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Introduction to building

The Bechtler Museum, located in downtown Charlotte, North

Carolina, was designed by Swiss architect Mario Botta. Established on the 2nd

of January 2010, Bechtler museum exhibits modern artworks from the mid 20 th

century. This 3390 square meter four-story structure has a soaring glass

atrium that extends throughout the museum’s core and diffuses natural light

into the building. The dominant feature of this solid structure is its fourth floor

which extends from the core of the building, cantilevered and supported by the

signature column rising from the open atrium below.

A rigorous, yet elegant simplicity selection has been made by

Botta in the palette of materials used which includes the combination of glass,

steel, black granite, terracotta, polished concrete and wood. Botta had

designed intending for a strong, contemporary structures that layer the

colours, texture and materials for a solid architectural and sculptural power

that connects to the dynamic art inside it.

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Orthographic drawings

Second Floor Plan

Third Floor PlanFourth Floor Plan

A A

First Floor Plan

B

B

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Front elevation Section A-A

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2

4

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Section B-B

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1. Skylight2. Terracotta Cladding3. Wall4. Composite Concrete Slab5. Column with Terracotta

Tile

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Load Distributions

The cantilever of the building is supported by W40 x 362 wide flange steel beams installed in the roof structure and fourth floor. Above and below each walls at the cantilever there will be a cross beam.

The loads from the top are transferred downward through the load transferring walls to the foundation footings.

The column is an important part of the structure to support the fourth floor. It is placed in the middle of the cantilever and directly under the steel beams To transfer the load more effectively.

The longer the span of the cantilever and the further it is from the supporting structure, the larger the load.

The cross bracing tension cables are used to strengthen the structure of the glass atrium especially when large loads are transferred from the top.

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Detailing1. Skylight

The load from the top is distributed to the wide flange steel girders that spans across the roof and is transferred to the wall system.

The coffered design of the skylight is used to lighten the roof weight while concealing the large steel beams and mechanical structures.

Front section of skylight

Side section of skylight

Air conditioning duct

Wide flange steel girder

Water resistant roof membrane

Wall

Terracotta tile cladding

Metal decking

Parapet

Wall

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Detailing

2. Terracotta cladding

The custom engineered TerraClad™ used is composed of fire clays, colored aggregate, and fluxes that were fired to a specific firing curve allowing the terracotta to be frost resistant and high freeze thaw.

Sectional view of the cladding system

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Clip with isolator

Installation of cladding system

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Ship lapped design

The incorporation of ship lapped open joint design of the panel had shield the structure from moisture that enter the ventilated cavity. Gaskets and isolators of the rain screen provide a snug fit between panels and the framing system to prevent wind induced rattle and allow for movement of the aluminum framing due to thermal expansion.

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3

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Detailing

3. Wall

Gypsum Board

Insulation

Plaster

Plywood

The drywalls of the Bechtler Museum allow for equal load transfers as the walls are more stable. The insulation also maintains the temperature in the interior due to the four seasons experienced in North Carolina. The gypsum board on the drywall is also fire-proof and acoustically beneficial causing it to be a preferable building material.

Construction detail of Drywall

Terracotta Cladding

Waterproof Membrane

Metal Stud

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Granite Flooring

Concrete

Wide flange steel girder

C-Channel

4. Composite Concrete Slab

Metal Decking

The composite concrete wall slab acts as a support for Bechtler museum. It works by increasing the load capacity of flooring system. The concrete slab together with in-situ infill in conjunction with welded shear studs onto I-beam to enable the slabs and the steel beams to act compositely.

Construction detail of composite floor system

Detailing

Wide flange steel girders are set up to form the structure of the cantilever. Then metal decking are fixed to the steel beams using shear studs. The edge of the metal decking was folded up to prevent the poured concrete from flowing out. A layer of black granite and insulation is used as the floor finishes.

For the exterior wall, steel studs used as terracotta tile tracks system are fixed onto the c-channel.

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Detailing

5. Column with terracotta tile cladding

(Pic) The column was first assembled for visual inspection prior to its disassembly and transportation to site.

The sculptural column rising up 3 story (47 feet tall) was constructed with the use of hot dipped galvanized attachments in place of stainless steel fasteners onto the concrete column.

The column is made of concrete with specified 28-days compressive strength of 12,000 psi. The reason concrete is used because it could support larger load with a slender frame compared to other materials.

Corrugated Decking

Crossbeam

Flange Girder

Flange Steel

Terra-cotta Pavers

Concrete Floor Slab Aluminum Cladding

Convex Steel Frame

Aluminum Cladding

Column connects with Steel Anchor Bolts

Terra-cotta Ceiling Cladding

Before applying the cement to the decking, concrete ratio experiments had been done to find out the most suitable ratio for the concrete flooring. First trials of concrete mixing used no sands as the binding agent, the ratio of cement to water is 2: 1.

After mixing it, the mixture was left for several hours under the sun to let it dry.

The final product of the cement was smooth and powdery. It was easily crack as it did not has aggregates such as sand to hold the concrete mixture.

Corrugated paper was used as metal decking as it has corrugated surface similar to the metal decking. Smooth sand was added into the concrete mixture. The ratio of cement to sand to water is 2: 1.5: 1.

As the result, the mixture did not go under the wire mesh as the sand particles are not small enough to pass through the wire mesh. The corrugated paper was not suitable as metal decking as it absorbs the water of the concrete mixture.

Modelling processComposite concrete

flooring

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Corrugated paper had been replaced with plastic board. Plastic board is more suitable than corrugated paper as it is light and waterproof. It had been cut into metal decking shape and sprayed for metallic surface purpose.

The sand mixture was filtered by using wire mesh to enable smoother surface for the final product compared to previous batches of concrete mixtures. The ratio of cement to sand to water is 2: 1: 0.5.

During the process of drying, many bubbles appeared on the surface of concrete as the narrow gap between the metal decking was not completely filled in with concrete. As the result, the concrete cracked on the next day.

The ratio of cement to sand to water is adjusted to 5: 1.5.

Wood shreds were added into the concrete mixture to reduce the possibility of cracking of concrete.

Composite concrete flooring

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Metal Decking Process

Balsa wood is used as the material for I-beam under the metal decking. This is because balsa wood is available in different type of thickness. It is also a light material hence the floor system will not be too heavy as the cantilever section is only supported by one column.

After aligning, both structural system is ready to be glued. Each connections of the structural systems was connected using hot glue gun to increase the durability and strength of the structures.

Plastic model pipes are used as c-channels as it is light and available in different sizes. Cutting mat was used to make sure all the c-channels are aligned.

The floor system with materials representing the black granite, concrete with metal decking, steel girders, c-channels and metal studs.

Composite concrete flooring

Column making

A white modelling board I-beam was added in the center of the column acting as the load structural system and to also hold the concrete together.

First trial of the concrete column without an I-beam in the middle. The column was made by filling up the straw mold. It broke off into pieces.

First trial of the frame for the terracotta tiles of the column. Soldering tool and alloy were used to combine the alloy rings. The alloy could not combine properly and it took too much time.

Hot glue gun was used instead for the joint of the frames. A protractor was used to determine the position of the vertical frames on the rings.

Load bearing column

After completion of the internal framing, excess glue stains were removed with nail polish remover. It was then sprayed with gray paint.

The column was then inserted into the alloy frame and column specific terracotta cladding were attached onto frame.

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Grey board was used as a substitute for the Terracotta cladding. This is due to the texture and thickness. Different colours and paint to water ratio were tested on the board.

The grey board was cut upon the surface, the measurements were scaled from the length and width to simulate the gaps between alternating cladding.

A separate set of grey board was cut into individual pieces to be used as the ship-lapped design of the panels.

The grey boards was then painted with brown with a slight addition of peach in order to match the colour of the original cladding.

An issue faced during the cutting of the cladding is that the pieces tend to come loose, or break completely mainly because each cladding were cut individually and the minute scale of the cladding.

Due to the cutting of the coloured grey board into individual strips of cladding, the grey board was repainted . This caused excess water from the paint to be absorbed by the board making the strips flimsy during the assembly and completion of the cladding.

Terracotta cladding

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Dry wall composed of several layers; the first exterior layer was made of a 0.2mm thick balsa wood to represent ply wood, 0.1mm balsa wood as gypsum board and wool in between the two as insulation.

Long plastic sticks matching the height of the wall are placed in intervals along the wall as steel studs

Putty filler was applied onto the 0.1mm balsa as the internal plastering and was smoothened out.

The tile cladding tracks system made with plastic sticks was glued onto the external wall.

The terracotta cladding was then attached to the exterior surface of the wall.

Dry wall

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White model making board was used for the flat surface whereas the curved surface of the skylight uses white card as it is more flexible.

Plastic sheets were curved and attached onto the gaps of the upper surface of the skylight.

A difficulty faced during construction of the curved surface was the accurate gradient of the curve causing numerous attempts of different measurements in order to achieve the proper curvature.

The plastic sheets were then engraved with vertical lines to allow bending of the sheets.

Due to the fact that the skylight spans horizontally over the whole model with minimal support from the wall, the weight distribution of the roof and skylight were an initial problem. It was then solved with the addition of I-beams made from mounting boards inserted in between the skylight to act as support.

Skylight

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After this project, we realized appropriate construction method is important to avoid uneven load distribution and cause structural failure of the building. The materials used should be considerate and tested first before applying it in final model. In this case, concrete is hard to handle as it may crack easily due to the improper mixture.

During the modelling phase, parts that are made separately required thorough planning to ensure premade parts are able to connect to one another accurately. This applies to real life construction too as precast parts must be precise to avoid problems.

In addition, the progress of the model and report should be simultaneous. The materials and model should be kept properly to avoid loss or damage as this is also a common issue on actual construction sites. As such, our group should work systematically and on time to meet the deadline requirements.

Conclusion & Final Model

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Architecture Week, (2010). Bechtler Museum. [image] Available at: http://www.architectureweek.com/2010/0407/design_4-3.html

[Accessed 14 Jun. 2014].

Architecture Week, (2010). Bechtler Museum by Botta. [image] Available at: http://www.architectureweek.com/2010/0217/design_1-

2.html [Accessed 13 Jun. 2014].

ArchwebDWG, (2014). Bechtler Museum of Modern Art. [image] Available at:

http://www.archweb.it/dwg/arch_arredi_famosi/mario_botta/Bechtler_Museum/Bechtler_museum_dwg.htm [Accessed 10 Jun. 2014].

Bechtler Museum of Modern Art. (n.d.). 1st ed. [ebook] Available at: http://www.kingguinn.com/libraries/portfolio/publications/317.pdf

[Accessed 13 Jun. 2014].

Boston Valley Terra Cotta. (2014). 1st ed. [ebook] Institute. Available at: http://www.swrionline.org/UserFiles/File/Fall09/Project

%20Showcase%20Presentations/Architectural%20Terra%20Cotta%20Ventilated%20Ceramic%20Screen%20Wall%20Systems%20by

%20Sheri%20Carter.pdf [Accessed 14 Jun. 2014].

Innovative Manufacturing in Architectural Ceramics. (n.d.). 1st ed. [ebook] New York: Boston Valley. Available at: http://www.triton-

ca.com/pdf_files/BV_TerraClad%20Design%20Guide.pdf [Accessed 13 Jun. 2014].

Steelconstruction.info, (2014). Acoustic performance of floors. [online] Available at:

http://www.steelconstruction.info/Acoustic_performance_of_floors [Accessed 15 Jun. 2014].

Worldarchitecturemap.org, (2014). WAM | Bechtler Museum of Modern Art | Charlotte. [online] Available at:

http://www.worldarchitecturemap.org/buildings/bechtler-museum-of-modern-art [Accessed 15 Jun. 2014].

Reference