing membrane is self-terminating which improves its durability against delamination despite the inability to raise it well-above the paver surface that will collect snow and ice.

BL-01: TYPICAL BALCONY WATERPROOFING ASSEMBLY

The balcony slab slopes towards two internal drains on either side, a few inches in front of the balcony curtain wall. The drain bodies are in serviceable condition and will remain in place. The new waterproofing membrane will turn down into the existing drain body.

To meet the ADA requirements of the door threshold and maintain historic appearance of the paver elevation, the pavers at the door must be set not more than 1/4 in. below the door threshold. This will require slight sloping of the pavers away from the doors so that the paver elevation at the perimeter of the balcony is level with the cast-in-place perimeter curb. The balcony pavers will be custom sized and slightly trapezoidal to follow the radial pattern of the building in addition to using a custom concrete mix with exposed aggregate finish to match the appearance of the new panels .

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ROOFING ASSEMBLY

Based on the drain locations, structural capacity of the roof slab, parapet height limitations and current code-exceptions for minimum membrane slope, the most appropriate roof replacement membrane is a hot-applied rubberized asphalt (HRA) membrane in a protected membrane roofing assembly. Properly designed and constructed HRA membranes are durable with a long track record of successful performance in similar applications over structural concrete decks. With this approach, the roofing is applied directly to the substrate, and insulation and ballast are provided above the membrane.

The existing roof assembly including the membrane, insulation, asphaltic vapor retarder, perimeter flashings, curb blocking, and drains will be removed. The concrete substrate will be cleaned of previous membranes and residue. Because the condition of the existing concrete structural slab is unknown, the slab will be prepared, as necessary, with a low-shrinkage grout at locations of damage and to overcome areas with negative slope. If portions of the concrete slab have a surface finish that is not appropriate for the membrane application (e.g., smooth surface finish or surface damage), additional preparatory work (e.g., mechanical preparation) of the surface will also be required.

The proposed roofing assembly will include a HRA membrane bonded continuously to the existing structural concrete roof slab, which has been documented of having approximately 1/16 to 1/8 in. per ft of slope to a flat circular valley concentric with the building’s perimeter. Para. 1511.1 of the 2018 IBC and Section 705 of the 2018 IEBC allow existing low-sloped roofs to be replaced without meeting contemporary slope requirements for new construction, although model building codes typically include a minimum membrane-level slope-to-drain of 1/4 in. per ft to reduce ponding and improve membrane service life. In addition, Para. 1507.18.1 of the 2013 DC Building Code does not require a minimum slope for new hot-applied rubberized-asphalt roofing. The creation of additional slope in the concrete slab substrate is impractical with weight limitations, existing parapet geometry that must be preserved to maintain the historic appearance of the building, and existing drain locations.

The proposed roofing assembly (RF-01) consists of the following, from interior to exterior:

• Existing concrete roof deck, prepared as required, 5 to 7 in. thick;

• Hot-applied rubberized-asphalt with fabric-reinforcing, 215 mils thick;

• Uncured neoprene at all inside and outside corners and cracks, 60 mils thick;

• Embedded protection sheet, 80 mils;

• Loose-laid protection board, 1/4 in. thick;

• Drainage composite, 1/2 in. thick;

• Extruded polystyrene insulation, 6 in. thick;

• Filter fabric, negligible thickness;

• Pedestals for pavers, 1/2 in. thick;

• Concrete pavers, 2 in. thick.

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RF-01: TYPICAL ROOF ASSEMBLY

The insulation provided in the proposed assembly meets the prescriptive minimum R-value of the 2018 IECC, and the standard concrete paver is adequate ballast per analysis according to ANSI SPRI RP-4. The roofing equipment will be set on new or modified cast-in-place concrete curbs. The design includes two waterproofing details at roofing curbs: one where the roofing membrane is continuous underneath the curb (i.e., supporting ductwork and EF-16) and one where the roofing membrane turns up the vertical face of the curb (i.e., surrounding openings in the roof slab), and is counter-flashed by rooftop equipment. At upturns, the roofing membrane will extend a minimum of 8 in. above the paver surface, except where noted on the Drawings to minimize impact to equipment sight-lines from the National Mall. The latter represent performance compromises to prevent changes to the building’s historic appearance. All vertical leading edges of the roofing membrane will be secured with a termination bar and protected from mechanical damage and UV-exposure by metal counter-flashings and granular-surfaced UV-stable cap sheets.

The roof currently does not have a functional fall arrest system or adequate fall protection. Design for new post-installed perimeter fall arrest anchors have been removed from the scope and we understand that SI plans to re-certify the existing system around the inner parapet, which will remain in place. While the design will not provide a complete fall arrest system, the design includes two new vertical posts with “U-bolts” serving as tie-off anchors; one post at the roof hatch and an additional post 10’-0” away from the inner parapet. The additional post intent is to provide safe access to the inner parapet fall arrest system when it becomes functional. These posts should be installed prior to the roofing membrane and are subject to the same upturn requirements as the other roof elements. In the future, if SI decides to provide a new system at the inner parapet and/or the outer parapet, there is ample space on the

CallisonRTKL | 23 existing parapet(s) to attach new anchors without the need to re-roof.

At the perimeter, the roofing membrane will turn up and terminate on the vertical face of the parapet walls; however, due to the need to match the existing aesthetic of the exposed cast-in-place parapet, the roofing membrane will not integrate with the air and water barrier applied to the cast-in-place concrete drum on the exterior wall.

The elevator overrun is a concrete structure that extends approximately 3 feet above the current surface of the main roof. Like the main roof, it is also currently covered with a built-up roofing system and has one drain with apparent slope-to-drain using tapered insulation. The replacement roof assembly for the overrun consists of a three-ply modified-bituminous exposed roofing over tapered rigid insulation to create slope-to-drain.

The proposed elevator overrun roofing assembly (RF-02) consists of the following, from interior to exterior:

• Existing concrete roof deck;

• Vapor retarder, 114 mils thick;

• Tapered polyisocyanurate insulation, thickness varies;

• Cover board, 1/2 in. thick;

• Modified-bitumen base-ply, 114 mils thick;

• Modified-bitumen inter-ply, 114 mils thick;

• Modified-bitumen cap-ply, 138 mils thick.

RF-02: TYPICAL ELEVATOR OVERRUN ROOFING ASSEMBLY

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IV. STRUCTURAL SYSTEMS

A. Applicable Codes and Design Criteria

• 2018 International Building Code (IBC)

• 2018 International Existing Building Code (IEBC)

• ACI 318-14 Building Code Requirements for Structural Concrete

• AISC 360-16 Specifications for Structural Steel Buildings

• ASCE 7-16 Minimum Design Loads for Buildings and Other Structures

B. Proposed Systems

ROOF REPLACEMENT

Structural intervention will be limited in the roof replacement to the replacement of multiple cast-in-place drains and new cast-in-place curbs. Analysis was completed to evaluate the structural capacity of the roof and was documented in the drawings.

Existing art-racks are currently installed on the underside of the roof slab in specific area’s noted on the roof loading plan. Roof loading for both work associated with the current project and loading for future green roof were evaluated and documented on the roof loading plan.

PANEL REPLACEMENT

New tradition precast panels are proposed to match the existing panel size, thickness and exposed aggregate finish. Both new small and new large panels are proposed to be independently supported with two dead load / lateral load connections at the base and two lateral load connections at the top of panels. New panels are designed for current wind loading and load factors. New panel connections are designed for blast loading to retain the panel in place during a blast event to protect the plaza structure. Panels are assumed to be damaged to the point of needing replacement but are not expected to break into small pieces per coordination with blast consultant. Blast loading criteria was from “Project Methodology and Approach – Blast/Physical Security (Rev. 1)” and from the ISC Risk Management Process for Federal Facilities Appendix A: The Design Basis Threat Report. Additional references include the October 2015 Smithsonian Institution

26 | HMSG ENVELOPE REPAIR - BASIS OF DESIGN

STRUCTURAL SYSTEMS

Security Design Criteria and the October 2013 Review of Additional Threat Scenarios for the Hirshhorn Museum. Installation challenges will be prevalent due to the restricted access from the back side due to the solid concrete drum wall, therefore all connections must be made from the front. The balcony will further restrict access to the panels installed tight to the underside of the balcony. The top panel and bottom panels have small return legs that restrict access to the cavity. The precast panel attachment details indicate proposed solutions in the way of installation sequences and leave-out holes to be patched later.

Panel Reaction (kips) Small 7.5 Large 2.4 Small (Alternate) 5 Large (Alternate) 5 Large to Small (Alternate) 2.5

BALCONY GLAZING

Balcony glazing is being replaced with new custom structural silacone glazed stick build curtain wall.