Michael D. Antonovich Antelope Valley Courthouse

Challenge

To meet the justice support needs of a growing rural high desert region of one of the largest and most populous urban counties in the United States, and to architecturally design the new construction to accurately reflect the local character, the fundamental strength of the institution, as well as the progressiveness of the County’s judiciary body.

Solution

A new courthouse, situated in the geographical heart of the rural area, comprised of a four-storey structure of 382,000 gross square feet designed to house twenty-one (21) Superior Courtrooms and numerous county support departments, including the Sheriff’s Department, District Attorney’s Offices, Public Defender’s Offices, Probation Department, Jury Services, etc.

Benefit

Through overall massing and blending of exterior materials and finishes compatible with the surrounding desert elements, the completed structure meets specific aesthetic, performance, durability and maintenance objectives.  And, perhaps most importantly, the new courthouse brings the county’s rural population symbolically closer to its urban core while providing a lasting monument that uniquely reflects the region’s character.

Design requirements

Early in the design process, architectural precast was determined to be the material best suited to solve the many design and cladding challenges facing the project.  Although other materials were considered, architectural precast concrete helped meet and exceed design expectations across the following range of challenging requirements:

  • Hardened Secure Building Envelope
  • Seismic Performance
  • Acoustical Performance
  • Durability & Maintenance
  • Budget & Schedule Constraints
  • Architectural Aesthetics & Environmental Cladding

Hardened Secure Building Envelope

The use of precast concrete panels provided the hardened secure building envelope required for all new County public buildings. Since the catastrophic Oklahoma City event in 1995, many enforcement and jurisdictional agencies including this County owner have raised building design guidelines for Public Buildings to safely preserve, protect and evacuate occupants.

During the design process it was determined that reinforced concrete panels would mitigate many structural failure, penetration, and accessibility issues raised by the County’s Building and Sheriff’s Departments. By its nature, reinforced concrete resists penetration while absorbing a significant amount of energy. These performance qualities serve well to preserve the overall structural integrity while protecting building occupants from volatile intrusion.

Precast concrete panels provided the most protection for the longest period of time in the most economical manner. Several other exterior cladding materials were studied including poured in-place concrete, masonry walls, GFRC and metal panels.  These other materials were all proven to either decrease usable space, decrease flexibility, reduce durability or increase costs compared to an architectural precast concrete solution.

Seismic Performance

The Courthouse is located in a relatively active seismic area. The structural engineer’s concept was to design a braced frame structural steel building with some flexibility to absorb energy and ground motion. It was determined early in the design process, that masonry units and metal panels typically damage easier than concrete, and cast-in-place concrete was not  flexible enough. The use of large span architectural precast concrete panels simplified erection, accommodated the floor-to-floor heights, allowed more storey drift, and reduced costs.

Acoustical Performance

The Courthouse is located adjacent to a regional airport utilized by commercial and military interests. The high noise levels caused by the air traffic (especially the high-performance military aircraft using the airfield) presented unique acoustical challenges for the project that had to be mitigated by the building envelope.

Because of concrete’s natural sound attenuation properties, the precast concrete panels and roof structure had only to be treated with inexpensive interior drywall, studs and insulation to meet sound transmission ratings (STC) stipulated by the Courthouse Design Program. The glazed areas of the building, on the other hand, used much more expensive acoustical and composite high performance assemblies to comply with the acoustical ratings.

Durability & Maintenance

The design program indicated this building needed to have a useful life span of at least fifty (50) years with minimal repair and maintenance costs. Precast concrete panels traditionally have been proven to stand the test of time with little maintenance.

The on-going maintenance of the precast concrete panels will be relatively low for a public building located in a relatively remote area of the County. The only anticipated maintenance is normal weather protection caulking of the precast panels and the occasional re-application of anti-graffiti coatings for the perimeter ground floor.

Deterioration by design

One of the design team’s early concerns was that the building would be subjected to the harsh environmental forces of the high desert: high winds, wide temperature swings, typically dry conditions, but subject to torrential rainfall and occasional flash flooding.  The design concept was to anticipate, mitigate, and, when possible, use these naturally deteriorating environmental conditions to actually further blend this large structure into the surrounding desert landscape.

Environmentally, due to prevailing winds and sandy conditions, the building is subject to almost daily natural sandblasting, which was one of the primary reasons for using integral colored concrete and penetrating concrete stains. Given the normally dry conditions, discoloring and leaching will likely be minimal. However, as they occur over time, these conditions will blend in and likely enhance the long term aesthetics of the precast panels since the integral and multiple penetrating-stained colors offer a range of acceptability in terms of matching the surrounding landscape.

Incidental moisture protection

Given torrential rainstorms in the spring, the design team took additional precautions in terms of potential incidental water intrusion caused by joint and window leaks. An innovative, patent-pending  “secondary drainage system” designed and installed by Clark Pacific, collects and drains incidental moisture penetration to the exterior. It provides an additional line of defense and potentially reduces the chance of interior water damage and any subsequent mold development.  The extruded silicone system is 100% compatible with the exterior silicone sealants and has a one-way check valve that minimizes air and water infiltration back into the building at the drain valve. The system significantly enhances the ability of the envelope to protect the building’s contents.

Budget & Schedule

After numerous cost analyses by the general contractor, it was determined that the precast concrete wall assembly would be the most economical for use as a cladding material and envelope enclosure.  Based on the size, location, availability and costs of skilled labor, all other building envelope and cladding systems proved to be more expensive, more restrictive, and more time- and labor-intensive. Additionally, off-site fabrication allowed for accelerated construction schedules that reduced time, costs, and other overhead associated with the overall envelope installation. Precast concrete was the most cost-effective solution for the project.

Architectural Aesthetics & Environmental Cladding

The use of architectural precast allowed the design team to develop a color and finish palette that complemented the surrounding high desert. The integral color concrete matched the local desert floor, while the unique replicated sandstone finish brought the look and feel of sandstone to the structure in a very efficient and cost effective manner.

The story of how this monumental structure drew its design inspiration from the environment, and how it was engineered and built of precast concrete is a story of innovation, ingenuity, and inspiration for the industry.

From nature to precast…

Working in concert, the architects and Clark Pacific developed a process to economically produce architectural panels that replicated the look of real sandstone and developed color mixes to match the palette of the desert floor.

Finding model stone

Clark Pacific and the architects made trips to different quarries seeking and eventually finding sandstone veneers with the right amount of relief (1/4” – 3/8”) to replicate a cleft stone finish, without compromising the structural integrity of the precast panels and embed plates.

Precast Plant: From Raw Stone to Replicating Forms

A few pallets of sandstone with the appropriate relief were ordered and delivered to Clark Pacific.  Clark Pacific made numerous rubber mat molds from the stone veneers in various sizes and shapes (from single pieces to series sets) which could then be randomly elevated, rotated, and mixed and matched within each precast concrete panel to ensure a natural, random appearance, and limit overall image redundancy.

In this research and development phase, Clark Pacfic experimented with various aesthetic treatments, crafting innovative solutions to achieve ever more “natural” appearance in the replicated product. In this way, for instance, a more “natural” edge was achieved.

Coloring Nature

The architects and Clark Pacific developed numerous colored mock-up panels (testing various integral colors and stains in combination) to produce the right mix of desert color hues. Various stone aggregates were also tested in order to best replicate the natural sandstone surface appearance.

The two integral colors eventually chosen for the project were a terra cotta red and a yellow sandstone. Palettes of complementary colors were likewise developed for each of the integral colors.  These colors were used in the penetrating stains which were randomly applied to blocks and clefting on each architectural precast panel.

The final finishing process involved a light sandblasting of the entire panel to ensure some color and overall finish continuity across the replicated stones.

Engineered Randomness

Clark Pacific’s engineering staff and craftsmen designed an algorithm to ensure random patterns across the face of the structure. Besides using individual stone mats as well as series stone mats, they also altered mat orientation within panels to vary the relief pattern.  The relief patterns on the mats were alternately reduced or increased through the random use of miscellaneous filler inserts and, after initial curing, penetrating stains of complementary colors were applied to further randomize the pattern and appearance of the replicated sandstone.

This elaborate up-front design activity allowed Clark Pacfic and the architects to maximize a few pallets, and turn 1,200 square feet of quarried stone into 50,000 square feet of replicated sandstone façade.

Specialty Pieces

Clark Pacific developed various specialty pieces, including one-piece corner molds with return faces for exposed columns covers. Single piece hybrid finish parapet forms and panels were also developed – using replicated stone and a second color parapet detail with medium sandblast finish. Radius C-channel panels were created to span the main entrance rotunda.

Erecting Replicated Desert

In a little over four years from initial design to occupancy, a Courthouse rose from the desert floor.  More important than aesthetically reflecting the character and hue of its environment, the new courthouse brings the County’s rural population symbolically closer to its urban core while providing a lasting monument that uniquely reflects the region’s character.

Summary

The creation of replicated sandstone panels has established a new and more affordable market for the precast concrete industry in this region. The aesthetic qualities of multi-colored stone replicated finishes will offer design teams new economical cladding solutions for many years to come.

Project Facts & Highlights

City: PalmdaleState: CABuilding Type: CourthouseSquare Feet: 40,000Year Completed: 2004Job Number: 367Architect: Mosakowski LindseyGeneral Contractor: Haskell ConstructionStructural Engineer: Martin & Huang InternationalOwner: Los Angeles County